Xtensa Instruction Set Architecture (ISA) Reference Manual ASSEMBLER GUIDE

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Xtensa®
Instruction Set Architecture (ISA)
Reference Manual
For All Xtensa Processor Cores
Tensilica, Inc.
3255-6 Scott Blvd.
Santa Clara, CA 95054
(408) 986-8000
fax (408) 986-8919
www.tensilica.com
© 2010 Tensilica, Inc.
Printed in the United States of America
All Rights Reserved
This publication is provided “AS IS.” Tensilica, Inc. (hereafter “Tensilica”) does not make any warranty of any kind, either ex-
pressed or implied, including, but not limited to, the implied warranties of merchantability and fitness for a particular purpose.
Information in this document is provided solely to enable system and software developers to use Tensilica processors. Unless
specifically set forth herein, there are no express or implied patent, copyright or any other intellectual property rights or licens-
es granted hereunder to design or fabricate Tensilica integrated circuits or integrated circuits based on the information in this
document. Tensilica does not warrant that the contents of this publication, whether individually or as one or more groups,
meets your requirements or that the publication is error-free. This publication could include technical inaccuracies or typo-
graphical errors. Changes may be made to the information herein, and these changes may be incorporated in new editions of
this publication.
Tensilica and Xtensa are registered trademarks of Tensilica, Inc. The following terms are trademarks of Tensilica, Inc.: FLIX,
OSKit, Sea of Processors, TurboXim, Vectra, Xenergy, Xplorer, and XPRES. All other trademarks and registered trademarks
are the property of their respective companies.
Issue Date: 4/2010
RC-2010.1 Release
PD-09-0801-10-01
Tensilica, Inc.
3255-6 Scott Blvd.
Santa Clara, CA 95054
(408) 986-8000
fax (408) 986-8919
www.tensilica.com
Digitally signed by Tensilica
Technical Publications
Reason: Certified original
Tensilica document 04/2010
Contents
Xtensa Instruction Set Architecture (ISA) Reference Manual iii
Contents
1. Introduction
................................................................................................................... 1
1.1 What Problem is Tensilica Solving?............................................................................. 1
1.1.1 Adding Architectural Enhancements ..................................................................1
1.1.2 Creating Custom Processor Configurations ........................................................ 4
1.1.3 Mapping the Architecture into Hardware............................................................. 4
1.1.4 Development and Verification Tools ................................................................... 5
1.2 The Xtensa Instruction Set Architecture....................................................................... 5
1.2.1 Configurability .................................................................................................7
1.2.2 Extensibility.....................................................................................................8
1.2.2.1 State Extensions ..................................................................................... 9
1.2.2.2 Register File Extensions ..........................................................................9
1.2.2.3 Instruction Extensions..............................................................................9
1.2.2.4 Coprocessor Extensions ..........................................................................9
1.2.3 Time-to-Market ................................................................................................ 9
1.2.4 Code Density ................................................................................................ 10
1.2.5 Low Implementation Cost ............................................................................... 10
1.2.6 Low-Power.................................................................................................... 11
1.2.7 Performance ................................................................................................. 11
1.2.8 Pipelines.......................................................................................................12
1.3 The Xtensa Processor Generator..............................................................................13
1.3.1 Processor Configuration ................................................................................. 13
1.3.2 System-Specific Instructions—The TIE Language ............................................. 13
2. Notation
....................................................................................................................... 17
2.1 Bit and Byte Order ..................................................................................................17
2.2 Expressions ...........................................................................................................19
2.3 Unsigned Semantics ............................................................................................... 20
2.4 Case ..................................................................................................................... 20
2.5 Statements .............................................................................................................21
2.6 Instruction Fields..................................................................................................... 21
3. Core Architecture
.........................................................................................................23
3.1 Overview of the Core Architecture ............................................................................ 23
3.2 Processor-Configuration Parameters.........................................................................23
3.3 Registers ............................................................................................................... 24
3.3.1 General (AR) Registers ...................................................................................24
3.3.2 Shifts and the Shift Amount Register (SAR)....................................................... 25
3.3.3 Reading and Writing the Special Registers ....................................................... 26
3.4 Data Formats and Alignment ....................................................................................26
3.5 Memory .................................................................................................................27
3.5.1 Memory Addressing .......................................................................................27
3.5.2 Addressing Modes .........................................................................................28
3.5.3 Program Counter ...........................................................................................29
3.5.4 Instruction Fetch............................................................................................29
3.5.4.1 Little-Endian Fetch Semantics ................................................................ 29
Contents
iv Xtensa Instruction Set Architecture (ISA) Reference Manual
3.5.4.2 Big-Endian Fetch Semantics................................................................... 31
3.6 Reset..................................................................................................................... 32
3.7 Exceptions and Interrupts ........................................................................................ 32
3.8 Instruction Summary ............................................................................................... 33
3.8.1 Load Instructions ........................................................................................... 33
3.8.2 Store Instructions........................................................................................... 36
3.8.3 Memory Access Ordering ............................................................................... 39
3.8.4 Jump and Call Instructions.............................................................................. 40
3.8.5 Conditional Branch Instructions ....................................................................... 40
3.8.6 Move Instructions .......................................................................................... 42
3.8.7 Arithmetic Instructions .................................................................................... 43
3.8.8 Bitwise Logical Instructions ............................................................................. 44
3.8.9 Shift Instructions ............................................................................................ 44
3.8.10 Processor Control Instructions....................................................................... 45
4. Architectural Options
.................................................................................................... 47
4.1 Overview of Options ................................................................................................ 47
4.2 Core Architecture.................................................................................................... 50
4.3 Options for Additional Instructions............................................................................. 53
4.3.1 Code Density Option ...................................................................................... 53
4.3.1.1 Code Density Option Architectural Additions ............................................ 53
4.3.1.2 Branches.............................................................................................. 54
4.3.2 Loop Option .................................................................................................. 54
4.3.2.1 Loop Option Architectural Additions......................................................... 55
4.3.2.2 Restrictions on Loops ............................................................................ 55
4.3.2.3 Loops Disabled During Exceptions .......................................................... 56
4.3.2.4 Loopback Semantics ............................................................................. 56
4.3.3 Extended L32R Option ................................................................................... 56
4.3.3.1 Extended L32R Option Architectural Additions.......................................... 56
4.3.3.2 The Literal Base Register ....................................................................... 57
4.3.4 16-bit Integer Multiply Option .......................................................................... 57
4.3.4.1 16-bit Integer Multiply Option Architectural Additions................................. 58
4.3.5 32-bit Integer Multiply Option .......................................................................... 58
4.3.5.1 32-bit Integer Multiply Option Architectural Additions................................. 58
4.3.6 32-bit Integer Divide Option ............................................................................ 59
4.3.6.1 32-bit Integer Divide Option Architectural Additions ................................... 59
4.3.7 MAC16 Option............................................................................................... 60
4.3.7.1 MAC16 Option Architectural Additions ..................................................... 60
4.3.7.2 Use With CLAMPS Instruction ................................................................ 62
4.3.8 Miscellaneous Operations Option .................................................................... 62
4.3.8.1 Miscellaneous Operations Option Architectural Additions........................... 62
4.3.9 Coprocessor Option ....................................................................................... 63
4.3.9.1 Coprocessor Option Architectural Additions ............................................. 64
4.3.9.2 Coprocessor Context Switch................................................................... 64
4.3.10 Boolean Option............................................................................................ 65
4.3.10.1 Boolean Option Architectural Additions .................................................. 65
4.3.10.2 Booleans ............................................................................................ 66
4.3.11 Floating-Point Coprocessor Option................................................................. 67
4.3.11.1 Floating-Point Coprocessor Option Architectural Additions ....................... 67
Contents
Xtensa Instruction Set Architecture (ISA) Reference Manual v
4.3.11.2 Floating-Point Representation ............................................................... 69
4.3.11.3 Floating-Point State.............................................................................. 69
4.3.11.4 Floating-Point Exceptions ..................................................................... 71
4.3.11.5 Floating-Point Instructions .................................................................... 71
4.3.12 Multiprocessor Synchronization Option........................................................... 74
4.3.12.1 Memory Access Ordering ..................................................................... 74
4.3.12.2 Multiprocessor Synchronization Option Architectural Additions ................. 75
4.3.12.3 Inter-Processor Communication with the L32AI and S32RI Instructions ... 76
4.3.13 Conditional Store Option ...............................................................................77
4.3.13.1 Conditional Store Option Architectural Additions ..................................... 77
4.3.13.2 Exclusive Access with the S32C1I Instruction ........................................ 78
4.3.13.3 Use Models for the S32C1I Instruction .................................................. 79
4.3.13.4 The Atomic Operation Control Register (ATOMCTL) under the Conditional
Store Option .................................................................................................... 80
4.3.13.5 Memory Ordering and the S32C1I Instruction ........................................ 81
4.4 Options for Interrupts and Exceptions........................................................................ 82
4.4.1 Exception Option ........................................................................................... 82
4.4.1.1 Exception Option Architectural Additions.................................................. 83
4.4.1.2 Exception Causes under the Exception Option ......................................... 85
4.4.1.3 The Miscellaneous Program State Register (PS) under the Exception Option ...
87
4.4.1.4 Value of Variables under the Exception Option ......................................... 88
4.4.1.5 The Exception Cause Register (EXCCAUSE) under the Exception Option..... 89
4.4.1.6 The Exception Virtual Address Register (EXCVADDR) under the Exception
Option.............................................................................................................91
4.4.1.7 The Exception Program Counter (EPC) under the Exception Option ............ 91
4.4.1.8 The Double Exception Program Counter (DEPC) under the Exception Option ...
92
4.4.1.9 The Exception Save Register (EXCSAVE) under the Exception Option......... 92
4.4.1.10 Handling of Exceptional Conditions under the Exception Option ............... 93
4.4.1.11 Exception Priority under the Exception Option......................................... 96
4.4.2 Relocatable Vector Option ..............................................................................98
4.4.2.1 Relocatable Vector Option Architectural Additions..................................... 99
4.4.3 Unaligned Exception Option............................................................................ 99
4.4.3.1 Unaligned Exception Option Architectural Additions ................................100
4.4.4 Interrupt Option ........................................................................................... 100
4.4.4.1 Interrupt Option Architectural Additions ..................................................101
4.4.4.2 Specifying Interrupts ............................................................................102
4.4.4.3 The Level-1 Interrupt Process...............................................................105
4.4.4.4 Use of Interrupt Instructions..................................................................106
4.4.5 High-Priority Interrupt Option......................................................................... 106
4.4.5.1 High-Priority Interrupt Option Architectural Additions ............................... 106
4.4.5.2 Specifying High-Priority Interrupts ......................................................... 108
4.4.5.3 The High-Priority Interrupt Process........................................................ 108
4.4.5.4 Checking for Interrupts......................................................................... 109
4.4.6 Timer Interrupt Option .................................................................................. 110
4.4.6.1 Timer Interrupt Option Architectural Additions......................................... 110
4.4.6.2 Clock Counting and Comparison ........................................................... 111
4.5 Options for Local Memory ...................................................................................... 111
Contents
vi Xtensa Instruction Set Architecture (ISA) Reference Manual
4.5.1 General Cache Option Features .....................................................................111
4.5.1.1 Cache Terminology.............................................................................. 112
4.5.1.2 Cache Tag Format............................................................................... 112
4.5.1.3 Cache Prefetch ................................................................................... 113
4.5.2 Instruction Cache Option .............................................................................. 115
4.5.2.1 Instruction Cache Option Architectural Additions..................................... 115
4.5.3 Instruction Cache Test Option ....................................................................... 116
4.5.3.1 Instruction Cache Test Option Architectural Additions.............................. 116
4.5.4 Instruction Cache Index Lock Option.............................................................. 117
4.5.4.1 Instruction Cache Index Lock Option Architectural Additions .................... 117
4.5.5 Data Cache Option ...................................................................................... 118
4.5.5.1 Data Cache Option Architectural Additions............................................. 119
4.5.6 Data Cache Test Option ...............................................................................121
4.5.6.1 Data Cache Test Option Architectural Additions ...................................... 121
4.5.7 Data Cache Index Lock Option...................................................................... 122
4.5.7.1 Data Cache Index Lock Option Architectural Additions ............................ 122
4.5.8 General RAM/ROM Option Features.............................................................. 123
4.5.9 Instruction RAM Option ................................................................................124
4.5.9.1 Instruction RAM Option Architectural Additions....................................... 124
4.5.10 Instruction ROM Option .............................................................................. 125
4.5.10.1 Instruction ROM Option Architectural Additions..................................... 125
4.5.11 Data RAM Option ....................................................................................... 126
4.5.11.1 Data RAM Option Architectural Additions ............................................. 126
4.5.12 Data ROM Option ...................................................................................... 126
4.5.12.1 Data ROM Option Architectural Additions ............................................. 127
4.5.13 XLMI Option .............................................................................................. 127
4.5.13.1 XLMI Option Architectural Additions .................................................... 127
4.5.14 Hardware Alignment Option ........................................................................ 128
4.5.15 Memory ECC/Parity Option ......................................................................... 128
4.5.15.1 Memory ECC/Parity Option Architectural Additions ............................... 129
4.5.15.2 Memory Error Information Registers .................................................... 130
4.5.15.3 The Exception Registers .................................................................... 137
4.5.15.4 Memory Error Semantics.................................................................... 137
4.6 Options for Memory Protection and Translation ........................................................ 138
4.6.1 Overview of Memory Management Concepts.................................................. 139
4.6.1.1 Overview of Memory Translation ........................................................... 139
4.6.1.2 Overview of Memory Protection ............................................................ 142
4.6.1.3 Overview of Attributes.......................................................................... 144
4.6.2 The Memory Access Process........................................................................ 145
4.6.2.1 Choose the TLB .................................................................................. 146
4.6.2.2 Lookup in the TLB ............................................................................... 147
4.6.2.3 Check the Access Rights ..................................................................... 148
4.6.2.4 Direct the Access to Local Memory ....................................................... 148
4.6.2.5 Direct the Access to PIF....................................................................... 150
4.6.2.6 Direct the Access to Cache ..................................................................150
4.6.3 Region Protection Option.............................................................................. 150
4.6.3.1 Region Protection Option Architectural Additions .................................... 151
4.6.3.2 Formats for Accessing Region Protection Option TLB Entries .................. 152
4.6.3.3 Region Protection Option Memory Attributes .......................................... 154
Contents
Xtensa Instruction Set Architecture (ISA) Reference Manual vii
4.6.4 Region Translation Option ............................................................................156
4.6.4.1 Region Translation Option Architectural Additions ................................... 156
4.6.4.2 Region Translation Option Formats for Accessing TLB Entries .................156
4.6.4.3 Region Translation Option Memory Attributes......................................... 158
4.6.5 MMU Option................................................................................................ 158
4.6.5.1 MMU Option Architectural Additions ...................................................... 159
4.6.5.2 MMU Option Register Formats.............................................................. 161
PTEVADDR ............................................................................................161
RASID....................................................................................................161
ITLBCFG ................................................................................................ 162
DTLBCFG...............................................................................................162
4.6.5.3 The Structure of the MMU Option TLBs ................................................. 163
4.6.5.4 The MMU Option Memory Map ............................................................. 164
4.6.5.5 Formats for Writing MMU Option TLB Entries ......................................... 165
4.6.5.6 Formats for Reading MMU Option TLB Entries ....................................... 168
4.6.5.7 Formats for Probing MMU Option TLB Entries ........................................ 171
4.6.5.8 Format for Invalidating MMU Option TLB Entries .................................... 172
4.6.5.9 MMU Option Auto-Refill TLB Ways and PTE Format ............................... 174
4.6.5.10 MMU Option Memory Attributes .......................................................... 175
4.6.5.11 MMU Option Operation Semantics....................................................... 178
4.7 Options for Other Purposes....................................................................................179
4.7.1 Windowed Register Option ...........................................................................180
4.7.1.1 Windowed Register Option Architectural Additions .................................. 181
4.7.1.2 Managing Physical Registers................................................................ 183
4.7.1.3 Window Overflow Check ...................................................................... 184
4.7.1.4 Call, Entry, and Return Mechanism .......................................................186
4.7.1.5 Windowed Procedure-Call Protocol .......................................................187
4.7.1.6 Window Overflow and Underflow to and from the Program Stack.............. 192
4.7.2 Processor Interface Option ...........................................................................194
4.7.2.1 Processor Interface Option Architectural Additions .................................. 195
4.7.3 Miscellaneous Special Registers Option ......................................................... 195
4.7.3.1 Miscellaneous Special Registers Option Architectural Additions ............... 195
4.7.4 Thread Pointer Option ..................................................................................196
4.7.4.1 Thread Pointer Option Architectural Additions ........................................196
4.7.5 Processor ID Option..................................................................................... 196
4.7.5.1 Processor ID Option Architectural Additions ........................................... 196
4.7.6 Debug Option ..............................................................................................197
4.7.6.1 Debug Option Architectural Additions ....................................................197
4.7.6.2 Debug Cause Register.........................................................................198
4.7.6.3 Using Breakpoints ...............................................................................199
4.7.6.4 Debug Exceptions ............................................................................... 201
4.7.6.5 Instruction Counting............................................................................. 201
4.7.6.6 Debug Registers ................................................................................. 202
4.7.6.7 Debug Interrupts ................................................................................. 203
4.7.6.8 The checkIcount Procedure.............................................................. 203
4.7.7 Trace Port Option ........................................................................................203
4.7.7.1 Trace Port Option Architectural Additions ............................................... 204
5. Processor State
..........................................................................................................205
Contents
viii Xtensa Instruction Set Architecture (ISA) Reference Manual
5.1 General Registers ................................................................................................. 208
5.2 Program Counter .................................................................................................. 208
5.3 Special Registers .................................................................................................. 208
5.3.1 Reading and Writing Special Registers........................................................... 211
5.3.2 LOOP Special Registers ...............................................................................212
5.3.3 MAC16 Special Registers ............................................................................. 213
5.3.4 Other Unprivileged Special Registers ............................................................. 215
5.3.5 Processor Status Special Register ................................................................. 216
5.3.6 Windowed Register Option Special Registers ................................................. 221
5.3.7 Memory Management Special Registers ........................................................ 221
5.3.8 Exception Support Special Registers ............................................................. 223
5.3.9 Exception State Special Registers ................................................................. 226
5.3.10 Interrupt Special Registers .......................................................................... 229
5.3.11 Timing Special Registers ............................................................................. 231
5.3.12 Breakpoint Special Registers....................................................................... 233
5.3.13 Other Privileged Special Registers ............................................................... 235
5.4 User Registers...................................................................................................... 237
5.4.1 Reading and Writing User Registers .............................................................. 237
5.4.2 The List of User Registers ............................................................................ 238
5.5 TLB Entries .......................................................................................................... 239
5.6 Additional Register Files ........................................................................................ 240
5.7 Caches and Local Memories .................................................................................. 240
6. Instruction Descriptions
.............................................................................................. 243
7. Instruction Formats and Opcodes
................................................................................ 569
7.1 Formats ............................................................................................................... 569
7.1.1 RRR...........................................................................................................569
7.1.2 RRI4 ..........................................................................................................569
7.1.3 RRI8 ..........................................................................................................570
7.1.4 RI16 ...........................................................................................................570
7.1.5 RSR ...........................................................................................................570
7.1.6 CALL..........................................................................................................571
7.1.7 CALLX........................................................................................................ 571
7.1.8 BRI8........................................................................................................... 571
7.1.9 BRI12.........................................................................................................572
7.1.10 RRRN....................................................................................................... 572
7.1.11 RI7 ........................................................................................................... 572
7.1.12 RI6 ........................................................................................................... 573
7.2 Instruction Fields................................................................................................... 573
7.3 Opcode Encodings................................................................................................ 574
7.3.1 Opcode Maps.............................................................................................. 575
7.3.2 CUST0 and CUST1 Opcode Encodings ......................................................... 586
7.3.3 Cache-Option Opcode Encodings (Implementation-Specific) ............................ 586
8. Using the Xtensa Architecture
..................................................................................... 587
8.1 The Windowed Register and CALL0 ABIs ................................................................ 587
8.1.1 Windowed Register Usage and Stack Layout.................................................. 587
8.1.2 CALL0 Register Usage and Stack Layout ....................................................... 589
8.1.3 Data Types and Alignment ............................................................................ 589
8.1.4 Argument Passing ....................................................................................... 590
Contents
Xtensa Instruction Set Architecture (ISA) Reference Manual ix
8.1.5 Return Values..............................................................................................591
8.1.6 Variable Arguments...................................................................................... 592
8.1.7 Other Register Conventions ..........................................................................592
8.1.8 Nested Functions......................................................................................... 593
8.1.9 Stack Initialization ........................................................................................594
8.2 Other Conventions ................................................................................................ 595
8.2.1 Break Instruction Operands .......................................................................... 595
8.2.2 System Calls ...............................................................................................597
8.3 Assembly Code ....................................................................................................598
8.3.1 Assembler Replacements and the Underscore Form ....................................... 598
8.3.2 Instruction Idioms ........................................................................................598
8.3.3 Example: A FIR Filter with MAC16 Option ......................................................600
8.4 Performance ........................................................................................................ 605
8.4.1 Processor Performance Terminology and Modeling ......................................... 605
8.4.2 Xtensa Processor Family..............................................................................608
A. Differences Between Old and Current Hardware ........................................................ 611
A.1 Added Instructions ................................................................................................ 611
A.2 Xtensa Exception Architecture 1............................................................................. 611
A.2.1 Differences in the PS Register ......................................................................612
A.2.2 Exception Semantics ................................................................................... 612
A.2.3 Checking ICOUNT....................................................................................... 614
A.2.4 The BREAK and BREAK.N Instructions ........................................................... 614
A.2.5 The RETW and RETW.N Instructions ...............................................................614
A.2.6 The RFDE Instruction ................................................................................... 614
A.2.7 The RFE Instruction ..................................................................................... 614
A.2.8 The RFUE Instruction ................................................................................... 615
A.2.9 The RFWO and RFWU Instructions...................................................................616
A.2.10 Exception Virtual Address Register.............................................................. 616
A.2.11 Double Exceptions .....................................................................................616
A.2.12 Use of the RSIL Instruction ......................................................................... 616
A.2.13 Writeback Cache ....................................................................................... 616
A.2.14 The Cache Attribute Register ......................................................................617
A.3 New Exception Cause Values ................................................................................619
A.4 ICOUNTLEVEL ....................................................................................................620
A.5 MMU Option Memory Attributes ............................................................................. 620
A.6 Special Register Read and Write ............................................................................620
A.7 MMU Modification................................................................................................. 621
A.8 Reduction of SYNC Instruction Requirements.......................................................... 621
Contents
x Xtensa Instruction Set Architecture (ISA) Reference Manual
List of Figures
Xtensa Instruction Set Architecture (ISA) Reference Manual xi
List of Figures
Figure 1–1. Xtensa LX Hardware Architecture Block Diagram ............................................... 6
Figure 1–2. Example Implementation Pipeline ...................................................................12
Figure 1–3. The Xtensa Design Flow................................................................................15
Figure 2–4. Big and Little Bit Numbering for BBC/BBS Instructions...................................... 17
Figure 2–5. Big and Little Endian Byte Ordering ................................................................ 18
Figure 3–6. Virtual Address Fields.................................................................................... 27
Figure 4–7. LITBASE Register Format.............................................................................. 57
Figure 4–8. PS Register Format.......................................................................................87
Figure 4–9. EXCCAUSE Register ....................................................................................89
Figure 4–10. EXCVADDR Register Format .........................................................................91
Figure 4–11. EPC Register Format for Exception Option ......................................................92
Figure 4–12. DEPC Register Format ..................................................................................92
Figure 4–13. EXCSAVE Register Format............................................................................ 93
Figure 4–14. Instruction and Data Cache Tag Format for Xtensa ......................................... 113
Figure 4–15. MESR Register Format ...............................................................................130
Figure 4–16. MECR Register Format ...............................................................................135
Figure 4–17. MEVADDR Register Format .........................................................................136
Figure 4–18. Virtual-to-Physical Address Translation ......................................................... 140
Figure 4–19. A Single Process’ Rings .............................................................................. 143
Figure 4–20. Nested Rings of Multiple Processes with Some Sharing.................................. 143
Figure 4–21. Region Protection Option Addressing (as) Format for WxTLB, RxTLB1, & PxTLB ....
152
Figure 4–22. Region Protection Option Data (at) Format for WxTLB.................................... 153
Figure 4–23. Region Protection Option Data (at) Format for RxTLB1..................................153
Figure 4–24. Region Protection Option Data (at) Format for PxTLB ................................... 153
Figure 4–25. Region Translation Option Addressing (as) Format for WxTLB, RxTLB1, & PxTLB ...
157
Figure 4–26. Region Translation Option Data (at) Format for WxTLB .................................. 157
Figure 4–27. Region Translation Option Data (at) Format for RxTLB1 ................................ 158
Figure 4–28. Region Translation Option Data (at) Format for PxTLB ..................................158
Figure 4–29. MMU Option PTEVADDR Register Format .................................................... 161
Figure 4–30. MMU Option RASID Register Format ............................................................ 162
Figure 4–31. MMU Option DTLBCFG Register Format.......................................................163
Figure 4–32. MMU Option Address Map with IVARWAY56 and DVARWAY56 Fixed ................ 165
Figure 4–33. MMU Option Addressing (as) Format for WxTLB ............................................ 167
Figure 4–34. MMU Option Data (at) Format for WxTLB...................................................... 168
Figure 4–35. MMU Option Addressing (as) Format for RxTLB0 and RxTLB1....................... 169
Figure 4–36. MMU Option Data (at) Format for RxTLB0....................................................170
Figure 4–37. MMU Option Data (at) Format for RxTLB1....................................................171
Figure 4–38. MMU Option Addressing (as) Format for PxTLB ............................................ 172
Figure 4–39. MMU Option Data (at) Format for PITLB...................................................... 172
Figure 4–40. MMU Option Data (at) Format for PDTLB...................................................... 172
Figure 4–41. MMU Option Addressing (as) Format for IxTLB ............................................ 173
Figure 4–42. MMU Option Page Table Entry (PTE) Format................................................. 174
List of Figures
xii Xtensa Instruction Set Architecture (ISA) Reference Manual
Figure 4–43. Conceptual Register Window Read............................................................... 183
Figure 4–44. Faster Register Window Read...................................................................... 184
Figure 4–45. Fastest Register Window Read .................................................................... 184
Figure 4–46. Register Window Near Overflow ................................................................... 185
Figure 4–47. Register Window Just Before Underflow........................................................ 187
Figure 4–48. Stack Frame Before alloca() .................................................................... 189
Figure 4–49. Stack Frame After First alloca() ............................................................... 190
Figure 4–50. Stack Frame Layout .................................................................................... 191
Figure 4–51. DEBUGCAUSE Register ............................................................................. 199
Figure 4–52. DBREAKC[i] Format .................................................................................. 202
Figure 8–53. Stack Frame for the Windowed Register ABI.................................................. 588
Figure 8–54. Instruction Operand Dependency Interlock .................................................... 607
Figure 8–55. Functional Unit Interlock .............................................................................. 607
Figure 8–56. Xtensa Pipeline Effects................................................................................ 609
Figure 9-57. CACHEATTR Register ................................................................................ 618
List of Tables
Xtensa Instruction Set Architecture (ISA) Reference Manual xiii
List of Tables
Table 1–1. Huffman Decode Example ............................................................................... 2
Table 1–2. Comparison of Typical RISC and Xtensa ISA Features ....................................... 6
Table 1–3. Modular Components ......................................................................................7
Table 2–4. Instruction-Description Expressions ................................................................19
Table 2–5. Instruction-Description Statements..................................................................21
Table 2–6. Uses Of Instruction Fields .............................................................................. 21
Table 3–7. Core Processor-Configuration Parameters....................................................... 24
Table 3–8. Core-Architecture Set ....................................................................................24
Table 3–9. Reading and Writing Special Registers............................................................26
Table 3–10. Operand Formats and Alignment .................................................................... 27
Table 3–11. Core Instruction Summary .............................................................................33
Table 3–12. Load Instructions .......................................................................................... 34
Table 3–13. Store Instructions .......................................................................................... 36
Table 3–14. Memory Order Instructions............................................................................. 39
Table 3–15. Jump and Call Instructions............................................................................. 40
Table 3–16. Conditional Branch Instructions ......................................................................40
Table 3–17. Branch Immediate (b4const) Encodings ........................................................ 41
Table 3–18. Branch Unsigned Immediate (b4constu) Encodings........................................ 42
Table 3–19. Move Instructions.......................................................................................... 43
Table 3–20. Arithmetic Instructions ................................................................................... 43
Table 3–21. Bitwise Logical Instructions ............................................................................44
Table 3–22. Shift Instructions ........................................................................................... 44
Table 3–23. Processor Control Instructions........................................................................ 46
Table 4–24. Core Architecture Processor-Configurations .................................................... 50
Table 4–25. Core Architecture Processor-State.................................................................. 51
Table 4–26. Core Architecture Instructions ........................................................................51
Table 4–27. Code Density Option Instruction Additions ....................................................... 54
Table 4–28. Loop Option Processor-State Additions ........................................................... 55
Table 4–29. Loop Option Instruction Additions ................................................................... 55
Table 4–30. Extended L32R Option Processor-State Additions ............................................ 57
Table 4–31. 16-bit Integer Multiply Option Instruction Additions............................................ 58
Table 4–32. 32-bit Integer Multiply Option Processor-Configuration Additions........................ 59
Table 4–33. 32-Bit Integer Multiply Instruction Additions...................................................... 59
Table 4–34. 32-bit Integer Divide Option Processor-Configuration Additions.......................... 59
Table 4–35. 32-bit Integer Divide Option Exception Additions .............................................. 60
Table 4–36. 32-bit Integer Divide Option Instruction Additions.............................................. 60
Table 4–37. MAC16 Option Processor-State Additions........................................................ 61
Table 4–38. MAC16 Option Instruction Additions................................................................ 61
Table 4–39. Miscellaneous Operations Option Processor-Configuration Additions ................. 62
Table 4–40. Miscellaneous Operations Instruction Additions................................................ 63
Table 4–41. Coprocessor Option Exception Additions ......................................................... 64
Table 4–42. Coprocessor Option Processor-State Additions ................................................ 64
Table 4–43. Boolean Option Processor-State Additions....................................................... 65
Table 4–44. Boolean Option Instruction Additions...............................................................66
List of Tables
xiv Xtensa Instruction Set Architecture (ISA) Reference Manual
Table 4–45. Floating-Point Coprocessor Option Processor-State Additions ........................... 67
Table 4–46. Floating-Point Coprocessor Option Instruction Additions ................................... 67
Table 4–47. FCR fields.................................................................................................... 70
Table 4–48. FSR fields .................................................................................................... 70
Table 4–49. Floating-Point Coprocessor Option Load/Store Instructions ............................... 72
Table 4–50. Floating-Point Coprocessor Option Operation Instructions................................. 72
Table 4–51. Multiprocessor Synchronization Option Instruction Additions ............................. 76
Table 4–52. Conditional Store Option Processor-State Additions.......................................... 78
Table 4–53. Conditional Store Option Instruction Additions.................................................. 78
Table 4–54. ATOMCTL Register Fields ............................................................................. 81
Table 4–55. Exception Option Constant Additions (Exception Causes) ................................. 83
Table 4–56. Exception Option Processor-Configuration Additions ........................................ 83
Table 4–57. Exception Option Processor-State Additions .................................................... 84
Table 4–58. Exception Option Instruction Additions ............................................................ 84
Table 4–59. Instruction Exceptions under the Exception Option ........................................... 85
Table 4–60. Interrupts under the Exception Option ............................................................. 86
Table 4–61. Machine Checks under the Exception Option ................................................... 86
Table 4–63. PS Register Fields ........................................................................................ 87
Table 4–62. Debug Conditions under the Exception Option ................................................. 87
Table 4–64. Exception Causes ........................................................................................ 89
Table 4–65. Exception and Interrupt Information Registers by Vector ................................... 94
Table 4–66. Exception and Interrupt Exception Registers by Vector ..................................... 95
Table 4–67. Relocatable Vector Option Processor-State Additions ....................................... 99
Table 4–68. Unaligned Exception Option Constant Additions (Exception Causes)................ 100
Table 4–69. Interrupt Option Constant Additions (Exception Causes) ................................. 101
Table 4–70. Interrupt Option Processor-Configuration Additions ........................................ 101
Table 4–71. Interrupt Option Processor-State Additions .................................................... 101
Table 4–72. Interrupt Option Instruction Additions ............................................................ 102
Table 4–73. Interrupt Types ........................................................................................... 103
Table 4–74. High-Priority Interrupt Option Processor-Configuration Additions...................... 107
Table 4–75. High-Priority Interrupt Option Processor-State Additions.................................. 107
Table 4–76. High-Priority Interrupt Option Instruction Additions.......................................... 107
Table 4–77. Timer Interrupt Option Processor-Configuration Additions ............................... 110
Table 4–78. Timer Interrupt Option Processor-State Additions ............................................111
Table 4–79. Instruction Cache Option Processor-Configuration Additions ........................... 115
Table 4–80. Instruction Cache Option Instruction Additions ............................................... 116
Table 4–81. Instruction Cache Test Option Instruction Additions ........................................ 117
Table 4–82. Instruction Cache Index Lock Option Instruction Additions............................... 118
Table 4–83. Data Cache Option Processor-Configuration Additions ................................... 119
Table 4–84. Data Cache Option Instruction Additions ....................................................... 119
Table 4–85. Data Cache Test Option Instruction Additions................................................. 121
Table 4–86. Data Cache Index Lock Option Instruction Additions ....................................... 122
Table 4–87. RAM/ROM Access Restrictions .................................................................... 124
Table 4–88. Instruction RAM Option Processor-Configuration Additions ............................. 124
Table 4–89. Instruction ROM Option Processor-Configuration Additions ............................. 125
Table 4–90. Data RAM Option Processor-Configuration Additions...................................... 126
Table 4–91. Data ROM Option Processor-Configuration Additions ..................................... 127
Table 4–92. XLMI Option Processor-Configuration Additions ............................................. 127
Table 4–93. Memory ECC/Parity Option Processor-Configuration Additions ........................ 129
List of Tables
Xtensa Instruction Set Architecture (ISA) Reference Manual xv
Table 4–94. Memory ECC/Parity Option Processor-State Additions.................................... 129
Table 4–95. Memory ECC/Parity Option Instruction Additions ............................................ 130
Table 4–96. MESR Register Fields ................................................................................. 131
Table 4–97. MECR Register Fields .................................................................................135
Table 4–98. MEVADDR Contents ...................................................................................136
Table 4–99. Access Characteristics Encoded in the Attributes ........................................... 144
Table 4–100. Local Memory Accesses .............................................................................. 149
Table 4–101. Region Protection Option Exception Additions ............................................... 151
Table 4–102. Region Protection Option Processor-State Additions.......................................151
Table 4–103. Region Protection Option Instruction Additions...............................................151
Table 4–104. Region Protection Option Attribute Field Values ............................................. 155
Table 4–105. MMU Option Processor-Configuration Additions.............................................159
Table 4–106. MMU Option Exception Additions .................................................................159
Table 4–107. MMU Option Processor-State Additions......................................................... 160
Table 4–108. MMU Option Instruction Additions.................................................................160
Table 4–109. MMU Option Attribute Field Values ............................................................... 178
Table 4–110. Windowed Register Option Constant Additions (Exception Causes) ................. 181
Table 4–111. Windowed Register Option Processor-Configuration Additions ........................181
Table 4–112. Windowed Register Option Processor-State Additions and Changes ................ 181
Table 4–113. Windowed Register Option Instruction Additions ............................................ 182
Table 4–114. Windowed Register Usage...........................................................................188
Table 4–115. Processor Interface Option Constant Additions (Exception Causes) ................. 195
Table 4–116. Miscellaneous Special Registers Option Processor-Configuration Additions ...... 195
Table 4–117. Miscellaneous Special Registers Option Processor-State Additions .................. 196
Table 4–118. Thread Pointer Option Processor-State Additions ........................................... 196
Table 4–119. Processor ID Option Special Register Additions ............................................. 197
Table 4–120. Debug Option Processor-Configuration Additions ........................................... 197
Table 4–121. Debug Option Processor-State Additions ....................................................... 198
Table 4–122. Debug Option Instruction Additions ............................................................... 198
Table 4–123. DEBUGCAUSE Fields.................................................................................199
Table 4–124. DBREAK Fields .......................................................................................... 200
Table 4–125. DBREAKC[i] Register Fields .......................................................................202
Table 4–126. Trace Port Option Special Register Additions ................................................. 204
Table 5–127. Alphabetical List of Processor State ............................................................. 205
Table 5–128. Numerical List of Special Registers ............................................................... 209
Table 5–129. LBEG - Special Register #0 ....................................................................... 212
Table 5–130. LEND - Special Register #1 ....................................................................... 213
Table 5–131. LCOUNT - Special Register #2.......................................................................213
Table 5–132. ACCLO - Special Register #16....................................................................214
Table 5–133. ACCHI - Special Register #17....................................................................214
Table 5–134. M0..3 - Special Register #32-35 ...............................................................214
Table 5–135. SAR - Special Register #3 .........................................................................215
Table 5–136. BR - Special Register #4 ...........................................................................215
Table 5–137. LITBASE - Special Register #5..................................................................216
Table 5–138. SCOMPARE1 - Special Register #12 ............................................................ 216
Table 5–139. PS - Special Register #230........................................................................217
Table 5–140. PS.INTLEVEL - Special Register #230 (part).............................................. 217
Table 5–141. PS.EXCM - Special Register #230 (part) .....................................................218
Table 5–142. PS.UM - Special Register #230 (part) .........................................................219
List of Tables
xvi Xtensa Instruction Set Architecture (ISA) Reference Manual
Table 5–143. PS.RING - Special Register #230 (part) .....................................................219
Table 5–144. PS.OWB - Special Register #230 (part) ....................................................... 220
Table 5–145. PS.CALLINC - Special Register #230 (part)................................................ 220
Table 5–146. PS.WOE - Special Register #230 (part) ....................................................... 220
Table 5–147. WindowBase - Special Register #72 .......................................................... 221
Table 5–148. WindowStart - Special Register #73 ........................................................ 221
Table 5–149. PTEVADDR - Special Register #83.............................................................. 222
Table 5–150. RASID - Special Register #90.................................................................... 222
Table 5–151. ITLBCFG - Special Register #91................................................................ 223
Table 5–152. DTLBCFG - Special Register #92................................................................ 223
Table 5–153. EXCCAUSE - Special Register #232 ............................................................ 224
Table 5–154. EXCVADDR - Special Register #238 ............................................................ 224
Table 5–155. VECBASE - Special Register #231 .............................................................. 224
Table 5–156. MESR - Special Register #109.................................................................... 225
Table 5–157. MECR - Special Register #110 .................................................................... 225
Table 5–158. MEVADDR - Special Register #111 .............................................................. 225
Table 5–159. DEBUGCAUSE - Special Register #233 ........................................................ 226
Table 5–160. EPC1 - Special Register #177.................................................................... 226
Table 5–161. EPC2..7 - Special Register #178-183........................................................ 226
Table 5–162. DEPC - Special Register #192.................................................................... 227
Table 5–163. MEPC - Special Register #106.................................................................... 227
Table 5–164. EPS2..7 - Special Register #194-199........................................................ 227
Table 5–165. MEPS - Special Register #107.................................................................... 228
Table 5–166. EXCSAVE1 - Special Register #192 ............................................................ 228
Table 5–167. EXCSAVE2..7- Special Register #210-215.................................................. 228
Table 5–168. MESAVE- Special Register #108 .................................................................. 229
Table 5–169. INTERRUPT - Special Register #226 (read)................................................. 229
Table 5–170. INTSET - Special Register #226 (write) ...................................................... 230
Table 5–171. INTCLEAR - Special Register #227 ............................................................ 230
Table 5–172. INTENABLE - Special Register #228 .......................................................... 231
Table 5–173. ICOUNT - Special Register #236 ................................................................ 231
Table 5–174. ICOUNTLEVEL - Special Register #237 ...................................................... 232
Table 5–175. CCOUNT - Special Register #234 ................................................................ 232
Table 5–176. CCOMPARE0..2 - Special Register #240-242.............................................. 233
Table 5–177. IBREAKENABLE - Special Register #96 ...................................................... 233
Table 5–178. IBREAKA0..1 - Special Register #128-129................................................ 234
Table 5–179. DBREAKC0..1 - Special Register #160-161................................................ 234
Table 5–180. DBREAKA0..1 - Special Register #144-145................................................ 235
Table 5–181. PRID - Special Register #235.................................................................... 235
Table 5–182. MMID - Special Register #89...................................................................... 235
Table 5–183. DDR - Special Register #104...................................................................... 236
Table 5–184. CPENABLE - Special Register #224 ............................................................ 236
Table 5–185. MISC0..3 - Special Register #244-247...................................................... 236
Table 5–186. ATOMCTL - Special Register #99................................................................ 237
Table 5–187. Numerical List of User Registers .................................................................. 237
Table 5–188. THREADPTR - User Register #231.............................................................. 238
Table 5–189. FCR - User Register #232 ......................................................................... 239
Table 5–190. FSR - User Register #233 ......................................................................... 239
Table 7–191. Uses Of Instruction Fields............................................................................ 573
List of Tables
Xtensa Instruction Set Architecture (ISA) Reference Manual xvii
Table 7–192. Whole Opcode Space.................................................................................. 575
Table 7–193. QRST (from Table 7–192) Formats RRR, CALLX, and RSR (t, s, r, op2 vary) .... 575
Table 7–194. RST0 (from Table 7–193) Formats RRR and CALLX (t, s, r vary) ..................... 576
Table 7–195. ST0 (from Table 7–194 Formats RRR and CALLX (t, s vary)............................ 576
Table 7–196. SNM0 (from Table 7–195) Format CALLX (n, s vary) ......................................576
Table 7–197. JR (from Table 7–196) Format CALLX (s varies) ............................................ 576
Table 7–198. CALLX (from Table 7–196) Format CALLX (s varies) ......................................576
Table 7–199. SYNC (from Table 7–195) Format RRR (s varies)...........................................576
Table 7–200. RFEI (from Table 7–195) Format RRR (s varies) ............................................ 577
Table 7–201. RFET (from Table 7–200) Format RRR (no bits vary)...................................... 577
Table 7–202. ST1 (from Table 7–194) Format RRR (t, s vary).............................................. 577
Table 7–203. TLB (from Table 7–194) Format RRR (t, s vary).............................................. 577
Table 7–204. RT0 (from Table 7–194) Format RRR (t, r vary) .............................................. 578
Table 7–205. RST1 (from Table 7–193) Format RRR (t, s, r vary) ........................................578
Table 7–206. ACCER (from Table 7–205) Format RRR (t, s vary) ........................................ 578
Table 7–207. IMP (from Table 7–205) Format RRR (t, s vary) (Section 7.3.3)........................ 578
Table 7–208. RFDX (from Table 7–207) Format RRR (s varies) ........................................... 579
Table 7–209. RST2 (from Table 7–193) Format RRR (t, s, r vary) ........................................579
Table 7–210. RST3 (from Table 7–193) Formats RRR and RSR (t, s, r vary)......................... 579
Table 7–211. LSCX (from Table 7–193) Format RRR (t, s, r vary) ........................................579
Table 7–212. LSC4 (from Table 7–193) Format RRI4 (t, s, r vary) ........................................ 580
Table 7–213. FP0 (from Table 7–193) Format RRR (t, s, r vary)........................................... 580
Table 7–214. FP1OP (from Table 7–213) Format RRR (s, r vary)......................................... 580
Table 7–215. FP1 (from Table 7–193) Format RRR (t, s, r vary)........................................... 580
Table 7–216. LSAI (from Table 7–192) Formats RRI8 and RRI4 (t, s, imm8 vary) .................. 581
Table 7–217. CACHE (from Table 7–216) Formats RRI8 and RRI4 (s, imm8 vary)................. 581
Table 7–218. DCE (from Table 7–217) Format RRI4 (s, imm4 vary) .....................................581
Table 7–219. ICE (from Table 7–217) Format RRI4 (s, imm4 vary).......................................581
Table 7–220. LSCI (from Table 7–192) Format RRI8 (t, s, imm8 vary) ..................................582
Table 7–221. MAC16 (from Table 7–192) Format RRR (t, s, r, op1 vary)............................... 582
Table 7–222. MACID (from Table 7–221) Format RRR (t, s, r vary) ...................................... 582
Table 7–223. MACIA (from Table 7–221) Format RRR (t, s, r vary) ...................................... 582
Table 7–224. MACDD (from Table 7–221) Format RRR (t, s, r vary)..................................... 583
Table 7–225. MACAD (from Table 7–221) Format RRR (t, s, r vary) ..................................... 583
Table 7–226. MACCD (from Table 7–221) Format RRR (t, s, r vary)..................................... 583
Table 7–227. MACCA (from Table 7–221) Format RRR (t, s, r vary) .....................................583
Table 7–228. MACDA (from Table 7–221) Format RRR (t, s, r vary) .....................................584
Table 7–229. MACAA (from Table 7–221) Format RRR (t, s, r vary) .....................................584
Table 7–230. MACI (from Table 7–221) Format RRR (t, s, r vary) ........................................584
Table 7–231. MACC (from Table 7–221) Format RRR (t, s, r vary) ....................................... 584
Table 7–232. CALLN (from Table 7–192) Format CALL (offset varies) ..................................584
Table 7–233. SI (from Table 7–192) Formats CALL, BRI8 and BRI12(offset varies) ............... 585
Table 7–234. BZ (from Table 7–233) Format BRI12 (s, imm12 vary).....................................585
Table 7–235. BI0 (from Table 7–233) Format BRI8 (s, r, imm8 vary)..................................... 585
Table 7–236. BI1 (from Table 7–233) Formats BRI8 and BRI12 (s, r, imm8 vary) ................... 585
Table 7–237. B1 (from Table 7–236) Format BRI8 (s, imm8 vary) ........................................ 585
Table 7–238. B (from Table 7–192) Format RRI8 (t, s, imm8 vary) ....................................... 585
Table 7–239. ST2 (from Table 7–192) Formats RI7 and RI6 (s, r vary).................................. 586
Table 7–240. ST3 (from Table 7–192) Format RRRN (t, s vary) ........................................... 586
List of Tables
xviii Xtensa Instruction Set Architecture (ISA) Reference Manual
Table 7–241. S3 (from Table 7–240) Format RRRN (no fields vary) ..................................... 586
Table 8–242. Windowed Register Usage........................................................................... 587
Table 8–243. CALL0 Register Usage................................................................................ 589
Table 8–244. Data Types and Alignment ........................................................................... 589
Table 8–245. Breakpoint Instruction Operand Conventions ................................................. 596
Table 8–246. Instruction Idioms........................................................................................ 599
Table 8–247. Xtensa Pipeline .......................................................................................... 608
Table 9-248. Instructions Added ...................................................................................... 611
Table 9-249. Cache Attribute Register.............................................................................. 617
Table 9-250. Cache Attribute Special Register ..................................................................617
Table 9–251. T1050 Additional SYNC Requirements.......................................................... 621
Preface
Xtensa Instruction Set Architecture (ISA) Reference Manual xix
Preface
This manual is written for Tensilica customers who are experienced in working with mi-
croprocessors or in writing assembly code or compilers. It is NOT a specification for one
particular implementation of the Architecture, but rather a reference for the ongoing
Instruction Set Architecture. For a detailed specification for specific products, refer to a
specific Tensilica processor data book.
Notation
italic_name indicates a program or file name, document title, or term being defined.
$ represents your shell prompt, in user-session examples.
literal_input indicates literal command-line input.
variable indicates a user parameter.
literal_keyword (in text paragraphs) indicates a literal command keyword.
literal_output indicates literal program output.
... output ... indicates unspecified program output.
[optional-variable] indicates an optional parameter.
[variable] indicates a parameter within literal square-braces.
{variable} indicates a parameter within literal curly-braces.
(variable) indicates a parameter within literal parentheses.
| means OR.
(var1 | var2) indicates a required choice between one of multiple parameters.
[var1 | var2] indicates an optional choice between one of multiple parameters.
var1 [, varn]* indicates a list of 1 or more parameters (0 or more repetitions).
4'b0010 is a 4-bit value specified in binary.
12'o7016 is a 12-bit value specified in octal.
10'd4839 is a 10-bit value specified in decimal.
32'hff2a or 32'HFF2A is a 32-bit value specified in hexadecimal.
Terms
0x at the beginning of a value indicates a hexadecimal value.
b means bit.
B means byte.
Preface
xx Xtensa Instruction Set Architecture (ISA) Reference Manual
flush is deprecated due to potential ambiguity (it may mean write-back or discard).
Mb means megabit.
MB means megabyte.
PC means program counter.
word means 4 bytes.
Preface
Xtensa Instruction Set Architecture (ISA) Reference Manual xxi
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xxii Xtensa Instruction Set Architecture (ISA) Reference Manual
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Changes from the Previous Version
Xtensa Instruction Set Architecture (ISA) Reference Manual xxiii
Changes from the Previous Version
The following changes have been made to this document for the Tensilica RC-2010.1
release:
Deleted several extraneous blank pages in between each chapter in previous re-
lease.
Corrected erroneous cross-references to Tab le 4–55 through Ta b l e 4–58 in
Section 4.4.1.1 on page 83
Clarified information about lookup rings in Section 4.6.2.2 and Section 4.6.2.3.
The following changes have been made to this document for the Tensilica RC-2009.0
release:
A new register, ATOMCL, has been added to Section 4.3.13 “Conditional Store Op-
tion” on page 91. The ATOMCTL register controls the interaction of the S32C1I in-
struction with the memory system.
The description of attributes for the Section 4.6.3 “Region Protection Option” on
page 187 and the Section 4.6.5.10 “MMU Option Memory Attributes” on page 213
have been improved. There are no actual changes to the attributes.
The Section 4.6.5 “MMU Option” on page 196 has gained a new option. Way5 and
Way6 can now be either variable or fixed. The variable version provides more flexi-
bility in the address map and has a setting where the MMU puts out a physical ad-
dress equal to the virtual address and is, in that sense, turned off.
Many of the SYNC instruction requirements listed in Section 5.3 “Special Registers”
on page 259 have not actually been needed after T1050. Those requirements have
now been removed from Section 5.3 but retained in Appendix A.
The RER and WER instructions have been added to Chapter 6.
Changes from the Previous Version
xxiv Xtensa Instruction Set Architecture (ISA) Reference Manual
Chapter 1. Introduction
Xtensa Instruction Set Architecture (ISA) Reference Manual 1
1. Introduction
This chapter provides an overview of Tensilica, the Xtensa Instruction Set Architecture
(ISA), and the Xtensa Processor Generator.
1.1 What Problem is Tensilica Solving?
Processors have traditionally been extremely difficult to design and modify. Therefore,
most systems contain rigid processors that were designed and verified once for general-
purpose use and then embedded into multiple applications over time. Because these
processors are general-purpose designs, their suitability to any particular application is
less than ideal. Although it would be preferable to have a processor specifically de-
signed to execute a particular application’s code better (for example, to run faster, or
consume less power, or cost less), this is rarely possible because of the difficulty; the
time, cost, and risk of modifying an existing processor or developing a new processor is
very high.
It is also not appropriate to simply design traditional processors with more features to
cover all applications, because any given application only requires a particular set of
features — a processor with features not required by the application is overly costly and
consumes unnecessary power. It is also not possible to know all of the potential applica-
tion targets when a processor is initially designed.
If processor configuration could be automated and made reliable, then system designers
would have the option and ability to create truly efficient application solutions.
This is just what Tensilica is about: Tensilica provides a set of techniques and tools for
designing an application solution that contains one or more processors, each one con-
figured and enhanced at design-time to fine-tune its suitability for a specific application.
Fine-tuning an architecture can consist of any combination of:
Extensibility: Adding architectural enhancements.
Configurability: Creating custom processor configurations.
Retargetability: Mapping the architecture into hardware to meet different speed, ar-
ea, and power targets in different processes.
1.1.1 Adding Architectural Enhancements
As an example of an architectural enhancement, consider a device designed to transmit
and receive data over a channel using a complex protocol. Because the protocol is com-
plex, the processing cannot be reasonably accomplished entirely in hard logic, and in-
Chapter 1. Introduction
2 Xtensa Instruction Set Architecture (ISA) Reference Manual
stead a programmable processor is introduced into the system for protocol processing.
This processor’s programmability also allows bug fixes and upgrades to later protocols
to be done by loading the instruction memories with new software. However, the proces-
sor was probably not designed for this particular application (the application may not
have even existed when the processor was designed), and the application may perform
operations that require many instructions — operations that could be accomplished with
a trivial amount of additional processor logic.
Before the introduction of Tensilica’s Xtensa technology, processors could not be
enhanced easily. Because of this, many system designers are forced to solve problems
by executing the inefficient pure-software solution on the available general-purpose
processor. This results in a solution that may be slower, or higher power, or costlier than
necessary (for example, it may require a larger, more powerful processor to execute the
program at sufficient speed).
Other designers choose to provide some of the processing requirements in special-
purpose hardware that they design for the application. This approach requires special
code to access the custom hardware at various points in the program. However, the time
to transfer data between the processor and the custom hardware limits the utility of this
approach to fairly large units of work; small computations cannot sufficiently amortize
the communication overhead introduced by this approach to provide a reasonable
speed-up.
In the communication-channel application example, the protocol might require encryp-
tion, error-correction, or compression/decompression processing. Such processing
often operates on individual bits rather than a processor’s larger words. The circuitry for
a computation may be rather modest, but the need for the processor to extract each bit,
sequentially process it, and then repack the bits adds considerable overhead.
As a specific example, consider the Huffman decode shown in Table 1–1.
Table 1–1. Huffman Decode Example
Input Value Length
00xxxxxx 0 2
01xxxxxx 1 2
10xxxxxx 2 2
110xxxxx 3 3
1110xxxx 4 4
11110xxx 5 5
111110xx 6 6
1111110x 7 7
11111110 8 8
11111111 9 8
Chapter 1. Introduction
Xtensa Instruction Set Architecture (ISA) Reference Manual 3
Both the value and the length must be computed, so that length bits can be shifted off to
find the start of the next token. (A similar encoding is used in the MPEG compression
standard.) There are many ways to code this for a conventional RISC instruction set, but
all of them require many instructions, because there are many tests to be done, and
each test requires a single cycle (as opposed to a single gate delay for logic). For exam-
ple, in the MIPS instruction set, the above decode procedure might look like this:
/* input in t0, value out in t1, length out in t2 */
srl t1, t0, 6
li t3, 3
beq t3, t4, 2f
li t2, 2
andi t3, t0, 0x20
beq t3, r0, 1f
li t2, 3
andi t3, t0, 0x10
beq t3, r0, 1f
li t2, 4
andi t3, t0, 0x08
beq t3, r0, 1f
li t2, 5
andi t3, t0, 0x04
beq t3, r0, 1f
li t2, 6
andi t3, t0, 0x02
beq t3, r0, 1f
li t2, 7
andi t3, t0, 0x01
beq t3, r0, 1f
li t2, 8
b2f
li t1, 9
1: /* length = value */
move t1, t2
2: /* done */
This is so expensive that a 256-entry lookup table is typically used instead. However, a
256-entry lookup table takes significant space and can take many cycles to access. For
longer Huffman encodings, the table size would become prohibitive, leading to more
complex and slower code.
The logic to decode this requires roughly 30 gates (just the combinatorial logic function,
not counting instruction decode and so forth) — less than 0.1% of a processor gate-
count — and can be computed by a special-purpose processor instruction in a single cy-
cle. This is a factor of 4 to 20 speed-up over using general-purpose instructions only. A
processor extended to have this logic in the form of an instruction would simply do:
huff8t1, t0 /* t1[3:0] is length, t1[7:0] is value */
Chapter 1. Introduction
4 Xtensa Instruction Set Architecture (ISA) Reference Manual
Tensilica’s solution is to provide a mechanism with which to easily and efficiently extend
processor architecture with application-specific instructions.
1.1.2 Creating Custom Processor Configurations
While the ability to extend processor architecture, which we call extensibility, lets system
designers incorporate new functionality into a processor, configurability lets processor
designers specify whether (or how much) pre-designed functionality is required for a
particular product.
The simplest sort of configurability is a binary choice: an architectural feature is either
present or absent in a particular processor configuration. For example, a processor
might be offered either with or without floating-point hardware. Multiple configurations of
a set of architectural features could be created by the processor designer, not the
system designer.
System-design flexibility is improved by having finer gradations in processor-configura-
tion choices. For example, a processor configuration might allow the system designer to
specify the number of registers in the register file, memory width, cache size, cache
associativity, and so on.
1.1.3 Mapping the Architecture into Hardware
Extensibility and configurability provide great flexibility. However, the resulting design
must still be mapped into physical hardware. Synthesis, placement, and routing tools
allow high-level representations of a design to be automatically mapped into more
detailed designs. While these mapping operations do not change the functionality of the
design, they are important building blocks that facilitate extensibility and configurability.
Many processors are manually designed all the way to the layout. For such a processor
design, extensibility and configurability would require changes to the layout. By contrast,
the Tensilica system builds on existing synthesis, placement, and routing tools so that
configuration need only change the input to synthesis, and conventional mapping tech-
niques are used to create physical hardware.
Some synthesis tools choose different mapping based on the designer’s goal specifica-
tions, allowing the mapping to optimize for speed, power, area, or target components.
This is as close to providing configurability that existing mapping tools come: the design-
er can specify different synthesis parameters for a fixed input. By contrast, the Tensilica
approach lets the designer alter the input to synthesis, and change its functionality.
Chapter 1. Introduction
Xtensa Instruction Set Architecture (ISA) Reference Manual 5
1.1.4 Development and Verification Tools
Extending an architecture and reconfiguring a processor may require widespread
changes in processor logic to keep pipeline stages synchronized. Such reconfiguration
requires that the processor be re-verified. Tensilica automates these changes and
makes them reliable.
In addition, when the processor changes, the software tool chain — compilers, assem-
blers, linkers, debuggers, simulators, and profilers — must change as well. In the past,
the cost of software changes associated with processor reconfigurations has been a
major impediment. Tensilica automates these changes also.
Finally, it should be possible to get feedback on the performance, cost, power, and other
effects of processor reconfiguration without taking the design through the entire map-
ping process. This feedback can be used to direct further reconfiguration of the proces-
sor until the system design goals are achieved. Tensilica’s technology dramatically
improves the feedback loop.
1.2 The Xtensa Instruction Set Architecture
The Xtensa Instruction Set Architecture (ISA) is a new post-RISC ISA targeted at
embedded, communication, and consumer products. The ISA is designed to provide:
A high degree of extensibility
Industry-leading code density
Optimized low-power implementation
High performance
Low-cost implementation
This manual describes the Xtensa ISA — both the core architecture and the architectur-
al options. Figure 1–1 illustrates the general organization of the processor hardware in
which the Xtensa ISA is implemented. This manual does not describe the memory map,
protection model, or peripherals that can be implemented in particular configurations of
the Xtensa ISA.
Chapter 1. Introduction
6 Xtensa Instruction Set Architecture (ISA) Reference Manual
Figure 1–1. Xtensa LX Hardware Architecture Block Diagram
Table 1–2 compares the architectural features provided by the Xtensa ISA to those of
typical RISC architectures. Each of the Xtensa features are described in this manual.
Table 1–2. Comparison of Typical RISC and Xtensa ISA Features
Architectural Feature Typical RISC Xtensa
Instruction size 32 bits 24 and 16 bit
Compare and branch no or partial total
Application-specific instructions no yes
Zero-overhead loop no yes
Funnel shift no (except 29000) yes
Variable-increment register windows no yes
Conditional move recently yes
Compound multiply/add recently yes
Advanced multiprocessor synchronization recently yes
Designer-Defined
Queues and Ports
Instruction
Dispatch
Instruction Fetch / Decode
Vectra LX DSP Engine
Data Memory
Management &
Protection
Data ROMs
Data RAMs
Data Cache
PIF
Base ISA
Execution Pipeline
Base ALU
Floating Point
MAC 16 DSP
MUL 16/32
Base Register File
Designer-Defined
Execution Units
Designer-Defined FLIX parallel
execution pipelines - "N" wide
Instruction ROM
Instruction RAM
Instruction
Cache
Inst. Memory
Management &
Protection
Designer-Defined Features (TIE)
Base ISA Feature
Configurable Function
Optional Function
Optional & Configurable
Processor Controls
Trace Port
JTAG Tap Control
On-Chip Debug
Timers
Interrupt Control
Data Address
Watch Registers
Instruction Address Watch
Registers
Exception Support
Exception Handling
Registers
JTAG
Trace
Interrupts
Designer-Defined Data
Load/Store Unit
Data
Load/Store
Unit
External Interface
Xtensa LX
Processor Interface
Control
Write Buffer
Xtensa
Local
Memory
Interface
Designer-Defined Execution Units,
Register Files, and Interfaces
Designer-Defined Execution Units,
Register Files, and Interfaces
Chapter 1. Introduction
Xtensa Instruction Set Architecture (ISA) Reference Manual 7
1.2.1 Configurability
The Xtensa ISA goes further than incorporating post-RISC features: it is modular,
consisting of a core architecture and architectural options. Table 1–3 lists the initial set
of modular components.
Table 1–3. Modular Components
Component Reference
Core Architecture Chapter 3, "Core Architecture" on page 23
Core Architecture Section 4.2 “Core Architecture” on page 50
Options for Additional Instructions
Code Density Option "Code Density Option" on page 53
Loop Option "Loop Option" on page 54
Extended L32R Option "Extended L32R Option" on page 56
16-bit Integer Multiply Option "16-bit Integer Multiply Option" on page 57
32-bit Integer Multiply Option "32-bit Integer Multiply Option" on page 58
MAC16 Option "MAC16 Option" on page 60
Miscellaneous Operations Option "Miscellaneous Operations Option" on page 62
Coprocessor Option "Coprocessor Option" on page 63
Boolean Option "Boolean Option" on page 65
Floating-Point Coprocessor Option "Floating-Point Coprocessor Option" on page 67
Multiprocessor Synchronization Option "Multiprocessor Synchronization Option" on page 74
Conditional Store Option "Conditional Store Option" on page 77
Options for Interrupts and Exceptions
Exception Option "Exception Option" on page 82
Unaligned Exception Option "Unaligned Exception Option" on page 99
Interrupt Option "Interrupt Option" on page 100
High-Priority Interrupt Option "High-Priority Interrupt Option" on page 106
Timer Interrupt Option "Timer Interrupt Option" on page 110
Chapter 1. Introduction
8 Xtensa Instruction Set Architecture (ISA) Reference Manual
1.2.2 Extensibility
In addition to the Xtensa components shown in Table 1–3, designers can extend the
Xtensa architecture by adding States, Register Files, and instructions that operate both
on the AR Register File and on the additional states the designer has added. These in-
structions can be single cycle or multiple cycles, and share or re-use logic.
Options for Memory
Instruction Cache Option "Instruction Cache Option" on page 115
Instruction Cache Test Option "Instruction Cache Test Option" on page 116
Instruction Cache Index Lock Option "Instruction Cache Index Lock Option" on page 117
Data Cache Option "Data Cache Option" on page 118
Data Cache Test Option "Data Cache Test Option" on page 121
Data Cache Index Lock Option "Data Cache Index Lock Option" on page 122
Instruction RAM Option "Instruction RAM Option" on page 124
Instruction ROM Option "Instruction ROM Option" on page 125
Data RAM Option "Data RAM Option" on page 126
Data ROM Option "Data ROM Option" on page 126
XLMI Option "XLMI Option" on page 127
Hardware Alignment Option "Hardware Alignment Option" on page 128
Memory ECC/Parity Option "Memory ECC/Parity Option" on page 128
Options for Memory Protection
Region Protection Option "Region Protection Option" on page 150
Region Translation Option "Region Translation Option" on page 156
MMU Option "MMU Option" on page 158
Options for Other Purposes
Windowed Register Option "Windowed Register Option" on page 180
Processor Interface Option "Processor Interface Option" on page 194
Miscellaneous Special Registers Option "Miscellaneous Special Registers Option" on page 195
Thread Pointer Option "Thread Pointer Option" on page 196
Processor ID Option "Processor ID Option" on page 196
Debug Option "Debug Option" on page 197
Trace Port Option "Trace Port Option" on page 203
Table 1–3. Modular Components
(continued)
Component Reference
Chapter 1. Introduction
Xtensa Instruction Set Architecture (ISA) Reference Manual 9
1.2.2.1 State Extensions
The designer can add State Registers. These State Registers can be the source or
destination of various instructions and are saved and restored by the operating system.
1.2.2.2 Register File Extensions
The designer can add Register Files of widely varying size. These Register Files can be
the source or destination of various instructions and are saved and restored by the
operating system. The registers within them are allocated by the compiler, which can
spill and re-fill them if necessary.
1.2.2.3 Instruction Extensions
The designer can define new instructions that contain simple functions consisting of
combinatorial logic that takes one or two source operands from registers and produces a
result to be written to a register:
AR[r] ← f(AR[s], AR[t])
Instructions can also be much more complex with register file values and State appear-
ing as both inputs and outputs. These Instructions are described using the Tensilica
Instruction Extension (TIE) language (see Section 1.3.2).
1.2.2.4 Coprocessor Extensions
Another mechanism to extend the Xtensa ISA is to use the Coprocessor Option. A co-
processor is defined as a combination of registers, other state, and logic that operates
on that state, including loads, stores and setting of Booleans for branch true/false oper-
ations. A particular coprocessor can be enabled or disabled to control with one bit
whether or not instructions accessing that combination of registers and other state may
or may not execute.
1.2.3 Time-to-Market
The Xtensa Software Development Toolkit includes automatically generated software
that matches the designer’s processor configuration and eliminates tool headaches. The
ISA’s rich set of features (for example, interrupt and debug facilities) makes the system
designer’s job easier. The ability to create custom instructions with the TIE language
allows the designer to reach performance goals with less code-tuning or hard-to-
interface-to external logic.
Chapter 1. Introduction
10 Xtensa Instruction Set Architecture (ISA) Reference Manual
1.2.4 Code Density
The Xtensa core ISA is implemented as 24-bit instructions. This instruction width pro-
vides a direct 25% reduction in code size compared with 32-bit ISAs. The instructions
provide access to the entire processor hardware and support special functions, such as
single-instruction compare-and-branch, which reduce the number of instructions re-
quired to implement various applications. These special functions result in further code-
size reductions.
The Xtensa ISA also includes a Code Density Option that further reduces code size.
This option adds 16-bit instructions that are distinguished by opcode, and that can be
freely intermixed with 24-bit instructions to achieve higher code density than competing
ISAs without giving up the performance of a 32-bit ISA. The 16-bit instructions add no
new functionality but provide compact encoding of the most frequently used 24-bit in-
structions. In typical code, roughly half of all instructions can be encoded in 16 bits.
The core ISA omits the branch delay slots required by some RISC ISAs. This increases
code density by eliminating NOPs the compiler uses to fill the slot after a branch when it
cannot find a real instruction to put there (only 50% of the branch delay slots are filled on
some RISC architectures).
The Xtensa ISA provides a Windowed Registers Option. Xtensa windowed registers re-
duce code size by:
Eliminating register saves and restores at procedure entry and exit
Reducing argument shuffling
Allowing more local variables to live permanently in registers
1.2.5 Low Implementation Cost
The Xtensa architecture is designed to facilitate efficient implementation. It can be im-
plemented with simple instruction pipelines and direct hardware execution without micro
code. Operations that are too complex to easily implement with single instructions are
synthesized into appropriate instruction sequences by the compiler. The base architec-
ture avoids instructions that would need extra register file read or write ports. This keeps
the minimal configuration low-cost and low-power.
The Xtensa architecture fully supports the common data types and operations found in a
broad range of applications. The base architecture omits special-purpose data types
and operations. Optional instructions, the TIE language (see Section 1.3.2), and option-
al coprocessors allow the designer to add exactly the functionality needed, thus reduc-
ing the cost and performance due to unused general-purpose functions.
Chapter 1. Introduction
Xtensa Instruction Set Architecture (ISA) Reference Manual 11
The Xtensa ISA’s improvements in code size help reduce system cost (for example, by
reducing the amount of ROM, Flash, or RAM required). Making features like the number
of debug registers configurable allows the system designer, instead of the processor
designer, to decide the cost/benefit trade-off.
1.2.6 Low-Power
The Xtensa ISA has several energy-efficient attributes that enhance battery-operated
systems. The core ISA is built on 32-bit operations; some embedded processors of sim-
ilar performance have 64-bit base operations, which consumes additional power, often
unnecessarily. (TIE does allow 64-bit or greater computations to be added to the proces-
sor for those algorithms that require it, but these can be used selectively to achieve a
balance between performance and power consumption.)
The core ISA uses a register file with only two read ports and one write port, a configura-
tion that requires fewer transistors and less power than architectures with more ports.
The Xtensa Windowed Registers Option saves power by reducing the number of dy-
namic data-memory references and increasing the opportunities for variables to reside
in registers, where accesses require less power than memory accesses.
The WAITI (Wait for Interrupt) instruction, which is a part of the Interrupt Option, saves
power by setting the current interrupt level, powering down the processor’s logic, and
waiting for an interrupt.
1.2.7 Performance
The Xtensa ISA achieves its extensibility, code density, and low-power advantages with-
out sacrificing performance. For example, the Thumb and MIPS16 extensions of the
ARM and MIPS ISAs, respectively, provide improved code density by using only eight
registers and by reducing operand flexibility. By contrast, the Xtensa 24-bit instructions
can access 16 virtual registers with 3 register operands, and 16-bit instructions can
access all 16 registers with 1 to 3 register operands. The mapping of the 16 virtual
registers to the physical register file can eliminate register saves and restores at proce-
dure entry and exit, also increasing performance.
The Xtensa ISA also enhances performance by providing:
A complete set of compare-and-branch instructions, eliminating the need for sepa-
rate comparison instructions
LOOP, LOOPNEZ, and LOOPGTZ instructions that provide zero-overhead looping
These features are described in Section 3.8 of this manual. Other features of the archi-
tecture minimize critical paths, allow better compiler scheduling, and require fewer exe-
cuted instructions to implement a given program.
Chapter 1. Introduction
12 Xtensa Instruction Set Architecture (ISA) Reference Manual
1.2.8 Pipelines
The Xtensa ISA can be implemented using a variety of pipelines. A 5-stage load-store
oriented pipeline, such as is used in many RISC processors, is supported by Xtensa im-
plementations and illustrated in Figure 1–2. Many other variations are possible. A 7-
stage load-store oriented pipeline is supported by some Xtensa implementations. In-
structions can also have computation in later pipe stages so that the computation can
use memory data loaded by the same instruction.
Figure 1–2. Example Implementation Pipeline
The instruction set was also designed with a 2-read, 1-write general register file (called
Address Registers) in mind. While this approach results in lower implementation cost, it
prevents the inclusion of auto-incrementing loads and indexed stores to or from the
Address Registers. For the sake of symmetry, the ISA therefore does not include auto-
incrementing stores and indexed loads. However, all of these addressing modes are
I: Instruction Fetch
Decode
General
Registers
(AR Registers)
ALU
Address
Generation
Instruction
RAM
Instruction
Cache
Instruction
ROM
Exception
Resolution
and Write
Back
Xtensa Local
Memory
Interface
(XLMI)
Data
RAM
Data
Cache
Data
ROM
R: Instruction Decode/
Register Fetch Cycle
E: Execute/Effective
Address Cycle
M: Memory Access/
Branch Complete Cycle
W: Write Back Cycle
Coprocessor
Registers
Coprocessor
ALU
Chapter 1. Introduction
Xtensa Instruction Set Architecture (ISA) Reference Manual 13
possible for designer defined loads and stores. Designers can implement register files
with more read and write ports. For example, the Xtensa Floating-Point Coprocessor
Option contains a floating point register file with three read ports.
1.3 The Xtensa Processor Generator
The Xtensa Processor Generator is the key to rapid, optimal creation of application-
specific processors. Using this tool, the designer can specify and generate a complete
processor subsystem. The designer can select the instruction set, memory hierarchy,
peripherals and interface options to fit the target application.
The Generator user interface captures designer input in several ways, including:
Configuration of the processor micro-architecture
Configuration of Tensilica-provided instruction and coprocessor options
Specification of designer-defined instruction and coprocessor extensions, using the
Tensilica Instruction Extension (TIE) language
Together, these specifications make up the configuration database shown near the top
of Figure 1–3. This file is used to generate all the software tools and hardware descrip-
tions for the final application-specific processor.
1.3.1 Processor Configuration
The Generator interface drives the creation and optimization of all forms of the proces-
sor needed for integration into the system design flow. Based on the designer’s specifi-
cations, it creates synthesizable Verilog or VHDL code, synthesis scripts, an HDL test
bench, and physical placement files. Simultaneously, an optimized C and C++ compiler,
assembler, linker, symbolic debugger, Instruction Set Simulator, libraries and verification
tests are built for the designer’s software development.
The Generator interface lets the designer specify implementation targets for speed, area
and process technology, as well as the optimization priorities used in synthesis and lay-
out.
1.3.2 System-Specific Instructions—The TIE Language
The Tensilica Instruction Extension (TIE) language lets the designer add instructions to
the processor implementation, including full software support for generated instructions.
The specification of instruction extensions can include the following aspects as well as
many others:
Instruction Operation — Defines the operation of an additional instruction
Chapter 1. Introduction
14 Xtensa Instruction Set Architecture (ISA) Reference Manual
Immediate and Constant Tables — Defines constant values in instructions
Register File — Defines new register files
State — Defines new single processor states for instructions to operate on
Length and Format — The FLIX extensions to TIE allow for multiple instruction sizes
and the defining of multiple operations in a single instruction
Queues and Ports — Defines input and output queue ports and other ports for the
Xtensa processor
Types — Defines new C/C++ data types associated with user defined register files.
Allows type checking and automatic loading, storing and register allocation
Prototypes — Defines the argument types of C/C++ intrinsics for each instruction
and the instruction sequences for loading, storing, and moving the added types
Schedule — Defines the pipeline stages at which instructions use input values and
produce output values
In addition to designer-defined register and register file operands, instructions can use
AR registers as source values. They may generate multiple results, including AR register
file results. These instructions should be designed to have circuit delays appropriate to
the number cycles specified in the schedule specifications to avoid limiting the proces-
sor clock frequency. The instruction semantics are expressed in a subset of Verilog,
including all commonly used operators (multiply, add, subtract, minus, not, or, compari-
sons, reduction operators, shifts, concatenation, and conditionals).
The use of TIE for the creation of new instructions and coprocessors is described in the
Tensilica Instruction Extension (TIE) Language User’s Guide. The TIE language is de-
scribed in the Tensilica Instruction Extension (TIE) Language Reference Manual.
Chapter 1. Introduction
Xtensa Instruction Set Architecture (ISA) Reference Manual 15
Figure 1–3 illustrates the Xtensa design flow.
Figure 1–3. The Xtensa Design Flow
Configure Processor
(including Custom TIE
Instructions)
Configuration-Specific
Database
Configuration-Specific
HDL Description and
CAD Scripts
Simulate, Debug & Profile
Application Software:
Add Custom Instructions
Compile, Assemble and
Link Application Software
Install Software:
Set up Environment Synthesize Logic
Place and Route
Verify Timing
Hardware
Configuration-
Specific
Software
Development
Tools
Configuration
-Independent
XtTools
Software
Hardware User
Tasks
Automatically
Generated
Software User
Tasks
Chapter 1. Introduction
16 Xtensa Instruction Set Architecture (ISA) Reference Manual
Chapter 2. Notation
Xtensa Instruction Set Architecture (ISA) Reference Manual 17
2. Notation
This manual uses the following notation for instruction descriptions. Additional notation
specific to opcode encodings is provided in "Opcode Encodings" on page 574.
2.1 Bit and Byte Order
This manual consistently uses little-endian bit ordering for describing instructions and
registers. Bits in little-endian notation are numbered starting from 0 for the least-signifi-
cant bit of a field. However, this notation convention is independent of how an Xtensa
processor actually numbers bits, because a given processor can be configured for either
little- or big-endian byte and bit ordering. For most Xtensa instructions, bit numbering is
irrelevant; only the BBC and BBS instructions assign bit numbers to values on which the
processor operates. The BBC/BBS instructions use big-endian bit ordering (0 is the most-
significant bit) on a big-endian processor configuration. Bit numbering by the BBC/BBS
instructions is illustrated in Figure 2–4.
In specifying little- or big-endian ordering during actual processor configuration, you are
specifying both the bit and the byte order; the two orderings have the same most-signifi-
cant and least-significant ends.
Figure 2–5 on page 18 illustrates big- and little-endian byte order, as implemented by
Xtensa load (page 33) and store (page 36) instructions. Xtensa processors transfer data
to and from the system using interfaces that are configurable in width (32, 64, or 128 bits
in current implementations). These interfaces arrange their n bits according to their sig-
nificance representing an n-bit unsigned integer value (that is, 0 to 2n-1). Load and store
instructions that reference quantities less than n bits access different bits of this integer
in little-endian and big-endian byte orderings (for example, by changing the selection al-
gorithm for loads). Xtensa processors do not rearrange bits of a word to implement endi-
anness (for example, swapping bytes for big-endian operation).
Figure 2–4. Big and Little Bit Numbering for BBC/BBS Instructions
Littl
e-
E
n
di
an
bit
num
b
er
i
ng
f
or BBC
/
BBS
i
ns
t
ruc
ti
ons:
Big-Endian bit numbering for BBC/BBS instructions:
313029282726252423222120191817161514131211109876543210
←most-significant least-significant→
012345678910111213141516171819202122232425262728293031
←most-significant least-significant→
Chapter 2. Notation
18 Xtensa Instruction Set Architecture (ISA) Reference Manual
Figure 2–5. Big and Little Endian Byte Ordering
Littl
e-
E
n
di
an
b
y
t
e a
dd
resses,
128
-
bit
processor
i
n
t
er
f
ace:
Big-Endian byte addresses, 128-bit processor interface:
Little-Endian byte addresses, 64-bit processor interface:
Big-Endian byte addresses, 64-bit processor interface:
Little-Endian byte addresses, 32-bit processor interface:
Big-Endian byte addresses, 32-bit processor interface:
127 (←most-significant) (least-significant→) 0
word 01514131211109876543210
word 1 31302928272625242322212019181716
word 2 …32
127 (←most-significant) (least-significant→) 0
word 0 0123456789101112131415
word 1 16171819202122232425262728293031
word 2 32 …
63 (←most-significant) (least-significant→) 0
word 0 76543210
word 1 151413121110 9 8
word 2 …16
63 (←most-significant) (least-significant→) 0
word 0 01234567
word 1 8 9 101112131415
word 2 16 …
31 0
word 0 3210
word 1 7654
word 2 …8
31 0
word 0 0123
word 1 4567
word 2 8 …
Chapter 2. Notation
Xtensa Instruction Set Architecture (ISA) Reference Manual 19
2.2 Expressions
Table 2–4 defines notational forms used in expressions that describe the operation of in-
structions. In the table, v is an n-bit quantity, u is an m-bit quantity, and t is a 1-bit
quantity.
Table 2–4. Instruction-Description Expressions
Expression Notation
1
Definition
vx Bit x of v. The result is 1 bit.
vx..y Bits from position x to y of v. The result is x-y+1 bits.
vy The value v replicated y times. The result is n×y bits.
array[i] Reference to element i of array.
u || v The catenation of bit strings u and v. The result is m+n bits.
not v Bitwise logical complement of v. The result is n bits.
u and v Bitwise logical and of u and v. u and v must be the same width. The result is n
bits.
u or v Bitwise logical or of u and v. u and v must be the same width. The result is n
bits.
u xor v Bitwise logical exclusive or of u and v. u and v must be the same width. The
result is n bits.
u = v Test for exact equality of u and v. u and v must be the same width. The result
is 1 bit.
u ≠ v Test for inequality of u and v. u and v must be the same width. The result is 1
bit.
u < v Two’s complement less-than test on u and v. u and v must be the same width.
The result is 1 bit.
u ≤ v Two’s complement less-than or equal-to test on u and v. u and v must be the
same width. The result is 1 bit.
u > v Two’s complement greater-than test on u and v. u and v must be the same
width. The result is 1 bit.
u ≥ v Two’s complement greater-than or equal-to test on u and v. u and v must be
the same width. The result is 1 bit.
u + v Two’s complement addition of u and v. u and v must be the same width. The
result is n bits.
u - v Two’s complement subtraction of u and v. u and v must be the same width.
The result is n bits.
u x v Low-order product of two’s complement multiplication of u and v. u and v must
be the same width. The result is n bits.
1. t is a 1-bit quantity, u is a m-bit quantity, v is an n-bit quantity. Constants are written either as decimal numbers, in which case the width is
determined from context, or in binary.
Chapter 2. Notation
20 Xtensa Instruction Set Architecture (ISA) Reference Manual
2.3 Unsigned Semantics
In this notation, prepending a zero bit is often used for unsigned semantics. For
example, the following notation indicates an unsigned less-than test:
(0 || u) < (0 || v)
2.4 Case
Processor-state variables (for example, registers) are shown in UPPER CASE.
Temporary variables are shown in lower case. If a particular variable is in italics
(variable), it is local in the sense that it has no meaning outside the local instruction
flow. If it is plain (variable), it comes from or is used outside of the local instruction
flow such as an instruction field or the next PC.
u quo v Quotient of two’s complement division of u by v. u and v must be the same
width. The result is n bits.
u rem v Remainder of two’s complement division of u by v. u and v must be the same
width. The result is n bits.
if t then u else v Conditional expression. The value is u if t = 1. The value is v if t = 0.
u +s v IEEE754 single-precision floating-point addition of u and v. u and v must be
32 bits. The result is 32 bits.
u -s v IEEE754 single-precision floating-point subtraction of u and v. u and v must
be 32 bits. The result is 32 bits.
u Xs v IEEE754 single-precision floating-point multiplication of u and v. u and v must
be 32 bits. The result is 32 bits.
u ÷s v IEEE754 single-precision floating-point division of u by v. u and v must be 32
bits. The result is 32 bits.
sqrts(u) IEEE754 single-precision floating-point square root of u. u must be 32 bits. The
result is 32 bits.
pows(u,v) IEEE754 single-precision floating-point power function where u is raised to the
v power. u must be 32 bits. The result is 32 bits.
Table 2–4. Instruction-Description Expressions
(continued)
Expression Notation
1
Definition
1. t is a 1-bit quantity, u is a m-bit quantity, v is an n-bit quantity. Constants are written either as decimal numbers, in which case the width is
determined from context, or in binary.
Chapter 2. Notation
Xtensa Instruction Set Architecture (ISA) Reference Manual 21
2.5 Statements
Table 2–5 defines notational forms used in statements used to describe the operation of
instructions.
2.6 Instruction Fields
The fields in Table 2–6 are used in the descriptions of the instructions. Instruction for-
mats and opcodes are described in Chapter 7, "Instruction Formats and Opcodes" on
page 569.
Table 2–5. Instruction-Description Statements
Statement Notation Definition
v ← expr Assignment of expr to v.
if t1 then
s1
[elseif t2 then
s2]
.
.
.
[else
sn]
endif
Conditional statement. If t1 = 1 then execute statements s1. Otherwise, if t2 =
1 then execute statements s2, etc. Finally if none of the previous tests are true,
execute statements sn.
label: Define label for use as a goto target.
goto label Transfer control to label.
Table 2–6. Uses Of Instruction Fields
Field Definition
op0 Major opcode
op1 4-bit sub-opcode for 24-bit instructions
op2 4-bit sub-opcode for 24-bit instructions
r
AR target (result), BR target (result),
4-bit immediate,
4-bit sub-opcode
sAR source, BR source,
AR target
t
AR target, BR target,
AR source, BR source,
4-bit sub-opcode
Chapter 2. Notation
22 Xtensa Instruction Set Architecture (ISA) Reference Manual
n
Register window increment,
2-bit sub-opcode,
n||2'b00 is used as a AR target on CALLn/CALLXn
m2-bit sub-opcode
i1-bit sub-opcode
z1-bit sub-opcode
imm4 4-bit immediate
imm6 6-bit immediate (PC-relative offset)
imm7 7-bit immediate (for MOVI.N)
imm8 8-bit immediate
imm12 12-bit immediate
imm16 16-bit immediate
offset 18-bit PC-relative offset
ai4const 4-bit immediate, if 0 interpreted as -1, else sign-extended
b4const 4-bit encoded constant value
bbi 5-bit selector for Booleans in registers
sa 4- or 5-bit shift amount
sr 8-bit special register selector
x1-bit MAC16 data register selector (m0 or m1 only)
y1-bit MAC16 data register selector (m2 or m3 only)
w2-bit MAC16 data register selector (m0, m1, m2, or m3)
Table 2–6. Uses Of Instruction Fields
(continued)
Field Definition
Chapter 3. Core Architecture
Xtensa Instruction Set Architecture (ISA) Reference Manual 23
3. Core Architecture
The Xtensa Core Architecture provides a baseline set of instructions available in every
Xtensa implementation. Having such a baseline eases the implementation of core soft-
ware such as operating system ports and a compiler. This chapter describes that Core
Architecture.
3.1 Overview of the Core Architecture
The Xtensa Instruction Set is the product of extensive research into the right balance of
features to best address the needs of the embedded processor market. It borrows the
best features of other architectures as well as bringing new ISA innovations of its own.
While the Xtensa ISA derives most of its features from RISC, it has targeted areas in
which older CISC architectures have been strongest, such as compact code.
The Xtensa core ISA is implemented as a set of 24-bit instructions that perform 32-bit
operations. The instruction width was chosen primarily with code-size economy in mind.
The instructions themselves were selected for their utility in a wide range of embedded
applications. The core ISA has many powerful features, such as compound operation
instructions, that enhance its fit to embedded applications, but it avoids features that
would benefit some applications at the expense of cost or power on others (for example,
features that require extra register-file ports). Such features can be implemented in the
Xtensa architecture using options and coprocessors specifically targeted at a particular
application area.
The Xtensa ISA is organized as a core set of instructions with various optional packages
that extend the functionality for specific application areas. This allows the designer to
include only the required functionality in the processor core, maximizing the efficiency of
the solution. The core ISA provides the functionality required for general control applica-
tions, and excels at decision-making and bit and byte manipulation. The core also pro-
vides a target for third-party software, and for this reason deletions from the core are not
supported. Conversely, numeric computing applications such as digital signal process-
ing are best done with optional ISA packages appropriate for specific application areas,
such as the MAC16 Option for integer filters, or the Floating-Point Coprocessor Option
for high-end audio processing.
3.2 Processor-Configuration Parameters
Table 3–7 lists the processor-configuration parameters that are required in the core ar-
chitecture. Additional processor-configuration parameters are listed with each option
described in Chapter 4, "Architectural Options" on page 47.
Chapter 3. Core Architecture
24 Xtensa Instruction Set Architecture (ISA) Reference Manual
3.3 Registers
Table 3–8 lists the core-architecture registers. Each register is described in the sections
that follow. Additional registers are added with many of the options described in
Chapter 4. The complete set of registers that are predefined in the architecture, includ-
ing all registers used by the architectural options, is listed in Table 5–127 on page 205.
3.3.1 General (
AR
) Registers
Each instruction contains up to three 4-bit general-register specifiers, each of which can
select one of 16 32-bit registers. These general registers are named address registers
(AR) to distinguish them from coprocessor registers, which in many systems might serve
as “data” registers. However, the AR registers are not restricted to holding addresses;
they can also hold data.
If the Windowed Register Option is configured, the address register file is extended and
a mapping from virtual to physical registers is used.
The contents of the address register file are undefined after reset.
Table 3–7. Core Processor-Configuration Parameters
Parameter Description Valid Values
msbFirst
Byte order
0 or 1
0 → Little-endian (least significant bit first)
1 → Big-endian (most significant bit first)
Table 3–8. Core-Architecture Set
Register
Mnemonic Quantity Width
(bits) Register Name R/W
Special
Register
Number
1
AR 16232 Address registers
(general registers)
R/W —
PC 132 Program counter R/W —
SAR 1 6 Shift-amount register R/W 3
1. Registers with a Special Register assignment are read and/or written with the RSR, WSR, and XSR instructions. See Table 5–127 on
page 205. A dash (—) means that the register is not a Special Register.
2. See "Windowed Register Option" on page 180.
Chapter 3. Core Architecture
Xtensa Instruction Set Architecture (ISA) Reference Manual 25
3.3.2 Shifts and the Shift Amount Register (
SAR
)
The ISA provides conventional immediate shifts (logical left, logical right, and arithmetic
right), but it does not provide single-instruction shifts in which the shift amount is a regis-
ter operand. Taking the shift amount from a general register can create a critical timing
path. Also, simple shifts do not extend efficiently to larger widths. Funnel shifts (where
two data values are catenated on input to the shifter) solve this problem, but require too
many operands. The ISA solves both problems by providing a funnel shift in which the
shift amount is taken from the SAR register. Variable shifts are synthesized by the com-
piler using an instruction to compute SAR from the shift amount in a general register,
followed by a funnel shift.
Another advantage is that a unidirectional funnel shifter can be manipulated to provide
either right or left shifts based on the order of the source operands and transformation of
the shift amount. The ISA facilitates implementations that exploit this to reduce the logic
required by the shifter.
Funnel shifts are also useful for working with the 40-bit accumulator values created by
the MAC16 Option.
To facilitate unsigned bit-field extraction, the EXTUI instructions take a 4-bit mask field
that specifies the number of bits to mask the result of the shift. The 4-bit field specifies
masks of one to 16 ones. The SRLI instruction provides shifting without a mask.
The legal range of values for SAR is zero to 32, not zero to 31, so SAR is defined as six
bits. The use of SRC, SRA, SLL, or SRL when SAR > 32 is undefined.
SAR is undefined after processor reset.
The funnel shifter can also be used efficiently for byte alignment of unaligned memory
data. To load four bytes from an arbitrary byte boundary (in a processor that does not
have the Unaligned Exception Option), use the following code:
l32i a4,a3,0
l32i a5,a3,4
ssa8l a3
src a4,a5,a4
An unaligned block copy can be done (in a processor that does not have the Unaligned
Exception Option) with the following code for little-endian and small changes for big-en-
dian:
l32i a6,a3,0
ssa8l a3
loopnez a4,endloop
loop:
l32i a7,a3,4
Chapter 3. Core Architecture
26 Xtensa Instruction Set Architecture (ISA) Reference Manual
src a8,a7,a6
s32i a8,a2,0
l32i a6,a3,8
src a8,a6,a7
s32i a8,a2,4
addi a2,a2,8
addi a3,a3,8
endloop:
The overhead, compared to an aligned copy, is only one SRC per L32I.
3.3.3 Reading and Writing the Special Registers
The SAR register is part of the Non-Privileged Special Register set in the Xtensa ISA (the
other registers in this set are associated with the architectural options). The contents of
the special register in the Core Architecture can be read to an AR register with the read
special register (RSR.SAR) instruction or written from an AR register with the write spe-
cial register (WSR.SAR) instruction as shown in Table 3–9. The exchange special regis-
ter (XSR.SAR) instruction accomplishes the combined action of the read and write in-
structions.
3.4 Data Formats and Alignment
The Core Architecture supports byte, 2-byte, and 4-byte data formats. Two additional
data formats are used in architectural options — a 32-bit single-precision format for the
Floating-Point Coprocessor Option, and a 40-bit accumulator value for the MAC16 Op-
tion. The MAC16 format is not a memory-operand format, but rather a temporary format
held in a special 40-bit accumulator register during MAC16 execution; the result can be
moved to two 32-bit registers for further operation or storage.
Table 3–10 summarizes the width and alignment of each data type. The processor uses
byte addressing for all data types stored in memory (that is, all except the MAC16 accu-
mulator). Byte order can be specified as either big-endian or little-endian. In big-endian
byte order, byte 0 is the most-significant (left-most) byte. In little-endian byte order, byte
0 is the least-significant (right-most) byte. When specifying a byte order, both the byte
order and the bit order are specified: the two orderings always have the same most-
significant and least-significant ends.
Table 3–9. Reading and Writing Special Registers
Register Name Special Register Number RSR .SAR Instruction WSR .SAR Instruction
SAR 3AR[t] ← 026||SAR SAR ← AR[t]5..0
Chapter 3. Core Architecture
Xtensa Instruction Set Architecture (ISA) Reference Manual 27
3.5 Memory
The Xtensa ISA is based on 32-bit virtual and physical memory addresses, which
provides a 232 or 4 GB address space for instructions and data.
3.5.1 Memory Addressing
Figure 3–6 shows an example of the processor’s interpretation of addresses when con-
figured with caches. The widths of all fields are configurable, and in some cases the
width may be zero (in particular, there are always zero ignored bits today). The cache in-
dex and cache tag will overlap if the page size is smaller than the size of a single way of
the cache and if physical tags are used.
Figure 3–6. Virtual Address Fields
Without the Region Protection Option or the MMU Option, virtual and physical address-
es are identical; if physical addresses are configured to be smaller than virtual address-
es, virtual addresses are mapped to physical addresses only by truncation (high-order
bits are ignored). With the Region Protection Option or the MMU Option, virtual page
numbers are translated to physical page numbers.
Table 3–10. Operand Formats and Alignment
Operand Length Alignment Address in Memory
Byte 8 bit xxxx
2-byte 16 bits xxx0
4-byte (word) 32 bits xx00
IEEE-754 single-precision (Floating-Point Coprocessor Option) 32 bits xx00
MAC16 accumulator (MAC16 Option) 40 bits register image only (not in memory)
Cache Tag
31
Cache Index
Ignored
Line Index
Attribute
Region
Offset in Page
Physical Address
0
32-Bit Virtual Address
Chapter 3. Core Architecture
28 Xtensa Instruction Set Architecture (ISA) Reference Manual
Without the Region Protection Option or the MMU Option, the formal definition of virtual
to physical translation is as follows (note that the ring parameter is ignored):
function ftranslate(vAddr, ring)-- fetch translate
b ← vAddr(VABITS-1)..(VABITS-3)
cacheattr ← CACHEATTR(b||2'b11)..(b||2'b00)
attributes ← fcadecode(cacheattr)
cause
←
invalid(attributes) then InstructionFetchErrorCause else 0
ftranslate ← (vAddrPABITS-1..0, attributes, cause)
endfunction ftranslate
function ltranslate(vAddr, ring)-- load translate
b ← vAddr(VABITS-1)..(VABITS-3)
cacheattr ← CACHEATTR(b||2'b11)..(b||2'b00)
attributes ← lcadecode(cacheattr)
cause ← invalid(attributes) then LoadStoreErrorCause else 0
ltranslate ← (vAddrPABITS-1..0, attributes, cause)
endfunction ltranslate
function stranslate(vAddr, ring)-- store translate
b ← vAddr(VABITS-1)..(VABITS-3)
cacheattr ← CACHEATTR(b||2'b11)..(b||2'b00)
attributes ← scadecode(cacheattr)
cause ← invalid(attributes) then LoadStoreErrorCause else 0
stranslate ← (vAddrPABITS-1..0, attributes, cause)
endfunction stranslate
Translation with the MMU Option is described in Section 4.6.5.
The core ISA supports both little-endian (PC compatible) and big-endian (Internet com-
patible) address models as a configuration parameter. In this manual:
msbFirst = 1 is big-endian.
msbFirst = 0 is little-endian.
3.5.2 Addressing Modes
The core instruction set implements the register + immediate addressing mode. The
core ISA does not implement auto-incrementing stores or indexed loads. However, such
addressing modes are possible for coprocessors. For example, the Floating-Point
Coprocessor Option implements indexed as well as immediate addressing modes.
Chapter 3. Core Architecture
Xtensa Instruction Set Architecture (ISA) Reference Manual 29
3.5.3 Program Counter
The 32-bit program counter (PC) holds a byte address and can address 4 GB of virtual
memory for instructions. However, when the Windowed Register Option is configured,
the register-window call instructions only store the low 30 bits of the return address.
Register-window return instructions leave the two most-significant bits of the PC un-
changed. Therefore, subroutines called using register window instructions must be
placed in the same 1 GB address region as the call.
3.5.4 Instruction Fetch
This section describes the execution loop of the processor using the notation of
Chapter 2. The individual instruction actions are represented by the Inst() statement,
and are detailed in subsequent sections. Two versions of this code are supported; one
for little-endian (msbFirst = 0) and one for big-endian (msbFirst = 1). This definition
is in terms of a hypothetical aligned 64-bit fetch, and should not be confused with the
fetch algorithms used by specific Xtensa ISA implementations. Aligned 32-bit fetch and
unaligned fetch are other possible implementations, which would produce logically
equivalent results, but with different timings. Also, actual implementations would be ex-
pected to access memory only once for each fetch unit, not once per instruction as in the
definition in Section 3.5.4.1 and Section 3.5.4.2.
The processor may speculatively fetch instructions following the address in the program
counter. To facilitate this and to allow flexibility in the implementation, software must not
position instructions within the last 64 bytes before a boundary where protection or
cache attributes change. This exclusion does not apply if one of the two protections or
attributes is invalid. Instructions may be placed within 64 bytes before a transition from
valid to invalid or from invalid to valid — but not before any other transition. In addition, if
the Windowed Register Option is implemented, software must not position instructions
within the last 16 bytes of a 230 (1 GB) boundary, to allow flexibility in the implementation
of the register-window call and return instructions. The operation of the processor in
these exclusion regions is not defined.
3.5.4.1 Little-Endian Fetch Semantics
Little-endian instruction fetch is defined as follows for a 64-bit fetch width (other fetch
sizes are similar):
checkInterrupts() -- see "Checking for Interrupts" on page 109
vAddr0 ← PC31..3||3'b000 -- this example is 64-bit fetch
(pAddr0, attributes, cause) ← ftranslate(vAddr0, CRING)
if invalid(attributes) then
EXCVADDR ← vAddr0
Exception (cause)
Chapter 3. Core Architecture
30 Xtensa Instruction Set Architecture (ISA) Reference Manual
goto abortInstruction
endif
(mem0, error) ← ReadInstMemory(pAddr0, attributes, 8'b11111111)
-- get start of instruction
if error then
EXCVADDR ← vAddr0
Exception (InstructionFetchErrorCause)
goto abortInstruction
endif
b ← 0||PC2..0
if b2 = 0 or b1 = 0 or (b0 = 0 and mem0(b||3'b011) = 1) then
-- instruction contained within a single fetch (64 bits in this example)
inst ← (undefined64||mem0)((b+2)||3'b111)..(b||3'b000)
else
-- instruction crosses a fetch boundary (64 bits in this example)
vAddr1 ← vaddr0 + 32'd8
(pAddr1, attributes, cause) ← ftranslate(vAddr1, CRING)
if invalid(attributes) then
EXCVADDR ← vAddr1
Exception (cause)
goto abortInstruction
endif
(mem1, error) ← ReadInstMemory(pAddr1,
attributes, 8'b11111111)
if error then
EXCVADDR ← vAddr1
Exception (InstructionFetchErrorCause)
goto abortInstruction
endif
inst ← (mem1||mem0)((b+2)||3'b111)..(b||3'b000)
endif
-- now have a 24-bit instruction (8 bits undefined if 16-bit), break it into fields
op0 ← inst3..0
t ← inst7..4
s ← inst11..8
r ← inst15..12
op1 ← inst19..16
op2 ← inst23..20
imm8 ← inst23..16
imm12 ← inst23..12
imm16 ← inst23..8
offset ← inst23..6
n ← inst5..4
m ← inst7..6
-- compute nextPC (may be overridden by branches, etc.)
nextPC ← PC + (030 || (if op03 then 2'b10 else 2'b11))
if LCOUNT ≠ 032 and CLOOPENABLE and nextPC = LEND then
LCOUNT ← LCOUNT − 1
nextPC ← LBEG
Chapter 3. Core Architecture
Xtensa Instruction Set Architecture (ISA) Reference Manual 31
endif
-- execute instruction
Inst()
checkIcount ()
abortInstruction:
PC ← nextPC
3.5.4.2 Big-Endian Fetch Semantics
Big-endian instruction fetch is defined as follows for a 64-bit fetch width (other fetch
sizes are similar):
checkInterrupts() -- see "Checking for Interrupts" on page 109
vAddr0 ← PC31..3||3'b000 -- this example is 64-bit fetch
(pAddr0, attributes, cause) ← ftranslate(vAddr0, CRING)
if invalid(attributes) then
EXCVADDR ← vAddr0
Exception (cause)
goto abortInstruction
endif
(mem0, error) ← ReadInstMemory(pAddr0, attributes, 8'b11111111)
-- get start of instruction
if error then
EXCVADDR ← vAddr0
Exception (InstructionFetchErrorCause)
goto abortInstruction
endif
b ← 0||PC2..0
p0 ← b xor 14
p2 ← (b + 2) xor 14
if b2 = 0 or b1 = 0 or (b0 = 0 and (mem0||undefined64)(p0||3'b111) = 1)
then
-- instruction contained within a single fetch (64 bits in this example)
inst ← (mem0||undefined64)(p0||3'b111)..(p2||3'b000)
else
-- instruction crosses a fetch boundary (64 bits in this example)
vAddr1 ← vaddr0 + 32'd8
(pAddr1, attributes, cause) ← ftranslate(vAddr1, CRING)
if invalid(attributes) then
EXCVADDR ← vAddr1
Exception (cause)
goto abortInstruction
endif
(mem1, error) ← ReadInstMemory(pAddr1,
attributes, 8'b11111111)
if error then
EXCVADDR ← vAddr1
Exception (InstructionFetchErrorCause)
Chapter 3. Core Architecture
32 Xtensa Instruction Set Architecture (ISA) Reference Manual
goto abortInstruction
endif
inst ← (mem0||mem1)(p0||3'b111)..(p2||3'b000)
endif
-- now have a 24-bit instruction (8 bits undefined if 16-bit), break it into fields
op0 ← inst23..20
t ← inst19..16
s ← inst15..12
r ← inst11..8
op1 ← inst7..4
op2 ← inst3..0
imm8 ← inst7..0
imm12 ← inst11..0
imm16 ← inst15..0
offset ← inst17..0
n ← inst19..18
m ← inst17..16
-- compute nextPC (may be overridden by branches, etc.)
nextPC ← PC + (030 || (if op03 then 2'b10 else 3'b11))
if LCOUNT ≠ 032 and CLOOPENABLE and nextPC = LEND then
LCOUNT ← LCOUNT − 1
nextPC ← LBEG
endif
-- execute instruction
Inst()
checkIcount ()
abortInstruction:
PC ← nextPC
3.6 Reset
When the processor emerges from the reset state, it initializes many registers. The ISA
guarantees the values of some states after reset but leaves many others undefined.
Actual Xtensa processor implementations will often define the values of state left
undefined by the ISA. Chapter 5, "Processor State" on page 205 contains information
about each state value, including the value to which it is reset.
3.7 Exceptions and Interrupts
The core ISA does not include support for exceptions or interrupts. These are architec-
tural options are described in Section 4.4. Software running on a processor that is con-
figured without an Exception Option should be well tested, as such a processor will do
something unexpected if it encounters a software error.
Chapter 3. Core Architecture
Xtensa Instruction Set Architecture (ISA) Reference Manual 33
3.8 Instruction Summary
Table 3–11 summarizes the core instructions included in all versions of the Xtensa archi-
tecture. The remainder of this section gives an overview of the core instructions.
3.8.1 Load Instructions
Load instructions form a virtual address by adding a base register and an 8-bit unsigned
offset. This virtual address is translated to a physical address if necessary. The physical
address is then used to access the memory system (often through a cache). The memo-
ry system returns a data item (either 32, 64, or 128 bits, depending on the configura-
tion). The load instructions then extract the referenced data from that memory item and
either zero-extend or sign-extend the result to be written into a register. Unless the
Table 3–11. Core Instruction Summary
Instruction Category Instructions
1
Reference
Load L8UI, L16SI, L16UI, L32I,
L32R
"Load Instructions" on page 33
Store S8I, S16I, S32I "Store Instructions" on page 36
Memory ordering MEMW, EXTW "Memory Access Ordering" on page 39
Jump, Call CALL0, CALLX0, RET
J, JX
"Jump and Call Instructions" on page
40
Conditional branch BALL, BNALL, BANY, BNONE
BBC, BBCI, BBS, BBSI
BEQ, BEQI, BEQZ
BNE, BNEI, BNEZ
BGE, BGEI, BGEU, BGEUI, BGEZ
BLT, BLTI, BLTU, BLTUI, BLTZ
"Conditional Branch Instructions" on
page 40
Move MOVI, MOVEQZ, MOVGEZ,
MOVLTZ, MOVNEZ
"Move Instructions" on page 42
Arithmetic ADDI, ADDMI,
ADD, ADDX2, ADDX4, ADDX8,
SUB, SUBX2, SUBX4, SUBX8,
NEG, ABS
"Arithmetic Instructions" on page 43
Bitwise logical AND, OR, XOR "Bitwise Logical Instructions" on page
44
Shift EXTUI, SRLI, SRAI, SLLI
SRC, SLL, SRL, SRA
SSL, SSR, SSAI, SSA8B, SSA8L
"Shift Instructions" on page 44
Processor control RSR, WSR, XSR, RUR, WUR,
ISYNC, RSYNC, ESYNC, DSYNC,
NOP
"Processor Control Instructions" on
page 45
1. These instructions are fully described in Chapter 6, "Instruction Descriptions" on page 243.
Chapter 3. Core Architecture
34 Xtensa Instruction Set Architecture (ISA) Reference Manual
Unaligned Exception Option is enabled, the processor does not handle misaligned data
or trap when a misaligned address is used; instead it simply loads the aligned data item
containing the computed virtual address. This allows the funnel shifter to be used with a
pair of loads to reference data on any byte address.
Only the loads L32I, L32I.N, and L32R can access InstRAM and InstROM locations.
Table 3–12 shows the loads in the Core Architecture.
Because the operation of caches is implementation-specific, this manual does not pro-
vide a formal specification of cache access.
The following routines define the load instructions:
function ReadMemory (pAddr, attributes, bytemask)
ReadMemory ← (Memory[pAddr], 0) -- for now, no cache
endfunction ReadMemory
function Load8 (vAddr)
(pAddr, attributes, cause) ← ltranslate(vAddr, CRING)
if invalid(attributes) then
EXCVADDR ← vAddr
Exception (cause)
goto abortInstruction
endif
p ← pAddr2..0 xor msbFirst3
(mem64, error) ← ReadMemory(pAddr31..3, attributes, 07-p||1||0p)
mem8 ← mem64(p||3'b111)..(p||3'b000)
Load8 ← (mem8, error)
endfunction Load8
function Load16 (vAddr)
if UnalignedExceptionOption & Vaddr0 ≠ 1’b0 then
EXCVADDR ← vAddr
Exception (LoadStoreAlignmentCause)
goto abortInstruction
Table 3–12. Load Instructions
Instruction Format Definition
L8UI RRI8 8-bit unsigned load (8-bit offset)
L16SI RRI8 16-bit signed load (8-bit shifted offset)
L16UI RRI8 16-bit unsigned load (8-bit shifted offset)
L32I RRI8 32-bit load (8-bit shifted offset)
L32R RI16 32-bit load PC-relative (16-bit negative word offset)
Chapter 3. Core Architecture
Xtensa Instruction Set Architecture (ISA) Reference Manual 35
endif
(pAddr, attributes, cause) ← ltranslate(vAddr, CRING)
if invalid(attributes) then
EXCVADDR ← vAddr
Exception (cause)
goto abortInstruction
endif
p ← pAddr2..1 xor msbFirst2
(mem64, error) ← ReadMemory(pAddr31..3, attributes,
(2'b00)3-p||2'b11||(2'b00)p)
mem16 ← mem64(p||4'b1111)..(p||4'b0000)
Load16 ← (mem16, error)
endfunction Load16
function Load32 (vAddr)
if UnalignedExceptionOption & Vaddr1..0 ≠ 2’b00 then
EXCVADDR ← vAddr
Exception (LoadStoreAlignmentCause)
goto abortInstruction
endif
(pAddr, attributes, cause) ← ltranslate(vAddr, CRING)
if invalid(attributes) then
EXCVADDR ← vAddr
Exception (cause)
goto abortInstruction
endif
p ← pAddr2 xor msbFirst
(mem64, error) ← ReadMemory(pAddr31..3, attributes,
(4'b0000)1-p||4'b1111||(4'b0000)p)
mem32 ← mem64(p||5'b11111)..(p||5'b00000)
Load32 ← (mem32, error)
endfunction Load32
function Load32Ring (vAddr, ring)
if UnalignedExceptionOption & Vaddr1..0 ≠ 2’b00 then
EXCVADDR ← vAddr
Exception (LoadStoreAlignmentCause)
goto abortInstruction
endif
(pAddr, attributes, cause) ← ltranslate(vAddr, ring)
if invalid(attributes) then
EXCVADDR ← vAddr
Exception (cause)
goto abortInstruction
endif
p ← pAddr2 xor msbFirst
(mem64, error) ← ReadMemory(pAddr31..3, attributes,
(4'b0000)1-p||4'b1111||(4'b0000)p)
mem32 ← mem64(p||5'b11111)..(p||5'b00000)
Chapter 3. Core Architecture
36 Xtensa Instruction Set Architecture (ISA) Reference Manual
Load32 ← (mem32, error)
endfunction Load32Ring
function Load64 (vAddr)
if UnalignedExceptionOption & Vaddr2..0 ≠ 3’b000 then
EXCVADDR ← vAddr
Exception (LoadStoreAlignmentCause)
goto abortInstruction
endif
(pAddr, attributes, cause) ← ltranslate(vAddr, CRING)
if invalid(attributes) then
EXCVADDR ← vAddr
Exception (cause)
goto abortInstruction
endif
Load64 ← ReadMemory(pAddr31..3, attributes, 8'b11111111)
endfunction Load64
3.8.2 Store Instructions
Store instructions are similar to load instructions in address formation. Store memory
errors are not synchronous exceptions; it is expected that the memory system will use
an interrupt to indicate an error on a store.
Only the stores S32I and S32I.N can access InstRAM.
Table 3–13 shows the loads in the Core Architecture.
The following routines define the store instructions:
procedure WriteMemory (pAddr, attributes, bytemask, data64)
-- for now, no cache
if bytemask0 then
Memory[pAddr]7..0 ← data647..0
endif
if bytemask1 then
Memory[pAddr]15..8 ← data6415..8
endif
if bytemask2 then
Table 3–13. Store Instructions
Instruction Format Definition
S8I RRI8 8-bit store (8-bit offset)
S16I RRI8 16-bit store (8-bit shifted offset)
S32I RRI8 32-bit store (8-bit shifted offset)
Chapter 3. Core Architecture
Xtensa Instruction Set Architecture (ISA) Reference Manual 37
Memory[pAddr]23..16 ← data6423..16
endif
if bytemask3 then
Memory[pAddr]31..24 ← data6431..24
endif
if bytemask4 then
Memory[pAddr]39..32 ← data6439..32
endif
if bytemask5 then
Memory[pAddr]47..40 ← data6447..40
endif
if bytemask6 then
Memory[pAddr]55..48 ← data6455..48
endif
if bytemask7 then
Memory[pAddr]63..56 ← data6463..56
endif
endprocedure WriteMemory
procedure Store8 (vAddr, data8)
(pAddr, attributes, cause) ← stranslate(vAddr, CRING)
if invalid(attributes) then
EXCVADDR ← vAddr
Exception (cause)
goto abortInstruction
endif
p ← pAddr2..0 xor msbFirst3
WriteMemory(pAddr31..3, attributes, 07−p||1||0p,
undefined(7−p)||3'b000||data8||undefinedp||3'b000)
endprocedure Store8
procedure Store16 (vAddr, data16)
if UnalignedExceptionOption & Vaddr0 ≠ 1’b0 then
EXCVADDR ← vAddr
Exception (LoadStoreAlignmentCause)
goto abortInstruction
endif
(pAddr, attributes, cause) ← stranslate(vAddr, CRING)
if invalid(attributes) then
EXCVADDR ← vAddr
Exception (cause)
goto abortInstruction
endif
p ← pAddr2..1 xor msbFirst2
WriteMemory(pAddr31..3, attributes, (2'b00)3-p||2'b11||(2'b00)p,
undefined(3-p)||4'b0000||data16||undefinedp||4'b0000)
endprocedure Store16
procedure Store32 (vAddr, data32)
Chapter 3. Core Architecture
38 Xtensa Instruction Set Architecture (ISA) Reference Manual
if UnalignedExceptionOption & Vaddr1..0 ≠ 2’b00 then
EXCVADDR ← vAddr
Exception (LoadStoreAlignmentCause)
goto abortInstruction
endif
(pAddr, attributes, cause) ← stranslate(vAddr, CRING)
if invalid(attributes) then
EXCVADDR ← vAddr
Exception (cause)
goto abortInstruction
endif
p ← pAddr2 xor msbFirst
WriteMemory(pAddr31..3, attributes, (4'b0000)1-
p||4'b1111||(4'b0000)p,
undefined(1-p)||5'b00000||data32||undefinedp||5'b00000)
endprocedure Store32
procedure Store32Ring (vAddr, data32, ring)
if UnalignedExceptionOption & Vaddr1..0 ≠ 2’b00 then
EXCVADDR ← vAddr
Exception (LoadStoreAlignmentCause)
goto abortInstruction
endif
(pAddr, attributes, cause) ← stranslate(vAddr, ring)
if invalid(attributes) then
EXCVADDR ← vAddr
Exception (cause)
goto abortInstruction
endif
p ← pAddr2 xor msbFirst
WriteMemory(pAddr31..3, attributes, (4'b0000)1-
p||4'b1111||(4'b0000)p,
undefined(1-p)||5'b00000||data32||undefinedp||5'b00000)
endprocedure Store32Ring
procedure Store64 (vAddr, data64)
if UnalignedExceptionOption & Vaddr2..0 ≠ 3’b000 then
EXCVADDR ← vAddr
Exception (LoadStoreAlignmentCause)
goto abortInstruction
endif
(pAddr, attributes, cause) ← stranslate(vAddr, CRING)
if invalid(attributes) then
EXCVADDR ← vAddr
Exception (cause)
goto abortInstruction
endif
WriteMemory(pAddr31..3, attributes, 8'b11111111, data64)
endprocedure Store64
Chapter 3. Core Architecture
Xtensa Instruction Set Architecture (ISA) Reference Manual 39
3.8.3 Memory Access Ordering
Xtensa implementations can perform ordinary load and store operations in any order, as
long as loads return the last (as defined by program execution order) values stored to
each byte of the load address for a single processor and a simple memory. This flexibili-
ty is appropriate because most memory accesses require only these semantics and
some implementations may be able to execute programs significantly faster by exploit-
ing non-program order memory access. The Xtensa ISA only requires that implementa-
tions follow a simplified version of the Release Consistency model1 of memory access
ordering, although many implement stricter orderings for simplicity. For more on the
Xtensa memory order semantics, see "Multiprocessor Synchronization Option" on page
74.
However, some load and store instructions are executed not just to read and write stor-
age, but to cause some side effects on some other part of the system (for example,
another processor or an I/O device). In C and C++, such variables must be declared
volatile. Loads and stores to such locations must be executed in program order. The
Xtensa ISA therefore provides an instruction that can be used to give program ordering
of load and store memory accesses.
The MEMW instruction causes all memory and cache accesses (loads, stores, acquires,
releases, prefetches, and cache operations, but not instruction fetches) before itself in
program order to access memory before all memory and cache accesses (but not in-
struction fetches) after. At least one MEMW should be executed in between every load or
store to a volatile variable. The Multiprocessor Synchronization Option provides
some additional instructions that also affect memory ordering in a more focused fashion.
MEMW has broader applications than these other instructions (for example, when reading
and writing device registers), but it also may affect performance more than the synchro-
nization instructions.
The EXTW instruction is similar to MEMW, but it separates all external effects of instruc-
tions before the EXTW in program order from all external effects of instructions after the
EXTW in program order. EXTW is a superset of MEMW, and includes memory accesses in
what it orders.
Table 3–14 shows the memory ordering instructions in the Core Architecture.
1. Kourosh Gharachorloo, Dan Lenoski, James Laudon, Phillip Gibbons, Anoop Gupta, and John Hennessy, “Memory consistency and event order-
ing in scalable shared-memory multiprocessors,” Proceedings of the 17th Annual International Symposium on Computer Architecture, pages 15-
26, May 1990.
Table 3–14. Memory Order Instructions
Instruction Format Definition
MEMW RRR Order memory accesses before with memory access after
EXTW RRR Order all external effects before with all external effects after
Chapter 3. Core Architecture
40 Xtensa Instruction Set Architecture (ISA) Reference Manual
3.8.4 Jump and Call Instructions
The unconditional branch instruction, J, has a longer range (PC-relative) than condition-
al branches. Calls have a slightly longer range because they target 32-bit aligned
addresses. In addition, jump and call indirect instructions provide support for case
dispatch, function variables, and dynamic linking.
Table 3–15 shows the jump and call instructions.
3.8.5 Conditional Branch Instructions
The branch instructions in Table 3–16 compare a register operand against zero, an im-
mediate, or a second register value and conditional branch based on the result of the
comparison. Compound compare and branch instructions improve code density and
performance compared to other ISAs. All branches are PC-relative; the immediate field
contains the difference between the target PC and the current PC plus four. The use of a
PC-relative offset of minus three to zero is illegal and reserved for future use.
Table 3–15. Jump and Call Instructions
Instruction Format Definition
CALL0 CALL Call subroutine, PC-relative
CALLX0 CALLX Call subroutine, address in register
JCALL Unconditional jump, PC-relative
JX CALLX Unconditional jump, address in register
RET CALLX Subroutine return—jump to return address. Used to return from a routine
called by CALL0/CALLX0.
Table 3–16. Conditional Branch Instructions
Instruction Format Definition
BEQZ BRI12 Branch if equal to zero
BNEZ BRI12 Branch if not equal to zero
BGEZ BRI12 Branch if greater than or equal to zero
BLTZ BRI12 Branch if less than zero
BEQI BRI8 Branch if equal immediate1
BNEI BRI8 Branch if not equal immediate1
BGEI BRI8 Branch if greater than or equal immediate1
BLTI BRI8 Branch if less than immediate1
BGEUI BRI8 Branch if greater than or equal unsigned immediate2
1. See Table 3–17 for encoding of signed immediate constants.
2. See Table 3–18 for encoding of unsigned immediate constants.
Chapter 3. Core Architecture
Xtensa Instruction Set Architecture (ISA) Reference Manual 41
The encodings for the branch immediate constant (b4const) field and the branch
unsigned immediate constant (b4constu) fields, shown in Table 3–17 and Table 3–18,
specify one of the sixteen most frequent compare immediates for each type of constant.
BLTUI BRI8 Branch if less than unsigned immediate2
BBCI RRI8 Branch if bit clear immediate
BBSI RRI8 Branch if bit set immediate
BEQ RRI8 Branch if equal
BNE RRI8 Branch if not equal
BGE RRI8 Branch if greater than or equal
BLT RRI8 Branch if less than
BGEU RRI8 Branch if greater than or equal unsigned
BLTU RRI8 Branch if less than Unsigned
BANY RRI8 Branch if any of masked bits set
BNONE RRI8 Branch if none of masked bits set (All Clear)
BALL RRI8 Branch if all of masked bits set
BNALL RRI8 Branch if not all of masked bits set
BBC RRI8 Branch if bit clear
BBS RRI8 Branch if bit set
Table 3–17. Branch Immediate (
b4const
) Encodings
Encoding Decimal Value of Immediate Hex Value of Immediate
0-1 32’hFFFFFFFF
1 1 32’h00000001
2 2 32’h00000002
3 3 32’h00000003
4 4 32’h00000004
5 5 32’h00000005
6 6 32’h00000006
7 7 32’h00000007
8 8 32’h00000008
910 32’h0000000A
10 12 32’h0000000C
Table 3–16. Conditional Branch Instructions
(continued)
Instruction Format Definition
1. See Table 3–17 for encoding of signed immediate constants.
2. See Table 3–18 for encoding of unsigned immediate constants.
Chapter 3. Core Architecture
42 Xtensa Instruction Set Architecture (ISA) Reference Manual
3.8.6 Move Instructions
MOVI sets a register to a constant encoded in the instruction. The conditional move
instructions shown in Table 3–19 are used for branch avoidance.
11 16 32’h00000010
12 32 32’h00000020
13 64 32’h00000040
14 128 32’h00000080
15 256 32’h00000100
Table 3–18. Branch Unsigned Immediate (
b4constu
) Encodings
Encoding Decimal Value of Immediate Hex Value of Immediate
032768 32’h00008000
165536 32’h00010000
2 2 32’h00000002
3 3 32’h00000003
4 4 32’h00000004
5 5 32’h00000005
6 6 32’h00000006
7 7 32’h00000007
8 8 32’h00000008
910 32’h0000000A
10 12 32’h0000000C
11 16 32’h00000010
12 32 32’h00000020
13 64 32’h00000040
14 128 32’h00000080
15 256 32’h00000100
Table 3–17. Branch Immediate (
b4const
) Encodings
(continued)
Encoding Decimal Value of Immediate Hex Value of Immediate
Chapter 3. Core Architecture
Xtensa Instruction Set Architecture (ISA) Reference Manual 43
3.8.7 Arithmetic Instructions
The arithmetic instructions that Table 3–20 lists include add and subtract with a small
shift for address calculations and for synthesizing constant multiplies. The ADDMI in-
struction is included for extending the range of load and store instructions.
Table 3–19. Move Instructions
Instruction Format Definition
MOVI RRI8 Load register with 12-bit signed constant
MOVEQZ RRR Conditional move if zero
MOVNEZ RRR Conditional move if non-zero
MOVLTZ RRR Conditional move if less than zero
MOVGEZ RRR Conditional move if greater than or equal to zero
Table 3–20. Arithmetic Instructions
Instruction Format Definition
ADD RRR Add two registers
AR[r] ← AR[s] + AR[t]
ADDX2 RRR Add register to register shifted by 1
AR[r] ← (AR[s]30..0 || 0) + AR[t]
ADDX4 RRR Add register to register shifted by 2
AR[r] ← (AR[s]29..0 || 02) + AR[t]
ADDX8 RRR Add register to register shifted by 3
AR[r] ← (AR[s]28..0 || 03) + AR[t]
SUB RRR Subtract two registers
AR[r] ← AR[s] − AR[t]
SUBX2 RRR Subtract register from register shifted by 1
AR[r] ← (AR[s]30..0 || 0) − AR[t]
SUBX4 RRR Subtract register from register shifted by 2
AR[r] ← (AR[s]29..0 || 02) − AR[t]
SUBX8 RRR Subtract register from register shifted by 3
AR[r] ← (AR[s]28..0 || 03) − AR[t]
NEG RRR Negate
AR[r] ← 0 − AR[t]
Chapter 3. Core Architecture
44 Xtensa Instruction Set Architecture (ISA) Reference Manual
3.8.8 Bitwise Logical Instructions
The bitwise logical instructions in Table 3–21 provide a core set from which other logi-
cals can be synthesized. Immediate forms of these instructions are not provided be-
cause the immediate would be only four bits.
3.8.9 Shift Instructions
The shift instructions in Table 3–22 provide a rich set of operations while avoiding critical
timing paths. See Section 3.3.2 on page 25 for more information.
ABS RRR Absolute value
AR[r] ← if AR[s]31 then 0 − AR[s] else AR[s]
ADDI RRI8 Add signed constant to register
AR[t] ← AR[s] + (imm8724||imm8)
ADDMI RRI8 Add signed constant shifted by 8 to register
AR[t] ← AR[s] + (imm8716||imm8||08)
Table 3–21. Bitwise Logical Instructions
Instruction Format Definition
AND RRR Bitwise logical AND
AR[r] ← AR[s] and AR[t]
OR RRR Bitwise logical OR
AR[r] ← AR[s] or AR[t]
XOR RRR Bitwise logical exclusive OR
AR[r] ← AR[s] xor AR[t]
Table 3–22. Shift Instructions
Instruction Format Definition
EXTUI
RRR Extract unsigned field immediate
Shifts right by 0..31 and ANDs with a mask of 1..16 ones
The operation of this instruction when the number of mask bits exceeds the number of
significant bits remaining after the shift is undefined and reserved for future use.
SLLI RRR Shift left logical immediate by 1..31 bit positions (see page 525 for encoding of the
immediate value).
SRLI RRR Shift right logical immediate by 0..15 bit positions
There is no SRLI for shifts ≥ 16; use EXTUI instead.
SRAI RRR Shift right arithmetic immediate by 0..31 bit positions
Table 3–20. Arithmetic Instructions
(continued)
Instruction Format Definition
Chapter 3. Core Architecture
Xtensa Instruction Set Architecture (ISA) Reference Manual 45
3.8.10 Processor Control Instructions
Table 3–23 contains processor control instructions. The RSR.*, WSR.*, and XSR.*
instructions read, write, and exchange Special Registers for both the Core Architecture
and the architectural options, as detailed in Table 5–128 on page 209. They save and
restore context, process interrupts and exceptions, and control address translation and
attributes. The XSR.* instruction reads and writes both the Special Register, and
AR[t]. It combines the RSR.* and WSR.* operations to exchange the Special Register
with AR[t]. The XSR.* instruction is not present in T1030 and earlier processors.
The xSYNC instructions synchronize Special Register writes and their uses. See
Chapter 5 for more information on how xSYNC instructions are used. These synchroni-
zation instructions are separate from the synchronization instructions used for multipro-
cessors, which are described in Section 4.3.12 on page 74.
On some Xtensa implementations the latency of RSR is greater than one cycle, and so it
is advantageous to schedule uses of the RSR result away from the RSR to avoid an
interlock.
The point at which WSR.* or XSR.* to most Special Registers affects subsequent in-
structions is not defined (SAR and ACC are exceptions). In these cases, Table 5–128 on
page 209 explains how to ensure the effects are seen by a particular point in the instruc-
tion stream (typically involving the use of one of the ISYNC, RSYNC, ESYNC, or DSYNC
SRC
RRR Shift right combined (a funnel shift with shift amount from SAR)
The two source registers are catenated, shifted, and the least significant 32 bits
returned.
SRA RRR Shift right arithmetic (shift amount from SAR)
SLL RRR Shift left logical
(Funnel shift AR[s] and 0 by shift amount from SAR)
SRL RRR Shift right logical
(Funnel shift 0 and AR[s] by shift amount from SAR)
SSA8B RRR Set shift amount register (SAR) for big-endian byte align
The t field must be zero.
SSA8L RRR Set shift amount register (SAR) for little-endian byte align
SSR
RRR Set shift amount register (SAR) for shift right logical
This instruction differs from WSR to SAR in that only the five least significant bits of the
register are used.
SSL RRR Set shift amount register (SAR) for shift left logical
SSAI RRR Set shift amount register (SAR) immediate
Table 3–22. Shift Instructions
(continued)
Instruction Format Definition
Chapter 3. Core Architecture
46 Xtensa Instruction Set Architecture (ISA) Reference Manual
instructions). A WSR.* or XSR.* followed by a RSR.* of the same register must be sep-
arated by an ESYNC instruction to guarantee the value written is read back. A WSR.PS or
XSR.PS followed by a RSIL also requires an ESYNC instruction.
Table 3–23. Processor Control Instructions
Instruction Format Definition
RSR RSR Read Special Register
WSR RSR Write Special Register
XSR
RSR Exchange Special Register
(combined RSR and WSR)
Not present in T1030 and earlier processors
ISYNC
RRR Instruction fetch synchronize: Waits for all previously fetched load, store, cache, and
special register write instructions that affect instruction fetch to be performed before
fetching the next instruction.
RSYNC
RRR Instruction register synchronize: Waits for all previously fetched WSR and XSR
instructions to be performed before interpreting the register fields of the next
instruction. This operation is also performed as part of ISYNC.
ESYNC
RRR Register value synchronize: Waits for all previously fetched WSR and XSR instructions
to be performed before the next instruction uses any register values. This operation is
also performed as part of ISYNC and RSYNC.
DSYNC
RRR Load/store synchronize: Waits for all previously fetched WSR and XSR instructions to
be performed before interpreting the virtual address of the next load or store
instruction. This operation is also performed as part of ISYNC, RSYNC, and ESYNC.
NOP RRR No operation
Chapter 4. Architectural Options
Xtensa Instruction Set Architecture (ISA) Reference Manual 47
4. Architectural Options
This chapter defines the Xtensa ISA options. Each option adds some associated config-
uration resources and capabilities. Some options are dependent on the implementation
of other options. These interdependencies, if any, are listed as Prerequisites at the be-
ginning of the description of each option. The additional parameters required to define
the option, the new state and instructions added by the option, and any other new fea-
tures (such as exceptions) added by the option are listed and the operation of the option
is described.
4.1 Overview of Options
Section 4.2 provides a synopsis of the Core Architecture (covered in more detail in
Chapter 3) in a format similar to the format used for the options. The Instruction Set op-
tions available with an Xtensa processor are listed in five groups below.
"Options for Additional Instructions" on page 53 lists options whose primary function is
to add new instructions to the processor’s instruction set, including:
The Code Density Option on page 53 adds 16-bit encodings of the most frequently
used 24-bit instructions for higher code density.
The Loop Option on page 54 adds a “zero overhead loop,” which requires neither
the extra instruction for a branch at the end of a loop nor the additional delay slots
that would result from the taken branch. A few fixed cycles of overhead mean that
each iteration of the loop pays no cost for the loop branch.
The Extended L32R Option on page 56 allows an additional choice in the address-
ing mode of the L32R instruction.
The 16-bit Integer Multiply Option on page 57 adds signed and unsigned 16x16
multiplication instructions that produce 32-bit results.
The 32-bit Integer Multiply Option on page 58 adds signed and unsigned 32x32
multiplication instructions that produce high and low parts of a 64-bit result.
The 32-bit Integer Divide Option on page 59 implements signed and unsigned 32-
bit division and remainder instructions.
The MAC16 Option on page 60 adds multiply-accumulate functions that are useful
in digital signal processing (DSP).
The Miscellaneous Operations Option on page 62 provides a series of instruc-
tions useful for some applications, but which are not necessary for others. By mak-
ing these optional, the Xtensa architecture allows the designer to choose only those
additional instructions that benefit the application.
Chapter 4. Architectural Options
48 Xtensa Instruction Set Architecture (ISA) Reference Manual
The Coprocessor Option on page 63 allows the grouping of certain states in the
processor and adds an enable bit, which allows for lazy context switching.
The Boolean Option on page 65 adds a set of Boolean registers, which can be set
and cleared by user instructions and that can be used as branch conditions.
The Floating-Point Coprocessor Option on page 67 adds a floating-point unit for
single precision floating point.
The Multiprocessor Synchronization Option on page 74 adds acquire and re-
lease instructions with specific memory ordering relationships to the other Xtensa
memory access instructions.
The Conditional Store Option on page 77 adds a compare and swap type atomic
operation to the instruction set.
"Options for Interrupts and Exceptions" on page 82 lists options whose primary function
is to add and control exceptions and interrupts, including:
The Exception Option on page 82 adds the basic functions needed for the proces-
sor to take exceptions.
The Relocatable Vector Option on page 98 adds the ability for the exception vec-
tors to be relocated at run time.
The Unaligned Exception Option on page 99 adds an exception for memory ac-
cesses that are not aligned by their own size. They may then be emulated in soft-
ware.
The Interrupt Option on page 100 builds upon the Exception Option to add a flexi-
ble software prioritized interrupt system.
The High-Priority Interrupt Option on page 106 adds a hardware prioritized inter-
rupt system for higher performance.
The Timer Interrupt Option on page 110 adds timers and interrupts, which are
caused when the timer expires.
"Options for Local Memory" on page 111 lists options whose primary function is to add
different kinds of memory, such as RAMs, ROMs, or caches to the processor, including:
The Instruction Cache Option on page 115 adds an interface for a direct-mapped
or set-associative instruction cache.
The Instruction Cache Test Option on page 116 adds instructions to access the in-
struction cache tag and data.
The Instruction Cache Index Lock Option on page 117 adds per-index locking to
the instruction cache.
The Data Cache Option on page 118 adds an interface for a direct-mapped or set-
associative data cache.
The Data Cache Test Option on page 121 adds instructions to access the data
cache tag.
Chapter 4. Architectural Options
Xtensa Instruction Set Architecture (ISA) Reference Manual 49
The Data Cache Index Lock Option on page 122 adds per-index locking to the
data cache.
The Instruction RAM Option on page 124 adds an interface for a local instruction
memory.
The Instruction ROM Option on page 125 adds an interface for a local instruction
Read Only Memory.
The Data RAM Option on page 126 adds an interface for a local data memory.
The Data ROM Option on page 126 adds an interface for a local data read-only
memory.
The XLMI Option on page 127 adds an interface with the timing of the local memory
interfaces, but with a full enough signal set to support non-memory devices.
The Hardware Alignment Option on page 128 adds the ability for the hardware to
handle unaligned accesses to data memory.
The Memory ECC/Parity Option on page 128 provides the ability to add parity or
ECC to cache and local memories.
"Options for Memory Protection and Translation" on page 138 lists options whose prima-
ry function is to control access to and manage memory, including:
The Region Protection Option on page 150 adds protection on memory in eight
segments.
The Region Translation Option on page 156 adds protection on memory in eight
segments and allows translations from one segment to another.
The MMU Option on page 158 adds full paging virtual memory management hard-
ware.
"Options for Other Purposes" on page 179 lists options that do not fall conveniently into
one of the other groups, including:
The Windowed Register Option on page 180 adds additional physical AR regis-
ters and a mapping mechanism, which together lead to smaller code size and higher
performance.
The Processor Interface Option on page 194 adds a bus interface used by memo-
ry accesses, which are to locations other than local memories. It is used for cache
misses for cacheable addresses as well as for cache bypass memory accesses.
The Miscellaneous Special Registers Option on page 195 provides one to four
scratch registers within the processor readable and writable by RSR, WSR, and XSR,
which may be used for application-specific exceptions and interrupt processing
tasks.
The Thread Pointer Option on page 196 provides a Special Register that may be
used for a thread pointer.
Chapter 4. Architectural Options
50 Xtensa Instruction Set Architecture (ISA) Reference Manual
The Processor ID Option on page 196 adds a register that software can use to dis-
tinguish which of several processors it is running on.
The Debug Option on page 197 adds instructions-counting and breakpoint excep-
tions for debugging by software or external hardware.
The Trace Port Option on page 203 architectural features for supporting hardware
tracing of the processor.
The functionality of a fairly complete micro-controller is provided by enabling the Code
Density Option, the Exception Option, the Interrupt Option, the High-Priority Interrupt
Option, the Timer Interrupt Option, the Debug Option, and the Windowed Register Op-
tion.
The primary reason to disable the Code Density Option (16-bit instructions) is to provide
maximum opcode space for extensions. The primary reason to disable the other options
listed above is reduce the processor core area.
The choice of Cache, RAM, or ROM Options for instruction and data depends on the
characteristics of the application. RAM is not as flexible as Cache, but it requires slightly
less area because tags are not required. RAM may also be desirable when performance
predictability is required. ROM is even less flexible than RAM, but avoids the need to
load the memory and offers some protection from program errors and tampering.
4.2 Core Architecture
The Core Architecture is not an option, but rather a minimum base of processor state
and instructions, which allows system software and compiled code to run on all Xtensa
implementations. There are no prerequisites or incompatible options, but the tables nor-
mally used to show option additions are used here to give the base set. Table 4–24
through Table 4–26 show Core Architecture processor configurations, processor state,
and instructions.
Table 4–24. Core Architecture Processor-Configurations
Parameter Description Valid Values
msbFirst
Byte order for memory accesses 0 or 1
0 → Little-endian (least significant bit first)
1 → Big-endian (most significant bit first)
Chapter 4. Architectural Options
Xtensa Instruction Set Architecture (ISA) Reference Manual 51
Table 4–25. Core Architecture Processor-State
Register
Mnemonic Quantity Width (bits) Register Name R/W
Special
Register
Number
1
AR 16 32 Address register file R/W —
PC 132 Program counter — —
SAR 1 6 Shift amount register R/W 3
1. Registers with a Special Register assignment are read and/or written with the RSR, WSR, and XSR instructions. See Table 3–23 on page 46.
Table 4–26. Core Architecture Instructions
Instruction
1
Format Definition
ABS RRR Absolute value
ADD RRR Add two registers
ADDI RRI8 Add a register and an 8-bit immediate
ADDMI RRI8 Add a register and a shifted 8-bit immediate
ADDX2/4/8 RRR Add two registers with one of them shifted left by one/two/three
AND RRR Bitwise AND of two registers
BALL/BANY RRI8 Branch if all/any bits specified by a mask in one register are set in another register
BBC/BBS RRI8 Branch if the bit specified by another register is clear/set
BBCI/BBSI RRI8 Branch if the bit specified by an immediate is clear/set
BEQ RRI8 Branch if a register equals another register
BEQI RRI8 Branch if a register equals an encoded constant
BEQZ BRI12 Branch if a register equals zero
BGE RRI8 Branch if one register is greater than or equal to a register
BGEI RRI8 Branch if one register is greater than or equal to an encoded constant
BGEU RRI8 Branch if one register is greater or equal to a register as unsigned
BGEUI BRI8 Branch if one register is greater or equal to an encoded constant as unsigned
BGEZ BRI12 Branch if a register is greater than or equal to zero
BLT RRI8 Branch if one register is less than a register
BLTI BRI8 Branch if one register is less than an encoded constant
BLTU RRI8 Branch if one register is less than a register as unsigned
BLTUI RRI8 Branch if one register is less than an encoded constant as unsigned
BLTZ BRI12 Branch if a register is less than zero
1. These instructions are fully described in Chapter 6, "Instruction Descriptions" on page 243.
Chapter 4. Architectural Options
52 Xtensa Instruction Set Architecture (ISA) Reference Manual
BNALL/BNONE RRI8 Branch if some/all bits specified by a mask in a register are clear in another
register
BNE RRI8 Branch if a register does not equal a register
BNEI RRI8 Branch if a register does not equal an encoded constant
BNEZ BRI12 Branch if a register does not equal zero
CALL0 CALL Call subroutine at PC plus offset, place return address in A0
CALLX0 CALLX Call subroutine register specified location, place return address in A0
DSYNC/ESYNC RRR Wait for data memory/execution related changes to resolve
EXTUI RRR Extract field specified by immediates from a register
EXTW RRR Wait for any possible external ordering requirement (added in RA-2004.1)
ISYNC RRR Wait for instruction fetch related changes to resolve
JCALL Jump to PC plus offset
JX CALLX Jump to register specified location
L8UI RRI8 Load zero extended byte
L16SI/L16UI RRI8 Load sign/zero extended 16-bit quantity
L32I RRI8 Load 32-bit quantity
L32R RI16 Load literal at offset from PC (or from LITBASE with the Extended L32R Option)
MEMW RRR Wait for any possible memory ordering requirement
MOVEQZ RRR Move register if the contents of a register is zero
MOVGEZ RRR Move register if the contents of a register is greater than or equal to zero
MOVI RRI8 Move a 12-bit immediate to a register
MOVLTZ RRR Move register if the contents of a register is less than zero
MOVNEZ RRR Move register if the contents of a register is not zero
NEG RRR Negate a register
NOP RRR No operation (added as a full instruction in RA-2004.1)
OR RRR Bitwise OR two registers
RET CALLX Subroutine return through A0
RSR.* RSR Read a Special Register
RSYNC RRR Wait for dispatch related changes to resolve
S8I/S16I/S32I RRI8 Store byte/16-bit quantity/32-bit quantity
SLL/SLLI RRR Shift left logical by SAR/immediate
SRA/SRAI RRR Shift right arithmetic by SAR/immediate
SRC RRR Shift right combined by SAR with two registers as input and one as output
Table 4–26. Core Architecture Instructions
(continued)
Instruction
1
Format Definition
1. These instructions are fully described in Chapter 6, "Instruction Descriptions" on page 243.
Chapter 4. Architectural Options
Xtensa Instruction Set Architecture (ISA) Reference Manual 53
4.3 Options for Additional Instructions
The options in this section have the primary function of adding new instructions to the
processor’s instruction set. The new instructions cover a variety of purposes including
new architectural capabilities, higher performance on existing capabilities, and smaller
code.
4.3.1 Code Density Option
This option adds 16-bit encodings of the most frequently used 24-bit instructions. When
a 24-bit instruction can be encoded into a 16-bit form, the code-size savings is signifi-
cant.
Prerequisites: None
Incompatible options: None
Compatibility note: The additions made by this option were once considered part of
the core architecture, thus compatibility with binaries for previous hardware might
require the use of this option. Many available third-party software packages includ-
ing some currently supported operating systems require the Code Density Option.
4.3.1.1 Code Density Option Architectural Additions
Table 4–27 shows this option’s architectural additions.
SRL/SRLI RRR Shift right logical by SAR/immediate
SSA8B/SSA8L RRR Use low 2-bits of address register to prepare SAR for SRC assuming big/little
endian
SSAI RRR Set SAR to immediate value
SSL/SSR RRR Set SAR from register for left/right shift
SUB RRR Subtract two registers
SUBX2/4/8 RRR Subtract two registers with the un-negated one shifted left by one/two/three
WSR.* RSR Write a special register
XOR RRR Bitwise XOR two registers
XSR.* RRR Read and write a special register in an exchange (added in T1040)
Table 4–26. Core Architecture Instructions
(continued)
Instruction
1
Format Definition
1. These instructions are fully described in Chapter 6, "Instruction Descriptions" on page 243.
Chapter 4. Architectural Options
54 Xtensa Instruction Set Architecture (ISA) Reference Manual
4.3.1.2 Branches
For some implementations, branches to an instruction that crosses a 32-bit memory
boundary may suffer a small performance penalty. The compiler (or assembler) is ex-
pected to align performance-critical branch targets such that their byte address is 0 mod
4, 1 mod 4, or for 16-bit instructions, 2 mod 4. This can be accomplished either by con-
verting some previous 16-bit-encoded instructions back to their 24-bit form, or by insert-
ing a 16-bit NOP.N.
4.3.2 Loop Option
The Loop Option adds the ability for the processor to execute a zero-overhead loop
where the number of iterations (not counting an early exit) can be determined prior to
entering the loop. This capability is useful in digital signal processing applications where
the overhead of a branch in a heavily used loop is unacceptable. A single loop instruc-
tion defines both the beginning and end of a loop, as well as a count of how many times
the loop will execute.
Prerequisites: None
Incompatible options: None
Table 4–27. Code Density Option Instruction Additions
Instruction
1
Format Definition
ADD.N RRRN Add two registers (same as ADD instruction but with a 16-bit encoding).
ADDI.N RRRN Add register and immediate (-1 and 1..15).
BEQZ.N RI16 Branch if register is zero with a 6-bit unsigned offset (forward only).
BNEZ.N RI16 Branch if register is non-zero with a 6-bit unsigned offset (forward only).
BREAK.N2RRRN This instruction is the same as BREAK but with a 16-bit encoding.
L32I.N RRRN Load 32 bits, 4-bit offset
MOV.N RRRN Narrow move
MOVI.N RI7 Load register with immediate (-32..95).
NOP.N RRRN This instruction performs no operation. It is typically used for instruction alignment.
RET.N RRRN The same as RET but with a 16-bit encoding.
RETW.N3RRRN The same as RETW but with a 16-bit encoding.
S32I.N RRRN Store 32 bits, 4-bit offset
1. These instructions are fully described in Chapter 6, "Instruction Descriptions" on page 243.
2. Exists only if the Debug Option described in Section 4.7.6 on page 197 is configured.
3. Exists only if the Windowed Register Option described in Section 4.7.1 on page 180 is configured.
Chapter 4. Architectural Options
Xtensa Instruction Set Architecture (ISA) Reference Manual 55
Compatibility note: The additions made by this option were once considered part of
the core architecture, thus compatibility with binaries for previous hardware might
require the use of this option. Many available third-party software packages includ-
ing some currently supported operating systems require the Loop Option.
4.3.2.1 Loop Option Architectural Additions
Table 4–28 and Table 4–29 show this option’s architectural additions.
LBEG and LEND are undefined after processor reset. LCOUNT is initialized to zero after
processor reset.
4.3.2.2 Restrictions on Loops
There is a restriction on instruction alignment for zero-overhead loops. The first instruc-
tion after the LOOP instruction, which begins at the address written to LBEG by the LOOP
instruction, must be entirely contained within a naturally aligned, power of two sized unit
of a particular size. That size is the next larger power of two equal to or greater than the
instruction length, but not less than 4 bytes. Thus a 16-bit instruction, if it is the first in a
loop, may be at 0 mod 4, 1 mod 4, or 2 mod 4. A 24-bit instruction, if it is the first in a
loop, may be at 0 mod 4 or at 1 mod 4. As an example of a potential larger instruction, a
64-bit instruction must be aligned at 0 mod 8.
Table 4–28. Loop Option Processor-State Additions
Register
Mnemonic Quantity Width (bits) Register Name R/W
Special
Register
Number
1
LBEG 132 Loop begin R/W 0
LEND 132 Loop end R/W 1
LCOUNT 132 Loop count R/W 2
1. Registers with a Special Register assignment are read and/or written with the RSR, WSR, and XSR instructions. See Table 3–23 on page 46.
Table 4–29. Loop Option Instruction Additions
Instruction
1
Format Definition
LOOP BRI8 Set up a zero-overhead loop by setting LBEG, LEND, and LCOUNT special
registers.
LOOPGTZ BRI8 Set up a zero-overhead loop by setting LBEG, LEND, and LCOUNT special
registers. Skip loop if LCOUNT is not positive.
LOOPNEZ BRI8 Set up a zero-overhead loop by setting LBEG, LEND, and LCOUNT special
registers. Skip loop if LCOUNT is zero.
1. These instructions are fully described in Chapter 6, "Instruction Descriptions" on page 243.
Chapter 4. Architectural Options
56 Xtensa Instruction Set Architecture (ISA) Reference Manual
The last instruction of the loop must not be a call, ISYNC, WAITI, or RSR.LCOUNT. If the
last instruction of the loop is a taken branch, then the value of LCOUNT is undefined.
Thus, a taken branch may be used to exit the loop (in which case the value of LCOUNT is
irrelevant), but not to iterate within the loop.
4.3.2.3 Loops Disabled During Exceptions
Loops are disabled when PS.EXCM is set in Xtensa Exception Architecture 2 and above.
This prevents program code from maliciously or accidentally setting LEND to an address
in an exception handler and then causing the exception, thereby transitioning to Ring 0
while retaining control of the processor.
4.3.2.4 Loopback Semantics
The processor includes the following to compute the PC of the next instruction:
if LCOUNT ≠ 0 and CLOOPENABLE and nextPC = LEND then
LCOUNT ← LCOUNT − 1
nextPC ← LBEG
endif
The semantics above have some non-obvious consequences. A taken branch to the ad-
dress in LEND does not cause a transfer to LBEG. Thus a taken branch to the LEND in-
struction can be used to exit the loop prematurely. This is why a call instruction as the
last instruction of a loop will not do the obvious thing (the return will branch to the LEND
address and exit the loop). To conditionally begin the next loop iteration, a branch to a
NOP before LEND may be used.
4.3.3 Extended
L32R
Option
The Extended L32R Option adds functionality to the standard L32R instruction. The
standard L32R instruction has an offset that can reach as far as 256kB below the current
PC. In the case where an instruction RAM approaches or exceeds 256kB in size, ac-
cessing literal data becomes much more difficult. This option is intended to ease the ac-
cess to literal data by providing an optional separate literal base register.
Prerequisites: None
Incompatible options: MMU Option (page 158)
4.3.3.1 Extended L32R Option Architectural Additions
Table 4–30 shows this option’s architectural additions.
Chapter 4. Architectural Options
Xtensa Instruction Set Architecture (ISA) Reference Manual 57
4.3.3.2 The Literal Base Register
The literal base (LITBASE) register contains 20 upper bits, which define the location of
the literal base and one enable bit (En). When the enable bit is clear, the L32R instruc-
tion loads a literal at a negative offset from the PC. When the enable bit is set, the L32R
instruction loads a literal at a negative offset from the address formed by the 20 upper
bits of literal base and 12 lower bits of 12’h000. See the L32R instruction description in
Chapter 6. Figure 4–7 shows the LITBASE register format.
Figure 4–7. LITBASE Register Format
The enable bit of the literal base register is cleared after reset. The remaining bits are
undefined after reset.
4.3.4 16-bit Integer Multiply Option
This option provides two instructions that perform 16×16 multiplication, producing a 32-
bit result. It is typically useful for digital signal processing (DSP) algorithms that require
16 bits or less of input precision (32 bits of input precision is provided by the 32-bit Inte-
ger Multiply Option) and do not require more than 32-bit accumulation (as provided by
the MAC16 Option). Because a 16×16 multiplier is one-fourth the area of a 32×32 multi-
plier, this option is less costly than the 32-bit Integer Multiply Option. Because it lacks an
accumulator and data registers, it is less costly than the MAC16 Option.
Prerequisites: None
Incompatible options: None
See Also "MAC16 Option" on page 60 and "32-bit Integer Multiply Option" on page
58
Table 4–30. Extended L32R Option Processor-State Additions
Register
Mnemonic Quantity Width
(bits) Register Name R/W
Special
Register
Number
1
LITBASE 1 21 Literal base2R/W 5
1. Registers with a Special Register assignment are read and/or written with the RSR, WSR, and XSR instructions. See Table 3–23 on page 46.
2. See Figure 4–7 on page 57 for the format of this register.
31 12 11 1 0
Literal Base Address reserved En
20 11 1
Chapter 4. Architectural Options
58 Xtensa Instruction Set Architecture (ISA) Reference Manual
4.3.4.1 16-bit Integer Multiply Option Architectural Additions
Table 4–31 shows this option’s architectural additions. There are no configuration pa-
rameters associated with the MUL16 Option and no additional processor state.
4.3.5 32-bit Integer Multiply Option
This option provides instructions that implement 32-bit integer multiplication as instruc-
tions. This provides single instruction targets for the multiplication operators of program-
ming languages such as C. When this option is not enabled, the Xtensa compiler uses
subroutine calls to implement 32-bit integer multiplication. Note that various algorithms
may be used to implement multiplication, and some hardware implementations may be
slower than the software implementations for some operand values. Implementations
may allow a choice of algorithms through configuration parameters to optimize among
area, speed, and other characteristics.
There is one sub-option within this option: Mul32High. It controls whether the MULSH
and MULUH instructions are included or not. For some implementations, generating the
high 32 bits of the product requires additional hardware, and so disabling this sub-option
may reduce cost.
Prerequisites: None
Incompatible options: None
See Also: "MAC16 Option" on page 60 and "16-bit Integer Multiply Option" on page
57
4.3.5.1 32-bit Integer Multiply Option Architectural Additions
Table 4–32 and Table 4–33 show this option’s architectural additions. This option adds
no new processor state.
Table 4–31. 16-bit Integer Multiply Option Instruction Additions
Instruction
1
Format Definition
MUL16S RRR Signed 16×16 multiplication of the least-significant 16 bits of AR[s] and
AR[t], with the 32-bit product written to AR[r]
MUL16U RRR Unsigned 16×16 multiplication of the least-significant 16 bits of AR[s] and
AR[t], with the 32-bit product written to AR[r]
1. These instructions are fully described in Chapter 6, "Instruction Descriptions" on page 243.
Chapter 4. Architectural Options
Xtensa Instruction Set Architecture (ISA) Reference Manual 59
4.3.6 32-bit Integer Divide Option
This option provides instructions that implement 32-bit integer division and remainder
operations. When this option is not enabled, the Xtensa compiler uses subroutine calls
to implement division and remainder. Note that various algorithms may be used to imple-
ment these instructions, and some hardware implementations may be slower than the
software implementations for some operand values.
Prerequisites: None
Incompatible Options: None
4.3.6.1 32-bit Integer Divide Option Architectural Additions
Table 4–34 through Table 4–36 show this option’s architectural additions. This option
adds no new processor state. This option does add a new exception, Integer Divide by
Zero, which is raised when the divisor operand of a QUOS, QUOU, REMS, or REMU instruc-
tion contains zero.
Table 4–32. 32-bit Integer Multiply Option Processor-Configuration Additions
Parameter Description Valid Values
Mul32High Determines whether the MULSH and MULUH
instructions are included
0 or 1
MulAlgorithm Determines the multiplication algorithm employed Implementation-dependent
Table 4–33. 32-Bit Integer Multiply Instruction Additions
Instruction
1
Format Definition
MULL RRR Multiply low
(return least-significant 32 bits of product)
MULUH2RRR Multiply unsigned high
(return most-significant 32 bits of product)
MULSH2RRR Multiply signed high
(return most-significant 32 bits of product)
1. These instructions are fully described in Chapter 6, "Instruction Descriptions" on page 243.
2. These instructions are part of the Mul32High sub-option of 32-bit Integer Multiply Option.
Table 4–34. 32-bit Integer Divide Option Processor-Configuration Additions
Parameter Description Valid Values
DivAlgorithm Determines the division algorithm employed Implementation-dependent
Chapter 4. Architectural Options
60 Xtensa Instruction Set Architecture (ISA) Reference Manual
4.3.7 MAC16 Option
The MAC16 Option adds multiply-accumulate functions that are useful in DSP and other
media-processing operations. The option adds a 40-bit accumulator (ACC), four 32-bit
data registers (MR[n]), and 72 instructions.
The multiplier operates on two 16-bits operands from either the address registers (AR) or
MAC16 registers (MR). Each operand may be taken from either the low or high half of a
register. The result of the operation is placed in the 40-bit accumulator. The MR regis-
ters and the low 32 bits and high 8 bits of the accumulator are readable and writable with
the RSR, WSR, and XSR instructions. MR[0] and MR[1] can be used as the first multiplier
input, and MR[2] and MR[3] can be used as the second multiplier input. Four of the 72
added instructions can load the MR registers with 32-bit values from memory in parallel
with multiply-accumulate operations.
The accumulator (ACC) and data registers (MR) are undefined after reset.
Prerequisites: None
Incompatible options: None
4.3.7.1 MAC16 Option Architectural Additions
Table 4–37 and Table 4–38 show this option’s architectural additions.
Table 4–35. 32-bit Integer Divide Option Exception Additions
Exception Description
EXCCAUSE
value
IntegerDivideByZero Exception raised when divisor is zero 6
Table 4–36. 32-bit Integer Divide Option Instruction Additions
Instruction
1
Format Definition
QUOS RRR Quotient Signed
(divide giving 32-bit quotient)
QUOU RRR Quotient Unsigned
(divide giving 32-bit quotient)
REMS RRR Remainder Signed
(divide giving 32-bit remainder)
REMU RRR Remainder Unsigned
(divide giving 32-bit remainder)
1. These instructions are fully described in Chapter 6, "Instruction Descriptions" on page 243
Chapter 4. Architectural Options
Xtensa Instruction Set Architecture (ISA) Reference Manual 61
Table 4–37. MAC16 Option Processor-State Additions
Register
Mnemonic Quantity Width
(bits) Register Name R/W
Special
Register
Number
1
ACCLO 132 Accumulator low R/W 16
ACCHI 1 8 Accumulator high R/W 17
MR[0]2132 MAC16 register 0 (m0 in assembler) R/W 32
MR[1]2132 MAC16 register 1 (m1 in assembler) R/W 33
MR[2]2132 MAC16 register 2 (m2 in assembler) R/W 34
MR[3]2132 MAC16 register 3 (m3 in assembler) R/W 35
1. Registers with a Special Register assignment are read and/or written with the RSR, WSR, and XSR instructions. See Table 3–23 on page 46.
2. These registers are known as MR[0..3] in hardware and as m0..3 in the software.
Table 4–38. MAC16 Option Instruction Additions
Instruction
1, 2
Definition
3
LDDEC Load MAC16 data register (MR) with auto decrement
LDINC Load MAC16 data register (MR) with auto increment
MUL.AA.qq Signed multiply of two address registers
MUL.AD.qq Signed multiply of an address register and a MAC16 data register
MUL.DA.qq Signed multiply of a MAC16 data register and an address register
MUL.DD.qq Signed multiply of two MAC16 data registers
MULA.AA.qq Signed multiply-accumulate of two address registers
MULA.AD.qq Signed multiply-accumulate of an address register and a MAC16 data register
MULA.DA.qq Signed multiply-accumulate of a MAC16 data register and an address register
MULA.DD.qq Signed multiply-accumulate of two MAC16 data registers
MULS.AA.qq Signed multiply/subtract of two address registers
MULS.AD.qq Signed multiply/subtract of an address register and a MAC16 data register
MULS.DA.qq Signed multiply/subtract of a MAC16 data register and an address register
MULS.DD.qq Signed multiply/subtract of two MAC16 data registers
MULA.DA.qq.LDDEC Signed multiply-accumulate of a MAC16 data register and an address register, and load
a MAC16 data register with auto decrement
MULA.DA.qq.LDINC Signed multiply-accumulate of a MAC16 data register and an address register, and load
a MAC16 data register with auto increment
1. These instructions are fully described in Chapter 6, "Instruction Descriptions" on page 243.
2. The qq opcode parameter indicates (by HH, HL, LH, or LL) whether the operands are taken from the Low or High 16-bit half of the AR or MR
registers. The first q represents the location of the first operand; the second q represents the location of the second operand.
3. The destination for all product and accumulate results is the MAC16 accumulator
Chapter 4. Architectural Options
62 Xtensa Instruction Set Architecture (ISA) Reference Manual
4.3.7.2 Use With CLAMPS Instruction
The CLAMPS instruction, implemented with the Miscellaneous Operations Option, is use-
ful in conjunction with the MAC16 Option. It allows clamping results to 16 bits before
storing to memory.
4.3.8 Miscellaneous Operations Option
These instructions can be individually enabled in groups to provide computational capa-
bility required by a few applications.
Prerequisites: None
Incompatible options: None
4.3.8.1 Miscellaneous Operations Option Architectural Additions
Table 4–39 and Table 4–40 show this option’s architectural additions.
MULA.DD.qq.LDDEC Signed multiply-accumulate of two MAC16 data registers, and load a MAC16 data
register with auto decrement
MULA.DD.qq.LDINC Signed multiply-accumulate of two MAC16 data registers, and load a MAC16 data
register with auto increment
UMUL.AA.qq Unsigned multiply of two address registers
Table 4–39. Miscellaneous Operations Option Processor-Configuration Additions
Parameter Description Valid Values
InstructionCLAMPS Enable the signed clamp instruction: CLAMPS 0 or 1
InstructionMINMAX Enable the minimum and maximum value instructions: MIN,
MAX, MINU, MAXU
0 or 1
InstructionNSA Enabled the normalization shift amount instructions: NSA,
NSAU
0 or 1
InstructionSEXT Enable the sign extend instruction: SEXT 0 or 1
Table 4–38. MAC16 Option Instruction Additions
(continued)
Instruction
1, 2
Definition
3
1. These instructions are fully described in Chapter 6, "Instruction Descriptions" on page 243.
2. The qq opcode parameter indicates (by HH, HL, LH, or LL) whether the operands are taken from the Low or High 16-bit half of the AR or MR
registers. The first q represents the location of the first operand; the second q represents the location of the second operand.
3. The destination for all product and accumulate results is the MAC16 accumulator
Chapter 4. Architectural Options
Xtensa Instruction Set Architecture (ISA) Reference Manual 63
4.3.9 Coprocessor Option
A coprocessor is a combination of additional state, instructions and logic that operates
on that state, including moves and the setting of Booleans for branch true/false opera-
tions. The Coprocessor Option is general in nature: it adds state that is shared by all co-
Table 4–40. Miscellaneous Operations Instruction Additions
Instruction
1
Format Definition
CLAMPS
RRR Clamp to signed power of two range
sign ← AR[s]31
AR[r] ← if AR[s]30..(t+7) = sign24−t
then AR[s]
else sign(25−t) || (not sign)t+7
MAX RRR Maximum value signed
AR[r] ← if AR[s] < AR[t] then AR[t] else AR[s]
MAXU
RRR Maximum value unsigned
AR[r] ← if (0||AR[s]) < (0||AR[t])
then AR[t]
else AR[s]
MIN RRR Minimum value signed
AR[r] ← if AR[s] < AR[t] then AR[s] else AR[t]
MINU
RRR Minimum value unsigned
AR[r] ← if (0||AR[s]) < (0||AR[t])
then AR[s]
else AR[t]
NSA
RRR Normalization shift amount signed
AR[r] ← nsa1(AR[s]31, AR[s])
NSA returns the number of contiguous bits in the most significant end of
AR[s] that are equal to the sign bit (not counting the sign bit itself), or 31 if
AR[s] = 0 or AR[s] = -1. The result may be used as a left shift amount
such that the result of SLL on AR[s] will have bit31 ≠ bit30 (if AR[s] ≠
0).
NSAU
RRR Normalization shift amount unsigned
AR[r] ← nsa1(0, AR[s])
NSAU returns the number of contiguous zero bits in the most significant end
of AR[s], or 32 if AR[s] = 0. The result may be used as a left shift
amount such that the result of SLL on AR[s] will have bit31 ≠ 0 (if
AR[s] ≠ 0).
SEXT
RRR Sign extend
sign ← AR[s]t+7
AR[r] ← sign(24−t) || AR[s]t+7..0
1. These instructions are fully described in Chapter 6, "Instruction Descriptions" on page 243.
Chapter 4. Architectural Options
64 Xtensa Instruction Set Architecture (ISA) Reference Manual
processors. After the Coprocessor Option is added, specific coprocessors, such as the
Floating-Point Coprocessor Option, can be added, along with system-specific instruc-
tions for coprocessor operations.
Prerequisites: Exception Option (page 82)
Incompatible options: None
4.3.9.1 Coprocessor Option Architectural Additions
Table 4–41 and Table 4–42 show this option’s architectural additions.
4.3.9.2 Coprocessor Context Switch
RUR and WUR are not created by the Coprocessor Option, but rather by TIE language
constructs. They provide a uniform way for reading and writing miscellaneous state add-
ed via the TIE language. The TIE user_register construct associates TIE state reg-
isters with RUR/WUR register numbers in 32-bit quantities. RUR reads 32 bits of TIE state
into an address register, and WUR writes 32 bits to a TIE state register from an address
register. The ISA does not define the result of additional bits read by RUR when fewer
than 32 bits of TIE state are associated with the user register.
Table 4–41. Coprocessor Option Exception Additions
Exception Description
EXCCAUSE
value
Coprocessor0Disabled Coprocessor 0 instruction while cp0 disabled 32
Coprocessor1Disabled Coprocessor 1 instruction while cp1 disabled 33
Coprocessor2Disabled Coprocessor 2 instruction while cp2 disabled 34
Coprocessor3Disabled Coprocessor 3 instruction while cp3 disabled 35
Coprocessor4Disabled Coprocessor 4 instruction while cp4 disabled 36
Coprocessor5Disabled Coprocessor 5 instruction while cp5 disabled 37
Coprocessor6Disabled Coprocessor 6 instruction while cp6 disabled 38
Coprocessor7Disabled Coprocessor 7 instruction while cp7 disabled 39
Table 4–42. Coprocessor Option Processor-State Additions
Register
Mnemonic Quantity Width
(bits) Register Name R/W Special Register
Number
1
CPENABLE 1 8 Coprocessor enable bits R/W 224
1. Registers with a Special Register assignment are read and/or written with the RSR, WSR, and XSR instructions. See Table 3–23 on page 46.
Chapter 4. Architectural Options
Xtensa Instruction Set Architecture (ISA) Reference Manual 65
The TIE compiler automatically generates for each coprocessor the assembly code to
save the state associated with a coprocessor to memory and to restore coprocessor
state from memory.
Tensilica reserves user register numbers for RUR and WUR in the range 192 to 255.
The CPENABLE register allows a “lazy” context switch of the coprocessor state. Any in-
struction that references coprocessor n state (not including the shared Boolean regis-
ters) when that coprocessor’s enable bit (bit n) is clear raises a
CoprocessornDisabled exception. CPENABLE can be cleared on context switch, and
the exception used to unload the previous task’s coprocessor state and load the current
task’s. The appropriate CPENABLE bit is then set by the exception handler, which then
returns to execute the coprocessor instruction. An RSYNC instruction must be executed
after writing CPENABLE before executing any instruction that references state controlled
by the changed bits of CPENABLE. This register is undefined after reset.
If a single instruction references state from more than one coprocessor not enabled in
CPENABLE, then one of CoprocessornDisabled exceptions is raised. The prioritiza-
tion among multiple CoprocessornDisabled exceptions is implementation-specific.
4.3.10 Boolean Option
This option makes a set of Boolean registers available, along with branches and other
operations that refer to them. Multiple coprocessors and other TIE language extensions
can use this set.
Prerequisites: None
Incompatible options: None
4.3.10.1 Boolean Option Architectural Additions
Table 4–43 and Table 4–44 show this option’s architectural additions.
Table 4–43. Boolean Option Processor-State Additions
Register
Mnemonic Quantity Width
(bits) Register Name R/W Special Register
Number
1
BR216 1Boolean registers R/W 4
1. Registers with a Special Register assignment are read and/or written with the RSR, WSR, and XSR instructions. See Tab le 3–23 on page 46.
2. This register is known as Special Register BR or as individual Boolean bits b0..15.
Chapter 4. Architectural Options
66 Xtensa Instruction Set Architecture (ISA) Reference Manual
4.3.10.2 Booleans
A coprocessor test or comparison produces a Boolean result. The Boolean Option pro-
vides 16 single-bit Boolean registers for storing the results of coprocessor comparisons
for testing in conditional move and branch instructions. Boolean logic may replace
branches in some situations. Compared to condition codes used by other ISAs, these
Booleans eliminate the bottleneck of having only a single place to store comparison re-
sults. It is possible, for example, to do multiple comparisons before the comparison re-
sults are used. For Single-Instruction Multiple-Data (SIMD) operations, Booleans pro-
vide up to 16 simultaneous compare results and conditionals.
Boolean-producing instructions generate only one sense of the condition (for example, =
but not ≠); all Boolean uses allow for complementing of the Boolean. Multiple Booleans
may be combined into a single Boolean using the ANY4, ALL4, and so forth instructions.
For example, this is useful after a SIMD comparison to test if any or all of the elements
satisfy the test, such as testing if any byte of a word is zero. ANY2 and ALL2 instructions
are not provided; ANDB and ORB provide this functionality given bs+0 and bs+1 as argu-
ments.
Table 4–44. Boolean Option Instruction Additions
Instruction
1
Format Definition
ALL4 RRR 4-Boolean and reduction
(result is 1 if all of the 4 Booleans are true)
ALL8 RRR 8-Boolean and reduction
(result is 1 if all of the 8 Booleans are true)
ANDB RRR Boolean and
ANDBC RRR Boolean and with complement
ANY4 RRR 4-Boolean or reduction
(result is 1 if any of the 4 Booleans is true)
ANY8 RRR 8-Boolean or reduction
(result is 1 if any of the 8 Booleans is true)
BF RRI8 Branch if Boolean false
BT RRI8 Branch if Boolean true
MOVF RRR Conditional move if false
MOVT RRR Conditional move if true
ORB RRR Boolean or
ORBC RRR Boolean or with complement
XORB RRR Boolean exclusive or
1. These instructions are fully described in Chapter 6, "Instruction Descriptions" on page 243.
Chapter 4. Architectural Options
Xtensa Instruction Set Architecture (ISA) Reference Manual 67
The Boolean registers are undefined after reset.
The Boolean registers are accessible from C using the xtbool, xtbool2, xtbool4,
xtbool8, and xtbool16 data types. See the Xtensa C and C++ Compiler User’s
Guide for details.
4.3.11 Floating-Point Coprocessor Option
The Floating-Point Coprocessor Option adds the logic and architectural components
needed for IEEE754 single-precision floating-point operations. These operations are
useful for DSP that requires >16 bits of precision, such as audio compression and de-
compression. Also, DSP algorithms for less precise data are more easily coded using
floating-point, and good performance is obtainable when programming in languages
such as C.
Prerequisites: Coprocessor Option (page 63) and Boolean Option (page 65)
Incompatible options: None
4.3.11.1 Floating-Point Coprocessor Option Architectural Additions
Table 4–45 through Table 4–46 show this option’s architectural additions.
Table 4–45. Floating-Point Coprocessor Option Processor-State Additions
Register
Mnemonic Quantity Width (bits) Register Name R/W Register
Number
1
FR 16 32 Floating-point register R/W -
FCR 132 Floating-point control register R/W User 232
FSR 132 Floating-point status register R/W User 233
1. See Tabl e 3–23 on page 46.
Table 4–46. Floating-Point Coprocessor Option Instruction Additions
Instruction
1
Format Definition
ABS.S RRR Single-precision absolute value
ADD.S RRR Single-precision add
CEIL.S RRR Single-precision floating-point to signed integer conversion with round to +∞
FLOAT.S RRR Signed integer to single-precision floating-point conversion (current rounding mode)
FLOOR.S RRR Single-precision floating-point to signed integer conversion with round to -∞
LSI RRI8 Load single-precision immediate
LSIU RRI8 Load single-precision immediate with base update
1. These instructions are fully described in Chapter 6, "Instruction Descriptions" on page 243.
Chapter 4. Architectural Options
68 Xtensa Instruction Set Architecture (ISA) Reference Manual
LSX RRR Load single-precision indexed
LSXU RRR Load single-precision indexed with base update
MADD.S RRR Single-precision multiply-add
MOV.S RRR Single-precision move
MOVEQZ.S RRR Single-precision move if equal to zero
MOVF.S RRR Single-precision move if Boolean condition false
MOVGEZ.S RRR Single-precision move if greater than or equal to zero
MOVLTZ.S RRR Single-precision move if less than zero
MOVNEZ.S RRR Single-precision move if not equal to zero
MOVT.S RRR Single-precision move if Boolean condition true
MSUB.S RRR Single-precision multiply-subtract
MUL.S RRR Single-precision multiply
NEG.S RRR Single-precision negate
OEQ.S RRR Single-precision compare equal
OLE.S RRR Single-precision compare less than or equal
OLT.S RRR Single-precision compare less than
RFR RRR Read floating-point register (FR to AR)
ROUND.S RRR Single-precision floating-point to signed integer conversion with round to nearest
SSI RRI8 Store single-precision immediate
SSIU RRI8 Store single-precision immediate with base update
SSX RRR Store single-precision indexed
SSXU RRR Store single-precision indexed with base update
SUB.S RRR Single-precision subtract
TRUNC.S RRR Single-precision floating-point to signed integer conversion with round to 0
UEQ.S RRR Single-precision compare unordered or equal
UFLOAT.S RRR Unsigned integer to single-precision floating-point conversion (current rounding mode)
ULE.S RRR Single-precision compare unordered or less than or equal
ULT.S RRR Single-precision compare unordered or less than
UN.S RRR Single-precision compare unordered
UTRUNC.S RRR Single-precision floating-point to unsigned integer conversion with round to 0
WFR RRR Write floating-point register (AR to FR)
Table 4–46. Floating-Point Coprocessor Option Instruction Additions
(continued)
Instruction
1
Format Definition
1. These instructions are fully described in Chapter 6, "Instruction Descriptions" on page 243.
Chapter 4. Architectural Options
Xtensa Instruction Set Architecture (ISA) Reference Manual 69
4.3.11.2 Floating-Point Representation
The primary floating-point data type is IEEE754 single-precision:
The other data format is a signed, 32-bit integer used by the FLOAT.S, TRUNC.S,
ROUND.S, FLOOR.S, and CEIL.S instructions.
IEEE754 uses a sign-magnitude format, with a 1-bit sign, an 8-bit exponent with bias
127, and a 24-bit significand formed from 23 stored bits representing the binary digits to
the right the binary point, and an implicit bit to the left of the binary point (0 if exponent is
zero, 1 if exponent is non-zero). Thus, the value of the number is:
(−1)s × 2exp−127 × implicit.fraction
Thus, the representation for 1.0 is 0x3F800000, with a sign of 0, exp of 127, a zero frac-
tion, and an implicit 1 to the left of the binary point.
The Xtensa ISA includes IEEE754 signed-zero, infinity, quiet NaN, and sub-normal rep-
resentations and processing rules. The ISA does not include IEEE754 signaling NaNs or
exceptions. Integer ⇔ floating-point conversions include a binary scale factor to make
conversion into and out of fixed-point formats faster.
4.3.11.3 Floating-Point State
Table 4–45 summarizes the processor state added by the floating-point coprocessor.
The FR register file consists of 16 registers of 32 bits each and is used for all data com-
putation. Load and store instructions transfer data between the FR’s and memory. The
FCR register file has one field that may be changed at run-time to control the operation
of various instructions. Table 4–47 lists FCR fields and their associated meanings. The
format of FCR is
31 30 23 22 0
sexp fraction
1 8 23
31 12 11 76543210
reserved ignore V Z O U I RM
20 5 1 1 1 1 1 2
Chapter 4. Architectural Options
70 Xtensa Instruction Set Architecture (ISA) Reference Manual
The FSR register file provides the status flags required by IEEE754. These flags are set
by any operation that raises a non-enabled exception (see Section 4.3.11.4). Enabled
exceptions abort the operation with a floating-point exception and the flags are not writ-
ten:
Table 4–47. FCR fields
FCR Field Meaning
RM Rounding mode
0 → round to nearest
1 → round toward 0 (TRUNC)
2 → round toward +∞ (CEIL)
3 → round toward −∞ (FLOOR)
IInexact exception enable (0 → disabled, 1 → enabled)
UUnderflow exception enable (0 → disabled, 1 → enabled)
OOverflow exception enable (0 → disabled, 1 → enabled)
ZDivide-by-zero exception enable (0 → disabled, 1 → enabled)
VInvalid exception enable (0 → disabled, 1 → enabled)
ignore Reads as 0, ignored on write
reserved Reads back last value written. Non-zero values cause a floating-point exception on any
floating-point instruction (see Section 4.3.11.4)
31 12 11 10 9876 0
reserved V Z O U I ignore
20 1 1 1 1 1 7
Table 4–48. FSR fields
FSR Field Meaning
IInexact exception flag
UUnderflow exception flag
OOverflow exception flag
ZDivide-by-zero flag
VInvalid exception flag
ignore Reads as 0, ignored on write
reserved Reads back last value written. Non-zero values cause a floating-point exception on any
floating-point instruction (see Section 4.3.11.4)
Chapter 4. Architectural Options
Xtensa Instruction Set Architecture (ISA) Reference Manual 71
Most architectures have a combined floating-point control and status register, instead of
separate registers. In high-performance pipelines, this combination can compromise
performance, as reads and writes must access all bits, even ones that are not required
by the program. Xtensa’s FCR may be read and written without waiting for the results of
pending floating-point operations. Writes to FCR affect subsequent floating-point opera-
tions, but there is usually little performance cost from this dependency. Only reads of
FSR need cause a significant pipeline interlock.
FCR and FSR are organized to allow implementation with a single 32-bit physical regis-
ter. The separate register numbers affect only the bits read and written of this underlying
physical register. It is also possible for software to bitwise logical OR the RUR’s of FCR
and FSR to create the appearance of a single register and to write this combined value
to FCR and FSR.
The reserved bits of FCR and FSR must store the last value written, but if that value is
non-zero, this causes all floating-point operations to raise a floating-point exception.
This allows future extensions to define additional control values that if used in earlier im-
plementations, can be emulated in software.
4.3.11.4 Floating-Point Exceptions
Current implementations neither raise exceptions enabled by FCR bits nor set flag bits in
FSR. They also do not raise an exception when one of the reserved bits of FCR or FSR is
non-zero.
4.3.11.5 Floating-Point Instructions
The floating-point instructions are defined in Table 4–49 and Table 4–50. The instruc-
tions operate on data in the floating-point register file, which consists of 16 32-bit regis-
ters.
The floating-point ISA requires a triple read-port FR register file for the MADD.S and
MSUB.S operations.
Chapter 4. Architectural Options
72 Xtensa Instruction Set Architecture (ISA) Reference Manual
Table 4–49. Floating-Point Coprocessor Option Load/Store Instructions
Instruction
1
Format Definition
LSI
RRI8 Load single-precision immediate
vAddr ← AR[s] + (022||imm8||02)
FR[t] ← Load32(vAddr)
LSIU
RRI8 Load single-Precision Immediate with Base Update
vAddr ← AR[s] + (022||imm8||02)
FR[t] ← Load32(vAddr)
AR[s] ← vAddr
LSX
RRR Load single-Precision Indexed
vAddr ← AR[s] + AR[t]
FR[t] ← Load32(vAddr)
LSXU
RRR Load single-Precision Indexed with Base Update
vAddr ← AR[s] + AR[t]
FR[t] ← Load32(vAddr)
AR[s] ← vAddr
SSI
RRI8 Store single-Precision Immediate
vAddr ← AR[s] + (022||imm8||02)
Store32 (vAddr, FR[t])
SSIU
RRI8 Store single-Precision Immediate with Base Update
vAddr ← AR[s] + (022||imm8||02)
Store32 (vAddr, FR[t])
AR[s] ← vAddr
SSX
RRR Store single-Precision Indexed
vAddr ← AR[s] + AR[t]
Store32 (vAddr, FR[r])
SSXU
RRR Store single-Precision Indexed with Base Update
vAddr ← AR[s] + AR[t]
Store32 (vAddr, FR[r])
AR[s] ← vAddr
1. These instructions are fully described in Chapter 6, "Instruction Descriptions" on page 243
Table 4–50. Floating-Point Coprocessor Option Operation Instructions
Instruction
1
Format Definition
ABS.S RRR Single-precision absolute value
FR[r] ← abss(FR[s])
ADD.S RRR Single-precision add
FR[r] ← FR[s] +s FR[t]
CEIL.S RRR Scale and convert single-precision to integer, round to +∞
AR[r] ← ceils(FR[s] ×s pows(2.0,t))
1. These instructions are fully described in Chapter 6, "Instruction Descriptions" on page 243.
Chapter 4. Architectural Options
Xtensa Instruction Set Architecture (ISA) Reference Manual 73
FLOAT.S RRR Convert signed integer to single-precision and scale
FR[r] ← floats(AR[s]) ×s pows(2.0,-t)
FLOOR.S RRR Scale and convert single-precision to integer, round to −∞
AR[r] ← floors(FR[s] ×s pows(2.0,t))
MADD.S RRR Single-precision multiply/add
FR[r] ← FR[r] +s (FR[s] ×s FR[t])
MOV.S RRR Single-precision move
FR[r] ← FR[s]
MOVEQZ.S RRR Single-precision conditional move if equal to zero
if AR[t] = 032 then FR[r] ← FR[s] endif
MOVF.S RRR Single-precision conditional move if false
if BRt = 0 then FR[r] ← FR[s] endif
MOVGEZ.S RRR Single-precision conditional move if greater than or equal to zero
if AR[t]31 = 0 then FR[r] ← FR[s] endif
MOVLTZ.S RRR Single-precision conditional move if less than zero
if AR[t]31 ≠ 0 then FR[r] ← FR[s] endif
MOVNEZ.S RRR Single-precision conditional move if not equal to zero
if AR[t] ≠ 032 then FR[r] ← FR[s] endif
MOVT.S RRR Single-precision conditional move if true
if BRt ≠ 0 then FR[r] ← FR[s] endif
MSUB.S RRR Single-precision multiply/subtract
FR[r] ← FR[r] −s (FR[s] ×s FR[t])
MUL.S RRR Single-precision multiply
FR[r] ← FR[s] ×s FR[t]
NEG.S RRR Single-precision negate
FR[r] ← −s FR[s]
OEQ.S RRR Single-precision compare equal
BRr ← FR[s] OEQs FR[t];
OLE.S RRR Single-precision compare less than or equal
BRr ← FR[s] OLEs FR[t];
OLT.S RRR Single-precision compare less than
BRr ← FR[s] OLTs FR[t];
RFR RRR Move from FR to AR
AR[r] ← FR[s]
ROUND.S RRR Scale and convert single-precision to integer, round to nearest
AR[r] ← rounds(FR[s] ×s pows(2.0,t))
SUB.S RRR Single-precision subtract
FR[r] ← FR[s] −s FR[t]
Table 4–50. Floating-Point Coprocessor Option Operation Instructions
(continued)
Instruction
1
Format Definition
1. These instructions are fully described in Chapter 6, "Instruction Descriptions" on page 243.
Chapter 4. Architectural Options
74 Xtensa Instruction Set Architecture (ISA) Reference Manual
4.3.12 Multiprocessor Synchronization Option
When multiple processors are used in a system, some sort of communication and syn-
chronization between processors is required. (Note that multiprocessor synchronization
is distinct from pipeline synchronization between instructions as represented by the
ISYNC, RSYNC, ESYNC, and DSYNC instructions, despite the name similarity). In some
cases, self-synchronizing communication, such as input and output queues, is used. In
other cases, a shared memory model is used for communication, and it is necessary to
provide instruction-set support for synchronization because shared memory does not
provide the required semantics. The Multiprocessor Synchronization Option is designed
for this shared memory case.
Prerequisites: None
Incompatible Options: None
4.3.12.1 Memory Access Ordering
The Xtensa ISA requires that valid programs follow a simplified version of the Release
Consistency model of memory access ordering. Xtensa implementations may perform
ordinary load and store operations to non-overlapping addresses in any order. Loads
and stores to overlapping addresses on a single processor must be executed in program
order. This flexibility is appropriate because most memory accesses require only these
TRUNC.S RRR Scale and convert single-precision to signed integer, round to 0
AR[r] ← truncs(FR[s] ×s pows(2.0,t))
UEQ.S RRR Single-precision compare unordered or equal
BRr ← FR[s] UEQs FR[t];
UFLOAT.S RRR Convert unsigned integer to single-precision and scale
FR[r] ← ufloats(AR[s]) ×s pows(2.0,-t))
ULE.S RRR Single-precision compare unordered or less than or equal
BRr ← FR[s] ULEs FR[t];
ULT.S RRR Single-precision compare unordered or less than
BRr ← FR[s] ULTs FR[t];
UN.S RRR Single-precision compare unordered
BRr ← FR[s] UNs FR[t];
UTRUNC.S RRR Scale and convert single-precision to unsigned integer, round to 0
AR[r] ← utruncs(FR[s] ×s pows(2.0,t))
WFR RRR Move from AR to FR
FR[r] ← AR[s]
Table 4–50. Floating-Point Coprocessor Option Operation Instructions
(continued)
Instruction
1
Format Definition
1. These instructions are fully described in Chapter 6, "Instruction Descriptions" on page 243.
Chapter 4. Architectural Options
Xtensa Instruction Set Architecture (ISA) Reference Manual 75
semantics and some implementations may be able to execute programs significantly
faster by exploiting non-program order memory access. While these semantics are ap-
propriate for most loads and stores, order does matter when synchronizing between pro-
cessors. Xtensa’s Multiprocessor Synchronization Option therefore augments ordinary
loads and stores with acquire and release operations, which are respectively loads and
stores with more constrained memory ordering semantics relative to each other and rel-
ative to ordinary loads and stores.
The Xtensa version of Release Consistency is adapted from Memory Consistency and
Event Ordering in Scalable Shared-Memory Multiprocessors by Gharachorloo et. al. in
the Proceedings of the 17th Annual International Symposium on Computer Architecture,
1990, from which the following three definitions are directly borrowed:
A load by processor i is considered performed with respect to processor k at a point
in time when the issuing of a store to the same address by processor k cannot affect
the value returned by the load.
A store by processor i is considered performed with respect to processor k at a point
in time when an issued load to the same address by processor k returns the value
defined by this store (or a subsequent store to the same location).
An access is performed when it is performed with respect to all processors.
Using these definitions, Xtensa places the following requirements on memory access:
Before an ordinary load or store access is allowed to perform with respect to any
other processor, all previous acquire accesses must be performed, and
Before a release access is allowed to perform with respect to any other processor,
all previous ordinary load, store, acquire, and release accesses must be performed,
and
Before an acquire is allowed to perform with respect to any other processor, all pre-
vious acquire accesses must be performed.
Many Xtensa implementations will adopt stricter memory orderings for simplicity. How-
ever, programs should not rely on any stricter memory ordering semantics than those
specified here.
4.3.12.2 Multiprocessor Synchronization Option Architectural Additions
Table 4–51 shows this option’s architectural additions.
Chapter 4. Architectural Options
76 Xtensa Instruction Set Architecture (ISA) Reference Manual
4.3.12.3 Inter-Processor Communication with the
L32AI
and
S32RI
Instructions
L32AI and S32RI are 32-bit load and store instructions with acquire and release se-
mantics. These instructions are useful for controlling the ordering of memory references
in multiprocessor systems, where different memory locations may be used for synchro-
nization and data, so that precise ordering between synchronization references must be
maintained. Other load and store instructions may be executed by processor implemen-
tations in any order that produces the same uniprocessor result.
The MEMW instruction is somewhat similar in that it enforces load and store ordering, but
is less selective. MEMW is intended for implementing C’s volatile attribute, and not for
high performance synchronization between processors.
L32AI is used to load a synchronization variable. This load will be performed before any
subsequent load, store, acquire, or release is begun. This ensures that subsequent
loads and stores do not see or modify data that is protected by the synchronization vari-
able.
S32RI is used to store to a synchronization variable. This store will not begin until all
previous loads, stores, acquires, or releases are performed. This ensures that any loads
of the synchronization variable that see the new value will also find all protected data
available as well.
Consider the following example:
volatile uint incount = 0;
volatile uint outcount = 0;
const uint bsize = 8;
data_t buffer[bsize];
void producer (uint n)
{
Table 4–51. Multiprocessor Synchronization Option Instruction Additions
Instruction
1
Format Definition
L32AI
RRI8 Load 32-bit acquire (8-bit shifted offset)
This load will perform before any subsequent loads, stores, or acquires are
performed. It is typically used to test the synchronization variable protecting a
critical region (for example, to acquire a lock).
S32RI
RRI8 Store 32-bit release (8-bit shifted offset)
All prior loads, stores, acquires, and releases will be performed before this
store is performed. It is typically used to write a synchronization variable to
indicate that this processor is no longer in a critical region (for example, to
release a lock).
1. These instructions are fully described in Chapter 6, "Instruction Descriptions" on page 243.
Chapter 4. Architectural Options
Xtensa Instruction Set Architecture (ISA) Reference Manual 77
for (uint i = 0; i < n; i += 1) {
data_t d = newdata(); // produce next datum
while (outcount == i - bsize); // wait for room
buffer[i % bsize] = d; // put data in buffer
incount = i+1; // signal data is ready
}
}
void consumer (uint n)
{
for (uint i = 0; i < n; i += 1) {
while (incount == i); // wait for data
data_t d = buffer[i % bsize]; // read next datum
outcount = i+1; // signal data read
usedata (d); // use datum
}
}
Here, incount and outcount are synchronization variables, and buffer is a shared
data variable. producer’s writes to incount and consumer’s writes to outcount
must use S32RI and producer’s reads of outcount and consumer’s reads of
incount must use L32AI. If producer’s write to incount were done with a simple
S32I, the processor or memory system might reorder the write to buffer after the write
to incount, thereby allowing consumer to see the wrong data. Similarly, if
consumer’s read of incount were done with a simple L32I, the processor or memory
system might reorder the read to buffer before the read of incount, also causing
consumer to see the wrong data.
4.3.13 Conditional Store Option
In addition to the memory ordering needs satisfied by the Multiprocessor Synchroniza-
tion Option, a multiprocessor system can require mutual exclusion, which cannot easily
be programmed using the Multiprocessor Synchronization Option. The Conditional Store
Option is intended to add that capability. It does so by adding a single instruction
(S32C1I), which atomically stores to a memory location only if its current value is the
expected one. A state register (SCOMPARE1) is also added to provide the additional op-
erand required. Some implementations also have a state register (ATOMCTL) for further
control of the atomic operation in cache and on the PIF bus.
Prerequisites: Multiprocessor Synchronization Option (page 74)
Incompatible Options: None
When the atomic operation reaches the PIF bus, it causes a Read-Compare-Write
(RCW) transaction on the PIF, which is different from normal reads and writes.
4.3.13.1 Conditional Store Option Architectural Additions
Table 4–52 through Table 4–53 show this option’s architectural additions.
Chapter 4. Architectural Options
78 Xtensa Instruction Set Architecture (ISA) Reference Manual
4.3.13.2 Exclusive Access with the
S32C1I
Instruction
L32AI and S32RI allow inter-processor communication, as in the producer-consumer
example in Section 4.3.12.3 (barrier synchronization is another example), but they are
not efficient for guaranteeing exclusive access to data (for example, locks). Some sys-
tems may provide efficient, tailored, application-specific exclusion support. When this is
not appropriate, the ISA provides another general-purpose mechanism for atomic up-
dates of memory-based synchronization variables that can be used for exclusion algo-
rithms. The S32C1I instruction stores to a location if the location contains the value in
the SCOMPARE1 register. The comparison of the old value and the conditional store are
atomic. S32C1I also returns the old value of the memory location, so it looks like both a
load and a store; this allows the program to determine whether the store succeeded,
and if not it can use the new value as the comparison for the next S32C1I. For example,
an atomic increment could be done as follows:
l32ai a3, a2, 0 // current value of memory
loop:
wsr a3, scompare1 // put current value in SCOMPARE1
mov a4, a3 // save for comparison
addi a3, a3, 1 // increment value
s32c1i a3, a2, 0 // store new value if memory
// still contains SCOMPARE1
bne a3, a4, loop // if value changed, try again
Table 4–52. Conditional Store Option Processor-State Additions
Register
Mnemonic Quantity Width
(bits) Register Name R/W
Special
Register
Number
1
SCOMPARE1 1 32 Conditional store comparison data R/W 12
ATOMCTL21 6 Atomic Operation Control R/W 99
1. Registers with a Special Register assignment are read and/or written with the RSR, WSR, and XSR instructions. See Table 3–23 on page 46.
2. Register exists only in some implementations.
Table 4–53. Conditional Store Option Instruction Additions
Instruction
1
Format Definition
S32C1I RRI8
Store 32-Bit compare conditional
Stores to a location only if the location contains the value in the SCOMPARE1
register. The comparison of the old value and the store, if equal, is atomic. The
instruction also returns the old value of the memory location.
1. These instructions are fully described in Chapter 6, "Instruction Descriptions" on page 243.
Chapter 4. Architectural Options
Xtensa Instruction Set Architecture (ISA) Reference Manual 79
Semaphores and other exclusion operations are equally simple to create using S32C1I.
There are many possible atomic memory primitives. S32C1I was chosen for the Xtensa
ISA because it can easily synthesize all other primitives that operate on a single memory
location. Many other primitives (for example, test and set, or fetch and add) are not as
universal. Only primitives that operate on multiple memory locations are more powerful
than S32C1I. Note that there can be subtle issues with some algorithms if between a
read and an S32C1I, there are multiple changes to the target which bring the value
back to the original one.
The SCOMPARE1 register is undefined after reset.
4.3.13.3 Use Models for the
S32C1I
Instruction
Because of its nature as an atomic read-compare-write instruction, the S32C1I instruc-
tion is unusual in its relationships to local memories, caches, and system memories. Fol-
lowing is a list of ways that the S32C1I instruction is able to interact with memory. Some
implementations use the ATOMCTL Special Register described below to control which
way the instruction interacts with each memory type. Other implementations interact in a
fixed way with each memory type. Refer to a specific Xtensa processor data book for
more detailed information on how a specific processor handles S32C1I instructions.
Local Memory — Xtensa processors with the Conditional Store Option and the Data
RAM Option configured will execute S32C1I instructions whose address resolves to
a DataRAM address directly on that DataRAM. Unless access to the DataRAM is
shared with another master, no external logic is necessary in this case. None of the
other ways listed below may be used for addresses resolving to a DataRAM.
Exception — Xtensa processors with the Conditional Store Option and the Excep-
tion Option configured can execute the S32C1I instruction by taking an exception
(LoadStoreErrorCause). The exception may be considered an error, or it may
be used as a way to emulate the effect of the S32C1I instruction. Exception may be
the only method available for certain memory types or it may be directed by the
ATOMCTL register.
RCW Transaction — Xtensa processors with the Conditional Store Option and the
Processor Interface Option configured can execute the S32C1I instruction by send-
ing an RCW transaction on the PIF bus. External logic must then implement the
atomic read-compare-write on the memory location. If the Data Cache Option is con-
figured and the memory region is cacheable, any corresponding cache line will be
flushed out of the cache by the S32C1I instruction using the equivalent of a DHWBI
instruction before the RCW transaction is sent. RCW Transaction may be the only
method available for certain memory types or it may be directed by the ATOMCTL
register.
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80 Xtensa Instruction Set Architecture (ISA) Reference Manual
If the address of the RCW transaction targets the Inbound PIF port of another
Xtensa processor, the targeted Xtensa processor has the Conditional Store Option
and the Data RAM Option configured, and the RCW address targets the DataRAM,
the RCW will be performed atomically on the target processor’s DataRAM. No exter-
nal logic other than PIF bus interconnects is necessary to allow an Xtensa processor
to atomically access a DataRAM location in another Xtensa processor in this way.
Internal Operation — Xtensa processors with the Conditional Store Option and the
Data Cache Option configured can execute the S32C1I instruction by allocating and
filling the line in the cache and accessing the location atomically there. No external
logic is necessary in this case. Internal Operation may be the only method available
for certain memory types or it may be directed by the ATOMCTL register.
4.3.13.4 The Atomic Operation Control Register (ATOMCTL) under the Conditional Store
Option
The ATOMCTL register exists in some implementations of the Conditional Store Option to
control how the S32C1I instruction interacts with the cache and with the PIF bus. Imple-
mentations without the ATOMCTL register allow only one behavior per memory type.
Table 4–54 shows the ATOMCTL register. Table 4–54 describes the fields of the
ATOMCTL register. See Section 4.3.13.4 above for the meaning of the codes in the table.
31 6543210
reserved WB WT BY
24 2 2 2
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Xtensa Instruction Set Architecture (ISA) Reference Manual 81
ATOMCTL is defined after processor reset as shown in Table 5–186 on page 237.
An older, fixed operation, Xtensa processor which operates on all cacheable and bypass
regions by RCW transaction may be emulated by setting the ATOMCTL register to 0x15.
One which operates only on bypass regions by RCW transaction may be emulated by
setting the ATOMCTL register to 0x01.
Bits of the ATOMCTL register are present even when they correspond to a memory type
which is not configured in the Xtensa processor. For example, a processor configured
without a Data Cache will still contain the fields WB and WT and those fields may contain
any value. But in this case, no cacheable memory will be addressable and so it will not
be possible to make use of these fields.
In an Xtensa processor with the Data RAM Option configured, the ATOMCTL register
does not affect the "Local Memory" use model or the receiving of Inbound PIF transac-
tions as described under the "RCW Transaction" use model in Section 4.3.13.3.
4.3.13.5 Memory Ordering and the
S32C1I
Instruction
With regard to the memory ordering defined for L32AI and S32RI in Section 4.3.12.1,
S32C1I plays the role of both acquire and release. That is, before the atomic pair of
memory accesses can perform, all ordinary loads, stores, acquires, and releases must
have performed. In addition, before any following ordinary load, store, acquire, or re-
Table 4–54. ATOMCTL Register Fields
Field Width
(bits) Definition
WB 2
S32C1I to Writeback Cacheable Memory (including Writeback NoAllocate Memory)
0 → Exception - LoadStoreErrorCause
1 → RCW Transaction
2 → Internal Operation
3 → Reserved
WT 2
S32C1I to Writethrough Cacheable Memory (including Cached-NoAllocate Memory)
0 → Exception - LoadStoreErrorCause
1 → RCW Transaction
2 → Internal Operation1
3 → Reserved
BY 2
S32C1I to Bypass Memory
0 → Exception - LoadStoreErrorCause
1 → RCW Transaction
2 → Reserved
3 → Reserved
1. Some implementations do not implement this case and take an exception (LoadStoreErrorCause)instead.
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82 Xtensa Instruction Set Architecture (ISA) Reference Manual
lease can be allowed to perform, the atomic pair of the S32C1I must have performed.
This allows the conditional store to make atomic changes to variables with ordering re-
quirements, such as the counts discussed in the example in Section 4.3.12.3.
4.4 Options for Interrupts and Exceptions
The options in this section have the primary function of adding and controlling the be-
havior of the processor in the presence of exceptional conditions. These conditions in-
clude representatives of at least the following broad categories:
Instruction exceptions are unusual situations or errors encountered in the execu-
tion of the current instruction stream.
Interrupts are requests from outside the instruction stream that, if enabled, can start
the processor executing a different instruction stream.
Machine checks are failures of the processor hardware or related hardware that
need special handling to avoid causing the overall system to fail.
Debug conditions do not arise from the execution of the program or the surrounding
hardware, but rather from the desire of another agent to track the execution of the
processor.
Reset redirects the processor from any state, usually the undefined state after pow-
er-on, and starts it on a known execution path.
There are many ways of handling these conditions ranging from ignoring the conditions
or freezing the clock and asserting an output signal to multi-threaded self-handling of ex-
ceptional conditions. The Exception Option provides for the self-handling of instruction
exceptions and reset. Its self-handling mechanisms for these can be extended by the
Relocatable Vector Option and the Unaligned Exception Option. In addition, it provides a
foundation for additional options such as the Interrupt Option, the High-Priority Interrupt
Option, or the Timer Interrupt Option. Again, the Debug Option can be added to provide
for hardware debugging.
4.4.1 Exception Option
The Exception Option implements basic functions needed in the management of all
types of exceptional conditions. These conditions are handled by the processor itself by
redirecting execution to an exception vector to handle the condition with the possibility of
returning to continue execution at the original code stream. The option only fully imple-
ments the management of a subset of exceptional conditions. Additional options provid-
ing additional exception types use the Exception Option as a foundation.
Prerequisites: None
Incompatible options: None
Chapter 4. Architectural Options
Xtensa Instruction Set Architecture (ISA) Reference Manual 83
Compatibility Note: Currently available hardware supports Xtensa Exception Archi-
tecture 2 (XEA2) and the descriptions in this chapter cover only XEA2. Differences
between this and Xtensa Exception Architecture 1 (XEA1) are described, for purpos-
es of writing system software for XEA1 processors, in Section A.2 on page 611.
4.4.1.1 Exception Option Architectural Additions
Table 4–55 through Table 4–58 show this option’s architectural additions.
Table 4–55. Exception Option Constant Additions (Exception Causes)
Exception Cause Constant Value
IllegalInstructionCause 6'b000000 (decimal 0)
SyscallCause 6'b000001 (decimal 1)
InstructionFetchErrorCause 6'b000010 (decimal 2)
LoadStoreErrorCause 6'b000011 (decimal 3)
Table 4–56. Exception Option Processor-Configuration Additions
Parameter Description Valid Values
NDEPC Existence (number) of DEPC 0..1
ResetVector Reset exception vector
(PC of first instruction executed after reset)
32-bit address
UserExceptionVector Vector for exceptions and level-1 interrupts
when PS.EXCM = 0 and PS.UM = 1
32-bit address
KernelExceptionVector Vector for exceptions and level-1 interrupts
when PS.EXCM = 0 and PS.UM = 0
32-bit address
DoubleExceptionVector Vector for exceptions when
PS.EXCM = 1
32-bit address
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84 Xtensa Instruction Set Architecture (ISA) Reference Manual
Table 4–57. Exception Option Processor-State Additions
Register
Mnemonic Quantity Width
(bits) Register Name R/W
Special
Register
Number
1
EPC[1] 132 Exception program counter2R/W 177
EXCCAUSE 1 6 Cause of last exception3R/W 232
EXCSAVE[1] 132 Save location for last exception2R/W 209
PS 1 -4Miscellaneous processor state5R/W 230
PS.EXCM 1 4 Exception mode (see Table 4–63 on
page 87)
R/W 230
PS.UM 1 1 User vector mode (see Table 4–63 on
page 87)
R/W 230
EXCVADDR 132 Virtual address that caused last fetch, load,
or store exception
R/W 238
DEPC 132 Double exception PC (exists if NDEPC=1)R/W 192
1. Registers with a Special Register assignment are read and/or written with the RSR, WSR, and XSR instructions. See Table 3–23 on page 46.
2. The EPC[i] and EXCSAVE[i] registers for interrupts above level 1 are part of the High-Priority Interrupt Option (Table 4–75 on page 107).
3. See Table 4–64 on page 89 for the format of this register and Table 4–65 on page 94 for which vectors have causes reported in this register.
4. Width depends on other configuration options.
5. See "The Miscellaneous Program State Register (PS) under the Exception Option" on page 87.
Table 4–58. Exception Option Instruction Additions
Instruction
1
Format Definition
EXCW
RRR Exception wait
Waits for any exceptions of previously executed
instructions to occur.
SYSCALL RRR System call
Generates an exception.
RFE RRR Returns from the KernelExceptionVector
exception.
RFDE RRR Returns from double exception (uses EPC if NDEPC=0)
ILL or illegal
instruction
—Illegal instruction executed
The opcode ILL is guaranteed to always be an illegal
instruction
1. These instructions are fully described in Chapter 6, "Instruction Descriptions" on page 243.
Chapter 4. Architectural Options
Xtensa Instruction Set Architecture (ISA) Reference Manual 85
4.4.1.2 Exception Causes under the Exception Option
A broad set of interrupts and exceptions can be handled by the processor itself under
the Exception Option. Table 4–59 through Table 4–62 list the types of exceptional condi-
tions other than reset that can be handled under the Exception Option either natively or
with the help of an additional option. In each table, the first column contains the name of
the condition. The second column contains a description of the condition and the third
column contains both the option required for the condition to be handled and the name
of the vector to which execution will be redirected. Reset is provided by the Exception
Option and redirects execution to ResetVector.
Table 4–59. Instruction Exceptions under the Exception Option
Condition Description Required Option & Vector
Illegal instruction Attempt to execute an illegal instruction or a legal
instruction under illegal conditions
Exception Option
General vector1
System call Attempt to execute the SYSCALL instruction Exception Option
General vector1
Instruction fetch error Internal physical address or a data error during
instruction fetch
Exception Option
General vector1
Load or store error Internal physical address or data error during
load or store
Exception Option
General vector1
Unaligned data exception Attempt to load or store data at an address which
cannot be handled due to alignment
Unaligned Exception Option
General vector1
Privileged instruction Attempt to execute a privileged operation without
sufficient privilege
MMU Option
General vector1
Memory access prohibited Attempt to access data or instructions at a
prohibited address
Region Protection Option or MMU
Option — General vector1
Memory privilege violation Attempt to access data or instructions without
sufficient privilege
MMU Option
General vector1
Address translation failure Memory access needs translation information it
does not have available
MMU Option
General vector1
PIF bus error Address or data error external to the processor
on the PIF bus2
Processor Interface Option
General vector1
1. General vector means.DoubleExceptionVector if PS.EXCM is set. Otherwise it means UserExceptionVector if PS.UM is
set or KernelExceptionVector if PS.UM is clear.
2. Imprecise errors on writes are not included.
3. n can take on the values 4, 8, or 12 in each of overflow and underflow making a total of 6 vectors.
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86 Xtensa Instruction Set Architecture (ISA) Reference Manual
Window exception Attempt to execute an instruction needing AR
values moved between registers and stack
Windowed Register Option
WindowOverflown3, or
WindowUnderflown3
Alloca exception Attempt to move the stack pointer when it would
cause an illegal condition on the stack
Windowed Register Option
General vector1
Coprocessor disabled Attempt to execute an instruction requiring the
state of a disabled coprocessor
Coprocessor Option
General vector1
Table 4–60. Interrupts under the Exception Option
Condition Description Required Option & Vector
Level-1 interrupt Level or edge interrupt pin assertion handled as
part of general vector with software check
Interrupt Option
General vector1
Level-1 SW interrupt Version of level-1 interrupt caused by software
using WSR.INTSET
Interrupt Option
General vector1
Medium-Level interrupt Level/edge interrupt pin assertion handled with
special interrupt level, masked on stack unusable
High-Priority Interrupt Option
InterruptVector[2..6]2
Medium-Level SW
interrupt
Version of medium level interrupt caused by
software using WSR.INTSET
High-Priority Interrupt Option
InterruptVector[2..6]2
High-Level interrupt Level/edge interrupt pin assertion handled with
special interrupt level, extra stack care needed
High-Priority Interrupt Option
InterruptVector[2..6]2
High-level SW interrupt Version of high level interrupt caused by software
using WSR.INTSET
High-Priority Interrupt Option
InterruptVector[2..6]2
Non-maskable interrupt Edge triggered interrupt pin that cannot be
masked by software
High-Priority Interrupt Option
InterruptVector[2..7]2
Peripheral interrupt Internal hardware (e.g., timers) causes one of the
above interrupts without an external pin
Timer Interrupt Option
(asserts another interrupt type)
1. General vector means.DoubleExceptionVector if PS.EXCM is set. Otherwise it means UserExceptionVector if PS.UM is
set or KernelExceptionVector if PS.UM is clear.
2. Medium and high level interrupts may use levels any level 2..6 not used for debug conditions. NMI is one level higher than the highest medium,
high, or debug level.
Table 4–61. Machine Checks under the Exception Option
Condition Description Required Option & Vector
ECC/parity error An access to cache or local memory
produced an ECC or parity error
Memory ECC/Parity Option
MemoryErrorVector
Table 4–59. Instruction Exceptions under the Exception Option
(continued)
Condition Description Required Option & Vector
1. General vector means.DoubleExceptionVector if PS.EXCM is set. Otherwise it means UserExceptionVector if PS.UM is
set or KernelExceptionVector if PS.UM is clear.
2. Imprecise errors on writes are not included.
3. n can take on the values 4, 8, or 12 in each of overflow and underflow making a total of 6 vectors.
Chapter 4. Architectural Options
Xtensa Instruction Set Architecture (ISA) Reference Manual 87
4.4.1.3 The Miscellaneous Program State Register (
PS
) under the Exception Option
The PS register contains miscellaneous fields that are grouped together primarily so that
they can be saved and restored easily for interrupts and context switching. Figure 4–8
shows its layout and Table 4–63 describes its fields. Section 5.3.5 “Processor Status
Special Register” describes the fields of this register in greater detail. The processor ini-
tializes these fields on processor reset: PS.INTLEVEL is set to 15, if it exists and
PS.EXCM is set to 1, and the other fields are set to zero.
Figure 4–8. PS Register Format
Table 4–62. Debug Conditions under the Exception Option
Condition Description Required Option & Vector
ICOUNT exception An instruction would have incremented the
ICOUNT register to zero.
Debug Option
InterruptVector[dbg]1
BREAK exception Attempt to execute the BREAK or BREAK.N
instruction.
Debug Option
InterruptVector[dbg]1
Instruction breakpoint Attempt to execute an instruction matching one of
the instruction breakpoint registers
Debug Option
InterruptVector[dbg]1
Data breakpoint Attempt to load or store to a data location
matching one of the data breakpoint registers.
Debug Option
InterruptVector[dbg]1
Debug interrupt An interrupt through OCD Debug Option2
InterruptVector[dbg]1
1. Debug exceptions use an interrupt level provided by the High-Priority Interrupt Option. That level is labeled "dbg" in this table.
2. The debug interrupt is actually created by the OCD Option under the Debug Option.
31 19 18 17 16 15 12 11 876543 0
*
WOE
CALLINC
*OWB RING
UM
EXCM
INTLEVEL
13 1 2 4 4 2 1 1 4
Table 4–63. PS Register Fields
Field Width
(bits) Definition [Required Option]
INTLEVEL 4Interrupt-level disable [Interrupt Option]
Used to compute the current interrupt level of the processor (Section 4.4.1.4).
EXCM
1Exception mode [Exception Option]
0 → normal operation
1 → exception mode
Overrides the values of certain other PS fields (Section 4.4.1.4)
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88 Xtensa Instruction Set Architecture (ISA) Reference Manual
4.4.1.4 Value of Variables under the Exception Option
The fields of the PS register listed in Table 4–63 affect many functions in the processor
through these variables:
The current interrupt level (CINTLEVEL) defines which levels of interrupts are currently
enabled and which are not. Interrupts at levels above CINTLEVEL are enabled. Those at
or below CINTLEVEL are disabled. To enable a given interrupt, CINTLEVEL must be
less than its level, and its INTENABLE bit must be 1. The level is defined by:
CINTLEVEL ← max(PS.EXCM∗EXCMLEVEL,PS.INTLEVEL)
PS.EXCM and PS.INTLEVEL are part of the PS register in Table 4–63. EXCMLEVEL is
defined in Table 4–74. CINTLEVEL is also used by the Debug Option.
The current ring (CRING) determines which ASIDs from the RASID register will cause a
privilege violation. ASIDs with position (in RASID) equal to or greater than CRING may
be used in translation while those with position less than CRING will cause a privilege vi-
olation. Privileged instructions may only be executed if CRING is zero. CRING is defined
by:
CRING ← if (MMU Option configured && PS.EXCM = 0) then PS.RING else 0
PS.EXCM and PS.RING are part of the PS register in Table 4–63.
UM
1User vector mode [Exception Option]
0 → kernel vector mode — exceptions do not need to switch stacks
1 → user vector mode — exceptions need to switch stacks
This bit does not affect protection. It is modified by software and affects the vector
used for a general exception.
RING 2Privilege level [MMU Option]
OWB 4Old window base [Windowed Register Option]
The value of WindowBase before window overflow or underflow.
CALLINC 2Call increment [Windowed Register Option]
Set to window increment by CALL instructions. Used by ENTRY to rotate window.
WOE
1Window overflow-detection enable [Windowed Register Option]
0 → overflow detection disabled
1 → overflow detection enabled
Used to compute the current window overflow enable (Section 4.4.1.4)
*Reserved for future use.
Writing a non-zero value to these fields results in undefined processor behavior.
Table 4–63. PS Register Fields
(continued)
Field Width
(bits) Definition [Required Option]
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Xtensa Instruction Set Architecture (ISA) Reference Manual 89
The current window overflow enable (CWOE) defines whether window overflow excep-
tions are currently enabled. It is defined by:
CWOE ← if PS.EXCM then 0 else PS.WOE
PS.EXCM and PS.WOE are part of the PS register in Table 4–63.
The current loop enable (CLOOPENABLE) determines whether the loop-back function of
the zero-overhead loop instruction is enabled or not.
CLOOPENABLE ← PS.EXCM = 0
PS.EXCM is part of the PS register in Table 4–63.
4.4.1.5 The Exception Cause Register (
EXCCAUSE
) under the Exception Option
After an exception that redirects execution to one of the general exception vectors
(UserExceptionVector, KernelExceptionVector, or DoubleExceptionVec-
tor), the EXCCAUSE register contains a value that specifies the cause of the last excep-
tion. Figure 4–9 shows the EXCCAUSE register. Table 4–64 describes the 6-bit binary-
value encodings for the register. EXCCAUSE is undefined after processor reset.
Figure 4–9. EXCCAUSE Register
31 6 5 0
reserved EXCCAUSE
26 6
Table 4–64. Exception Causes
EXC-
CAUSE
Code
Cause Name Cause Description [Required Option]
EXC-
VADDR
Loaded
0IllegalInstructionCause Illegal instruction [Exception Option]No
1SyscallCause SYSCALL instruction [Exception Option]No
2InstructionFetchErrorCause Processor internal physical address or data error
during instruction fetch [Exception Option]
Yes
3LoadStoreErrorCause Processor internal physical address or data error
during load or store [Exception Option]
Yes
4Level1InterruptCause Level-1 interrupt as indicated by set level-1 bits
in the INTERRUPT register [Interrupt Option]
No
5AllocaCause MOVSP instruction, if caller’s registers are not in
the register file [Windowed Register Option]
No
Chapter 4. Architectural Options
90 Xtensa Instruction Set Architecture (ISA) Reference Manual
6IntegerDivideByZeroCause QUOS, QUOU, REMS, or REMU divisor operand
is zero [32-bit Integer Divide Option]
No
7Reserved for Tensilica
8PrivilegedCause Attempt to execute a privileged operation when
CRING ≠ 0 [MMU Option]
No
9LoadStoreAlignmentCause Load or store to an unaligned address
[Unaligned Exception Option]
Yes
10..11 Reserved for Tensilica
12 InstrPIFDataErrorCause PIF data error during instruction fetch [Processor
Interface Option]
Yes
13 LoadStorePIFDataErrorCause Synchronous PIF data error during LoadStore
access [Processor Interface Option]
Yes
14 InstrPIFAddrErrorCause PIF address error during instruction fetch
[Processor Interface Option]
Yes
15 LoadStorePIFAddrErrorCause Synchronous PIF address error during
LoadStore access [Processor Interface Option]
Yes
16 InstTLBMissCause Error during Instruction TLB refill [MMU Option]Yes
17 InstTLBMultiHitCause Multiple instruction TLB entries matched [MMU
Option]
Yes
18 InstFetchPrivilegeCause An instruction fetch referenced a virtual address
at a ring level less than CRING [MMU Option]
Yes
19 Reserved for Tensilica
20
InstFetchProhibitedCause
An instruction fetch referenced a page mapped
with an attribute that does not permit instruction
fetch [Region Protection Option or MMU Option]
Yes
21..23 Reserved for Tensilica
24 LoadStoreTLBMissCause Error during TLB refill for a load or store [MMU
Option]
Yes
25 LoadStoreTLBMultiHitCause Multiple TLB entries matched for a load or store
[MMU Option]
Yes
26 LoadStorePrivilegeCause A load or store referenced a virtual address at a
ring level less than CRING [MMU Option]
Yes
27 Reserved for Tensilica
28
LoadProhibitedCause
A load referenced a page mapped with an
attribute that does not permit loads [Region
Protection Option or MMU Option]
Yes
Table 4–64. Exception Causes
(continued)
EXC-
CAUSE
Code
Cause Name Cause Description [Required Option]
EXC-
VADDR
Loaded
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Xtensa Instruction Set Architecture (ISA) Reference Manual 91
Exceptions that redirect execution to other vectors that do not use EXCCAUSE may either
report details in a different cause register or may have only a single cause and no need
for additional cause information.
4.4.1.6 The Exception Virtual Address Register (
EXCVADDR
) under the Exception Option
The exception virtual address (EXCVADDR) register contains the virtual byte address that
caused the most recent fetch, load, or store exception. Table 4–64 shows, for every ex-
ception cause value, whether or not the exception virtual address register will be set.
This register is undefined after processor reset. Because EXCVADDR may be changed
by any TLB miss, even if the miss is handled entirely by processor hardware, code that
counts on it not changing value must guarantee that no TLB miss is possible by using
only static translations for both instruction and data accesses. Figure 4–10 shows the
EXCVADDR register format.
Figure 4–10. EXCVADDR Register Format
4.4.1.7 The Exception Program Counter (
EPC
) under the Exception Option
The exception program counter (EPC) register contains the virtual byte address of the
instruction that caused the most recent exception or the next instruction to be executed
in the case of a level-1 interrupt. This instruction has not been executed. Software may
restart execution at this address by using the RFE instruction after fixing the cause of the
exception or handling and clearing the interrupt. This register is undefined after proces-
sor reset and its value might change whenever PS.EXCM is 0.
29
StoreProhibitedCause
A store referenced a page mapped with an
attribute that does not permit stores [Region
Protection Option or MMU Option]
Yes
30..31 Reserved for Tensilica
32..39 CoprocessornDisabled Coprocessor n instruction when cpn disabled. n
varies 0..7 as the cause varies 32..39
[Coprocessor Option]
No
40..63 Reserved
31 0
Exception Virtual Address
32
Table 4–64. Exception Causes
(continued)
EXC-
CAUSE
Code
Cause Name Cause Description [Required Option]
EXC-
VADDR
Loaded
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92 Xtensa Instruction Set Architecture (ISA) Reference Manual
The Exception Option defines only one EPC value (EPC[1]). The High-Priority Interrupt
Option extends the EPC concept by adding one EPC value per high-priority interrupt
level (EPC[2..NLEVEL+NNMI]).
Figure 4–11 shows the EPC register format.
Figure 4–11. EPC Register Format for Exception Option
4.4.1.8 The Double Exception Program Counter (
DEPC
) under the Exception Option
The double exception program counter (DEPC) register contains the virtual byte ad-
dress of the instruction that caused the most recent double exception. A double excep-
tion is one that is raised when PS.EXCM is set. This instruction has not been executed.
Many double exceptions cannot be restarted, but those that can may be restarted at this
address by using an RFDE instruction after fixing the cause of the exception.
The DEPC register exists only if the configuration parameter NDEPC=1. If DEPC does not
exist, the EPC register is used in its place when a double exception is taken and when
the RFDE instruction is executed. The consequence is that it is not possible to recover
from most double exceptions. NDEPC=1 is required if both the Windowed Register
Option and the MMU Option are configured. DEPC is undefined after processor reset.
Figure 4–12 shows the DEPC register format.
Figure 4–12. DEPC Register Format
4.4.1.9 The Exception Save Register (
EXCSAVE
) under the Exception Option
The exception save register (EXCSAVE[1]) is simply a read/write 32-bit register intend-
ed for saving one AR register in the exception vector software. This register is undefined
after processor reset and there are many software reasons its value might change
whenever PS.EXCM is 0.
The Exception Option defines only one exception save register (EXCSAVE[1]). The
High-Priority Interrupt Option extends this concept by adding one EXCSAVE register per
high-priority interrupt level (EXCSAVE[2..NLEVEL+NNMI]).
31 0
Exception Instruction Virtual Address
32
31 0
Exception Instruction Virtual Address
32
Chapter 4. Architectural Options
Xtensa Instruction Set Architecture (ISA) Reference Manual 93
Figure 4–13 shows the EXCSAVE register format.
Figure 4–13. EXCSAVE Register Format
4.4.1.10 Handling of Exceptional Conditions under the Exception Option
Under the Exception Option, exceptional conditions are handled by saving some state
and redirecting execution to one of a set of exception vector locations as listed in
Table 4–59 through Table 4–62 along with ResetVector. This section looks at this pro-
cess from the other end and describes how the code at a vector can determine the na-
ture of the exceptional condition that has just occurred.
Table 4–65 shows, for each vector, how the code can determine what has happened.
The first column lists the possible vectors, not just for the Exception Option itself, but
also for other options that add on to the Exception Option. For vectors which can be
reached for more than one cause, the second column indicates the register containing
the main indicator of that cause. The third column indicates other registers that may
contain secondary information under that vector. The last column shows the option that
is required for the vector and the other listed registers to exist.
The three exception vectors that use EXCCAUSE for the primary cause information form
a set called the “general vector.” If PS.EXCM is set when one of the exceptional condi-
tions is raised, then the processor is already handling an exceptional condition and the
exception goes to the DoubleExceptionVector. Only a few double exceptions are
recoverable, including a TLB miss during a register window overflow or underflow ex-
ception. For these, EXCCAUSE (and EXCSAVE in Table 4–66) must be well enough un-
derstood not to need duplication. Otherwise (PS.EXCM clear), if PS.UM is set the excep-
tion goes to the UserExceptionVector, and if not the exception goes to the
KernelExceptionVector. The Exception Option effectively defines two operating
modes: user vector mode and kernel vector mode, controlled by the PS.UM bit. The
combination of user vector mode and kernel vector mode is provided so that the user
vector exception handler can switch to an exception stack before processing the excep-
tion, whereas the kernel vector exception handler can continue using the kernel stack.
Single or multiple high-priority interrupts can be configured for any hardware prioritized
levels 2..6. These will redirect to the InterruptVector[i] where “i” is the level. One
of those levels, often the highest one, can be chosen as the debug level and will redirect
execution to InterruptVector[d] where “d” is the debug level. The level one higher
than the highest high-priority interrupt can be chosen as an NMI, which will redirect exe-
cution to InterruptVector[n] where “n” is the NMI level (2..7).
31 0
For Software Use
32
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94 Xtensa Instruction Set Architecture (ISA) Reference Manual
In addition to these characteristics of Vectors, when the Relocatable Vector Option
(page 98) is configured, the vectors are divided into two groups and within each group
are required to be in increasing address order as listed below:
Static Vector Group:
ResetVector
MemoryErrorVector
Dynamic Vector Group:
WindowOverflow4
WindowUnderflow4
WindowOverflow8
WindowUnderflow8
WindowOverflow12
WindowUnderflow12
InterruptVector[2]
Table 4–65. Exception and Interrupt Information Registers by Vector
Vector Main Cause Other Information Required Option
ResetVector — — Exception Option
UserExceptionVector EXCCAUSE INTERRUPT, EXCVADDR Exception Option
KernelExceptionVector EXCCAUSE INTERRUPT, EXCVADDR Exception Option
DoubleExceptionVector EXCCAUSE EXCVADDR Exception Option
WindowOverflow4 — — Windowed Register Option
WindowOverflow8 — — Windowed Register Option
WindowOverflow12 — — Windowed Register Option
WindowUnderflow4 — — Windowed Register Option
WindowUnderflow8 — — Windowed Register Option
WindowUnderflow12 — — Windowed Register Option
MemoryErrorVector MESR MECR, MEVADDR High-Priority Interrupt Option
InterruptVector[i]1 INTERRUPT —High-Priority Interrupt Option
InterruptVector[d]2DEBUGCAUSE —Debug Option
InterruptVector[n]3 — — High-Priority Interrupt Option
1. "i" indicates an arbitrary interrupt level. Medium- and high-level interrupts may be levels 2..6.
2. "d" indicates the debug level. It may be levels 2..6 but is usually the highest level other than NMI.
3. "n" indicates the NMI level. It may be levels 2..7. It must be the highest level but contiguous with other levels.
Chapter 4. Architectural Options
Xtensa Instruction Set Architecture (ISA) Reference Manual 95
InterruptVector[3]
InterruptVector[4]
InterruptVector[5]
InterruptVector[6]
InterruptVector[7]
KernelExceptionVector
UserExceptionVector
DoubleExceptionVector
Table 4–66 shows, for each vector in the first column, which registers are involved in the
process of taking the exception and returning from it for that vector. Since there is no re-
turn from the ResetVector, it has no entries in the other four columns of this table.
Otherwise all entries have a second column entry of where the PC is saved and a fifth
column entry of the instruction which should be used for returning. The third column
shows where the current PS register value is saved before being changed, while the
fourth column shows where the handler may find a scratch register. Note that the gener-
al vector entries and the window vector entries modify the PS only in ways that their re-
spective return instructions undo, and therefore there is no required PS save register.
The window vector entries do not need scratch space because they are loading and
storing a block of AR registers that they can use for scratch where they need it.
Table 4–66. Exception and Interrupt Exception Registers by Vector
Vector PC PS Scratch Return Instr.
ResetVector — — — —
UserExceptionVector EPC —EXCSAVE RFE
KernelExceptionVector EPC —EXCSAVE RFE
DoubleExceptionVector DEPC —EXCSAVE RFDE
WindowOverflow4 EPC — — RFWO
WindowOverflow8 EPC — — RFWO
WindowOverflow12 EPC — — RFWO
WindowUnderflow4 EPC — — RFWU
WindowUnderflow8 EPC — — RFWU
WindowUnderflow12 EPC — — RFWU
MemoryErrorVector MEPC MEPS MESAVE RFME
1. "i" indicates an arbitrary interrupt level. Medium- and high-level interrupts may be levels 2..6.
2"d" indicates the debug level. It may be levels 2..6 but is usually the highest level other than NMI.
3. "n" indicates the NMI level. It may be levels 2..7. It must be the highest level but contiguous with other levels.
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The taking of an exception under the Exception Option has the following semantics:
procedure Exception(cause)
if (PS.EXCM & NDEPC=1) then
DEPC ← PC
nextPC ← DoubleExceptionVector
elseif PS.EXCM then
EPC[1] ← PC
nextPC ← DoubleExceptionVector
elseif PS.UM then
EPC[1] ← PC
nextPC ← UserExceptionVector
else
EPC[1] ← PC
nextPC ← KernelExceptionVector
endif
EXCCAUSE ← cause
PS.EXCM ← 1
endprocedure Exception
4.4.1.11 Exception Priority under the Exception Option
In implementations where instruction execution is overlapped (for example, via a pipe-
line), multiple instructions can cause exceptions. In this case, priority is given to the ex-
ception caused by the earliest instruction.
When a given instruction causes multiple exceptions, the priority order for choosing the
exception to be reported is listed below from highest priority to lowest. In cases where it
is possible to have more than one occurrence of the same cause within the same in-
struction, the priority among the occurrences is undefined.
Pre-Instruction Exceptions:
Non-maskable interrupt
High-priority interrupt (including debug exception for DEBUG INTERRUPT)
Level1InterruptCause
InterruptVector[i]1 EPCi1EPSi1EXCSAVEi1RFIi1
InterruptVector[d]2EPCd2EPSd2EXCSAVEd2RFId2
InterruptVector[n]3 EPCn3EPSn3EXCSAVEn3RFIn3
Table 4–66. Exception and Interrupt Exception Registers by Vector
(continued)
Vector PC PS Scratch Return Instr.
1. "i" indicates an arbitrary interrupt level. Medium- and high-level interrupts may be levels 2..6.
2"d" indicates the debug level. It may be levels 2..6 but is usually the highest level other than NMI.
3. "n" indicates the NMI level. It may be levels 2..7. It must be the highest level but contiguous with other levels.
Chapter 4. Architectural Options
Xtensa Instruction Set Architecture (ISA) Reference Manual 97
Debug exception for ICOUNT
Debug exception for IBREAK
Fetch Exceptions:
Instruction-fetch translation errors
- InstTLBMultiHitCause
- InstTLBMissCause
- InstFetchPrivilegeCause
- InstFetchProhibitedCause
InstructionFetchErrorCause (Instruction-fetch address or instruction data errors)
ECC/parity exception for Instruction-fetch
Decode Exceptions:
IllegalInstructionCause
PrivilegedCause
SyscallCause (SYSCALL instruction)
Debug exception for BREAK (BREAK, BREAK.N instructions)
Execute Register Exceptions:
Register window overflow
Register window underflow (RETW, RETW.N instructions)
AllocaCause (MOVSP instruction)
CoprocessornDisabledCause
Execute Data Exceptions:
Divide by Zero
Execute Memory Exceptions:
LoadStoreAlignmentCause (in the absence of the Hardware Alignment Option)
Debug exception for DBREAK
IHI, PITLB, IPF, or IPFL, or IHU target translation errors, in order of priority:
- InstTLBMultiHitCause
- InstTLBMissCause
- InstFetchPrivilegeCause
- InstFetchProhibitedCause
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98 Xtensa Instruction Set Architecture (ISA) Reference Manual
Load, store, translation errors, in order of priority:
- LoadStoreTLBMultiHitCause
- LoadStoreTLBMissCause
- LoadStorePrivilegeCause
- LoadProhibitedCause
- StoreProhibitedCause
InstructionFetchErrorCause (IPFL target address or data errors)
LoadStoreAlignmentCause (in the presence of the Hardware Alignment Option)
LoadStoreErrorCause (Load or store external address or data errors)
ECC/parity exception for all accesses except instruction-fetch
Exceptions are grouped in the priority list by what information is necessary to determine
whether or not the exception is to be raised. The pre-instruction exceptions may be eval-
uated before the instruction begins because they require nothing but the PC of the in-
struction. Fetch exceptions are encountered in the process of fetching the instruction.
Decode exceptions may be evaluated after obtaining the instruction itself. Execute regis-
ter exceptions require internal register state and execute memory exceptions involve the
process of accessing the memory on which the instruction operates.
Exceptions are not necessarily precise. On some implementations, some exceptions are
raised after subsequent instructions have been executed. In such implementations, the
EXCW instruction can be used to prevent unwanted effects of imprecise exceptions. The
EXCW instruction causes the processor to wait until all previous instructions have taken
their exceptions, if any.
Interrupts have an implicit EXCW; when an interrupt is taken, all instructions prior to the
instruction addressed by EPC have been executed and any exceptions caused by those
instructions have been raised. Interrupts are listed at the top of the priority list. Because
the relative cycle position of an internal instruction and an interrupt pin assertion is not
well-defined, the priority of interrupts with respect to exceptions is not truly well-defined
either.
4.4.2 Relocatable Vector Option
This option splits Exception Vectors into two groups and adds a choice of two base ad-
dresses for one group and a Special Register as a base for the other group.
Prerequisites: Exception Option (page 82)
Incompatible options: None
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Xtensa Instruction Set Architecture (ISA) Reference Manual 99
Under the Relocatable Vector Option, exception vectors are more restricted than they
are without it. The vectors are organized into two groups, a "Static" group and a "Dy-
namic" group. Within each group there is a required order among the vectors which ex-
ist. The list immediately after Table 4–65 (page 94) indicates both the group and the or-
der within the group. Some implementations may place an upper bound on the size of
each group of vectors as measured by the difference between the address of the high-
est numbered vector in the group and the address of the lowest numbered vector in the
group.
The Static group of vectors is not movable under software control. Two base addresses
for the Static group are set by the designer at configuration time and an input pin of the
processor is sampled at reset to determine which of the two configured addresses will
be used. The base address will not change after reset. The offsets from this base are
also chosen at configuration time and will not change.
The Dynamic group of vectors is movable under software control. The Special Register,
VECBASE, described in Table 5–155 on page 224, holds the current base for the Dynam-
ic group. The special register resets to a value set by the designer at configuration time
but is freely writable using the WSR.VECBASE instruction. The offsets from the base
must increase in the order indicated by Table 4–66 and are also set by the designer at
configuration time.
4.4.2.1 Relocatable Vector Option Architectural Additions
Table 4–67 shows this option’s architectural additions.
4.4.3 Unaligned Exception Option
This option causes an exception to be raised on any unaligned memory access whether
it is generated by core architecture memory instructions, by optional instructions, or by a
designer’s TIE instructions.1 With system software cooperation, occasional unaligned
accesses can be handled correctly.
Table 4–67. Relocatable Vector Option Processor-State Additions
Register
Mnemonic Quantity Width
(bits) Register Name R/W
Special
Register
Number
1
VECBASE 128 Vector base R/W Table 5–155
1. In the T1050 release, which was the first for the Unaligned Exception Option, only Core Architecture memory instructions raise the unaligned
exception.
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100 Xtensa Instruction Set Architecture (ISA) Reference Manual
Cache line oriented instructions such as prefetch and cache management instructions
will not raise the unaligned exception. Special instructions such as LICW that use a gen-
erated address for something other than an actual memory address also will not raise
the exception. Individual instruction listings list the unaligned exception when it can be
raised by that instruction.
Memory access instructions will raise the exception when address and size indicate it.
Any address that is not a multiple of the size associated with the instruction will raise the
unaligned exception whether or not the access crosses any particular size boundary. For
example, an L16UI instruction that generates the address 32’h00000005, will raise
the unaligned exception, even though the access is entirely within a single 32-bit ac-
cess.
The exception cause register will contain LoadStoreAlignmentCause as indicated
below and the exception virtual address register will contain the virtual address of the
unaligned access.
Prerequisites: Exception Option (page 82)
Incompatible options: None
4.4.3.1 Unaligned Exception Option Architectural Additions
Table 4–68 shows this option’s architectural additions.
4.4.4 Interrupt Option
The Interrupt Option implements level-1 interrupts. These are asynchronous exceptions
on processor input signals or software exceptions. They have the lowest priority of all in-
terrupts. Level-1 interrupts are handled differently than the high-priority interrupts at pri-
ority levels 2 through 6 or NMI. The Interrupt Option is a prerequisite for the High-Priority
Interrupt Option, Timer Interrupt Option, and Debug Option.
Certain aspects of high-priority interrupts are specified along with those of level-1 inter-
rupts in the Interrupt Option. Specifically, the following parameters are specified:
NINTERRUPT—Total number of level-1 plus high-priority interrupts.
INTTYPE[0..NINTERRUPT-1]—Interrupt type (level, edge, software, or internal)
for level-1 plus high-priority interrupts.
INTENABLE—Interrupt-enable mask for level-1 plus high-priority interrupts.
Table 4–68. Unaligned Exception Option Constant Additions (Exception Causes)
Exception Cause Description Constant Value
LoadStoreAlignmentCause Load or store to an unaligned address.
(seeTable 4–64 on page 89)
6'b001001 (decimal 9)
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Xtensa Instruction Set Architecture (ISA) Reference Manual 101
INTERRUPT—Interrupt-request register for level-1 plus high-priority interrupts.
Nevertheless, high-priority interrupts specified in the Interrupt Option are not operational
without implementation of the High-Priority Interrupt Option.
Prerequisites: Exception Option (page 82)
Incompatible options: None
4.4.4.1 Interrupt Option Architectural Additions
Table 4–69 through Table 4–72 show this option’s architectural additions.
Table 4–69. Interrupt Option Constant Additions (Exception Causes)
Exception Cause Description Constant Value
Level1InterruptCause Level-1 interrupt (seeTable 4–64 on
page 89)
6'b000100 (decimal 4)
Table 4–70. Interrupt Option Processor-Configuration Additions
Parameter Description Valid
Values
NINTERRUPT Number of level-1, high-priority, and non-maskable
interrupts
1..32
INTTYPE[0..NINTERRUPT-1] Interrupt type for level-1, high-priority, and non-maskable
interrupts Section 4.4.4.2
See
Table 4–73
LEVEL[0..NINTERRUPT-1] Priority level of level-1 interrupts11
1. This parameter has a fixed, implicit value. The parameter associates the level-1 interrupts with their interrupt priority (level) which, by defini-
tion, is always level 1 (lowest priority), The parameter must be explicitly specified only for the high-priority interrupts (Tab le 4–74 on page 107),
each of which can be assigned different priority levels, from 2 to 15.
Table 4–71. Interrupt Option Processor-State Additions
Register
Mnemonic Quantity Width
(bits) Register Name R/W
Special
Register
Number
1
PS.INTLEVEL 1 4 Interrupt-level disable
(see Table 4–63 on page 87)
R/W See Table 4–63
on page 87
1. Registers with a Special Register assignment are read and/or written with the RSR, WSR, and XSR instructions. See Table 3–23 on page 46.
2. Level-sensitive interrupt bits are read-only, edge-triggered interrupt bits are read/clear, and software interrupt bits are read/write. Two register
numbers are provided for software modification to the INTERRUPT register: one that sets bits, and one that clears them.
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102 Xtensa Instruction Set Architecture (ISA) Reference Manual
4.4.4.2 Specifying Interrupts
Interrupt types (INTTYPE in Table 4–70) can be any of the values listed in Table 4–73.
The column labeled “Priority” shows the possible range of priorities for the interrupt type.
The column labeled “Pin” indicates whether there is an Xtensa core pin associated with
the interrupt, while the column labeled “Bit” indicates whether or not there is a bit in the
INTERRUPT and INTENABLE Special Registers corresponding to the interrupt. The last
two columns indicate how the interrupt may be set and how it may be cleared.
INTENABLE
1
NINTERRUPT
Interrupt enable mask
(Level-1 and high-priority interrupts)
There is one bit for each level-1 and
high-priority interrupt, except non-
maskable interrupt (NMI) and
Debug interrupt. To enable a given
interrupt, CINTLEVEL
(Table 4–57 on page 84) must be
less than the level assigned by
LEVEL[i] to that interrupt, and
the INTENABLE bit for that
interrupt must be set to 1.
R/W 228
INTERRUPT
(the mnemonics
INTERRUPT,
INTSET, and
INTCLEAR are
used depending on
the type of access)
1
NINTERRUPT
Interrupt request register
(level-1 and high-priority interrupts)
This holds pending level-1 and high-
priority interrupt requests. There is 1
bit per pending interrupt, except
non-maskable interrupt (NMI). If the
bit is set to 1, an interrupt request is
pending. External level interrupt bits
are not writable.
R or
R/W2
226 for read,
226 for set, and
227 for clear
Table 4–72. Interrupt Option Instruction Additions
Instruction
1
Format Definition
RSIL RRR Read and set interrupt level
WAITI RRR Wait for interrupt
1. These instructions are fully described in Chapter 6, "Instruction Descriptions" on page 243.
Table 4–71. Interrupt Option Processor-State Additions
(continued)
Register
Mnemonic Quantity Width
(bits) Register Name R/W
Special
Register
Number
1
1. Registers with a Special Register assignment are read and/or written with the RSR, WSR, and XSR instructions. See Table 3–23 on page 46.
2. Level-sensitive interrupt bits are read-only, edge-triggered interrupt bits are read/clear, and software interrupt bits are read/write. Two register
numbers are provided for software modification to the INTERRUPT register: one that sets bits, and one that clears them.
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Xtensa Instruction Set Architecture (ISA) Reference Manual 103
A variable number (NINTERRUPT) of interrupts can be defined during processor configu-
ration. External interrupt requests are signaled to the processor by either level-sensitive
or edge-triggered inputs. Software can test these interrupt requests at any time by read-
ing the INTERRUPT register. An arbitrary number of software interrupts, not tied to an
external signal, can also be configured. Level-1 interrupts use either the
UserExceptionVector or KernelExceptionVector defined in Table 4–56 on
page 83, depending on the current setting of the PS.UM bit.
Software can manipulate the interrupt-enable bits (INTENABLE register) and then set
PS.INTLEVEL back to 0 to re-enable other interrupts, and thereby create arbitrary prior-
itizations. This is illustrated by the following C++ code:
class Interrupt {
public:
uint32_t bit;
void handler();
};
class Level1Interrupt {
const uint NPRIORITY = 4; // number of priority groupings of level1 interrupts
struct InterruptGroup {
uint32_t allbits; // all INTERRUPT register bits at this priority
uint32_t mask; // mask of interrupt bits at this priority and lower
vector<Interrupt> intlist; // list of interrupts at this priority
} priority[NPRIORITY];
public:
Table 4–73. Interrupt Types
Type Priority
1
Pin? Bit? How Interrupt is Set How Interrupt is Cleared
Level 1 to N Yes Yes Signal level from device At device
Edge 1 to N Yes Yes Signal rising edge WSR.INTCLEAR ‘1’
NMI N+1 Yes No Signal rising edge Automatically cleared by HW
Software 1 to N No Yes WSR.INTSET ‘1’ WSR.INTCLEAR ‘1’
Timer 1 to N No Yes CCOUNT=CCOMPAREn WSR.CCOMPAREn
Debug22 to N No2No Debug hardware2Automatically cleared by HW
WriteErr 1 to N No Yes Bus error on write WSR.INTCLEAR ‘1’
1. Possible priorities where N is NLEVEL
2. SeeSection 4.7.6 “Debug Option” on page 197 for more detail
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104 Xtensa Instruction Set Architecture (ISA) Reference Manual
void handler();
};
// Called for all Level1 Interrupts
void
Level1Interrupt::handler ()
{
// determine software priority of this level1 interrupt
uint32_t interrupts = rsr(INTERRUPT);
uint p;
for (p = NPRIORITY-1; (interrupts & priority[p].allbits) == 0; p -= 1) {
if (p == 0)
return;
}
// found interrupts at priority p
uint32_t save_enable = rsr(INTENABLE);// save interrupt enables
wsr (INTENABLE, save_enable &~ priority[p].mask);// disable lower-priority ints
// no xSYNC instruction should be necessary here because INTENABLE and
// PS.INTLEVEL are both written and both used in the same pipe stages
uint32_t save_ps = rsil (0); // save PS, then set level to 0
// now higher-priority level1 interrupts are enabled
// service all the priority p interrupts
do {
// first service the priority p interrupts we read earlier
for (vector<Interrupt>::iterator i = priority[p].intlist.begin();
i = priority[p].intlist.end(); i++) {
if (interrupts & i->bit) {
// interrupt i is asserted
i->handler(); // call i’s handler
// this should clear the interrupt condition before it returns
interrupts &= ~i->bit;// clear i’s bit from request
if ((interrupts & priority[p].allbits) == 0)// early check for done
break;
}
}
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Xtensa Instruction Set Architecture (ISA) Reference Manual 105
// check if any more priority p interrupts arrived while we were servicing the previous batch
interrupts = rsr(INTERRUPT);
} while ((interrupts & priority[p].allbits) == 0);
// no more priority p interrupts
wsr (PS, save_ps); // return to PS.INTLEVEL=1, disabling
// all level1 interrupts, before returning
wsr (INTENABLE, save_enable); // restore original enables to allow lower
// priority level1 interrupts
// return to general exception handler
}
4.4.4.3 The Level-1 Interrupt Process
With respect to level-1 interrupts, the processor takes an interrupt when any level-1 in-
terrupt, i, satisfies:
INTERRUPTi and INTENABLEi and (1 > CINTLEVEL)
Level-1 interrupts use the UserExceptionVector and KernelExceptionVector,
implemented by the Exception Option (Table 4–56 on page 83). The interrupt cause is
reported as Level1InterruptCause (Table 4–64). The interrupt handler can deter-
mine which level-1 interrupt caused the exception by doing an RSR of the INTERRUPT
register and ANDing with the contents of the INTENABLE register. The exact semantics
of the check for interrupts is given in "Checking for Interrupts" on page 109.
The process of taking an interrupt does not clear the interrupt request. The process
does set PS.EXCM to 1, which disables level-1 interrupts in the interrupt handler. Typi-
cally, PS.EXCM is reset to 0 by the handler, after it has set up the stack frame and
masked the interrupt. This allows other level-1 interrupts to be serviced. For level-sensi-
tive interrupts, the handler must cause the source of the interrupt to deassert its interrupt
request before re-enabling the interrupt. For edge-triggered interrupts or software inter-
rupts, the handler clears the interrupt condition by writing to the INTCLEAR register.
The WAITI instruction sets the current interrupt level in the PS.INTLEVEL register. In
some implementations it also powers down the processor’s logic, and waits for an inter-
rupt. After executing the interrupt handler, execution continues with the instruction fol-
lowing the WAITI.
The INTENABLE register and the software and edge-triggered bits of the INTERRUPT
register are undefined after processor reset.
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106 Xtensa Instruction Set Architecture (ISA) Reference Manual
4.4.4.4 Use of Interrupt Instructions
The RSIL instruction reads the PS register and sets the interrupt level. It is typically
used as follows:
RSIL a2, newlevel
code to be executed at newlevel
WSR a2, PS
A SYNC instruction is not required after the RSIL.
4.4.5 High-Priority Interrupt Option
The High-Priority Interrupt Option implements a configurable number of interrupt levels
between level 2 and level 6, and an optional non-maskable interrupt (NMI) at an implicit
infinite priority level. Like level-1 interrupts, high-priority interrupts are external, internal
or software interrupts. Unlike level-1 interrupts, however, each high-priority interrupt lev-
el has its own interrupt vector and special registers dedicated for saving state
(EPC[level], EPS[level] and EXCSAVE[level]). This allows much lower latency
interrupts as well as very efficient handler mechanisms. The EPC, EPS and EXCSAVE
registers are undefined after reset.
Certain aspects of high-priority interrupts are specified along with those of level-1 inter-
rupts in the Interrupt Option, including the total number of level-1 plus high-priority inter-
rupts (NINTERRUPT), the interrupt type for level-1 plus high-priority interrupts
(INTTYPE), the interrupt-enable mask for level-1 plus high-priority interrupts
(INTENABLE), and the interrupt-request register for level-1 plus high-priority interrupts
(INTERRUPT).
Prerequisites: Interrupt Option (page 100)
Incompatible options: None
4.4.5.1 High-Priority Interrupt Option Architectural Additions
Table 4–74 through Table 4–76 show this option’s architectural additions.
Chapter 4. Architectural Options
Xtensa Instruction Set Architecture (ISA) Reference Manual 107
Table 4–74. High-Priority Interrupt Option Processor-Configuration Additions
Parameter Description Valid Values
NLEVEL Number of high-priority interrupt levels 2..61
EXCMLEVEL Highest level masked by PS.EXCM 1..NLEVEL2
NNMI Number of non-maskable interrupts
(NMI)
0 or 1
LEVEL[0..NINTERRUPT-1] Priority levels of interrupts 1..NLEVEL3
InterruptVector[2..NLEVEL+NNMI]
High-priority interrupt vectors 32-bit address,
aligned on a 4-
byte boundary
LEVELMASK[1..NLEVEL-1] Interrupt-level masks computed4
1. An interrupt’s “level” expresses its priority. The NLEVEL parameter defines the number of total interrupt levels (including level 1). Without the
High-Priority Interrupt Option, NLEVEL is fixed at 1. With the High-Priority Interrupt Option, NLEVEL ≥ 2.
2. EXCMLEVEL was required to be 1 before the RA-2004.1 release. In the presence of the Debug Option, it still must be less than
DEBUGLEVEL.
3. This parameter associates interrupt levels (priorities) with interrupt numbers. level-1 interrupts, by definition, are always priority level 1 (lowest
priority), and are defined in Ta ble 4–70 on page 101. Non-maskable interrupts (NMI) have many characteristics of the level NLEVEL+1. There
is no level 0.
4. This is computed as: LEVELMASK[j]i = (LEVEL[i] = j), where j is the level specified for interrupt i, and the width of each LEVELMASK is NIN-
TERRUPT. Thus, there are NLEVEL-1 masks (one for each high-priority interrupt level), and each mask is NINTERRUPT bits wide. A bit num-
ber set to 1 in a LEVELMASK means that the corresponding interrupt number has that priority level. The masks are used in the formal
semantics to test whether an interrupt is taken on a given instruction ("Checking for Interrupts" on page 109).
Table 4–75. High-Priority Interrupt Option Processor-State Additions
Register Mnemonic Quantity Width
(bits) Register Name R/W
Special
Register
Number
1
EPC
[2..NLEVEL+NNMI] NLEVEL+NNMI-1
32
Exception program
counter
R/W 178-183
EPS
[2..NLEVEL+NNMI] NLEVEL+NNMI-1 same as PS
register
Exception program
state
R/W 194-199
EXCSAVE
[2..NLEVEL+NNMI] NLEVEL+NNMI-1
32
Save Location for
high-priority
interrupt handler
R/W 210-215
1. Registers with a Special Register assignment are read and/or written with the RSR, WSR, and XSR instructions. See Ta ble 3–23 on page 46.
Table 4–76. High-Priority Interrupt Option Instruction Additions
Instruction
1
Format Definition
RFI RRR Return from high-priority interrupt
1. These instructions are fully described in Chapter 6, "Instruction Descriptions" on page 243.
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108 Xtensa Instruction Set Architecture (ISA) Reference Manual
4.4.5.2 Specifying High-Priority Interrupts
The total number of level-1 plus high-priority interrupts (NINTERRUPT) and the interrupt
type for level-1 plus high-priority interrupts (INTTYPE) are specified in Table 4–70 on
page 101. The type of each high-priority interrupt level may be edge-triggered, level-
sensitive, timer, write-error, or software.
The interrupt-enable mask for level-1 plus high-priority interrupts (INTENABLE) and the
interrupt-request register for level-1 plus high-priority interrupts (INTERRUPT) are speci-
fied in Table 4–71 on page 101.
The total number of interrupt levels is NLEVEL+NNMI (see Table 4–74). Specific interrupt
numbers are assigned interrupt levels using the LEVEL parameter in Table 4–74. A non-
maskable interrupt may be configured with the NNMI parameter in Table 4–74. The non-
maskable interrupt signal, if implemented, will be edge-triggered. Unlike other edge-trig-
gered interrupts, there is no need to reset the NMI interrupt by writing to INTCLEAR.
4.4.5.3 The High-Priority Interrupt Process
Each high-priority interrupt level has three registers used to save processor state, as
shown in Table 4–75. The processor sets EPC[i] and EPS[i] when the interrupt is tak-
en. EXCSAVE[i] exists for software. The RFI instruction reverses the interrupt process,
restoring processor state from EPC[i] and EPS[i].
The number of high-priority interrupt levels is expected to be small, due to the cost of
providing separate exception-state registers for each level. Interrupt numbers that share
level 1 are not limited to a single priority, because software can manipulate the interrupt-
enables bits (INTENABLE register) to create arbitrary prioritizations.
The processor takes an interrupt only when some interrupt i satisfies:
INTERRUPTi and INTENABLEi and (level[i] > CINTLEVEL)
where level[i] is the configured interrupt level of interrupt number i. Each level of
high-priority interrupt has its own interrupt vector (InterruptVector in Table 4–74).
Interrupt numbers that share a level (and associated vector) can read the INTERRUPT
register (and INTENABLE) with the RSR instruction to determine which interrupt(s) raised
the exception. The non-maskable interrupt (NMI), if implemented, is taken regardless of
the current interrupt level (CINTLEVEL) or of INTENABLE.
The value of CINTLEVEL is set to at least EXCMLEVEL whenever PS.EXCM=1. Thus, all
interrupts at level EXCMLEVEL and below are masked during the time PS.EXCM=1. This
is done to allow high-level language coding with the Windowed Register Option of inter-
rupt handlers for interrupts whose level is not greater than EXCMLEVEL. High-priority in-
Chapter 4. Architectural Options
Xtensa Instruction Set Architecture (ISA) Reference Manual 109
terrupts with levels at or below EXCMLEVEL are often called medium-priority interrupts.
The interrupt latency is somewhat lower for levels greater than EXCMLEVEL, but han-
dlers are more flexible for those whose level is not greater than EXCMLEVEL.
There are other conditions besides those in this section that can postpone the taking of
an interrupt. For more descriptions on these, refer to a specific Xtensa processor data
book.
4.4.5.4 Checking for Interrupts
The example below checks for interrupts. This is the checkInterrupts() procedure
called in the code example shown in Section 3.5.4 “Instruction Fetch” on page 29. The
procedure itself checks for interrupts and takes the highest priority interrupt that is pend-
ing.
The chkinterrupt() function for non-NMI levels returns one if:
the current interrupt level is not masking the interrupt (CINTLEVEL < level)
the interrupt is asserted (INTERRUPT)
the corresponding interrupt enable is set (INTENABLE), and
the interrupt is of the current level (LEVELMASK[level])
For NMI level interrupts, the no masking is done, but the edge sensor (made from
NMIinput and lastNMIinput) is explicitly included to avoid repeating the NMI every
cycle.
The takeinterrupt() function saves PC and PS in registers and changes them to
take the interrupt.
procedure checkInterrupts()
if chkinterrupt(NLEVEL+NNMI) then
takeinterrupt[NLEVEL+NNMI]
elseif chkinterrupt(NLEVEL+NNMI-1) then
.
.
.
elseif chkinterrupt(2) then
takeinterrupt[2]
elseif chkinterrupt(1) then
Exception (Level1InterruptCause)
endif
endprocedure checkInterrupts
where chkinterrupt and takeinterrupt are defined as:
function chkinterrupt(level)
Chapter 4. Architectural Options
110 Xtensa Instruction Set Architecture (ISA) Reference Manual
if level = NLEVEL+1 and NNMI = 1 then
chkinterrupt ← NMIinput = 1 and LastNMIinput = 0
lastNMIinput ← NMIinput
elseif level ≤ NLEVEL then
chkinterrupt ← (CINTLEVEL < level) and
((LEVELMASK[level] and INTERRUPT and INTENABLE) ≠ 0)
else
chkinterrupt ← 0
endif
endfunction chkinterrupt
function takeinterrupt(level)
EPC[level] ← PC
EPS[level] ← PS
PC ← InterruptVector[level]
PS.INTLEVEL ← level
PS.EXCM ← 1
endfunction takeinterrupt
4.4.6 Timer Interrupt Option
The Timer Interrupt Option is an in-core peripheral option for Xtensa processors. The
Timer Interrupt Option can be used to generate periodic interrupts from a 32-bit counter
and up to three 32-bit comparators. One counter period typically represents a number of
seconds of elapsed time, depending on the clock rate at which the processor is config-
ured.
Prerequisites: Interrupt Option (page 100)
Incompatible options: None
4.4.6.1 Timer Interrupt Option Architectural Additions
Table 4–77 and Table 4–78 show this option’s architectural additions.
Table 4–77. Timer Interrupt Option Processor-Configuration Additions
Parameter Description Valid Values
NCCOMPARE Number of 32-bit comparators 0..31,2
TIMERINT[0..NCCOMPARE-1] Interrupt number for each comparator 0..NINTERRUPT-13
1. The comparison registers can easily be multiplexed among multiple uses, so more than one comparator is usually not useful unless each com-
parator uses a different TIMERINT interrupt level.
2. NCCOMPARE=0 with the Timer Interrupt Option specifies that CCOUNT exists, but there are no CCOMPARE registers or interrupts.
3. NINTERRUPT is defined in the Interrupt Option, Tab le 4–70.
Chapter 4. Architectural Options
Xtensa Instruction Set Architecture (ISA) Reference Manual 111
4.4.6.2 Clock Counting and Comparison
The CCOUNT register increments on every processor-clock cycle. When CCOUNT =
CCOMPARE[i], a TIMERINT[i] interrupt request is generated. Although CCOUNT con-
tinues to increment and thus matches for only one cycle, the interrupt request is remem-
bered until the interrupt is taken. In spite of this, timer interrupts are cleared by writing
CCOMPARE[i], not by writing INTCLEAR. Interrupt configuration determines the inter-
rupt number and level. It is automatically an Internal interrupt type (the INTTYPE[i]
configuration parameter, Table 4–70).
For most applications, only one CCOMPARE register is required, because it can easily be
shared for multiple uses. Applications that require a greater range of counting than that
provided by the 32-bit CCOMPARE register can maintain a 64-bit cycle count and com-
pare the upper bits in software.
CCOUNT and CCOMPARE[0..NCCOMPARE-1] are undefined after processor reset.
4.5 Options for Local Memory
The options in this section have the primary function of adding different kinds of memo-
ry, such as RAMs, ROMs, or caches to the processor. The added memories are tightly
integrated into the processor pipeline for highest performance.
4.5.1 General Cache Option Features
This subsection describes general characteristics of caches that are referred to in multi-
ple later subsections about specific cache options.
Table 4–78. Timer Interrupt Option Processor-State Additions
Register
Mnemonic Quantity Width
(bits) Register Name R/W
Special
Register
Number
1
CCOUNT 132 Processor-clock count R/W2234
CCOMPARE NCCOMPARE
32 Processor-clock compare
(CCOUNT value at which an interrupt is
generated)
R/W3240-242
1. Registers with a Special Register assignment are read and/or written with the RSR, WSR, and XSR instructions. See Table 3–23 on page 46.
2. This register is not normally written except after reset; it is writable primarily for testing purposes.
3. Writing CCOMPARE clears a pending interrupt.
Chapter 4. Architectural Options
112 Xtensa Instruction Set Architecture (ISA) Reference Manual
4.5.1.1 Cache Terminology
In the cache documentation a “line” is the smallest unit of data that can be moved be-
tween the cache and other parts of the system. If the cache is “direct-mapped,” each
byte of memory may be placed in only one position in the cache. In a direct-mapped
cache, the “index” refers to the portion of the address that is necessary to identify the
cache line containing the access.
A cache is “set-associative” if there is more than one location in the cache into which
any given line may be placed. It is “N-way set-associative” if there are N locations into
which any given line may be placed. The set of all locations into which one line may be
placed is called a “set” and the “index” refers to the portion of the address that is neces-
sary to identify the set containing the access. The various locations within the set that
are capable of containing a line are called the “ways” of the set. And the union of the Nth
way of each set of the cache is the Nth “way” of the cache.
For example, a 4-way set-associative, 16k-byte cache with a 32-byte line size contains
512 lines. There are 128 sets of 4 lines each. The index is a 7-bit value that would most
likely consist of Address<11:5> and is used to determine what set contains the line. The
cache consists of 4 ways, each of which is 4k-bytes in size. A set represents 128 bytes
of storage made up of four lines of 32 bytes each.
4.5.1.2 Cache Tag Format
Figure 4–14 shows the instruction- and data-cache tag format for Xtensa. The number of
bits in the tag is a configuration parameter. So that all lines may be differentiated, the tag
field must always be at least 32−log2(CacheBytes/CacheWayCount) bits wide. If
an MMU with pages smaller than a way of the cache is used, the tag field must also be
at least 32−log2(MinPageSize) bits wide. The actual tag field size is the maximum of
these two values. The bits used in the tag field are the upper bits of the virtual address
left justified in the register (the most significant bit of the register represents the most
significant bit of the virtual address, bit 31). For example:
A 16 kB direct-mapped cache would have an 18-bit tag field.
A 16 kB 2-way associative cache would have a 19-bit tag field.
A 16 kB 2-way associative cache in conjunction with an MMU with a 4kB minimum
page size would have a 20-bit tag field.
The V bit is the line valid bit; 0 → invalid, 1 → valid. The three flag bits exist only for cer-
tain cache configurations. Any of the flag bits in Figure 4–14 not used in a particular con-
figuration are reserved for future use and writing nonzero values to them gives unde-
fined behavior. If the cache is set-associative, then bit[1] is the F bit and is used for
cache miss refill way selection. If the cache is a data cache with writeback functionality,
then the lowest remaining bit is the D bit, or dirty bit, and is used to signify whether the
cache contains a value more recent than its backing store and must be written back. If
Chapter 4. Architectural Options
Xtensa Instruction Set Architecture (ISA) Reference Manual 113
the Index Lock Option is selected for that cache, the lowest remaining bit is the L bit, or
lock bit, and is used to signify whether or not the line is locked and may not be re-
placed.1
Figure 4–14. Instruction and Data Cache Tag Format for Xtensa
4.5.1.3 Cache Prefetch
There are two types of cache prefetch instructions. Normal prefetch instructions make
no change in the architecturally visible state but simply attempt to move cache lines
closer to the processor core. Any exception that might be raised causes the instruction
to become a NOP rather than actually raising an exception. This allows prefetch instruc-
tions to be used without penalty in places where their addresses may not represent legal
memory locations.
IPF attempts to move cache lines to the instruction cache. DPFR, DPFRO, DPFW, and
DPFWO attempt to move cache lines to the data cache. The differences are that the *R*
versions indicate that a write is not expected to the location in the immediate future while
the *W* versions indicate that a write to the location is likely in the near future. The *O
versions indicate that the most likely behavior is that the location is accessed in the near
future, but that it is not worth keeping after that access as another access is not expect-
ed. DPFWO indicates that either a write or a read followed by a write is expected soon.
The *O versions may be placed in different cache ways or kept in a separate buffer in
some implementations.
The second type of prefetch instructions, prefetch and lock instructions, are only avail-
able under their respective Cache Index Lock Options. They also do not change the op-
eration of memory loads and stores and they affect only cache tag state, which affects
only future invalidation or line replacement operations on these lines. They are heavy-
weight operations and, unlike normal prefetch instructions, are only expected to be exe-
cuted by code that sets up the caches for best performance.
The functions iprefetch and dprefetch are described below. Because they modify
no architectural state, they are described only by comments.
1. Note that the three flag bits are added sequentially from the right. The bits that exist are always contiguous with each other and with the V bit on
the right. For the instruction cache, the valid combinations are 0-L-F, 0-0-F, and 0-0-0 because the instruction cache cannot be writeback and the
Index Lock Option is only available for set-associative caches. For the data cache, the valid combinations are 0-L-F, 0-0-F, 0-0-0, L-D-F, 0-D-F, and
0-0-D, which are the same three with and without the dirty bit inserted in its order.
31 43210
Tag reserved Flag V
n 28-n3 1
Chapter 4. Architectural Options
114 Xtensa Instruction Set Architecture (ISA) Reference Manual
function iprefetch(vAddr, pAddr, lock)-- instruction prefetch
if lock then
-- move the line specified by vAddr/pAddr into the instruction cache
-- mark the line locked
else
-- no architecturally visible operation performed
-- no exception raised
-- try to move the line specified by vAddr/pAddr into the instruction cache
endif
endfunction iprefetch
function dprefetch(vAddr, pAddr, excl, once, lock)-- data prefetch
if lock then
-- move the line specified by vAddr/pAddr into the data cache
-- mark the line locked
else if excl then
-- no architecturally visible operation performed
-- no exception raised
-- if caches are coherent, get an exclusive copy
if once then
-- try to move the line specified by vAddr/pAddr where it can be
-- read and written once
else
-- try to move the line specified by vAddr/pAddr into the data cache
endif
else
-- no architecturally visible operation performed
-- no exception raised
if once then
-- try to move the line specified by vAddr/pAddr where it can be
read once
else
-- try to move the line specified by vAddr/pAddr into the data cache
endif
endif
endfunction dprefetch
Chapter 4. Architectural Options
Xtensa Instruction Set Architecture (ISA) Reference Manual 115
4.5.2 Instruction Cache Option
The Instruction Cache Option adds on-chip first-level instruction cache. The Instruction
Cache Option also adds a few new instructions for prefetching and invalidation.
Prerequisites: Processor Interface Option (page 194)
Incompatible options: None
4.5.2.1 Instruction Cache Option Architectural Additions
Table 4–79 through Table 4–80 show this option’s architectural additions.
Table 4–79. Instruction Cache Option Processor-Configuration Additions
Parameter Description Valid Values
InstCacheWayCount Instruction-cache set associativity
(ways)
1..41
InstCacheLineBytes Instruction-cache line size (bytes) 16, 32, 64, 128, 2561
InstCacheBytes Instruction-cache size (bytes) 1kB, 1.5kB, 2kB, 3kB, ... 32kB1
MemErrDetection Error detection type2None, parity, ECC
MemErrEnable Error enable No-detect, detect3
1. Valid values vary per implementation. Refer to information on local memories in a specific Xtensa processor data book.
2. Must be identical for every instruction memory
3. Detection may be enabled only when the Memory ECC/Parity Option is configured.
Chapter 4. Architectural Options
116 Xtensa Instruction Set Architecture (ISA) Reference Manual
See Section 5.7 “Caches and Local Memories” on page 240 for more information about
synchronizations required when using the instruction cache.
4.5.3 Instruction Cache Test Option
The Instruction Cache Test Option is currently added to every processor that has an In-
struction Cache Option; therefore, it is not actually a separate option. It adds instructions
capable of reading and writing the tag and data of the instruction cache. These instruc-
tions are intended to be used in testing the instruction cache, rather than in operational
code and may not be implemented in a binary compatible way in all future processors.
Prerequisites: Processor Interface Option (page 194) and Instruction Cache Option
(page 115)
Incompatible options: None
4.5.3.1 Instruction Cache Test Option Architectural Additions
Table 4–81 shows this option’s architectural additions.
Table 4–80. Instruction Cache Option Instruction Additions
Instruction
1
Format Definition
IPF
RRI8 Instruction-cache prefetch
This instruction checks whether the line containing the specified address is
present in the instruction cache, and if not, begins the transfer of the line from
memory to the cache. In some implementations, prefetching an instruction line
may prevent the processor from taking an instruction cache miss later.
IHI
RRI8 Instruction-cache hit invalidate
This instruction invalidates a line in the instruction cache if present and not
locked. If the specified address is not in the instruction cache then this
instruction has no effect. If the specified line is present and not locked, it is
invalidated. This instruction is required before executing instructions that have
been written by this processor, another processor, or DMA.
III
RRI8 Instruction-cache index invalidate
This instruction uses the virtual address to choose a location in the instruction
cache and invalidates the specified line if it is not locked. The method for
mapping the virtual address to an instruction cache location is implementation-
specific. This instruction is primarily useful for instruction cache initialization
after power-up (note that if the Instruction Cache Index Lock Option is
implemented, an IIU instruction should precede the III).
1. These instructions are fully described in Chapter 6, "Instruction Descriptions" on page 243
Chapter 4. Architectural Options
Xtensa Instruction Set Architecture (ISA) Reference Manual 117
The instruction-cache access instructions must be fetched from a region of memory that
has the bypass attribute. Use an ISYNC instruction before transferring back to cached
instruction space. See Section 5.7 “Caches and Local Memories” for more information
about synchronizations required when using the instruction cache.
4.5.4 Instruction Cache Index Lock Option
The Instruction Cache Index Lock Option adds the capability of individually locking each
line of the instruction cache. This option may only be added to a cache, which has two or
more ways. One bit is added to the instruction cache tag RAM format. The Instruction
Cache Index Lock Option also adds new instructions for locking and unlocking lines.
Prerequisites: Processor Interface Option (page 194) and Instruction Cache Option
(page 115)
Incompatible options: None
4.5.4.1 Instruction Cache Index Lock Option Architectural Additions
Table 4–82 shows this option’s architectural additions.
Table 4–81. Instruction Cache Test Option Instruction Additions
Instruction
1
Format Definition
LICT
RRR Load instruction cache tag
This instruction uses its address to specify a line in the Instruction Cache and
loads the tag for that line into a register.
LICW
RRR Load instruction cache word
This instruction uses its address to specify a word in the instruction cache and
loads that word into a register.
SICT
RRR Store instruction cache tag
This instruction uses its address to specify a line in the instruction cache and
stores the tag for that line from a register.
SICW
RRR Store instruction cache word
This instruction uses its address to specify a word in the instruction cache and
stores that word from a register.
1. These instructions are fully described in Chapter 6, "Instruction Descriptions" on page 243.
Chapter 4. Architectural Options
118 Xtensa Instruction Set Architecture (ISA) Reference Manual
See Section 5.7 “Caches and Local Memories” for more information about synchroniza-
tions required when using the instruction cache.
4.5.5 Data Cache Option
The Data Cache Option adds on-chip first-level data cache. It supports prefetching, writ-
ing back, and invalidation.
The data-cache prefetch read/write/once instructions have been provided to improve
performance, not to affect the processor state. Therefore, some implementations may
choose to implement these instructions as no-op instructions. In general, the perfor-
mance improvement from using these instructions is implementation-dependent. In
some implementations, these instructions check whether the line containing the speci-
fied address is present in the data cache, and if not, begin the transfer of the line from
memory.
Prerequisites: Processor Interface Option (page 194)
Incompatible options: None
Table 4–82. Instruction Cache Index Lock Option Instruction Additions
Instruction
1
Format Definition
IPFL
RRI4 Instruction-cache prefetch and lock
This instruction checks whether the line containing the specified address is present in
the instruction cache, and if not, begins the transfer of the line from memory to the
cache. The line is placed in the instruction cache and the line marked as locked, that is,
not replaceable by ordinary instruction cache misses. To unlock the line, use IHU or
IIU. This instruction raises an illegal instruction exception on implementations that do
not support instruction cache locking.
IHU
RRI4 Instruction-cache hit unlock
This instruction unlocks a line in the instruction cache if present. If the specified
address is not in the instruction cache then this instruction has no effect. If the
specified line is present, it is unlocked. This instruction (or IIU) is required before
invalidating a line if it is locked.
IIU
RRI4 Instruction-cache index unlock
This instruction uses the virtual address to choose a location in the instruction cache
and unlocks the specified line. The method for mapping the virtual address to an
instruction cache location is implementation-specific. This instruction is primarily useful
for unlocking the entire instruction cache. This instruction (or IHU) is required before
invalidating a line if it is locked.
1. These instructions are fully described in Chapter 6, "Instruction Descriptions" on page 243.
Chapter 4. Architectural Options
Xtensa Instruction Set Architecture (ISA) Reference Manual 119
4.5.5.1 Data Cache Option Architectural Additions
Table 4–83 and Table 4–84 show this option’s architectural additions.
Table 4–83. Data Cache Option Processor-Configuration Additions
Parameter Description Valid Values
DataCacheWayCount Data-cache set associativity (ways) 1..41
DataCacheLineBytes Data-cache line size (bytes) 16, 32, 64, 128, 2561
DataCacheBytes Data-cache size (bytes) 1kB, 1.5kB, 2kB, 3kB, ... 32kB1
IsWriteback Data-cache configured as writeback Yes, No
MemErrDetection Error detection type2None, parity, ECC
MemErrEnable Error enable No-detect, detect3
1. Valid values vary per implementation. Refer to information on local memories in a specific Xtensa processor data book.
2. Must be identical for every data memory
3. Detection may be enabled only when the Memory ECC/Parity Option is configured.
Table 4–84. Data Cache Option Instruction Additions
Instruction
1
Format Definition
DPFR,
DPFW,
DPFRO,
DPFWO
RRI8 Data-cache prefetch {read,write}{,once}
The four variants specify various “hints” about how the data is likely to be used in the
future. DPFW and DPFWO indicate that the data is likely to be written in the near
future. On some systems this is used to fetch the data with write permission (e.g. in a
system with shared and exclusive states). DPFR and DPFRO indicate that the data is
likely only to be read. The once forms, DPFRO and DPFWO, indicate that the data is
likely to be read or written only once before it is replaced in the cache. On some
implementations this might be used to select a specific cache way, or to select a
streaming buffer instead of the cache.
DHWB
RRI8 Data-cache hit writeback
If IsWriteback, this instruction forces dirty data in the data cache to be written
back to memory. If the specified address is not in the data cache, or is present but
unmodified, then this instruction has no effect. If the specified address is present and
modified in the data cache, the line containing it is written back, and marked
unmodified. This instruction is useful before a DMA read from memory, or to force
writes to a frame buffer to become visible, or to force writes to memory shared by two
processors.
If not IsWriteback, DHWB is a no-op.
1. These instructions are fully described in Chapter 6, "Instruction Descriptions" on page 243
Chapter 4. Architectural Options
120 Xtensa Instruction Set Architecture (ISA) Reference Manual
See Section 5.7 “Caches and Local Memories” for more information about synchroniza-
tions required when using the data cache.
DHWBI
RRI8 Data-cache hit writeback invalidate
If IsWriteback, this instruction forces dirty data in the data cache to be written
back to memory. If the specified address is not in the data cache then this instruction
has no effect. If the specified address is present and modified in the data cache, the
line containing it is written back. After the writeback, if any, the line containing the
specified address is invalidated if present and not locked. This instruction is useful in
the same circumstances as DHWB and also before a DMA write to memory that does
not completely overwrite the line.
If not IsWriteback, DHWBI is identical to DHI except for privilege.
DIWB
RRI4 Data-cache Index writeback (added in T1050)
If IsWriteback, this instruction forces dirty data in the data cache to be written
back to memory. The virtual address is used, in an implementation dependent manner,
to choose a cache line to write back. If the chosen line is unmodified, then this
instruction has no effect. If the chosen line is modified in the data cache, the line
containing it is written back, and marked unmodified. This instruction is useful for
writing back the entire cache.
If not IsWriteback, DIWB is a no-op.
DIWBI
RRI4 Data-cache index writeback invalidate (added in T1050)
If IsWriteback, this instruction forces dirty data in the data cache to be written
back to memory. The virtual address is used, in an implementation dependent manner,
to choose a cache line to write back. If the chosen line is modified in the data cache,
the line containing it is written back, and marked unmodified. After the writeback, if
any, the chosen line is invalidated if it is not locked. This instruction is useful for writing
back and invalidating the entire cache.
If not IsWriteback, DIWBI simply invalidates without writeback.
DHI
RRI8 Data-cache hit invalidate
This instruction invalidates a line in the data cache if present and not locked. If the
specified address is not in the data cache then this instruction has no effect. If the
specified address is present and not locked, it is invalidated. This instruction is useful
before a DMA write to memory that overwrites the entire line.
DII
RRI4 Data-cache index invalidate
This instruction uses the virtual address to choose a location in the data cache and
invalidates the specified line if it is not locked. The method for mapping the virtual
address to a data cache location is implementation-specific. This instruction is
primarily useful for data cache initialization after power-up.
Table 4–84. Data Cache Option Instruction Additions
(continued)
Instruction
1
Format Definition
1. These instructions are fully described in Chapter 6, "Instruction Descriptions" on page 243
Chapter 4. Architectural Options
Xtensa Instruction Set Architecture (ISA) Reference Manual 121
If IsWriteback, there is a dirty bit added to the data cache tag RAM format. The at-
tributes described in Section 4.6.3.3 and Section 4.6.5.10 are then capable of setting a
region of memory to be either write-back or write-through. If not IsWriteback, both at-
tribute settings result in write-through semantics.
When a region of memory is marked write-back, any store that hits in the cache writes
only the cache (setting the dirty bit, if it is not already set) and does not send a write on
the PIF. Any store that does not hit in the cache causes a miss. When the line is filled,
the semantics of a cache hit described above are followed. If a dirty line is evicted to use
the space in the cache, the entire line will be written on the PIF. The DHWB, DHWBI, DI-
WB, and DIWBI instructions will also write back a line if it is marked dirty.
4.5.6 Data Cache Test Option
The Data Cache Test Option is currently added to every processor, which has a Data
Cache Option and therefore, is not actually a separate option. It adds instructions capa-
ble of reading and writing the tag of the data cache. These instructions are intended to
be used in testing the data cache, rather than in operational code and may not be imple-
mented in a binary compatible way in all future processors.
Prerequisites: Processor Interface Option (page 194) and Data Cache Option (page
118)
Incompatible options: None
4.5.6.1 Data Cache Test Option Architectural Additions
Table 4–85 shows this option’s architectural additions.
There are no instructions to access the data-cache data array. Normal loads and stores
can be used for this purpose with the isolate attribute.
See Section 5.7 “Caches and Local Memories” for more information about synchroniza-
tions required when using the data cache.
Table 4–85. Data Cache Test Option Instruction Additions
Instruction
1
Format Definition
LDCT
RRR Load data cache tag
This instruction uses its address to specify a line in the instruction cache and
loads the tag for that line into a register.
SDCT
RRR Store data cache tag
This instruction uses its address to specify a line in the instruction cache and
stores the tag for that line from a register.
1. These instructions are fully described in Chapter 6, "Instruction Descriptions" on page 243.
Chapter 4. Architectural Options
122 Xtensa Instruction Set Architecture (ISA) Reference Manual
4.5.7 Data Cache Index Lock Option
The Data Cache Index Lock Option adds the capability of individually locking each line
of the data cache. One bit is added to the data cache tag RAM format. The Data Cache
Index Lock Option also adds new instructions for locking and unlocking lines.
Prerequisites: Processor Interface Option (page 194) and Data Cache Option (page
118)
Incompatible options: None
4.5.7.1 Data Cache Index Lock Option Architectural Additions
Table 4–86 shows this option’s architectural additions.
See Section 5.7 “Caches and Local Memories” for more information about synchroniza-
tions required when using the data cache.
Table 4–86. Data Cache Index Lock Option Instruction Additions
Instruction
1
Format Definition
DPFL
RRI4 Data-cache prefetch and lock
This instruction checks whether the line containing the specified address is
present in the data cache, and if not, begins the transfer of the line from
memory to the cache. The line is placed in the data cache and the line marked
as locked, that is, not replaceable by ordinary data cache misses. To unlock
the line, use DHU or DIU. This instruction raises an illegal instruction
exception on implementations that do not support data cache locking.
DHU
RRI4 Data-cache hit unlock
This instruction unlocks a line in the data cache if present. If the specified
address is not in the data cache then this instruction has no effect. If the
specified address is present, it is unlocked. This instruction (or DIU) is
required before invalidating a line if it is locked.
DIU
RRI4 Data-cache index unlock
This instruction uses the virtual address to choose a location in the data cache
and unlocks the specified line. The method for mapping the virtual address to a
data cache location is implementation-specific. This instruction is primarily
useful for unlocking the entire data cache. This instruction (or DHU) is required
before invalidating a line if it is locked.
1. These instructions are fully described in Chapter 6, "Instruction Descriptions" on page 243.
Chapter 4. Architectural Options
Xtensa Instruction Set Architecture (ISA) Reference Manual 123
4.5.8 General RAM/ROM Option Features
The RAM and ROM options both provide internal memories that are part of the proces-
sor’s address space and are accessed with the same timing as cache. These memories
should not be confused with system RAM and ROM located outside of the processor,
which are often larger, and may be used for both instructions and data, and shared be-
tween processors and other processing elements.
The basic configuration parameters are the size and base address of the memory. It is
possible to configure cache, RAM, and ROM independently for both instruction and da-
ta, however some implementations may require an increased clock period if multiple in-
struction or multiple data memories are specified, or if the memory sizes are large. It is
sometimes appropriate for the system designer to instead place RAMs and ROMs exter-
nal to the processor and access these through the cache.
Every Instruction and Data RAM and ROM is always required to be naturally aligned
(aligned on a boundary of a power of two which is equal to or larger than the size of the
RAM/ROM) in physical address space. The mapping from virtual address space to phys-
ical address space must have the property that the Index bits of the RAM/ROM are iden-
tity mapped. This is a slightly less restrictive condition than requiring that the RAM/ROM
must be contiguous and naturally aligned in virtual address space but this latter condi-
tion will always meet the requirement.
Instruction RAM can be referenced as data only by the L32I, L32R and S32I instruc-
tions and Instruction ROM referenced as data only by the L32I and L32R instructions.
This functionality is provided for initialization and test purposes, for which performance
is not critical, so these operations may be significantly slower on some Xtensa imple-
mentations. Most Xtensa code makes extensive use of L32R instructions, which load
values from a location relative to the current PC. For this to perform well for code located
in an instruction RAM or ROM, some sort of data memory (either internal or external)
should be located within the 256 KB range of the L32R instruction or else the Extended
L32R Option should be used.
Table 4–87 summarizes the restrictions on instruction and data RAM and ROM access.
The exceptions listed assume no memory protection exception has already been raised
on the access.
Chapter 4. Architectural Options
124 Xtensa Instruction Set Architecture (ISA) Reference Manual
4.5.9 Instruction RAM Option
This option provides an internal, read-write instruction memory. It is typically useful as
the only processor instruction store (no instruction cache) when all of the code for an ap-
plication will fit in a small memory, or as an additional instruction store in parallel with the
cache for code that must have constant access time for performance reasons.
Prerequisites: None
Incompatible options: None
4.5.9.1 Instruction RAM Option Architectural Additions
Table 4–88 shows this option’s configuration parameters. There are no processor state
or instruction additions.
Table 4–87. RAM/ROM Access Restrictions
Memory Instruction
Fetch
L32R L32I
L32I.N Other Loads S32I S32I.N Other Stores
InstROM ok ok1undefined LSE3LSE3
InstRAM ok ok1undefined ok1undefined
DataROM IFE2ok ok LSE3LSE3
DataRAM IFE2ok ok ok ok
UnifiedRAM ok ok ok ok ok
1. Reduced performance on some Xtensa implementations
2. Instruction fetch error exception
3. Load store error exception
Table 4–88. Instruction RAM Option Processor-Configuration Additions
Parameter Description Valid Values
InstRAMBytes Instruction RAM size (bytes) 512, 1kB, 2kB, 4kB, ... 256kB1
InstRAMPAddr Instruction RAM base physical
address
32-bit address, aligned on multiple of
its size
MemErrDetection Error detection type2None, parity, ECC
MemErrEnable Error enable No-detect, detect3
1. Refer to information on local memories in a specific Xtensa processor data book.
2. Must be identical for every instruction memory
3. Detection may be enabled only when the Memory ECC/Parity Option is configured.
Chapter 4. Architectural Options
Xtensa Instruction Set Architecture (ISA) Reference Manual 125
Instruction RAM may be accessed as data using the L32I, L32R, and S32I instruc-
tions. The operation of other loads and stores on InstRAM addresses is not defined.
S32I is useful for copying code into the InstRAM; L32I is useful for diagnostic testing of
InstRAM, and L32R allows constants to be loaded from InstRAM if no data memory is
within range. While L32I, L32R, and S32I to InstRAM are defined, on many implemen-
tations these accesses are much slower than references to data RAM, ROM, or cache,
and thus the use of InstRAM for data storage is not recommended.
4.5.10 Instruction ROM Option
This option provides an internal, read-only instruction memory. It is typically useful as
the only processor instruction store (no instruction cache) when all of the code for an ap-
plication will fit in a small memory, or as an additional instruction store in parallel with the
cache for code that must have constant access time for performance reasons. Because
ROM is read-only, only code that is not subject to change should be put here.
Prerequisites: None
Incompatible options: None
4.5.10.1 Instruction ROM Option Architectural Additions
Table 4–89 shows this option’s configuration parameters. There are no processor state
or instruction additions.
Instruction ROM may be accessed as data using the L32I and L32R instructions. The
operation of other loads on InstROM addresses is not defined. L32I is useful for diag-
nostic testing of InstROM, and L32R allows constants to be loaded from InstROM if no
data memory is within range. While L32I and L32R to InstROM are defined, on many
implementations these accesses are much slower than references to data RAM, ROM,
or cache, and thus the use of InstROM for data storage is not recommended.
Table 4–89. Instruction ROM Option Processor-Configuration Additions
Parameter Description Valid Values
InstROMBytes Instruction ROM size (bytes) 512, 1kB, 2kB, 4kB, ... 256kB1
InstROMPAddr Instruction ROM base physical
address
32-bit address, aligned on multiple of
its size
1. Refer to information on Local Memories in a specific Xtensa processor data book.
Chapter 4. Architectural Options
126 Xtensa Instruction Set Architecture (ISA) Reference Manual
4.5.11 Data RAM Option
This option provides an internal, read-write data memory. It is typically useful as the only
processor data store (no data cache) when all of the data for an application will fit in a
small memory, or as an additional data store in parallel with the cache for data that must
be constant access time for performance reasons.
Prerequisites: None
Incompatible options: None
4.5.11.1 Data RAM Option Architectural Additions
Table 4–90 shows this option’s configuration parameters. There are no processor state
or instruction additions.
In the absence of the Extended L32R Option it is recommended that processors with
data RAM or ROM and no data cache be configured with the DataRAMPAddr or
DataROMPAddr below the lowest instruction address and above the highest instruction
address minus 256 KB, so that the L32R literals can be stored in RAM or ROM for fast
access. The processor will fetch L32R literals from the instruction RAM, or ROM, but in
many implementations several cycles are required for the fetch, making the use of this
feature undesirable. The Extended L32R Option allows less restricted placement.
4.5.12 Data ROM Option
This option provides an internal, read-only data memory. It is typically useful as an addi-
tional data store in parallel with the cache for data that must be constant access time for
performance reasons.
Prerequisites: None
Incompatible options: None
Table 4–90. Data RAM Option Processor-Configuration Additions
Parameter Description Valid Values
DataRAMBytes Data RAM size (bytes) 512, 1kB, 2kB, 4kB, ... 256kB1
DataRAMPAddr Data RAM base physical address 32-bit address, aligned on multiple of
its size
MemErrDetection Error detection type2None, parity, ECC
MemErrEnable Error enable No-detect, detect3
1. Refer to information on Local Memories in a specific Xtensa processor data book.
2. Must be identical for every data memory
3. Detection may be enabled only when the Memory ECC/Parity Option is configured.
Chapter 4. Architectural Options
Xtensa Instruction Set Architecture (ISA) Reference Manual 127
4.5.12.1 Data ROM Option Architectural Additions
Table 4–91 shows this option’s configuration parameters. There are no processor state
or instruction additions.
4.5.13 XLMI Option
The XLMI Option, or Xtensa Local Memory Interface Option, allows the attachment of
hardware other than caches, RAMs, and ROMs into the pipeline of the processor rather
than on the processor interface bus. The advantage of the XLMI is that the latency is
lower. The disadvantage is that speculation must be explicitly allowed for on loads. The
XLMI port contains signals that inform external devices after the fact concerning whether
a load was or was not speculative. Stores are never speculative. Refer to a specific
Xtensa processor data book for more detail.
Prerequisites: None
Incompatible options: None
Instructions may not be fetched from an XLMI interface. The virtual and physical ad-
dresses of the entire XLMI region must be identical in all bits.
4.5.13.1 XLMI Option Architectural Additions
Table 4–92 shows this option’s configuration parameters. There are no processor state
or instruction additions.
Table 4–91. Data ROM Option Processor-Configuration Additions
Parameter Description Valid Values
DataROMBytes Data ROM size (bytes) 512, 1kB, 2kB, 4kB, ... 256kB1
DataROMPAddr Data ROM base physical address 32-bit address, aligned on multiple of
its size
1. Refer to information on local memories in a specific Xtensa processor data book.
Table 4–92. XLMI Option Processor-Configuration Additions
Parameter Description Valid Values
XLMIBytes XLMI size (bytes) 512, 1kB, 2kB, 4kB, ... 256kB1
XLMIPAddr XLMI base physical address 32-bit address, aligned on multiple of
its size
1. Refer to information on local memories in a specific Xtensa processor data book.
Chapter 4. Architectural Options
128 Xtensa Instruction Set Architecture (ISA) Reference Manual
4.5.14 Hardware Alignment Option
The Hardware Alignment Option adds hardware to the processor which allows loads and
stores to work correctly at any arbitrary alignment. It does this by making multiple ac-
cesses where necessary and combining the results. Unaligned accesses are still slower
than aligned accesses, but this option is more efficient than the Unaligned Exception
Option with software handler. In addition, the Hardware Alignment Option will work in sit-
uations where a software handler is difficult to write (for example, a load and operate in-
struction).
Prerequisites: Unaligned Exception Option (page 99)
Incompatible options: None
The Hardware Alignment Option builds on the Unaligned Exception Option so that al-
most all potential LoadStoreAlignmentCause exceptions are handled transparently
by hardware instead. A few situations, which are never expected to happen in real soft-
ware, still raise a LoadStoreAlignmentCause exception. In order to properly handle
all TLB misses and other exceptions, the priority of the LoadStoreAlignmentCause
exception is lower when the Hardware Alignment Option is present than when it is not.
Exception priorities are listed in Section 4.4.1.11.
A LoadStoreAlignmentCause exception may still be raised in some implementations
with the Hardware Alignment Option if the address of a load or store instruction is not a
multiple of its size and any of the following conditions is also true:
The instruction is one of L32AI, S32RI, or S32C1I.
The memory type for either portion is XLMI, IRAM, or IROM.
The memory types (cache, DataRAM, bypass) of the two portions differ.
The cache attribute for either portion is Isolate.
The column labeled "Meaning for Cache Access" in either Table 4–104 on page 155
or Tab le 4–109 on page 178 is different for the two portions of the access.
4.5.15 Memory ECC/Parity Option
The Memory ECC/Parity Option allows the local memories and caches of Xtensa pro-
cessors to be protected against errors by either parity or error correcting code (ECC). It
does not affect the processor interface and system memories must maintain their own
error detection and correction. Local memories must be wide enough to contain the ad-
ditional bits required. The generation and checking of parity or ECC is done in the
Xtensa core through a combination of hardware and software mechanisms.
Prerequisites: Exception Option (page 82)
Incompatible options: None
Chapter 4. Architectural Options
Xtensa Instruction Set Architecture (ISA) Reference Manual 129
Each memory may be protected or not protected individually. All protected instruction
memories must use a single protection type (parity or ECC). Likewise, all protected data
memories must use a single protection type. For parity protection, data memories re-
quire one additional bit per byte while instruction memories require one additional bit per
four bytes and cache tags require one additional bit per tag. For ECC protection, instruc-
tion memories require 7 additional bits per 32-bit word, data memories require 5 addi-
tional bits per byte, and cache tags require 7 additional bits per tag.
The core computes parity or ECC bits on every store without doing a read-modify-write.
On every load or instruction fetch, these bits are checked and an exception is raised for
parity errors or for uncorrectable ECC errors. For correctable errors, a control bit in the
memory error status register (Table 4–94) indicates whether to raise an exception or
simply correct the value to be used (but not the value in memory) and continue. In addi-
tion, correctable ECC errors assert an output pin which may be used as an interrupt. Im-
plementations may or may not implement hardware correction. If they do not implement
it, the exception is always raised.
4.5.15.1 Memory ECC/Parity Option Architectural Additions
Table 4–93 through Table 4–95 show this option’s architectural additions.
Table 4–93. Memory ECC/Parity Option Processor-Configuration Additions
Parameter Description Valid Values
MemoryErrorVector Exception vector for memory errors 32-bit address
Each RAM/Cache has configuration
additions valid when the Memory
ECC/Parity Option is configured
Table 4–94. Memory ECC/Parity Option Processor-State Additions
Register
Mnemonic Quantity Width
(bits) Register Name R/W Access
MEPC 132 Memory error PC register R/W 106
MEPS
1same as
PS
register1
Memory error PS register R/W 107
MESAVE 132 Memory error save register R/W 108
MESR 119 Memory error status register R/W 109
MECR 122 Memory error check register R/W 110
MEVADDR 132 Memory error virtual address
register
R/W 111
1. There are enough bits to save all configured PS Register Fields. See Table 4–63 on page 87.
Chapter 4. Architectural Options
130 Xtensa Instruction Set Architecture (ISA) Reference Manual
4.5.15.2 Memory Error Information Registers
Three registers are used to maintain information about a memory error. They are updat-
ed for memory errors which do not raise an exception, as well as those which do. The
memory error status register (MESR), shown in Figure 4–15 with further description in
Table 4–98, contains control bits that control the operation of memory errors and status
bits that hold information about memory errors that have occurred.
Under normal operation, check bits are always calculated and written to local memories.
When ECC is enabled, an uncorrectable error, or a correctable error for which the
MESR.DataExc or MESR.InstExc bit is set, will raise an exception whenever it is en-
countered during either a load or a dirty castout. Inbound PIF operations return an error
when appropriate but the error will not be noted by the local processor. Correctable er-
rors during a dirty castout when MESR.DataExc is clear may, in some implementations,
correct the error on the fly without setting MESR.RCE or associated status.
When ECC is enabled and either the MESR.DataExc bit or the MESR.InstExc bit is
clear or the MESR.MemE bit is set, hardware may be able to correct an error without rais-
ing an exception. This may cause MESR.RCE (along with many other fields),
MESR.DLCE, or MESR.ILCE to be set by hardware at an arbitrary time.
In addition, an external pin reflects the state of MESR.RCE and can be connected to an
interrupt input on the Xtensa processor itself or on another processor. This interrupt may
be at a much lower priority than the memory error exception handler, but it can still re-
pair the memory itself and/or log the error much as the memory error exception handler
might. MESR.RCE must be cleared by software to return the external pin to zero and to
re-arm the mechanism for recording correctable errors.
Figure 4–15. MESR Register Format
Table 4–95. Memory ECC/Parity Option Instruction Additions
Instruction
1
Format Definition
RFME RRR Return from memory error
1. These instructions are fully described in Chapter 6, "Instruction Descriptions" on page 243.
31 30 29 28 27 24 23 22 21 20 19 18 17 16 15 12 11 10 9876543210
Error
Type
*Memory Type *Acc.
Type
*Way
Numb.
*
InstExc
DataExc
ErrTest
ErrEnab
*
ILCE
DLCE
RCE
*
DME
MemE
2 2 4 2 2 2 2 4 1 1 1 1 1 1 1 1 2 1 1
Chapter 4. Architectural Options
Xtensa Instruction Set Architecture (ISA) Reference Manual 131
Table 4–96. MESR Register Fields
Field Width
(bits) Definition
MemE
1Memory error.
0 → Memory error exception not in progress.
1 → Memory error exception in progress.
Set on taking memory error exception. Cleared by RFME instruction. Software reads
and writes MemE normally.
DME
1Double Memory error.
0 → Normal memory error exception.
1 → Current memory error exception encountered during a Memory error exception.
Set on taking memory error exception while MemE is set. Hardware does not clear.
Software reads and writes DME normally.
RCE (ECC1)
1Recorded correctable error. (Exists only if ECC is configured.)
0 → Status refers to something else.
1 → Status refers to an error corrected by hardware.
RCE means that status refers to a correctable memory error that has been fixed in
hardware. Status, here, means the group of state that contains information about a
memory error. It consists of the status fields of MESR (Way Number, Access
Type, Memory Type, and Error Type) and the contents of the MECR and
MEVADDR registers. The recorded information may be used to fix the error in the
memory copy or to log the error.
RCE is set by hardware whenever MemE is clear, RCE is clear, and a correctable
error is fixed in hardware. RCE is cleared by hardware when a memory exception is
raised as the recorded information is lost and either DLCE or ILCE is set in its place.
Software reads and writes RCE normally.
DLCE (ECC1)
1Data lost correctable error. (Exists only if ECC is configured.)
0 → No information has been lost about data hardware corrected memory errors.
1 → Information has been lost about data hardware corrected memory errors.
DLCE means that there has been a correctable error on a data (execute) access
which has not been recorded because 1) it happened during a memory error exception
(MemE set), 2) a memory error exception happened before it was recorded (RCE now
cleared), or 3) it happened after another correctable error and before that error was
recorded (RCE also set).
DLCE is set by hardware whenever any data (execute) correctable error is fixed in
hardware but MemE or RCE is set and the new Access Type is not instruction
fetch. DLCE is also set by hardware when any memory exception is raised with RCE
set and with the current Access Type is not instruction fetch. DLCE is never
cleared by hardware. Software reads and writes DLCE normally.
1. In some implementations the bits used with ECC may exist as state bits without effect even when only parity is configured.
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132 Xtensa Instruction Set Architecture (ISA) Reference Manual
ILCE (ECC1)
1Instruction fetch (Ifetch) lost correctable error. (Exists only if ECC is configured.)
0 → No information has been lost about ifetch hardware corrected memory errors.
1 → Information has been lost about ifetch hardware corrected memory errors.
ILCE means that there has been a correctable error on an Ifetch access which has
not been recorded because 1) it happened during a memory error exception (MemE
set), 2) a memory error exception happened before it was recorded (RCE now
cleared), or 3) it happened after another correctable error and before that error was
recorded (RCE also set).
ILCE is set by hardware whenever any Ifetch correctable error is fixed in hardware
but MemE or RCE is set and the new Access Type is instruction fetch. ILCE is
also set by hardware when any memory exception is raised with RCE set and with the
current Access Type is instruction fetch. ILCE is never cleared by hardware.
Software reads and writes ILCE normally.
ErrEnab
1Enable Memory ECC/Parity Option errors.
0 → Memory errors are disabled.
1 → Memory errors are enabled.
When ErrEnab is set, memory error exceptions and corrections are enabled. When
ErrEnab is clear, the same values are written to memories, but no checks and no
exceptions are raised on memory reads. Operation is undefined when both
ErrEnab and ErrTest are set. ErrEnab is not modified by hardware.
ErrTest
1Memory error test mode.
0 → Normal memory error operation.
1 → Special memory error test operation.
When ErrTest is set, the memory write instructions S32I, S32I.N, SICT,
SICW, and SDCT insert the actual contents of the MECR register into the memory
check bits and the memory read instructions L32I, L32I.N, LICT, LICW, and
LDCT always place the actual check bits read from memory into the MECR register.
The operation of other memory access instructions is undefined when ErrTest is
set. When ErrTest is clear, memory writes compute appropriate check bits for
each write and memory reads do not affect the MECR register (unless a memory error
is detected). Cache fills and Inbound PIF operations are unaffected by the setting of
the ErrTest bit. Operation is undefined when both ErrEnab and ErrTest are
set. ErrTest is not modified by hardware.
Table 4–96. MESR Register Fields
(continued)
Field Width
(bits) Definition
1. In some implementations the bits used with ECC may exist as state bits without effect even when only parity is configured.
Chapter 4. Architectural Options
Xtensa Instruction Set Architecture (ISA) Reference Manual 133
DataExc
(ECC1)
1Data exception. (Exists only if ECC is configured.)
0 → No exception on hardware correctable data memory errors.
1 → Memory error exception on hardware correctable data memory errors.
Set by software to cause memory errors which might be handled in hardware on data
accesses to raise the memory error exception instead. This bit is forced to 1 (cannot
be cleared) if hardware is unable to handle any data access errors. If MemE is set, no
exception is raised for errors which hardware can handle even if DataExc is set.
DataExc is not modified by hardware.
InstExc
(ECC1)
1Instruction exception. (Exists only if ECC is configured.)
0 → No exception on hardware correctable instruction fetch memory errors.
1 → Memory error exception on hardware correctable instr. fetch memory errors.
Set by software to cause memory errors which might be handled in hardware on
instruction fetches to raise the memory error exception instead. This bit is forced to 1
(cannot be cleared) if hardware is unable to handle any instruction fetch errors. If
MemE is set, no exception is raised for errors which hardware can handle even if
InstExc is set. InstExc is not modified by hardware.
Way Number
2Cache way number of a memory error. (Exists only if a multiway cache is configured.)
When RCE or MemE is set and the Memory Type field points to a cache, this field
contains the cache way number containing the error.
Way Number is set by hardware whenever MemE is clear, RCE is clear, and a
correctable error is fixed in hardware or whenever a memory exception is raised.
Access Type
2Access type of an access with memory error.
0 → Memory error during load or store
1 → Memory error during instruction fetch
2 → Memory error during instruction memory access (such as IPFL or IHI)
3 → Memory error during dirty line castout
When RCE or MemE is set, this field contains an indication of the access type which
caused the memory error.
Access Type is set by hardware whenever MemE is clear, RCE is clear, and a
correctable error is fixed in hardware or whenever a memory exception is raised.
Table 4–96. MESR Register Fields
(continued)
Field Width
(bits) Definition
1. In some implementations the bits used with ECC may exist as state bits without effect even when only parity is configured.
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134 Xtensa Instruction Set Architecture (ISA) Reference Manual
The memory error check register (MECR), shown in Figure 4–16 with further description
in Table 4–97, contains syndrome bits that indicate what error occurred. For data memo-
ries, all four check fields are used so that all bytes may be covered. For instruction
memories or for cache tags, only the Check 0 field is used.
When the ErrEnab bit of the MESR register is set and the RCE or MemE bit of the MESR
register is turned on, this register contains error syndromes. For parity memories, the er-
ror syndrome is ’1’ corresponding to a parity error and ’0’ corresponding to no parity er-
ror. For ECC memories, the error syndrome is a set of bits equal in length to the number
of check bits associated with that portion of memory. The bits are all zero where there is
Memory Type
4Memory type to which the access with memory error was directed.
0 → Error in instruction RAM 0.
1 → Error in data RAM 0.
2 → Error in instruction cache data array.
3 → Error in data cache data array
4 → Error in instruction RAM 1.
5 → Error in data RAM 1.
6 → Error in Instruction cache tag array.
7 → Error in data cache tag array
8-15 → Reserved
When RCE or MemE is set, this field contains a pointer to the memory which caused
the memory error.
Memory Type is set by hardware whenever MemE is clear, RCE is clear, and a
correctable error is fixed in hardware or whenever a memory exception is raised.
Error Type
2Type of memory error.
0 → Reserved
1 → Parity error
2 → Correctable ECC error
3 → Uncorrectable ECC error
When RCE or MemE is set, this field contains an indicator of the type of memory error
which caused the memory error.
Error Type is set by hardware whenever MemE is clear, RCE is clear, and a
correctable error is fixed in hardware or whenever a memory exception is raised.
*
Reserved for future use
Writing a non-zero value to one of these fields results in undefined processor behavior.
These bits read as undefined.
Table 4–96. MESR Register Fields
(continued)
Field Width
(bits) Definition
1. In some implementations the bits used with ECC may exist as state bits without effect even when only parity is configured.
Chapter 4. Architectural Options
Xtensa Instruction Set Architecture (ISA) Reference Manual 135
no error. Non-zero values give more information about which bit or bits are in error. The
exact encoding depends on the implementation. See the Xtensa Microprocessor Data
Book for more information on the encoding.
When the ErrTest bit of the MESR register is set, MECR is loaded by every L32I,
L32I.N, LICT, LICW, and LDCT instruction with the actual check bits which have been
read from memory. When the ErrTest bit of the MESR register is set, the fields of MECR
are used by the S32I, S32I.N, SICT, SICW, and SDCT instructions to write the memory
check bits. Operation of other memory access instructions is not defined when ErrTest
is set. Operation is not defined if both ErrEnab and ErrTest are set.
Error addresses are reported with reference to the 32-bit word containing the error re-
gardless of the size of the access and for all errors MEVADDR contains an address
aligned to 32-bits. For data memories, the check field(s) in MECR corresponding to the
damaged byte(s) contains a non-zero syndrome. For tag memories and instruction
memories, the Check 0 field of MECR contains the syndrome for the entire word. Errors
in portions of the word not actually used by the access may or may not be reported in
MECR.
Figure 4–16. MECR Register Format
31 29 28 24 23 21 20 16 15 13 12 8 7 6 0
*Check 3 *Check 2 *Check 1 *Check 0
35353517
Table 4–97. MECR Register Fields
Field Width
(bits) Definition
Check 3
5Check bits for the high order byte of a 32 bit data word.
This field is valid for accesses to data RAM and data cache. It contains 5 check bits for
ECC memories and 1 check bit (at the right end of the field) for parity memories. The
field is associated with the highest address byte in little endian processors and the
lowest address byte in big endian processors.
Check 2
5Check bits for the next high order byte of a 32 bit data word.
This field is valid for accesses to data RAM and data cache. It contains 5 check bits for
ECC memories and 1 check bit (at the right end of the field) for parity memories. The
field is associated with the second highest address byte in little endian processors and
the second lowest address byte in big endian processors.
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136 Xtensa Instruction Set Architecture (ISA) Reference Manual
The memory error virtual address register (MEVADDR), shown in Figure 4–17, contains
address information regarding the location of the error. Table 4–98 details its contents as
a function of two fields of the MESR register. For errors in cache tags and for errors in
castout data, MEVADDR contains only index information. Along with the Way Number
field in MESR, this allows the incorrect memory bits to be located. For errors in instruc-
tions or data being accessed, MEVADDR contains the full virtual address used by the in-
struction. Along with other status information, MEVADDR is written when the ErrEnab bit
of the MESR register is set and the RCE or MemE bit of the MESR register is turned on.
Figure 4–17. MEVADDR Register Format
Check 1
5Check bits for the next low order byte of a 32 bit data word.
This field is valid for accesses to data RAM and data cache. It contains 5 check bits for
ECC memories and 1 check bit (at the right end of the field) for parity memories. The
field is associated with the second lowest address byte in little endian processors and
the second highest address byte in big endian processors.
Check 0
7Check bits for the low order byte of a 32 bit data word.
For accesses to data RAM and data cache this field contains 5 check bits for ECC
memories and 1 check bit (at the right end of the field) for parity memories and is
associated with the lowest address byte in little endian processors and the highest
address byte in big endian processors.
For accesses to instruction RAM, instruction cache and all cache tags, this field
contains 7 check bits for ECC memories and 1 check bit (at the right end of the field)
for parity memories and covers the whole 32-bit word or tag.
*
Reserved for future use
Writing a non-zero value to one of these fields results in undefined processor behavior.
These bits read as undefined.
31 0
Memory Error Virtual Address
32
Table 4–98. MEVADDR Contents
MESR Memory Type MESR Access Type MEVADDR Contents
Instruction RAM nFull virtual address used in instruction.
Data RAM nFull virtual address used in instruction.
1. For LICW instructions or Isolate cache attributes, only the index and way bits along with lower order bits are valid.
Table 4–97. MECR Register Fields
(continued)
Field Width
(bits) Definition
Chapter 4. Architectural Options
Xtensa Instruction Set Architecture (ISA) Reference Manual 137
4.5.15.3 The Exception Registers
Three of the new registers created by this option are used in order to be able to take a
memory error exception at any time and return. As an exception, memory error cannot
be masked except by the MESR.ErrEnab bit. Whenever the exception is taken, the PC
of the instruction taking the error is saved in the MEPC register, the PS register is saved
in the MEPS register, and the MESAVE register is available for software use in the excep-
tion handler.
When an actual memory error exception is taken, the MEPC and MEPS registers are load-
ed with the original values of PC and PS, and then PS.INTLEVEL is raised to NLEVEL so
that all interrupts except NMI are masked and the PS.EXCM bit is set so that an ordinary
exception will cause a double exception. When hardware corrects a correctable memory
error, these actions are not taken, allowing memory error corrections even in the memo-
ry error exception handler.
A memory error exception may be taken at any time. This means that, even without
hardware correction, a memory error can be handled any time except during a memory
error handler. With hardware correction, only an uncorrectable memory error taken dur-
ing a handler for another uncorrectable memory error is fatal.
4.5.15.4 Memory Error Semantics
Memory errors have the following semantics:
procedure MemoryError
return if !MESR.ErrEnab
exc ← ParityError | UncorrectableECCError
exc ← 1 if !MESR.MemE & MESR.InsExc & AccessType = IFetch
exc ← 1 if !MESR.MemE & MESR.DatExc & AccessType ≠ IFetch
MESR.ILCE ← 1 if exc & MESR.RCE & MESR.AccessType = IFetch
MESR.DLCE ← 1 if exc & MESR.RCE & MESR.AccessType ≠ IFetch
MESR.ILCE ← 1 if !exc & MESR.RCE & AccessType = IFetch
MESR.DLCE ← 1 if !exc & MESR.RCE & AccessType ≠ IFetch
Instruction cache tag array Index bits are valid, other bits are undefined.
Instruction cache data array Full virtual address used in instruction.1
Data cache tag array Index bits are valid, other bits are undefined.
Data cache data array LoadStore Full virtual address used in instruction.1
Data cache data array Castout Index bits are valid, other bits are undefined.
Table 4–98. MEVADDR Contents
(continued)
MESR Memory Type MESR Access Type MEVADDR Contents
1. For LICW instructions or Isolate cache attributes, only the index and way bits along with lower order bits are valid.
Chapter 4. Architectural Options
138 Xtensa Instruction Set Architecture (ISA) Reference Manual
MESR.ILCE ← 1 if !exc & MESR.MemE & AccessType = IFetch
MESR.DLCE ← 1 if !exc & MESR.MemE & AccessType ≠ IFetch
if exc | !MESR.RCE then
MESR.WayNumber ← WayNumber
MESR.AccessType ← AccessType
MESR.MemoryType ← MemoryType
MESR.ErrorType ← ErrorType
MECR ← CheckBits
if MESR.AccessType = Castout then
MEVADDR ← Undefined||CacheIndex||Undefined
elsif MESR.MemoryType = Tag then
MEVADDR ← Undefined||CacheIndex||Undefined
else
MEVADDR ← VAddr
endif
MESR.RCE ← !exc
endif
if exc then
MESR.DME ← MESR.MemE
MESR.MemE ← 1
MEPC ← PC
MEPS ← PS
nextPC ← MemoryErrorExceptionVector
PS.INTLEVEL ← NLEVEL
PS.EXCM ← 1
endif
endprocedure MemoryError
4.6 Options for Memory Protection and Translation
Xtensa processors employ one of the options in this section for memory protection and
translation. The introduction in Section 4.6.1 provides background information for the
options in this section. The Region Protection Option described in Section 4.6.3 pro-
vides control of memory by 512 MB regions. Within each region, accessibility, cacheabil-
ity, and characteristics of cacheability can be controlled. The Region Translation Option
described in Section 4.6.4 builds on that and adds a translation table with an entry for
each region so that virtual addresses in that region can be translated to corresponding
physical addresses in any of the 512 MB regions. The MMU Option described in
Section 4.6.5 is a full paging memory management unit. It supports hardware refill of the
TLB from page tables in memory.
Chapter 4. Architectural Options
Xtensa Instruction Set Architecture (ISA) Reference Manual 139
4.6.1 Overview of Memory Management Concepts
Section 4.6.1.1 gives an overview of the basic memory translation scheme used in
Xtensa processors. Section 4.6.1.2 gives an overview of the basic memory protection
scheme used in Xtensa processors, and Section 4.6.1.3 gives an overview of the con-
cept of attributes. These subsections take a broader view of the overall process and in-
dicate the direction future memory protection and translation options may take.
4.6.1.1 Overview of Memory Translation
This subsection presents an overview of the thinking behind the memory translation in
the available options. It also provides insight into the kinds of extensions that are likely
in the future.
The available memory protection and translations options that support virtual-to-physical
address translation do so via an instruction TLB and a data TLB. (“TLB” was originally
an acronym for translation lookaside buffer, but this meaning is no longer entirely accu-
rate; in this document TLB simply means the translation hardware.) These two hardware
structures may, in some configurations, act as translation caches that are refilled by
hardware from a common page table structure in memory. In other configurations, a TLB
may be self-sufficient for its translations, and no page tables are required.
A TLB consists of several entries, each of which maps one page (the page size may
vary with each entry). Virtual-to-physical address translation consists of searching the
TLB for an entry that matches the most significant bits of the virtual address and replac-
ing those bits with bits from the TLB entry. The least significant bits of the virtual address
are identical between the virtual and physical addresses. The translation input and out-
put are called the virtual page number (VPN) and the physical page number (PPN) re-
spectively. The TLB search also involves matching the address space identifier (ASID)
bits of the TLB entry to one of the current ASIDs stored in the RASID register (more on
this below). The number of bits not translated is determined by the page size, which can
be dynamically programmed from a set of configuration specified values. The TLB entry
also supplies some attribute bits for the page, including bits that determine the cache-
ability of the page’s data, whether it is writable or not, and so forth. This is illustrated in
Figure 4–18.
It is illegal for more than one TLB entry to match both the virtual address and the ASID.
This is true even if the entries have different ASIDs which match at different ring levels.
Software is responsible for making sure the address range of all TLB entries visible ac-
cording to the ASID values in the RASID register never overlap. Implementations may
detect this situation and take a MultiHit exception in this situation to aid in debugging.
Chapter 4. Architectural Options
140 Xtensa Instruction Set Architecture (ISA) Reference Manual
The instruction and data TLBs can be configured independently for most parameters,
which is appropriate because the instruction and data references of processors can
have fairly different requirements, and in some systems additional flexibility may be ap-
propriate on one but not the other. However, when the two TLBs both refill from the com-
mon memory page table, the associated parameters are shared.
Figure 4–18. Virtual-to-Physical Address Translation
Xtensa implementations may perform virtual-to-physical address translation in parallel
or series with cache, RAM, ROM, and XLMI access. However, the translated physical
address is always used to decide which cache, RAM, or ROM access to use. Thus cach-
es are potentially virtually indexed, even though they are always physically tagged.
When the number of cache index bits (that is log2(CacheBytes/WayCount)) is
greater than a page index and the same physical memory is mapped at multiple virtual
addresses, there is the possibility of multiple cache locations being used for the same
physical memory line, which can lead to the multiple views of memory being inconsis-
tent. In such a system, software typically avoids this situation by restricting the virtual
addresses for multiply mapped physical memory. This software restriction is often re-
ferred to as “page coloring.” If physically indexed caches are necessary (and generally
they are not), the system designer may configure the TLBs such that cache index is a
physical address by using a large page size or a high cache associativity so that the
cache index bits are within the portion of the virtual and physical addresses that are
identical.
ASID3
ASID2 VABITS-1 0
VPN Page Index
TLB
ASID1
ASID0
Attributes
RASID
Virtual Address
PABITS-1 0
PPN Page Index
Physical Address
Chapter 4. Architectural Options
Xtensa Instruction Set Architecture (ISA) Reference Manual 141
The TLBs are N-way set-associative structures with heterogeneous “ways” and a config-
urable N. Each way has its own parameters, such as the number of entries, page
size(s), constant or variable virtual address, and constant or variable physical address
and attributes. It is the ability to specify constant translations in some or all of the ways
that allows Xtensa’s TLBs to span smoothly from a fixed memory map to a fully pro-
grammable one. Fully or partially constant entries can be converted to logic gates in the
TLB at significantly lower cost than a run-time programmable way. In addition, even pro-
cessors with generally programmable MMUs often have a few hardwired translations.
Xtensa can easily represent these hardwired translations with its constant TLB entries.
Xtensa actually requires a few constant TLB entries to provide translation in some cir-
cumstances, such as at reset and during exception handling.
The virtual address input to the TLBs is actually the catenation of an address space
identifier (ASID) specified in a processor register with the 32-bit virtual address from the
fetch, load, or store address calculation. ASIDs allow software to change the address
space seen by the processor (for example, on a context switch) with a simple register
write without changing the TLB contents. The TLB stores an ASID with each entry, and
so can simultaneously hold translations for multiple address spaces. The number of
ASID bits is configurable. ASIDs are also an integral part of protection, as they specify
the accessibility of memory by the processor at different privilege levels, as described in
the next section.
Xtensa TLBs do not have a separate valid bit in each entry. Instead, a reserved ASID
value of 0 is used to indicate an invalid entry. This can be viewed as saving a bit, or as
almost doubling the number of ASIDs for the same number of hardware bits stored in a
TLB entry.
Non-constant ways may be configured as AutoRefill. If no entry matching an access is
found in a TLB with one or more AutoRefill ways, the processor will attempt to load a
page table entry (PTE) from memory and write it into an entry of one of the AutoRefill
ways. A TLB with no AutoRefill ways does not use the page table.
Each way of a TLB is configured with a list of page sizes (expressed as the number of
bits in a page index). If the list has one element, the page size for that way is fixed. If the
list has more than one element, the page size of the way may be varied at runtime via
the ITLBCFG or DTLBCFG registers. When AutoRefill ways have programmable page
size, the PTE has a page size field (the value is an index into the PTEPageSizes con-
figuration parameter), and hardware refill restricts the refill way selection to ways pro-
grammed with a page size matching the page size in the PTE. When looking up an ad-
dress in the TLB, each way’s page size determines which bits are used to select one of
the way’s entries for comparison: vAddrP+log2(IndexCount)-1..P is the way index where P is
the number of bits configured or programmed for the way page size.
Chapter 4. Architectural Options
142 Xtensa Instruction Set Architecture (ISA) Reference Manual
4.6.1.2 Overview of Memory Protection
Many processors implement two levels of privilege, often called kernel and user, so that
the most privileged code need not depend on the correctness of less privileged code.
The operating system kernel has access to the entire processor, but disables access to
certain features while application code runs to prevent the application from accessing or
corrupting the kernel or other applications. This mechanism facilitates debugging and
improves system reliability.
Some processors implement multiple levels of decreasing privilege, called rings, often
with elaborate mechanisms for switching between rings. The Xtensa processor provides
a configurable number of rings (RingCount), but without the elaborate ring-to-ring tran-
sition mechanisms. When configured with two rings, it provides the common kernel/user
modes of operation, with Ring 0 being kernel and Ring 1 being user. With three or four
rings configured, the Xtensa processor provides the same functionality as more ad-
vanced processors, but with the requirement that ring-to-ring transitions must be provid-
ed by Ring 0 (kernel) software.
Without the MMU Option, or with the MMU Option and RingCount = 1, the Xtensa pro-
cessor has a single level of privilege, and all instructions are always available.
With RingCount > 1, software executing with CRING = 0 (see Table 4–63 on page 87
and the description of PS.EXCM) is able to execute all Xtensa instructions; other rings
may only execute non-privileged instructions. The only distinction between the rings
greater than zero is those created by software in the virtual-to-physical translations in
the page table. The name “ring” is derived from an accessibility diagram for a single pro-
cess such as that shown in Figure 4–19. At Ring 0 (that is, when CRING = 0), the pro-
cessor can access all of the current process’ pages (that is, Ring 0 to RingCount-1
pages). At Ring 1 it can access all Ring 1 to RingCount-1 pages. Thus, when the pro-
cessor is executing with Ring 1 privileges, its address space is a subset of that at Ring 0
privilege, as Figure 4–19 illustrates. This concentric nesting of privilege levels continues
to ring
RingCount-1, which can access only ring RingCount-1 pages.
It is illegal for more than one TLB entry to match both the virtual address and the ASID.
This is true even if the entries have different ASIDs which match at different ring levels.
One ring’s mapping cannot not override another.
It is illegal for two or more TLB entries to match a virtual address, even if they are at dif-
ferent ring levels; one ring’s mapping cannot not override another.
Systems that require only traditional kernel/user privilege levels can, of course, config-
ure RingCount to be 2. However, rings can also be useful for sharing. Many operating
systems implement the notion of multiple threads sharing an address space, except for
Chapter 4. Architectural Options
Xtensa Instruction Set Architecture (ISA) Reference Manual 143
a small number of per-thread pages. Such a system could use Ring 0 for the shared ker-
nel address space, Ring 1 for per-process kernel address space, Ring 2 for shared ap-
plication address space, and Ring 3 for per-thread application address space.
Figure 4–19. A Single Process’ Rings
Each Xtensa ring has its own ASID. Ring 0’s ASID is hardwired to 1. The ASIDs for
Rings 1 to RingCount-1 are specified in the RASID register. The ASIDs for each ring
in RASID must be different. Each ASID has a single ring level, though there may be
many ASIDs at the same ring level (except Ring 0). This allows nested privileges with
sharing such as shown in Figure 4–20. The ring number of a page is not stored in the
TLB; only the ASID is stored. When a TLB is searched for a virtual address match, the
ASIDs of all rings specified in RASID are tried. The position of the matching ASID in
RASID gives the ring number of the page. If the page’s ring number is less than the pro-
cessor’s current ring number (CRING), then the access is denied with an exception (ei-
ther InstFetchPrivilegeCause or LoadStorePrivilegeCause, as appropriate).
Figure 4–20. Nested Rings of Multiple Processes with Some Sharing
Ring 1
•
•
•
N-1
Ring 0
Ring 1
•
•
•
N-1
Ring 1
•
•
•
N-1
•
•
•
N-1
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144 Xtensa Instruction Set Architecture (ISA) Reference Manual
Why not store the ring number of the page in the TLB, and then use a single ASID for all
rings, instead of having an ASID per ring? Because the latter allows sharing of TLB en-
tries, and the former does not. For example, it is desirable at the very least to reuse the
same TLB entries for all kernel mapped addresses, instead of having the same PTEs
loaded into the TLB with different ASIDs. The Xtensa mechanism is more general than
adding a “global” bit to each entry (to ignore the ASID match) in that it allows finer gran-
ularity, as Figure 4–20 illustrates, not just all or nothing.
The kernel typically assigns ASIDs dynamically as it runs code in different address spac-
es. When no more ASIDs are available for a new address space, the kernel flushes the
Instruction and Data TLBs, and begins assigning ASIDs anew. For example, with
ASIDBits = 8 and RingCount = 2, a TLB flush need occur at most every 254 context
switches, if every context switch is to a new address space.
Note that CRING = 0 is the only requirement for privileged instructions to execute and
CRING is the only field that controls access to memory. The PS.UM bit is named User
Vector Mode and has nothing to do with privilege for either instructions or memory ac-
cess. It controls only which exception vector is taken for general exceptions.
4.6.1.3 Overview of Attributes
Both page table entries (PTEs) and TLB entries store attribute bits that control whether
and how the processor accesses memory. The number of potential attributes required
by systems is large; to encode all the access capabilities required by any potential sys-
tem would make this field too big to fit into a 4-byte PTE. However, the subset of values
required for any particular system is usually much smaller. Each memory protection and
translation option has a set of attributes, each of which encodes a set of capabilities
from Table 4–99 for loads along with a set for stores and a set for instruction fetches.
More capabilities are likely to be added in future implementations.
Table 4–99. Access Characteristics Encoded in the Attributes
Characteristic Description Used by
Invalid Exception on access Fetch, Load, Store
Isolate Read/write cache contents regardless of tag compare Load, Store
Bypass Ignore cache contents regardless of tag compare — always
access memory for this page
Fetch, Load, Store
No-allocate Do not refill cache on miss Fetch, Load, Store
Write-through Write memory in addition to DataCache Store
Guarded
Access bytes on this page exactly when required by the
program (i.e. neither speculative references to reduce latency
nor multiple accesses are allowed).
Load1
1. Instruction fetch is always non-guarded. Stores are always guarded.
Chapter 4. Architectural Options
Xtensa Instruction Set Architecture (ISA) Reference Manual 145
The assignment of capabilities to the attribute field of PTEs may be done with only one
encoding for each distinct set of capabilities, or in such a way that each characteristic
has its own bit, or anything in between. Often, single bits are used for a valid bit and a
write-enable. For a valid bit, all of the attribute values with this bit zero would specify the
Invalid characteristic so that any access causes an InstFetchProhibitedCause,
LoadProhibitedCause, or StoreProhibitedCause exception, depending on the
type of access. Similarly for the write-enable bit, all attribute values with write-enable
zero would specify the Invalid characteristic to cause a StoreProhibitedCause
exception on any store.
For systems that implement demand paging, software requires a page dirty bit to indi-
cate that the page has been modified and must be written back to disk if it is replaced.
This may be provided by creating a write-enable bit as described above, and using it as
the per-page dirty bit. The first write to a clean (non-dirty) page causes a
StoreProhibitedCause exception. The exception handler checks one of the soft-
ware bits, which indicates whether the page is really writable or not; if it is, it then sets
the hardware write-enable bit in both the TLB and the page table, and continues execu-
tion.
4.6.2 The Memory Access Process
All accesses to memory, whether to cache, local memories, XLMI, or PIF and whether
caused by instruction fetch, the instructions themselves, or hardware TLB refill, follow
certain steps. Following is a short description of these steps; each is discussed in more
detail in Section 4.6.2.1 through Section 4.6.2.6.
1. Choose the TLB: Determine from the instruction opcode or the reason for hard-
ware access, which TLB if any, is used for the access (see Section 4.6.2.1 on
page 146 for details).
2. Lookup in the TLB: In that TLB, find an entry whose virtual page number
matches the upper bits of the virtual address of the access and, for appropriate
options, whose ASID matches one of the entries in the RASID register. Exactly
one match is needed to continue beyond this point, although exceptions may be
handled and the memory access process restarted (see Section 4.6.2.2 on
page 147 for details).
3. Check the access rights: If the attribute is invalid or, for appropriate options, if
the ring corresponding the ASID matched in the RASID register is too low, raise
an exception. The operating system may, among other choices, modify the TLB
entries and retry the access (see Section 4.6.2.3 on page 148 for details).
4. Direct the access to local memory: If the physical address of the access
matches an instruction RAM or ROM, a data RAM or ROM, or an XLMI port then
direct the access to that local memory or XLMI. An exception is possible at this
stage for certain conditions, such as attempting to write to a ROM (see
Section 4.6.2.4 on page 148 for details).
Chapter 4. Architectural Options
146 Xtensa Instruction Set Architecture (ISA) Reference Manual
5. Direct the access to PIF: For the given cache configuration and using the at-
tribute, determine whether to execute the required access on the processor in-
terface bus (PIF) and make that access if necessary (see Section 4.6.2.5 on
page 150 for details).
6. Direct the access to cache: Using the cache that corresponds to the TLB in
Step 1 above, look up the memory location in the cache, using the value if it is
there. If not, fill the cache from the PIF and then do the access (see
Section 4.6.2.6 on page 150 for details).
Logically, the steps are done in order. The TLB lookup is done first (in steps 1 through 3
above) and the memory access afterwards (in steps 4 through 6 above). For perfor-
mance reasons, they are actually done in parallel. This has two consequences:
1. First, the virtual and physical addresses of an access to an XLMI port must be iden-
tical so that the full address can be provided at the desired time.
2. Second, for all other local memory accesses and cacheable addresses, the index
bits of the cache or local memory must be the same in both virtual and physical ad-
dress. This means that caches which contain ways larger than the smallest page
size in the system require “page coloring” as described in Section 4.6.1.1 on
page 139.
For local memories, the second consequence requires a similar restriction on how they
can be mapped. Note that local memories do not require that sequential virtual pages be
mapped to sequential physical pages, but only that each virtual page be mapped to a
physical page with which it shares the values of index bits.
For the purposes of understanding exceptions raised by memory accesses, all the steps
above are done sequentially and the first exception encountered takes priority over later
ones. For performance reasons, again, all steps are done in parallel and the results pri-
oritized afterward.
The above steps are further expanded in the following subsections.
4.6.2.1 Choose the TLB
Several instructions do not actually address memory. They simply use the bits of an ad-
dress to access a cache and do something directly to it. The following groups of instruc-
tions have this property:
-III, IIU
-DII, DIU, DIWB, DIWBI
-LICT, SICT, LICW, SICW
-LDCT, SDCT
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Xtensa Instruction Set Architecture (ISA) Reference Manual 147
For each of these instructions, no TLB is accessed and the remainder of the steps are
not followed. No memory access exceptions are possible as the addresses are not really
addresses but only pointers to cache locations.
For the data accesses of instructions IHI, IHU, IPF, and IPFL, as well as all instruction
fetches, the instruction TLB is used for subsequent steps.
For the data accesses of all other instructions and for the hardware TLB refill accesses
(regardless of which TLB is being refilled) the data TLB is used for subsequent steps.
The above choices are reflected in Table 4–100 in the second column.
For compatibility the two TLBs should never give conflicting translations or protection at-
tributes for any access as future processors may implement them with only a single set
of entries.
4.6.2.2 Lookup in the TLB
Each TLB lookup takes a virtual address as an operand and produces a physical ad-
dress, a lookup ring, and attributes as a result. This process is described in more detail
in Section 4.6.1.1. Each way of the TLB is read using the appropriate address bits for
that way as index bits. For variable sized ways, the ITLBCFG or DTLBCFG register helps
determine which address bits are the index bits.
For options without ASIDs (Region Protection Option), a way matches the access if its
virtual page number (VPN) matches the VPN of the access. The lookup ring produced is
defined to be 0.
For options with ASIDs (MMU Option), a way matches the access if its Virtual Page
Number (VPN) matches the VPN of the access and the ASID of the way matches one of
the ASIDs in the RASID register. The lookup ring is determined by which ASID in the
RASID register is matched. Because the four entries in the RASID register are required
to be different and non-zero, the lookup ring is well determined.
There should not be a match for more than one of the ways. However, this condition cur-
rently raises an InstTLBMultiHitCause or a LoadStoreTLBMultiHitCause ex-
ception as a debugging aid. If two entries contain the same VPN, but different ASIDs,
they may co-exist in the TLB at the same time as long as the RASID never contains both
ASIDs at the same time.
If none of the ways match, options without auto-refill ways (Region Protection Option)
will raise an InstTLBMissCause or a LoadStoreTLBMissCause exception so that
system software can take appropriate action and possibly retry the access. Options with
auto-refill ways (MMU Option) will, automatically in hardware, use PTEVADDR to access
page tables in memory and replace an entry in one of the auto-refill ways. The access
will then be automatically retried. An error of any sort during the automatic refill process
Chapter 4. Architectural Options
148 Xtensa Instruction Set Architecture (ISA) Reference Manual
will raise an InstTLBMissCause or a LoadStoreTLBMissCause exception to be
raised so that system software can take appropriate action and possibly retry the ac-
cess.
If no exception is raised, the physical page number and attributes of the matching entry
along with the lookup ring defined above are the results of the lookup and the access
continues with the next step.
4.6.2.3 Check the Access Rights
First, the lookup ring of the entry is checked against the ring of the access. The ring of
the access is usually CRING, but for L32E and S32E, for example, it is PS.RING instead.
If the lookup ring of the entry is smaller than the ring of the access, an
InstFetchPrivilegeCause or a LoadStorePrivilegeCause exception is raised.
This situation means that an instruction has attempted access to a region of memory at
a lower numbered ring than the one for which it has privilege.
Second, the attribute of the lookup is checked for validity. If the attribute is not valid, an
exception is raised. If the access chose the Instruction TLB in Section 4.6.2.1, it raises
an InstFetchProhibitedCause exception. If it chose the data TLB, it raises either a
LoadProhibitedCause exception or a StoreProhibitedCause exception, depend-
ing on whether it was a load or a store.
If no exception is raised, the access continues with the next step using the physical ad-
dress and the attribute (which is known to be valid for access, but may still affect how
caches are used).
4.6.2.4 Direct the Access to Local Memory
The physical address of each access is compared to the address ranges of any instruc-
tion RAM, instruction ROM, data RAM, data ROM, or XLMI options that may exist in the
processor. Table 4–100 indicates what will happen in the case that an access initiated
by what is indicated in the Instruction column (which will use the TLB in the second col-
umn) if its address compares to an (abbreviated) option in one of the last six columns.
OK means the access is completed normally. NOP means the access is completed but
by its nature does nothing. IFE and LSE mean that an exception is raised. TLBI and
TLBD mean that an InstTLBMissCause or a LoadStoreTLBMissCause exception is
raised. Undef means the behavior is not defined.
Chapter 4. Architectural Options
Xtensa Instruction Set Architecture (ISA) Reference Manual 149
Using the definition of guarded in Table 4–99, instruction-fetch accesses are never
guarded. Stores are always guarded. Loads to instruction RAM, instruction ROM, data
RAM, and data ROM are never guarded. These ports are assumed to be connected only
to devices with memory semantics so that no guarding is needed for loads. Loads to
Table 4–100. Local Memory Accesses
Instruction TLB Used
1
Inst-
RAM
Inst-
ROM
Data-
RAM
Data-
ROM XLMI
Instruction-fetch ITLB OK OK IFE2IFE2IFE2
IHI, IHU, IPF ITLB NOP NOP NOP NOP NOP
III, IIU none —————
IPFL ITLB IFE5IFE5IFE2IFE2IFE2
L32I, L32R DTLB OK3OK3OK OK OK
L8UI, L16SI, L16UI, L32AI,
L32E, FP Loads, MAC16 Loads
DTLB LSE4LSE4OK OK OK
LICT, LICW, LDCT none —————
S32I DTLB OK3LSE4OK LSE4OK
S8I, S16I, S32E, S32RI, FP
Stores
DTLB LSE4LSE4OK LSE4OK
S32C1I DTLB LSE4LSE4OK7LSE4Undef
SICT, SICW, SDCT none —————
DHI, DHU, DHWB, DHWBI DTLB NOP NOP NOP NOP NOP
DII, DIU, DIWB, DIWBI none —————
DPFR, DPFRO, DPFW, DPFWO DTLB NOP NOP NOP NOP NOP
DPFL DTLB LSE4LSE4LSE6LSE6LSE6
Hardware ITLB Refill DTLB TLBI8TLBI8OK OK OK
Hardware DTLB Refill DTLB TLBD8TLBD8OK OK OK
Designer defined loads DTLB LSE4LSE4OK OK OK
Designer defined stores DTLB LSE4LSE4OK LSE4OK
1. As described in Section 4.6.2.1 on page 146
2. Raises exception - InstFetchErrorCause
3. These accesses may be slow in some implementations.
4. Raises exception - LoadStoreErrorCause
5. Raises exception - InstFetchErrorCause - but not in all implementations
6. Raises exception - LoadStoreErrorCause - but not in all implementations
7. Works in newer implementations but in some older implementations raises an exception.
8. Raises exception - InstTLBMissCause or a LoadStoreTLBMissCause depending on the original access.
Chapter 4. Architectural Options
150 Xtensa Instruction Set Architecture (ISA) Reference Manual
XLMI are only guarded in the sense that the load will be retired only under the conditions
for a guarded access. For all these memories, assertion of the memory enable is no
guarantee that the load was needed.
If none of the comparisons produces a match, the access continues with the next step
using the physical address and the attribute.
4.6.2.5 Direct the Access to PIF
The access is sent to the processor interface if any of the following is true:
The attribute indicates that the cache should be bypassed.
The chosen TLB in Section 4.6.2.1 and in Tab le 4–100 is the ITLB and the Instruc-
tion Cache Option is not configured.
The chosen TLB in Section 4.6.2.1 and in Tab le 4–100 is the DTLB and the Data
Cache Option is not configured.
Using the definition of guarded in Table 4–99 on page 144, instruction-fetch accesses to
the PIF are never guarded. Stores to the PIF are always guarded. Loads that are sent to
the PIF under this section (without being cached) are guarded if the attribute says that
they should be.
If the conditions of this section are not met, the access is cached and continues with the
next step using the physical address and the attribute.
4.6.2.6 Direct the Access to Cache
The access is cached. The attribute determines how the cache operates, including the
possibility of a write-through to the PIF.
The concept of guarding cannot be carried out for loads through the cache. Extra bytes
have been loaded simply to fill the cache line and the line may have been filled long be-
fore the access. Inherently, the line is filled a different number of times than an access is
executed and the line may be invalidated or evicted at any time and refilled later. Cach-
ing should not be used on ranges of memory address where guarding is important.
4.6.3 Region Protection Option
The simplest of the options, the Region Protection Option, provides a protection field for
each of the eight 512 MB regions in the address space. The field can allow access to the
region and it can set caching characteristics for the region, such as whether or not the
cache is used and if it is write-through or write-back.
Prerequisites: Exception Option (page 82)
Chapter 4. Architectural Options
Xtensa Instruction Set Architecture (ISA) Reference Manual 151
Incompatible options: MMU Option (page 158)
This simple option is built from the capabilities discussed in the introduction
(Section 4.6.1). It uses RingCount = 1, so the processor can always execute privileged
instructions. It sets ASIDBits to 0, which disables the ASID feature. The instruction
and data TLBs are programmed to each have one way of eight entries, and the VPNs
(virtual page numbers) and PPNs (physical page numbers) of these entries are constant
and hardwired to the identity map (that is, PPN = VPN). Only the attributes are not con-
stant; they are writable using the WITLB and WDTLB instructions.
4.6.3.1 Region Protection Option Architectural Additions
Table 4–101 through Table 4–103 show this option’s architectural additions.
Table 4–101. Region Protection Option Exception Additions
Exception Description
EXCCAUSE
value
InstFetchProhibitedCause Instruction fetch is not allowed in region 20
LoadProhibitedCause Load is not allowed in region 28
StoreProhibitedCause Store is not allowed in region 29
Table 4–102. Region Protection Option Processor-State Additions
Register
Mnemonic Quantity Width
(bits) Register Name R/W Access
ITLB Entries 8 4 Instruction TLB entries R/W see Table 4–103
DTLB Entries 8 4 Data TLB entries R/W see Table 4–103
Table 4–103. Region Protection Option Instruction Additions
Instruction
1
Format Definition
IDTLB RRR Invalidate data TLB entry
IITLB RRR Invalidate instruction TLB entry
PDTLB RRR Probe data TLB
PITLB RRR Probe instruction TLB
RDTLB0 RRR Read data TLB virtual
RDTLB1 RRR Read data TLB translation
RITLB0 RRR Read instruction TLB virtual
1. These instructions are fully described in Chapter 6, "Instruction Descriptions" on page 243.
Chapter 4. Architectural Options
152 Xtensa Instruction Set Architecture (ISA) Reference Manual
4.6.3.2 Formats for Accessing Region Protection Option TLB Entries
During normal operation when instructions and data are being accessed from memory,
only lookups are being done in the TLBs. For maintenance of the TLBs, however, the
entries in the TLBs are accessed by the instructions in Table 4–103. Note that unused
bits at Bit 12 and above are ignored on write, and zero on read, so that those bits may
simply contain the address for access to all ways of both TLBs. Unused bits at Bit 11 and
below are required to be zero on write and undefined on read for forward compatibility.
The format of the as register used in all instructions in the table is shown in Figure 4–21.
The upper three bits are used as an index among the TLB entries just as they would be
when addressing memory. They are the Virtual Page Number (VPN) or upper three bits
of address. The remaining bits are ignored.
Figure 4–21. Region Protection Option Addressing (
as
) Format for
WxTLB
,
RxTLB1
, &
PxTLB
The WITLB and WDTLB instructions write the TLB entries. The as register is formatted
according to Figure 4–21, while the at register is formatted according to Figure 4–22.
The attribute for the region is described in detail in Section 4.6.3.3. The remaining bits
are ignored or required to be zero.
After modifying any TLB entry with a WITLB instruction, an ISYNC must be executed be-
fore executing any instruction from that region. In the special case of the WITLB chang-
ing the attribute of its own region, the ISYNC must immediately follow the WITLB and
both must be within the same memory region and, if the region is cacheable, within the
same cache line.
RITLB1 RRR Read instruction TLB translation
WDTLB RRR Write data TLB
WITLB RRR Write instruction TLB
31 29 28 0
VPN Ignored
329
Table 4–103. Region Protection Option Instruction Additions
(continued)
Instruction
1
Format Definition
1. These instructions are fully described in Chapter 6, "Instruction Descriptions" on page 243.
Chapter 4. Architectural Options
Xtensa Instruction Set Architecture (ISA) Reference Manual 153
Figure 4–22. Region Protection Option Data (
at
) Format for
WxTLB
The RITLB0 and RDTLB0 instructions exist under this option but do not return interest-
ing information because the entire VPN is used as an index. The as register is formatted
according to Figure 4–21. The read instructions return zero in the at register.
The RITLB1 and RDTLB1 instructions return the at data format in Figure 4–23. The At-
tribute for the region is described in detail in Section 4.6.3.3. The VPN is returned in the
upper three bits as the Physical Page Number (PPN) because there is no translation.
The remaining bits are zero or undefined. The as register is formatted according to
Figure 4–21.
Figure 4–23. Region Protection Option Data (
at
) Format for
RxTLB1
The PITLB and PDTLB instructions exist under this option but do not return interesting
information because all accesses hit in the respective TLBs and the TLBs have only a
single way. The as register is formatted according to Figure 4–21. The TLB probe in-
structions return the at data format in Figure 4–24. The VPN is returned in the upper
bits. The low bit is set because the probe always hits and the remaining bits are zero or
undefined.
Figure 4–24. Region Protection Option Data (
at
) Format for
PxTLB
The IITLB and IDTLB instructions exist under this option and their as register is for-
matted according to Figure 4–21, but they have no effect because the entries cannot be
removed from the respective TLBs.
31 12 11 4 3 0
Ignored Zero Attribute
20 8 4
31 29 28 12 11 4 3 0
PPN Zero Undefined Attribute
317 8 4
31 29 28 12 11 1 0
VPN Zero Undefined 1
317 11 1
Chapter 4. Architectural Options
154 Xtensa Instruction Set Architecture (ISA) Reference Manual
4.6.3.3 Region Protection Option Memory Attributes
The memory attributes written into the TLB entries by the WxTLB instructions and read
from them by the RxTLB1 instructions control access to memory and, where there is a
cache, how the cache is used. Table 4–104 shows the meanings of the attributes for in-
struction fetch, data load, and data store. For a more detailed description of the memory
access process and the place of these attributes in it, see Section 4.6.2.
The first column in Table 4–104 indicates the attribute attribute from the TLB while the
remaining columns indicate various effects on the access. The columns are described in
the following bullets:
Attr — the value of the 4-bit Attribute field of the TLB entry.
Rights — whether the TLB entry may successfully translate a data load, a data
store, or an instruction fetch.
- The first character is an r if the entry is valid for a data load and a dash ("-")if
not.
- The second character is a w if the entry is valid for a data store and a dash
("-")if not.
- The third character is an x if the entry is valid for an instruction fetch and a dash
("-")if not.
If the translation is not successful, an exception is raised.
Local memory accesses (including XLMI) consult only the Rights column.
WB — some rows are split by whether or not the configured cache is writeback or
not. Rows without an entry apply to both cache types.
Meaning for Cache Access — the verbal description of the type of access made to
the cache.
Access Cache — indicates whether the cache provides the data.
- The first character is an h if the cache provides the data when the tag indicates
hit and a dash ("-")if it does not.
- The second character is an m if the cache provides the data when the tag indi-
cates a miss and a dash ("-")if it does not. This capability is used only for Iso-
late mode.
Fill Cache — indicates whether an allocate and fill is done to the cache if the tag in-
dicates a miss.
- The first character is an r if the cache is filled on a data load and a dash ("-")if
it is not.
- The second character is a w if the cache is filled on a data store and a dash ("-
")if it is not.
- The third character is an x if the cache is filled on an instruction fetch and a
dash ("-")if it is not.
Chapter 4. Architectural Options
Xtensa Instruction Set Architecture (ISA) Reference Manual 155
Guard Load — refers to the guarded attribute as described in Table 4–99 on
page 144. Stores are always guarded and instruction fetches are never guarded, but
loads are guarded where there is a “yes” in this column. Local memory loads are not
guarded.
Write Thru — indicates whether a write is done through the PIF interface.
- The first character is an h if a Write Thru occurs when the tag indicates hit and a
dash ("-")if it does not.
- The second character is an m if a Write Thru occurs when the tag indicates a
miss and a dash ("-")if it does not.
Writes to local memories are never Write-Thru. In most implementations, a write-thru will
only occur after any needed cache fill is complete.
All attribute entries in the ITLB and DTLB are set to cache bypass (4’h2) after reset.
In the absence of the Instruction Cache Option, Cached regions behave as Bypass re-
gions on instruction fetch. In the absence of the Data Cache Option, Cached regions be-
have as Bypass regions on data load or store. If the Data Cache is not configured as
writeback (Section 4.5.5.1 on page 119) Attributes 4 and 5 behave as Attribute 1 instead
of as they are listed in Table 4–104.
After changing the attribute of any memory region with a WITLB instruction, an ISYNC
must be executed before executing any instruction from that region. In the special case
of the WITLB changing the attribute of its own region, the ISYNC must immediately fol-
low the WITLB and both must be within the same cache line.
Table 4–104. Region Protection Option Attribute Field Values
Attr Rights Meaning for Cache Access Access
Cache
Fill
Cache
Guard
Load
Write
Thru
0rw-Cached, No Allocate h- --- - hm
1rwxCached, WrtThru h- r-x - hm
2rwxBypass cache -- --- yes hm
3--xCached1h- --x - --
4rwxCached, WrtBack alloc h- rwx - --
5rwxCached, WrtBack noalloc1h- r-x - -m
6-13 --- Reserved2————
14 rw- Cache Isolated3hm --- - --
15 --- illegal2-- --- - --
1 Attribute not supported in all implementations. Please refer to a specific Xtensa processor data book for supported attributes.
2 Raises exception. EXCCAUSE is set to InstFetchProhibitedCause, LoadProhibitedCause, or StoreProhibitedCause depending on access type
3 For test only, implementation dependent, uses data cache like local memories and ignores tag.
Chapter 4. Architectural Options
156 Xtensa Instruction Set Architecture (ISA) Reference Manual
After changing the attribute of a region by WDTLB, the operation of loads from and stores
to that region are undefined until a DSYNC instruction is executed.
4.6.4 Region Translation Option
Building on the Region Protection Option is the Region Translation Option, which adds a
virtual-to-physical translation on the upper three bits of the address. Thus, each of the
eight 512 MB regions, in addition to the attributes provided by the Region Protection Op-
tion, may be redirected to access a different region of physical address space.
Prerequisites: Exception Option (page 82) and Region Protection Option (page 150)
Incompatible options: MMU Option (page 158)
With this option, the Physical Page Numbers (PPNs) of each of the TLB entries is now
writable instead of constant and identity mapped. In this way, the same region of memo-
ry may be accessed with different attributes by the use of different virtual addresses.
This simple option is built from the capabilities discussed in the introduction (see
Section 4.6.1). It uses RingCount = 1, so the processor can always execute privileged
instructions. It sets ASIDBits to 0, which disables the ASID feature. The instruction
and data TLBs are programmed to each have one way of eight entries, and only the at-
tributes and Physical Page Numbers (PPNs) are not constant; they are writable using
the WITLB and WDTLB instructions.
4.6.4.1 Region Translation Option Architectural Additions
There are no new exceptions, no new state registers, and no new Instructions added to
those in the Region Protection Option. The TLB entries contain three additional bits of
state. Access to these bits is described in Section 4.6.4.2.
4.6.4.2 Region Translation Option Formats for Accessing TLB Entries
During normal operation when instructions and data are being accessed from memory,
only lookups are being done in the TLBs. For maintenance of the TLBs, however, the
entries in the TLBs are accessed by the instructions in Table 4–103 on page 151. Note
that unused bits at Bit 12 and above are ignored on write and zero on read so that those
bits may simply contain the address for access to all ways of both TLBs. Unused bits at
Bit 11 and below are required to be zero on write and undefined on read for forward
compatibility.
The register formats used by the TLB instructions are very similar to those described in
Section 4.6.3.2 for the Region Protection Option. The only difference is the presence of
a Physical Page Number (PPN) in the upper three bits of the WxTLB, RxTLB1, and
PxTLB register formats.
Chapter 4. Architectural Options
Xtensa Instruction Set Architecture (ISA) Reference Manual 157
The format of the as register used in all instructions in the table is shown in Figure 4–25.
The upper three bits are used as an index among the TLB entries just as they would be
when addressing memory. They are the Virtual Page Number (VPN) or upper three bits
of address. The remaining bits are ignored.
Figure 4–25. Region Translation Option Addressing (
as
) Format for
WxTLB
,
RxTLB1
, &
PxTLB
The WITLB and WDTLB instructions write the TLB entries. The as register is formatted
according to Figure 4–25, while the at register is formatted according to Figure 4–26.
The attribute for the region is described in detail in Section 4.6.3.3 on page 154. The re-
maining bits are ignored or required to be zero.
After modifying any TLB entry with a WITLB instruction, an ISYNC must be executed be-
fore executing any instruction from that region. In the special case of the WITLB chang-
ing the attribute of its own region, the ISYNC must immediately follow the WITLB and
both must be within the same memory region and, if the region is cacheable, within the
same cache line.
After modifying any TLB entry with a WDTLB instruction, the operation of loads from and
stores to that region are undefined until a DSYNC instruction is executed.
Figure 4–26. Region Translation Option Data (
at
) Format for
WxTLB
The RITLB0 and RDTLB0 instructions exist under this option but do not return interest-
ing information because the entire VPN is used as an index. The as register is formatted
according to Figure 4–25. The read instructions return zero in the at register.
The RITLB1 and RDTLB1 instructions return the at data format in Figure 4–27. The at-
tribute for the region is described in detail in Section 4.6.3.3. The Physical Page Number
(PPN) is returned in the upper three bits. The remaining bits are zero or undefined. The
as register is formatted according to Figure 4–25.
31 29 28 0
VPN Ignored
329
31 12 11 4 3 0
PPN Ignored Zero Attribute
317 8 4
Chapter 4. Architectural Options
158 Xtensa Instruction Set Architecture (ISA) Reference Manual
Figure 4–27. Region Translation Option Data (
at
) Format for
RxTLB1
The PITLB and PDTLB instructions return the at data format in Figure 4–28. The Virtual
Page Number (VPN) is returned in the upper bits. The low bit is set because the probe
always hits, and the remaining bits are zero or undefined. The as register is formatted
according to Figure 4–25. These instructions work for their intended purpose, but do not
provide useful information under this simple option because the TLBs always hit and
have only a single way.
Figure 4–28. Region Translation Option Data (
at
) Format for
PxTLB
The IITLB and IDTLB instructions exist under this option and their as register is for-
matted according to Figure 4–25, but they have no effect because the entries cannot be
removed from the respective TLBs.
4.6.4.3 Region Translation Option Memory Attributes
The memory attributes written into the TLB entries by the WxTLB instructions and read
from them by the RxTLB1 instructions are exactly the same as under the Region Protec-
tion Option.
As with the Region Protection Option, all attributes in both TLBs are set to cache bypass
(4’b0010) after reset. In addition, the translation entries in both TLBs are set to identity
map after reset.
4.6.5 MMU Option
The MMU Option is a memory management unit created to run protected operating sys-
tems such as Linux on the Xtensa processor with demand paging hardware with a mem-
ory-based page table.
Prerequisites: Exception Option (page 82)
31 29 28 12 11 4 3 0
PPN Zero Undefined Attribute
317 8 4
31 29 28 1 0
VPN Zero Undefined 1
317 11 1
Chapter 4. Architectural Options
Xtensa Instruction Set Architecture (ISA) Reference Manual 159
Incompatible options: Region Protection Option (page 150), Extended L32R Option
(page 56)
This option is also built from the capabilities discussed in the introduction
(Section 4.6.1). It uses RingCount = 4 and only Ring 0 may execute privileged instruc-
tions. The option sets ASIDBits to 8, which allows for lower TLB management over-
head.
The instruction and data TLBs are programmed to have seven and ten ways, respective-
ly (see Section 4.6.5.3). Some of the ways are constants; others can be set to arbitrary
values. Still others auto-refill from a page table in memory that contains 4-byte PTEs,
each mapping a 4kB page with a 20-bit PPN, a 2-bit ring number, a 4-bit attribute, and 6
bits reserved for software. For a programmer’s view of the MMU, refer to the Xtensa
Microprocessor Programmer’s Guide.
4.6.5.1 MMU Option Architectural Additions
Table 4–105 through Table 4–108 show this option’s architectural additions.
Table 4–105. MMU Option Processor-Configuration Additions
Parameter Description Valid Values
NIREFILLENTRIES Number of auto-refill entries in the ITLB
(divided among 4 ways)
16,32
(4, 8 entries per TLB way)
NDREFILLENTRIES Number of auto-refill entries in the DTLB
(divided among 4 ways)
16,32
(4, 8 entries per TLB way)
IVARWAY56 Ways 5&6 of the ITLB can be variable for
greater flexibility in mapping memory
Variable or Fixed1
DVARWAY56 Ways 5&6 of the DTLB can be varialble
for greater flexitiblity in mapping memory
Variable or Fixed1
1. Implementations may allow only Fixed, only Variable or a choice of either for this value.
Table 4–106. MMU Option Exception Additions
Exception Description
EXCCAUSE
Value
PrivilegedCause Privileged instruction attempted with CRING ≠ 08
InstTLBMissCause Instruction fetch finds no entry in ITLB 16
InstTLBMultiHitCause Instruction fetch finds multiple entries in ITLB 17
InstFetchPrivilegeCause Instruction fetch matching entry requires lower CRING 18
InstFetchProhibitedCause Instruction fetch is not allowed in region 20
LoadStoreTLBMissCause Load/store finds no entry in DTLB 24
Chapter 4. Architectural Options
160 Xtensa Instruction Set Architecture (ISA) Reference Manual
LoadStoreTLBMultiHitCause Load/store finds multiple entries in DTLB 25
LoadStorePrivilegeCause Load/store matching entry requires lower CRING 26
LoadProhibitedCause Load is not allowed in region 28
StoreProhibitedCause Store is not allowed in region 29
Table 4–107. MMU Option Processor-State Additions
Register
Mnemonic Quantity Width
(bits) Register Name R/W
Special
Register
Number
1
PS.RING 1 2 Privilege level (see Table 4–63 on
page 87)
R/W 230
PTEVADDR 132 Page Table Virtual Address R/W 83
RASID 132 Per-ring ASIDs R/W 90
ITLBCFG 12/4 Instruction TLB configuration R/W 91
DTLBCFG 12/4 Data TLB configuration R/W 92
ITLB Entries 24,32,40,482variable Instruction TLB entries R/W Table 4–108
DTLB Entries 27,35,43,512variable Data TLB entries R/W Table 4–108
1. Registers with a Special Register assignment are read and/or written with the RSR, WSR, and XSR instructions. See Tabl e 5–127 on
page 205. The TLB Entries are not Special Registers, but are accessed by the instructions in Table 4–108 on page 160.
2. See Section 4.6.5.3 on page 163 for more information on TLB structure.
Table 4–108. MMU Option Instruction Additions
Instruction
1
Format Definition
IDTLB RRR Invalidate data TLB entry
IITLB RRR Invalidate instruction TLB entry
PDTLB RRR Probe data TLB
PITLB RRR Probe instruction TLB
RDTLB0 RRR Read data TLB virtual
RDTLB1 RRR Read data TLB Translation
RITLB0 RRR Read instruction TLB virtual
1. These instructions are fully described in Chapter 6, "Instruction Descriptions" on page 243.
Table 4–106. MMU Option Exception Additions
(continued)
Exception Description
EXCCAUSE
Value
Chapter 4. Architectural Options
Xtensa Instruction Set Architecture (ISA) Reference Manual 161
4.6.5.2 MMU Option Register Formats
This section describes the address and data formats needed for reading and writing the
instruction and data TLBs.
PTEVADDR
Because four ways of each TLB are configured as AutoRefill, the MMU Option supports
hardware refill of the TLB from a page table (Section 4.6.5.9). The base virtual address
of the current page table is specified in the PTEBase field of the PTEVADDR register.
When read, PTEVADDR returns the PTEBase field in its upper bits as shown in
Figure 4–29, EXCVADDR31..12 in the field labeled VPN below followed by two zero bits.
When PTEVADDR is written, only the PTEBase field is modified. PTEVADDR is undefined
after reset. Figure 4–29 shows the PTEVADDR register format.
Figure 4–29. MMU Option PTEVADDR Register Format
RASID
The Ring ASID (RASID) register holds the current ASIDs for each ring. The register is
divided into four 8-bit sections, one for each ASID. The Ring 0 ASID is hardwired to 1.
The operation of the processor is undefined if any two of the four ASIDs are equal or if
it contains an ASID of zero. RASID is 32’h04030201 after reset. Figure 4–30 shows
the RASID register format.
RITLB1 RRR Read instruction TLB translation
WDTLB RRR Write data TLB
WITLB RRR Write instruction TLB
31 22 21 210
PTEBase VPN 0
10 20 2
Table 4–108. MMU Option Instruction Additions
(continued)
Instruction
1
Format Definition
1. These instructions are fully described in Chapter 6, "Instruction Descriptions" on page 243.
Chapter 4. Architectural Options
162 Xtensa Instruction Set Architecture (ISA) Reference Manual
Figure 4–30. MMU Option RASID Register Format
ITLBCFG
Because one or three ways of the instruction TLB are configured with variable page siz-
es (depending on whether IVARWAY56 is, respectively, fixed or variable), the ITLBCFG
register specifies the page size for those ways. Regardless of IVARWAY56, the Size
field in bits[17:16] of the register controls the size of the entries in Way 4 and has the
values 2’b00 = 1 MB, 2’b01 = 4 MB, 2’b10 = 16 MB, and 2’b11 = 64 MB. If IVARWAY56 is
Variable, the Sz field in bit[20] of the register controls the size of the entries in Way 5 and
has the values 1’b0 = 128MB and 1’b1 = 256MB. If IVARWAY56 is Variable, the Sz field
in bit[24] of the register controls the size of the entries in Way 6 and has the values 1’b0
= 512MB and 1’b1 = 256MB. MBZ means “must be zero”. The entire TLB way should be
invalidated when its size is changed. The ITLBCFG register is zero after reset. The fol-
lowing shows the ITLBCFG register format.
MMU Option ITLBCFG Register Format
DTLBCFG
Because one or three ways of the data TLB are configured with variable page sizes (de-
pending on whether DVARWAY56 is, respectively, fixed or variable), the DTLBCFG regis-
ter specifies the page size for those ways. Regardless of DVARWAY56, the Size field in
bits[17:16] of the register controls the size of the entries in Way 4 and has the values
2’b00 = 1 MB, 2’b01 = 4 MB, 2’b10 = 16 MB, and 2’b11 = 64 MB. If DVARWAY56 is Vari-
able, the Sz field in bit[20] of the register controls the size of the entries in Way 5 and
has the values 1’b0 = 128MB and 1’b1 = 256MB. If DVARWAY56 is Variable, the Sz field
in bit[24] of the register controls the size of the entries in Way 6 and has the values 1’b0
= 512MB and 1’b1 = 256MB. MBZ means “must be zero”. The entire TLB way should be
invalidated when its size is changed. The DTLBCFG register is zero after reset.
Figure 4–31 shows the DTLBCFG register format.
31 24 23 16 15 8 7 0
Ring3 ASID Ring2 ASID Ring1 ASID 8’h01
8888
31 25 24 23 21 20 19 18 17 16 15 0
MBZ Sz MBZ Sz MBZ Size MBZ
7 1 3 1 2 2 16
Chapter 4. Architectural Options
Xtensa Instruction Set Architecture (ISA) Reference Manual 163
Figure 4–31. MMU Option DTLBCFG Register Format
4.6.5.3 The Structure of the MMU Option TLBs
The instruction TLB is 7-way set-associative. Ways 0-3 are AutoRefill ways used for
hardware refill of 4 kB page table entries from the page table when no matching TLB en-
try is found. The AutoRefill ways contain a total of either 16 entries (four per way) or 32
entries (eight per way) depending on NIREFILLENTRIES. Way 4 is a variable size way
of four entries and is used for mapping large pages of 1 MB, 4 MB, 16 MB, or 64 MB as
configured by the ITLBCFG register. The ASID fields in these ways are set to zero (in-
valid) after reset.
Way 5 (IVARWAY56 Fixed), with two constant entries, statically maps the 128 MB region
32'hD0000000–32'hD7FFFFFF to the first 128 MB of physical memory
(32'h00000000–32'h07FFFFFF) as cached memory (attribute 4’h7 as described in
Section 4.6.5.10), and the next 128 MB region (32'hD8000000–32'hDFFFFFFF) to
the same 128 MB of physical memory as cache bypassed memory (attribute 4’h3 as de-
scribed in Section 4.6.5.10). The ASID entries for both entries is 8’h01. These 128 MB
regions are intended for the operating system kernel’s first 128 MB of code and data
(see Figure 4–32). Using a pair of large static mappings reduces the load on the de-
mand refill portion of the instruction TLB and also provides access using two attributes
for the same memory. Physical memory above the first 128 MB is accessed via dynami-
cally mapped virtual address space.
Way 5 (IVARWAY56 Variable), is a variable size way of four entries and is used for map-
ping very large pages of 128 MB or 256 MB as configured by the ITLBCFG register. The
ASID fields in this way are set to zero (invalid) after reset. This way may be used to em-
ulateWay 5 (IVARWAY56 Fixed), or it may be used for a more flexible arrangement.
Way 6 (IVARWAY56 Fixed), also with 2 constant entries, statically maps the 256 MB re-
gion 32'hE0000000–32'hEFFFFFFF to the last 256 MB of physical memory
(32'hF0000000–32'hFFFFFFFF) as cached memory (attribute 4’h7 as described in
Section 4.6.5.10), and the next 256 MB region (32'hF0000000–32'hFFFFFFFF) to
the same 256MB of physical memory as cache bypassed memory (attribute 4’h3 as de-
scribed in Section 4.6.5.10). The ASID entries for both entries is 8’h01. These 256 MB
regions are intended for addressing the system peripherals (for example, a PCI or other
I/O bus) and system ROM (see Figure 4–32).
31 25 24 23 21 20 19 18 17 16 15 0
MBZ Sz MBZ Sz MBZ Size MBZ
7 1 3 1 2 2 16
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164 Xtensa Instruction Set Architecture (ISA) Reference Manual
Way 6 (IVARWAY56 Variable), is a variable size way of eight entries and is used for
mapping very large pages of 512 MB or 256 MB as configured by the ITLBCFG register.
The ASID fields in this way are set one and the Attribute fields in this way are set to 4’h2
(Bypass) after reset, and the other fields are set so that this way directly maps all of
memory after reset. This way may be used to emulate Way 6 (IVARWAY56 Fixed), it may
be used to effectively "turn off" the ITLB, or it may be used for a more flexible arrange-
ment.
The data TLB is 10-way set-associative. It has the same seven ways as the instruction
TLB above (using DTLBCFG/DVARWAY56, instead of ITLBCFG/IVARWAY56), with the
addition of Ways 7-9, which are single-entry ways for 4 kB pages. These ways are in-
tended to hold translations required to map the page table for hardware refill and for en-
tries that are not to be replaced by refill. The ASID fields in these ways are set to zero
(invalid) after reset.
All ASID fields in the ITLB and DTLB, except those in Way 5 & Way 6, are set to zero (in-
valid) after reset. ASID fields in Way 5 are set to zero (invalid) after reset if
IVARWAY56/DVARWAY56 is Variable.
4.6.5.4 The MMU Option Memory Map
The memory map is determined by the TLB configurations given in Section 4.6.5.3.
Figure 4–32 shows a graphical representation of the constant translations in Way 5 and
Way 6 when IVARWAY56 and DVARWAY56 are Fixed, as well as the regions that are
mapped by more flexible ways than these. Way 5 and Way 6 may be used to emulate
this same arrangement when IVARWAY56 and DVARWAY56 are Variable.
Chapter 4. Architectural Options
Xtensa Instruction Set Architecture (ISA) Reference Manual 165
Figure 4–32. MMU Option Address Map with
IVARWAY56
and
DVARWAY56
Fixed
This configuration provides both bypass and cached access to peripherals. Bypass ac-
cess is used for devices and cached access is used for ROMs, for example. It also pro-
vides bypass and cached access to the low 128 MB of memory. This allows system soft-
ware to access its memory without competing with user code for other TLB entries.
These are available after reset. The large page way (Way 4) and the auto-refill ways
(Ways 0-3) may be used to map as much additional space as desired (Section 4.6.5.9).
In the data TLB, Ways 7-9 may be used to map single pages so that they are always
available.
4.6.5.5 Formats for Writing MMU Option TLB Entries
During normal operation when instructions and data are being accessed from memory,
only lookups are being done in the TLBs. For maintenance of the TLBs, however, the
entries in the TLBs are accessed by the instructions in Table 4–108 on page 160.
Virtual Physical
FFFFFFFF FFFFFFFF
bypass peripherals
F0000000 F0000000
cached
E0000000
D8000000 bypass
D0000000 cached
mapped
08000000
00000000 00000000
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166 Xtensa Instruction Set Architecture (ISA) Reference Manual
Writing the TLB with the WITLB and WDTLB instructions requires the formats for the as
and at registers shown in Figure 4–33 and Figure 4–34. These figures show, in parallel,
the formats for different ways of the cache and different conditions. For Ways 0-3, there
are two conditions that depend on the configuration parameter NIREFILLENTRIES or
NDREFILLENTRIES (see Figure 4–105 on page 159) and can have the values of 16 or
32 auto-refill entries per TLB (four or eight per TLB way). For Way 4, there are four con-
ditions, which are the four values of the respectiveITLBCFG or DTLBCFG fields and indi-
cate the size of pages currently contained within that way. Ways 5 and 6 can be Fixed or
Variable as determined by the IVARWAY56 and DVARWAY56 parameters. If they are vari-
able then there are still two conditions which are the two values of the respective ITLB-
CFG or DTLBCFG fields and indicate the size of pages currently contained within that
way. Each row, then, contains the format for the way and condition indicated in the left
column. Note that writing to Way-5 and Way-6 when the IVARWAY56 and DVARWAY56
parameters are "Fixed" causes no changes because those ways are constant.
Writing ITLB Ways 7-15 or DTLB ways 10-15 is undefined.
The format of the as register used for the WITLB and WDTLB instructions is shown in
Figure 4–33. The low order four bits contain the way to be accessed. The upper bits
contain the Virtual Page Number (VPN). For clarity, the Index bits are separated out
from the rest of the VPN in this figure. Note that unused bits at Bit 12 and above are ig-
nored so that those bits may simply contain the address for access to all ways of both
TLBs. Unused bits at Bit 11 and below are reserved for forward compatibility. They may
either be zero or they may be the result of the probe instruction (Section 4.6.5.7).
Chapter 4. Architectural Options
Xtensa Instruction Set Architecture (ISA) Reference Manual 167
Figure 4–33. MMU Option Addressing (
as
) Format for
WxTLB
The format of the at register used for the WITLB and WDTLB instructions is shown in
Figure 4–34. The low order four bits contain the attribute to be written (see
Section 4.6.5.10). The two bits above those contain the ring for which this TLB entry is
to be written. The ASID taken from the RASID register (see Section 4.6.5.2) correspond-
ing to this ring is stored with the TLB entry. It is not possible to write an entry with an
ASID which is not currently in the RASID register. The upper bits contain the Physical
Page Number (PPN) of the translation. Way-5 and Way-6 are constant ways when the
IVARWAY56 and DVARWAY56 parameters are "Fixed": The PPN remains as described in
Section 4.6.5.3, the ASID is not written but always matches Ring 0, and the attribute re-
mains as described in Section 4.6.5.3, no matter what is in register at. As with the ad-
dress format, unused bits at Bit 12 and above are ignored so that a 20-bit PPN may be
used with all ways of the TLB, and unused bits at Bit 11 and below are required to be
zero for forward compatibility.
Way 31 30 29 28 27 26 25 24 23 22 21 20 19 15 14 13 12 11 4 3 2 1 0
0-3 (16entry) VPN without Index Index Reserved 4’h0,1,2,3
0-3 (32entry) VPN without Index Index Reserved 4’h0,1,2,3
4 (1MB) VPN without Index Index Ignored Reserved 4’h4
4 (4MB) VPN without Index Index Ignored Reserved 4’h4
4 (16MB) VPN without Index Index Ignored Reserved 4’h4
4 (64MB) VPN w/o Idx Index Ignored Reserved 4’h4
5 (Fixed) Ignored Reserved 4’h5
5 (128MB) VPN Index Ignored Reserved 4’h5
5 (256MB) VPN Index Ignored Reserved 4’h5
6 (Fixed) Ignored Reserved 4’h6
6 (512MB) Index Ignored Reserved 4’h6
6 (256MB) VIndex Ignored Reserved 4’h6
Chapter 4. Architectural Options
168 Xtensa Instruction Set Architecture (ISA) Reference Manual
Figure 4–34. MMU Option Data (
at
) Format for
WxTLB
After modifying any TLB entry with a WITLB instruction, an ISYNC must be executed be-
fore executing any instruction that depends on the modification. The ITLB entry currently
being used for instruction fetch may not be changed.
After modifying any TLB entry with a WDTLB instruction, the operation of loads and
stores that depend on that TLB entry are undefined until a DSYNC instruction is execut-
ed.
4.6.5.6 Formats for Reading MMU Option TLB Entries
Reading the TLB with the RITLB0, RITLB1, RDTLB0, and RDTLB1 instructions requires
the formats for the as and at registers shown in Figure 4–35 through Figure 4–37.
These figures show, in parallel, the formats for different ways of the cache and different
conditions. For Ways 0-3, there are two conditions that depend on the configuration pa-
rameter NIREFILLENTRIES or NDREFILLENTRIES (see Figure 4–105 on page 159)
and can have the values of 16 or 32 auto-refill entries per TLB (four or eight per TLB
way). For Way 4, there are four conditions, which are the four values of the respec-
tiveITLBCFG or DTLBCFG fields and indicate the size of pages currently contained within
Way 31 29 28 27 26 25 24 23 22 21 20 19 18 17 12 11 6 5 4 3 0
0-3 (16entry) PPN 6’h00 Ring Attribute
0-3 (32entry) PPN 6’h00 Ring Attribute
4 (1MB) PPN Ignored 6’h00 Ring Attribute
4 (4MB) PPN Ignored 6’h00 Ring Attribute
4 (16MB) PPN Ignored 6’h00 Ring Attrbute
4 (64MB) PPN Ignored 6’h00 Ring Attribute
5 (Fixed) Ignored 6’h00 Ignored
5 (128MB) PPN Ignored 6’h00 Ring Attribute
5 (256MB) PPN Ignored 6’h00 Ring Attribute
6 (Fixed) Ignored 6’h00 Ignored
6 (512MB) PPN Ignored 6’h00 Ring Attribute
6 (256MB) PPN Ignored 6’h00 Ring Attribute
7-9(DTLB) PPN 6’h00 Ring Attribute
31 29 28 27 26 25 24 23 22 21 20 19 18 17 12 11 6 5 4 3 0
Chapter 4. Architectural Options
Xtensa Instruction Set Architecture (ISA) Reference Manual 169
that way. Ways 5 and 6 can be Fixed or Variable as determined by the IVARWAY56 and
DVARWAY56 parameters. If they are variable then there are still two conditions which are
the two values of the respective ITLBCFG or DTLBCFG fields and indicate the size of
pages currently contained within that way. Each row, then, contains the format for the
way and condition indicated in the left column.
Reading ITLB ways 7-15 or DTLB ways 10-15 is undefined.
The format of the as register used for the RITLB0, RITLB1, RDTLB0, and RDTLB1 in-
structions is shown in Figure 4–35. The low order four bits contain the way to be access-
ed. Besides the Way bits, only the Index bits are needed for reading the TLB. Depending
on the TLB way being accessed, and other conditions such as the size assigned to the
variable size way or the number of auto refill entries in the TLB, different bits of address
may be needed as shown. Note that unused bits at Bit 12 and above are ignored so that
an entire 20-bit VPN may be used when accessing all ways of both TLBs. Unused bits at
Bit 11 and below are reserved for forward compatibility. They may either be zero or they
may be the result of the probe instruction (Section 4.6.5.7).
Figure 4–35. MMU Option Addressing (
as
) Format for
RxTLB0
and
RxTLB1
Way 31 29 28 27 26 25 24 23 22 21 20 19 15 14 13 12 11 4 3 2 1 0
0-3 (16entry) Ignored Index Reserved 4’h0,1,2,3
0-3 (32entry) Ignored Index Reserved 4’h0,1,2,3
4 (1MB) Ignored Index Ignored Reserved 4’h4
4 (4MB) Ignored Index Ignored Reserved 4’h4
4 (16MB) Ignored Index Ignored Reserved 4’h4
4 (64MB) Ignored Index Ignored Reserved 4’h4
5 (Fixed) Ignored Ix Ignored Reserved 4’h5
5 (128MB) Ignored Index Ignored Reserved 4’h5
5 (256MB) Ig Index Ignored Reserved 4’h5
6 (Fixed) Ignored Ix Ignored Reserved 4’h6
6 (512MB) Index Ignored Reserved 4’h6
6 (256MB) Ig Index Ignored Reserved 4’h6
7-9(DTLB) Ignored Reserved 4’h7,8,9
31 29 28 27 26 25 24 23 22 21 20 19 15 14 13 12 11 4 3 2 1 0
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170 Xtensa Instruction Set Architecture (ISA) Reference Manual
Because reading generates more information than can fit in one 32-bit register, there are
two read instructions that return different values. The data resulting from the RITLB0
and RDTLB0 instructions is shown in Figure 4–36. The low bits contain the ASID stored
with the entry, while the upper bits contain the Virtual Page Number (VPN) without the
Index bits that were used in the address of the read. Unused bits at Bit 12 and above of
the data result of these instructions are defined to be zero so that the entire 20-bit field
may always be used as a VPN whatever the size of the way. Unused bits at Bit 11 and
below are undefined for forward compatibility.
Figure 4–36. MMU Option Data (
at
) Format for
RxTLB0
The data resulting from the RITLB1, and RDTLB1 instructions is shown in Figure 4–37.
The low order four bits contain the attribute stored with the TLB entry (Section 4.6.5.10).
The upper bits contain the Physical Page Number (PPN) of the entry. Unused bits at Bit
12 and above of the data result of these instructions are defined to be zero so that the
entire 20-bit field may always be used as a PPN, whatever the size of the way. Unused
bits at Bit 11 and below are undefined for forward compatibility.
Way 31 30 29 28 27 26 25 24 23 22 21 15 14 13 12 11 8 7 0
0-3 (16entry) VPN without Index 2’b00 Undefined ASID
0-3 (32entry) VPN withoutIndex 3’b000 Undefined ASID
4 (1MB) VPN without Index 10’h000 Undefined ASID
4 (4MB) VPN without Index 12’h000 Undefined ASID
4 (16MB) VPN without Index 14’h0000 Undefined ASID
4 (64MB) VPN w/o Idx 16’h0000 Undefined ASID
5 (Fixed) 4’b1101 16’h0000 Undefined ASID
5 (128MB) VPN 17’h00000 Undefined ASID
5 (256MB) VPN 18’h00000 Undefined ASID
6 (Fixed) 3’b111 17’h00000 Undefined ASID
6 (512MB) 20’h00000 Undefined ASID
6 (256MB) V19’h00000 Undefined ASID
7-9(DTLB) VPN Undefined ASID
31 30 29 28 27 26 25 24 23 22 21 15 14 13 12 11 8 7 0
Chapter 4. Architectural Options
Xtensa Instruction Set Architecture (ISA) Reference Manual 171
Figure 4–37. MMU Option Data (
at
) Format for
RxTLB1
4.6.5.7 Formats for Probing MMU Option TLB Entries
Probing the TLB with the PITLB and PDTLB instructions requires the formats for the as
and at registers shown in Figure 4–38 and Figure 4–39. Unlike writing and reading the
TLBs as explained in the previous two sections, the operation of probing a TLB begins
without knowing the way containing the sought after value. The formats do not, there-
fore, vary with the way being accessed. The probe instructions answer the question of
what entry in this TLB, if any, would be used to translate an access with a particular ad-
dress from a particular ring. The sought for address is given in the as register as shown
in Figure 4–38 and the ring is given by PS.RING (not CRING, so that while PS.EXCM is
set, a probe may be done for a user program). If, for example, there is an entry that
matches in address, but its ASID does not match any ASID in the RASID register, or an
entry that matches in address, but the ASID corresponds in the RASID register to a ring
of lower number than the current PS.RING, the probe will not return a hit.
The format of the as register used for the PITLB and PDTLB instructions is shown in
Figure 4–38. Any address may be used as input to the probe instructions.
Way 31 29 28 27 26 25 24 23 22 21 20 19 12 11 4 3 0
0-3 (16entry) PPN Undefined Attribute
0-3 (32entry) PPN Undefined Attribute
4 (1MB) PPN 8’h00 Undefined Attribute
4 (4MB) PPN 10’h000 Undefined Attribute
4 (16MB) PPN 12’h000 Undefined Attribute
4 (64MB) PPN 14’h0000 Undefined Attribute
5 (Fixed) 5’b00000 15’h0000 Undefined Attribute
5 (128MB) PPN 15’h0000 Undefined Attribute
5 (256MB) PPN 16’h0000 Undefined Attribute
6 (Fixed) 4’b1111 16’h0000 Undefined Attribute
6 (512MB) PPN 17’h0000 Undefined Attribute
6 (256MB) PPN 16’h0000 Undefined Attribute
7-9(DTLB) PPN Undefined Attribute
31 29 28 27 26 25 24 23 22 21 20 19 12 11 4 3 0
Chapter 4. Architectural Options
172 Xtensa Instruction Set Architecture (ISA) Reference Manual
Figure 4–38. MMU Option Addressing (
as
) Format for
PxTLB
The data resulting from the PITLB and PDTLB instructions is shown in Figure 4–39 and
Figure 4–40. The low three/four bits contain the Way (if any), which would be used to
translate the address and the next bit up is set if there is a translation in the TLB, and
clear if there is not. Some bits are undefined for forward compatibility but the result is
such that, if Hit=1, it may be used as the as register for WxTLB, RxTLB0, RxTLB1, or
IxTLB.
Figure 4–39. MMU Option Data (
at
) Format for
PITLB
Figure 4–40. MMU Option Data (
at
) Format for
PDTLB
4.6.5.8 Format for Invalidating MMU Option TLB Entries
Invalidating the TLB with the IITLB and IDTLB instructions requires the formats for the
as register shown in Figure 4–41. This figure shows, in parallel, the formats for different
ways of the cache and different conditions. For Ways 0-3, there are two conditions that
depend on the configuration parameter NIREFILLENTRIES or NDREFILLENTRIES
(Figure 4–105) and can have the values of 16 or 32 auto-refill entries per TLB (4 or 8 per
TLB way). For Way 4, there are four conditions, which are the four values of the respec-
tiveITLBCFG or DTLBCFG fields and indicate the size of pages currently contained within
that way. Ways 5 and 6 can be Fixed or Variable as determined by the IVARWAY56 and
DVARWAY56 parameters. If they are variable then there are still two conditions which are
the two values of the respective ITLBCFG or DTLBCFG fields and indicate the size of
pages currently contained within that way. Each row, then, contains the format for the
31 0
Probe Address
32
31 12 11 4 3 2 0
VPN Undefined Hit Way
20 8 1 3
31 12 11 5 4 3 0
VPN Undefined Hit Way
20 7 1 4
Chapter 4. Architectural Options
Xtensa Instruction Set Architecture (ISA) Reference Manual 173
way and condition indicated in the left column. Note that invalidating Way-5 and Way-6
when the IVARWAY56 and DVARWAY56 parameters are "Fixed" causes no changes be-
cause those ways are constant.
Invalidation of ITLB ways 7-15 or DTLB ways 10-15 is undefined.
The format of the as register used for the IITLB and IDTLB instructions is shown in
Figure 4–41. The low order four bits contain the way to be accessed. The upper bits
contain at least the Index from the Virtual Page Number (VPN). Note that unused bits at
Bit 12 and above are ignored so that those bits may simply contain the address for ac-
cess to all ways of both TLBs. Unused bits at Bit 11 and below are reserved for forward
compatibility. They may either be zero or they may be the result of the probe instruction
(Section 4.6.5.7 on page 171).
Invalidation of an entry sets the corresponding ASID to zero so that it no longer re-
sponds when an address is looked up in the TLB.
Figure 4–41. MMU Option Addressing (
as
) Format for
IxTLB
Way 31 30 29 28 27 26 25 24 23 22 21 20 19 15 14 13 12 11 43210
0-3 (16entry) Ignored Index Reserved 4’h0,1,2,3
0-3 (32entry) Ignored Index Reserved 4’h0,1,2,3
4 (1MB) Ignored Index Ignored Reserved 4’h4
4 (4MB) Ignored Index Ignored Reserved 4’h4
4 (16MB) Ignored Index Ignored Reserved 4’h4
4 (64MB) Ignored Index Ignored Reserved 4’h4
5 (Fixed) Ignored Reserved 4’h5
5 (128MB) Ignored Index Ignored Reserved 4’h5
5 (256MB) Ig Index Ignored Reserved 4’h5
6 (Fixed) Ignored Reserved 4’h6
6 (512MB) Index Ignored Reserved 4’h6
6 (256MB) Ig Index Ignored Reserved 4’h6
7-9(DTLB) Ignored Reserved 4’h7,8,9
31 30 29 28 27 26 25 24 23 22 21 20 19 15 14 13 12 11 43210
Chapter 4. Architectural Options
174 Xtensa Instruction Set Architecture (ISA) Reference Manual
After modifying any TLB entry with a IITLB instruction, an ISYNC must be executed be-
fore executing any instruction that depends on the modification. After modifying any TLB
entries with an IDTLB instruction, the operation of loads from and stores that depend on
that TLB entry are undefined until a DSYNC instruction is executed.
4.6.5.9 MMU Option Auto-Refill TLB Ways and PTE Format
When no TLB entry matches the ASIDs and the virtual address presented to the MMU,
the MMU attempts to automatically load the appropriate page table entry (PTE) from the
page table and write it into the TLB in one of the AutoRefill ways. This hardware- gener-
ated load from the page table itself requires virtual-to-physical address translation,
which executes at Ring 0 so that it has access to the page table and uses the DTLB. An
error of any sort during the automatic refill process will cause an InstTLBMissCause
or a LoadStoreTLBMissCause exception to be raised so that system software can
take appropriate action and possibly retry the access. This combination of hardware and
software refill gives excellent performance while minimizing processor complexity. If the
second translation succeeds, the PTE load is done through the DataCache, if one is
configured, and the attributes for the page containing the PTE enable such a cache ac-
cess. The PTE’s Ring field is then used as an index into the RASID register, and the re-
sulting ASID is written together with the rest of the PTE into the TLB.
Xtensa’s TLB refill mechanism requires the page table for the current address space to
reside in the current virtual address space. The PTEBase field of the PTEVADDR register
gives the base address of the page table. On a TLB miss, the processor forms the virtual
address of the PTE by catenating the PTEBase portion of PTEVADDR, the Virtual Page
Number (VPN) bits of the miss virtual address, and 2 zero bits. The bits used from
PTEVADDR and from the virtual address are configuration dependent; the exact calcula-
tion for 4-byte PTEs is
PTEVADDR31..22||vAddr31..12||2'b00
The format of the PTEs is shown in Figure 4–42. The most significant bits hold the Phys-
ical Page Number (PPN), the translation of the virtual address corresponding to this en-
try. The Sw bits are available for software use in the page table (they are not stored in
the TLB). The Ring field specifies the privilege level required to access this page; this is
used to choose one of the four ASIDs from RASID when the TLB is written. The attribute
field gives the access attributes for this page (see Section 4.6.5.10).
Figure 4–42. MMU Option Page Table Entry (PTE) Format
31 12 11 6543 0
PPN Sw Ring Attribute
20 6 2 4
Chapter 4. Architectural Options
Xtensa Instruction Set Architecture (ISA) Reference Manual 175
The configuration described in Section 4.6.5.4 (with IVARWAY56/DVARWAY56 Fixed)
provides a maximum of 3328 MB of dynamically mapped space (4 GB of total virtual ad-
dress space with 768 MB of statically mapped space). The page table for this maximum
size requires 851968 PTEs (3328MB/4 kB). The entire set of PTEs require 3328 kB of
virtual address space (at 4 bytes per PTE). The PTEs themselves are at virtual address-
es and, therefore, 832 of the PTEs in the table are for mapping the page table itself.
These PTEs for mapping the page table will fit onto a single page, the mapping for which
may be written into one of the single-entry ways (Ways 7-9) of the data TLB for guaran-
teed access.
For example, if PTEVADDR is set to 32’hCFC00000, then the virtual address space be-
tween there and 32’hCFF3FFFF is used as the page table. That page table is mapped
by the 832 entries between 32’hCFF3F000 and 32’hCFF3FCFF. The translation for the
page at 32’hCFF3F000 is placed in one of the single-entry ways of the data TLB. (The
accesses that might have used the remaining 192 PTE entries on that page would al-
ready have been translated by one of the constant ways.) Many of those 832 entries
may be marked invalid and the physical address space required for the page table may
be made very small.
In systems with large memories, the above maximum configuration may be improved in
performance by mapping the entire page table into the constant way (Way 5). If
PTEVADDR is set to 32’hD4000000, for example, the virtual address space between
there and 32’hD433FFFF, which maps to the physical address space between
32’h04000000 and 32’h0433FFFF (between 64 MB and about 68 MB) is used for a
flat page table mapping all of memory. Any TLB miss will now be handled by the hard-
ware refill as the translation for the PTE will be handled by the constant way. The disad-
vantage is that over 3 MB of memory must be allocated to the page table.
In a small system, where all processes are limited to the first 8 MB of virtual space,
PTEVADDR might be set to 32’hCFC00000 and two of the single entry ways set to map
the page at 32’hCFC00000 and the page at 32’hCFC01000. One or both pages of
PTEs could be used for translations and the hardware refill would always succeed for le-
gal addresses.
4.6.5.10 MMU Option Memory Attributes
Currently available hardware supports the memory attributes described in this section.
T1050 hardware supported somewhat different memory attributes, which are described
in Section A.5 “MMU Option Memory Attributes”. System software may use the subset of
attributes (1, 3, 5, 7, 12, 13, and 14) which have not changed to support all Xtensa pro-
cessors.
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176 Xtensa Instruction Set Architecture (ISA) Reference Manual
The memory attributes discussed in this section apply both to attribute values written in
and read from the TLBs (see Section 4.6.5.5 and Section 4.6.5.6) and to attribute values
stored in the PTE entries and written into the AutoRefill ways of the TLBs (see
Section 4.6.5.9).
For a more detailed description of the memory access process and the place of these at-
tributes in it, see Section 4.6.2.
Table 4–109 shows the meanings of the attributes for instruction fetch, data load, and
data store. For a more detailed description of the memory access process and the place
of these attributes in it, see Section 4.6.2.
The first column in Table 4–109 indicates the attribute from the TLB while the remaining
columns indicate various effects on the access. The columns are described in the follow-
ing bullets:
Attr — the value of the 4-bit Attribute field of the TLB entry.
Rights — whether the TLB entry may successfully translate a data load, a data
store, or an instruction fetch.
- The first character is an r if the entry is valid for a data load and a dash ("-")if
not.
- The second character is a w if the entry is valid for a data store and a dash
("-")if not.
- The third character is an x if the entry is valid for an instruction fetch and a dash
("-")if not.
If the translation is not successful, an exception is raised.
Local memory accesses (including XLMI) consult only the Rights column.
WB — some rows are split by whether or not the configured cache is writeback or
not. Rows without an entry apply to both cache types.
Meaning for Cache Access — the verbal description of the type of access made to
the cache.
Access Cache — indicates whether the cache provides the data.
- The first character is an h if the cache provides the data when the tag indicates
hit and a dash ("-")if it does not.
- The second character is an m if the cache provides the data when the tag indi-
cates a miss and a dash ("-")if it does not. This capability is used only for Iso-
late mode.
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Xtensa Instruction Set Architecture (ISA) Reference Manual 177
Fill Cache — indicates whether an allocate and fill is done to the cache if the tag in-
dicates a miss.
- The first character is an r if the cache is filled on a data load and a dash ("-")if
it is not.
- The second character is a w if the cache is filled on a data store and a dash ("-
")if it is not.
- The third character is an x if the cache is filled on an instruction fetch and a
dash ("-")if it is not.
Guard Load — refers to the guarded attribute as described in Table 4–99 on
page 144. Stores are always guarded and instruction fetches are never guarded,
but loads are guarded where there is a “yes” in this column. Local memory loads are
not guarded.
Write Thru — indicates whether a write is done through the PIF interface.
- The first character is an h if a Write Thru occurs when the tag indicates hit and a
dash ("-")if it does not.
- The second character is an m if a Write Thru occurs when the tag indicates a
miss and a dash ("-")if it does not.
Writes to local memories are never Write-Thru. In most implementations, a write-thru will
only occur after any needed cache fill is complete.
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178 Xtensa Instruction Set Architecture (ISA) Reference Manual
In the absence of the Instruction Cache Option, Cached regions behave as Bypass re-
gions on instruction fetch. In the absence of the Data Cache Option, Cached regions be-
have as Bypass regions on data load or store. If the Data Cache is not configured as
writeback (Section 4.5.5.1 on page 119) Attributes 4, 5, 6, and 7 behave as Attributes 8,
9, 10, and 11 respectively instead of as they are listed in Table 4–109.
4.6.5.11 MMU Option Operation Semantics
The following functions are used in the operation sections of the individual instruction
definitions:
function ltranslate(vAddr, ring)
ltranslate ← (pAddr, attributes, cause)
endfunction ltranslate
function ASID(ring)
ASID ← RASIDring*8+ASIDBits-1..ring*8
endfunction ASID
Table 4–109. MMU Option Attribute Field Values
Attr Rights Meaning for Cache Access Access
Cache
Fill
Cache
Guard
Load
Write
Thru
0 r-- Bypass cache -- --- yes --
1 r-x Bypass cache -- --- yes --
2 rw- Bypass cache -- --- yes hm
3 rwx Bypass cache -- --- yes hm
4 r-- Cached, WrtBack alloc h- r-- - --
5 r-x Cached, WrtBack alloc h- r-x - --
6 rw- Cached, WrtBack alloc h- rw- - --
7 rwx Cached, WrtBack alloc h- rwx - --
8 r-- Cached, WrtThru h- r-- - --
9 r-x Cached, WrtThru h- r-x - --
10 rw- Cached, WrtThru h- r-- - hm
11 rwx Cached, WrtThru h- r-x - hm
12 --- illegal1-- --- - --
13 rw- Cache Isolated2hm --- - --
14 --- illegal1-- --- - --
15 --- Reserved1————
1 Raises exception. EXCCAUSE is set to InstFetchProhibitedCause, LoadProhibitedCause, or StoreProhibitedCause depending on access type
2 For test only, implementation dependent, uses data cache like local memories and ignores tag.
Chapter 4. Architectural Options
Xtensa Instruction Set Architecture (ISA) Reference Manual 179
function InstPageBits(wi)
sizecodebits ← ceil(log2(InstTLB[wi].PageSizeCount))
sizecode ← IPAGESIZEwi*4+sizecodebits-1..wi*4
InstPageBits ← InstTLB[wi].PageBits[sizecode]
endfunction InstPageBits
function SplitInstTLBEntrySpec(spec)
wih ← ceil(log2(InstTLBWayCount)) − 1
wi ← specwih..0
eil ← InstPageBits(wi)
eih ← eil + log2(InstTLB[wi].IndexCount)
ei ← speceih..eil
vpn ← specInstTLBVAddrBits-1..eih+1
SplitInstTLBEntrySpec ← (vpn, ei, wi)
endfunction SplitInstTLBEntrySpec
function ProbeInstTLB (vAddr)
match ← 0
vpn ← undefined
ei ← undefined
wi ← undefined
for i in 0..InstTLBWayCount-1 do
if then
match ← match + 1
vpn ← x
ei ← x
wi ← i
endif
endfor
ProbeInstTLB ← (match, vpn, ei, wi)
endfunction ProbeInstTLB
4.7 Options for Other Purposes
This section contains options that do not fit easily into the previous sections. The Win-
dowed Register Option provides the hardware for a memory efficient ABI. The Proces-
sor Interface Option provides a standard interface to system memory. The Miscella-
neous Special Registers Option provides additional scratch registers. The Processor ID
Option provides the ability for software to determine on which processor it is running.
The Debug Option provides hardware to assist in debugging processors.
Chapter 4. Architectural Options
180 Xtensa Instruction Set Architecture (ISA) Reference Manual
4.7.1 Windowed Register Option
The Windowed Register Option replaces the simple 16-entry AR register file with a larg-
er register file from which a window of 16 entries is visible at any given time. The window
is rotated on subroutine entry and exit, automatically saving and restoring some regis-
ters. When the window is rotated far enough to require registers to be saved to or re-
stored from the program stack, an exception is raised to move some of the register val-
ues between the register file and the program stack. The option reduces code size and
increases performance of programs by eliminating register saves and restores at proce-
dure entry and exit, and by reducing argument-shuffling at calls. It allows more local
variables to live permanently in registers, reducing the need for stack-frame mainte-
nance in non-leaf routines.
Xtensa ISA register windows are different from register windows in other instruction
sets. Xtensa register increments are 4, 8, and 12 on a per-call basis, not a fixed incre-
ment as in other instruction sets. Also, Xtensa processors have no global address regis-
ters. The caller specifies the increment amount, while the callee performs the actual in-
crement by the ENTRY instruction. The compiler uses an increment sufficient to hide the
registers that are live at the point of the call (which the compiler can pack into the fewest
possible at the low end of the register-number space). The number of physical registers
is 32 or 64, which makes this a more economical configuration. Sixteen registers are vis-
ible at one time. Assuming that the average number of live registers at the point of call is
6.5 (return address, stack pointer, and 4.5 local variables), and that the last routine uses
12 registers at its peak, this allows nine call levels to live in 64 registers (8×6.5+12=64).
As an example, an average of 6.5 live registers might represent 50% of the calls using
an increment of 4, 38% using an increment of 8, and 12% using an increment of 12.
Prerequisites: Exception Option (page 82)
Incompatible options: None
The rotation of the 16-entry visible window within the larger register file is controlled by
the WindowBase Special Register added by the option. The rotation always occurs in
units of four registers, causing the number of bits in WindowBase to be log2(NAREG/4).
Rotation at the time of a call can instantly save some registers and provide new regis-
ters for the called routine. Each saved register has a reserved location on the stack, to
which it may be saved if the call stack extends enough farther to need to re-use the
physical registers. The WindowStart Special Register, which is also added by the option
and consists of NAREG/4 bits, indicates which four register units are currently cached in
the physical register file instead of residing in their stack locations. An attempt to use
registers live with values from a parent routine raises an Overflow Exception which
saves those values and frees the registers for use. A return to a calling routine whose
registers have been previously saved to the stack raises an Underflow Exception which
restores those values. Programs without wide swings in the depth of the call stack save
and restore values only occasionally.
Chapter 4. Architectural Options
Xtensa Instruction Set Architecture (ISA) Reference Manual 181
4.7.1.1 Windowed Register Option Architectural Additions
Table 4–110 through Table 4–113 show this option’s architectural additions.
Table 4–110. Windowed Register Option Constant Additions (Exception Causes)
Exception Cause Description Constant Value
AllocaCause
MOVSP instruction, if the caller’s registers are not
present in the register file
(seeTable 4–64 on page 89)
6'b000101 (decimal 5)
Table 4–111. Windowed Register Option Processor-Configuration Additions
Parameter Description Valid Values
WindowOverflow4 Window overflow exception vector for 4-register
stack frame
32-bit address1
WindowUnderflow4 Window underflow exception vector for 4-register
stack frame
32-bit address1
WindowOverflow8 Window overflow exception vector for 8-register
stack frame
32-bit address1
WindowUnderflow8 Window underflow exception vector for 8-register
stack frame
32-bit address1
WindowOverflow12 Window overflow exception vector for 12- register
stack frame
32-bit address1
WindowUnderflow12 Window underflow exception vector for 12-
register stack frame
32-bit address1
NAREG Number of address registers 32 or 64
1. Some implementations have restrictions on the alignment and relative location of the WindowOverflowN and WindowUnderflowN vectors. See
“procedure WindowCheck (wr, ws, wt)” in Section 4.7.1.3 “Window Overflow Check” on page 184 for how these are used.
Table 4–112. Windowed Register Option Processor-State Additions and Changes
Register
Mnemonic Quantity Width
(bits) Register Name R/W
Special
Register
Number
1
AR NAREG 32 Address registers
(general registers)
R/W —
WindowBase 1log2(
NAREG/4)
Base of current address-register
window
R/W 72
WindowStart 1NAREG/4 Call-window start bits R/W 73
1. Registers with a Special Register assignment are read and/or written with the RSR, WSR, and XSR instructions. See Table 5–127 on
page 205.
Chapter 4. Architectural Options
182 Xtensa Instruction Set Architecture (ISA) Reference Manual
PS.CALLINC
1 2 Miscellaneous processor state,
window increment from call
(see Table 4–63 on page 87)
R/W 230
PS.OWB
1 4 Miscellaneous processor state,
old window base
(see Table 4–63 on page 87)
R/W 230
PS.WOE
1 1 Miscellaneous processor state,
window overflow enable
(see Table 4–63 on page 87)
R/W 230
Table 4–113. Windowed Register Option Instruction Additions
Instruction
1
Format Definition
MOVSP RRR Atomic check window and move
CALL4,
CALL8,
CALL12
CALL Call subroutine, PC-relative. These instructions communicate the number of registers to
hide using PS.CALLINC in addition to the operation of CALL0.
CALLX4,
CALLX8,
CALLX12
CALLX Call subroutine, address in register. These instructions communicate the number of
registers to hide using PS.CALLINC in addition to the operation of CALLX0.
ENTRY BRI12 Subroutine entry—rotate registers, adjust stack pointer. This instruction should not be
used in a routine called by CALL0 or CALLX0.
RETW CALLX Subroutine return—unrotate registers, jump to return address. Used to return from a
routine called by CALL4, CALL8, CALL12, CALLX4, CALLX8, or CALLX12.
RETW.N2RRRN Same at RETW in a 16-bit encoding
ROTW RRR Rotate window by a constant. ROTW is intended for use in exception handlers and
context switch.
L32E RRI4 Load 32 bits for window exception
S32E RRI4 Store 32 bits for window exception
RFWO RRR Return from window overflow exception
RFWU RRR Return from window underflow exception
1. These instructions are fully described in Chapter 6, "Instruction Descriptions" on page 243.
2. Exists only if the Code Density Option described in Section 4.3.1 on page 53 is configured.
Table 4–112. Windowed Register Option Processor-State Additions and Changes
Register
Mnemonic Quantity Width
(bits) Register Name R/W
Special
Register
Number
1
1. Registers with a Special Register assignment are read and/or written with the RSR, WSR, and XSR instructions. See Table 5–127 on
page 205.
Chapter 4. Architectural Options
Xtensa Instruction Set Architecture (ISA) Reference Manual 183
4.7.1.2 Managing Physical Registers
The WindowBase Special Register gives the position of the current window into the
physical register file. In the instruction descriptions, AR[i] is a short-hand for a refer-
ence to the physical register file AddressRegister defined as follows:
AddressRegister[((2'b00||i3..2) + WindowBase) || i1..0]
The WindowStart Special Register gives the state of physical registers (unused or part
of a window). WindowStart is used both to detect overflow and underflow on register
use and procedure return, as well as to determine the number of registers to be saved in
a given stack frame when handling exceptions and switching contexts. There is one bit
in WindowStart for each four physical registers. This bit is set if those four registers
are AR[0] to AR[3] for some call. WindowStart bits are set by ENTRY and cleared by
RETW.
The WindowBase and WindowStart registers are undefined after processor reset, and
should be initialized by the reset exception vector code.
Figure 4–43 through Figure 4–45 show three functionally identical implementations of
windowed registers. Figure 4–43 shows the concept of how the registers are addressed.
Figure 4–44 shows logic with the same functional result but with little or no penalty paid
in timing for the addition of the WindowBase value. Figure 4–45 shows a third version of
the logic with the same functional result but with no timing loss at all caused by the addi-
tion of the WindowBase value.
Figure 4–43. Conceptual Register Window Read
t
s+
4
00
26
4
WindowBase
Inst
64 32-bit
registers
32 x 64
+
4
00
26
4
32
32
64:1
64:1
4
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184 Xtensa Instruction Set Architecture (ISA) Reference Manual
Figure 4–44. Faster Register Window Read
Figure 4–45. Fastest Register Window Read
4.7.1.3 Window Overflow Check
The ENTRY instruction moves the register window, but does not guarantee that all the
registers in the current window are available for use. Instead, the processor waits for the
first reference to an occupied physical register before triggering a window overflow. This
prevents unnecessary overflows, because many routines do not use all 16 of their virtual
t
s+
4
00
2
4
WindowBase
Inst
+
4
00
2
4
4
64 32-bit
registers
32 x 64
432
32
4:1
4:1
16:1
16:1
4
t
s4
WindowBase
Inst
4
64 32-bit
registers
32
32
16:1
16:1
16:1
16:1
4
32 x 64
Chapter 4. Architectural Options
Xtensa Instruction Set Architecture (ISA) Reference Manual 185
registers. Figure 4–46 shows the state of the register file just prior to a reference that
causes an overflow. The WS(n) notation shows which WindowStart bits are set in this
example, and gives the distance to the next bit set (that is, the number of registers
stored for the corresponding stack frame). In the figure, “rmax” indicates the maximum
register that the current procedure uses and “Base” is an abbreviation for WindowBase.
Note that registers are considered in groups of four here.
Figure 4–46. Register Window Near Overflow
The check for overflow is done as follows:
WindowCheck ( if ref(AR[r]) then r3..2 else 2'b00,
if ref(AR[s]) then s3..2 else 2'b00,
if ref(AR[t]) then t3..2 else 2'b00)
where ref() is 1 if the register is used by the instruction, and 0 otherwise, and
WindowCheck is defined as follows:
procedure WindowCheck (wr, ws, wt)
n ← if (wr ≠ 2'b00 or ws ≠ 2'b00 or wt ≠ 2'b00)
and WindowStartWindowBase+1 then 2’b01
else if (wr1 or ws1 or wt1)
and WindowStartWindowBase+2 then 2’b10
else if (wr = 2'b11 or ws = 2'b11 or wt = 2'b11)
and WindowStartWindowBase+3 then 2’b11
else 2’b00
if CWOE = 1 and n ≠ 2’b00 then
PS.OWB ← WindowBase
m ← WindowBase + (2'b00||n)
PS.EXCM ← 1
EPC[1] ← PC
nextPC ← if WindowStartm+1 then WindowOverflow4
else if WindowStartm+2 then WindowOverflow8
else WindowOverflow12
Base Base+
Valid Data
Window
Base
rmax
Valid Data
+16
Active regs
Invalid
WS(1)
WS(2) WS(2)
WS(2) WS(3) WSWS(1) WS(2)
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186 Xtensa Instruction Set Architecture (ISA) Reference Manual
WindowBase ← m
endif
endprocedure WindowCheck
A single instruction may raise multiple window overflow exceptions. For example, sup-
pose that registers 4..7 of the current window still contain a previous call frame’s val-
ues (WindowStartWindowBase+1 is set), and 8..15 are part of the subroutine called by
that frame (WindowStartWindowBase+2 is also set), and an instruction references regis-
ter 10. The processor will raise an exception to spill registers 4..7 and then return to
retry the instruction, which will then raise another exception to spill registers 8..15. On
return from this overflow handler, the reference will finally succeed.
4.7.1.4 Call, Entry, and Return Mechanism
The register window mechanics of the {CALL, CALLX}{4,8,12}, ENTRY, and {RETW,
RETW.N} instructions are:
CALLn/CALLXn
WindowCheck (2'b00, 2'b00, n)
PS.CALLINC ← n
AR[n||2'b00] ← n || (PC + 3)29..0
ENTRY s, imm12
AR[PS.CALLINC||s1..0] ← AR[s] − (017||imm12||03)
WindowBase ← WindowBase + (02||PS.CALLINC)
WindowStartWindowBase ← 1
In the definition of ENTRY above, the AR read and the AR write refer to different registers.
RETW/RETW.N
n ← AR[0]31..30
nextPC ← PC31..30 || AR[0]29..0
owb ← WindowBase
m ← if WindowStartWindowBase-4’b0001 then 2’b01
elsif WindowStartWindowBase-4’b0010 then 2’b10
elsif WindowStartWindowBase-4’b0011 then 2’b11
else 2’b00
if n = 2’b00 | (m ≠ 2’b00 & m ≠ n) | PS.WOE=0 | PS.EXCM=1 then
-- undefined operation
-- may raise illegal instruction exception
else
WindowBase ← WindowBase − (02||n)
if WindowStartWindowBase ≠ 0 then
WindowStartowb ← 0
else
-- Underflow exception
PS.EXCM ← 1
Chapter 4. Architectural Options
Xtensa Instruction Set Architecture (ISA) Reference Manual 187
EPC[1] ← PC
PS.OWB ← owb
nextPC ← if n = 2'b01 then WindowUnderflow4
else if n = 2'b10 then WindowUnderflow8
else WindowUnderflow12
endif
endif
The RETW opcode assignment is such that the s and t fields are both zero, so that the
hardware may use either AR[s] or AR[t] in place of AR[0] above. Underflow is de-
tected by the caller’s window’s WindowStart bit being clear (that is, not valid).
Figure 4–47 shows the register file just before a RETW that raises an underflow excep-
tion. window overflow and window underflow exceptions leave PS.UM unchanged.
Figure 4–47. Register Window Just Before Underflow
4.7.1.5 Windowed Procedure-Call Protocol
While the procedure-call protocol is a matter for the compiler and ABI, the Xtensa ISA,
and particularly the Windowed Register Option was designed with the following goals in
mind:
Provide highly efficient call/return (measured in both code size and execution time)
Support per-call register window increments
Use a single stack for both register save/restore and local variables
Support variable frame sizes (for example, alloca)
Support programming language exception handling (for example,
setjmp/longjmp, catch/throw, and so forth)
Support debuggers
Base Base+rmax
Valid Data
InvalidInvalid
Base +16
Active Regs
WS
Window
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188 Xtensa Instruction Set Architecture (ISA) Reference Manual
Require minimal special ISA features (special registers and so forth)
Table 4–114 shows the register usage in the Windowed Register Option. Refer to
Section 8.1 “The Windowed Register and CALL0 ABIs” for a more complete description
of the Windowed Register ABI.
Calls to routines that use only a2..a3 as parameters may use the CALL4, CALL8, or
CALL12 instructions to save 4, 8, or 12 live registers. Calls to routines that use a2..a7
for parameters may use only CALL4 or CALL8. The following assembly language illus-
trates the call protocol.
// In procedure g, the call
// z = f(x, y)
// would compile into
mov a6, x // a6 is f’s a2 (x)
mov a7, y // a7 is f’s a3 (y)
call4 f // put return address in f’s a0,
// goto f
mov z, a6 // a6 is f’s a2 (return value)
// The function
// int f(int a, int *b) { return a + *b; }
// would compile into
f: entry sp, framesize// allocate stack frame, rotate regs
// on entry, a0/ return address, a1/ stack pointer,
// a2/ a, a3/ *b
l32i a3, a3, 0 // *b
add a2, a2, a3// *b + a
retw
The “highly efficient call/return” goal requires that there not be separate stack and frame
pointer registers in cases where they would differ by a constant (that is, no alloca is
used). There are simply not enough registers to waste. For routines that do call alloca,
the compiler will copy the initial stack pointer to another register and use that for ad-
dressing all locals.
The variable allocation,
p1 = alloca(n1);
will be implemented as
Table 4–114. Windowed Register Usage
Callee Register Register Name Usage
0a0 Return address
1a1/sp Stack pointer
2..7 a2..a7 In, out, inout, and return values
Chapter 4. Architectural Options
Xtensa Instruction Set Architecture (ISA) Reference Manual 189
movi t4, -16 // for alignment to 16-byte boundary
sub t5, sp, n1 // reserve stack space
and t4, t5, t4 // ...
movsp sp, t4 // atomically set sp
addi p1, sp, -16+botsize// save pointer
The botsize in the last statement allows the compiler to maintain a block of words at
the bottom of the stack (for example, this block might be for memory arguments to rou-
tines). The -16 is a constant of the call protocol; it puts 16 bytes of the bottom area be-
low the stack pointer (since they are infrequently referenced), leaving the limited range
of the ISA’s load/store offsets available for more frequently referenced locals.
Figure 4–48 and Figure 4–49 show the stack frame before and after alloca.
Figure 4–48. Stack Frame Before
alloca()
sp
locals Minimum Frame size
bottom
(specified in ENTRY instruction)
lp
sp-16
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190 Xtensa Instruction Set Architecture (ISA) Reference Manual
Figure 4–49. Stack Frame After First
alloca()
Figure 4–50 shows the stacking of frames when the stack grows downward, as on most
other systems. The window save area for a frame is addressed with negative offsets
from the next stack frame’s sp. Four registers are saved in the base save area. If more
than four registers are saved, they are stored at the top of the stack frame, in the extra
save area, which can be found with negative offsets from the previous stack frame’s sp.
This unusual split allows for simple backtrace while providing for a variable sized save
area.
sp
locals
bottom
lp
sp-16
n1 bytes
p1
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Xtensa Instruction Set Architecture (ISA) Reference Manual 191
Figure 4–50. Stack Frame Layout
Several of the goals listed on page 187 require that call stacks be backward-traceable.
That is, from the state of call[i], it must be possible to determine the state of
call[i-1]. It is best if the state of call[i] can be summarized in a single pointer (at
least when the registers have been saved), in which case this requirement is best de-
scribed as: There must be a means of determining the pointer for call[i-1] from the
pointer of call[i]. For managing register-window overflow or underflow, this method
should also be very efficient; it should not, for example, involve routine-specific informa-
tion or other table lookup (for example, frame size or stack offsets).
The Xtensa ISA represents the state of call[i] with its stack pointer (not the frame
pointer, as that is routine-specific and would cost too much to lookup). This can be made
to work even with alloca. Therefore it must be possible to read the stack pointer for
Stack Pointer (a1/sp)
locals i
extra save area i
Stack Pointer i-1
Frame i (current frame)
locals i-1
extra save area i-1
Frame i-1 (previous frame)
base save area i-1
base save area i-2
smaller addresses
larger addresses
Stack Pointer i-2
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192 Xtensa Instruction Set Architecture (ISA) Reference Manual
call[i-1] at a fixed offset from the stack pointer (not the frame pointer) for call[i].
Thus, the stack pointer for call[i-1] is stored in the area labeled “base save area i-1”
in Figure 4–48.
For efficiency, the call[i-1] stack pointer is only stored into call[i]’s frame when
call[i-1]’s registers are stored into the stack on overflow. This is sufficient for regis-
ter window underflow handling. Other back-tracing operations should begin by storing
registers of all call frames back into the stack.
Because the call[i-1] stack pointer is referenced infrequently, it is stored at a nega-
tive offset from the stack pointer. This leaves the ISA’s limited positive offsets available
for more frequent uses. Thus, the stack always reaches to 16 bytes below the contents
of the stack pointer. Interrupts and such must respect this 16-byte reserved space below
the stack pointer. Because the minimum number of registers to save is four, the proces-
sor stores four of call[i-1]’s registers, a0..a3, in this space; the rest (if any) are
saved in call[i-1]’s own frame.
The register-window call instructions only store the least-significant 30 bits of the return
address. Register-window return instructions leave the two most-significant bits of the
PC unchanged. Therefore, subroutines called using register window instructions must
be placed in the same 1 GB address region as the call.
4.7.1.6 Window Overflow and Underflow to and from the Program Stack
Register-window underflow occurs when a return instruction decrements to a window
that has been spilled (indicated by its WindowStart bit being cleared). The processor
saves the current PC in EPC[1] and transfers to one of three underflow handlers based
on the register window decrement. When the MMU Option is configured, it is necessary
for the handlers to access the stack with the same privilege level as the code that raised
the exception. Two special instructions, L32E and S32E, are therefore added by the
Windowed Register Option for this purpose. In addition, these instructions use negative
offsets in the formation of the virtual address, which saves several instructions in the
handlers. The exception handlers could be as simple as the following:
WindowOverflow4: // inside call[i] referencing a register that
// contains data from call[j]
// On entry here: window rotated to call[j] start point; the
// registers to be saved are a0-a3; a4-a15 must be preserved
// a5 is call[j+1]’s stack pointer
s32e a0, a5, -16 // save a0 to call[j+1]’s frame
s32e a1, a5, -12 // save a1 to call[j+1]’s frame
s32e a2, a5, -8 // save a2 to call[j+1]’s frame
s32e a3, a5, -4 // save a3 to call[j+1]’s frame
rfwo // rotates back to call[i] position
WindowUnderflow4: // returning from call[i+1] to call[i] where
Chapter 4. Architectural Options
Xtensa Instruction Set Architecture (ISA) Reference Manual 193
// call[i]’s registers must be reloaded
// On entry here: a0-a3 are to be reloaded with
// call[i].reg[0..3] but initially contain garbage.
// a4-a15 are call[i+1].reg[0..11],
// (in particular, a5 is call[i+1]’s stack pointer)
// and must be preserved
l32e a0, a5, -16 // restore a0 from call[i+1]’s frame
l32e a1, a5, -12 // restore a1 from call[i+1]’s frame
l32e a2, a5, -8 // restore a2 from call[i+1]’s frame
l32e a3, a5, -4 // restore a3 from call[i+1]’s frame
rfwu
WindowOverflow8:
// On entry here: window rotated to call[j]; the registers to be
// saved are a0-a7; a8-a15 must be preserved
// a9 is call[j+1]’s stack pointer
s32e a0, a9, -16 // save a0 to call[j+1]’s frame
l32e a0, a1, -12 // a0 <- call[j-1]’s sp
s32e a1, a9, -12 // save a1 to call[j+1]’s frame
s32e a2, a9, -8 // save a2 to call[j+1]’s frame
s32e a3, a9, -4 // save a3 to call[j+1]’s frame
s32e a4, a0, -32 // save a4 to call[j]’s frame
s32e a5, a0, -28 // save a5 to call[j]’s frame
s32e a6, a0, -24 // save a6 to call[j]’s frame
s32e a7, a0, -20 // save a7 to call[j]’s frame
rfwo // rotates back to call[i] position
WindowUnderflow8:
// On entry here: a0-a7 are call[i].reg[0..7] and initially
// contain garbage, a8-a15 are call[i+1].reg[0..7],
// (in particular, a9 is call[i+1]’s stack pointer)
// and must be preserved
l32e a0, a9, -16 // restore a0 from call[i+1]’s frame
l32e a1, a9, -12 // restore a1 from call[i+1]’s frame
l32e a2, a9, -8 // restore a2 from call[i+1]’s frame
l32e a7, a1, -12 // a7 <- call[i-1]’s sp
l32e a3, a9, -4 // restore a3 from call[i+1]’s frame
l32e a4, a7, -32 // restore a4 from call[i]’s frame
l32e a5, a7, -28 // restore a5 from call[i]’s frame
l32e a6, a7, -24 // restore a6 from call[i]’s frame
l32e a7, a7, -20 // restore a7 from call[i]’s frame
rfwu
WindowOverflow12:
// On entry here: window rotated to call[j]; the registers to be
// saved are a0-a11; a12-a15 must be preserved
// a13 is call[j+1]’s stack pointer
s32e a0, a13, -16 // save a0 to call[j+1]’s frame
l32e a0, a1, -12 // a0 <- call[j-1]’s sp
Chapter 4. Architectural Options
194 Xtensa Instruction Set Architecture (ISA) Reference Manual
s32e a1, a13, -12 // save a1 to call[j+1]’s frame
s32e a2, a13, -8 // save a2 to call[j+1]’s frame
s32e a3, a13, -4 // save a3 to call[j+1]’s frame
s32e a4, a0, -48 // save a4 to end of call[j]’s frame
s32e a5, a0, -44 // save a5 to end of call[j]’s frame
s32e a6, a0, -40 // save a6 to end of call[j]’s frame
s32e a7, a0, -36 // save a7 to end of call[j]’s frame
s32e a8, a0, -32 // save a8 to end of call[j]’s frame
s32e a9, a0, -28 // save a9 to end of call[j]’s frame
s32e a10, a0, -24 // save a10 to end of call[j]’s frame
s32e a11, a0, -20 // save a11 to end of call[j]’s frame
rfwo // rotates back to call[i] position
WindowUnderflow12:
// On entry here: a0-a11 are call[i].reg[0..11] and initially
// contain garbage, a12-a15 are call[i+1].reg[0..3],
// (in particular, a13 is call[i+1]’s stack pointer)
// and must be preserved
l32e a0, a13, -16 // restore a0 from call[i+1]’s frame
l32e a1, a13, -12 // restore a1 from call[i+1]’s frame
l32e a2, a13, -8 // restore a2 from call[i+1]’s frame
l32e a11, a1, -12 // a11 <- call[i-1]’s sp
l32e a3, a13, -4 // restore a3 from call[i+1]’s frame
l32e a4, a11, -48 // restore a4 from end of call[i]’s frame
l32e a5, a11, -44 // restore a5 from end of call[i]’s frame
l32e a6, a11, -40 // restore a6 from end of call[i]’s frame
l32e a7, a11, -36 // restore a7 from end of call[i]’s frame
l32e a8, a11, -32 // restore a8 from end of call[i]’s frame
l32e a9, a11, -28 // restore a9 from end of call[i]’s frame
l32e a10, a11, -24 // restore a10 from end of call[i]’s frame
l32e a11, a11, -20 // restore a11 from end of call[i]’s frame
rfwu
4.7.2 Processor Interface Option
The Processor Interface Option adds a bus interface used by memory accesses, which
are to locations other than local memories (page 123 through page 126). It is used for
cache misses for cacheable addresses (page 111 through page 122), as well as for
cache bypass memory accesses.
Direct memory access to local memories from outside may also be configured through
the bus interface added by the Processor Interface Option. The direct memory access
may either be top priority for highest bandwidth or intermediate priority for greatest effi-
ciency.
Prerequisites: None
Incompatible options: None
Chapter 4. Architectural Options
Xtensa Instruction Set Architecture (ISA) Reference Manual 195
Historical note: The additions made by this option were once considered part of the
Core Architecture and so compatibility with previous hardware might require the use
of this option.
Refer to a specific Xtensa processor data book for more detail on the Processor Inter-
face Option.
4.7.2.1 Processor Interface Option Architectural Additions
Table 4–115 shows this option’s architectural additions (seeTable 4–64 on page 89 for
more). Note that asynchronous load/store errors are delivered via a configuration-de-
pendent interrupt.
4.7.3 Miscellaneous Special Registers Option
The Miscellaneous Special Registers Option provides zero to four scratch registers with-
in the processor readable and writable by RSR, WSR, and XSR. These registers are privi-
leged. They may be useful for some application-specific exception and interrupt pro-
cessing tasks in the kernel. The MISC registers are undefined after reset.
Prerequisites: None
Incompatible options: None
4.7.3.1 Miscellaneous Special Registers Option Architectural Additions
Table 4–116 and Table 4–117 show this option’s architectural additions.
Table 4–115. Processor Interface Option Constant Additions (Exception Causes)
Exception Cause Description Constant Value
InstrPIFDataErrorCause PIF data error during instruction fetch 6'b001100 (decimal 12)
LoadStorePIFDataErrorCause Synchronous PIF data error during
LoadStore access
6'b001101 (decimal 13)
InstrPIFAddrErrorCause PIF address error during instruction fetch 6'b001110 (decimal 14)
LoadStorePIFAddrErrorCause Synchronous PIF address error during
LoadStore access
6'b001111 (decimal 15)
Table 4–116. Miscellaneous Special Registers Option Processor-Configuration
Additions
Parameter Description Valid Values
NMISC Number of miscellaneous 32-bit
Special Registers
0..4
Chapter 4. Architectural Options
196 Xtensa Instruction Set Architecture (ISA) Reference Manual
4.7.4 Thread Pointer Option
The Thread Pointer Option provides an additional register to facilitate implementation of
Thread Local Storage by operating systems and tools. The register is readable and writ-
able by RUR and WUR. The register is unprivileged and is undefined after reset.
Prerequisites: None
Incompatible options: None
4.7.4.1 Thread Pointer Option Architectural Additions
Table 4–118 shows this option’s architectural additions.
4.7.5 Processor ID Option
In some applications there are multiple Xtensa processors executing from the same in-
struction memory, and there is a need to distinguish one processor from another. This
option allows the system logic to provide each processor an identity by reading the PRID
register. The PRID value for each processor is typically in the range
0..NPROCESSORS-1, but this is not required. The PRID register is constant after reset.
Prerequisites: None
Incompatible options: None
4.7.5.1 Processor ID Option Architectural Additions
Table 4–119 shows this option’s architectural additions.
Table 4–117. Miscellaneous Special Registers Option Processor-State Additions
Register
Mnemonic Quantity Width
(bits) Register Name R/W
Special
Register
Number
1
MISC NMISC 32 Miscellaneous privileged register R/W 244-247
1. Registers with a Special Register assignment are read and/or written with the RSR, WSR, and XSR instructions. See Table 5–127 on
page 205.
Table 4–118. Thread Pointer Option Processor-State Additions
Register
Mnemonic Quantity Width
(bits) Register Name R/W Register Number
1
THREADPTR 132 Thread pointer R/W User 231
1. See Table 5–127 on page 205.
Chapter 4. Architectural Options
Xtensa Instruction Set Architecture (ISA) Reference Manual 197
4.7.6 Debug Option
The Debug Option implements instruction-counting and breakpoint exceptions for de-
bugging by software or external hardware. The option uses an interrupt level previously
defined in the High-Priority Interrupt Option. In some implementations, some debug in-
terrupts may not be masked by PS.INTLEVEL (see the Tensilica On-Chip Debugging
Guide). The Debug Option is useful when configuring a new (not previously debugged)
Xtensa processor configuration or for running previously untested software on a proces-
sor.
Prerequisites: High-Priority Interrupt Option (page 106)
Incompatible options: None
Some of the features listed below are added only when the OCD Option (see the Tensil-
ica On-Chip Debugging Guide) is configured in addition to the Debug Option. Those fea-
tures are included here, under the Debug Option, so that their architectural aspects are
documented, but marked as “available only with OCD Option.”
4.7.6.1 Debug Option Architectural Additions
Table 4–120 through Table 4–122 show this option’s architectural additions.
Table 4–119. Processor ID Option Special Register Additions
Register
Mnemonic Quantity Width
(bits) Register Name R/W Special Register
Number
1
PRID 1322Processor Id R235
1. Registers with a Special Register assignment are read with the RSR instruction. See Tabl e 5–127 on page 205.
2. Some implementations may support only the low 16 bits of the PRID register.
Table 4–120. Debug Option Processor-Configuration Additions
Parameter Description Valid Values
DEBUGLEVEL Debug interrupt level 2..NLEVEL1,2
NIBREAK Number of instruction breakpoints (break registers) 0..2
NDBREAK Number of data breakpoints (break registers) 0..2
SZICOUNT Number of bits in the ICOUNT register 2, 32
1. NLEVEL is specified in the High-Priority Interrupt Option, Table 4–74 on page 107.
2. DEBUGLEVEL must be greater than EXCMLEVEL (see Tab le 4–74 on page 107)
Chapter 4. Architectural Options
198 Xtensa Instruction Set Architecture (ISA) Reference Manual
4.7.6.2 Debug Cause Register
The DEBUGCAUSE register contains a coded value giving the reason(s) that the proces-
sor took the debug exception. It is implementation-specific whether all applicable bits
are set or whether lower-priority conditions are undetected in the presence of higher-pri-
ority conditions.
For the priority of the bits in the DEBUGCAUSE register, see Section 4.4.1.11.
Figure 4–51 below shows the bits in the DEBUGCAUSE register, and Table 4–123 de-
scribes more fully the meaning of each bit.
Table 4–121. Debug Option Processor-State Additions
Register
Mnemonic Quantity Width
(bits) Register Name R/W
Special
Register
Number
1
ICOUNT 12,32 Instruction count R/W 236
ICOUNTLEVEL 14Instruction-count level R/W 237
IBREAKA NIBREAK 32 Instruction-break address R/W 128-129
IBREAKENABLE 1NIBREAK Instruction-break enable bits R/W 96
DBREAKA NDBREAK 32 Data-break address R/W 144-145
DBREAKC NDBREAK 82Data break control R/W 160-161
DEBUGCAUSE 110 Cause of last debug exception R233
DDR31332 Debug data register R/W 104
1. Registers with a Special Register assignment are read and/or written with the RSR, WSR, and XSR instructions. See Table 5–127 on page 205.
2. See Figure 4–52 on page 202 for the DBREAKC register format.
3. The DDR register may have separate physical registers for in and out directions in some implementations. The register is only available with
the OCD Option, for which the Debug Option is a prerequisite.
Table 4–122. Debug Option Instruction Additions
Instruction
1
Format Definition
BREAK RRR Breakpoint
BREAK.N2RRRN Narrow breakpoint
1. These instructions are fully described in Chapter 6, "Instruction Descriptions" on page 243.
2. Exists only if the Code Density Option described in Section 4.3.1 on page 53 is configured.
Chapter 4. Architectural Options
Xtensa Instruction Set Architecture (ISA) Reference Manual 199
Figure 4–51. DEBUGCAUSE Register
The DEBUGCAUSE register is undefined after processor reset and when CINTLEVEL <
DEBUGLEVEL.
4.7.6.3 Using Breakpoints
BREAK and BREAK.N are 24-bit and 16-bit instructions that simply raise a DEBUGLEVEL
exception with DEBUGCAUSE bit 3 or 4 set, respectively, when executed. Software can
replace an instruction with a breakpoint instruction to transfer control to a debug monitor
when execution reaches the replaced instruction.
The BREAK and BREAK.N instructions cannot be used on ROM code, and so the ISA
provides a configurable number of instruction-address breakpoint registers. When the
processor is about to complete the execution of the instruction fetched from virtual ad-
dress IBREAKA[i], and IBREAKENABLEi is set, it raises an exception instead. It is up
to the software to compare the PC to the various IBREAKA/IBREAKENABLE pairs to de-
termine which comparison caused the exception.
The processor also provides a configurable number of data-address breakpoint regis-
ters. Each breakpoint specifies a naturally aligned power of two-sized block of bytes be-
tween one byte and 64 bytes in the processor’s address space and whether the break
should occur on a load or a store or both. The lowest address of the covered block of
31 12 11 876543210
reserved DBNUM re-
served
D
I
B
N
B
I
D
B
I
B
I
C
4 6
Table 4–123. DEBUGCAUSE Fields
Bit Field Meaning
0IC ICOUNT exception
1IB IBREAK exception
2DB DBREAK exception
3BI BREAK instruction
4BN BREAK.N instruction
5DI Debug interrupt1
11-8 DBNUM Which of the DBREAK registers matched (added in RA-2004.1 release)
1. The debug interrupt is only available with the OCD Option.
Chapter 4. Architectural Options
200 Xtensa Instruction Set Architecture (ISA) Reference Manual
bytes is placed in one of the DBREAKA registers. The size of the covered block of bytes
is placed in the low bits of the corresponding DBREAKC register while the upper two bits
of the DBREAKC register contain an indication of which access types should raise the ex-
ception. The settings for each possible block size are shown in Table 4–124. The ‘x’ val-
ues under DBREAKA[i]5..0 allow any naturally aligned address to be specified for that
size. The result of other combinations of DBREAKC and DBREAKA is not defined.
When any of the bytes accessed by a load or store matches any of the bytes of the block
specified by one of the DBREAK[i] register pairs, the processor raises an exception in-
stead of executing the load or store. Specifically, “match” is defined as:
(if load then DBREAKC[i]30 else DBREAKC[i]31) and
(DBREAKA[i] >= (126||DBREAKC[i]5..0 and vAddr)) and
(DBREAKA[i] <= (126||DBREAKC[i]5..0 and (vAddr+sz-1)))
where sz is the number of bytes in the memory access. That is, both the first and last
byte of the memory access are masked by (126||DBREAKC[i]5..0). This operation aligns
both byte addresses to the DBREAK size indicated by DBREAKC[i]as in Table 4–124. If
the first or last masked address or any address between them matches DBREAKA[i]
then a match exists. Note that bits in DBREAKA[i]5..0 corresponding to clear bits in
DBREAKC[i]5..0 should also be clear.
For the DBREAK exception, the DBNUM field of the DEBUGCAUSE register records, as a
four bit encoded number, which of the possible DBREAK[i] registers raised the excep-
tion. If more than one DBREAK[i] matches, one of the ones that matched is recorded in
DBNUM.
The processor clears IBREAKENABLE on processor reset; the IBREAKA, DBREAKA, and
DBREAKC registers are undefined after reset.
Table 4–124. DBREAK Fields
Desired
DBREAK
Size
DBREAKC[i]5..0 DBREAKA[i]5..0
1 Byte 6’b111111 6’bxxxxxx
2 Bytes 6’b111110 6’bxxxxx0
4 Bytes 6’b111100 6’bxxxx00
8 Bytes 6’b111000 6’bxxx000
16 Bytes 6’b110000 6’bxx0000
32 Bytes 6’b100000 6’bx00000
64 Bytes 6’b000000 6’b000000
Chapter 4. Architectural Options
Xtensa Instruction Set Architecture (ISA) Reference Manual 201
4.7.6.4 Debug Exceptions
Typically DEBUGLEVEL is set to NLEVEL (highest priority for maskable interrupts) to al-
low debugging of other exception handlers. DEBUGLEVEL may, in certain cases be set to
a lower level than NLEVEL.
The relation between the current interrupt level (CINTLEVEL, Table 4–63) and the spec-
ified debug interrupt level (DEBUGLEVEL, Table 4–120) determine whether debug inter-
rupts can be taken. All debug exceptions (ICOUNT, IBREAK, DBREAK, BREAK, BREAK.N)
are disabled when CINTLEVEL ≥ DEBUGLEVEL. In this case, the BREAK and BREAK.N
instructions perform no operation.
4.7.6.5 Instruction Counting
The ICOUNT register counts instruction completions when CINTLEVEL is less than
ICOUNTLEVEL. Instructions that raise an exception (including the ICOUNT exception) do
not increment ICOUNT. When ICOUNT would increment to 0, it instead generates an
ICOUNT exception. (See "The checkIcount Procedure" on page 203 for the formal spec-
ification.) Because ICOUNT has priority ahead of other exceptions (see
Section 4.4.1.11), it is taken even if another exception would have kept the instruction
from completing and, therefore, ICOUNT from incrementing.
When ICOUNTLEVEL is 1, for example, ICOUNT stops counting when an interrupt or ex-
ception occurs and starts again at the return. Neither the instruction not executed nor
the return increment ICOUNT, but the re-execution of the instruction does. By this
mechanism, the count of instructions can be made the same whether or not the interrupt
or exception is taken. When incrementing is turned on or off by RSIL, WSR.PS, or
XSR.PS instructions, the state of CINTLEVEL and ICOUNTLEVEL before the instruction
begins determines whether or not the increment is done, as well as whether or not the
exception is raised.
Instruction counting may be used to implement single or multi-stepping. For repeatable
programs, it can also be used to determine the instruction count of the point of failure,
and allow the program to be re-run up to some point before the point of failure so that
the failure can be directly observed with tracing or stepping.
The purpose of the ICOUNTLEVEL register is to allow various levels of exception and in-
terrupt processing to be visible or invisible for debugging. An ICOUNTLEVEL setting of 1
causes single-stepping to ignore exceptions and interrupts, whereas setting it to
DEBUGLEVEL allows the programmer to debug exception and interrupt handlers. The
ICOUNTLEVEL register should only be modified while PS.INTLEVEL or PS.EXCM is
high enough that both before and after the change, ICOUNT is not incrementing.
Chapter 4. Architectural Options
202 Xtensa Instruction Set Architecture (ISA) Reference Manual
This discussion applies for SZICOUNT=32. If SZICOUNT=2, then the upper bits appear
as all ones for all purposes of reading with RSR and for comparing. In that case,
WSR.ICOUNT affects only the lower two bits. The result is that the feature is really only
useful for single stepping because it cannot count very far. But in other respects it be-
haves in the same fashion.
ICOUNTLEVEL is undefined after reset. The ICOUNT register should be read or written
only when CINTLEVEL is greater than or equal to ICOUNTLEVEL, where the ICOUNT
register is not incrementing (see Table 5–173).
4.7.6.6 Debug Registers
Like all special registers, the IBREAKA, IBREAKENABLE, DBREAKA, DBREAKC, and
ICOUNT registers are read and written using the RSR, WSR, and XSR instructions.
Figure 4–52 shows the format of the DBREAKC registers and Table 4–125 shows the
DBREAKC[i] register fields.
Figure 4–52.
DBREAKC[i]
Format
31 30 29 6 5 0
SB LB reserved MASK
1 1 6
Table 4–125.
DBREAKC[i]
Register Fields
Field Width
(bits) Definition
MASK 6Mask specifying which bits of vAddr to compare to DBREAKA[i]
See "Using Breakpoints" on page 199 for details.
LB
1Load data address match enable
0 → no exception on load data address match
1 → exception on load data address match
SB
1Store data address match enable
0 → no exception on store data address match
1 → exception on store data address match
reserved
Reserved for future use
Writing a non-zero value to one of these fields results in undefined processor
behavior.
Chapter 4. Architectural Options
Xtensa Instruction Set Architecture (ISA) Reference Manual 203
4.7.6.7 Debug Interrupts
The debug data register (DDR) allows communication between a debug supervisor exe-
cuting on the processor and a debugger executing on a remote host. To stop an execut-
ing program being debugged, the external debugger may use a debug interrupt. Debug
interrupts share the same vector as other debug exceptions
(InterruptVector[DEBUGLEVEL]), but are distinguished by the setting of the DI bit of the
DEBUGCAUSE register. Both the DDR register and the debug interrupt are only available
with the OCD option (see the Tensilica On-Chip Debugging Guide).
The INTENABLE register (see Section 4.4.4) does not contain a bit for the debug inter-
rupt.
4.7.6.8 The
checkIcount
Procedure
The definition of checkIcount, used in Section 3.5.4.1 “Little-Endian Fetch Semantics”
on page 29 and Section 3.5.4.2 “Big-Endian Fetch Semantics” on page 31, is:
procedure checkIcount ()
if CINTLEVEL < ICOUNTLEVEL then
if ICOUNT ≠ -1 then
ICOUNT ← ICOUNT + 1
elseif CINTLEVEL < DEBUGLEVEL then
-- Exception
DEBUGCAUSE ← 1
EPC[DEBUGLEVEL] ← PC
EPS[DEBUGLEVEL] ← PS
PC ← InterruptVector[DEBUGLEVEL]
PS.EXCM ← 1
PS.INTLEVEL ← DEBUGLEVEL
endif
endif
endprocedure checkIcount
4.7.7 Trace Port Option
The Trace Port Option provides outputs for tracing the processor’s activity without the
affect on processor timing that would happen with software profiling. For more informa-
tion on this option, see the Xtensa Microprocessor Data Book. Because the Trace Port
Option provides only additional outputs, it adds only the few architectural features listed
below.
Prerequisites: None
Incompatible options: None
Chapter 4. Architectural Options
204 Xtensa Instruction Set Architecture (ISA) Reference Manual
4.7.7.1 Trace Port Option Architectural Additions
Table 4–119 shows this option’s architectural additions.
The MMID register is a write only location whose contents affect the output to the trace
port and help in decoding the trace output by defining the which memory map is in force.
Table 4–126. Trace Port Option Special Register Additions
Register
Mnemonic Quantity Width
(bits) Register Name R/W Special Register
Number
1
MMID 132 Memory Map Id W89
1. Registers with a Special Register assignment are read with the RSR instruction. See Table 5–127 on page 205.
Chapter 5. Processor State
Xtensa Instruction Set Architecture (ISA) Reference Manual 205
5. Processor State
The architectural state of an Xtensa machine consists of its AR register file, a PC, Special
Registers, User Registers, TLB entries, and additional register files (added by options
and designer’s TIE). The Windowed Register Option causes an increase in the physical
size of the AR register file but does not change the number of registers visible by instruc-
tions at any given time. To a lesser extent, caches and local memories can be consid-
ered in some ways to be architectural state. The subsections of this chapter cover each
of these categories of state in turn.
The Floating-Point Coprocessor Option adds the FR register file and two User Registers
called FCR and FSR. The Region Protection Option and the MMU Option add ITLB En-
tries and DTLB Entries. Other options add only Special Registers. Designer’s TIE may
add User Registers, and additional register files. Only the AR register file, the PC, and
SAR are in all Xtensa processors.
Table 5–127 contains an alphabetical list of all Tensilica-defined registers that make up
Xtensa processor state, including the registers added by all architectural options. The
Special Register number column of most entries contains a Special Register number,
which can be looked up in Section 5.3 for more information. The last column contains a
reference where more information can be found in the pages following the table.
Table 5–127. Alphabetical List of Processor State
Name
1
Description Required Configuration
Option
Special
Register
Number
More Detail
ACCHI Accumulator high bits MAC16 Option 17 Table 5–133
ACCLO Accumulator low bits MAC16 Option 16 Table 5–132
AR Address registers (general
registers)
Core Architecture —Section 5.1
ATOMCTL Atomic Operation Control Conditional Store Option 99 Table 5–186
BR Boolean registers / register file Boolean Option 4Table 5–136
CACHEATTR Cache attribute XEA1 Only — see page 611 98 Table 9-250
CCOMPARE0..2 Cycle number to interrupt Timer Interrupt Option 240-242 Table 5–176
CCOUNT Cycle count Timer Interrupt Option 234 Table 5–175
CPENABLE Coprocessor enable bits Coprocessor Option 224 Table 5–184
DBREAKA0..2 Data break address Debug Option 144-145 Table 5–180
DBREAKC0..2 Data break control Debug Option 160-161 Table 5–179
1 Used in RSR, WSR, and XSR instructions.
2 FCR & FSR are User Registers where most are system registers. These names are used in RUR and WUR instructions.
Chapter 5. Processor State
206 Xtensa Instruction Set Architecture (ISA) Reference Manual
DEBUGCAUSE Cause of last debug exception Debug Option 233 Table 5–159
DDR Debug data register Debug Option 104 Table 5–183
DEPC Double exception PC Exception Option 192 Table 5–162
DTLB Entries Data TLB entries Region Protection Option or
MMU Option
—Section 5.5
DTLBCFG Data TLB configuration MMU Option 92 Table 5–152
EPC1 Level-1 exception PC Exception Option 177 Table 5–160
EPC2..7 High level exception PC High-Priority Interrupt Option 178-183 Table 5–161
EPS2..7 High level exception PS High-Priority Interrupt Option 194-199 Table 5–164
EXCCAUSE Cause of last exception Exception Option 232 Table 5–153
EXCSAVE1 Level-1 exception save location Exception Option 209 Table 5–166
EXCSAVE2..7 High level exception save
location
High-Priority Interrupt Option 210-215 Table 5–167
EXCVADDR Exception virtual address Exception Option 238 Table 5–154
FCR Floating point control register Floating-Point Coprocessor
Option
—Table 5–189
FR Floating point registers Floating-Point Coprocessor
Option
—Section 5.6
FSR Floating point status register Floating-Point Coprocessor
Option
—Table 5–190
IBREAKA0..2 Instruction break address Debug Option 128-129 Table 5–178
IBREAKENABLE Instruction break enable bits Debug Option 96 Table 5–177
ICOUNT Instruction count Debug Option 236 Table 5–173
ICOUNTLEVEL Instruction count level Debug Option 237 Table 5–174
INTCLEAR Clear requests in
INTERRUPT
Interrupt Option 227 Table 5–171
INTENABLE Interrupt enable bits Interrupt Option 228 Table 5–172
INTERRUPT Interrupt request bits Interrupt Option 226 Table 5–169
INTSET Set Requests in INTERRUPT Interrupt Option 226 Table 5–170
ITLB Entries Instruction TLB entries Region Protection Option or
MMU Option
—Section 5.5
ITLBCFG Instruction TLB configuration MMU Option 91 Table 5–151
Table 5–127. Alphabetical List of Processor State
(continued)
Name
1
Description Required Configuration
Option
Special
Register
Number
More Detail
1 Used in RSR, WSR, and XSR instructions.
2 FCR & FSR are User Registers where most are system registers. These names are used in RUR and WUR instructions.
Chapter 5. Processor State
Xtensa Instruction Set Architecture (ISA) Reference Manual 207
LBEG Loop-begin address Loop Option 0Table 5–129
LCOUNT Loop count Loop Option 2Table 5–131
LEND Loop-end address Loop Option 1Table 5–130
LITBASE Literal base Extended L32R Option 5Table 5–137
M0..3 MAC16 data registers/register
file
MAC16 Option 32-35 Table 5–134
MECR Memory error check register Memory ECC/Parity Option 110 Table 5–157
MEPC Memory error PC register Memory ECC/Parity Option 106 Table 5–163
MEPS Memory error PS register Memory ECC/Parity Option 107 Table 5–165
MESAVE Memory error save register Memory ECC/Parity Option 108 Table 5–168
MESR Memory error status register Memory ECC/Parity Option 109 Table 5–156
MEVADDR Memory error virtual addr
register
Memory ECC/Parity Option 111 Table 5–158
MISC0..3 Misc register 0-3 Miscellaneous Special
Registers Option
244-247 Table 5–185
MMID Memory map ID Trace Port Option 89 Table 5–182
MR MAC16 Data registers/register
file
MAC16 Option 32-35 Table 5–134
PC Program counter Core Architecture —Section 5.2
PRID Processor Id Processor ID Option 235 Table 5–181
PS Processor state See Table 4–63 on page 87 230 Table 5–139
PTEVADDR Page table virtual address MMU Option 83 Table 5–149
RASID Ring ASID values MMU Option 90 Table 5–150
SAR Shift-amount register Core Architecture 3Table 5–135
SCOMPARE1 Expected data value for
S32C1I
Multiprocessor
Synchronization Option
12 Table 5–138
THREADPTR Thread pointer Thread Pointer Option —Table 5–188
VECBASE Vector Base Relocatable Vector Option 231 Table 5–155
WindowBase Base of current AR window Windowed Register Option 72 Table 5–147
WindowStart Call-window start bits Windowed Register Option 73 Table 5–148
Table 5–127. Alphabetical List of Processor State
(continued)
Name
1
Description Required Configuration
Option
Special
Register
Number
More Detail
1 Used in RSR, WSR, and XSR instructions.
2 FCR & FSR are User Registers where most are system registers. These names are used in RUR and WUR instructions.
Chapter 5. Processor State
208 Xtensa Instruction Set Architecture (ISA) Reference Manual
5.1 General Registers
Many Xtensa instructions operate on the general registers in the AR register file. The in-
structions view sixteen such registers at any given time and usually have a 4-bit specifi-
er field in the instruction for each register they access.
These general registers are named address registers (AR) to distinguish them from the
many different types of data registers that can be added to the instruction set
(Section 5.6). Although the AR registers can be used to hold data as well, they are in-
volved with both the instruction set and the execution pipeline in such a way as to make
them ideally suited to contain addresses and the information used to compute address-
es. They are ideally suited to computing branch conditions and targets as well, and as
such fill the role of general registers in the Xtensa instruction set.
When the Windowed Register Option is enabled, there are actually more than sixteen
registers in the AR register file. The windowed register ABI, described in Section 8.1,
can be used in combination with the Windowed Register Option to make use of the addi-
tional registers and avoid many of the register saves and restores that would normally
be associated with calls and returns. This improves both the speed and the code density
of Xtensa processors.
Reads from and writes to the AR register file are always interlocked by hardware. No
synchronization instructions are ever required by them.
The contents of the AR register file are undefined after reset.
5.2 Program Counter
The program counter (PC) holds the address of the next instruction to execute. It is
updated by instructions as they execute. Non-branch instructions simply increment it by
their length. Branch instructions, when taken, load it with a new value. Call and return in-
structions exist, which move values between the PC and general register AR[0]. Op-
tions such as the Loop Option change the PC in other useful ways.
Changes to and uses of the PC are always interlocked by hardware. No synchronization
instructions are ever required by them.
5.3 Special Registers
Special Registers hold the majority of the state added to the processor by the Options
listed in Chapter 4. Table 5–128 shows the Special Registers in numerical order with ref-
erences to a more detailed description. Special Registers not listed in Table 5–128 are
reserved for future use.
Chapter 5. Processor State
Xtensa Instruction Set Architecture (ISA) Reference Manual 209
Table 5–128. Numerical List of Special Registers
Name
1
Description Required Configuration
Option
Special
Register
Number
More Detail
LBEG Loop-begin address Loop Option 0Table 5–129
LEND Loop-end address Loop Option 1Table 5–130
LCOUNT Loop count Loop Option 2Table 5–131
SAR Shift-amount register Core Architecture 3Table 5–135
BR Boolean registers / register file Boolean Option 4Table 5–136
LITBASE Literal base Extended L32R Option 5Table 5–137
SCOMPARE1 Expected data value for
S32C1I
Conditional Store Option 12 Tab le 5–138
ACCLO Accumulator low bits MAC16 Option 16 Table 5–132
ACCHI Accumulator high bits MAC16 Option 17 Table 5–133
M0..3 / MR MAC16 data registers / register
file
MAC16 Option 32-35 Table 5–134
WindowBase Base of current AR window Windowed Register Option 72 Table 5–147
WindowStart Call-window start bits Windowed Register Option 73 Table 5–148
PTEVADDR Page table virtual address MMU Option 83 Table 5–149
MMID Memory map ID Trace Port Option 89 Table 5–182
RASID Ring ASID values MMU Option 90 Table 5–150
ITLBCFG Instruction TLB configuration MMU Option 91 Tabl e 5–151
DTLBCFG Data TLB configuration MMU Option 92 Table 5–152
IBREAKENABLE Instruction break enable bits Debug Option 96 Table 5–177
CACHEATTR Cache attribute XEA1 Only - see page 611 98 Table 9-250
ATOMCTL Atomic Operation Control Conditional Store Option 99 Table 5–186
DDR Debug data register Debug Option 104 Tab le 5–183
MEPC Memory error PC register Memory ECC/Parity Option 106 Table 5–163
MEPS Memory error PS register Memory ECC/Parity Option 107 Table 5–165
MESAVE Memory error save register Memory ECC/Parity Option 108 Table 5–168
MESR Memory error status register Memory ECC/Parity Option 109 Tabl e 5–156
MECR Memory error check register Memory ECC/Parity Option 110 Table 5–157
MEVADDR Memory error virtual addr
register
Memory ECC/Parity Option 111 Table 5–158
IBREAKA0..1 Instruction break address Debug Option 128-129 Table 5–178
1 Used in RSR, WSR, and XSR instructions.
Chapter 5. Processor State
210 Xtensa Instruction Set Architecture (ISA) Reference Manual
Section 5.3.1 describes the process of reading and writing these special registers, while
the sections that follow describe groups of specific Special Registers in more detail. A
table is included for each special register, which includes information specific to that
special register. The gray shaded rows describe the information that is contained in the
unshaded rows immediately below them.
DBREAKA0..1 Data break address Debug Option 144-145 Table 5–180
DBREAKC0..1 Data break control Debug Option 160-161 Table 5–179
EPC1 Level-1 exception PC Exception Option 177 Table 5–160
EPC2..7 High level exception PC High-Priority Interrupt Option 178-183 Table 5–161
DEPC Double exception PC Exception Option 192 Table 5–162
EPS2..7 High level exception PS High-Priority Interrupt Option 194-199 Table 5–164
EXCSAVE1 Level-1 exception save location Exception Option 209 Table 5–166
EXCSAVE2..7 High level exception save
location
High-Priority Interrupt Option 210-215 Table 5–167
CPENABLE Coprocessor enable bits Coprocessor Option 224 Table 5–184
INTERRUPT Interrupt request bits Interrupt Option 226 Table 5–169
INTSET Set requests in INTERRUPT Interrupt Option 226 Table 5–170
INTCLEAR Clear requests in INTERRUPT Interrupt Option 227 Table 5–171
INTENABLE Interrupt enable bits Interrupt Option 228 Table 5–172
PS Processor state See Table 4–63 on page 87 230 Tab le 5–139
VECBASE Vector Base Relocatable Vector Option 231 Table 5–155
EXCCAUSE Cause of last exception Exception Option 232 Table 5–153
DEBUGCAUSE Cause of last debug exception Debug Option 233 Tab le 5–159
CCOUNT Cycle count Timer Interrupt Option 234 Table 5–175
PRID Processor Id Processor ID Option 235 Table 5–181
ICOUNT Instruction count Debug Option 236 Table 5–173
ICOUNTLEVEL Instruction count level Debug Option 237 Tab le 5–174
EXCVADDR Exception virtual address Exception Option 238 Table 5–154
CCOMPARE0..2 Cycle number to generate
interrupt
Timer Interrupt Option 240-242 Table 5–176
MISC0..3 Misc register 0-3 Miscellaneous Special
Registers Option
244-247 Table 5–185
Table 5–128. Numerical List of Special Registers
(continued)
Name
1
Description Required Configuration
Option
Special
Register
Number
More Detail
1 Used in RSR, WSR, and XSR instructions.
Chapter 5. Processor State
Xtensa Instruction Set Architecture (ISA) Reference Manual 211
The first row shows the Special Register number, the Name (which is used in the RSR.*,
WSR.*, and XSR.* instruction names), a short description, and the value immediately
after reset.
The second row shows the Option that creates the Special Register, the count or num-
ber of such special registers, the number of bits in the special register, whether access
to the register is privileged (requires CRING=0) or not, and whether XSR.* is a legal in-
struction or not. The Option that creates the Special Register is described in Chapter 4
including more information on each Special Register.
The third row shows the function of the WSR.* and RSR.* instructions for this Special
Register. The function of the XSR.* instruction is the combination of the RSR.* and the
WSR.* instructions.
The fourth row shows the other instructions that affect or are affected by this Special
Register.
The last row of each Special Register’s table shows what SYNC instructions are
required when using this Special Register. If no SYNC instructions are ever required, the
row is left out. On the left is an instruction or other action that changes the value of the
Special Register. On the right is an instruction or other action that makes use of the val-
ue of the Special Register. If a SYNC instruction is required for this pair of operations to
work as they should, it is listed in the middle. Wherever a DSYNC is required an ISYNC,
RSYNC, or ESYNC can also be used. Wherever an ESYNC is required an ISYNC or RSYNC
can also be used. Wherever an RSYNC is required an ISYNC can also be used. Note that
the 16-bit versions (*.N) of 24-bit instructions are not listed separately but always have
exactly the same requirements. Versions T1050 and before required additional SYNC
instructions in some cases as described in Section A.8 on page 621.
Because of the importance of its subfields, the PS Special Register is a special case. Its
subfields are listed in the same format as special registers. The synchronizations need-
ed simply because the register has been written are listed under the entire register,
while the synchronizations needed because the value of a subfield has been changed
are listed under the subfield.
5.3.1 Reading and Writing Special Registers
The RSR.*, WSR.*, and XSR.* instructions access the special registers. The accesses
to the Special Registers act as separate instructions in many ways. For the full instruc-
tion name, replace the ‘*’ in the instructions with the name as given in the Special
Register Tables in this section.
Each RSR.* instruction moves a value from a Special Register to a general (AR) regis-
ter. Each WSR.* instruction moves a value from a general (AR) register to a Special Reg-
ister. Each XSR.* instruction exchanges the values in a general (AR) register and a Spe-
Chapter 5. Processor State
212 Xtensa Instruction Set Architecture (ISA) Reference Manual
cial Register. Some Special Registers do not allow this exchange. The Special Register
tables in this section show which do and do not allow this exchange. The exchange
takes place with the two reads taking place first, and then the two writes. In some cases,
the write of a Special Register can affect other behavior of the processor. In general, this
behavior change does not occur until after the instruction (including XSR.*) has com-
pleted execution.
Some of the Special Registers have interactions with other instructions or with hardware
execution. These interactions are also listed in the Special Register tables in this sec-
tion. Because modification of many Special Registers is an unusual occurrence, syn-
chronization instructions are used to ensure that their values have propagated every-
where before certain other actions are allowed to take place. Some of the interlocks
would be costly in performance or in gates if done in hardware, and the synchronization
instructions can be the most efficient solution.
5.3.2 LOOP Special Registers
The Loop Option adds the three registers shown in Table 5–129 through Table 5–131 for
controlling zero overhead loops. When the PC reaches LEND, it executes at LBEG in-
stead and decrements LCOUNT. When LCOUNT reaches zero, the loop back does not oc-
cur.
Table 5–129.
LBEG -
Special Register #0
SR# Name Description Reset Value
0LBEG Loop begin - address of beginning of zero overhead loop Undefined
Option Count Bits Privileged? XSR Legal?
Loop Option 132 No Yes
WSR Function RSR Function
LBEG ← AR[t] AR[t] ← LBEG
Other Changes to the Register Other Effects of the Register
LOOP/LOOPGTZ/LOOPNEZ Branch at end of zero overhead loop
Instruction
⇒
xSYNC
⇒
Instruction
WSR/XSR LBEG ⇒ ISYNC ⇒ Potential branch caused by attempt to execute LEND
Chapter 5. Processor State
Xtensa Instruction Set Architecture (ISA) Reference Manual 213
5.3.3 MAC16 Special Registers
The MAC16 Option adds the six registers described in Table 5–132 through
Table 5–134.
Table 5–130.
LEND -
Special Register #1
SR# Name Description Reset Value
1LEND Loop end - address of instruction after zero overhead loop Undefined
Option Count Bits Privileged? XSR Legal?
Loop Option 132 No Yes
WSR Function RSR Function
LEND ← AR[t] AR[t] ← LEND
Other Changes to the Register Other Effects of the Register
LOOP/LOOPGTZ/LOOPNEZ Branch at end of zero overhead loop
Instruction
⇒
xSYNC
⇒
Instruction
WSR/XSR LEND ⇒ ISYNC ⇒ Potential branch caused by attempt to execute LEND
Table 5–131.
LCOUNT
- Special Register #2
SR# Name Description Reset Value
2LCOUNT Loop count remaining Undefined
Option Count Bits Privileged? XSR Legal?
Loop Option 132 No Yes
WSR Function RSR Function
LCOUNT ← AR[t] AR[t] ← LCOUNT
Other Changes to the Register Other Effects of the Register
LOOP/LOOPGTZ/LOOPNEZ Branch at end of zero overhead loop
Instruction
⇒
xSYNC
⇒
Instruction
WSR/XSR LCOUNT ⇒ ESYNC ⇒ RSR/XSR LCOUNT
WSR/XSR LCOUNT ⇒ ISYNC ⇒ Potential branch caused by attempt to execute LEND
WSR/XSR LCOUNT to zero⇒ ISYNC ⇒ WSR/XSR PS.EXCM with zero (for protection)
Chapter 5. Processor State
214 Xtensa Instruction Set Architecture (ISA) Reference Manual
Table 5–132.
ACCLO -
Special Register #16
SR# Name Description Reset Value
16 ACCLO Accumulator - low bits Undefined
Option Count Bits Privileged? XSR Legal?
MAC16 Option 132 No Yes
WSR Function RSR Function
ACC31..0 ← AR[t] AR[t] ← ACC31..0
Other Changes to the Register Other Effects of the Register
MUL.*/MULA.*/MULS.*/UMUL.* MULA.*/MULS.*
Table 5–133.
ACCHI -
Special Register #17
SR# Name Description Reset Value
17 ACCHI Accumulator - high bits Undefined
Option Count Bits Privileged? XSR Legal?
MAC16 Option 1 8 No Yes
WSR Function RSR Function
ACC39..32 ← AR[t]7..0
Undefined if AR[t]31..8 ≠ AR[t]724 AR[t] ← ACC3924||ACC39..32
Other Changes to the Register Other Effects of the Register
MUL.*/MULA.*/MULS.*/UMUL.* MULA.*/MULS.*
Table 5–134.
M0..3 -
Special Register #32-35
SR# Name Description Reset Value
32-35 M0..3 / MR1MAC16 data registers / register file1Undefined
Option Count Bits Privileged? XSR Legal?
MAC16 Option 432 No Yes
WSR Function RSR Function
M[sr1..0] ← AR[t] AR[t] ← M[sr1..0]
Other Changes to the Register Other Effects of the Register
LDDEC/LDINC/MULA*.LDDEC/MULA*.LDINC MUL.*D*/MULA.*D*/MULS.*D*
1 These registers are known as MR[0..3] in hardware and as m0..3 in the software.
Chapter 5. Processor State
Xtensa Instruction Set Architecture (ISA) Reference Manual 215
5.3.4 Other Unprivileged Special Registers
The SAR Special Register is included in the Xtensa Core Architecture, while the BR,
LITBASE, and SCOMPARE1 Special Registers are added by the options shown along
with other information about them in Table 5–135 through Table 5–138.
Table 5–135.
SAR -
Special Register #3
SR# Name Description Reset Value
3SAR Shift amount register Undefined
Option Count Bits Privileged? XSR Legal?
Core Architecture (see page 25) 1 6 No Yes
WSR Function RSR Function
SAR ← AR[t]5..0
Undefined if AR[t]31..6 ≠ 026 AR[t] ← 026||SAR
Other Changes to the Register Other Effects of the Register
SSL/SSR/SSAI/SSA8B/SSA8L SLL/SRL/SRA/SRC
Table 5–136.
BR -
Special Register #4
SR# Name Description Reset Value
4BR / b0..151Boolean register / register file1Undefined
Option Count Bits Privileged? XSR Legal?
Boolean Option 116 No Yes
WSR Function RSR Function
BR ← AR[t]15..0
Undefined if AR[t]31..16 ≠ 016 AR[t] ← 016||BR
Other Changes to the Register Other Effects of the Register
ALL4/ALL8/ANDB/ANDBC/ANY4/ANY8/
ORB/ORBC/XORB/OEQ.S/OLE.S/OLT.S/
UEQ.S/ULE.S/ULT.S/UN.S/User TIE
ALL4/ALL8/ANDB/ANDBC/ANY4/ANY8/
ORB/ORBC/XORB/
BF/BT/MOVF/MOVF.S/MOVT/MOVT.S
1 This register is known as Special Register BR or as individual Boolean bits b0..15.
Chapter 5. Processor State
216 Xtensa Instruction Set Architecture (ISA) Reference Manual
5.3.5 Processor Status Special Register
The Processor Status Special Register is made up of multiple fields with different pur-
poses within the processor. They are combined into one register to simplify the saving
and restoring of state for exceptions, interrupts, and context switches. Table 5–139
describes the register as a whole, while Table 5–140 through Table 5–146 describe the
individual pieces of the register in a similar format.
The synchronization section of Table 5–139 gives requirements that must be met when-
ever the PS register is written regardless of whether any of its bits are changed. The
synchronization sections of Table 5–140 through Table 5–146 give requirements that
must be met only if that portion of the PS register is being modified.
Table 5–137.
LITBASE -
Special Register #5
SR# Name Description Reset Value
5LITBASE Literal base register bit-0 clear1
Option Count Bits Privileged? XSR Legal?
Extended L32R Option 121 No Yes
WSR Function RSR Function
LITBASE ← AR[t]31..12||011||AR[t]0
Undefined if AR[t]11..1 ≠ 011 AR[t] ← LITBASE31..12||011||LITBASE0
Other Changes to the Register Other Effects of the Register
L32R
1 After reset bit-0 is clear but the remainder of the register is undefined.
Table 5–138.
SCOMPARE1 -
Special Register #12
SR# Name Description Reset Value
12 SCOMPARE1 Comparison register for the S32C1I instruction Undefined
Option Count Bits Privileged? XSR Legal?
Conditional Store Option 132 No Yes
WSR Function RSR Function
SCOMPARE1 ← AR[t] AR[t] ← SCOMPARE1
Other Changes to the Register Other Effects of the Register
S32C1I
Chapter 5. Processor State
Xtensa Instruction Set Architecture (ISA) Reference Manual 217
Table 5–139.
PS -
Special Register #230
SR# Name Description Reset Value
230 PS Miscellaneous program state 0x10 or 0x1F1
Option Count Bits Privileged? XSR Legal?
Exception Option 115 Yes Yes
WSR Function RSR Function
PS ← 013||AR[t]18..16||04||AR[t]11..0
PS.RING should be changed only when CEXCM=1
before the instruction making the change.
AR[t] ← PS
Other Changes to the Register Other Effects of the Register
CALL[X]4-12/RFE/RFDO/RFDD/RFWO/RFWU/RFI
RSIL/WAITI/interrupts/exceptions
CALL[X]4-12/ENTRY/RETW/interrupts/loop-back
Privileged-instructions/ld-st-instructions/exceptions
Instruction
⇒
xSYNC
⇒
Instruction
See following entries for subfields of PS. Write to PS.X means a write to PS that changes subfield X.
1 PS is 5’h1F after reset if the.Interrupt Option is configured but reads as 5’h10 if it is not.
Table 5–140.
PS.INTLEVEL -
Special Register #230 (part)
SR# Name Description Reset Value
230 Part PS.INTLEVEL Interrupt level mask part of PS (Table 5–139)0x0 or 0xF1
Option Count Bits Privileged? XSR Legal?
Interrupt Option 1 4 Yes Yes
WSR Function RSR Function
(see Table 5–139)(see Table 5–139)
Other Changes to the Register Other Effects of the Register
RFI/RFDD/RFDO/RSIL/WAITI/
Hi-level-interrupts/debug-exceptions/NMI RSIL/interrupts/debug-exceptions
Instruction
⇒
xSYNC
⇒
Instruction
Write to PS.INTLEVEL is a write to PS that changes subfield INTLEVEL.
WSR/XSR PS.INTLEVEL ⇒ RSYNC ⇒ Change in accepting interrupts
If PS.EXCM and PS.INTLEVEL are both changed in the same WSR.PS or XSR.PS instruction in such a way
that a particular interrupt is forbidden both before and after the instruction, there will be no cycle during the instruction
where the interrupt may be taken. Thus PS.EXCM may be cleared and PS.INTLEVEL raised (or PS.EXCM set
and PS.INTLEVEL lowered) in the same instruction and no gap is opened between them.
WSR/XSR PS.INTLEVEL ⇒ DSYNC ⇒ Change in taking debug exception (interrupt level)
RFI/RFDD/RFDO/RSIL/WAITI ⇒ (none) ⇒ RSIL or change in accepting interrupts/debug-exceptions
Hi-level-interrupts/debug-excep/NMI ⇒ (none) ⇒ RSIL or change in accepting interrupts/debug-exceptions
1 PS.INTLEVEL is 4’hF after reset if the.Interrupt Option is configured but reads as 4’h0 if it is not.
Chapter 5. Processor State
218 Xtensa Instruction Set Architecture (ISA) Reference Manual
Table 5–141.
PS.EXCM -
Special Register #230 (part)
SR# Name Description Reset Value
230 Part PS.EXCM Exception mask part of PS (Table 5–139)0x1
Option Count Bits Privileged? XSR Legal?
Exception Option 1 1 Yes Yes
WSR Function RSR Function
(see Table 5–139)(see Table 5–139)
Other Changes to the Register Other Effects of the Register
RFI/RFDD/RFDO/RFE/RFWO/RFWU
interrupts/exceptions
CALL[X]4-12/ENTRY/RETW/interrupts/loop-back
Ifetch/privileged-instr/ld-st-instructions/exceptions
Instruction
⇒
xSYNC
⇒
Instruction
Write to PS.EXCM is a write to PS that changes subfield EXCM.
WSR/XSR PS.EXCM ⇒ ISYNC ⇒ Changes in instruction fetch privilege
WSR/XSR PS.EXCM ⇒ RSYNC ⇒ Change in accepting Interrupts
If PS.EXCM and PS.INTLEVEL are both changed in the same WSR.PS or XSR.PS instruction in such a way
that a particular interrupt is forbidden both before and after the instruction, there will be no cycle during the instruction
where the interrupt may be taken. Thus PS.EXCM may be cleared and PS.INTLEVEL raised (or PS.EXCM set
and PS.INTLEVEL lowered) in the same instruction without a gap in interrupt masking.
WSR/XSR PS.EXCM to one ⇒ (none) ⇒ Restore non-zero LCOUNT value
WSR/XSR LCOUNT to zero ⇒ ISYNC ⇒ WSR/XSR PS.EXCM with zero (for protection)
WSR/XSR PS.EXCM ⇒ ESYNC ⇒ CALL[X]4-12/ENTRY/RETW
Note: In the Windowed Register Option, any instruction with an AR register operand can cause overflow exceptions.
WSR/XSR PS.EXCM ⇒ DSYNC ⇒ Changes in data fetch privilege
WSR/XSR PS.EXCM ⇒ (none) ⇒ Double exception vector or not
RFI/RFDD/RFDO/RFE ⇒ (none) ⇒ Anything
RFWO/RFWU ⇒ (none) ⇒ Anything
Interrupts/exceptions⇒ (none) ⇒ Anything
Chapter 5. Processor State
Xtensa Instruction Set Architecture (ISA) Reference Manual 219
Table 5–142.
PS.UM -
Special Register #230 (part)
SR# Name Description Reset Value
230 Part PS.UM User vector mode part of PS (Table 5–139)0x0
Option Count Bits Privileged? XSR Legal?
Exception Option 1 1 Yes Yes
WSR Function RSR Function
(see Table 5–139)(see Table 5–139)
Other Changes to the Register Other Effects of the Register
RFI/RFDD/RFDO RSIL/level-1-interrupts
general-exceptionsdebug-exceptions
Instruction
⇒
xSYNC
⇒
Instruction
Write to PS.UM is a write to PS that changes subfield UM.
WSR/XSR PS.UM ⇒ RSYNC ⇒ Level-1-interrupts/general-exceptions/debug-exceptions
Note: In the Windowed Register Option, any instruction with an AR register operand can cause overflow exceptions.
Table 5–143.
PS.RING -
Special Register #230 (part)
SR# Name Description Reset Value
230 Part PS.RING Ring part of PS (Table 5–139)0x0
Option Count Bits Privileged? XSR Legal?
MMU Option 1 2 Yes Yes
WSR Function RSR Function
(see Table 5–139)(see Table 5–139)
Other Changes to the Register Other Effects of the Register
RFI/RFDD/RFDO Hi-level-interrupts/debug-exception/
Privileged-instructions/ld-st-instructions
Instruction
⇒
xSYNC
⇒
Instruction
Write to PS.RING is a write to PS that changes subfield RING.
WSR/XSR PS.RING ⇒ ISYNC ⇒ Changes in instruction fetch privilege
WSR/XSR PS.RING ⇒ DSYNC ⇒ Changes in data fetch privilege
Chapter 5. Processor State
220 Xtensa Instruction Set Architecture (ISA) Reference Manual
Table 5–144.
PS.OWB -
Special Register #230 (part)
SR# Name Description Reset Value
230 Part PS.OWB Old window base part of PS (Table 5–139) 0x0
Option Count Bits Privileged? XSR Legal?
Windowed Register Option 1 4 Yes Yes
WSR Function RSR Function
(see Table 5–139)(see Table 5–139)
Other Changes to the Register Other Effects of the Register
RFI/RFDD/RFDO/overflow-or-underflow-exception RFWO/RFWU/RSIL/hi-level-interrupt/debug-exception
Table 5–145.
PS.CALLINC -
Special Register #230 (part)
SR# Name Description Reset Value
230 Part PS.CALLINC Call increment part of PS (Table 5–139)0x0
Option Count Bits Privileged? XSR Legal?
Windowed Register Option 1 2 Yes Yes
WSR Function RSR Function
(see Table 5–139)(see Table 5–139)
Other Changes to the Register Other Effects of the Register
CALL[X]4-12/RFI/RFDD/RFDO ENTRY/RSIL/hi-level-interrupt/debug-exception
Table 5–146.
PS.WOE -
Special Register #230 (part)
SR# Name Description Reset Value
230 Part PS.WOE Window overflow enable part of PS (Table 5–139)0x0
Option Count Bits Privileged? XSR Legal?
Windowed Register Option 1 1 Yes Yes
WSR Function RSR Function
(see Table 5–139)(see Table 5–139)
Other Changes to the Register Other Effects of the Register
RFI/RFDD/RFDO CALL4-12/CALLX4-12/ENTRY/RETW/RSIL/
Hi-level-interrupt/debug-exception/overflow-exception
Instruction
⇒
xSYNC
⇒
Instruction
Write to PS.WOE is a write to PS that changes subfield WOE.
WSR/XSR PS.WOE ⇒ RSYNC ⇒ CALL4-12/CALLX4-12/ENTRY/RETW
WSR/XSR PS.WOE ⇒ RSYNC ⇒ Overflow-exception
Note: In the Windowed Register Option, any instruction with an AR register operand can cause overflow exceptions.
Chapter 5. Processor State
Xtensa Instruction Set Architecture (ISA) Reference Manual 221
5.3.6 Windowed Register Option Special Registers
The Windowed Register Option Special registers are described in Table 5–147 and
Table 5–148.
5.3.7 Memory Management Special Registers
The Special Registers for managing memory are described in Table 5–149 through
Table 5–152.
Table 5–147.
WindowBase -
Special Register #72
SR# Name Description Reset Value
72 WindowBase Base of current AR register window Undefined
Option Count Bits Privileged? XSR Legal?
Windowed Register Option 1log2(NAREG/4) Yes Yes
WSR Function RSR Function
WindowBase ← AR[t]X-1..0
Undefined if AR[t]31..X ≠ 032-X
X = log2(NAREG/4)
AR[t] ← 032-X||WindowBase
X = log2(NAREG/4)
Other Changes to the Register Other Effects of the Register
ENTRY/MOVSP/RETW/RFW*/ROTW
Overflow/underflow-exception Any instruction which accesses the AR register file
Instruction
⇒
xSYNC
⇒
Instruction
WSR/XSR WINDOWBASE ⇒ RSYNC ⇒ Any use or def of an ARregister
Table 5–148.
WindowStart -
Special Register #73
SR# Name Description Reset Value
73 WindowStart Call-window start bits Undefined
Option Count Bits Privileged? XSR Legal?
Windowed Register Option 1NAREG/4 Yes Yes
WSR Function RSR Function
WindowStart ← AR[t]NAREG/4-1..0
Undefined if AR[t]31..NAREG/4 ≠ 032-NAREG/4 AR[t] ← 032-NAREG/4||WindowStart
Other Changes to the Register Other Effects of the Register
ENTRY/MOVSP/RETW/RFWO/RFWU Any instruction which accesses the AR register file
Instruction
⇒
xSYNC
⇒
Instruction
WSR/XSR WINDOWSTART ⇒ RSYNC ⇒ Any use of an AR register when CWOE=1
WSR/XSR WINDOWSTART ⇒ RSYNC ⇒ Any def of an AR register when CWOE=1
Chapter 5. Processor State
222 Xtensa Instruction Set Architecture (ISA) Reference Manual
Table 5–149.
PTEVADDR -
Special Register #83
SR# Name Description Reset Value
83 PTEVADDR Virtual address for page table lookups Undefined
Option Count Bits Privileged? XSR Legal?
MMU Option 132 Yes Yes
WSR Function RSR Function
PTEVADDRVABITS-1..X ← AR[t]VABITS-1..X
X = VABITS+log2(PTEbytes)-
min(PTEPageSizes)
AR[t] ← PTEVADDRVABITS-1..Y||0Y
Y = log2(PTEbytes)
Other Changes to the Register Other Effects of the Register
Any instruction/data address translation
Instruction
⇒
xSYNC
⇒
Instruction
WSR/XSR PTEVADDR ⇒ ISYNC ⇒ Any instruction access that might miss the ITLB
WSR/XSR PTEVADDR ⇒ DSYNC ⇒ Any load/store access that might miss the DTLB
Table 5–150.
RASID -
Special Register #90
SR# Name Description Reset Value
90 RASID Current ASID values for each protection ring 0x04030201
Option Count Bits Privileged? XSR Legal?
MMU Option 132 Yes Yes
WSR Function RSR Function
RASID ← AR[t]31..8||07||11AR[t] ← RASID
Other Changes to the Register Other Effects of the Register
Any instruction/data address translation
Instruction
⇒
xSYNC
⇒
Instruction
WSR/XSR RASID ⇒ ISYNC ⇒ Instruction address translation that depends on the change
WSR/XSR RASID ⇒ DSYNC ⇒ Data address translation that depends on the change
Chapter 5. Processor State
Xtensa Instruction Set Architecture (ISA) Reference Manual 223
5.3.8 Exception Support Special Registers
The Special Registers that provide information for the handling of an exception are
described in Table 5–153 through Table 5–159.
Table 5–151.
ITLBCFG -
Special Register #91
SR# Name Description Reset Value
91 ITLBCFG Instruction TLB configuration 0x00000000
Option Count Bits Privileged? XSR Legal?
MMU Option 132 Yes Yes
WSR Function RSR Function
ITLBCFG ← AR[t]
Affected ways should be invalidated after change. AR[t] ← ITLBCFG
Other Changes to the Register Other Effects of the Register
Any instruction address translation
Instruction
⇒
xSYNC
⇒
Instruction
WSR/XSR ITLBCFG ⇒ ISYNC ⇒ Instruction address translation that depends on the change
Table 5–152.
DTLBCFG -
Special Register #92
SR# Name Description Reset Value
92 DTLBCFG Data TLB configuration 0x00000000
Option Count Bits Privileged? XSR Legal?
MMU Option 132 Yes Yes
WSR Function RSR Function
DTLBCFG ← AR[t]
Affected ways should be invalidated after change. AR[t] ← DTLBCFG
Other Changes to the Register Other Effects of the Register
Any data address translation
Instruction
⇒
xSYNC
⇒
Instruction
WSR/XSR DTLBCFG ⇒ DSYNC ⇒ Any data address translation that depends on the change
Chapter 5. Processor State
224 Xtensa Instruction Set Architecture (ISA) Reference Manual
Table 5–153.
EXCCAUSE -
Special Register #232
SR# Name Description Reset Value
232 EXCCAUSE Exception cause register Undefined
Option Count Bits Privileged? XSR Legal?
Exception Option 1 6 Yes Yes
WSR Function RSR Function
EXCCAUSE ← AR[t]5..0
Undefined if AR[t]31..6 ≠ 026 AR[t] ← 026||EXCCAUSE
Other Changes to the Register Other Effects of the Register
Exception or interrupt
Table 5–154.
EXCVADDR -
Special Register #238
SR# Name Description Reset Value
238 EXCVADDR Exception virtual address register Undefined
Option Count Bits Privileged? XSR Legal?
Exception Option 132 Yes Yes
WSR Function RSR Function
EXCVADDR ← AR[t] AR[t] ← EXCVADDR
AR[t] is undefined if CEXCM = 0
Other Changes to the Register Other Effects of the Register
Some exceptions (see Table 4–64 on page 89), hardware
table walk (see Section 4.6.5.9 on page 174)
Table 5–155.
VECBASE -
Special Register #231
SR# Name Description Reset Value
231 VECBASE Vector Base User Defined1
Option Count Bits Privileged? XSR Legal?
Relocatable Vector Option 132 Yes Yes
WSR Function RSR Function
VECBASE ← AR[t] AR[t] ← VECBASE
Other Changes to the Register Other Effects of the Register
Exception Vector Locations
1 The reset value of VECBASE is set by the user as part of the configuration
Chapter 5. Processor State
Xtensa Instruction Set Architecture (ISA) Reference Manual 225
Table 5–156.
MESR -
Special Register #109
SR# Name Description Reset Value
109 MESR Memory error status register 32’hXXXX0C00
Option Count Bits Privileged? XSR Legal?
Memory ECC/Parity Option 132 Yes Yes
WSR Function RSR Function
MESR ← AR[t] AR[t] ← MESR
Other Changes to the Register Other Effects of the Register
Memoryerror-exception, memory error without exception Controls memory error logic
Instruction
⇒
xSYNC
⇒
Instruction
WSR/XSR MESR ⇒ ISYNC ⇒ Change in error behavior on instruction memories
WSR/XSR MESR ⇒ DSYNC ⇒ Change in error behavior on data memories
Table 5–157.
MECR -
Special Register #110
SR# Name Description Reset Value
110 MECR Memory error check register Undefined
Option Count Bits Privileged? XSR Legal?
Memory ECC/Parity Option 122 Yes Yes
WSR Function RSR Function
MECR ← AR[t] AR[t] ← MECR
Other Changes to the Register Other Effects of the Register
Memoryerror-exception, memory error without exception,
Loads when MESR[9] is set. Stores when MESR[9] is set.
Instruction
⇒
xSYNC
⇒
Instruction
WSR/XSR MECR ⇒ ISYNC ⇒ Check bit write to instruction memories
WSR/XSR MECR ⇒ DSYNC ⇒ Check bit write to data memories
Table 5–158.
MEVADDR -
Special Register #111
SR# Name Description Reset Value
111 MEVADDR Memory error virtual address register Undefined
Option Count Bits Privileged? XSR Legal?
Memory ECC/Parity Option 132 Yes Yes
WSR Function RSR Function
MEVADDR ← AR[t] AR[t] ← MEVADDR
Other Changes to the Register Other Effects of the Register
Memoryerror-exception, memory error without exception
Chapter 5. Processor State
226 Xtensa Instruction Set Architecture (ISA) Reference Manual
5.3.9 Exception State Special Registers
The Special Registers that save the PC and PS values and an initial register value for
each of the levels are described in Table 5–160 through Table 5–162.
Table 5–159.
DEBUGCAUSE -
Special Register #233
SR# Name Description Reset Value
233 DEBUGCAUSE Debug cause register Undefined
Option Count Bits Privileged? XSR Legal?
Debug Option 112 Yes No
WSR Function RSR Function
Reserved AR[t] ← 020||DEBUGCAUSE
Other Changes to the Register Other Effects of the Register
Debug exception or interrupt
Table 5–160.
EPC1 -
Special Register #177
SR# Name Description Reset Value
177 EPC1 Exception PC[1] Undefined
Option Count Bits Privileged? XSR Legal?
Exception Option 1 32 Yes Yes
WSR Function RSR Function
EPC[1] ← AR[t] AR[t] ← EPC[1]
Other Changes to the Register Other Effects of the Register
General-exception/overflow-or-underflow-exception RFE/RFWO/RFWU
Table 5–161.
EPC2..7 -
Special Register #178-183
SR# Name Description Reset Value
178-183 EPC2..7 Exception PC[2..7] Undefined
Option Count Bits Privileged? XSR Legal?
High-Priority Interrupt Option NLEVEL
+NNMI-1
32 Yes Yes
WSR Function RSR Function
EPC[sr3..0] ← AR[t] AR[t] ← EPC[sr3..0]
AR[t] is undefined if sr3..0 > NLEVEL+NNMI
Other Changes to the Register Other Effects of the Register
Level[sr3..0]-Interrupt/debug-exception/NMI RFI[sr3..0]/RFDO/RFDD
Chapter 5. Processor State
Xtensa Instruction Set Architecture (ISA) Reference Manual 227
Table 5–162.
DEPC -
Special Register #192
SR# Name Description Reset Value
192 DEPC Double exception PC Undefined
Option Count Bits Privileged? XSR Legal?
Exception Option 132 Yes Yes
WSR Function RSR Function
DEPC ← AR[t] AR[t] ← DEPC
Other Changes to the Register Other Effects of the Register
Double exception RFDE
Table 5–163.
MEPC -
Special Register #106
SR# Name Description Reset Value
106 MEPC Memory error PC register Undefined
Option Count Bits Privileged? XSR Legal?
Memory ECC/Parity Option 132 Yes Yes
WSR Function RSR Function
MEPC ← AR[t] AR[t] ← MEPC
AR[t] is undefined unless MESR[0] is set.
Other Changes to the Register Other Effects of the Register
Memoryerror-exception RFME
Table 5–164.
EPS2..7 -
Special Register #194-199
SR# Name Description Reset Value
194-199 EPS2..7 Exception processor status register[2..7]Undefined
Option Count Bits Privileged? XSR Legal?
High-Priority Interrupt Option NLEVEL
+NNMI-1
32 Yes Yes
WSR Function RSR Function
EPS[sr3..0] ← AR[t] AR[t] ← EPS[sr3..0]
AR[t] is undefined if sr3..0 > NLEVEL+NNMI
Other Changes to the Register Other Effects of the Register
Level[sr3..0]-Interrupt/debug-exception/NMI RFI[sr3..0]/RFDO/RFDD
Chapter 5. Processor State
228 Xtensa Instruction Set Architecture (ISA) Reference Manual
Table 5–165.
MEPS -
Special Register #107
SR# Name Description Reset Value
107 MEPS Memory error PS register Undefined
Option Count Bits Privileged? XSR Legal?
Memory ECC/Parity Option 132 Yes Yes
WSR Function RSR Function
MEPS ← AR[t] AR[t] ← MEPS
AR[t] is undefined unless MESR[0] is set.
Other Changes to the Register Other Effects of the Register
Memoryerror-exception RFME
Table 5–166.
EXCSAVE1 -
Special Register #192
SR# Name Description Reset Value
192 EXCSAVE1 Exception save register[1] Undefined
Option Count Bits Privileged? XSR Legal?
Exception Option 132 Yes Yes
WSR Function RSR Function
EXCSAVE[1] ← AR[t] AR[t] ← EXCSAVE[1]
Other Changes to the Register Other Effects of the Register
Table 5–167.
EXCSAVE2..7-
Special Register #210-215
SR# Name Description Reset Value
210-215 EXCSAVE2..7 Exception save register[2..7] Undefined
Option Count Bits Privileged? XSR Legal?
High-Priority Interrupt Option NLEVEL
+NNMI-1
32 Yes Yes
WSR Function RSR Function
EXCSAVE[sr3..0] ← AR[t] AR[t] ← EXCSAVE[sr3..0]
AR[t] is undefined if sr3..0 > NLEVEL+NNMI
Other Changes to the Register Other Effects of the Register
Chapter 5. Processor State
Xtensa Instruction Set Architecture (ISA) Reference Manual 229
5.3.10 Interrupt Special Registers
The Special Registers that manage interrupt handling are described in Table 5–169
through Table 5–172.
Table 5–168.
MESAVE-
Special Register #108
SR# Name Description Reset Value
109 MESAVE Memory error save register Undefined
Option Count Bits Privileged? XSR Legal?
Memory ECC/Parity Option 132 Yes Yes
WSR Function RSR Function
MESAVE ← AR[t] AR[t] ← MESAVE
Other Changes to the Register Other Effects of the Register
Table 5–169.
INTERRUPT -
Special Register #226 (read)
SR# Name Description Reset Value
226 INTERRUPT Interrupt pending register Undefined
Option Count Bits Privileged? XSR Legal?
Interrupt Option 1NINTERRUPT Yes No
WSR Function RSR Function
see Table 5–170 and Table 5–171 AR[t] ← 032-NINTERRUPT||INTERRUPT
Other Changes to the Register Other Effects of the Register
Assertion/deassertion of interrupt signals/
WSR.CCOMPAREn Pipeline takes interrupt
Instruction
⇒
xSYNC
⇒
Instruction
WSR INTSET ⇒ ESYNC ⇒ RSR INTERRUPT
WSR INTCLEAR ⇒ ESYNC ⇒ RSR INTERRUPT
Chapter 5. Processor State
230 Xtensa Instruction Set Architecture (ISA) Reference Manual
Table 5–170.
INTSET -
Special Register #226 (write)
SR# Name Description Reset Value
226 INTSET Interrupt set register No separate state
Option Count Bits Privileged? XSR Legal?
Interrupt Option 1NINTERRUPT Yes No
WSR Function RSR Function
INTERRUPT ← INTERRUPT or AR[t]X-1..0
Undefined if AR[t]31..X ≠ 032-X
X = NINTERRUPT
Only software interrupt bits can be set.
see Table 5–169
Other Changes to the Register Other Effects of the Register
(State is INTERRUPT)(State is INTERRUPT)
Instruction
⇒
xSYNC
⇒
Instruction
WSR INTSET ⇒ ESYNC ⇒ RSR INTERRUPT
WSR INTSET⇒ RSYNC ⇒ Instruction which must execute after the software interrupt
Table 5–171.
INTCLEAR -
Special Register #227
SR# Name Description Reset Value
227 INTCLEAR Interrupt clear register No separate state
Option Count Bits Privileged? XSR Legal?
Interrupt Option 1NINTERRUPT Yes No
WSR Function RSR Function
INTERRUPT ← INTERRUPT and not AR[t]X-1..0
Undefined if AR[t]31..X ≠ 032-X
X = NINTERRUPT
Bits in AR[t]X-1..0 may be set without causing harm.
Only bits which can be cleared by this write are affected.
AR[t] ← undefined32
Other Changes to the Register Other Effects of the Register
(State is INTERRUPT)(State is INTERRUPT)
Instruction
⇒
xSYNC
⇒
Instruction
WSR INTCLEAR ⇒ ESYNC ⇒ RSR INTERRUPT
WSR INTCLEAR⇒ RSYNC ⇒ Instruction which must execute after the cleared interrupt
Chapter 5. Processor State
Xtensa Instruction Set Architecture (ISA) Reference Manual 231
5.3.11 Timing Special Registers
The Special Registers that manage instruction counting and cycle counting, including
timer interrupts are described in Table 5–173 through Table 5–176.
Table 5–172.
INTENABLE -
Special Register #228
SR# Name Description Reset Value
228 INTENABLE Interrupt enable register Undefined
Option Count Bits Privileged? XSR Legal?
Interrupt Option 1NINTERRUPT Yes Yes
WSR Function RSR Function
INTENABLE ← AR[t]NINTERRUPT-1..0
Undefined if AR[t]31..X ≠ 032-X
X = NINTERRUPT
AR[t] ← 032-NINTERRUPT||INTENABLE
Other Changes to the Register Other Effects of the Register
Pipeline takes interrupt
Instruction
⇒
xSYNC
⇒
Instruction
WSR/XSR INTENABLE ⇒ ESYNC ⇒ RSR/XSR INTENABLE
WSR/XSR INTENABLE⇒ RSYNC ⇒ Any instruction which must wait for INTENABLE changes
Table 5–173.
ICOUNT -
Special Register #236
SR# Name Description Reset Value
236 ICOUNT Instruction count register Undefined
Option Count Bits Privileged? XSR Legal?
Debug Option 12 or 32 Yes Yes
WSR Function RSR Function
ICOUNT ← AR[t]
Write when CINTLEVEL ≥ ICOUNTLEVEL
AR[t] ← ICOUNT
Defined only when CINTLEVEL ≥ ICOUNTLEVEL
Other Changes to the Register Other Effects of the Register
Increment on appropriate cycles Debug exception
Instruction
⇒
xSYNC
⇒
Instruction
WSR/XSR ICOUNT ⇒ ESYNC ⇒ RSR/XSR ICOUNT
WSR/XSR ICOUNT⇒ ISYNC ⇒ Ending CINTLEVEL ≥ ICOUNTLEVEL
Chapter 5. Processor State
232 Xtensa Instruction Set Architecture (ISA) Reference Manual
Table 5–174.
ICOUNTLEVEL -
Special Register #237
SR# Name Description Reset Value
237 ICOUNTLEVEL Instruction count level register Undefined
Option Count Bits Privileged? XSR Legal?
Debug Option 1 4 Yes Yes
WSR Function RSR Function
ICOUNTLEVEL ← AR[t]3..0
Undefined if AR[t]31..4 ≠ 028
Write when CINTLEVEL ≥ old ICOUNTLEVEL
Write when CINTLEVEL ≥ new ICOUNTLEVEL
AR[t] ← 028||ICOUNTLEVEL
Other Changes to the Register Other Effects of the Register
Debug exception
Instruction
⇒
xSYNC
⇒
Instruction
WSR/XSR ICOUNTLEVEL ⇒ ISYNC ⇒ Ending CINTLEVEL ≥ old ICOUNTLEVEL
WSR/XSR ICOUNTLEVEL ⇒ ISYNC ⇒ Ending CINTLEVEL ≥ new ICOUNTLEVEL
Table 5–175.
CCOUNT -
Special Register #234
SR# Name Description Reset Value
234 CCOUNT Cycle count register Undefined
Option Count Bits Privileged? XSR Legal?
Timer Interrupt Option 132 Yes Yes
WSR Function RSR Function
CCOUNT ← AR[t]
Precise cycle of write is not defined
Not usually written during normal operation.
AR[t] ← CCOUNT
Precise cycle of read is not defined.
Other Changes to the Register Other Effects of the Register
Increment each cycle Generates Timer Interrupt
Instruction
⇒
xSYNC
⇒
Instruction
WSR/XSR CCOUNT⇒ ESYNC ⇒ RSR/XSR CCOUNT
Chapter 5. Processor State
Xtensa Instruction Set Architecture (ISA) Reference Manual 233
5.3.12 Breakpoint Special Registers
The Special Registers that manage the handling of breakpoint exceptions are described
in Table 5–177 through Table 5–180.
Table 5–176.
CCOMPARE0..2 -
Special Register #240-242
SR# Name Description Reset Value
240-242 CCOMPARE0..2 Cycle count compare registers Undefined
Option Count Bits Privileged? XSR Legal?
Timer Interrupt Option NCCOMPARE 32 Yes Yes
WSR Function RSR Function
CCOMPARE[sr1..0] ← AR[t]
INTERRUPTi ← 0; i is position of timer interrupt
AR[t] ← CCOMPARE[sr1..0]
AR[t] is undefined if sr1..0 ≥ NCOMPARE
Other Changes to the Register Other Effects of the Register
Timer Interrupt
Instruction
⇒
xSYNC
⇒
Instruction
WSR/XSR CCOMPARE0..2 ⇒ ESYNC ⇒ RSR/XSR CCOUNT (to ensure CCOUNT<CCOMPAREn)
WSR/XSR CCOMPARE0..2⇒ RSYNC ⇒ Any instruction which must execute after the update
Table 5–177.
IBREAKENABLE -
Special Register #96
SR# Name Description Reset Value
96 IBREAKENABLE Instruction breakpoint enable register 0NIBREAK
Option Count Bits Privileged? XSR Legal?
Debug Option 1NIBREAK Yes Yes
WSR Function RSR Function
IBREAKENABLE ← AR[t]NIBREAK-1..0
Undefined if AR[t]31..NIBREAK ≠ 032-NIB AR[t] ← 032-NIBREAK||IBREAKENABLE
Other Changes to the Register Other Effects of the Register
Any instruction fetch
Instruction
⇒
xSYNC
⇒
Instruction
WSR/XSR IBREAKENABLE ⇒ ISYNC ⇒ Any instruction access that might raise a breakpoint
Chapter 5. Processor State
234 Xtensa Instruction Set Architecture (ISA) Reference Manual
Table 5–178.
IBREAKA0..1 -
Special Register #128-129
SR# Name Description Reset Value
128-129 IBREAKA0..1 Instruction breakpoint address registers Undefined
Option Count Bits Privileged? XSR Legal?
Debug Option NIBREAK 32 Yes Yes
WSR Function RSR Function
IBREAKA[sr3..0] ← AR[t]
Operation is undefined if sr3..0 ≥ NIBREAK
AR[t] ← IBREAKA[sr3..0]
AR[t] is undefined if sr3..0 ≥ NIBREAK
Other Changes to the Register Other Effects of the Register
Any instruction fetch
Instruction
⇒
xSYNC
⇒
Instruction
WSR/XSR IBREAKA0..1 ⇒ ISYNC ⇒ Any instruction access which might raise that breakpoint
Table 5–179.
DBREAKC0..1 -
Special Register #160-161
SR# Name Description Reset Value
160-161 DBREAKC0..1 Data breakpoint control registers Undefined
Option Count Bits Privileged? XSR Legal?
Debug Option NDBREAK 32 Yes Yes
WSR Function RSR Function
DBREAKC[sr3..0] ← AR[t]
Operation is undefined if sr3..0 ≥ NDBREAK
AR[t] ← DBREAKC[sr3..0]
AR[t] is undefined if sr3..0 ≥ NDBREAK
Other Changes to the Register Other Effects of the Register
Any data access
Instruction
⇒
xSYNC
⇒
Instruction
WSR/XSR DBREAKC0..1 ⇒ DSYNC ⇒ Any load/store access which might raise that breakpoint
Chapter 5. Processor State
Xtensa Instruction Set Architecture (ISA) Reference Manual 235
5.3.13 Other Privileged Special Registers
The Special Registers for other purposes are described in Table 5–181 through
Table 5–186.
Table 5–180.
DBREAKA0..1 -
Special Register #144-145
SR# Name Description Reset Value
144-145 DBREAKA0..1 Data breakpoint address registers Undefined
Option Count Bits Privileged? XSR Legal?
Debug Option NDBREAK 32 Yes Yes
WSR Function RSR Function
DBREAKA[sr3..0] ← AR[t]
Operation is undefined if sr3..0 ≥ NDBREAK
AR[t] ← DBREAKA[sr3..0]
AR[t] is undefined if sr3..0 ≥ NDBREAK
Other Changes to the Register Other Effects of the Register
Any data access
Instruction
⇒
xSYNC
⇒
Instruction
WSR/XSR DBREAKA0..1 ⇒ DSYNC ⇒ Any load/store access which might raise that breakpoint
Table 5–181.
PRID -
Special Register #235
SR# Name Description Reset Value
235 PRID Processor identification register Pins
Option Count Bits Privileged? XSR Legal?
Processor ID Option 132 Yes No
WSR Function RSR Function
Reserved AR[t] ← PRID
Other Changes to the Register Other Effects of the Register
Trailing edge of RESET
Table 5–182.
MMID -
Special Register #89
SR# Name Description Reset Value
89 MMID Memory map identification register Undefined
Option Count Bits Privileged? XSR Legal?
Trace Port Option 132 Yes No
WSR Function RSR Function
ID written to Trace Port Reserved
Other Changes to the Register Other Effects of the Register
Chapter 5. Processor State
236 Xtensa Instruction Set Architecture (ISA) Reference Manual
Table 5–183.
DDR -
Special Register #104
SR# Name Description Reset Value
104 DDR Debug data register Undefined
Option Count Bits Privileged? XSR Legal?
Debug Option1132 Yes Yes
WSR Function RSR Function
DDR ← AR[t]2AR[t] ← DDR2
Other Changes to the Register Other Effects of the Register
Instruction
⇒
xSYNC
⇒
Instruction
WSR/XSR DDR⇒ ESYNC ⇒ RSR/XSR DDR
1) The DDR register is actually created by the OCD Option but is listed with the Debug Option, which is a prerequisite for the OCD Option.
2) In some implementations the DDR state is different for reads and writes; WSR.DDR followed by RSR.DDR may not return the original value.
Table 5–184.
CPENABLE -
Special Register #224
SR# Name Description Reset Value
224 CPENABLE Coprocessor enable register Undefined
Option Count Bits Privileged? XSR Legal?
Coprocessor Option 11-8 Yes Yes
WSR Function RSR Function
CPENABLE ← AR[t]7..0
Undefined if AR[t]31..8 ≠ 024
AR[t] ← 024||CPENABLE (Bits corresponding to
unused coprocessors are not defined on read.)
Other Changes to the Register Other Effects of the Register
Every coprocessor instruction
Table 5–185.
MISC0..3 -
Special Register #244-247
SR# Name Description Reset Value
244-247 MISC0..3 Miscellaneous special registers Undefined
Option Count Bits Privileged? XSR Legal?
Miscellaneous Special Registers
Option
NMISC 32 Yes Yes
WSR Function RSR Function
MISC[sr1..0] ← AR[t] AR[t] ← MISC[sr1..0]
AR[t] is undefined if sr1..0 ≥ NMISC
Other Changes to the Register Other Effects of the Register
Chapter 5. Processor State
Xtensa Instruction Set Architecture (ISA) Reference Manual 237
5.4 User Registers
User Registers hold state added in support of designer’s TIE and in some cases of op-
tions that Tensilica provides. See the Tensilica Instruction Extension (TIE) Language
User’s Guide for more information on adding User Registers to a design. Table 5–187
shows the User Registers in numerical order with references to a more detailed descrip-
tion. User Registers with numbers greater than or equal to 224 but not listed in
Table 5–187 are reserved for future use.
5.4.1 Reading and Writing User Registers
Use the RUR.* and WUR.* instructions to access the user registers. The accesses to
the User Registers act as separate instructions in many ways. Replace the ‘*’ in the in-
structions with the name of the User Register as specified by the designer or given in
Table 5–189 and Table 5–190.
Table 5–186.
ATOMCTL -
Special Register #99
SR# Name Description Reset Value
99 ATOMCTL Atomic Operation Control 0x28
Option Count Bits Privileged? XSR Legal?
Conditional Store Option 1 6 Yes Yes
WSR Function RSR Function
ATOMCTL ← AR[t] AR[t] ← ATOMCTL
Other Changes to the Register Other Effects of the Register
Function of S32C1I
Table 5–187. Numerical List of User Registers
Name
1
Description Required Configuration
Option
User
Register
Number
More
Detail
Available for designer extensions 0-223
THREADPTR Thread pointer Thread Pointer Option 231 Table 5–1
88
FCR Floating point control register Floating-Point Coprocessor
Option
232 Table 5–1
89
FSR Floating point status register Floating-Point Coprocessor
Option
233 Table 5–1
90
1 Used in RUR and WUR instructions.
Chapter 5. Processor State
238 Xtensa Instruction Set Architecture (ISA) Reference Manual
RUR.* instructions move values from a User Register to a general (AR) register. WUR.*
instructions move values from a general (AR) register to a User Register. The User Reg-
isters are fully interlocked in hardware and do not need SYNC instructions.
5.4.2 The List of User Registers
Table 5–188 throughTable 5–190 list detailed information for each of the User Registers
that Tensilica Options define.
The first row shows the User Register number, the name (which is used in the RUR.*,
WUR.* instruction names), a short description, and the value immediately after reset.
The second row shows the Option that creates the User Register, the count or number
of such User Registers, the number of bits in the User Register, and whether access to
the register is privileged (requires CRING=0) or not. The option that creates the User
Register is described in Chapter 4 including more information on each User Register.
The third row shows the function of the WUR.* and RUR.* instructions for this User Reg-
ister.
The fourth row shows the other instructions that affect or are affected by this User Reg-
ister.
The last row of each User Register’s table shows that SYNC instructions are not
required.
User Registers 0-223 are reserved for designer’s use, and are never used by Tensilica
Options. User Registers 224-255 can be used by a designer but their use may prohibit
compatibility with some Tensilica-provided Options either now or in the future. Additional
state registers may be added without built-in access instructions.
Table 5–188.
THREADPTR -
User Register #231
UR# Name Description Reset Value
231 THREADPTR Thread pointer Undefined
Option Count Bits Privileged?
Thread Pointer Option 132 No
WUR Function RUR Function
THREADPTR ← AR[t] AR[t] ← THREADPTR
Other Changes to the Register Other Effects of the Register
Chapter 5. Processor State
Xtensa Instruction Set Architecture (ISA) Reference Manual 239
5.5 TLB Entries
Although some information for the instruction and data TLBs is held in the Special
Registers, the protection and translation entries themselves are held in a special type of
state called ITLB entries and DTLB entries. These entries are added by the Region Pro-
tection Option and the MMU Option.
These entries are accessed by special instructions for reading and writing the entries.
There are also instructions for probing to see if an entry exists that will match a particu-
lar virtual address. In addition, there are instructions for invalidating particular entries.
The instructions added for these purposes are listed under the Region Protection Option
and the MMU Option.
After changing an Instruction TLB entry, an ISYNC must be executed before executing
any instruction that is accessed using that TLB. After changing a data TLB entry, a
DSYNC must be executed before any load or store that uses that entry (see
Section 4.6.3.3, Section 4.6.4.2, Section 4.6.5.5, and Section 4.6.5.8 for more detailed
information).
Table 5–189.
FCR -
User Register #232
UR# Name Description Reset Value
232 FCR Floating point control register Undefined
Option Count Bits Privileged?
Floating-Point Coprocessor Option 1 7 No
WUR Function RUR Function
FCR ← AR[t] AR[t] ← FCR
Other Changes to the Register Other Effects of the Register
Most floating point computations
Table 5–190.
FSR -
User Register #233
UR# Name Description Reset Value
233 FSR Floating point status register Undefined
Option Count Bits Privileged?
Floating-Point Coprocessor Option 1 5 No
WUR Function RUR Function
FSR ← AR[t] AR[t] ← FSR
Other Changes to the Register Other Effects of the Register
Most floating point computations
Chapter 5. Processor State
240 Xtensa Instruction Set Architecture (ISA) Reference Manual
5.6 Additional Register Files
Additional register files also hold state added in support of designer’s TIE and in some
cases of Tensilica-provided Options. There are no built-in instructions for accessing add-
ed register files in the same manner as the RUR.*, and WUR.* instructions can be used
to access the user registers. See the Tensilica Instruction Extension (TIE) Language
User’s Guide for more information on adding register files to a design.
As shown in Table 5–127, the Floating-Point Coprocessor Option creates the FR register
file, which is an instance of this capability in a Tensilica-provided Option. The FR register
file contains sixteen registers of 32 bits each in support of the floating point instruction
set. There is no windowing in the FR register file.
Reads from and writes to these additional register files are always interlocked by hard-
ware. No synchronization instructions are ever required by them.
The contents of these additional register files are undefined after reset.
5.7 Caches and Local Memories
Local memories are always architectural state. However, for many purposes caches are
not architectural state in that they merely reflect the contents of main memory but pro-
vide lower latency access for the processor. When considering the cache control instruc-
tions added with the caches or the requirements placed upon software for maintaining
coherence between processors/devices in their views of memory, caches sometimes act
like architectural state.
Section 4.5.2 through Section 4.5.12 describe the options for adding caches and local
memories to Xtensa processors.
Self-modifying code is not automatically supported in Xtensa processors. The instruction
cache is not kept coherent with main memory because there is no hardware for observ-
ing writes to memory and determining whether or not those writes could have any affect
on the instruction cache. Any time memory that could possibly be contained in the in-
struction cache is changed, the OS must ensure that the changes have been written
back to system memory and invalidate either the specific locations that have been
changed or else the entire instruction cache. See the description of the ISYNC instruc-
tion for more details.
In addition, because the instruction unit of the Xtensa processor fetches ahead, syn-
chronization instructions are needed whenever an instruction local memory or instruc-
tion cache is modified before it can be certain that the instruction fetch engine will see
the changes. For local memories, this means an ISYNC instruction is needed after any
change to the instruction memory and before the execution of any instruction involved in
the change. For instruction caches, this means an ISYNC instruction is needed after any
Chapter 5. Processor State
Xtensa Instruction Set Architecture (ISA) Reference Manual 241
change to the cache data, or the cache tag (including the invalidation required when
main memory that could possibly be held in the icache is modified) and before the exe-
cution of any instruction involved in the change.
The operation of all instructions to data local memory or data cache is fully interlocked in
hardware. And except for the instruction fetch discussed above, the operation of all in-
structions to instruction local memory or instruction cache is fully interlocked in hard-
ware. Loads and stores, tag accesses, cache invalidations, cache line locks/unlocks,
prefetches, and write backs all operate in order to the same cache locations because of
the hardware interlocking. Accesses to different addresses are not necessarily in order
(see Section 4.3.12.1).
Both the data and the tag stores of instruction caches and data caches are ordinary syn-
chronous SRAMs, which are not expected to be defined after reset.
Chapter 5. Processor State
242 Xtensa Instruction Set Architecture (ISA) Reference Manual
Xtensa Instruction Set Architecture (ISA) Reference Manual 243
6. Instruction Descriptions
This chapter describes, in alphabetical order, each of the Xtensa ISA instructions in the
Core Architecture described in Chapter 3, or in Architecture Options described in
Chapter 4.
Before reading this chapter, Tensilica recommends reviewing the notation defined in
Table 2–6 on page 21, Uses Of Instruction Fields.
Note that instructions with a “Required Configuration Option” specification other than
“Core Architecture” are illegal if the corresponding option is not enabled, and will raise
an illegal instruction exception.
The instruction word included with each instruction is the little-endian version (see
Section 2.1 “Bit and Byte Order” and Chapter 7 "Instruction Formats and Opcodes" on
page 569). The big-endian instruction word may be determined for any instruction by
separating the little-endian instruction word at the vertical bars and reassembling the
pieces in the reverse order. For example, following is the little-endian instruction word
shown on page 273 for the BEQI instruction:
Following is the derived big-endian instruction word for the BEQI instruction:
The format listed after the instruction word at the top of each instruction page can also
be used along with Section 7.1 “Formats” to derive the big-endian encoding.
For each instruction, the exceptions that can possibly result from its execution are listed.
Because many of the potential exceptions are common to a large number of instruc-
tions, exception groups are used to save space and improve understanding. Following
are the common exception groups that are referenced in the instructions. A reference to
one of these groups means that any of the exceptions in the group can be raised by that
instruction. Note that the groups often include previous groups.
23 1615 1211 876543 0
imm8 r s 00100110
8 4 4224
0 345678 1112 1516 23
01101000 s r imm8
4224 4 8
244 Xtensa Instruction Set Architecture (ISA) Reference Manual
In the following groups and in the instruction descriptions, GenExcep() is a general
exception that goes to UserExceptionVector, KernelExceptionVector, or
DoubleExceptionVector; the parentheses contain the cause that will appear in
EXCCAUSE. DebugExcep() is a debug exception that goes to the high level interrupt for
debug and the parentheses contain the cause that will appear in DEBUGCAUSE. Win-
dowOverExcep is one of the three sizes of windowed register overflow exceptions1 and
WindowUnderExcep is one of the three sizes of windowed register underflow excep-
tions2. After any exceptions in the list there is an option without which that exception
cannot be taken.
EveryInst Group:
GenExcep(InstructionFetchErrorCause) if Exception Option
GenExcep(InstTLBMissCause) if Region Protection Option or MMU Option
GenExcep(InstTLBMultiHitCause) if Region Protection Option or MMU Option
GenExcep(InstFetchPrivilegeCause) if Region Protection Option or MMU Option
GenExcep(InstFetchProhibitedCause) if Region Protection Option or MMU Option
MemoryErrorException on Instruction-fetch if Memory ECC/Parity Option
DebugExcep(ICOUNT) if Debug Option
DebugExcep(IBREAK) if Debug Option
EveryInstR Group:
EveryInst Group (see page 244)
WindowOverExcep if Windowed Register Option
Memory Group:
EveryInstR Group (see page 244)
GenExcep(LoadStoreErrorCause) if Exception Option
GenExcep(LoadStoreTLBMissCause) if Region Protection Option or MMU Option
GenExcep(LoadStoreTLBMultiHitCause) if Region Protection Option or MMU Option
GenExcep(LoadStorePrivilegeCause) if Region Protection Option or MMU Option
MemoryErrorException on non-Instruction-fetch if Memory ECC/Parity Option
Memory Load Group:
Memory Group (see page 244)
1. WindowOverflow4, WindowOverflow8, or WindowOverflow12.
2. WindowUnderflow4, WindowUnderflow8, or WindowUnderflow12.
Xtensa Instruction Set Architecture (ISA) Reference Manual 245
GenExcep(LoadProhibitedCause) if Region Protection Option or MMU Option
GenExcep(LoadStoreAlignmentCause) if Unaligned Exception Option
DebugExcep(DBREAK) if Debug Option
Memory Store Group:
Memory Group (see page 244)
GenExcep(StoreProhibitedCause) if Region Protection Option or MMU Option
GenExcep(LoadStoreAlignmentCause) if Unaligned Exception Option
DebugExcep(DBREAK) if Debug Option
ABS Absolute Value
246 Xtensa Instruction Set Architecture (ISA) Reference Manual
Instruction Word (RRR)
Required Configuration Option
Core Architecture (See Section 4.2 on page 50)
Assembler Syntax
ABS ar, at
Description
ABS calculates the absolute value of the contents of address register at and writes it to
address register ar. Arithmetic overflow is not detected.
Operation
AR[r] ← if AR[t]31 then −AR[t] else AR[t]
Exceptions
EveryInstR Group (see page 244)
23 20 19 16 15 12 11 8 7 4 3 0
01100000 r 0001 t 0000
444444
Absolute Value Single ABS.S
Xtensa Instruction Set Architecture (ISA) Reference Manual 247
Instruction Word (RRR)
Required Configuration Option
Floating-Point Coprocessor Option (See Section 4.3.11 on page 67)
Assembler Syntax
ABS.S fr, fs
Description
ABS.S computes the single-precision absolute value of the contents of floating-point
register fs and writes the result to floating-point register fr.
Operation
FR[r] ← abss(FR[s])
Exceptions
EveryInst Group (see page 244)
GenExcep(Coprocessor0Disabled) if Coprocessor Option
23 20 19 16 15 12 11 8 7 4 3 0
11111010 r s 00010000
444444
ADD Add
248 Xtensa Instruction Set Architecture (ISA) Reference Manual
Instruction Word (RRR)
Required Configuration Option
Core Architecture (See Section 4.2 on page 50)
Assembler Syntax
ADD ar, as, at
Description
ADD calculates the two’s complement 32-bit sum of address registers as and at. The
low 32 bits of the sum are written to address register ar. Arithmetic overflow is not
detected.
ADD is a 24-bit instruction. The ADD.N density-option instruction performs the same
operation in a 16-bit encoding.
Assembler Note
The assembler may convert ADD instructions to ADD.N when the Code Density Option is
enabled. Prefixing the ADD instruction with an underscore (_ADD) disables this optimiza-
tion and forces the assembler to generate the wide form of the instruction.
Operation
AR[r] ← AR[s] + AR[t]
Exceptions
EveryInstR Group (see page 244)
23 20 19 16 15 12 11 8 7 4 3 0
10000000 r s t 0000
444444
Narrow Add ADD.N
Xtensa Instruction Set Architecture (ISA) Reference Manual 249
Instruction Word (RRRN)
Required Configuration Option
Code Density Option (See Section 4.3.1 on page 53)
Assembler Syntax
ADD.N ar, as, at
Description
This performs the same operation as the ADD instruction in a 16-bit encoding.
ADD.N calculates the two’s complement 32-bit sum of address registers as and at. The
low 32 bits of the sum are written to address register ar. Arithmetic overflow is not
detected.
Assembler Note
The assembler may convert ADD.N instructions to ADD. Prefixing the ADD.N instruction
with an underscore (_ADD.N) disables this optimization and forces the assembler to
generate the narrow form of the instruction.
Operation
AR[r] ← AR[s] + AR[t]
Exceptions
EveryInstR Group (see page 244)
15 12 11 8 7 4 3 0
r s t 1 0 1 0
4444
ADD.S Add Single
250 Xtensa Instruction Set Architecture (ISA) Reference Manual
Instruction Word (RRR)
Required Configuration Option
Floating-Point Coprocessor Option (See Section 4.3.11 on page 67)
Assembler Syntax
ADD.S fr, fs, ft
Description
ADD.S computes the IEEE754 single-precision sum of the contents of floating-point
registers fs and ft, and writes the result to floating-point register fr.
Operation
FR[r] ← FR[s] +s FR[t]
Exceptions
EveryInst Group (see page 244)
GenExcep(Coprocessor0Disabled) if Coprocessor Option
23 20 19 16 15 12 11 8 7 4 3 0
00001010 r s t 0000
444444
Add Immediate ADDI
Xtensa Instruction Set Architecture (ISA) Reference Manual 251
Instruction Word (RRI8)
Required Configuration Option
Core Architecture (See Section 4.2 on page 50)
Assembler Syntax
ADDI at, as, -128..127
Description
ADDI calculates the two’s complement 32-bit sum of address register as and a constant
encoded in the imm8 field. The low 32 bits of the sum are written to address register at.
Arithmetic overflow is not detected.
The immediate operand encoded in the instruction can range from -128 to 127. It is de-
coded by sign-extending imm8.
ADDI is a 24-bit instruction. The ADDI.N density-option instruction performs a similar
operation (the immediate operand has less range) in a 16-bit encoding.
Assembler Note
The assembler may convert ADDI instructions to ADDI.N when the Code Density
Option is enabled and the immediate operand falls within the available range. If the im-
mediate is too large the assembler may substitute an equivalent sequence. Prefixing the
ADDI instruction with an underscore (_ADDI) disables these optimizations and forces
the assembler to generate the wide form of the instruction or an error instead.
Operation
AR[t] ← AR[s] + (imm8724||imm8)
Exceptions
EveryInstR Group (see page 244)
23 16 15 12 11 8 7 4 3 0
imm8 1 1 0 0 s t 0 0 1 0
8 4444
ADDI.N Narrow Add Immediate
252 Xtensa Instruction Set Architecture (ISA) Reference Manual
Instruction Word (RRRN)
Required Configuration Option
Code Density Option (See Section 4.3.1 on page 53)
Assembler Syntax
ADDI.N ar, as, imm
Description
ADDI.N is similar to ADDI, but has a 16-bit encoding and supports a smaller range of
immediate operand values encoded in the instruction word.
ADDI.N calculates the two’s complement 32-bit sum of address register as and an
operand encoded in the t field. The low 32 bits of the sum are written to address regis-
ter ar. Arithmetic overflow is not detected.
The operand encoded in the instruction can be -1 or one to 15. If t is zero, then a value
of -1 is used, otherwise the value is the zero-extension of t.
Assembler Note
The assembler may convert ADDI.N instructions to ADDI. Prefixing the ADDI.N instruc-
tion with an underscore (_ADDI.N) disables this optimization and forces the assembler
to generate the narrow form of the instruction. In the assembler syntax, the number to
be added to the register operand is specified. When the specified value is -1, the assem-
bler encodes it as zero.
Operation
AR[r] ← AR[s] + (if t = 04 then 132 else 028||t)
Exceptions
EveryInstR Group (see page 244)
15 12 11 8 7 4 3 0
r s t 1 0 1 1
4444
Add Immediate with Shift by 8 ADDMI
Xtensa Instruction Set Architecture (ISA) Reference Manual 253
Instruction Word
(RRI8)
Required Configuration Option
Core Architecture (See Section 4.2 on page 50)
Assembler Syntax
ADDMI at, as, -32768..32512
Description
ADDMI extends the range of constant addition. It is often used in conjunction with load
and store instructions to extend the range of the base, plus offset the calculation.
ADDMI calculates the two’s complement 32-bit sum of address register as and an oper-
and encoded in the imm8 field. The low 32 bits of the sum are written to address register
at. Arithmetic overflow is not detected.
The operand encoded in the instruction can have values that are multiples of 256 rang-
ing from -32768 to 32512. It is decoded by sign-extending imm8 and shifting the result
left by eight bits.
Assembler Note
In the assembler syntax, the value to be added to the register operand is specified. The
assembler encodes this into the instruction by dividing by 256.
Operation
AR[t] ← AR[s] + (imm8716||imm8||08)
Exceptions
EveryInstR Group (see page 244)
23 16 15 12 11 8 7 4 3 0
imm8 1 1 0 1 s t 0 0 1 0
8 4444
ADDX2 Add with Shift by 1
254 Xtensa Instruction Set Architecture (ISA) Reference Manual
Instruction Word (RRR)
Required Configuration Option
Core Architecture (See Section 4.2 on page 50)
Assembler Syntax
ADDX2 ar, as, at
Description
ADDX2 calculates the two’s complement 32-bit sum of address register as shifted left by
one bit and address register at. The low 32 bits of the sum are written to address regis-
ter ar. Arithmetic overflow is not detected.
ADDX2 is frequently used for address calculation and as part of sequences to multiply by
small constants.
Operation
AR[r] ← (AR[s]30..0||0) + AR[t]
Exceptions
EveryInstR Group (see page 244)
23 20 19 16 15 12 11 8 7 4 3 0
10010000 r s t 0000
444444
Add with Shift by 2 ADDX4
Xtensa Instruction Set Architecture (ISA) Reference Manual 255
Instruction Word (RRR)
Required Configuration Option
Core Architecture (See Section 4.2 on page 50r)
Assembler Syntax
ADDX4 ar, as, at
Description
ADDX4 calculates the two’s complement 32-bit sum of address register as shifted left by
two bits and address register at. The low 32 bits of the sum are written to address reg-
ister ar. Arithmetic overflow is not detected.
ADDX4 is frequently used for address calculation and as part of sequences to multiply by
small constants.
Operation
AR[r] ← (AR[s]29..0||02) + AR[t]
Exceptions
EveryInstR Group (see page 244)
23 20 19 16 15 12 11 8 7 4 3 0
10100000 r s t 0000
444444
ADDX8 Add with Shift by 3
256 Xtensa Instruction Set Architecture (ISA) Reference Manual
Instruction Word (RRR)
Required Configuration Option
Core Architecture (See Section 4.2 on page 50)
Assembler Syntax
ADDX8 ar, as, at
Description
ADDX8 calculates the two’s complement 32-bit sum of address register as shifted left by
3 bits and address register at. The low 32 bits of the sum are written to address register
ar. Arithmetic overflow is not detected.
ADDX8 is frequently used for address calculation and as part of sequences to multiply by
small constants.
Operation
AR[r] ← (AR[s]28..0||03) + AR[t]
Exceptions
EveryInstR Group (see page 244)
23 20 19 16 15 12 11 8 7 4 3 0
10110000 r s t 0000
444444
All 4 Booleans True ALL4
Xtensa Instruction Set Architecture (ISA) Reference Manual 257
Instruction Word (RRR)
Required Configuration Option
Boolean Option (See Section 4.3.10 on page 65)
Assembler Syntax
ALL4 bt, bs
Description
ALL4 sets Boolean register bt to the logical and of the four Boolean registers bs+0,
bs+1, bs+2, and bs+3. bs must be a multiple of four (b0, b4, b8, or b12); otherwise the
operation of this instruction is not defined. ALL4 reduces four test results such that the
result is true if all four tests are true.
When the sense of the bs Booleans is inverted (0 → true, 1 → false), use ANY4 and an
inverted test of the result.
Operation
BRt ← BRs+3 and BRs+2 and BRs+1 and BRs+0
Exceptions
EveryInst Group (see page 244)
23 20 19 16 15 12 11 8 7 4 3 0
000000001001 s t 0000
444444
ALL8 All 8 Booleans True
258 Xtensa Instruction Set Architecture (ISA) Reference Manual
Instruction Word (RRR)
Required Configuration Option
Boolean Option (See Section 4.3.10 on page 65)
Assembler Syntax
ALL8 bt, bs
Description
ALL8 sets Boolean register bt to the logical and of the eight Boolean registers bs+0,
bs+1, … bs+6, and bs+7. bs must be a multiple of eight (b0 or b8); otherwise the oper-
ation of this instruction is not defined. ALL8 reduces eight test results such that the re-
sult is true if all eight tests are true.
When the sense of the bs Booleans is inverted (0 → true, 1 → false), use ANY8 and an
inverted test of the result.
Operation
BRt ← BRs+7 and ... and BRs+0
Exceptions
EveryInst Group (see page 244)
23 20 19 16 15 12 11 8 7 4 3 0
000000001011 s t 0000
444444
Bitwise Logical And AND
Xtensa Instruction Set Architecture (ISA) Reference Manual 259
Instruction Word (RRR)
Required Configuration Option
Core Architecture (See Section 4.2 on page 50)
Assembler Syntax
AND ar, as, at
Description
AND calculates the bitwise logical and of address registers as and at. The result is
written to address register ar.
Operation
AR[r] ← AR[s] and AR[t]
Exceptions
EveryInstR Group (see page 244)
23 20 19 16 15 12 11 8 7 4 3 0
00010000 r s t 0000
444444
ANDB Boolean And
260 Xtensa Instruction Set Architecture (ISA) Reference Manual
Instruction Word (RRR)
Required Configuration Option
Boolean Option (See Section 4.3.10 on page 65)
Assembler Syntax
ANDB br, bs, bt
Description
ANDB performs the logical and of Boolean registers bs and bt and writes the result to
Boolean register br.
When the sense of one of the source Booleans is inverted (0 → true, 1 → false), use
ANDBC. When the sense of both of the source Booleans is inverted, use ORB and an
inverted test of the result.
Operation
BRr ← BRs and BRt
Exceptions
EveryInst Group (see page 244)
23 20 19 16 15 12 11 8 7 4 3 0
00000010 r s t 0000
444444
Boolean And with Complement ANDBC
Xtensa Instruction Set Architecture (ISA) Reference Manual 261
Instruction Word (RRR)
Required Configuration Option
Boolean Option (See Section 4.3.10 on page 65)
Assembler Syntax
ANDBC br, bs, bt
Description
ANDBC performs the logical and of Boolean register bs with the logical complement of
Boolean register bt, and writes the result to Boolean register br.
Operation
BRr ← BRs and not BRt
Exceptions
EveryInst Group (see page 244)
23 20 19 16 15 12 11 8 7 4 3 0
00010010 r s t 0000
444444
ANY4 Any 4 Booleans True
262 Xtensa Instruction Set Architecture (ISA) Reference Manual
Instruction Word (RRR)
Required Configuration Option
Boolean Option (See Section 4.3.10 on page 65)
Assembler Syntax
ANY4 bt, bs
Description
ANY4 sets Boolean register bt to the logical or of the four Boolean registers bs+0,
bs+1, bs+2, and bs+3. bs must be a multiple of four (b0, b4, b8, or b12); otherwise the
operation of this instruction is not defined. ANY4 reduces four test results such that the
result is true if any of the four tests are true.
When the sense of the bs Booleans is inverted (0 → true, 1 → false), use ALL4 and an
inverted test of the result.
Operation
BRt ← BRs+3 or BRs+2 or BRs+1 or BRs+0
Exceptions
EveryInst Group (see page 244)
23 20 19 16 15 12 11 8 7 4 3 0
000000001000 s t 0000
444444
Any 8 Booleans True ANY8
Xtensa Instruction Set Architecture (ISA) Reference Manual 263
Instruction Word (RRR)
Required Configuration Option
Boolean Option (See Section 4.3.10 on page 65)
Assembler Syntax
ANY8 bt, bs
Description
ANY8 sets Boolean register bt to the logical or of the eight Boolean registers bs+0,
bs+1, … bs+6, and bs+7. bs must be a multiple of eight (b0 or b8); otherwise the oper-
ation of this instruction is not defined. ANY8 reduces eight test results such that the re-
sult is true if any of the eight tests are true.
When the sense of the bs Booleans is inverted (0 → true, 1 → false), use ALL8 and an
inverted test of the result.
Operation
BRt ← BRs+7 or ... or BRs+0
Exceptions
EveryInst Group (see page 244)
23 20 19 16 15 12 11 8 7 4 3 0
000000001010 s t 0000
444444
BALL Branch if All Bits Set
264 Xtensa Instruction Set Architecture (ISA) Reference Manual
Instruction Word
(RRI8)
Required Configuration Option
Core Architecture (See Section 4.2 on page 50)
Assembler Syntax
BALL as, at, label
Description
BALL branches if all the bits specified by the mask in address register at are set in ad-
dress register as. The test is performed by taking the bitwise logical and of at and the
complement of as, and testing if the result is zero.
The target instruction address of the branch is given by the address of the BALL instruc-
tion, plus the sign-extended 8-bit imm8 field of the instruction plus four. If any of the
masked bits are clear, execution continues with the next sequential instruction.
The inverse of BALL is BNALL.
Assembler Note
The assembler will substitute an equivalent sequence of instructions when the label is
out of range. Prefixing the instruction mnemonic with an underscore (_BALL) disables
this feature and forces the assembler to generate an error in this case.
Operation
if ((not AR[s]) and AR[t]) = 032 then
nextPC ← PC + (imm8724||imm8) + 4
endif
Exceptions
EveryInstR Group (see page 244)
23 16 15 12 11 8 7 4 3 0
imm8 0 1 0 0 s t 0 1 1 1
8 4444
Branch if Any Bit Set BANY
Xtensa Instruction Set Architecture (ISA) Reference Manual 265
Instruction Word
(RRI8)
Required Configuration Option
Core Architecture (See Section 4.2 on page 50)
Assembler Syntax
BANY as, at, label
Description
BANY branches if any of the bits specified by the mask in address register at are set in
address register as. The test is performed by taking the bitwise logical and of as and at
and testing if the result is non-zero.
The target instruction address of the branch is given by the address of the BANY instruc-
tion, plus the sign-extended 8-bit imm8 field of the instruction plus four. If all of the
masked bits are clear, execution continues with the next sequential instruction.
The inverse of BANY is BNONE.
Assembler Note
The assembler will substitute an equivalent sequence of instructions when the label is
out of range. Prefixing the instruction mnemonic with an underscore (_BANY) disables
this feature and forces the assembler to generate an error in this case.
Operation
if (AR[s] and AR[t]) ≠ 032 then
nextPC ← PC + (imm8724||imm8) + 4
endif
Exceptions
EveryInstR Group (see page 244)
23 16 15 12 11 8 7 4 3 0
imm8 1 0 0 0 s t 0 1 1 1
8 4444
BBC Branch if Bit Clear
266 Xtensa Instruction Set Architecture (ISA) Reference Manual
Instruction Word
(RRI8)
Required Configuration Option
Core Architecture (See Section 4.2 on page 50)
Assembler Syntax
BBC as, at, label
Description
BBC branches if the bit specified by the low five bits of address register at is clear in ad-
dress register as. For little-endian processors, bit 0 is the least significant bit and bit 31
is the most significant bit. For big-endian processors, bit 0 is the most significant bit and
bit 31 is the least significant bit.
The target instruction address of the branch is given by the address of the BBC instruc-
tion, plus the sign-extended 8-bit imm8 field of the instruction plus four. If the specified
bit is set, execution continues with the next sequential instruction.
The inverse of BBC is BBS.
Assembler Note
The assembler will substitute an equivalent sequence of instructions when the label is
out of range. Prefixing the instruction mnemonic with an underscore (_BBC) disables this
feature and forces the assembler to generate an error in this case.
Operation
b ← AR[t]4..0 xor msbFirst5
if AR[s]b = 0 then
nextPC ← PC + (imm8724||imm8) + 4
endif
Exceptions
EveryInstR Group (see page 244)
23 16 15 12 11 8 7 4 3 0
imm8 0 1 0 1 s t 0 1 1 1
8 4444
Branch if Bit Clear Immediate BBCI
Xtensa Instruction Set Architecture (ISA) Reference Manual 267
Instruction Word
(RRI8)
Required Configuration Option
Core Architecture (See Section 4.2 on page 50)
Assembler Syntax
BBCI as, 0..31, label
Description
BBCI branches if the bit specified by the constant encoded in the bbi field of the in-
struction word is clear in address register as. For little-endian processors, bit 0 is the
least significant bit and bit 31 is the most significant bit. For big-endian processors bit 0
is the most significant bit and bit 31 is the least significant bit. The bbi field is split, with
bits 3..0 in bits 7..4 of the instruction word, and bit 4 in bit 12 of the instruction word.
The target instruction address of the branch is given by the address of the BBCI instruc-
tion, plus the sign-extended 8-bit imm8 field of the instruction plus four. If the specified
bit is set, execution continues with the next sequential instruction.
The inverse of BBCI is BBSI.
Assembler Note
The assembler will substitute an equivalent sequence of instructions when the label is
out of range. Prefixing the instruction mnemonic with an underscore (_BBCI) disables
this feature and forces the assembler to generate an error in this case.
Operation
b ← bbi xor msbFirst5
if AR[s]b = 0 then
nextPC ← PC + (imm8724||imm8) + 4
endif
Exceptions
EveryInstR Group (see page 244)
23 16 15 12 11 8 7 4 3 0
imm8 0 1 1 bbi4sbbi3..0 0111
8 4444
BBCI.L Branch if Bit Clear Immediate LE
268 Xtensa Instruction Set Architecture (ISA) Reference Manual
Instruction Word
(RRI8)
Required Configuration Option
Assembler Macro
Assembler Syntax
BBCI.L as, 0..31, label
Description
BBCI.L is an assembler macro for BBCI that always uses little-endian bit numbering.
That is, it branches if the bit specified by its immediate is clear in address register as,
where bit 0 is the least significant bit and bit 31 is the most significant bit.
The inverse of BBCI.L is BBSI.L.
Assembler Note
For little-endian processors, BBCI.L and BBCI are identical. For big-endian processors,
the assembler will convert BBCI.L instructions to BBCI by changing the encoded imme-
diate value to 31-imm.
Exceptions
EveryInstR Group (see page 244)
23 16 15 12 11 8 7 4 3 0
imm8 0 1 1 bbi4sbbi3..0 0111
8 4444
Branch if Bit Set BBS
Xtensa Instruction Set Architecture (ISA) Reference Manual 269
Instruction Word
(RRI8)
Required Configuration Option
Core Architecture (See Section 4.2 on page 50)
Assembler Syntax
BBS as, at, label
Description
BBS branches if the bit specified by the low five bits of address register at is set in ad-
dress register as. For little-endian processors, bit 0 is the least significant bit and bit 31
is the most significant bit. For big-endian processors, bit 0 is the most significant bit and
bit 31 is the least significant bit.
The target instruction address of the branch is given by the address of the BBS instruc-
tion, plus the sign-extended 8-bit imm8 field of the instruction plus four. If the specified
bit is clear, execution continues with the next sequential instruction.
The inverse of BBS is BBC.
Assembler Note
The assembler will substitute an equivalent sequence of instructions when the label is
out of range. Prefixing the instruction mnemonic with an underscore (_BBS) disables this
feature and forces the assembler to generate an error in this case.
Operation
b ← AR[t]4..0 xor msbFirst5
if AR[s]b ≠ 0 then
nextPC ← PC + (imm8724||imm8) + 4
endif
Exceptions
EveryInstR Group (see page 244)
23 16 15 12 11 8 7 4 3 0
imm8 1 1 0 1 s t 0 1 1 1
8 4444
BBSI Branch if Bit Set Immediate
270 Xtensa Instruction Set Architecture (ISA) Reference Manual
Instruction Word
(RRI8)
Required Configuration Option
Core Architecture (See Section 4.2 on page 50)
Assembler Syntax
BBSI as, 0..31, label
Description
BBSI branches if the bit specified by the constant encoded in the bbi field of the in-
struction word is set in address register as. For little-endian processors, bit 0 is the least
significant bit and bit 31 is the most significant bit. For big-endian processors, bit 0 is the
most significant bit and bit 31 is the least significant bit. The bbi field is split, with bits
3..0 in bits 7..4 of the instruction word, and bit 4 in bit 12 of the instruction word.
The target instruction address of the branch is given by the address of the BBSI instruc-
tion, plus the sign-extended 8-bit imm8 field of the instruction plus four. If the specified
bit is clear, execution continues with the next sequential instruction.
The inverse of BBSI is BBCI.
Assembler Note
The assembler will substitute an equivalent sequence of instructions when the label is
out of range. Prefixing the instruction mnemonic with an underscore (_BBSI) disables
this feature and forces the assembler to generate an error in this case.
Operation
b ← bbi xor msbFirst5
if AR[s]b ≠ 0 then
nextPC ← PC + (imm8724||imm8) + 4
endif
Exceptions
EveryInstR Group (see page 244)
23 16 15 12 11 8 7 4 3 0
imm8 1 1 1 bbi4sbbi3..0 0111
8 4444
Branch if Bit Set Immediate LE BBSI.L
Xtensa Instruction Set Architecture (ISA) Reference Manual 271
Instruction Word
(RRI8)
Required Configuration Option
Assembler Macro
Assembler Syntax
BBSI.L as, 0..31, label
Description
BBSI.L is an assembler macro for BBSI that always uses little-endian bit numbering.
That is, it branches if the bit specified by its immediate is set in address register as,
where bit 0 is the least significant bit and bit 31 is the most significant bit.
The inverse of BBSI.L is BBCI.L.
Assembler Note
For little-endian processors, BBSI.L and BBSI are identical. For big-endian processors,
the assembler will convert BBSI.L instructions to BBSI by changing the encoded imme-
diate value to 31-imm.
Exceptions
EveryInstR Group (see page 244)
23 16 15 12 11 8 7 4 3 0
imm8 1 1 1 bbi4sbbi 0111
8 4444
BEQ Branch if Equal
272 Xtensa Instruction Set Architecture (ISA) Reference Manual
Instruction Word
(RRI8)
Required Configuration Option
Core Architecture (See Section 4.2 on page 50)
Assembler Syntax
BEQ as, at, label
Description
BEQ branches if address registers as and at are equal.
The target instruction address of the branch is given by the address of the BEQ instruc-
tion plus the sign-extended 8-bit imm8 field of the instruction plus four. If the registers
are not equal, execution continues with the next sequential instruction.
The inverse of BEQ is BNE.
Assembler Note
The assembler will substitute an equivalent sequence of instructions when the label is
out of range. Prefixing the instruction mnemonic with an underscore (_BEQ) disables this
feature and forces the assembler to generate an error in this case.
Operation
if AR[s] = AR[t] then
nextPC ← PC + (imm8724||imm8) + 4
endif
Exceptions
EveryInstR Group (see page 244)
23 16 15 12 11 8 7 4 3 0
imm8 0 0 0 1 s t 0 1 1 1
8 4444
Branch if Equal Immediate BEQI
Xtensa Instruction Set Architecture (ISA) Reference Manual 273
Instruction Word (RRI8)
Required Configuration Option
Core Architecture (See Section 4.2 on page 50)
Assembler Syntax
BEQI as, imm, label
Description
BEQI branches if address register as and a constant encoded in the r field are equal.
The constant values encoded in the r field are not simply 0..15. For the constant values
that can be encoded by r, see Table 3–17 on page 41.
The target instruction address of the branch is given by the address of the BEQI instruc-
tion, plus the sign-extended 8-bit imm8 field of the instruction plus four. If the register is
not equal to the constant, execution continues with the next sequential instruction.
The inverse of BEQI is BNEI.
Assembler Note
The assembler may convert BEQI instructions to BEQZ or BEQZ.N when given an imme-
diate operand that evaluates to zero. The assembler will substitute an equivalent se-
quence of instructions when the label is out of range. Prefixing the instruction mnemonic
with an underscore (_BEQI) disables these features and forces the assembler to gener-
ate an error instead.
Operation
if AR[s] = B4CONST(r) then
nextPC ← PC + (imm8724||imm8) + 4
endif
Exceptions
EveryInstR Group (see page 244)
23 16 15 12 11 876543 0
imm8 r s 00100110
8 4 4 2 2 4
BEQZ Branch if Equal to Zero
274 Xtensa Instruction Set Architecture (ISA) Reference Manual
Instruction Word BRI12
Required Configuration Option
Core Architecture (See Section 4.2 on page 50)
Assembler Syntax
BEQZ as, label
Description
BEQZ branches if address register as is equal to zero. BEQZ provides 12 bits of target
range instead of the eight bits available in most conditional branches.
The target instruction address of the branch is given by the address of the BEQZ instruc-
tion, plus the sign-extended 12-bit imm12 field of the instruction plus four. If register as
is not equal to zero, execution continues with the next sequential instruction.
The inverse of BEQZ is BNEZ.
Assembler Note
The assembler may convert BEQZ instructions to BEQZ.N when the Code Density
Option is enabled and the branch target is reachable with the shorter instruction. The
assembler will substitute an equivalent sequence of instructions when the label is out of
range. Prefixing the instruction mnemonic with an underscore (_BEQZ) disables these
features and forces the assembler to generate the wide form of the instruction and an
error when the label is out of range).
Operation
if AR[s] = 032 then
nextPC ← PC + (imm121120||imm12) + 4
endif
Exceptions
EveryInstR Group (see page 244)
23 12 11 876543 0
imm12 s 00010110
12 4 2 2 4
Narrow Branch if Equal Zero BEQZ.N
Xtensa Instruction Set Architecture (ISA) Reference Manual 275
Instruction Word (RI6)
Required Configuration Option
Code Density Option (See Section 4.3.1 on page 53)
Assembler Syntax
BEQZ.N as, label
Description
This performs the same operation as the BEQZ instruction in a 16-bit encoding. BEQZ.N
branches if address register as is equal to zero. BEQZ.N provides six bits of target
range instead of the 12 bits available in BEQZ.
The target instruction address of the branch is given by the address of the BEQZ.N in-
struction, plus the zero-extended 6-bit imm6 field of the instruction plus four. Because
the offset is unsigned, this instruction can only be used to branch forward. If register as
is not equal to zero, execution continues with the next sequential instruction.
The inverse of BEQZ.N is BNEZ.N.
Assembler Note
The assembler may convert BEQZ.N instructions to BEQZ. The assembler will substitute
an equivalent sequence of instructions when the label is out of range. Prefixing the in-
struction mnemonic with an underscore (_BEQZ.N) disables these features and forces
the assembler to generate the narrow form of the instruction and an error when the label
is out of range.
Operation
if AR[s] = 032 then
nextPC ← PC + (026||imm6) + 4
endif
Exceptions
EveryInstR Group (see page 244)
15 12 11 8 7 4 3 0
imm63..0 s 1 0 imm65..4 1100
4444
BF Branch if False
276 Xtensa Instruction Set Architecture (ISA) Reference Manual
Instruction Word
(RRI8)
Required Configuration Option
Boolean Option (See Section 4.3.10 on page 65)
Assembler Syntax
BF bs, label
Description
BF branches to the target address if Boolean register bs is false.
The target instruction address of the branch is given by the address of the BF instruction
plus the sign-extended 8-bit imm8 field of the instruction plus four. If the Boolean register
bs is true, execution continues with the next sequential instruction.
The inverse of BF is BT.
Assembler Note
The assembler will substitute an equivalent sequence of instructions when the label is
out of range. Prefixing the instruction mnemonic with an underscore (_BF) disables this
feature and forces the assembler to generate an error when the label is out of range.
Operation
if not BRs then
nextPC ← PC + (imm8724||imm8) + 4
endif
Exceptions
EveryInst Group (see page 244)
23 16 15 12 11 8 7 4 3 0
imm8 0000 s 01110110
8 4444
Branch if Greater Than or Equal BGE
Xtensa Instruction Set Architecture (ISA) Reference Manual 277
Instruction Word
(RRI8)
Required Configuration Option
Core Architecture (See Section 4.2 on page 50)
Assembler Syntax
BGE as, at, label
Description
BGE branches if address register as is two’s complement greater than or equal to ad-
dress register at.
The target instruction address of the branch is given by the address of the BGE instruc-
tion, plus the sign-extended 8-bit imm8 field of the instruction plus four. If the address
register as is less than address register at, execution continues with the next sequen-
tial instruction.
The inverse of BGE is BLT.
Assembler Note
The assembler will substitute an equivalent sequence of instructions when the label is
out of range. Prefixing the instruction mnemonic with an underscore (_BGE) disables this
feature and forces the assembler to generate an error in this case.
Operation
if AR[s] ≥ AR[t] then
nextPC ← PC + (imm8724||imm8) + 4
endif
Exceptions
EveryInstR Group (see page 244)
23 16 15 12 11 8 7 4 3 0
imm8 1 0 1 0 s t 0 1 1 1
8 4444
BGEI Branch if Greater Than or Equal Immediate
278 Xtensa Instruction Set Architecture (ISA) Reference Manual
Instruction Word (BRI8)
Required Configuration Option
Core Architecture (See Section 4.2 on page 50)
Assembler Syntax
BGEI as, imm, label
Description
BGEI branches if address register as is two’s complement greater than or equal to the
constant encoded in the r field. The constant values encoded in the r field are not sim-
ply 0..15. For the constant values that can be encoded by r, see Table 3–17 on page 41.
The target instruction address of the branch is given by the address of the BGEI instruc-
tion, plus the sign-extended 8-bit imm8 field of the instruction plus four. If the address
register as is less than the constant, execution continues with the next sequential
instruction.
The inverse of BGEI is BLTI.
Assembler Note
The assembler may convert BGEI instructions to BGEZ when given an immediate oper-
and that evaluates to zero. The assembler will substitute an equivalent sequence of in-
structions when the label is out of range. Prefixing the instruction mnemonic with an un-
derscore (_BGEI) disables these features and forces the assembler to generate an error
instead.
Operation
if AR[s] ≥ B4CONST(r) then
nextPC ← PC + (imm8724||imm8) + 4
endif
Exceptions
EveryInstR Group (see page 244)
23 16 15 12 11 876543 0
imm8 r s 11100110
8 4 4 2 2 4
Branch if Greater Than or Equal Unsigned BGEU
Xtensa Instruction Set Architecture (ISA) Reference Manual 279
Instruction Word
(RRI8)
Required Configuration Option
Core Architecture (See Section 4.2 on page 50)
Assembler Syntax
BGEU as, at, label
Description
BGEU branches if address register as is unsigned greater than or equal to address reg-
ister at.
The target instruction address of the branch is given by the address of the BGEU instruc-
tion, plus the sign-extended 8-bit imm8 field of the instruction plus four. If the address
register as is unsigned less than address register at, execution continues with the next
sequential instruction.
The inverse of BGEU is BLTU.
Assembler Note
The assembler will substitute an equivalent sequence of instructions when the label is
out of range. Prefixing the instruction mnemonic with an underscore (_BGEU) disables
this feature and forces the assembler to generate an error in this case.
Operation
if (0||AR[s]) ≥ (0||AR[t]) then
nextPC ← PC + (imm8724||imm8) + 4
endif
Exceptions
EveryInstR Group (see page 244)
23 16 15 12 11 8 7 4 3 0
imm8 1 0 1 1 s t 0 1 1 1
8 4444
BGEUI Branch if Greater Than or Eq Unsigned Imm
280 Xtensa Instruction Set Architecture (ISA) Reference Manual
Instruction Word (BRI8)
Required Configuration Option
Core Architecture (See Section 4.2 on page 50)
Assembler Syntax
BGEUI as, imm, label
Description
BGEUI branches if address register as is unsigned greater than or equal to the constant
encoded in the r field. The constant values encoded in the r field are not simply 0..15.
For the constant values that can be encoded by r, see Table 3–18 on page 42.
The target instruction address of the branch is given by the address of the BGEUI in-
struction plus the sign-extended 8-bit imm8 field of the instruction plus four. If the ad-
dress register as is less than the constant, execution continues with the next sequential
instruction.
The inverse of BGEUI is BLTUI.
Assembler Note
The assembler will substitute an equivalent sequence of instructions when the label is
out of range. Prefixing the instruction mnemonic with an underscore (_BGEUI) disables
this feature and forces the assembler to generate an error in this case.
Operation
if (0||AR[s]) ≥ (0||B4CONSTU(r)) then
nextPC ← PC + (imm8724||imm8) + 4
endif
Exceptions
EveryInstR Group (see page 244)
23 16 15 12 11 876543 0
imm8 r s 11110110
8 4 4 2 2 4
Branch if Greater Than or Equal to Zero BGEZ
Xtensa Instruction Set Architecture (ISA) Reference Manual 281
Instruction Word (BRI12)
Required Configuration Option
Core Architecture (See Section 4.2 on page 50)
Assembler Syntax
BGEZ as, label
Description
BGEZ branches if address register as is greater than or equal to zero (the most signifi-
cant bit is clear). BGEZ provides 12 bits of target range instead of the eight bits available
in most conditional branches.
The target instruction address of the branch is given by the address of the BGEZ instruc-
tion plus the sign-extended 12-bit imm12 field of the instruction plus four. If register as is
less than zero, execution continues with the next sequential instruction.
The inverse of BGEZ is BLTZ.
Assembler Note
The assembler will substitute an equivalent sequence of instructions when the label is
out of range. Prefixing the instruction mnemonic with an underscore (_BGEZ) disables
this feature and forces the assembler to generate an error in this case.
Operation
if AR[s]31 = 0 then
nextPC ← PC + (imm121120||imm12) + 4
endif
Exceptions
EveryInstR Group (see page 244)
23 12 11 876543 0
imm12 s 11010110
12 4 2 2 4
BLT Branch if Less Than
282 Xtensa Instruction Set Architecture (ISA) Reference Manual
Instruction Word
(RRI8)
Required Configuration Option
Core Architecture (See Section 4.2 on page 50)
Assembler Syntax
BLT as, at, label
Description
BLT branches if address register as is two’s complement less than address register at.
The target instruction address of the branch is given by the address of the BLT instruc-
tion plus the sign-extended 8-bit imm8 field of the instruction plus four. If the address
register as is greater than or equal to address register at, execution continues with the
next sequential instruction.
The inverse of BLT is BGE.
Assembler Note
The assembler will substitute an equivalent sequence of instructions when the label is
out of range. Prefixing the instruction mnemonic with an underscore (_BLT) disables this
feature and forces the assembler to generate an error in this case.
Operation
if AR[s] < AR[t] then
nextPC ← PC + (imm8724||imm8) + 4
endif
Exceptions
EveryInstR Group (see page 244)
23 16 15 12 11 8 7 4 3 0
imm8 0 0 1 0 s t 0 1 1 1
8 4444
Branch if Less Than Immediate BLTI
Xtensa Instruction Set Architecture (ISA) Reference Manual 283
Instruction Word (BRI8)
Required Configuration Option
Core Architecture (See Section 4.2 on page 50)
Assembler Syntax
BLTI as, imm, label
Description
BLTI branches if address register as is two’s complement less than the constant encod-
ed in the r field. The constant values encoded in the r field are not simply 0..15. For the
constant values that can be encoded by r, see Table 3–17 on page 41.
The target instruction address of the branch is given by the address of the BLTI instruc-
tion plus the sign-extended 8-bit imm8 field of the instruction plus four. If the address
register as is greater than or equal to the constant, execution continues with the next
sequential instruction.
The inverse of BLTI is BGEI.
Assembler Note
The assembler may convert BLTI instructions to BLTZ when given an immediate oper-
and that evaluates to zero. The assembler will substitute an equivalent sequence of in-
structions when the label is out of range. Prefixing the instruction mnemonic with an un-
derscore (_BLTI) disables these features and forces the assembler to generate an error
instead.
Operation
if AR[s] < B4CONST(r) then
nextPC ← PC + (imm8724||imm8) + 4
endif
Exceptions
EveryInstR Group (see page 244)
23 16 15 12 11 876543 0
imm8 r s 10100110
8 4 4 2 2 4
BLTU Branch if Less Than Unsigned
284 Xtensa Instruction Set Architecture (ISA) Reference Manual
Instruction Word
(RRI8)
Required Configuration Option
Core Architecture (See Section 4.2 on page 50)
Assembler Syntax
BLTU as, at, label
Description
BLTU branches if address register as is unsigned less than address register at.
The target instruction address of the branch is given by the address of the BLTU instruc-
tion, plus the sign-extended 8-bit imm8 field of the instruction plus four. If the address
register as is greater than or equal to address register at, execution continues with the
next sequential instruction.
The inverse of BLTU is BGEU.
Assembler Note
The assembler will substitute an equivalent sequence of instructions when the label is
out of range. Prefixing the instruction mnemonic with an underscore (_BLTU) disables
this feature and forces the assembler to generate an error in this case.
Operation
if (0||AR[s]) < (0||AR[t]) then
nextPC ← PC + (imm8724||imm8) + 4
endif
Exceptions
EveryInstR Group (see page 244)
23 16 15 12 11 8 7 4 3 0
imm8 0 0 1 1 s t 0 1 1 1
8 4444
Branch if Less Than Unsigned Immediate BLTUI
Xtensa Instruction Set Architecture (ISA) Reference Manual 285
Instruction Word (BRI8)
Required Configuration Option
Core Architecture (See Section 4.2 on page 50)
Assembler Syntax
BLTUI as, imm, label
Description
BLTUI branches if address register as is unsigned less than the constant encoded in
the r field. The constant values encoded in the r field are not simply 0..15. For the
constant values that can be encoded by r, see Table 3–18 on page 42.
The target instruction address of the branch is given by the address of the BLTUI in-
struction, plus the sign-extended 8-bit imm8 field of the instruction plus four. If the ad-
dress register as is greater than or equal to the constant, execution continues with the
next sequential instruction.
The inverse of BLTUI is BGEUI.
Assembler Note
The assembler will substitute an equivalent sequence of instructions when the label is
out of range. Prefixing the instruction mnemonic with an underscore (_BLTUI) disables
this feature and forces the assembler to generate an error in this case.
Operation
if (0||AR[s]) < (0||B4CONSTU(r)) then
nextPC ← PC + (imm8724||imm8) + 4
endif
Exceptions
EveryInstR Group (see page 244)
23 16 15 12 11 876543 0
imm8 r s 10110110
8 4 4 2 2 4
BLTZ Branch if Less Than Zero
286 Xtensa Instruction Set Architecture (ISA) Reference Manual
Instruction Word (BRI12)
Required Configuration Option
Core Architecture (See Section 4.2 on page 50)
Assembler Syntax
BLTZ as, label
Description
BLTZ branches if address register as is less than zero (the most significant bit is set).
BLTZ provides 12 bits of target range instead of the eight bits available in most condi-
tional branches.
The target instruction address of the branch is given by the address of the BLTZ instruc-
tion, plus the sign-extended 12-bit imm12 field of the instruction plus four. If register as
is greater than or equal to zero, execution continues with the next sequential instruction.
The inverse of BLTZ is BGEZ.
Assembler Note
The assembler will substitute an equivalent sequence of instructions when the label is
out of range. Prefixing the instruction mnemonic with an underscore (_BLTZ) disables
this feature and forces the assembler to generate an error in this case.
Operation
if AR[s]31 ≠ 0 then
nextPC ← PC + (imm121120||imm12) + 4
endif
Exceptions
EveryInstR Group (see page 244)
23 12 11 876543 0
imm12 s 10010110
12 4 2 2 4
Branch if Not-All Bits Set BNALL
Xtensa Instruction Set Architecture (ISA) Reference Manual 287
Instruction Word
(RRI8)
Required Configuration Option
Core Architecture (See Section 4.2 on page 50)
Assembler Syntax
BNALL as, at, label
Description
BNALL branches if any of the bits specified by the mask in address register at are clear
in address register as (that is, if they are not all set). The test is performed by taking the
bitwise logical and of at with the complement of as and testing if the result is non-zero.
The target instruction address of the branch is given by the address of the BNALL in-
struction, plus the sign-extended 8-bit imm8 field of the instruction plus four. If all of the
masked bits are set, execution continues with the next sequential instruction.
The inverse of BNALL is BALL.
Assembler Note
The assembler will substitute an equivalent sequence of instructions when the label is
out of range. Prefixing the instruction mnemonic with an underscore (_BNALL) disables
this feature and forces the assembler to generate an error in this case.
Operation
if ((not AR[s]) and AR[t]) ≠ 032 then
nextPC ← PC + (imm8724||imm8) + 4
endif
Exceptions
EveryInstR Group (see page 244)
23 16 15 12 11 8 7 4 3 0
imm8 1 1 0 0 s t 0 1 1 1
8 4444
BNE Branch if Not Equal
288 Xtensa Instruction Set Architecture (ISA) Reference Manual
Instruction Word
(RRI8)
Required Configuration Option
Core Architecture (See Section 4.2 on page 50)
Assembler Syntax
BNE as, at, label
Description
BNE branches if address registers as and at are not equal.
The target instruction address of the branch is given by the address of the BNE instruc-
tion, plus the sign-extended 8-bit imm8 field of the instruction plus four. If the registers
are equal, execution continues with the next sequential instruction.
The inverse of BNE is BEQ.
Assembler Note
The assembler will substitute an equivalent sequence of instructions when the label is
out of range. Prefixing the instruction mnemonic with an underscore (_BNE) disables this
feature and forces the assembler to generate an error in this case.
Operation
if AR[s] ≠ AR[t] then
nextPC ← PC + (imm8724||imm8) + 4
endif
Exceptions
EveryInstR Group (see page 244)
23 16 15 12 11 8 7 4 3 0
imm8 1 0 0 1 s t 0 1 1 1
8 4444
Branch if Not Equal Immediate BNEI
Xtensa Instruction Set Architecture (ISA) Reference Manual 289
Instruction Word (BRI8)
Required Configuration Option
Core Architecture (See Section 4.2 on page 50)
Assembler Syntax
BNEI as, imm, label
Description
BNEI branches if address register as and a constant encoded in the r field are not
equal. The constant values encoded in the r field are not simply 0..15. For the constant
values that can be encoded by r, see Table 3–17 on page 41.
The target instruction address of the branch is given by the address of the BNEI instruc-
tion, plus the sign-extended 8-bit imm8 field of the instruction plus four. If the register is
equal to the constant, execution continues with the next sequential instruction.
The inverse of BNEI is BEQI.
Assembler Note
The assembler may convert BNEI instructions to BNEZ or BNEZ.N when given an imme-
diate operand that evaluates to zero. The assembler will substitute an equivalent se-
quence of instructions when the label is out of range. Prefixing the instruction mnemonic
with an underscore (_BNEI) disables these features and forces the assembler to gener-
ate an error instead.
Operation
if AR[s] ≠ B4CONST(r) then
nextPC ← PC + (imm8724||imm8) + 4
endif
Exceptions
EveryInstR Group (see page 244)
23 16 15 12 11 876543 0
imm8 r s 01100110
8 4 4 2 2 4
BNEZ Branch if Not-Equal to Zero
290 Xtensa Instruction Set Architecture (ISA) Reference Manual
Instruction Word (BRI12)
Required Configuration Option
Core Architecture (See Section 4.2 on page 50)
Assembler Syntax
BNEZ as, label
Description
BNEZ branches if address register as is not equal to zero. BNEZ provides 12 bits of tar-
get range instead of the eight bits available in most conditional branches.
The target instruction address of the branch is given by the address of the BNEZ instruc-
tion, plus the sign-extended 12-bit imm12 field of the instruction plus four. If register as
is equal to zero, execution continues with the next sequential instruction.
The inverse of BNEZ is BEQZ.
Assembler Note
The assembler may convert BNEZ instructions to BNEZ.N when the Code Density
Option is enabled and the branch target is reachable with the shorter instruction. The
assembler will substitute an equivalent sequence of instructions when the label is out of
range. Prefixing the instruction mnemonic with an underscore (_BNEZ) disables these
features and forces the assembler to generate the BNEZ form of the instruction and an
error when the label is out of range.
Operation
if AR[s] ≠ 032 then
nextPC ← PC + (imm121120||imm12) + 4
endif
Exceptions
EveryInstR Group (see page 244)
23 12 11 876543 0
imm12 s 01010110
12 4 2 2 4
Narrow Branch if Not Equal Zero BNEZ.N
Xtensa Instruction Set Architecture (ISA) Reference Manual 291
Instruction Word (RI6)
Required Configuration Option
Code Density Option (See Section 4.3.1 on page 53))
Assembler Syntax
BNEZ.N as, label
Description
This performs the same operation as the BNEZ instruction in a 16-bit encoding. BNEZ.N
branches if address register as is not equal to zero. BNEZ.N provides six bits of target
range instead of the 12 bits available in BNEZ.
The target instruction address of the branch is given by the address of the BNEZ.N in-
struction, plus the zero-extended 6-bit imm6 field of the instruction plus four. Because
the offset is unsigned, this instruction can only be used to branch forward. If register as
is equal to zero, execution continues with the next sequential instruction.
The inverse of BNEZ.N is BEQZ.N.
Assembler Note
The assembler may convert BNEZ.N instructions to BNEZ. The assembler will substitute
an equivalent sequence of instructions when the label is out of range. Prefixing the in-
struction mnemonic with an underscore (_BNEZ.N) disables these features and forces
the assembler to generate the narrow form of the instruction and an error when the label
is out of range.
Operation
if AR[s] ≠ 032 then
nextPC ← PC + (026||imm6) + 4
endif
Exceptions
EveryInstR Group (see page 244)
15 12 11 8 7 4 3 0
imm63..0 s 1 1 imm65..4 1100
4444
BNONE Branch if No Bit Set
292 Xtensa Instruction Set Architecture (ISA) Reference Manual
Instruction Word
(RRI8)
Required Configuration Option
Core Architecture (See Section 4.2 on page 50)
Assembler Syntax
BNONE as, at, label
Description
BNONE branches if all of the bits specified by the mask in address register at are clear in
address register as (that is, if none of them are set). The test is performed by taking the
bitwise logical and of as with at and testing if the result is zero.
The target instruction address of the branch is given by the address of the BNONE in-
struction, plus the sign-extended 8-bit imm8 field of the instruction plus four. If any of the
masked bits are set, execution continues with the next sequential instruction.
The inverse of BNONE is BANY.
Assembler Note
The assembler will substitute an equivalent sequence of instructions when the label is
out of range. Prefixing the instruction mnemonic with an underscore (_BNONE) disables
this feature and forces the assembler to generate an error in this case.
Operation
if (AR[s] and AR[t]) = 032 then
nextPC ← PC + (imm8724||imm8) + 4
endif
Exceptions
EveryInstR Group (see page 244)
23 16 15 12 11 8 7 4 3 0
imm8 0 0 0 0 s t 0 1 1 1
8 4444
Breakpoint BREAK
Xtensa Instruction Set Architecture (ISA) Reference Manual 293
Instruction Word (RRR)
Required Configuration Option
Debug Option (See Section 4.7.6 on page 197)
Assembler Syntax
BREAK 0..15, 0..15
Description
This instruction simply raises an exception when it is executed and PS.INTLEVEL <
DEBUGLEVEL. The high-priority vector for DEBUGLEVEL is used. The DEBUGCAUSE reg-
ister is written as part of raising the exception to indicate that BREAK raised the debug
exception. The address of the BREAK instruction is stored in EPC[DEBUGLEVEL]. The s
and t fields of the instruction word are not used by the processor; they are available for
use by the software. When PS.INTLEVEL ≥ DEBUGLEVEL, BREAK is a no-op.
The BREAK instruction typically calls a debugger when program execution reaches a
certain point (a “breakpoint”). The instruction at the breakpoint is replaced with the
BREAK instruction. To continue execution after a breakpoint is reached, the debugger
must re-write the BREAK to the original instruction, single-step by one instruction, and
then put back the BREAK instruction again.
Writing instructions requires special consideration. See the ISYNC instruction for more
information.
When it is not possible to write the instruction memory (for example, for ROM code), the
IBREAKA feature provides breakpoint capabilities (see Debug Option).
Software can also use BREAK to indicate an error condition that requires the program-
mer’s attention. The s and t fields may encode information about the situation.
BREAK is a 24-bit instruction. The BREAK.N density-option instruction performs a similar
operation in a 16-bit encoding.
23 20 19 16 15 12 11 8 7 4 3 0
000000000100 s t 0000
444444
BREAK Breakpoint
294 Xtensa Instruction Set Architecture (ISA) Reference Manual
Assembler Note
The assembler may convert BREAK instructions to BREAK.N when the Code Density
Option is enabled and the second imm is zero. Prefixing the instruction mnemonic with
an underscore (_BREAK) disables this optimization and forces the assembler to gener-
ate the wide form of the instruction.
Operation
if PS.INTLEVEL < DEBUGLEVEL then
EPC[DEBUGLEVEL] ← PC
EPS[DEBUGLEVEL] ← PS
DEBUGCAUSE ← 001000
nextPC ← InterruptVector[DEBUGLEVEL]
PS.EXCM ← 1
PS.INTLEVEL ← DEBUGLEVEL
endif
Exceptions
EveryInst Group (see page 244)
DebugExcep(BREAK) if Debug Option
Narrow Breakpoint BREAK.N
Xtensa Instruction Set Architecture (ISA) Reference Manual 295
Instruction Word (RRRN)
Required Configuration Option
Debug Option (See Section 4.7.6 on page 197) and Code Density Option (See
Section 4.3.1 on page 53)
Assembler Syntax
BREAK.N 0..15
Description
BREAK.N is similar in operation to BREAK (page 293), except that it is encoded in a
16-bit format instead of 24 bits, there is only a 4-bit imm field, and a different bit is set in
DEBUGCAUSE. Use this instruction to set breakpoints on 16-bit instructions.
Assembler Note
The assembler may convert BREAK.N instructions to BREAK. Prefixing the BREAK.N
instruction with an underscore (_BREAK.N) disables this optimization and forces the
assembler to generate the narrow form of the instruction.
Operation
if PS.INTLEVEL < DEBUGLEVEL then
EPC[DEBUGLEVEL] ← PC
EPS[DEBUGLEVEL] ← PS
DEBUGCAUSE ← 010000
nextPC ← InterruptVector[DEBUGLEVEL]
PS.EXCM ← 1
PS.INTLEVEL ← DEBUGLEVEL
endif
Exceptions
EveryInst Group (see page 244)
DebugExcep(BREAK.N) if Debug Option
15 12 11 8 7 4 3 0
1111 s 00101101
4444
BT Branch if True
296 Xtensa Instruction Set Architecture (ISA) Reference Manual
Instruction Word
(RRI8)
Required Configuration Option
Boolean Option (See Section 4.3.10 on page 65)s
Assembler Syntax
BT bs, label
Description
BT branches to the target address if Boolean register bs is true.
The target instruction address of the branch is given by the address of the BT instruc-
tion, plus the sign-extended 8-bit imm8 field of the instruction plus four. If the Boolean
register bs is false, execution continues with the next sequential instruction.
The inverse of BT is BF.
Assembler Note
The assembler will substitute an equivalent sequence of instructions when the label is
out of range. Prefixing the instruction mnemonic with an underscore (_BT) disables this
feature and forces the assembler to generate an error when the label is out of range.
Operation
if BRs then
nextPC ← PC + (imm8724||imm8) + 4
endif
Exceptions
EveryInst Group (see page 244)
23 16 15 12 11 8 7 4 3 0
imm8 0001 s 01110110
8 4444
Non-windowed Call CALL0
Xtensa Instruction Set Architecture (ISA) Reference Manual 297
Instruction Word (CALL)
Required Configuration Option
Core Architecture (See Section 4.2 on page 50)
Assembler Syntax
CALL0 label
Description
CALL0 calls subroutines without using register windows. The return address is placed in
a0, and the processor then branches to the target address. The return address is the
address of the CALL0 instruction plus three.
The target instruction address must be 32-bit aligned. This allows CALL0 to have a larg-
er effective range (-524284 to 524288 bytes). The target instruction address of the call is
given by the address of the CALL0 instruction with the least significant two bits set to
zero plus the sign-extended 18-bit offset field of the instruction shifted by two, plus
four.
The RET and RET.N instructions are used to return from a subroutine called by CALL0.
See the CALLX0 instruction (page 304) for calling routines where the target address is
given by the contents of a register.
To call using the register window mechanism, see the CALL4, CALL8, and CALL12 in-
structions.
Operation
AR[0] ← PC + 3
nextPC ← (PC31..2 + (offset1712||offset) + 1)||00
Exceptions
EveryInst Group (see page 244)
23 6543 0
offset 000101
18 2 4
CALL4 Call PC-relative, Rotate Window by 4
298 Xtensa Instruction Set Architecture (ISA) Reference Manual
Instruction Word (CALL)
Required Configuration Option
Windowed Register Option (See Section 4.7.1 on page 180)
Assembler Syntax
CALL4 label
Description
CALL4 calls subroutines using the register windows mechanism, requesting the callee
rotate the window by four registers. The CALL4 instruction does not rotate the window it-
self, but instead stores the window increment for later use by the ENTRY instruction. The
return address and window increment are placed in the caller’s a4 (the callee’s a0), and
the processor then branches to the target address. The return address is the address of
the next instruction (the address of the CALL4 instruction plus three). The window incre-
ment is also stored in the CALLINC field of the PS register, where it is accessed by the
ENTRY instruction.
The target instruction address must be a 32-bit aligned ENTRY instruction. This allows
CALL4 to have a larger effective range (−524284 to 524288 bytes). The target instruc-
tion address of the call is given by the address of the CALL4 instruction with the two
least significant bits set to zero plus the sign-extended 18-bit offset field of the instruc-
tion shifted by two, plus four.
See the CALLX4 instruction for calling routines where the target address is given by the
contents of a register.
Use the RETW and RETW.N instructions to return from a subroutine called by CALL4.
The window increment stored with the return address register in a4 occupies the two
most significant bits of the register, and therefore those bits must be filled in by the sub-
routine return. The RETW and RETW.N instructions fill in these bits from the two most sig-
nificant bits of their own address. This prevents register-window calls from being used to
call a routine in a different 1GB region of the address space.
23 6543 0
offset 010101
18 2 4
Call PC-relative, Rotate Window by 4 CALL4
Xtensa Instruction Set Architecture (ISA) Reference Manual 299
See the CALL0 instruction for calling routines using the non-windowed subroutine proto-
col.
The caller’s a4..a15 are the same registers as the callee’s a0..a11 after the callee
executes the ENTRY instruction. You can use these registers for parameter passing. The
caller’s a0..a3 are hidden by CALL4, and therefore you can use them to keep values
that are live across the call.
Operation
WindowCheck (00, 00, 01)
PS.CALLINC ← 01
AR[0100] ← 01||(PC + 3)29..0
nextPC ← (PC31..2 + (offset1712||offset) + 1)||00
Exceptions
EveryInstR Group (see page 244)
CALL8 Call PC-relative, Rotate Window by 8
300 Xtensa Instruction Set Architecture (ISA) Reference Manual
Instruction Word (CALL)
Required Configuration Option
Windowed Register Option (See Section 4.7.1 on page 180)
Assembler Syntax
CALL8 label
Description
CALL8 calls subroutines using the register windows mechanism, requesting the callee
rotate the window by eight registers. The CALL8 instruction does not rotate the window
itself, but instead stores the window increment for later use by the ENTRY instruction.
The return address and window increment are placed in the caller’s a8 (the callee’s a0),
and the processor then branches to the target address. The return address is the ad-
dress of the next instruction (the address of the CALL8 instruction plus three). The win-
dow increment is also stored in the CALLINC field of the PS register, where it is access-
ed by the ENTRY instruction.
The target instruction address must be a 32-bit aligned ENTRY instruction. This allows
CALL8 to have a larger effective range (−524284 to 524288 bytes). The target instruc-
tion address of the call is given by the address of the CALL8 instruction with the two
least significant bits set to zero, plus the sign-extended 18-bit offset field of the in-
struction shifted by two, plus four.
See the CALLX8 instruction for calling routines where the target address is given by the
contents of a register.
Use the RETW and RETW.N instructions to return from a subroutine called by CALL8.
The window increment stored with the return address register in a8 occupies the two
most significant bits of the register, and therefore those bits must be filled in by the sub-
routine return. The RETW and RETW.N instructions fill in these bits from the two most sig-
nificant bits of their own address. This prevents register-window calls from being used to
call a routine in a different 1GB region of the address space.
23 6543 0
offset 100101
18 2 4
Call PC-relative, Rotate Window by 8 CALL8
Xtensa Instruction Set Architecture (ISA) Reference Manual 301
See the CALL0 instruction for calling routines using the non-windowed subroutine proto-
col.
The caller’s a8..a15 are the same registers as the callee’s a0..a7 after the callee exe-
cutes the ENTRY instruction. You can use these registers for parameter passing. The
caller’s a0..a7 are hidden by CALL8, and therefore you may use them to keep values
that are live across the call.
Operation
WindowCheck (00, 00, 10)
PS.CALLINC ← 10
AR[1000] ← 10||(PC + 3)29..0
nextPC ← (PC31..2 + (offset1712||offset) + 1)||00
Exceptions
EveryInstR Group (see page 244)
CALL12 Call PC-relative, Rotate Window by 12
302 Xtensa Instruction Set Architecture (ISA) Reference Manual
Instruction Word (CALL)
Required Configuration Option
Windowed Register Option (See Section 4.7.1 on page 180)
Assembler Syntax
CALL12 label
Description
CALL12 calls subroutines using the register windows mechanism, requesting the callee
rotate the window by 12 registers. The CALL12 instruction does not rotate the window it-
self, but instead stores the window increment for later use by the ENTRY instruction. The
return address and window increment are placed in the caller’s a12 (the callee’s a0),
and the processor then branches to the target address. The return address is the ad-
dress of the next instruction (the address of the CALL12 instruction plus three). The win-
dow increment is also stored in the CALLINC field of the PS register, where it is access-
ed by the ENTRY instruction.
The target instruction address must be a 32-bit aligned ENTRY instruction. This allows
CALL12 to have a larger effective range (−524284 to 524288 bytes). The target instruc-
tion address of the call is given by the address of the CALL12 instruction with the two
least significant bits set to zero, plus the sign-extended 18-bit offset field of the in-
struction shifted by two, plus four.
See the CALLX12 instruction for calling routines where the target address is given by
the contents of a register.
The RETW and RETW.N instructions return from a subroutine called by CALL12.
The window increment stored with the return address register in a12 occupies the two
most significant bits of the register, and therefore those bits must be filled in by the sub-
routine return. The RETW and RETW.N instructions fill in these bits from the two most sig-
nificant bits of their own address. This prevents register-window calls from being used to
call a routine in a different 1GB region of the address space.
23 6543 0
offset 110101
18 2 4
Call PC-relative, Rotate Window by 12 CALL12
Xtensa Instruction Set Architecture (ISA) Reference Manual 303
See the CALL0 instruction for calling routines using the non-windowed subroutine proto-
col.
The caller’s a12..a15 are the same registers as the callee’s a0..a3 after the callee exe-
cutes the ENTRY instruction. You can use these registers for parameter passing. The
caller’s a0..a11 are hidden by CALL12, and therefore you may use them to keep values
that are live across the call.
Operation
WindowCheck (00, 00, 11)
PS.CALLINC ← 11
AR[1100] ← 11||(PC + 3)29..0
nextPC ← (PC31..2 + (offset1712||offset) + 1)||00
Exceptions
EveryInstR Group (see page 244)
CALLX0 Non-windowed Call Register
304 Xtensa Instruction Set Architecture (ISA) Reference Manual
Instruction Word (CALLX)
Required Configuration Option
Core Architecture (See Section 4.2 on page 50)
Assembler Syntax
CALLX0 as
Description
CALLX0 calls subroutines without using register windows. The return address is placed
in a0, and the processor then branches to the target address. The return address is the
address of the CALLX0 instruction, plus three.
The target instruction address of the call is given by the contents of address register as.
The RET and RET.N instructions return from a subroutine called by CALLX0.
To call using the register window mechanism, see the CALLX4, CALLX8, and CALLX12
instructions.
Operation
nextPC ← AR[s]
AR[0] ← PC + 3
Exceptions
EveryInstR Group (see page 244)
23 20 19 16 15 12 11 876543 0
000000000000 s 11000000
4 4 4 4 2 2 4
Call Register, Rotate Window by 4 CALLX4
Xtensa Instruction Set Architecture (ISA) Reference Manual 305
Instruction Word (CALLX)
Required Configuration Option
Windowed Register Option (See Section 4.7.1 on page 180)
Assembler Syntax
CALLX4 as
Description
CALLX4 calls subroutines using the register windows mechanism, requesting the callee
rotate the window by four registers. The CALLX4 instruction does not rotate the window
itself, but instead stores the window increment for later use by the ENTRY instruction.
The return address and window increment are placed in the caller’s a4 (the callee’s a0),
and the processor then branches to the target address. The return address is the ad-
dress of the next instruction (the address of the CALLX4 instruction plus three). The win-
dow increment is also stored in the CALLINC field of the PS register, where it is access-
ed by the ENTRY instruction.
The target instruction address of the call is given by the contents of address register as.
The target instruction must be an ENTRY instruction.
See the CALL4 instruction for calling routines where the target address is given by a PC-
relative offset in the instruction.
The RETW and RETW.N instructions return from a subroutine called by CALLX4.
The window increment stored with the return address register in a4 occupies the two
most significant bits of the register, and therefore those bits must be filled in by the sub-
routine return. The RETW and RETW.N instructions fill in these bits from the two most sig-
nificant bits of their own address. This prevents register-window calls from being used to
call a routine in a different 1GB region of the address space.
See the CALLX0 instruction for calling routines using the non-windowed subroutine
protocol.
23 20 19 16 15 12 11 876543 0
000000000000 s 11010000
4 4 4 4 2 2 4
CALLX4 Call Register, Rotate Window by 4
306 Xtensa Instruction Set Architecture (ISA) Reference Manual
The caller’s a4..a15 are the same registers as the callee’s a0..a11 after the callee exe-
cutes the ENTRY instruction. You can use these registers for parameter passing. The
caller’s a0..a3 are hidden by CALLX4, and therefore you may use them to keep values
that are live across the call.
Operation
WindowCheck (00, 00, 01)
PS.CALLINC ← 01
AR[01||00] ← 01||(PC + 3)29..0
nextPC ← AR[s]
Exceptions
EveryInstR Group (see page 244)
Call Register, Rotate Window by 8 CALLX8
Xtensa Instruction Set Architecture (ISA) Reference Manual 307
Instruction Word (CALLX)
Required Configuration Option
Windowed Register Option (See Section 4.7.1 on page 180)
Assembler Syntax
CALLX8 as
Description
CALLX8 calls subroutines using the register windows mechanism, requesting the callee
rotate the window by eight registers. The CALLX8 instruction does not rotate the window
itself, but instead stores the window increment for later use by the ENTRY instruction.
The return address and window increment are placed in the caller’s a8 (the callee’s a0),
and the processor then branches to the target address. The return address is the ad-
dress of the next instruction (the address of the CALLX8 instruction plus three). The win-
dow increment is also stored in the CALLINC field of the PS register, where it is access-
ed by the ENTRY instruction.
The target instruction address of the call is given by the contents of address register as.
The target instruction must be an ENTRY instruction.
See the CALL8 instruction for calling routines where the target address is given by a PC-
relative offset in the instruction.
The RETW and RETW.N (page 482) instructions return from a subroutine called by
CALLX8.
The window increment stored with the return address register in a8 occupies the two
most significant bits of the register, and therefore those bits must be filled in by the sub-
routine return. The RETW and RETW.N instructions fill in these bits from the two most sig-
nificant bits of their own address. This prevents register-window calls from being used to
call a routine in a different 1GB region of the address space.
See the CALLX0 instruction for calling routines using the non-windowed subroutine pro-
tocol.
23 20 19 16 15 12 11 876543 0
000000000000 s 11100000
4 4 4 4 2 2 4
CALLX8 Call Register, Rotate Window by 8
308 Xtensa Instruction Set Architecture (ISA) Reference Manual
The caller’s a8..a15 are the same registers as the callee’s a0..a7 after the callee exe-
cutes the ENTRY instruction. You can use these registers for parameter passing. The
caller’s a0..a7 are hidden by CALLX8, and therefore you may use them to keep values
that are live across the call.
Operation
WindowCheck (00, 00, 10)
PS.CALLINC ← 10
AR[10||00] ← 10||(PC + 3)29..0
nextPC ← AR[s]
Exceptions
EveryInstR Group (see page 244)
Call Register, Rotate Window by 12 CALLX12
Xtensa Instruction Set Architecture (ISA) Reference Manual 309
Instruction Word (CALLX)
Required Configuration Option
Windowed Register Option (See Section 4.7.1 on page 180)
Assembler Syntax
CALLX12 as
Description
CALLX12 calls subroutines using the register windows mechanism, requesting the
callee rotate the window by 12 registers. The CALLX12 instruction does not rotate the
window itself, but instead stores the window increment for later use by the ENTRY in-
struction. The return address and window increment are placed in the caller’s a12 (the
callee’s a0), and the processor then branches to the target address. The return address
is the address of the next instruction (the address of the CALLX12 instruction plus
three). The window increment is also stored in the CALLINC field of the PS register,
where it is accessed by the ENTRY instruction.
The target instruction address of the call is given by the contents of address register as.
The target instruction must be an ENTRY instruction.
See the CALL12 instruction for calling routines where the target address is given by a
PC-relative offset in the instruction.
The RETW and RETW.N instructions return from a subroutine called by CALLX12.
The window increment stored with the return address register in a12 occupies the two
most significant bits of the register, and therefore those bits must be filled in by the sub-
routine return. The RETW and RETW.N instructions fill in these bits from the two most sig-
nificant bits of their own address. This prevents register-window calls from being used to
call a routine in a different 1GB region of the address space.
See the CALLX0 instruction for calling routines using the non-windowed subroutine
protocol.
23 20 19 16 15 12 11 876543 0
000000000000 s 11110000
4 4 4 4 2 2 4
CALLX12 Call Register, Rotate Window by 12
310 Xtensa Instruction Set Architecture (ISA) Reference Manual
The caller’s a12..a15 are the same registers as the callee’s a0..a3 after the callee exe-
cutes the ENTRY instruction. These registers may be used for parameter passing. The
caller’s a0..a11 are hidden by CALLX12, and therefore may be used to keep values that
are live across the call.
Operation
WindowCheck (00, 00, 11)
PS.CALLINC ← 11
AR[11||00] ← 11||(PC + 3)29..0
nextPC ← AR[s]
Exceptions
EveryInstR Group (see page 244)
Ceiling Single to Fixed CEIL.S
Xtensa Instruction Set Architecture (ISA) Reference Manual 311
Instruction Word (RRR)
Required Configuration Option
Floating-Point Coprocessor Option (See Section 4.3.11 on page 67)
Assembler Syntax
CEIL.S ar, fs, 0..15
Description
CEIL.S converts the contents of floating-point register fs from single-precision to
signed integer format, rounding toward +∞. The single-precision value is first scaled by a
power of two constant value encoded in the t field, with 0..15 representing 1.0, 2.0, 4.0,
…, 32768.0. The scaling allows for a fixed point notation where the binary point is at the
right end of the integer for t=0 and moves to the left as t increases, until for t=15 there
are 15 fractional bits represented in the fixed point number. For positive overflow (value
≥ 32'h7fffffff), positive infinity, or NaN, 32'h7fffffff is returned; for negative
overflow (value ≤ 32'h80000000) or negative infinity, 32'h80000000 is returned. The
result is written to address register ar.
Operation
AR[r] ← ceils(FR[s] ×s pows(2.0,t))
Exceptions
EveryInstR Group (see page 244)
GenExcep(Coprocessor0Disabled) if Coprocessor Option
23 20 19 16 15 12 11 8 7 4 3 0
10111010 r s t 0000
444444
CLAMPS Signed Clamp
312 Xtensa Instruction Set Architecture (ISA) Reference Manual
Instruction Word (RRR)
Required Configuration Option
Miscellaneous Operations Option (See Section 4.3.8 on page 62)
Assembler Syntax
CLAMPS ar, as, 7..22
Description
CLAMPS tests whether the contents of address register as fits as a signed value of
imm+1 bits (in the range 7 to 22). If so, the value is written to address register ar; if not,
the largest value of imm+1 bits with the same sign as as is written to ar. Thus CLAMPS
performs the function
y ← min(max(x, −2imm), 2imm−1)
CLAMPS may be used in conjunction with instructions such as ADD, SUB, MUL16S, and
so forth to implement saturating arithmetic.
Assembler Note
The immediate values accepted by the assembler are 7 to 22. The assembler encodes
these in the t field of the instruction using 0 to 15.
Operation
sign ← AR[s]31
AR[r] ← if AR[s]30..t+7 = sign24-t
then AR[s]
else sign25-t||(not sign)t+7
Exceptions
EveryInstR Group (see page 244)
23 20 19 16 15 12 11 8 7 4 3 0
00110011 r s t 0000
444444
Data Cache Hit Invalidate DHI
Xtensa Instruction Set Architecture (ISA) Reference Manual 313
Instruction Word
(RRI8)
Required Configuration Option
Data Cache Option (See Section 4.5.5 on page 118)
Assembler Syntax
DHI as, 0..1020
Description
DHI invalidates the specified line in the level-1 data cache, if it is present. If the specified
address is not in the data cache, then this instruction has no effect. If the specified ad-
dress is present, it is invalidated even if it contains dirty data. If the specified line has
been locked by a DPFL instruction, then no invalidation is done and no exception is
raised because of the lock. The line remains in the cache and must be unlocked by a
DHU or DIU instruction before it can be invalidated. This instruction is useful before a
DMA write to memory that overwrites the entire line.
DHI forms a virtual address by adding the contents of address register as and an 8-bit
zero-extended constant value encoded in the instruction word shifted left by two. There-
fore, the offset can specify multiples of four from zero to 1020. If the Region Translation
Option (page 156) or the MMU Option (page 158) is enabled, the virtual address is
translated to the physical address. If not, the physical address is identical to the virtual
address. If the translation encounters an error (for example, protection violation), the
processor raises an exception (see Section 4.4.1.5 on page 89) as if it were loading
from the virtual address.
Because the organization of caches is implementation-specific, the operation below
specifies only a call to the implementation’s dhitinval function.
DHI is a privileged instruction.
23 16 15 12 11 8 7 4 3 0
imm8 0111 s 01100010
8 4444
DHI Data Cache Hit Invalidate
314 Xtensa Instruction Set Architecture (ISA) Reference Manual
Assembler Note
To form a virtual address DHI calculates the sum of address register as and the imm8
field of the instruction word times four. Therefore, the machine-code offset is in terms of
32-bit (4 byte) units. However, the assembler expects a byte offset and encodes this into
the instruction by dividing by four.
Operation
if CRING ≠ 0 then
Exception (PrivilegedInstructionCause)
else
vAddr ← AR[s] + (022||imm8||02)
(pAddr, attributes, cause) ← ltranslate(vAddr, CRING)
if invalid(attributes) then
EXCVADDR ← vAddr
Exception (cause)
else
dhitinval(vAddr, pAddr)
endif
endif
Exceptions
EveryInstR Group (see page 244)
Memory Group (see page 244)
GenExcep(LoadProhibitedCause) if Region Protection Option or MMU Option
GenExcep(PrivilegedCause) if Exception Option
Data Cache Hit Unlock DHU
Xtensa Instruction Set Architecture (ISA) Reference Manual 315
Instruction Word (RRI4)
Required Configuration Option
Data Cache Index Lock Option (See Section 4.5.7 on page 122)
Assembler Syntax
DHU as, 0..240
Description
DHU performs a data cache unlock if hit. The purpose of DHU is to remove the lock creat-
ed by a DPFL instruction. Xtensa ISA implementations that do not implement cache lock-
ing must raise an illegal instruction exception when this opcode is executed.
DHU checks whether the line containing the specified address is present in the data
cache, and if so, it clears the lock associated with that line. To unlock by index without
knowing the address of the locked line, use the DIU instruction.
DHU forms a virtual address by adding the contents of address register as and a 4-bit
zero-extended constant value encoded in the instruction word shifted left by four. There-
fore, the offset can specify multiples of 16 from zero to 240. If the Region Translation
Option (page 156) or the MMU Option (page 158) is enabled, the virtual address is
translated to the physical address. If not, the physical address is identical to the virtual
address. If the translation encounters an error (for example, protection violation), the
processor raises an exception (see Section 4.4.1.5 on page 89) as if it were loading
from the virtual address.
DHU is a privileged instruction.
Assembler Note
To form a virtual address DHU calculates the sum of address register as and the imm4
field of the instruction word times 16. Therefore, the machine-code offset is in terms of
16 byte units. However, the assembler expects a byte offset and encodes this into the
instruction by dividing by 16.
23 20 19 16 15 12 11 8 7 4 3 0
imm4 00100111 s 10000010
444444
DHU Data Cache Hit Unlock
316 Xtensa Instruction Set Architecture (ISA) Reference Manual
Operation
if CRING ≠ 0 then
Exception (PrivilegedInstructionCause)
else
vAddr ← AR[s] + (024||imm4||04)
(pAddr, attributes, cause) ← ltranslate(vAddr, CRING)
if invalid(attributes) then
EXCVADDR ← vAddr
Exception (cause)
else
dhitunlock(vAddr, pAddr)
endif
endif
Exceptions
EveryInstR Group (see page 244)
Memory Group (see page 244)
GenExcep(LoadProhibitedCause) if Region Protection Option or MMU Option
GenExcep(PrivilegedCause) if Exception Option
Data Cache Hit Writeback DHWB
Xtensa Instruction Set Architecture (ISA) Reference Manual 317
Instruction Word
(RRI8)
Required Configuration Option
Data Cache Option (See Section 4.5.5 on page 118)
Assembler Syntax
DHWB as, 0..1020
Description
This instruction forces dirty data in the data cache to be written back to memory. If the
specified address is not in the data cache or is present but unmodified, then this instruc-
tion has no effect. If the specified address is present and modified in the data cache, the
line containing it is written back, and marked unmodified. This instruction is useful be-
fore a DMA read from memory, to force writes to a frame buffer to become visible, or to
force writes to memory shared by two processors.
DHWB forms a virtual address by adding the contents of address register as and an 8-bit
zero-extended constant value encoded in the instruction word shifted left by two. There-
fore, the offset can specify multiples of four from zero to 1020. If the Region Translation
Option (page 156) or the MMU Option (page 158) is enabled, the virtual address is
translated to the physical address. If not, the physical address is identical to the virtual
address. If the translation encounters an error (for example, protection violation), the
processor raises an exception (see Section 4.4.1.5 on page 89) as if it were loading
from the virtual address.
Because the organization of caches is implementation-specific, the operation below
specifies only a call to the implementation’s dhitwriteback function.
Assembler Note
To form a virtual address DHWB calculates the sum of address register as and the imm8
field of the instruction word times four. Therefore, the machine-code offset is in terms of
32-bit (4 byte) units. However, the assembler expects a byte offset and encodes this into
the instruction by dividing by four.
23 16 15 12 11 8 7 4 3 0
imm8 0111 s 01000010
8 4444
DHWB Data Cache Hit Writeback
318 Xtensa Instruction Set Architecture (ISA) Reference Manual
Operation
vAddr ← AR[s] + (022||imm8||02)
(pAddr, attributes, cause) ← ltranslate(vAddr, CRING)
if invalid(attributes) then
EXCVADDR ← vAddr
Exception (cause)
else
dhitwriteback(vAddr, pAddr)
endif
Exceptions
EveryInstR Group (see page 244)
Memory Group (see page 244)
GenExcep(LoadProhibitedCause) if Region Protection Option or MMU Option
Implementation Notes
Some Xtensa ISA implementations do not support write-back caches. For these imple-
mentations, the DHWB instruction performs no operation.
Data Cache Hit Writeback Invalidate DHWBI
Xtensa Instruction Set Architecture (ISA) Reference Manual 319
Instruction Word
(RRI8)
Required Configuration Option
Data Cache Option (See Section 4.5.5 on page 118)
Assembler Syntax
DHWBI as, 0..1020
Description
DHWBI forces dirty data in the data cache to be written back to memory. If the specified
address is not in the data cache, then this instruction has no effect. If the specified ad-
dress is present and modified in the data cache, the line containing it is written back.
After the write-back, if any, the line containing the specified address is invalidated if
present. If the specified line has been locked by a DPFL instruction, then no invalidation
is done and no exception is raised because of the lock. The line is written back but re-
mains in the cache unmodified and must be unlocked by a DHU or DIU instruction before
it can be invalidated. This instruction is useful in the same circumstances as DHWB and
before a DMA write to memory or write from another processor to memory. If the line is
certain to be completely overwritten by the write, you can use a DHI (as it is faster), but
otherwise use a DHWBI.
DHWBI forms a virtual address by adding the contents of address register as and an
8-bit zero-extended constant value encoded in the instruction word shifted left by two.
Therefore, the offset can specify multiples of four from zero to 1020. If the Region Trans-
lation Option (page 156) or the MMU Option (page 158) is enabled, the virtual address is
translated to the physical address. If not, the physical address is identical to the virtual
address. If the translation encounters an error (for example, protection violation), the
processor raises an exception (see Section 4.4.1.5 on page 89) as if it were loading
from the virtual address.
Because the organization of caches is implementation-specific, the operation section
below specifies only a call to the implementation’s dhitwritebackinval function.
23 16 15 12 11 8 7 4 3 0
imm8 0111 s 01010010
8 4444
DHWBI Data Cache Hit Writeback Invalidate
320 Xtensa Instruction Set Architecture (ISA) Reference Manual
Assembler Note
To form a virtual address, DHWBI calculates the sum of address register as and the
imm8 field of the instruction word times four. Therefore, the machine-code offset is in
terms of 32-bit (4 byte) units. However, the assembler expects a byte offset and encodes
this into the instruction by dividing by four.
Operation
vAddr ← AR[s] + (022||imm8||02)
(pAddr, attributes, cause) ← ltranslate(vAddr, CRING)
if invalid(attributes) then
EXCVADDR ← vAddr
Exception (cause)
else
dhitwritebackinval(vAddr, pAddr)
endif
Exceptions
EveryInstR Group (see page 244)
Memory Group (see page 244)
GenExcep(LoadProhibitedCause) if Region Protection Option or MMU Option
Implementation Notes
Some Xtensa ISA implementations do not support write-back caches. For these imple-
mentations DHWBI is identical to DHI.
Data Cache Index Invalidate DII
Xtensa Instruction Set Architecture (ISA) Reference Manual 321
Instruction Word
(RRI8)
Required Configuration Option
Data Cache Option (See Section 4.5.5 on page 118))
Assembler Syntax
DII as, 0..1020
Description
DII uses the virtual address to choose a location in the data cache and invalidates the
specified line. If the chosen line has been locked by a DPFL instruction, then no invalida-
tion is done and no exception is raised because of the lock. The line remains in the
cache and must be unlocked by a DHU or DIU instruction before it can be invalidat-
ed.The method for mapping the virtual address to a data cache location is implementa-
tion-specific. This instruction is primarily useful for data cache initialization after power-
up.
DII forms a virtual address by adding the contents of address register as and an 8-bit
zero-extended constant value encoded in the instruction word shifted left by two. There-
fore, the offset can specify multiples of four from zero to 1020. The virtual address
chooses a cache line without translation and without raising the associated exceptions.
Because the organization of caches is implementation-specific, the operation section
below specifies only a call to the implementation’s dindexinval function.
DII is a privileged instruction.
Assembler Note
To form a virtual address, DII calculates the sum of address register as and the imm8
field of the instruction word times four. Therefore, the machine-code offset is in terms of
32-bit (4 byte) units. However, the assembler expects a byte offset and encodes this into
the instruction by dividing by four.
Operation
if CRING ≠ 0 then
23 16 15 12 11 8 7 4 3 0
imm8 0111 s 01110010
8 4444
DII Data Cache Index Invalidate
322 Xtensa Instruction Set Architecture (ISA) Reference Manual
Exception (PrivilegedInstructionCause)
else
vAddr ← AR[s] + (022||imm8||02)
dindexinval(vAddr)
endif
Exceptions
EveryInstR Group (see page 244)
GenExcep(PrivilegedCause) if Exception Option
Implementation Notes
x ← ceil(log2(DataCacheBytes))
y ← log2(DataCacheBytes ÷ DataCacheWayCount)
z ← log2(DataCacheLineBytes)
The cache line specified by index Addrx-1..z in a direct-mapped cache or way
Addrx-1..y and index Addry-1..z in a set-associative cache is the chosen line. If the
specified cache way is not valid (the fourth way of a three way cache) the instruction
does nothing. In some implementations all ways at index Addry-1..z are invalidated
regardless of the specified way, but for future compatibility this behavior should not be
assumed.
The additional ways invalidated in some implementations mean that care is needed in
using this instruction with write-back caches. Dirty data in any way (at the specified in-
dex) of the cache will be lost and not just dirty data in the specified way. Because the in-
struction is primarily used at reset, this will not usually cause any difficulty.
Data Cache Index Unlock DIU
Xtensa Instruction Set Architecture (ISA) Reference Manual 323
Instruction Word (RRI4)
Required Configuration Option
Data Cache Index Lock Option (See Section 4.5.7 on page 122)
Assembler Syntax
DIU as, 0..240
Description
DIU uses the virtual address to choose a location in the data cache and unlocks the
chosen line. The purpose of DIU is to remove the lock created by a DPFL instruction.
The method for mapping the virtual address to a data cache location is implementation-
specific. This instruction is primarily useful for unlocking the entire data cache. Xtensa
ISA implementations that do not implement cache locking must raise an illegal instruc-
tion exception when this opcode is executed.
To unlock a specific cache line if it is in the cache, use the DHU instruction.
DII forms a virtual address by adding the contents of address register as and a 4-bit
zero-extended constant value encoded in the instruction word shifted left by four. There-
fore, the offset can specify multiples of 16 from zero to 240. The virtual address chooses
a cache line without translation and without raising the associated exceptions.
Because the organization of caches is implementation-specific, the operation section
below specifies only a call to the implementation’s dindexunlock function.
DIU is a privileged instruction.
Assembler Note
To form a virtual address DIU calculates the sum of address register as and the imm4
field of the instruction word times 16. Therefore, the machine-code offset is in terms of
16 byte units. However, the assembler expects a byte offset and encodes this into the
instruction by dividing by 16.
23 20 19 16 15 12 11 8 7 4 3 0
imm4 00110111 s 10000010
444444
DIU Data Cache Index Unlock
324 Xtensa Instruction Set Architecture (ISA) Reference Manual
Operation
if CRING ≠ 0 then
Exception (PrivilegedInstructionCause)
else
vAddr ← AR[s] + (024||imm4||04)
dindexunlock(vAddr)
endif
Exceptions
EveryInstR Group (see page 244)
GenExcep(PrivilegedCause) if Exception Option
MemoryErrorException if Memory ECC/Parity Option
Implementation Notes
x ← ceil(log2(DataCacheBytes))
y ← log2(DataCacheBytes ÷ DataCacheWayCount)
z ← log2(DataCacheLineBytes)
The cache line specified by index Addrx-1..z in a direct-mapped cache or way
Addrx-1..y and index Addry-1..z in a set-associative cache is the chosen line. If the
specified cache way is not valid (the fourth way of a three way cache), the instruction
does nothing.
Data Cache Index Write Back DIWB
Xtensa Instruction Set Architecture (ISA) Reference Manual 325
Instruction Word (RRI4)
Required Configuration Option
Data Cache Option (See Section 4.5.5 on page 118) (added in T1050)
Assembler Syntax
DIWB as, 0..240
Description
DIWB uses the virtual address to choose a line in the data cache and writes that line
back to memory if it is dirty. The method for mapping the virtual address to a data cache
line is implementation-specific. This instruction is primarily useful for forcing all dirty data
in the cache back to memory. If the chosen line is present but unmodified, then this in-
struction has no effect. If the chosen line is present and modified in the data cache, it is
written back, and marked unmodified. For set-associative caches, only one line out of
one way of the cache is written back. Some Xtensa ISA implementations do not support
writeback caches. For these implementations DIWB does nothing.
This instruction is useful for the same purposes as DHWB, but when either the address is
not known or when the range of addresses is large enough that it is faster to operate on
the entire cache.
DIWB forms a virtual address by adding the contents of address register as and a 4-bit
zero-extended constant value encoded in the instruction word shifted left by four. There-
fore, the offset can specify multiples of 16 from zero to 240. The virtual address chooses
a cache line without translation and without raising the associated exceptions.
Because the organization of caches is implementation-specific, the operation section
below specifies only a call to the implementation’s dindexwriteback function.
DIWB is a privileged instruction.
23 20 19 16 15 12 11 8 7 4 3 0
imm4 01000111 s 10000010
444444
DIWB Data Cache Index Write Back
326 Xtensa Instruction Set Architecture (ISA) Reference Manual
Assembler Note
To form a virtual address DIWB calculates the sum of address register as and the imm4
field of the instruction word times 16. Therefore, the machine-code offset is in terms of
16 byte units. However, the assembler expects a byte offset and encodes this into the in-
struction by dividing by 16.
Operation
if CRING ≠ 0 then
Exception (PrivilegedInstructionCause)
else
vAddr ← AR[s] + (024||imm4||04)
dindexwriteback(vAddr)
endif
Exceptions
EveryInstR Group (see page 244)
GenExcep(PrivilegedCause) if Exception Option
MemoryErrorException if Memory ECC/Parity Option
Implementation Notes
x ← ceil(log2(DataCacheBytes))
y ← log2(DataCacheBytes ÷ DataCacheWayCount)
z ← log2(DataCacheLineBytes)
The cache line specified by index Addrx-1..z in a direct-mapped cache or way
Addrx-1..y and index Addry-1..z in a set-associative cache is the chosen line. If the
specified cache way is not valid (the fourth way of a three way cache), the instruction
does nothing.
Some Xtensa ISA implementations do not support write-back caches. For these imple-
mentations, the DIWB instruction has no effect.
Data Cache Index Write Back Invalidate DIWBI
Xtensa Instruction Set Architecture (ISA) Reference Manual 327
Instruction Word
(RRI4)
Required Configuration Option
Data Cache Option (See Section 4.5.5 on page 118) (added in T1050)
Assembler Syntax
DIWBI as, 0..240
Description
DIWBI uses the virtual address to choose a line in the data cache and forces that line to
be written back to memory if it is dirty. After the writeback, if any, the line is invalidated.
The method for mapping the virtual address to a data cache location is implementation-
specific. If the chosen line is already invalid, then this instruction has no effect. If the
chosen line has been locked by a DPFL instruction, then dirty data is written back but no
invalidation is done and no exception is raised because of the lock. The line remains in
the cache and must be unlocked by a DHU or DIU instruction before it can be invalidat-
ed. For set-associative caches, only one line out of one way of the cache is written back
and invalidated. Some Xtensa ISA implementations do not support write-back caches.
For these implementations DIWBI is similar to DII but invalidates only one line.
This instruction is useful for the same purposes as the DHWBI but when either the ad-
dress is not known, or when the range of addresses is large enough that it is faster to
operate on the entire cache.
DIWBI forms a virtual address by adding the contents of address register as and a 4-bit
zero-extended constant value encoded in the instruction word shifted left by four. There-
fore, the offset can specify multiples of 16 from zero to 240. The virtual address chooses
a cache line without translation and without raising the associated exceptions.
Because the organization of caches is implementation-specific, the operation section
below specifies only a call to the implementation’s dindexwritebackinval function.
DIWBI is a privileged instruction.
23 20 19 16 15 12 11 8 7 4 3 0
imm4 01010111 s 10000010
444444
DIWBI Data Cache Index Write Back Invalidate
328 Xtensa Instruction Set Architecture (ISA) Reference Manual
Assembler Note
To form a virtual address, DIWBI calculates the sum of address register as and the
imm4 field of the instruction word times 16. Therefore, the machine-code offset is in
terms of 16 byte units. However, the assembler expects a byte offset and encodes this
into the instruction by dividing by 16.
Operation
if CRING ≠ 0 then
Exception (PrivilegedInstructionCause)
else
vAddr ← AR[s] + (024||imm4||04)
dindexwritebackinval(vAddr)
endif
Exceptions
EveryInstR Group (see page 244)
GenExcep(PrivilegedCause) if Exception Option
MemoryErrorException if Memory ECC/Parity Option
Implementation Notes
x ← ceil(log2(DataCacheBytes))
y ← log2(DataCacheBytes ÷ DataCacheWayCount)
z ← log2(DataCacheLineBytes)
The cache line specified by index Addrx-1..z in a direct-mapped cache or way
Addrx-1..y and index Addry-1..z in a set-associative cache is the chosen line. If the
specified cache way is not valid (the fourth way of a three way cache), the instruction
does nothing.
Data Cache Prefetch and Lock DPFL
Xtensa Instruction Set Architecture (ISA) Reference Manual 329
Instruction Word (RRI4)
Required Configuration Option
Data Cache Index Lock Option (See Section 4.5.7 on page 122)
Assembler Syntax
DPFL as, 0..240
Description
DPFL performs a data cache prefetch and lock. The purpose of DPFL is to improve per-
formance, and not to affect state defined by the ISA. Xtensa ISA implementations that
do not implement cache locking must raise an illegal instruction exception when this op-
code is executed. In general, the performance improvement from using this instruction is
implementation-dependent.
DPFL checks if the line containing the specified address is present in the data cache,
and if not, it begins the transfer of the line from memory to the cache. The line is placed
in the data cache and the line marked as locked, that is not replaceable by ordinary data
cache misses. To unlock the line, use DHU or DIU. To prefetch without locking, use the
DPFR, DPFW, DPFRO, or DPFWO instructions.
DPFL forms a virtual address by adding the contents of address register as and a 4-bit
zero-extended constant value encoded in the instruction word shifted left by four. There-
fore, the offset can specify multiples of 16 from zero to 240. If the Region Translation
Option (page 156) or the MMU Option (page 158) is enabled, the virtual address is
translated to the physical address. If not, the physical address is identical to the virtual
address. If the translation encounters an error (for example, protection violation), the
processor raises one of several exceptions (see Section 4.4.1.5 on page 89).
Because the organization of caches is implementation-specific, the operation section
below specifies only a call to the implementation’s dprefetch function.
DPFL is a privileged instruction.
23 20 19 16 15 12 11 8 7 4 3 0
imm4 00000111 s 10000010
24 44444
DPFL Data Cache Prefetch and Lock
330 Xtensa Instruction Set Architecture (ISA) Reference Manual
Assembler Note
To form a virtual address, DPFL calculates the sum of address register as and the imm4
field of the instruction word times 16. Therefore, the machine-code offset is in terms of
16 byte units. However, the assembler expects a byte offset and encodes this into the
instruction by dividing by 16.
Operation
if CRING ≠ 0 then
Exception (PrivilegedInstructionCause)
else
vAddr ← AR[s] + (024||imm4||04)
(pAddr, attributes, cause) ← ltranslate(vAddr, CRING)
if invalid(attributes) then
EXCVADDR ← vAddr
Exception (cause)
else
dprefetch(vAddr, pAddr, 0, 0, 1)
endif
endif
Exceptions
Memory Group (see page 244)
GenExcep(LoadProhibitedCause) if Region Protection Option or MMU Option
GenExcep(PrivilegedCause) if Exception Option
Implementation Notes
If, before the instruction executes, there are not two available DataCache ways at the re-
quired index, a Load Store Error exception is raised.
Data Cache Prefetch for Read DPFR
Xtensa Instruction Set Architecture (ISA) Reference Manual 331
Instruction Word
(RRI8)
Required Configuration Option
Data Cache Option (See Section 4.5.5 on page 118)
Assembler Syntax
DPFR as, 0..1020
Description
DPFR performs a data cache prefetch for read. The purpose of DPFR is to improve per-
formance, but not to affect state defined by the ISA. Therefore, some Xtensa ISA imple-
mentations may choose to implement this instruction as a simple “no-operation” instruc-
tion. In general, the performance improvement from using this instruction is
implementation-dependent.
In some Xtensa ISA implementations, DPFR checks whether the line containing the
specified address is present in the data cache, and if not, it begins the transfer of the
line from memory. The four data prefetch instructions provide different “hints” about how
the data is likely to be used in the future. DPFR indicates that the data is only likely to be
read, possibly more than once, before it is replaced by another line in the cache.
DPFR forms a virtual address by adding the contents of address register as and an 8-bit
zero-extended constant value encoded in the instruction word shifted left by two. There-
fore, the offset can specify multiples of four from zero to 1020. If the Region Translation
Option (page 156) or the MMU Option (page 158) is enabled, the virtual address is
translated to the physical address. If not, the physical address is identical to the virtual
address. If the translation or memory reference encounters an error (for example, pro-
tection violation or non-existent memory), the processor performs no operation. This al-
lows the instruction to be used to speculatively fetch an address that does not exist or is
protected without either causing an error or allowing inappropriate action.
Because the organization of caches is implementation-specific, the operation section
below specifies only a call to the implementation’s dprefetch function.
23 16 15 12 11 8 7 4 3 0
imm8 0111 s 00000010
8 4444
DPFR Data Cache Prefetch for Read
332 Xtensa Instruction Set Architecture (ISA) Reference Manual
Assembler Note
To form a virtual address, DPFR calculates the sum of address register as and the imm8
field of the instruction word times four. Therefore, the machine-code offset is in terms of
32-bit (4 byte) units. However, the assembler expects a byte offset and encodes this into
the instruction by dividing by four.
Operation
vAddr ← AR[s] + (022||imm8||02)
(pAddr, attributes, cause) ← ltranslate(vAddr, CRING)
if not invalid(attributes) then
dprefetch(vAddr, pAddr, 0, 0, 0)
endif
Exceptions
EveryInstR Group (see page 244)
Data Cache Prefetch for Read Once DPFRO
Xtensa Instruction Set Architecture (ISA) Reference Manual 333
Instruction Word
(RRI8)
Required Configuration Option
Data Cache Option (See Section 4.5.5 on page 118)
Assembler Syntax
DPFRO as, 0..1020
Description
DPFRO performs a data cache prefetch for read once. The purpose of DPFRO is to im-
prove performance, but not to affect state defined by the ISA. Therefore, some Xtensa
ISA implementations may choose to implement this instruction as a simple “no-opera-
tion” instruction. In general, the performance improvement from using this instruction is
implementation-dependent.
In some Xtensa ISA implementations, DPFRO checks whether the line containing the
specified address is present in the data cache, and if not, it begins the transfer of the
line from memory. Four data prefetch instructions provide different “hints” about how the
data is likely to be used in the future. DPFRO indicates that the data is only likely to be
read once before it is replaced by another line in the cache. In some implementations,
this hint might be used to select a specific cache way or to select a streaming buffer
instead of the cache.
DPFRO forms a virtual address by adding the contents of address register as and an 8-
bit zero-extended constant value encoded in the instruction word shifted left by two.
Therefore, the offset can specify multiples of four from zero to 1020. If the Region Trans-
lation Option (page 156) or the MMU Option (page 158) is enabled, the virtual address is
translated to the physical address. If not, the physical address is identical to the virtual
address. If the translation or memory reference encounters an error (for example, pro-
tection violation or non-existent memory), the processor performs no operation. This al-
lows the instruction to be used to speculatively fetch an address that does not exist or is
protected without either causing an error or allowing inappropriate action.
Because the organization of caches is implementation-specific, the operation section
below specifies only a call to the implementation’s dprefetch function.
23 16 15 12 11 8 7 4 3 0
imm8 0111 s 00100010
8 4444
DPFRO Data Cache Prefetch for Read Once
334 Xtensa Instruction Set Architecture (ISA) Reference Manual
Assembler Note
To form a virtual address, DPFRO calculates the sum of address register as and the
imm8 field of the instruction word times four. Therefore, the machine-code offset is in
terms of 32-bit (4 byte) units. However, the assembler expects a byte offset and encodes
this into the instruction by dividing by four.
Operation
vAddr ← AR[s] + (022||imm8||02)
(pAddr, attributes, cause) ← ltranslate(vAddr, CRING)
if not invalid(attributes) then
dprefetch(vAddr, pAddr, 0, 1, 0)
endif
Exceptions
EveryInstR Group (see page 244)
Data Cache Prefetch for Write DPFW
Xtensa Instruction Set Architecture (ISA) Reference Manual 335
Instruction Word
(RRI8)
Required Configuration Option
Data Cache Option (See Section 4.5.5 on page 118)
Assembler Syntax
DPFW as, 0..1020
Description
DPFW performs a data cache prefetch for write. The purpose of DPFW is to improve per-
formance, but not to affect the ISA state. Therefore, some Xtensa ISA implementations
may choose to implement this instruction as a simple “no-operation” instruction. In gen-
eral, the performance improvement from using this instruction is implementation-depen-
dent.
In some Xtensa ISA implementations, DPFW checks whether the line containing the
specified address is present in the data cache, and if not, begins the transfer of the line
from memory. Four data prefetch instructions provide different “hints” about how the
data is likely to be used in the future. DPFW indicates that the data is likely to be written
before it is replaced by another line in the cache. In some implementations, this fetches
the data with write permission (for example, in a system with shared and exclusive
states).
DPFW forms a virtual address by adding the contents of address register as and an 8-bit
zero-extended constant value encoded in the instruction word shifted left by two. There-
fore, the offset can specify multiples of four from zero to 1020. If the Region Translation
Option (page 156) or the MMU Option (page 158) is enabled, the virtual address is
translated to the physical address. If not, the physical address is identical to the virtual
address. If the translation or memory reference encounters an error (for example, pro-
tection violation or non-existent memory), the processor performs no operation. This al-
lows the instruction to be used to speculatively fetch an address that does not exist or is
protected without either causing an error or allowing inappropriate action.
Because the organization of caches is implementation-specific, the operation section
below specifies only a call to the implementation’s dprefetch function.
23 16 15 12 11 8 7 4 3 0
imm8 0111 s 00010010
8 4444
DPFW Data Cache Prefetch for Write
336 Xtensa Instruction Set Architecture (ISA) Reference Manual
Assembler Note
To form a virtual address DPFW calculates the sum of address register as and the imm8
field of the instruction word times four. Therefore, the machine-code offset is in terms of
32-bit (4 byte) units. However, the assembler expects a byte offsets and encodes this
into the instruction by dividing by four.
Operation
vAddr ← AR[s] + (022||imm8||02)
(pAddr, attributes, cause) ← ltranslate(vAddr, CRING)
if not invalid(attributes) then
dprefetch(vAddr, pAddr, 1, 0, 0)
endif
Exceptions
EveryInstR Group (see page 244)
Data Cache Prefetch for Write Once DPFWO
Xtensa Instruction Set Architecture (ISA) Reference Manual 337
Instruction Word
(RRI8)
Required Configuration Option
Data Cache Option (See Section 4.5.5 on page 118)
Assembler Syntax
DPFWO as, 0..1020
Description
DPFWO performs a data cache prefetch for write once. The purpose of DPFWO is to im-
prove performance, but not to affect the ISA state. Therefore, some Xtensa ISA imple-
mentations may choose to implement this instruction as a simple “no-operation” instruc-
tion. In general, the performance improvement from using this instruction is
implementation-dependent.
In some Xtensa ISA implementations, DPFWO checks whether the line containing the
specified address is present in the data cache, and if not, begins the transfer of the line
from memory. Four data prefetch instructions provide different “hints” about how the
data is likely to be used in the future. DPFWO indicates that the data is likely to be read
and written once before it is replaced by another line in the cache. In some implementa-
tions, this write hint fetches the data with write permission (for example, in a system with
shared and exclusive states). The write-once hint might be used to select a specific
cache way or to select a streaming buffer instead of the cache.
DPFWO forms a virtual address by adding the contents of address register as and an
8-bit zero-extended constant value encoded in the instruction word shifted left by two.
Therefore, the offset can specify multiples of four from zero to 1020. If the Region Trans-
lation Option (page 156) or the MMU Option (page 158) is enabled, the virtual address is
translated to the physical address. If not, the physical address is identical to the virtual
address. If the translation or memory reference encounters an error (for example, pro-
tection violation or non-existent memory), the processor performs no operation. This al-
lows the instruction to be used to speculatively fetch an address that does not exist or is
protected without either causing an error or allowing inappropriate action.
Because the organization of caches is implementation-specific, the operation section
below specifies only a call to the implementation’s dprefetch function.
23 16 15 12 11 8 7 4 3 0
imm8 0111 s 00110010
8 4444
DPFWO Data Cache Prefetch for Write Once
338 Xtensa Instruction Set Architecture (ISA) Reference Manual
Assembler Note
To form a virtual address DPFWO calculates the sum of address register as and the imm8
field of the instruction word times four. Therefore, the machine-code offset is in terms of
32-bit (4 byte) units. However, the assembler expects a byte offset and encodes this into
the instruction by dividing by four.
Operation
vAddr ← AR[s] + (022||imm8||02)
(pAddr, attributes, cause) ← ltranslate(vAddr, CRING)
if not invalid(attributes) then
dprefetch(vAddr, pAddr, 1, 1, 0)
endif
Exceptions
EveryInstR Group (see page 244)
Load/Store Synchronize DSYNC
Xtensa Instruction Set Architecture (ISA) Reference Manual 339
Instruction Word (RRR)
Required Configuration Option
Core Architecture (See Section 4.2 on page 50)
Assembler Syntax
DSYNC
Description
DSYNC waits for all previously fetched WSR.*, XSR.*, WDTLB, and IDTLB instructions to
be performed before interpreting the virtual address of the next load or store instruction.
This operation is also performed as part of ISYNC, RSYNC, and ESYNC.
This instruction is appropriate after WSR.DBREAKC* and WSR.DBREAKA* instructions.
See the Special Register Tables in Section 5.3 on page 208 and Section 5.5 on
page 239 for a complete description of the uses of the DSYNC instruction.
Because the instruction execution pipeline is implementation-specific, the operation sec-
tion below specifies only a call to the implementation’s dsync function.
Operation
dsync()
Exceptions
EveryInst Group (see page 244)
23 20 19 16 15 12 11 8 7 4 3 0
000000000010000000110000
444444
ENTRY Subroutine Entry
340 Xtensa Instruction Set Architecture (ISA) Reference Manual
Instruction Word (BRI12)
Required Configuration Option
Windowed Register Option (See Section 4.7.1 on page 180)
Assembler Syntax
ENTRY as, 0..32760
Description
ENTRY is intended to be the first instruction of all subroutines called with CALL4, CALL8,
CALL12, CALLX4, CALLX8, or CALLX12. This instruction is not intended to be used by a
routine called by CALL0 or CALLX0.
ENTRY serves two purposes:
1. First, it increments the register window pointer (WindowBase) by the amount re-
quested by the caller (as recorded in the PS.CALLINC field).
2. Second, it copies the stack pointer from caller to callee and allocates the callee’s
stack frame. The as operand specifies the stack pointer register; it must specify one
of a0..a3 or the operation of ENTRY is undefined. It is read before the window is
moved, the stack frame size is subtracted, and then the as register in the moved
window is written.
The stack frame size is specified as the 12-bit unsigned imm12 field in units of eight
bytes. The size is zero-extended, shifted left by 3, and subtracted from the caller’s stack
pointer to get the callee’s stack pointer. Therefore, stack frames up to 32760 bytes can
be specified. The initial stack frame size must be a constant, but subsequently the
MOVSP instruction can be used to allocate dynamically-sized objects on the stack, or to
further extend a constant stack frame larger than 32760 bytes.
The windowed subroutine call protocol is described in Section 4.7.1.5 on page 187.
ENTRY is undefined if PS.WOE is 0 or if PS.EXCM is 1. Some implementations raise an
illegal instruction exception in these cases, as a debugging aid.
23 12 11 876543 0
imm12 s 00110110
12 4 2 2 4
Subroutine Entry ENTRY
Xtensa Instruction Set Architecture (ISA) Reference Manual 341
Assembler Note
In the assembler syntax, the number of bytes to be subtracted from the stack pointer is
specified as the immediate. The assembler encodes this into the instruction by dividing
by eight.
Operation
WindowCheck (00, PS.CALLINC, 00)
if as > 3 | PS.WOE = 0 | PS.EXCM = 1 then
-- undefined operation
-- may raise illegal instruction exception
else
AR[PS.CALLINC||s1..0] ← AR[s] − (017||imm12||03)
WindowBase ← WindowBase + (02||PS.CALLINC)
WindowStartWindowBase ← 1
endif
Exceptions
EveryInstR Group (see page 244)
ESYNC Execute Synchronize
342 Xtensa Instruction Set Architecture (ISA) Reference Manual
Instruction Word (RRR)
Required Configuration Option
Core Architecture (See Section 4.2 on page 50)
Assembler Syntax
ESYNC
Description
ESYNC waits for all previously fetched WSR.*, and XSR.* instructions to be performed
before the next instruction uses any register values. This operation is also performed as
part of ISYNC and RSYNC. DSYNC is performed as part of this instruction.
This instruction is appropriate after WSR.EPC* instructions. See the Special Register
Tables in Section 5.3 on page 208 for a complete description of the uses of the ESYNC
instruction.
Because the instruction execution pipeline is implementation-specific, the operation sec-
tion below specifies only a call to the implementation’s esync function.
Operation
esync()
Exceptions
EveryInst Group (see page 244)
23 20 19 16 15 12 11 8 7 4 3 0
000000000010000000100000
444444
Exception Wait EXCW
Xtensa Instruction Set Architecture (ISA) Reference Manual 343
Instruction Word (RRR)
Required Configuration Option
Exception Option (See Section 4.4.1 on page 82)
Assembler Syntax
EXCW
Description
EXCW waits for any exceptions of previously fetched instructions to be handled. Some
Xtensa ISA implementations may have imprecise exceptions; on these implementations
EXCW waits until all previous instruction exceptions are taken or the instructions are
known to be exception-free. Because the instruction execution pipeline and exception
handling is implementation-specific, the operation section below specifies only a call to
the implementation’s ExceptionWait function.
Operation
ExceptionWait()
Exceptions
EveryInst Group (see page 244)
23 20 19 16 15 12 11 8 7 4 3 0
000000000010000010000000
444444
EXTUI Extract Unsigned Immediate
344 Xtensa Instruction Set Architecture (ISA) Reference Manual
Instruction Word (RRR)
Required Configuration Option
Core Architecture (See Section 4.2 on page 50)
Assembler Syntax
EXTUI ar, at, shiftimm, maskimm
Description
EXTUI performs an unsigned bit field extraction from a 32-bit register value. Specifically,
it shifts the contents of address register at right by the shift amount shiftimm, which is
a value 0..31 stored in bits 16 and 11..8 of the instruction word (the sa fields). The
shift result is then ANDed with a mask of maskimm least-significant 1 bits and the result
is written to address register ar. The number of mask bits, maskimm, may take the val-
ues 1..16, and is stored in the op2 field as maskimm-1. The bits extracted are there-
fore sa+op2..sa.
The operation of this instruction when sa+op2 > 31 is undefined and reserved for future
use.
Operation
mask ← 031-op2||1op2+1
AR[r] ← (032||AR[t])31+sa..sa and mask
Exceptions
EveryInstR Group (see page 244)
23 20 19 16 15 12 11 8 7 4 3 0
op2 010sa4rsae3..0 t 0000
444444
External Wait EXTW
Xtensa Instruction Set Architecture (ISA) Reference Manual 345
Instruction Word (RRR)
Required Configuration Option
Core Architecture (See Section 4.2 on page 50) (added in RA-2004.1)
Assembler Syntax
EXTW
Description
EXTW is a superset of MEMW. EXTW ensures that both
- all previous load, store, acquire, release, prefetch, and cache instructions; and
- any other effect of any previous instruction which is visible at the pins of the
Xtensa processor
complete (or perform as described in Section 4.3.12.1 on page 74) before either
- any subsequent load, store, acquire, release, prefetch, or cache instructions; or
- external effects of the execution of any following instruction is visible at the pins
of the Xtensa processor (not including instruction prefetch or TIE Queue pops)
is allowed to begin.
While MEMW is intended to implement the volatile attribute of languages such as C
and C++, EXTW is intended to be an ordering guarantee for all external effects that the
processor can have, including processor pins defined in TIE.
Because the instruction execution pipeline is implementation-specific, the operation sec-
tion below specifies only a call to the implementation’s extw function.
Operation
extw()
Exceptions
EveryInst Group (see page 244)
23 20 19 16 15 12 11 8 7 4 3 0
000000000010000011010000
444444
FLOAT.S Convert Fixed to Single
346 Xtensa Instruction Set Architecture (ISA) Reference Manual
Instruction Word (RRR)
Required Configuration Option
Floating-Point Coprocessor Option (See Section 4.3.11 on page 67)
Assembler Syntax
FLOAT.S fr, as, 0..15
Description
FLOAT.S converts the contents of address register as from signed integer to single-pre-
cision format, rounding according to the current rounding mode. The converted integer
value is then scaled by a power of two constant value encoded in the t field, with 0..15
representing 1.0, 0.5, 0.25, …, 1.0÷s32768.0. The scaling allows for a fixed point nota-
tion where the binary point is at the right end of the integer for t=0 and moves to the left
as t increases until for t=15 there are 15 fractional bits represented in the fixed point
number. The result is written to floating-point register fr.
Operation
FR[r] ← floats(AR[s]) ×s pows(2.0,-t)
Exceptions
EveryInstR Group (see page 244)
GenExcep(Coprocessor0Disabled) if Coprocessor Option
23 20 19 16 15 12 11 8 7 4 3 0
11001010 r s t 0000
444444
Floor Single to Fixed FLOOR.S
Xtensa Instruction Set Architecture (ISA) Reference Manual 347
Instruction Word (RRR)
Required Configuration Option
Floating-Point Coprocessor Option (See Section 4.3.11 on page 67)
Assembler Syntax
FLOOR.S ar, fs, 0..15
Description
FLOOR.S converts the contents of floating-point register fs from single-precision to
signed integer format, rounding toward -∞. The single-precision value is first scaled by a
power of two constant value encoded in the t field, with 0..15 representing 1.0, 2.0, 4.0,
…, 32768.0. The scaling allows for a fixed point notation where the binary point is at the
right end of the integer for t=0 and moves to the left as t increases until for t=15 there
are 15 fractional bits represented in the fixed point number. For positive overflow (value
≥ 32'h7fffffff), positive infinity, or NaN, 32'h7fffffff is returned; for negative
overflow (value ≤ 32'h80000000) or negative infinity, 32'h80000000 is returned. The
result is written to address register ar.
Operation
AR[r] ← floors(FR[s] ×s pows(2.0,t))
Exceptions
EveryInstR Group (see page 244)
GenExcep(Coprocessor0Disabled) if Coprocessor Option
23 20 19 16 15 12 11 8 7 4 3 0
10101010 r s t 0000
444444
IDTLB Invalidate Data TLB Entry
348 Xtensa Instruction Set Architecture (ISA) Reference Manual
Instruction Word (RRR)
Required Configuration Option
Region Protection Option (see Section 4.6.3 on page 150) or MMU Option (see
Section 4.6.5 on page 158)
Assembler Syntax
IDTLB as
Description
IDTLB invalidates the data TLB entry specified by the contents of address register as.
See Section 4.6 on page 138 for information on the address register formats for specific
Memory Protection and Translation Options. The point at which the invalidation is effect-
ed is implementation-specific. Any translation that would be affected by this invalidation
before the execution of a DSYNC instruction is therefore undefined.
IDTLB is a privileged instruction.
The representation of validity in Xtensa TLBs is implementation-specific, and thus the
operation section below writes the implementation-specific value
InvalidDataTLBEntry.
Operation
if CRING ≠ 0 then
Exception (PrivilegedInstructionCause)
else
(vpn, ei, wi) ← SplitDataTLBEntrySpec(AR[s])
DataTLB[wi][ei] ← InvalidDataTLBEntry
endif
Exceptions
EveryInstR Group (see page 244)
GenExcep(PrivilegedCause) if Exception Option
23 20 19 16 15 12 11 8 7 4 3 0
010100001100 s 00000000
444444
Instruction Cache Hit Invalidate IHI
Xtensa Instruction Set Architecture (ISA) Reference Manual 349
Instruction Word
(RRI8)
Required Configuration Option
Instruction Cache Option (See Section 4.5.2 on page 115)
Assembler Syntax
IHI as, 0..1020
Description
IHI performs an instruction cache hit invalidate. It invalidates the specified line in the in-
struction cache, if it is present. If the specified address is not in the instruction cache,
then this instruction has no effect. If the specified line is already invalid, then this instruc-
tion has no effect. If the specified line has been locked by an IPFL instruction, then no
invalidation is done and no exception is raised because of the lock. The line remains in
the cache and must be unlocked by an IHU or IIU instruction before it can be invalidat-
ed. Otherwise, if the specified line is present, it is invalidated.
This instruction is required before executing instructions from the instruction cache that
have been written by this processor, another processor, or DMA. The writes must first be
forced out of the data cache, either by using DHWB or by using stores that bypass or
write through the data cache. An ISYNC instruction should then be used to guarantee
that the modified instructions are visible to instruction cache misses. The instruction
cache should then be invalidated for the affected addresses using a series of IHI in-
structions. An ISYNC instruction should then be used to guarantee that this processor’s
fetch pipeline does not contain instructions from the invalidated lines.
Because the organization of caches is implementation-specific, the operation section
below specifies only a call to the implementation’s ihitinval function.
IHI forms a virtual address by adding the contents of address register as and an 8-bit
zero-extended constant value encoded in the instruction word shifted left by two. There-
fore, the offset can specify multiples of four from zero to 1020. If the Region Translation
Option (page 156) or the MMU Option (page 158) is enabled, the virtual address is
translated to the physical address. If not, the physical address is identical to the virtual
23 16 15 12 11 8 7 4 3 0
imm8 0111 s 11100010
8 4444
IHI Instruction Cache Hit Invalidate
350 Xtensa Instruction Set Architecture (ISA) Reference Manual
address. If the translation encounters an error (for example, protection violation), the
processor raises one of several exceptions (see Section 4.4.1.5 on page 89). The trans-
lation is done as if the address were for an instruction fetch.
Assembler Note
To form a virtual address, IHI calculates the sum of address register as and the imm8
field of the instruction word times four. Therefore, the machine-code offset is in terms of
32-bit (4 byte) units. However, the assembler expects a byte offset and encodes this into
the instruction by dividing by four.
Operation
vAddr ← AR[s] + (022||imm8||02)
(pAddr, attributes, cause) ← ftranslate(vAddr, CRING)
if invalid(attributes) then
EXCVADDR ← vAddr
Exception (cause)
else
ihitinval(vAddr, pAddr)
endif
Exceptions
EveryInstR Group (see page 244)
MemoryErrorException if Memory ECC/Parity Option
Instruction Cache Hit Unlock IHU
Xtensa Instruction Set Architecture (ISA) Reference Manual 351
Instruction Word (RRI4)
Required Configuration Option
Instruction Cache Index Lock Option (See Section 4.5.4 on page 117)
Assembler Syntax
IHU as, 0..240
Description
IHU performs an instruction cache unlock if hit. The purpose of IHU is to remove the
lock created by an IPFL instruction. Xtensa ISA implementations that do not implement
cache locking must raise an illegal instruction exception when this opcode is executed.
IHU checks whether the line containing the specified address is present in the instruc-
tion cache, and if so, it clears the lock associated with that line. To unlock by index with-
out knowing the address of the locked line, use the IIU instruction.
IHU forms a virtual address by adding the contents of address register as and a 4-bit
zero-extended constant value encoded in the instruction word shifted left by four. There-
fore, the offset can specify multiples of 16 from zero to 240. If the Region Translation
Option (page 156) or the MMU Option (page 158) is enabled, the virtual address is
translated to the physical address. If not, the physical address is identical to the virtual
address. If the translation encounters an error (for example or protection violation), the
processor takes one of several exceptions (see Section 4.4.1.5 on page 89). The trans-
lation is done as if the address were for an instruction fetch.
IHU is a privileged instruction.
Assembler Note
To form a virtual address, IHU calculates the sum of address register as and the imm4
field of the instruction word times 16. Therefore, the machine-code offset is in terms of
16 byte units. However, the assembler expects a byte offset and encodes this into the
instruction by dividing by 16.
23 20 19 16 15 12 11 8 7 4 3 0
imm4 00100111 s 11010010
444444
IHU Instruction Cache Hit Unlock
352 Xtensa Instruction Set Architecture (ISA) Reference Manual
Operation
if CRING ≠ 0 then
Exception (PrivilegedInstructionCause)
else
vAddr ← AR[s] + (024||imm4||04)
(pAddr, attributes, cause) ← ftranslate(vAddr, CRING)
if invalid(attributes) then
EXCVADDR ← vAddr
Exception (cause)
else
ihitunlock(vAddr, pAddr)
endif
endif
Exceptions
EveryInstR Group (see page 244)
GenExcep(PrivilegedCause) if Exception Option
MemoryErrorException if Memory ECC/Parity Option
Instruction Cache Index Invalidate III
Xtensa Instruction Set Architecture (ISA) Reference Manual 353
Instruction Word
(RRI8)
Required Configuration Option
Instruction Cache Option (See Section 4.5.2 on page 115)
Assembler Syntax
III as, 0..1020
Description
III performs an instruction cache index invalidate. This instruction uses the virtual
address to choose a location in the instruction cache and invalidates the specified line.
The method for mapping the virtual address to an instruction cache location is imple-
mentation-specific. If the chosen line is already invalid, then this instruction has no
effect. If the chosen line has been locked by an IPFL instruction, then no invalidation is
done and no exception is raised because of the lock. The line remains in the cache and
must be unlocked by an IHU or IIU instruction before it can be invalidated. This instruc-
tion is useful for instruction cache initialization after power-up or for invalidating the
entire instruction cache.
III forms a virtual address by adding the contents of address register as and an 8-bit
zero-extended constant value encoded in the instruction word shifted left by two. There-
fore, the offset can specify multiples of four from zero to 1020. The virtual address
chooses a cache line without translation and without raising the associated exceptions.
Because the organization of caches is implementation-specific, the operation section
below specifies only a call to the implementation’s iindexinval function.
III is a privileged instruction.
Assembler Note
To form a virtual address, III calculates the sum of address register as and the imm8
field of the instruction word times four. Therefore, the machine-code offset is in terms of
32-bit (4 byte) units. However, the assembler expects a byte offset and encodes this into
the instruction by dividing by four.
23 16 15 12 11 8 7 4 3 0
imm8 0111 s 11110010
8 4444
III Instruction Cache Index Invalidate
354 Xtensa Instruction Set Architecture (ISA) Reference Manual
Operation
if CRING ≠ 0 then
Exception (PrivilegedInstructionCause)
else
vAddr ← AR[s] + (022||imm8||02)
iindexinval(vAddr, pAddr)
endif
Exceptions
EveryInstR Group (see page 244)
GenExcep(PrivilegedCause) if Exception Option
Implementation Notes
x ← ceil(log2(InstCacheBytes))
y ← log2(InstCacheBytes ÷ InstCacheWayCount)
z ← log2(InstCacheLineBytes)
The cache line specified by index Addrx-1..z in a direct-mapped cache or way
Addrx-1..y and index Addry-1..z in a set-associative cache is the chosen line. If the
specified cache way is not valid (the fourth way of a three way cache), the instruction
does nothing. In some implementations all ways at index Addry-1..z are invalidated
regardless of the specified way, but for future compatibility this behavior should not be
assumed.
Invalidate Instruction TLB Entry IITLB
Xtensa Instruction Set Architecture (ISA) Reference Manual 355
Instruction Word (RRR)
Required Configuration Option
Region Protection Option (see Section 4.6.3 on page 150) or MMU Option (see
Section 4.6.5 on page 158)
Assembler Syntax
IITLB as
Description
IITLB invalidates the instruction TLB entry specified by the contents of address register
as. See Section 4.6 on page 138 for information on the address register formats for spe-
cific Memory Protection and Translation options. The point at which the invalidation is
effected is implementation-specific. Any translation that would be affected by this invali-
dation before the execution of an ISYNC instruction is therefore undefined.
IITLB is a privileged instruction.
The representation of validity in Xtensa TLBs is implementation-specific, and thus the
operation section below writes the implementation-specific value
InvalidInstTLBEntry.
Operation
if CRING ≠ 0 then
Exception (PrivilegedInstructionCause)
else
(vpn, ei, wi) ← SplitInstTLBEntrySpec(AR[s])
InstTLB[wi][ei] ← InvalidInstTLBEntry
endif
Exceptions
EveryInstR Group (see page 244)
GenExcep(PrivilegedCause) if Exception Option
23 20 19 16 15 12 11 8 7 4 3 0
010100000100 s 00000000
444444
IIU Instruction Cache Index Unlock
356 Xtensa Instruction Set Architecture (ISA) Reference Manual
Instruction Word (RRI4)
Required Configuration Option
Instruction Cache Index Lock Option (See Section 4.5.4 on page 117)
Assembler Syntax
IIU as, 0..240
Description
IIU uses the virtual address to choose a location in the instruction cache and unlocks
the chosen line. The purpose of IIU is to remove the lock created by an IPFL instruc-
tion. The method for mapping the virtual address to an instruction cache location is
implementation-specific. This instruction is primarily useful for unlocking the entire
instruction cache. Xtensa ISA implementations that do not implement cache locking
must raise an illegal instruction exception when this opcode is executed.
To unlock a specific cache line if it is in the cache, use the IHU instruction.
IIU forms a virtual address by adding the contents of address register as and a 4-bit
zero-extended constant value encoded in the instruction word shifted left by four. There-
fore, the offset can specify multiples of 16 from zero to 240. The virtual address chooses
a cache line without translation and without raising the associated exceptions.
Because the organization of caches is implementation-specific, the operation section
below specifies only a call to the implementation’s iindexunlock function.
IIU is a privileged instruction.
Assembler Note
To form a virtual address IIU calculates the sum of address register as and the imm4
field of the instruction word times 16. Therefore, the machine-code offset is in terms of
16 byte units. However, the assembler expects a byte offset and encodes this into the
instruction by dividing by 16.
23 20 19 16 15 12 11 8 7 4 3 0
imm4 00110111 s 11010010
444444
Instruction Cache Index Unlock IIU
Xtensa Instruction Set Architecture (ISA) Reference Manual 357
Operation
if CRING ≠ 0 then
Exception (PrivilegedInstructionCause)
else
vAddr ← AR[s] + (024||imm4||04)
iindexunlock(vAddr)
endif
Exceptions
EveryInstR Group (see page 244)
GenExcep(PrivilegedCause) if Exception Option
MemoryErrorException if Memory ECC/Parity Option
Implementation Notes
x ← ceil(log2(InstCacheBytes))
y ← log2(InstCacheBytes ÷ InstCacheWayCount)
z ← log2(InstCacheLineBytes)
The cache line specified by index Addrx-1..z in a direct-mapped cache or way
Addrx-1..y and index Addry-1..z in a set-associative cache is the chosen line. If the
specified cache way is not valid (the fourth way of a three way cache), the instruction
does nothing.
ILL Illegal Instruction
358 Xtensa Instruction Set Architecture (ISA) Reference Manual
Instruction Word (CALLX)
Required Configuration Option
Exception Option (See Section 4.4.1 on page 82)
Assembler Syntax
ILL
Description
ILL is an opcode that is guaranteed to raise an illegal instruction exception in all imple-
mentations.
Operation
Exception(IllegalInstructionCause)
Exceptions
EveryInst Group (see page 244)
GenExcep(IllegalInstructionCause) if Exception Option
23 20 19 16 15 12 11 876543 0
000000000000000000000000
4 4 4 4 2 2 4
Narrow Illegal Instruction ILL.N
Xtensa Instruction Set Architecture (ISA) Reference Manual 359
Instruction Word (RRRN)
Required Configuration Option
Code Density Option (See Section 4.3.1 on page 53) and Exception Option (See
Section 4.4.1 on page 82)
Assembler Syntax
ILL.N
Description
ILL.N is a 16-bit opcode that is guaranteed to raise an illegal instruction exception.
Operation
Exception(IllegalInstructionCause)
Exceptions
EveryInst Group (see page 244)
GenExcep(IllegalInstructionCause) if Exception Option
15 12 11 8 7 4 3 0
1111000001101101
4444
IPF Instruction Cache Prefetch
360 Xtensa Instruction Set Architecture (ISA) Reference Manual
Instruction Word
(RRI8)
Required Configuration Option
Instruction Cache Option (See Section 4.5.2 on page 115)
Assembler Syntax
IPF as, 0..1020
Description
IPF performs an instruction cache prefetch. The purpose of IPF is to improve perfor-
mance, but not to affect state defined by the ISA. Therefore, some Xtensa ISA imple-
mentations may choose to implement this instruction as a simple “no-operation” instruc-
tion. In general, the performance improvement from using this instruction is
implementation-dependent. In some implementations, IPF checks whether the line con-
taining the specified address is present in the instruction cache, and if not, it begins the
transfer of the line from memory to the instruction cache. Prefetching an instruction line
may prevent the processor from taking an instruction cache miss later.
IPF forms a virtual address by adding the contents of address register as and an 8-bit
zero-extended constant value encoded in the instruction word shifted left by two. There-
fore, the offset can specify multiples of four from zero to 1020. If the Region Translation
Option (page 156) or the MMU Option (page 158) is enabled, the virtual address is
translated to the physical address. If not, the physical address is identical to the virtual
address. If the translation or memory reference encounters an error (for example, pro-
tection violation, or non-existent memory), the processor performs no operation. This
allows the instruction to be used to speculatively fetch an address that does not exist or
is protected without either causing an error or allowing inappropriate action. The transla-
tion is done as if the address were for an instruction fetch.
Assembler Note
To form a virtual address, IPF calculates the sum of address register as and the imm8
field of the instruction word times four. Therefore, the machine-code offset is in terms of
32-bit (4 byte) units. However, the assembler expects a byte offset and encodes this into
the instruction by dividing by four.
23 16 15 12 11 8 7 4 3 0
imm8 0111 s 11000010
8 4444
Instruction Cache Prefetch IPF
Xtensa Instruction Set Architecture (ISA) Reference Manual 361
Operation
vAddr ← AR[s] + (022||imm8||02)
(pAddr, attributes, cause) ← ftranslate(vAddr, CRING)
if not invalid(attributes) then
iprefetch(vAddr, pAddr, 0)
endif
Exceptions
EveryInstR Group (see page 244)
IPFL Instruction Cache Prefetch and Lock
362 Xtensa Instruction Set Architecture (ISA) Reference Manual
Instruction Word (RRI4)
Required Configuration Option
Instruction Cache Index Lock Option (See Section 4.5.4 on page 117)
Assembler Syntax
IPFL as, 0..240
Description
IPFL performs an instruction cache prefetch and lock. The purpose of IPFL is to
improve performance, but not to affect state defined by the ISA. Xtensa ISA implementa-
tions that do not implement cache locking must raise an illegal instruction exception
when this opcode is executed. In general, the performance improvement from using this
instruction is implementation-dependent as implementations may not overlap the cache
fill with the execution of other instructions.
In some implementations, IPFL checks whether the line containing the specified
address is present in the instruction cache, and if not, begins the transfer of the line from
memory to the instruction cache. The line is placed in the instruction cache and marked
as locked, so it is not replaceable by ordinary instruction cache misses. To unlock the
line, use IHU or IIU. To prefetch without locking, use the IPF instruction.
IPFL forms a virtual address by adding the contents of address register as and a 4-bit
zero-extended constant value encoded in the instruction word shifted left by four. There-
fore, the offset can specify multiples of 16 from zero to 240. If the Region Translation
Option (page 156) or the MMU Option (page 158) is enabled, the virtual address is
translated to the physical address. If not, the physical address is identical to the virtual
address. If the translation encounters an error (for example, protection violation), the
processor raises one of several exceptions (see Section 4.4.1.5 on page 89). The trans-
lation is done as if the address were for an instruction fetch. If the line cannot be cached,
an exception is raised with cause InstructionFetchErrorCause.
IPFL is a privileged instruction.
23 20 19 16 15 12 11 8 7 4 3 0
imm4 00000111 s 11010010
444444
Instruction Cache Prefetch and Lock IPFL
Xtensa Instruction Set Architecture (ISA) Reference Manual 363
Assembler Note
To form a virtual address, IPFL calculates the sum of address register as and the imm4
field of the instruction word times 16. Therefore, the machine-code offset is in terms of
16 byte units. However, the assembler expects a byte offset and encodes this into the
instruction by dividing by 16.
Operation
if CRING ≠ 0 then
Exception (PrivilegedInstructionCause)
else
vAddr ← AR[s] + (024||imm4||04)
(pAddr, attributes, cause) ← ftranslate(vAddr, CRING)
if invalid(attributes) then
EXCVADDR ← vAddr
Exception (cause)
else
iprefetch(vAddr, pAddr, 1)
endif
endif
Exceptions
EveryInstR Group (see page 244)
GenExcep(PrivilegedCause) if Exception Option
Implementation Notes
If there are not two available InstCache ways at the required index before the instruction
executes, an exception is raised.
ISYNC Instruction Fetch Synchronize
364 Xtensa Instruction Set Architecture (ISA) Reference Manual
Instruction Word (RRR)
Required Configuration Option
Core Architecture (See Section 4.2 on page 50)
Assembler Syntax
ISYNC
Description
ISYNC waits for all previously fetched load, store, cache, TLB, WSR.*, and XSR.*
instructions that affect instruction fetch to be performed before fetching the next instruc-
tion. RSYNC, ESYNC, and DSYNC are performed as part of this instruction.
The proper sequence for writing instructions and then executing them is:
write instructions
use DHWB to force the data out of the data cache (this step may be skipped if write-
through, bypass, or no allocate stores were used)
use ISYNC to wait for the writes to be visible to instruction cache misses
use multiple IHI instructions to invalidate the instruction cache for any lines that
were modified (this step is not appropriate if the affected instructions are in InstRAM
or cannot be cached)
use ISYNC to ensure that fetch pipeline will see the new instructions
This instruction also waits for all previously executed WSR.* and XSR.* instructions that
affect instruction fetch or register access processor state, including:
WSR.LCOUNT, WSR.LBEG, WSR.LEND
WSR.IBREAKENABLE, WSR.IBREAKA[i]
WSR.CCOMPAREn
See the Special Register Tables in Section 5.3 on page 208 and Section 5.7 on
page 240, for a complete description of the ISYNC instruction’s uses.
23 20 19 16 15 12 11 8 7 4 3 0
000000000010000000000000
444444
Instruction Fetch Synchronize ISYNC
Xtensa Instruction Set Architecture (ISA) Reference Manual 365
Operation
isync()
Exceptions
EveryInst Group (see page 244)
Implementation Notes
In many implementations, ISYNC consumes considerably more cycles than RSYNC,
ESYNC, or DSYNC.
J Unconditional Jump
366 Xtensa Instruction Set Architecture (ISA) Reference Manual
Instruction Word (CALL)
Required Configuration Option
Core Architecture (See Section 4.2 on page 50)
Assembler Syntax
J label
Description
J performs an unconditional branch to the target address. It uses a signed, 18-bit PC-
relative offset to specify the target address. The target address is given by the address
of the J instruction plus the sign-extended 18-bit offset field of the instruction plus
four, giving a range of -131068 to +131075 bytes.
Operation
nextPC ← PC + (offset1714||offset) + 4
Exceptions
EveryInst Group (see page 244)
23 6543 0
offset 000110
18 2 4
Unconditional Jump Long J.L
Xtensa Instruction Set Architecture (ISA) Reference Manual 367
Instruction Word (CALL)
Required Configuration Option
Assembler Macro
Assembler Syntax
J.L label, an
Description
J.L is an assembler macro which generates exactly a J instruction as long as the offset
will reach the label. If the offset is not long enough, the assembler relaxes the instruction
to a literal load into an followed by a JX an.. The AR register an may or may not be
modified.
Exceptions
EveryInstR Group (see page 244)
23 6543 0
offset 000110
18 2 4
JX Unconditional Jump Register
368 Xtensa Instruction Set Architecture (ISA) Reference Manual
Instruction Word (CALLX)
Required Configuration Option
Core Architecture (See Section 4.2 on page 50)
Assembler Syntax
JX as
Description
JX performs an unconditional jump to the address in register as.
Operation
nextPC ← AR[s]
Exceptions
EveryInstR Group (see page 244)
23 20 19 16 15 12 11 876543 0
000000000000 s 10100000
4 4 4 4 2 2 4
Load 8-bit Unsigned L8UI
Xtensa Instruction Set Architecture (ISA) Reference Manual 369
Instruction Word
(RRI8)
Required Configuration Option
Core Architecture (See Section 4.2 on page 50)
Assembler Syntax
L8UI at, as, 0..255
Description
L8UI is an 8-bit unsigned load from memory. It forms a virtual address by adding the
contents of address register as and an 8-bit zero-extended constant value encoded in
the instruction word. Therefore, the offset ranges from 0 to 255. Eight bits (one byte) are
read from the physical address. This data is then zero-extended and written to address
register at.
If the Region Translation Option (page 156) or the MMU Option (page 158)is enabled,
the virtual address is translated to the physical address. If not, the physical address is
identical to the virtual address. If the translation or memory reference encounters an
error (for example, protection violation or non-existent memory), the processor raises
one of several exceptions (see Section 4.4.1.5 on page 89).
Operation
vAddr ← AR[s] + (024||imm8)
(mem8, error) ← Load8(vAddr)
if error then
EXCVADDR ← vAddr
Exception (LoadStoreErrorCause)
else
AR[t] ← 024||mem8
endif
Exceptions
Memory Group (see page 244)
GenExcep(LoadProhibitedCause) if Region Protection Option or MMU Option
DebugExcep(DBREAK) if Debug Option
23 16 15 12 11 8 7 4 3 0
imm8 0 0 0 0 s t 0 0 1 0
8 4444
L16SI Load 16-bit Signed
370 Xtensa Instruction Set Architecture (ISA) Reference Manual
Instruction Word
(RRI8)
Required Configuration Option
Core Architecture (See Section 4.2 on page 50)
Assembler Syntax
L16SI at, as, 0..510
Description
L16SI is a 16-bit signed load from memory. It forms a virtual address by adding the con-
tents of address register as and an 8-bit zero-extended constant value encoded in the
instruction word shifted left by 1. Therefore, the offset can specify multiples of two from
zero to 510. Sixteen bits (two bytes) are read from the physical address. This data is
then sign-extended and written to address register at.
If the Region Translation Option (page 156) or the MMU Option (page 158)is enabled,
the virtual address is translated to the physical address. If not, the physical address is
identical to the virtual address. If the translation or memory reference encounters an
error (for example, protection violation, non-existent memory), the processor raises one
of several exceptions (see Section 4.4.1.5 on page 89).
Without the Unaligned Exception Option (page 99), the least significant address bit is ig-
nored; a reference to an odd address produces the same result as a reference to the ad-
dress minus one. With the Unaligned Exception Option, such an access raises an
exception.
Assembler Note
To form a virtual address, L16SI calculates the sum of address register as and the
imm8 field of the instruction word times two. Therefore, the machine-code offset is in
terms of 16-bit (2 byte) units. However, the assembler expects a byte offset and encodes
this into the instruction by dividing by two.
Operation
vAddr ← AR[s] + (023||imm8||0)
(mem16, error) ← Load16(vAddr)
23 16 15 12 11 8 7 4 3 0
imm8 1 0 0 1 s t 0 0 1 0
8 4444
Load 16-bit Signed L16SI
Xtensa Instruction Set Architecture (ISA) Reference Manual 371
if error then
EXCVADDR ← vAddr
Exception (LoadStoreErrorCause)
else
AR[t] ← mem161516||mem16
endif
Exceptions
Memory Load Group (see page 244)
L16UI Load 16-bit Unsigned
372 Xtensa Instruction Set Architecture (ISA) Reference Manual
Instruction Word
(RRI8)
Required Configuration Option
Core Architecture (See Section 4.2 on page 50)
Assembler Syntax
L16UI at, as, 0..510
Description
L16UI is a 16-bit unsigned load from memory. It forms a virtual address by adding the
contents of address register as and an 8-bit zero-extended constant value encoded in
the instruction word shifted left by 1. Therefore, the offset can specify multiples of two
from zero to 510. Sixteen bits (two bytes) are read from the physical address. This data
is then zero-extended and written to address register at.
If the Region Translation Option (page 156) or the MMU Option (page 158) is enabled,
the virtual address is translated to the physical address. If not, the physical address is
identical to the virtual address. If the translation or memory reference encounters an
error (for example, protection violation or non-existent memory), the processor raises
one of several exceptions (see Section 4.4.1.5 on page 89).
Without the Unaligned Exception Option (page 99), the least significant address bit is ig-
nored; a reference to an odd address produces the same result as a reference to the ad-
dress minus one. With the Unaligned Exception Option, such an access raises an
exception.
Assembler Note
To form a virtual address, L16UI calculates the sum of address register as and the
imm8 field of the instruction word times two. Therefore, the machine-code offset is in
terms of 16-bit (2 byte) units. However, the assembler expects a byte offset and encodes
this into the instruction by dividing by two.
Operation
vAddr ← AR[s] + (023||imm8||0)
(mem16, error) ← Load16(vAddr)
23 16 15 12 11 8 7 4 3 0
imm8 0 0 0 1 s t 0 0 1 0
8 4444
Load 16-bit Unsigned L16UI
Xtensa Instruction Set Architecture (ISA) Reference Manual 373
if error then
EXCVADDR ← vAddr
Exception (LoadStoreErrorCause)
else
AR[t] ← 016||mem16
endif
Exceptions
Memory Load Group (see page 244)
L32AI Load 32-bit Acquire
374 Xtensa Instruction Set Architecture (ISA) Reference Manual
Instruction Word
(RRI8)
Required Configuration Option
Multiprocessor Synchronization Option (See Section 4.3.12 on page 74)
Assembler Syntax
L32AI at, as, 0..1020
Description
L32AI is a 32-bit load from memory with “acquire” semantics. This load performs before
any subsequent loads, stores, acquires, or releases are performed. It is typically used to
test a synchronization variable protecting a critical region (for example, to acquire a
lock).
L32AI forms a virtual address by adding the contents of address register as and an
8-bit zero-extended constant value encoded in the instruction word shifted left by two.
Therefore, the offset can specify multiples of four from zero to 1020. 32 bits (four bytes)
are read from the physical address. This data is then written to address register at.
L32AI causes the processor to delay processing of subsequent loads, stores, acquires,
and releases until the L32AI is performed. In some Xtensa ISA implementations, this
occurs automatically and L32AI is identical to L32I. Other implementations (for exam-
ple, those with multiple outstanding loads and stores) delay processing as described
above. Because the method of delay is implementation-dependent, this is indicated in
the operation section below by the implementation function acquire.
If the Region Translation Option (page 156) or the MMU Option (page 158) is enabled,
the virtual address is translated to the physical address. If not, the physical address is
identical to the virtual address. If the translation or memory reference encounters an
error (for example, protection violation or non-existent memory), the processor raises
one of several exceptions (see Section 4.4.1.5 on page 89).
Without the Unaligned Exception Option (page 99), the two least significant bits of the
address are ignored. A reference to an address that is not 0 mod 4 produces the same
result as a reference to the address with the least significant bits cleared. With the Un-
aligned Exception Option, such an access raises an exception.
23 16 15 12 11 8 7 4 3 0
imm8 1 0 1 1 s t 0 0 1 0
8 4444
Load 32-bit Acquire L32AI
Xtensa Instruction Set Architecture (ISA) Reference Manual 375
Assembler Note
To form a virtual address, L32AI calculates the sum of address register as and the
imm8 field of the instruction word times four. Therefore, the machine-code offset is in
terms of 32-bit (4 byte) units. However, the assembler expects a byte offset and encodes
this into the instruction by dividing by four.
Operation
vAddr ← AR[s] + (022||imm8||02)
(mem32, error) ← Load32(vAddr)
if error then
EXCVADDR ← vAddr
Exception (LoadStoreErrorCause)
else
AR[t] ← mem32
acquire()
endif
Exceptions
Memory Load Group (see page 244)
L32E Load 32-bit for Window Exceptions
376 Xtensa Instruction Set Architecture (ISA) Reference Manual
Instruction Word (RRI4)
Required Configuration Option
Windowed Register Option (See Section 4.7.1 on page 180)
Assembler Syntax
L32E at, as, -64..-4
Description
L32E is a 32-bit load instruction similar to L32I but with semantics required by window
overflow and window underflow exception handlers. In particular, memory access check-
ing is done with PS.RING instead of CRING, and the offset used to form the virtual ad-
dress is a 4-bit one-extended immediate. Therefore, the offset can specify multiples of
four from -64 to -4. In configurations without the MMU Option, there is no PS.RING, and
L32E is similar to L32I with a negative offset.
If the Region Translation Option (page 156) or the MMU Option (page 158) is enabled,
the virtual address is translated to the physical address. If not, the physical address is
identical to the virtual address. If the translation or memory reference encounters an
error (for example, protection violation or non-existent memory), the processor raises
one of several exceptions (see Section 4.4.1.5 on page 89).
Without the Unaligned Exception Option (page 99), the two least significant bits of the
address are ignored. A reference to an address that is not 0 mod 4 produces the same
result as a reference to the address with the least significant bits cleared. With the Un-
aligned Exception Option, such an access raises an exception.
L32E is a privileged instruction.
Assembler Note
To form a virtual address, L32E calculates the sum of address register as and the r field
of the instruction word times four (and one extended). Therefore, the machine-code
offset is in terms of 32-bit (4 byte) units. However, the assembler expects a byte offset
and encodes this into the instruction by dividing by four.
23 20 19 16 15 12 11 8 7 4 3 0
00001001 r s t 0000
444444
Load 32-bit for Window Exceptions L32E
Xtensa Instruction Set Architecture (ISA) Reference Manual 377
Operation
if CRING ≠ 0 then
Exception (PrivilegedInstructionCause)
else
vAddr ← AR[s] + (126||r||02)
ring ← if MMU Option then PS.RING else 0
(mem32, error) ← Load32Ring(vAddr, ring)
if error then
EXCVADDR ← vAddr
Exception (LoadStoreErrorCause)
else
AR[t] ← mem32
endif
endif
Exceptions
Memory Load Group (see page 244)
GenExcep(PrivilegedCause) if Exception Option
L32I Load 32-bit
378 Xtensa Instruction Set Architecture (ISA) Reference Manual
Instruction Word
(RRI8)
Required Configuration Option
Core Architecture (See Section 4.2 on page 50)
Assembler Syntax
L32I at, as, 0..1020
Description
L32I is a 32-bit load from memory. It forms a virtual address by adding the contents of
address register as and an 8-bit zero-extended constant value encoded in the instruc-
tion word shifted left by two. Therefore, the offset can specify multiples of four from zero
to 1020. Thirty-two bits (four bytes) are read from the physical address. This data is then
written to address register at.
If the Region Translation Option (page 156) or the MMU Option (page 158) is enabled,
the virtual address is translated to the physical address. If not, the physical address is
identical to the virtual address. If the translation or memory reference encounters an
error (for example, protection violation, non-existent memory), the processor raises one
of several exceptions (see Section 4.4.1.5 on page 89).
Without the Unaligned Exception Option (page 99), the two least significant bits of the
address are ignored. A reference to an address that is not 0 mod 4 produces the same
result as a reference to the address with the least significant bits cleared. With the Un-
aligned Exception Option, such an access raises an exception.
L32I is one of only a few memory reference instructions that can access instruction
RAM/ROM.
Assembler Note
The assembler may convert L32I instructions to L32I.N when the Code Density
Option is enabled and the immediate operand falls within the available range. Prefixing
the L32I instruction with an underscore (_L32I) disables this optimization and forces
the assembler to generate the wide form of the instruction.
23 16 15 12 11 8 7 4 3 0
imm8 0 0 1 0 s t 0 0 1 0
8 4444
Load 32-bit L32I
Xtensa Instruction Set Architecture (ISA) Reference Manual 379
To form a virtual address, L32I calculates the sum of address register as and the imm8
field of the instruction word times four. Therefore, the machine-code offset is in terms of
32-bit (4 byte) units. However, the assembler expects a byte offset and encodes this into
the instruction by dividing by four.
Operation
vAddr ← AR[s] + (022||imm8||02)
(mem32, error) ← Load32(vAddr)
if error then
EXCVADDR ← vAddr
Exception (LoadStoreErrorCause)
else
AR[t] ← mem32
endif
Exceptions
Memory Load Group (see page 244)
L32I.N Narrow Load 32-bit
380 Xtensa Instruction Set Architecture (ISA) Reference Manual
Instruction Word (RRRN)
Required Configuration Option
Code Density Option (See Section 4.3.1 on page 53)
Assembler Syntax
L32I.N at, as, 0..60
Description
L32I.N is similar to L32I, but has a 16-bit encoding and supports a smaller range of
offset values encoded in the instruction word.
L32I.N is a 32-bit load from memory. It forms a virtual address by adding the contents
of address register as and a 4-bit zero-extended constant value encoded in the instruc-
tion word shifted left by two. Therefore, the offset can specify multiples of four from zero
to 60. Thirty-two bits (four bytes) are read from the physical address. This data is then
written to address register at.
If the Region Translation Option (page 156) or the MMU Option (page 158) is enabled,
the virtual address is translated to the physical address. If not, the physical address is
identical to the virtual address. If the translation or memory reference encounters an
error (for example, protection violation or non-existent memory), the processor raises
one of several exceptions (see Section 4.4.1.5 on page 89).
Without the Unaligned Exception Option (page 99), the two least significant bits of the
address are ignored. A reference to an address that is not 0 mod 4 produces the same
result as a reference to the address with the least significant bits cleared. With the Un-
aligned Exception Option, such an access raises an exception.
L32I.N is one of only a few memory reference instructions that can access instruction
RAM/ROM.
15 12 11 8 7 4 3 0
imm4 s t 1 0 0 0
4444
Narrow Load 32-bit L32I.N
Xtensa Instruction Set Architecture (ISA) Reference Manual 381
Assembler Note
The assembler may convert L32I.N instructions to L32I. Prefixing the L32I.N instruc-
tion with an underscore (_L32I.N) disables this optimization and forces the assembler
to generate the narrow form of the instruction.
To form a virtual address, L32I.N calculates the sum of address register as and the
imm4 field of the instruction word times four. Therefore, the machine-code offset is in
terms of 32-bit (4 byte) units. However, the assembler expects a byte offset and encodes
this into the instruction by dividing by four.
Operation
vAddr ← AR[s] + (026||imm4||02)
(mem32, error) ← Load32(vAddr)
if error then
EXCVADDR ← vAddr
Exception (LoadStoreErrorCause)
else
AR[t] ← mem32
endif
Exceptions
Memory Load Group (see page 244)
L32R Load 32-bit PC-Relative
382 Xtensa Instruction Set Architecture (ISA) Reference Manual
Instruction Word (RI6)
Required Configuration Option
Core Architecture (See Section 4.2 on page 50)
Assembler Syntax
L32R at, label
Description
L32R is a PC-relative 32-bit load from memory. It is typically used to load constant
values into a register when the constant cannot be encoded in a MOVI instruction.
L32R forms a virtual address by adding the 16-bit one-extended constant value encoded
in the instruction word shifted left by two to the address of the L32R plus three with the
two least significant bits cleared. Therefore, the offset can always specify 32-bit aligned
addresses from -262141 to -4 bytes from the address of the L32R instruction. 32 bits
(four bytes) are read from the physical address. This data is then written to address
register at.
In the presence of the Extended L32R Option (Section 4.3.3 on page 56) when LIT-
BASE[0] is clear, the instruction has the identical operation. When LITBASE[0] is set,
L32R forms a virtual address by adding the 16-bit one extended constant value encoded
in the instruction word shifted left by two to the literal base address indicated by the up-
per 20 bits of LITBASE. The offset can specify 32-bit aligned addresses from -262144 to
-4 bytes from the literal base address.
If the Region Translation Option (page 156) or the MMU Option (page 158) is enabled,
the virtual address is translated to the physical address. If not, the physical address is
identical to the virtual address. If the translation or memory reference encounters an
error (for example, protection violation or non-existent memory), the processor raises
one of several exceptions (see Section 4.4.1.5 on page 89).
It is not possible to specify an unaligned address.
L32R is one of only a few memory reference instructions that can access instruction
RAM/ROM.
23 8 7 4 3 0
imm16 t 0001
16 4 4
Load 32-bit PC-Relative L32R
Xtensa Instruction Set Architecture (ISA) Reference Manual 383
Assembler Note
In the assembler syntax, the immediate operand is specified as the address of the loca-
tion to load from, rather than the offset from the current instruction address. The linker
and the assembler both assume that the location loaded by the L32R instruction has not
been and will not be accessed by any other type of load or store instruction and optimiz-
es according to that assumption.
Operation
if Extended L32R Option and LITBASE0 then
vAddr ← (LITBASE31..12||012) + (114||imm16||02)
else
vAddr ← ((PC + 3)31..2||02) + (114||imm16||02)
endif
(mem32, error) ← Load32(vAddr)
if error then
EXCVADDR ← vAddr
Exception (LoadStoreErrorCause)
else
AR[t] ← mem32
endif
Exceptions
Memory Group (see page 244)
GenExcep(LoadProhibitedCause) if Region Protection Option or MMU Option
DebugExcep(DBREAK) if Debug Option
LDCT Load Data Cache Tag
384 Xtensa Instruction Set Architecture (ISA) Reference Manual
Instruction Word (RRR)
Required Configuration Option
Data Cache Test Option (See Section 4.5.6 on page 121)
Assembler Syntax
LDCT at, as
Description
LDCT is not part of the Xtensa Instruction Set Architecture, but is instead specific to an
implementation. That is, it may not exist in all implementations of the Xtensa ISA.
LDCT is intended for reading the RAM array that implements the data cache tags as part
of manufacturing test.
LDCT uses the contents of address register as to select a line in the data cache, reads
the tag associated with this line, and writes the result to address register at. The value
written to at is described under Cache Tag Format in Section 4.5.1.2 on page 112.
LDCT is a privileged instruction.
Operation
if CRING ≠ 0 then
Exception (PrivilegedInstructionCause)
else
index ← AR[s]dih..dil
AR[t] ← DataCacheTag[index]
endif
Exceptions
EveryInstR Group (see page 244)
GenExcep(PrivilegedCause) if Exception Option
MemoryErrorException if Memory ECC/Parity Option
23 20 19 16 15 12 11 8 7 4 3 0
111100011000 s t 0000
444444
Load Data Cache Tag LDCT
Xtensa Instruction Set Architecture (ISA) Reference Manual 385
Implementation Notes
x ← ceil(log2(DataCacheBytes))
y ← log2(DataCacheBytes ÷ DataCacheWayCount)
z ← log2(DataCacheLineBytes)
The cache line specified by index AR[s]x-1..z in a direct-mapped cache or way
AR[s]x-1..y and index AR[s]y-1..z in a set-associative cache is the chosen line. If the
specified cache way is not valid (the fourth way of a three way cache), the instruction
loads an undefined value.
LDDEC Load with Autodecrement
386 Xtensa Instruction Set Architecture (ISA) Reference Manual
Instruction Word (RRR)
Required Configuration Option
MAC16 Option (See Section 4.3.7 on page 60)
Assembler Syntax
LDDEC mw, as
Description
LDDEC loads MAC16 register mw from memory using auto-decrement addressing. It
forms a virtual address by subtracting 4 from the contents of address register as. 32 bits
(four bytes) are read from the physical address. This data is then written to MAC16
register mw, and the virtual address is written back to address register as.
If the Region Translation Option (page 156) or the MMU Option (page 158) is enabled,
the virtual address is translated to the physical address. If not, the physical address is
identical to the virtual address. If the translation or memory reference encounters an
error (for example, protection violation or non-existent memory), the processor raises
one of several exceptions (see Section 4.4.1.5 on page 89).
Without the Unaligned Exception Option (page 99), the two least significant bits of the
address are ignored. A reference to an address that is not 0 mod 4 produces the same
result as a reference to the address with the least significant bits cleared. With the Un-
aligned Exception Option, such an access raises an exception.
Operation
vAddr ← AR[s] − 4
(mem32, error) ← Load32(vAddr)
if error then
EXCVADDR ← vAddr
Exception (LoadStoreErrorCause)
else
MR[w] ← mem32
AR[s] ← vAddr
endif
Exceptions
Memory Load Group (see page 244)
23 20 19 16 15 12 11 8 7 4 3 0
1001000000 w s 00000100
444444
Load with Autoincrement LDINC
Xtensa Instruction Set Architecture (ISA) Reference Manual 387
Instruction Word (RRR)
Required Configuration Option
MAC16 Option (See Section 4.3.7 on page 60)
Assembler Syntax
LDINC mw, as
Description
LDINC loads MAC16 register mw from memory using auto-increment addressing. It
forms a virtual address by adding 4 to the contents of address register as. 32 bits (four
bytes) are read from the physical address. This data is then written to MAC16 register
mw, and the virtual address is written back to address register as.
If the Region Translation Option (page 156) or the MMU Option (page 158)is enabled,
the virtual address is translated to the physical address. If not, the physical address is
identical to the virtual address. If the translation or memory reference encounters an
error (for example, protection violation or non-existent memory), the processor raises
one of several exceptions (see Section 4.4.1.5 on page 89).
Without the Unaligned Exception Option (page 99), the two least significant bits of the
address are ignored. A reference to an address that is not 0 mod 4 produces the same
result as a reference to the address with the least significant bits cleared. With the Un-
aligned Exception Option, such an access raises an exception.
Operation
vAddr ← AR[s] + 4
(mem32, error) ← Load32(vAddr)
if error then
EXCVADDR ← vAddr
Exception (LoadStoreErrorCause)
else
MR[w] ← mem32
AR[s] ← vAddr
endif
Exceptions
Memory Load Group (see page 244)
23 20 19 16 15 12 11 8 7 4 3 0
1000000000 w s 00000100
444444
LICT Load Instruction Cache Tag
388 Xtensa Instruction Set Architecture (ISA) Reference Manual
Instruction Word (RRR)
Required Configuration Option
Instruction Cache Test Option (See Section 4.5.3 on page 116)
Assembler Syntax
LICT at, as
Description
LICT is not part of the Xtensa Instruction Set Architecture, but is instead specific to an
implementation. That is, it may not exist in all implementations of the Xtensa ISA.
LICT is intended for reading the RAM array that implements the instruction cache tags
as part of manufacturing test.
LICT uses the contents of address register as to select a line in the instruction cache,
reads the tag associated with this line, and writes the result to address register at. The
value written to at is described under Cache Tag Format in Section 4.5.1.2 on
page 112.
LICT is a privileged instruction.
Operation
if CRING ≠ 0 then
Exception (PrivilegedInstructionCause)
else
index ← AR[s]iih..iil
AR[t] ← InstCacheTag[index]
endif
Exceptions
EveryInstR Group (see page 244)
GenExcep(PrivilegedCause) if Exception Option
23 20 19 16 15 12 11 8 7 4 3 0
111100010000 s t 0000
444444
Load Instruction Cache Tag LICT
Xtensa Instruction Set Architecture (ISA) Reference Manual 389
Implementation Notes
x ← ceil(log2(InstCacheBytes))
y ← log2(InstCacheBytes ÷ InstCacheWayCount)
z ← log2(InstCacheLineBytes)
The cache line specified by index AR[s]x-1..z in a direct-mapped cache or way
AR[s]x-1..y and index AR[s]y-1..z in a set-associative cache is the chosen line. If the
specified cache way is not valid (the fourth way of a three way cache), the instruction
loads an undefined value.
LICW Load Instruction Cache Word
390 Xtensa Instruction Set Architecture (ISA) Reference Manual
Instruction Word (RRR)
Required Configuration Option
Instruction Cache Test Option (See Section 4.5.3 on page 116)
Assembler Syntax
LICW at, as
Description
LICW is not part of the Xtensa Instruction Set Architecture, but is instead specific to an
implementation. That is, it may not exist in all implementations of the Xtensa ISA.
LICW is intended for reading the RAM array that implements the instruction cache as
part of manufacturing test.
LICW uses the contents of address register as to select a line in the instruction cache
and one 32-bit quantity within that line, reads that data, and writes the result to address
register at.
LICW is a privileged instruction.
Operation
if CRING ≠ 0 then
Exception (PrivilegedInstructionCause)
else
index ← AR[s]iih..2
AR[t] ← InstCacheData [index]
endif
Exceptions
EveryInstR Group (see page 244)
GenExcep(PrivilegedCause) if Exception Option
MemoryErrorException if Memory ECC/Parity Option
23 20 19 16 15 12 11 8 7 4 3 0
111100010010 s t 0000
444444
Load Instruction Cache Word LICW
Xtensa Instruction Set Architecture (ISA) Reference Manual 391
Implementation Notes
x ← ceil(log2(InstCacheBytes))
y ← log2(InstCacheBytes ÷ InstCacheWayCount)
z ← log2(InstCacheLineBytes)
The cache line specified by index AR[s]x-1..z in a direct-mapped cache or way
AR[s]x-1..y and index AR[s]y-1..z in a set-associative cache is the chosen line. If the
specified cache way is not valid (the fourth way of a three way cache), the instruction
loads an undefined value. Within the cache line, AR[s]z-1..2 is used to determine
which 32-bit quantity within the line is loaded.
LOOP Loop
392 Xtensa Instruction Set Architecture (ISA) Reference Manual
Instruction Word
(RRI8)
Required Configuration Option
Loop Option (See Section 4.3.2 on page 54)
Assembler Syntax
LOOP as, label
Description
LOOP sets up a zero-overhead loop by setting the LCOUNT, LBEG, and LEND special
registers, which control instruction fetch. The loop will iterate the number of times speci-
fied by address register as, with 0 causing the loop to iterate 232 times. LCOUNT, the
current loop iteration counter, is loaded from the contents of address register as minus
one. LEND is the loop end address and is loaded with the address of the LOOP instruc-
tion plus four, plus the zero-extended 8-bit offset encoded in the instruction (therefore,
the loop code may be up to 256 bytes in length). LBEG, the loop begin address, is loaded
with the address of the following instruction (the address of the LOOP instruction plus
three).
After the processor fetches an instruction that increments the PC to the value contained
in LEND, and LCOUNT is not zero, it loads the PC with the contents of LBEG and decre-
ments LCOUNT. LOOP is intended to be implemented with help from the instruction fetch
engine of the processor, and therefore should not incur a mispredict or taken branch
penalty. Branches and jumps to the address contained in LEND do not cause a loop
back, and therefore may be used to exit the loop prematurely. Likewise, a return from a
call instruction as the last instruction of the loop would not trigger loop back; this case
should be avoided.
There is no mechanism to proceed to the next iteration of the loop from the middle of the
loop. The compiler may insert a branch to a NOP placed as the last instruction of the loop
to implement this function if required.
Because LCOUNT, LBEG, and LEND are single registers, zero-overhead loops may not be
nested. Using conditional branch instructions to implement outer level loops is typically
not a performance issue. Because loops cannot be nested, it is usually inappropriate to
include a procedure call inside a loop (the callee might itself use a zero-overhead loop).
23 16 15 12 11 8 7 4 3 0
imm8 1000 s 01110110
8 4444
Loop LOOP
Xtensa Instruction Set Architecture (ISA) Reference Manual 393
To simplify the implementation of zero-overhead loops, the LBEG address, which is the
LOOP instruction address plus three, must be such that the first instruction must entirely
fit within a naturally aligned four byte region or, if the instruction is larger than four bytes,
a naturally aligned region which is the next power of two equal to or larger than the
instruction. When the LOOP instruction would not naturally be placed at such an
address, the insertion of NOP instructions or adjustment of which instructions are 16-bit
density instructions is sufficient to give it the required alignment.
The automatic loop-back when the PC increments to match LEND is disabled when
PS.EXCM is set. This prevents non-privileged code from affecting the operation of the
privileged exception vector code.
Assembler Note
The assembler automatically aligns the LOOP instruction as required.
When the label is out of range, the assembler may insert a number of instructions to
extend the size of the loop. Prefixing the instruction mnemonic with an underscore
(_LOOP) disables this feature and forces the assembler to generate an error in this case.
Operation
LCOUNT ← AR[s] − 1
LBEG ← PC + 3
LEND ← PC + (024||imm8) + 4
Exceptions
EveryInstR Group (see page 244)
Implementation Notes
In some implementations, LOOP takes an extra clock for the first loop back of certain
loops. In addition, certain instructions (such as ISYNC or a write to LEND) may cause an
additional cycle on the following loop back.
LOOPGTZ Loop if Greater Than Zero
394 Xtensa Instruction Set Architecture (ISA) Reference Manual
Instruction Word
(RRI8)
Required Configuration Option
Loop Option (See Section 4.3.2 on page 54)
Assembler Syntax
LOOPGTZ as, label
Description
LOOPGTZ sets up a zero-overhead loop by setting the LCOUNT, LBEG, and LEND special
registers, which control instruction fetch. The loop will iterate the number of times speci-
fied by address register as with values ≤ 0 causing the loop to be skipped altogether by
branching directly to the loop end address. LCOUNT, the current loop iteration counter, is
loaded from the contents of address register as minus one. LEND is the loop end
address and is loaded with the address of the LOOPGTZ instruction plus four, plus the
zero-extended 8-bit offset encoded in the instruction (therefore, the loop code may be
up to 256 bytes in length). LBEG, the loop begin address, is loaded with the address of
the following instruction (the address of the LOOPGTZ instruction plus three). LCOUNT,
LEND, and LBEG are still loaded even when the loop is skipped.
After the processor fetches an instruction that increments the PC to the value contained
in LEND, and LCOUNT is not zero, it loads the PC with the contents of LBEG and decre-
ments LCOUNT. LOOPGTZ is intended to be implemented with help from the instruction
fetch engine of the processor, and therefore should not incur a mispredict or taken
branch penalty. Branches and jumps to the address contained in LEND do not cause a
loop back, and therefore may be used to exit the loop prematurely. Similarly, a return
from a call instruction as the last instruction of the loop would not trigger loop back; this
case should be avoided.
There is no mechanism to proceed to the next iteration of the loop from the middle of the
loop. The compiler may insert a branch to a NOP placed as the last instruction of the loop
to implement this function if required.
23 16 15 12 11 8 7 4 3 0
imm8 1010 s 01110110
8 4444
Loop if Greater Than Zero LOOPGTZ
Xtensa Instruction Set Architecture (ISA) Reference Manual 395
Because LCOUNT, LBEG, and LEND are single registers, zero-overhead loops may not be
nested. Using conditional branch instructions to implement outer level loops is typically
not a performance issue. Because loops cannot be nested, it is usually inappropriate to
include a procedure call inside a loop (the callee might itself use a zero-overhead loop).
To simplify the implementation of zero-overhead loops, the LBEG address, which is the
LOOP instruction address plus three, must be such that the first instruction must entirely
fit within a naturally aligned four byte region or, if the instruction is larger than four bytes,
a naturally aligned region which is the next power of two equal to or larger than the
instruction. When the LOOP instruction would not naturally be placed at such an
address, the insertion of NOP instructions or adjustment of which instructions are 16-bit
density instructions is sufficient to give it the required alignment.
The automatic loop-back when the PC increments to match LEND is disabled when
PS.EXCM is set. This prevents non-privileged code from affecting the operation of the
privileged exception vector code.
Assembler Note
The assembler automatically aligns the LOOPGTZ instruction as required.
When the label is out of range, the assembler may insert a number of instructions to
extend the size of the loop. Prefixing the instruction mnemonic with an underscore
(_LOOPGTZ) disables this feature and forces the assembler to generate an error in this
case.
Operation
LCOUNT ← AR[s] − 1
LBEG ← PC + 3
LEND ← PC + (024||imm8) + 4
if AR[s] ≤ 032 then
nextPC ← PC + (024||imm8) + 4
endif
Exceptions
EveryInstR Group (see page 244)
Implementation Notes
In some implementations, LOOPGTZ takes an extra clock for the first loop back of certain
loops. In addition, certain instructions (such as ISYNC or a write to LEND) may cause an
additional cycle on the following loop back.
LOOPNEZ Loop if Not-Equal Zero
396 Xtensa Instruction Set Architecture (ISA) Reference Manual
Instruction Word
(RRI8)
Required Configuration Option
Loop Option (See Section 4.3.2 on page 54)
Assembler Syntax
LOOPNEZ as, label
Description
LOOPNEZ sets up a zero-overhead loop by setting the LCOUNT, LBEG, and LEND special
registers, which control instruction fetch. The loop will iterate the number of times speci-
fied by address register as with the zero value causing the loop to be skipped altogether
by branching directly to the loop end address. LCOUNT, the current loop iteration
counter, is loaded from the contents of address register as minus 1. LEND is the loop
end address and is loaded with the address of the LOOPNEZ instruction plus four plus
the zero-extended 8-bit offset encoded in the instruction (therefore, the loop code may
be up to 256 bytes in length). LBEG is loaded with the address of the following instruc-
tion (the address of the LOOPNEZ instruction plus three). LCOUNT, LEND, and LBEG are
still loaded even when the loop is skipped.
After the processor fetches an instruction that increments the PC to the value contained
in LEND, and LCOUNT is not zero, it loads the PC with the contents of LBEG and decre-
ments LCOUNT. LOOPNEZ is intended to be implemented with help from the instruction
fetch engine of the processor, and therefore should not incur a mispredict or taken
branch penalty. Branches and jumps to the address contained in LEND do not cause a
loop back, and therefore may be used to exit the loop prematurely. Similarly a return
from a call instruction as the last instruction of the loop would not trigger loop back; this
case should be avoided.
There is no mechanism to proceed to the next iteration of the loop from the middle of the
loop. The compiler may insert a branch to a NOP placed as the last instruction of the loop
to implement this function if required.
23 16 15 12 11 8 7 4 3 0
imm8 1001 s 01110110
8 4444
Loop if Not-Equal Zero LOOPNEZ
Xtensa Instruction Set Architecture (ISA) Reference Manual 397
Because LCOUNT, LBEG, and LEND are single registers, zero-overhead loops may not be
nested. Using conditional branch instructions to implement outer level loops is typically
not a performance issue. Because loops cannot be nested, it is usually inappropriate to
include a procedure call inside a loop (the callee might itself use a zero-overhead loop).
To simplify the implementation of zero-overhead loops, the LBEG address, which is the
LOOP instruction address plus three, must be such that the first instruction must entirely
fit within a naturally aligned four byte region or, if the instruction is larger than four bytes,
a naturally aligned region which is the next power of two equal to or larger than the
instruction. When the LOOP instruction would not naturally be placed at such an ad-
dress, the insertion of NOP instructions or adjustment of which instructions are 16-bit
density instructions is sufficient to give it the required alignment.
The automatic loop-back when the PC increments to match LEND is disabled when
PS.EXCM is set. This prevents non-privileged code from affecting the operation of the
privileged exception vector code.
Assembler Note
The assembler automatically aligns the LOOPNEZ instruction as required.
When the label is out of range, the assembler may insert a number of instructions to
extend the size of the loop. Prefixing the instruction mnemonic with an underscore
(_LOOPNEZ) disables this feature and forces the assembler to generate an error in this
case.
Operation
LCOUNT ← AR[s] − 1
LBEG ← PC + 3
LEND ← PC + (024||imm8) + 4)
if AR[s] = 032 then
nextPC ← PC + (024||imm8) + 4
endif
Exceptions
EveryInstR Group (see page 244)
Implementation Notes
In some implementations, LOOPNEZ takes an extra clock for the first loop back of certain
loops. In addition, certain instructions (such as ISYNC or a write to LEND) may cause an
additional cycle on the following loop back.
LSI Load Single Immediate
398 Xtensa Instruction Set Architecture (ISA) Reference Manual
Instruction Word
(RRI8)
Required Configuration Option
Floating-Point Coprocessor Option (See Section 4.3.11 on page 67)
Assembler Syntax
LSI ft, as, 0..1020
Description
LSI is a 32-bit load from memory to the floating-point register file. It forms a virtual ad-
dress by adding the contents of address register as and an 8-bit zero-extended constant
value encoded in the instruction word shifted left by two. Therefore, the offset can spec-
ify multiples of four from zero to 1020. Thirty-two bits (four bytes) are read from the
physical address. This data is then written to floating-point register ft.
If the Region Translation Option (page 156) or the MMU Option (page 158) is enabled,
the virtual address is translated to the physical address. If not, the physical address is
identical to the virtual address. If the translation or memory reference encounters an
error (for example, protection violation or non-existent memory), the processor raises
one of several exceptions (see Section 4.4.1.5 on page 89).
Without the Unaligned Exception Option (page 99), the two least significant bits of the
address are ignored. A reference to an address that is not 0 mod 4 produces the same
result as a reference to the address with the least significant bits cleared. With the Un-
aligned Exception Option, such an access raises an exception.
Assembler Note
To form a virtual address, LSI calculates the sum of address register as and the imm8
field of the instruction word times four. Therefore, the machine-code offset is in terms of
32-bit (4 byte) units. However, the assembler expects a byte offset and encodes this into
the instruction by dividing by four.
Operation
vAddr ← AR[s] + (022||imm8||02)
(mem32, error) ← Load32(vAddr)
23 16 15 12 11 8 7 4 3 0
imm8 0 0 0 0 s t 0 0 1 1
8 4444
Load Single Immediate LSI
Xtensa Instruction Set Architecture (ISA) Reference Manual 399
if error then
EXCVADDR ← vAddr
Exception (LoadStoreErrorCause)
else
FR[t] ← mem32
endif
Exceptions
Memory Load Group (see page 244)
GenExcep(Coprocessor0Disabled) if Coprocessor Option
LSIU Load Single Immediate with Update
400 Xtensa Instruction Set Architecture (ISA) Reference Manual
Instruction Word
(RRI8)
Required Configuration Option
Floating-Point Coprocessor Option (See Section 4.3.11 on page 67)
Assembler Syntax
LSIU ft, as, 0..1020
Description
LSIU is a 32-bit load from memory to the floating-point register file with base address
register update. It forms a virtual address by adding the contents of address register as
and an 8-bit zero-extended constant value encoded in the instruction word shifted left by
two. Therefore, the offset can specify multiples of four from zero to 1020. Thirty-two bits
(four bytes) are read from the physical address. This data is then written to floating-point
register ft and the virtual address is written back to address register as.
If the Region Translation Option (page 156) or the MMU Option (page 158)is enabled,
the virtual address is translated to the physical address. If not, the physical address is
identical to the virtual address. If the translation or memory reference encounters an
error (for example, protection violation or non-existent memory), the processor raises
one of several exceptions (see Section 4.4.1.5 on page 89).
Without the Unaligned Exception Option (page 99), the two least significant bits of the
address are ignored. A reference to an address that is not 0 mod 4 produces the same
result as a reference to the address with the least significant bits cleared. With the Un-
aligned Exception Option, such an access raises an exception.
Assembler Note
To form a virtual address, LSIU calculates the sum of address register as and the imm8
field of the instruction word times four. Therefore, the machine-code offset is in terms of
32-bit (4 byte) units. However, the assembler expects a byte offset and encodes this into
the instruction by dividing by four.
Operation
vAddr ← AR[s] + (022||imm8||02)
23 16 15 12 11 8 7 4 3 0
imm8 1 0 0 0 s t 0 0 1 1
8 4444
Load Single Immediate with Update LSIU
Xtensa Instruction Set Architecture (ISA) Reference Manual 401
(mem32, error) ← Load32(vAddr)
if error then
EXCVADDR ← vAddr
Exception (LoadStoreErrorCause)
else
FR[t] ← mem32
AS[s] ← vAddr
endif
Exceptions
Memory Load Group (see page 244)
GenExcep(Coprocessor0Disabled) if Coprocessor Option
LSX Load Single Indexed
402 Xtensa Instruction Set Architecture (ISA) Reference Manual
Instruction Word (RRR)
Required Configuration Option
Floating-Point Coprocessor Option (See Section 4.3.11 on page 67)
Assembler Syntax
LSX fr, as, at
Description
LSX is a 32-bit load from memory to the floating-point register file. It forms a virtual
address by adding the contents of address register as and the contents of address
register at. 32 bits (four bytes) are read from the physical address. This data is then
written to floating-point register fr.
If the Region Translation Option (page 156) or the MMU Option (page 158) is enabled,
the virtual address is translated to the physical address. If not, the physical address is
identical to the virtual address. If the translation or memory reference encounters an
error (for example, protection violation or non-existent memory), the processor raises
one of several exceptions (see Section 4.4.1.5 on page 89).
Without the Unaligned Exception Option (page 99), the two least significant bits of the
address are ignored. A reference to an address that is not 0 mod 4 produces the same
result as a reference to the address with the least significant bits cleared. With the Un-
aligned Exception Option, such an access raises an exception.
Operation
vAddr ← AR[s] + (AR[t])
(mem32, error) ← Load32(vAddr)
if error then
EXCVADDR ← vAddr
Exception (LoadStoreErrorCause)
else
FR[r] ← mem32
endif
23 20 19 16 15 12 11 8 7 4 3 0
00001000 r s t 0000
444444
Load Single Indexed LSX
Xtensa Instruction Set Architecture (ISA) Reference Manual 403
Exceptions
Memory Load Group (see page 244)
GenExcep(Coprocessor0Disabled) if Coprocessor Option
LSXU Load Single Indexed with Update
404 Xtensa Instruction Set Architecture (ISA) Reference Manual
Instruction Word (RRR)
Required Configuration Option
Floating-Point Coprocessor Option (See Section 4.3.11 on page 67)
Assembler Syntax
LSXU fr, as, at
Description
LSXU is a 32-bit load from memory to the floating-point register file with base address
register update. It forms a virtual address by adding the contents of address register as
and the contents of address register at. 32 bits (four bytes) are read from the physical
address. This data is then written to floating-point register fr and the virtual address is
written back to address register as.
If the Region Translation Option (page 156) or the MMU Option (page 158)is enabled,
the virtual address is translated to the physical address. If not, the physical address is
identical to the virtual address. If the translation or memory reference encounters an
error (for example, protection violation or non-existent memory), the processor raises
one of several exceptions (see Section 4.4.1.5 on page 89).
Without the Unaligned Exception Option (page 99), the two least significant bits of the
address are ignored. A reference to an address that is not 0 mod 4 produces the same
result as a reference to the address with the least significant bits cleared. With the Un-
aligned Exception Option, such an access raises an exception.
Operation
vAddr ← AR[s] + (AR[t])
(mem32, error) ← Load32(vAddr)
if error then
EXCVADDR ← vAddr
Exception (LoadStoreErrorCause)
else
FR[r] ← mem32
AR[s] ← vAddr
endif
23 20 19 16 15 12 11 8 7 4 3 0
00011000 r s t 0000
444444
Load Single Indexed with Update LSXU
Xtensa Instruction Set Architecture (ISA) Reference Manual 405
Exceptions
Memory Load Group (see page 244)
GenExcep(Coprocessor0Disabled) if Coprocessor Option
MADD.S Multiply and Add Single
406 Xtensa Instruction Set Architecture (ISA) Reference Manual
Instruction Word (RRR)
Required Configuration Option
Floating-Point Coprocessor Option (See Section 4.3.11 on page 67)
Assembler Syntax
MADD.S fr, fs, ft
Description
Using IEEE754 single-precision arithmetic, MADD.S multiplies the contents of floating-
point registers fs and ft, adds the product to the contents of floating-point register fr,
and then writes the sum back to floating-point register fr. The computation is performed
with no intermediate round.
Operation
FR[r] ← FR[r] +s (FR[s] ×s FR[t]) (×s does not round)
Exceptions
EveryInst Group (see page 244)
GenExcep(Coprocessor0Disabled) if Coprocessor Option
23 20 19 16 15 12 11 8 7 4 3 0
01001010 r s t 0000
444444
Maximum Value MAX
Xtensa Instruction Set Architecture (ISA) Reference Manual 407
Instruction Word (RRR)
Required Configuration Option
Miscellaneous Operations Option (See Section 4.3.8 on page 62)
Assembler Syntax
MAX ar, as, at
Description
MAX computes the maximum of the twos complement contents of address registers as
and at and writes the result to address register ar.
Operation
AR[r] ← if AR[s] < AR[t] then AR[t] else AR[s]
Exceptions
EveryInstR Group (see page 244)
23 20 19 16 15 12 11 8 7 4 3 0
01010011 r s t 0000
444444
MAXU Maximum Value Unsigned
408 Xtensa Instruction Set Architecture (ISA) Reference Manual
Instruction Word (RRR)
Required Configuration Option
Miscellaneous Operations Option (See Section 4.3.8 on page 62)
Assembler Syntax
MAXU ar, as, at
Description
MAXU computes the maximum of the unsigned contents of address registers as and at
and writes the result to address register ar.
Operation
AR[r] ← if (0||AR[s]) < (0||AR[t]) then AR[t] else AR[s]
Exceptions
EveryInstR Group (see page 244)
23 20 19 16 15 12 11 8 7 4 3 0
01110011 r s t 0000
444444
Memory Wait MEMW
Xtensa Instruction Set Architecture (ISA) Reference Manual 409
Instruction Word (RRR)
Required Configuration Option
Core Architecture (See Section 4.2 on page 50)
Assembler Syntax
MEMW
Description
MEMW ensures that all previous load, store, acquire, release, prefetch, and cache instruc-
tions perform before performing any subsequent load, store, acquire, release, prefetch,
or cache instructions. MEMW is intended to implement the volatile attribute of lan-
guages such as C and C++. The compiler should separate all volatile loads and
stores with a MEMW instruction. ISYNC should be used to cause instruction fetches to
wait as MEMW will have no effect on them.
On processor/system implementations that always reference memory in program order,
MEMW may be a no-op. Implementations that reorder load, store, or cache instructions, or
which perform merging of stores (for example, in a write buffer) must order such memo-
ry references so that all memory references executed before MEMW are performed before
any memory references that are executed after MEMW.
Because the instruction execution pipeline is implementation-specific, the operation
section below specifies only a call to the implementation’s memw function.
Operation
memw()
Exceptions
EveryInst Group (see page 244)
23 20 19 16 15 12 11 8 7 4 3 0
000000000010000011000000
444444
MIN Minimum Value
410 Xtensa Instruction Set Architecture (ISA) Reference Manual
Instruction Word (RRR)
Required Configuration Option
Miscellaneous Operations Option (See Section 4.3.8 on page 62)
Assembler Syntax
MIN ar, as, at
Description
MIN computes the minimum of the twos complement contents of address registers as
and at and writes the result to address register ar.
Operation
AR[r] ← if AR[s] < AR[t] then AR[s] else AR[t]
Exceptions
EveryInstR Group (see page 244)
23 20 19 16 15 12 11 8 7 4 3 0
01000011 r s t 0000
444444
Minimum Value Unsigned MINU
Xtensa Instruction Set Architecture (ISA) Reference Manual 411
Instruction Word (RRR)
Required Configuration Option
Miscellaneous Operations Option (See Section 4.3.8 on page 62)
Assembler Syntax
MINU ar, as, at
Description
MINU computes the minimum of the unsigned contents of address registers as and at,
and writes the result to address register ar.
Operation
AR[r] ← if (0||AR[s]) < (0||AR[t]) then AR[s] else AR[t]
Exceptions
EveryInstR Group (see page 244)
23 20 19 16 15 12 11 8 7 4 3 0
01100011 r s t 0000
444444
MOV Move
412 Xtensa Instruction Set Architecture (ISA) Reference Manual
Instruction Word (RRR)
Required Configuration Option
Assembler Macro
Assembler Syntax
MOV ar, as
Description
MOV is an assembler macro that uses the OR instruction (page 466) to move the contents
of address register as to address register ar. The assembler input
MOV ar, as
expands into
OR ar, as, as
ar and as should not specify the same register due to the MOV.N restriction.
Assembler Note
The assembler may convert MOV instructions to MOV.N when the Code Density Option is
enabled. Prefixing the MOV instruction with an underscore (_MOV) disables this optimiza-
tion and forces the assembler to generate the OR form of the instruction.
Operation
AR[r] ← AR[s]
Exceptions
EveryInstR Group (see page 244)
23 20 19 16 15 12 11 8 7 4 3 0
00100000 r s t 0000
444444
Narrow Move MOV.N
Xtensa Instruction Set Architecture (ISA) Reference Manual 413
Instruction Word (RRRN)
Required Configuration Option
Code Density Option (See Section 4.3.1 on page 53)
Assembler Syntax
MOV.N at, as
Description
MOV.N is similar in function to the assembler macro MOV, but has a 16-bit encoding.
MOV.N moves the contents of address register as to address register at.
The operation of the processor when at and as specify the same register is undefined
and reserved for future use.
Assembler Note
The assembler may convert MOV.N instructions to MOV. Prefixing the MOV.N instruction
with an underscore (_MOV.N) disables this optimization and forces the assembler to
generate the narrow form of the instruction.
Operation
AR[t] ← AR[s]
Exceptions
EveryInstR Group (see page 244)
15 12 11 8 7 4 3 0
0 0 0 0 s t 1 1 0 1
4444
MOV.S Move Single
414 Xtensa Instruction Set Architecture (ISA) Reference Manual
Instruction Word (RRR)
Required Configuration Option
Floating-Point Coprocessor Option (See Section 4.3.11 on page 67)
Assembler Syntax
MOV.S fr, fs
Description
MOV.S moves the contents of floating-point register fs to floating-point register fr. The
move is non-arithmetic; no floating-point exceptions are raised.
Operation
FR[r] ← FR[s]
Exceptions
EveryInst Group (see page 244)
GenExcep(Coprocessor0Disabled) if Coprocessor Option
23 20 19 16 15 12 11 8 7 4 3 0
11111010 r s 00000000
444444
Move if Equal to Zero MOVEQZ
Xtensa Instruction Set Architecture (ISA) Reference Manual 415
Instruction Word (RRR)
Required Configuration Option
Core Architecture (See Section 4.2 on page 50)
Assembler Syntax
MOVEQZ ar, as, at
Description
MOVEQZ performs a conditional move if equal to zero. If the contents of address register
at are zero, then the processor sets address register ar to the contents of address reg-
ister as. Otherwise, MOVEQZ performs no operation and leaves address register ar
unchanged.
The inverse of MOVEQZ is MOVNEZ.
Operation
if AR[t] = 032 then
AR[r] ← AR[s]
endif
Exceptions
EveryInstR Group (see page 244)
23 20 19 16 15 12 11 8 7 4 3 0
10000011 r s t 0000
444444
MOVEQZ.S Move Single if Equal to Zero
416 Xtensa Instruction Set Architecture (ISA) Reference Manual
Instruction Word (RRR)
Required Configuration Option
Floating-Point Coprocessor Option (See Section 4.3.11 on page 67)
Assembler Syntax
MOVEQZ.S fr, fs, at
Description
MOVEQZ.S is a conditional move between floating-point registers based on the value in
an address register. If address register at contains zero, the contents of floating-point
register fs are written to floating-point register fr. MOVEQZ.S is non-arithmetic; no
floating-point exceptions are raised.
The inverse of MOVEQZ.S is MOVNEZ.S.
Operation
if AR[t] = 032 then
FR[r] ← FR[s]
endif
Exceptions
EveryInstR Group (see page 244)
GenExcep(Coprocessor0Disabled) if Coprocessor Option
23 20 19 16 15 12 11 8 7 4 3 0
10001011 r s t 0000
444444
Move if False MOVF
Xtensa Instruction Set Architecture (ISA) Reference Manual 417
Instruction Word (RRR)
Required Configuration Option
Boolean Option (See Section 4.3.10 on page 65)
Assembler Syntax
MOVF ar, as, bt
Description
MOVF moves the contents of address register as to address register ar if Boolean regis-
ter bt is false. Address register ar is left unchanged if Boolean register bt is true.
The inverse of MOVF is MOVT.
Operation
if not BRt then
AR[r] ← AR[s]
endif
Exceptions
EveryInstR Group (see page 244)
23 20 19 16 15 12 11 8 7 4 3 0
11000011 r s t 0000
444444
MOVF.S Move Single if False
418 Xtensa Instruction Set Architecture (ISA) Reference Manual
Instruction Word (RRR)
Required Configuration Option
Floating-Point Coprocessor Option (See Section 4.3.11 on page 67)
Assembler Syntax
MOVF.S fr, fs, bt
Description
MOVF.S is a conditional move between floating-point registers based on the value in a
Boolean register. If Boolean register bt contains zero, the contents of floating-point reg-
ister fs are written to floating-point register fr. MOVF.S is non-arithmetic; no floating-
point exceptions are raised.
The inverse of MOVF.S is MOVT.S.
Operation
if not BRt then
FR[r] ← FR[s]
endif
Exceptions
EveryInst Group (see page 244)
GenExcep(Coprocessor0Disabled) if Coprocessor Option
23 20 19 16 15 12 11 8 7 4 3 0
11001011 r s t 0000
444444
Move if Greater Than or Equal to Zero MOVGEZ
Xtensa Instruction Set Architecture (ISA) Reference Manual 419
Instruction Word (RRR)
Required Configuration Option
Core Architecture (See Section 4.2 on page 50)
Assembler Syntax
MOVGEZ ar, as, at
Description
MOVGEZ performs a conditional move if greater than or equal to zero. If the contents of
address register at are greater than or equal to zero (that is, the most significant bit is
clear), then the processor sets address register ar to the contents of address register
as. Otherwise, MOVGEZ performs no operation and leaves address register ar
unchanged.
The inverse of MOVGEZ is MOVLTZ.
Operation
if AR[t]31 = 0 then
AR[r] ← AR[s]
endif
Exceptions
EveryInstR Group (see page 244)
23 20 19 16 15 12 11 8 7 4 3 0
10110011 r s t 0000
444444
MOVGEZ.S Move Single if Greater Than or Eq Zero
420 Xtensa Instruction Set Architecture (ISA) Reference Manual
Instruction Word (RRR)
Required Configuration Option
Floating-Point Coprocessor Option (See Section 4.3.11 on page 67)
Assembler Syntax
MOVGEZ.S fr, fs, at
Description
MOVGEZ.S is a conditional move between floating-point registers based on the value in
an address register. If the contents of address register at is greater than or equal to
zero (that is, the most significant bit is clear), the contents of floating-point register fs
are written to floating-point register fr. MOVGEZ.S is non-arithmetic; no floating-point
exceptions are raised.
The inverse of MOVGEZ.S is MOVLTZ.S.
Operation
if AR[t]31 = 0 then
FR[r] ← FR[s]
endif
Exceptions
EveryInstR Group (see page 244)
GenExcep(Coprocessor0Disabled) if Coprocessor Option
23 20 19 16 15 12 11 8 7 4 3 0
10111011 r s t 0000
444444
Move Immediate MOVI
Xtensa Instruction Set Architecture (ISA) Reference Manual 421
Instruction Word
(RRI8)
Required Configuration Option
Core Architecture (See Section 4.2 on page 50)
Assembler Syntax
MOVI at, -2048..2047
Description
MOVI sets address register at to a constant in the range -2048..2047 encoded in the
instruction word. The constant is stored in two non-contiguous fields of the instruction
word. The processor decodes the constant specification by concatenating the two fields
and sign-extending the 12-bit value.
Assembler Note
The assembler will convert MOVI instructions into a literal load when given an immediate
operand that evaluates to a value outside the range -2048..2047. The assembler will
convert MOVI instructions to MOVI.N when the Code Density Option is enabled and the
immediate operand falls within the available range. Prefixing the MOVI instruction with
an underscore (_MOVI) disables these features and forces the assembler to generate
an error for the first case and the wide form of the instruction for the second case.
Operation
AR[t] ← imm121120||imm12
Exceptions
EveryInstR Group (see page 244)
23 20 19 16 15 12 11 8 7 4 3 0
imm12b7..0 1 0 1 0 imm12b11..8 t 0010
8 4444
MOVI.N Narrow Move Immediate
422 Xtensa Instruction Set Architecture (ISA) Reference Manual
Instruction Word (RI7)
Required Configuration Option
Code Density Option (See Section 4.3.1 on page 53)
Assembler Syntax
MOVI.N as, -32..95
Description
MOVI.N is similar to MOVI, but has a 16-bit encoding and supports a smaller range of
constant values encoded in the instruction word.
MOVI.N sets address register as to a constant in the range -32..95 encoded in the
instruction word. The constant is stored in two non-contiguous fields of the instruction
word. The range is asymmetric around zero because positive constants are more fre-
quent than negative constants. The processor decodes the constant specification by
concatenating the two fields and sign-extending the 7-bit value with the logical and of its
two most significant bits.
Assembler Note
The assembler may convert MOVI.N instructions to MOVI. Prefixing the MOVI.N instruc-
tion with an underscore (_MOVI.N) disables this optimization and forces the assembler
to generate the narrow form of the instruction.
Operation
AR[s] ← (imm76 and imm75)25||imm7
Exceptions
EveryInstR Group (see page 244)
15 12 11 8 7 6 4 3 0
imm73..0 s 0 imm76..4 1100
4444
Move if Less Than Zero MOVLTZ
Xtensa Instruction Set Architecture (ISA) Reference Manual 423
Instruction Word (RRR)
Required Configuration Option
Core Architecture (See Section 4.2 on page 50)
Assembler Syntax
MOVLTZ ar, as, at
Description
MOVLTZ performs a conditional move if less than zero. If the contents of address register
at are less than zero (that is, the most significant bit is set), then the processor sets ad-
dress register ar to the contents of address register as. Otherwise, MOVLTZ performs
no operation and leaves address register ar unchanged.
The inverse of MOVLTZ is MOVGEZ.
Operation
if AR[t]31 ≠ 0 then
AR[r] ← AR[s]
endif
Exceptions
EveryInstR Group (see page 244)
23 20 19 16 15 12 11 8 7 4 3 0
10100011 r s t 0000
444444
MOVLTZ.S Move Single if Less Than Zero
424 Xtensa Instruction Set Architecture (ISA) Reference Manual
Instruction Word (RRR)
Required Configuration Option
Floating-Point Coprocessor Option (See Section 4.3.11 on page 67)
Assembler Syntax
MOVLTZ.S fr, fs, at
Description
MOVLTZ.S is a conditional move between floating-point registers based on the value in
an address register. If the contents of address register at is less than zero (that is, the
most significant bit is set), the contents of floating-point register fs are written to float-
ing-point register fr. MOVLTZ.S is non-arithmetic; no floating-point exceptions are
raised.
The inverse of MOVLTZ.S is MOVGEZ.S.
Operation
if AR[t]31 ≠ 0 then
FR[r] ← FR[s]
endif
Exceptions
EveryInstR Group (see page 244)
GenExcep(Coprocessor0Disabled) if Coprocessor Option
23 20 19 16 15 12 11 8 7 4 3 0
10101011 r s t 0000
444444
Move if Not-Equal to Zero MOVNEZ
Xtensa Instruction Set Architecture (ISA) Reference Manual 425
Instruction Word (RRR)
Required Configuration Option
Core Architecture (See Section 4.2 on page 50)
Assembler Syntax
MOVNEZ ar, as, at
Description
MOVNEZ performs a conditional move if not equal to zero. If the contents of address reg-
ister at are non-zero, then the processor sets address register ar to the contents of ad-
dress register as. Otherwise, MOVNEZ performs no operation and leaves address
register ar unchanged.
The inverse of MOVNEZ is MOVEQZ.
Operation
if AR[t] ≠ 032 then
AR[r] ← AR[s]
endif
Exceptions
EveryInstR Group (see page 244)
23 20 19 16 15 12 11 8 7 4 3 0
10010011 r s t 0000
444444
MOVNEZ.S Move Single if Not Equal to Zero
426 Xtensa Instruction Set Architecture (ISA) Reference Manual
Instruction Word (RRR)
Required Configuration Option
Floating-Point Coprocessor Option (See Section 4.3.11 on page 67)
Assembler Syntax
MOVNEZ.S fr, fs, at
Description
MOVNEZ.S is a conditional move between floating-point registers based on the value in
an address register. If the contents of address register at is non-zero, the contents of
floating-point register fs are written to floating-point register fr. MOVNEZ.S is non-arith-
metic; no floating-point exceptions are raised.
The inverse of MOVNEZ.S is MOVEQZ.S.
Operation
if AR[t] ≠ 032 then
FR[r] ← FR[s]
endif
Exceptions
EveryInstR Group (see page 244)
GenExcep(Coprocessor0Disabled) if Coprocessor Option
23 20 19 16 15 12 11 8 7 4 3 0
10011011 r s t 0000
444444
Move to Stack Pointer MOVSP
Xtensa Instruction Set Architecture (ISA) Reference Manual 427
Instruction Word (RRR)
Required Configuration Option
Windowed Register Option (See Section 4.7.1 on page 180)
Assembler Syntax
MOVSP at, as
Description
MOVSP provides an atomic window check and register-to-register move. If the caller’s
registers are present in the register file, this instruction simply moves the contents of
address register as to address register at. If the caller’s registers are not present,
MOVSP raises an Alloca exception.
MOVSP is typically used to perform variable-size stack frame allocation. The Xtensa ABI
specifies that the caller’s a0-a3 may be stored just below the callee’s stack pointer.
When the stack frame is extended, these values may need to be moved. They can only
be moved with interrupts and exceptions disabled. This instruction provides a mecha-
nism to test if they must be moved, and if so, to raise an exception to move the data with
interrupts and exceptions disabled. The Xtensa ABI also requires that the caller’s return
address be in a0 when MOVSP is executed.
Operation
if WindowStartWindowBase-0011..WindowBase-0001 = 03 then
Exception (AllocaCause)
else
AR[t] ← AR[s]
endif
Exceptions
EveryInstR Group (see page 244)
GenExcep(AllocaCause) if Windowed Register Option
23 20 19 16 15 12 11 8 7 4 3 0
000000000001 s t 0000
444444
MOVT Move if True
428 Xtensa Instruction Set Architecture (ISA) Reference Manual
Instruction Word (RRR)
Required Configuration Option
Boolean Option (See Section 4.3.10 on page 65)
Assembler Syntax
MOVT ar, as, bt
Description
MOVT moves the contents of address register as to address register ar if Boolean regis-
ter bt is true. Address register ar is left unchanged if Boolean register bt is false.
The inverse of MOVT is MOVF.
Operation
if BRt then
AR[r] ← AR[s]
endif
Exceptions
EveryInstR Group (see page 244)
23 20 19 16 15 12 11 8 7 4 3 0
11010011 r s t 0000
444444
Move Single if True MOVT.S
Xtensa Instruction Set Architecture (ISA) Reference Manual 429
Instruction Word (RRR)
Required Configuration Option
Floating-Point Coprocessor Option (See Section 4.3.11 on page 67)
Assembler Syntax
MOVT.S fr, fs, bt
Description
MOVT.S is a conditional move between floating-point registers based on the value in a
Boolean register. If Boolean register bt is set, the contents of floating-point register fs
are written to floating-point register fr. MOVT.S is non-arithmetic; no floating-point
exceptions are raised.
The inverse of MOVT.S is MOVF.S.
Operation
if BRt then
FR[r] ← FR[s]
endif
Exceptions
EveryInst Group (see page 244)
GenExcep(Coprocessor0Disabled) if Coprocessor Option
23 20 19 16 15 12 11 8 7 4 3 0
11011011 r s t 0000
444444
MSUB.S Multiply and Subtract Single
430 Xtensa Instruction Set Architecture (ISA) Reference Manual
Instruction Word (RRR)
Required Configuration Option
Floating-Point Coprocessor Option (See Section 4.3.11 on page 67)
Assembler Syntax
MSUB.S fr, fs, ft
Description
MSUB.S multiplies the contents of floating-point registers fs and ft, subtracts the prod-
uct from the contents of floating-point register fr, and then writes the difference back to
floating-point register fr. The computation is performed with no intermediate round.
Operation
FR[r] ← FR[r] −s (FR[s] ×s FR[t]) (×s does not round)
Exceptions
EveryInst Group (see page 244)
GenExcep(Coprocessor0Disabled) if Coprocessor Option
23 20 19 16 15 12 11 8 7 4 3 0
01011010 r s t 0000
444444
Signed Multiply MUL.AA.*
Xtensa Instruction Set Architecture (ISA) Reference Manual 431
Instruction Word (RRR)
Required Configuration Option
MAC16 Option (See Section 4.3.7 on page 60)
Assembler Syntax
MUL.AA.* as, at
Where * expands as follows:
MUL.AA.LL - for (half=0)
MUL.AA.HL - for (half=1)
MUL.AA.LH - for (half=2)
MUL.AA.HH - for (half=3)
Description
MUL.AA.* performs a two’s complement multiply of half of each of the address registers
as and at, producing a 32-bit result. The result is sign-extended to 40 bits and written to
the MAC16 accumulator.
Operation
m1 ← if half0 then AR[s]31..16 else AR[s]15..0
m2 ← if half1 then AR[t]31..16 else AR[t]15..0
ACC ← (m11524||m1) × (m21524||m2)
Exceptions
EveryInstR Group (see page 244)
23 20 19 16 15 12 11 8 7 4 3 0
011101 half 0 0 0 0 s t 0 1 0 0
444444
MUL.AD.* Signed Multiply
432 Xtensa Instruction Set Architecture (ISA) Reference Manual
Instruction Word (RRR)
Required Configuration Option
MAC16 Option (See Section 4.3.7 on page 60)
Assembler Syntax
MUL.AD.* as, my
Where * expands as follows:
MUL.AD.LL - for (half=0)
MUL.AD.HL - for (half=1)
MUL.AD.LH - for (half=2)
MUL.AD.HH - for (half=3)
Description
MUL.AD.* performs a two’s complement multiply of half of address register as and half
of MAC16 register my, producing a 32-bit result. The result is sign-extended to 40 bits
and written to the MAC16 accumulator. The my operand can designate either MAC16
register m2 or m3.
Operation
m1 ← if half0 then AR[s]31..16 else AR[s]15..0
m2 ← if half1 then MR[1||y]31..16 else MR[1||y]15..0
ACC ← (m11524||m1) × (m21524||m2)
Exceptions
EveryInstR Group (see page 244)
23 20 19 16 15 12 11 8 7 4 3 0
001101 half 0000 s 0y000100
444444
Signed Multiply MUL.DA.*
Xtensa Instruction Set Architecture (ISA) Reference Manual 433
Instruction Word (RRR)
Required Configuration Option
MAC16 Option (See Section 4.3.7 on page 60)
Assembler Syntax
MUL.DA.* mx, at
Where * expands as follows:
MUL.DA.LL - for (half=0)
MUL.DA.HL - for (half=1)
MUL.DA.LH - for (half=2)
MUL.DA.HH - for (half=3)
Description
MUL.DA.* performs a two’s complement multiply of half of MAC16 register mx and half
of address register at, producing a 32-bit result. The result is sign-extended to 40 bits
and written to the MAC16 accumulator. The mx operand can designate either MAC16
register m0 or m1.
Operation
m1 ← if half0 then MR[0||x]31..16 else MR[0||x]15..0
m2 ← if half1 then AR[t]31..16 else AR[t]15..0
ACC ← (m11524||m1) × (m21524||m2)
Exceptions
EveryInstR Group (see page 244)
23 20 19 16 15 12 11 8 7 4 3 0
011001 half 0x000000 t 0100
444444
MUL.DD.* Signed Multiply
434 Xtensa Instruction Set Architecture (ISA) Reference Manual
Instruction Word (RRR)
Required Configuration Option
MAC16 Option (See Section 4.3.7 on page 60)
Assembler Syntax
MUL.DD.* mx, my
Where * expands as follows:
MUL.DD.LL - for (half=0)
MUL.DD.HL - for (half=1)
MUL.DD.LH - for (half=2)
MUL.DD.HH - for (half=3)
Description
MUL.DD.* performs a two’s complement multiply of half of the MAC16 registers mx and
my, producing a 32-bit result. The result is sign-extended to 40 bits and written to the
MAC16 accumulator. The mx operand can designate either MAC16 register m0 or m1.
The my operand can designate either MAC16 register m2 or m3.
Operation
m1 ← if half0 then MR[0||x]31..16 else MR[0||x]15..0
m2 ← if half1 then MR[1||y]31..16 else MR[1||y]15..0
ACC ← (m11524||m1) × (m21524||m2)
Exceptions
EveryInst Group (see page 244)
23 20 19 16 15 12 11 8 7 4 3 0
001001 half 0x0000000y000100
444444
Multiply Single MUL.S
Xtensa Instruction Set Architecture (ISA) Reference Manual 435
Instruction Word (RRR)
Required Configuration Option
Floating-Point Coprocessor Option (See Section 4.3.11 on page 67)
Assembler Syntax
MUL.S fr, fs, ft
Description
MUL.S computes the IEEE754 single-precision product of the contents of floating-point
registers fs and ft and writes the result to floating-point register fr.
Operation
FR[r] ← FR[s] ×s FR[t]
Exceptions
EveryInst Group (see page 244)
GenExcep(Coprocessor0Disabled) if Coprocessor Option
23 20 19 16 15 12 11 8 7 4 3 0
00101010 r s t 0000
444444
MUL16S Multiply 16-bit Signed
436 Xtensa Instruction Set Architecture (ISA) Reference Manual
Instruction Word (RRR)
Required Configuration Option
16-bit Integer Multiply Option (See Section 4.3.4 on page 57)
Assembler Syntax
MUL16S ar, as, at
Description
MUL16S performs a two’s complement multiplication of the least-significant 16 bits of the
contents of address registers as and at and writes the 32-bit product to address regis-
ter ar.
Operation
AR[r] ← (AR[s]1516||AR[s]15..0) × (AR[t]1516||AR[t]15..0)
Exceptions
EveryInstR Group (see page 244)
23 20 19 16 15 12 11 8 7 4 3 0
11010001 r s t 0000
444444
Multiply 16-bit Unsigned MUL16U
Xtensa Instruction Set Architecture (ISA) Reference Manual 437
Instruction Word (RRR)
Required Configuration Option
16-bit Integer Multiply Option (See Section 4.3.4 on page 57)
Assembler Syntax
MUL16U ar, as, at
Description
MUL16U performs an unsigned multiplication of the least-significant 16 bits of the con-
tents of address registers as and at and writes the 32-bit product to address register
ar.
Operation
AR[r] ← (016||AR[s]15..0) × (016||AR[t]15..0)
Exceptions
EveryInstR Group (see page 244)
23 20 19 16 15 12 11 8 7 4 3 0
11000001 r s t 0000
444444
MULA.AA.* Signed Multiply/Accumulate
438 Xtensa Instruction Set Architecture (ISA) Reference Manual
Instruction Word (RRR)
Required Configuration Option
MAC16 Option (See Section 4.3.7 on page 60)
Assembler Syntax
MULA.AA.* as, at
Where * expands as follows:
MULA.AA.LL - for (half=0)
MULA.AA.HL - for (half=1)
MULA.AA.LH - for (half=2)
MULA.AA.HH - for (half=3)
Description
MULA.AA.* performs a two’s complement multiply of half of each of the address regis-
ters as and at, producing a 32-bit result. The result is sign-extended to 40 bits and add-
ed to the contents of the MAC16 accumulator.
Operation
m1 ← if half0 then AR[s]31..16 else AR[s]15..0
m2 ← if half1 then AR[t]31..16 else AR[t]15..0
ACC ← ACC + (m11524||m1) × (m21524||m2)
Exceptions
EveryInstR Group (see page 244)
23 20 19 16 15 12 11 8 7 4 3 0
011110 half 0 0 0 0 s t 0 1 0 0
4 4 4 4 4 4
Signed Multiply/Accumulate MULA.AD.*
Xtensa Instruction Set Architecture (ISA) Reference Manual 439
Instruction Word (RRR)
Required Configuration Option
MAC16 Option (See Section 4.3.7 on page 60)
Assembler Syntax
MULA.AD.* as, my
Where * expands as follows:
MULA.AD.LL - for (half=0)
MULA.AD.HL - for (half=1)
MULA.AD.LH - for (half=2)
MULA.AD.HH - for (half=3)
Description
MULA.AD.* performs a two’s complement multiply of half of address register as and
half of MAC16 register my, producing a 32-bit result. The result is sign-extended to 40
bits and added to the contents of the MAC16 accumulator. The my operand can desig-
nate either MAC16 register m2 or m3.
Operation
m1 ← if half0 then AR[s]31..16 else AR[s]15..0
m2 ← if half1 then MR[1||y]31..16 else MR[1||y]15..0
ACC ← ACC + (m11524||m1) × (m21524||m2)
Exceptions
EveryInstR Group (see page 244)
23 20 19 16 15 12 11 8 7 4 3 0
001110 half 0000 s 0y000100
444444
MULA.DA.* Signed Multiply/Accumulate
440 Xtensa Instruction Set Architecture (ISA) Reference Manual
Instruction Word (RRR)
Required Configuration Option
MAC16 Option (See Section 4.3.7 on page 60)
Assembler Syntax
MULA.DA.* mx, at
Where * expands as follows:
MULA.DA.LL - for (half=0)
MULA.DA.HL - for (half=1)
MULA.DA.LH - for (half=2)
MULA.DA.HH - for (half=3)
Description
MULA.DA.* performs a two’s complement multiply of half of MAC16 register mx and half
of address register at, producing a 32-bit result. The result is sign-extended to 40 bits
and added to the contents of the MAC16 accumulator. The mx operand can designate
either MAC16 register m0 or m1.
Operation
m1 ← if half0 then MR[0||x]31..16 else MR[0||x]15..0
m2 ← if half1 then AR[t]31..16 else AR[t]15..0
ACC ← ACC + (m11524||m1) × (m21524||m2)
Exceptions
EveryInstR Group (see page 244)
23 20 19 16 15 12 11 8 7 4 3 0
011010 half 0x000000 t 0100
444444
Signed Mult/Accum, Ld/Autodec MULA.DA.*.LDDEC
Xtensa Instruction Set Architecture (ISA) Reference Manual 441
Instruction Word (RRR)
Required Configuration Option
MAC16 Option (See Section 4.3.7 on page 60)
Assembler Syntax
MULA.DA.*.LDDEC mw, as, mx, at
Where * expands as follows:
MULA.DA.LL.LDDEC - for (half=0)
MULA.DA.HL.LDDEC - for (half=1)
MULA.DA.LH.LDDEC - for (half=2)
MULA.DA.HH.LDDEC - for (half=3)
Description
MULA.DA.*.LDDEC performs a parallel load and multiply/accumulate.
First, it performs a two’s complement multiply of half of MAC16 register mx and half of
address register at, producing a 32-bit result. The result is sign-extended to 40 bits and
added to the contents of the MAC16 accumulator. The mx operand can designate either
MAC16 register m0 or m1.
Next, it loads MAC16 register mw from memory using auto-decrement addressing. It
forms a virtual address by subtracting 4 from the contents of address register as. Thirty-
two bits (four bytes) are read from the physical address. This data is then written to
MAC16 register mw, and the virtual address is written back to address register as. The
mw operand can designate any of the four MAC16 registers.
If the Region Translation Option (page 156) or the MMU Option (page 158) is enabled,
the virtual address is translated to the physical address. If not, the physical address is
identical to the virtual address. If the translation or memory reference encounters an
error (for example, protection violation or non-existent memory), the processor raises
one of several exceptions (see Section 4.4.1.5 on page 89).
23 20 19 16 15 12 11 8 7 4 3 0
010110 half 0 x w s t 0 1 0 0
444444
MULA.DA.*.LDDEC Signed Mult/Accum, Ld/Autodec
442 Xtensa Instruction Set Architecture (ISA) Reference Manual
Without the Unaligned Exception Option (page 99), the two least significant bits of the
address are ignored. A reference to an address that is not 0 mod 4 produces the same
result as a reference to the address with the least significant bits cleared. With the Un-
aligned Exception Option, such an access raises an exception.
The MAC16 register source mx and the MAC16 register destination mw may be the
same. In this case, the instruction uses the contents of mx as the source operand prior to
loading mx with the load data.
Operation
vAddr ← AR[s] − 4
(mem32, error) ← Load32(vAddr)
if error then
EXCVADDR ← vAddr
Exception (LoadStoreErrorCause)
else
m1 ← if half0 then MR[0||x]31..16 else MR[0||x]15..0
m2 ← if half1 then AR[t]31..16 else AR[t]15..0
ACC ← ACC + (m11524||m1) × (m21524||m2)
AR[s] ← vAddr
MR[w] ← mem32
endif
Exceptions
Memory Load Group (see page 244)
Signed Mult/Accum, Ld/Autoinc MULA.DA.*.LDINC
Xtensa Instruction Set Architecture (ISA) Reference Manual 443
Instruction Word (RRR)
Required Configuration Option
MAC16 Option (See Section 4.3.7 on page 60)
Assembler Syntax
MULA.DA.*.LDINC mw, as, mx, at
Where * expands as follows:
MULA.DA.LL.LDINC - for (half=0)
MULA.DA.HL.LDINC - for (half=1)
MULA.DA.LH.LDINC - for (half=2)
MULA.DA.HH.LDINC - for (half=3)
Description
MULA.DA.*.LDINC performs a parallel load and multiply/accumulate.
First, it performs a two’s complement multiply of half of MAC16 register mx and half of
address register at, producing a 32-bit result. The result is sign-extended to 40 bits and
added to the contents of the MAC16 accumulator. The mx operand can designate either
MAC16 register m0 or m1.
Next, it loads MAC16 register mw from memory using auto-increment addressing. It
forms a virtual address by adding 4 to the contents of address register as. 32 bits (four
bytes) are read from the physical address. This data is then written to MAC16 register
mw, and the virtual address is written back to address register as. The mw operand can
designate any of the four MAC16 registers.
If the Region Translation Option (page 156) or the MMU Option (page 158)is enabled,
the virtual address is translated to the physical address. If not, the physical address is
identical to the virtual address. If the translation or memory reference encounters an
error (for example, protection violation or non-existent memory), the processor raises
one of several exceptions (see Section 4.4.1.5 on page 89).
23 20 19 16 15 12 11 8 7 4 3 0
010010 half 0 x w s t 0 1 0 0
444444
MULA.DA.*.LDINC Signed Mult/Accum, Ld/Autoinc
444 Xtensa Instruction Set Architecture (ISA) Reference Manual
Without the Unaligned Exception Option (page 99), the two least significant bits of the
address are ignored. A reference to an address that is not 0 mod 4 produces the same
result as a reference to the address with the least significant bits cleared. With the Un-
aligned Exception Option, such an access raises an exception.
The MAC16 register source mx and the MAC16 register destination mw may be the
same. In this case, the instruction uses the contents of mx as the source operand prior to
loading mx with the load data.
Operation
vAddr ← AR[s] + 4
(mem32, error) ← Load32(vAddr)
if error then
EXCVADDR ← vAddr
Exception (LoadStoreErrorCause)
else
m1 ← if half0 then MR[0||x]31..16 else MR[0||x]15..0
m2 ← if half1 then AR[t]31..16 else AR[t]15..0
ACC ← ACC + (m11524||m1) × (m21524||m2)
AR[s] ← vAddr
MR[w] ← mem32
endif
Exceptions
Memory Load Group (see page 244)
Signed Multiply/Accumulate MULA.DD.*
Xtensa Instruction Set Architecture (ISA) Reference Manual 445
Instruction Word (RRR)
Required Configuration Option
MAC16 Option (See Section 4.3.7 on page 60)
Assembler Syntax
MULA.DD.* mx, my
Where * expands as follows:
MULA.DD.LL - for (half=0)
MULA.DD.HL - for (half=1)
MULA.DD.LH - for (half=2)
MULA.DD.HH - for (half=3)
Description
MULA.DD.* performs a two’s complement multiply of half of each of the MAC16 regis-
ters mx and my, producing a 32-bit result. The result is sign-extended to 40 bits and add-
ed to the contents of the MAC16 accumulator. The mx operand can designate either
MAC16 register m0 or m1. The my operand can designate either MAC16 register m2 or
m3.
Operation
m1 ← if half0 then MR[0||x]31..16 else MR[0||x]15..0
m2 ← if half1 then MR[1||y]31..16 else MR[1||y]15..0
ACC ← ACC + (m11524||m1) × (m21524||m2)
Exceptions
EveryInst Group (see page 244)
23 20 19 16 15 12 11 8 7 4 3 0
001010 half 0x0000000y000100
444444
MULA.DD.*.LDDEC Signed Mult/Accum, Ld/Autodec
446 Xtensa Instruction Set Architecture (ISA) Reference Manual
Instruction Word (RRR)
Required Configuration Option
MAC16 Option (See Section 4.3.7 on page 60)
Assembler Syntax
MULA.DD.*.LDDEC mw, as, mx, my
Where * expands as follows:
MULA.DD.LL.LDDEC - for (half=0)
MULA.DD.HL.LDDEC - for (half=1)
MULA.DD.LH.LDDEC - for (half=2)
MULA.DD.HH.LDDEC - for (half=3)
Description
MULA.DD.*.LDDEC performs a parallel load and multiply/accumulate.
First, it performs a two’s complement multiply of half of the MAC16 registers mx and my,
producing a 32-bit result. The result is sign-extended to 40 bits and added to the con-
tents of the MAC16 accumulator. The mx operand can designate either MAC16 register
m0 or m1. The my operand can designate either MAC16 register m2 or m3.
Next, it loads MAC16 register mw from memory using auto-decrement addressing. It
forms a virtual address by subtracting 4 from the contents of address register as. Thirty-
two bits (four bytes) are read from the physical address. This data is then written to
MAC16 register mw, and the virtual address is written back to address register as. The
mw operand can designate any of the four MAC16 registers.
If the Region Translation Option (page 156) or the MMU Option (page 158) is enabled,
the virtual address is translated to the physical address. If not, the physical address is
identical to the virtual address. If the translation or memory reference encounters an
error (for example, protection violation or non-existent memory), the processor raises
one of several exceptions (see Section 4.4.1.5 on page 89).
23 20 19 16 15 12 11 8 7 4 3 0
000110 half 0 x w s 0 y 0 0 0 1 0 0
444444
Signed Mult/Accum, Ld/Autodec MULA.DD.*.LDDEC
Xtensa Instruction Set Architecture (ISA) Reference Manual 447
Without the Unaligned Exception Option (page 99), the two least significant bits of the
address are ignored. A reference to an address that is not 0 mod 4 produces the same
result as a reference to the address with the least significant bits cleared. With the Un-
aligned Exception Option, such an access raises an exception.
The MAC16 register destination mw may be the same as either MAC16 register source
mx or my. In this case, the instruction uses the contents of mx and my as the source oper-
ands prior to loading mw with the load data.
Operation
vAddr ← AR[s] − 4
(mem32, error) ← Load32(vAddr)
if error then
EXCVADDR ← vAddr
Exception (LoadStoreErrorCause)
else
m1 ← if half0 then MR[0||x]31..16 else MR[0||x]15..0
m2 ← if half1 then MR[1||y]31..16 else MR[1||y]15..0
ACC ← ACC + (m11524||m1) × (m21524||m2)
AR[s] ← vAddr
MR[w] ← mem32
endif
Exceptions
Memory Load Group (see page 244)
MULA.DD.*.LDINC Signed Mult/Accum, Ld/Autoinc
448 Xtensa Instruction Set Architecture (ISA) Reference Manual
Instruction Word (RRR)
Required Configuration Option
MAC16 Option (See Section 4.3.7 on page 60)
Assembler Syntax
MULA.DD.*.LDINC mw, as, mx, my
Where * expands as follows:
MULA.DD.LL.LDINC - for (half=0)
MULA.DD.HL.LDINC - for (half=1)
MULA.DD.LH.LDINC - for (half=2)
MULA.DD.HH.LDINC - for (half=3)
Description
MULA.DD.*.LDINC performs a parallel load and multiply/accumulate.
First, it performs a two’s complement multiply of half of each of the MAC16 registers mx
and my, producing a 32-bit result. The result is sign-extended to 40 bits and added to the
contents of the MAC16 accumulator. The mx operand can designate either MAC16 reg-
ister m0 or m1. The my operand can designate either MAC16 register m2 or m3.
Next, it loads MAC16 register mw from memory using auto-increment addressing. It
forms a virtual address by adding 4 to the contents of address register as. Thirty-two
bits (four bytes) are read from the physical address. This data is then written to MAC16
register mw, and the virtual address is written back to address register as. The mw oper-
and can designate any of the four MAC16 registers.
If the Region Translation Option (page 156) or the MMU Option (page 158) is enabled,
the virtual address is translated to the physical address. If not, the physical address is
identical to the virtual address. If the translation or memory reference encounters an
error (for example, protection violation or non-existent memory), the processor raises
one of several exceptions (see Section 4.4.1.5 on page 89).
23 20 19 16 15 12 11 8 7 4 3 0
000010 half 0 x w s 0 y 0 0 0 1 0 0
444444
Signed Mult/Accum, Ld/Autoinc MULA.DD.*.LDINC
Xtensa Instruction Set Architecture (ISA) Reference Manual 449
Without the Unaligned Exception Option (page 99), the two least significant bits of the
address are ignored. A reference to an address that is not 0 mod 4 produces the same
result as a reference to the address with the least significant bits cleared. With the Un-
aligned Exception Option, such an access raises an exception.
The MAC16 register destination mw may be the same as either MAC16 register source
mx or my. In this case, the instruction uses the contents of mx and my as the source
operands prior to loading mw with the load data.
Operation
vAddr ← AR[s] + 4
(mem32, error) ← Load32(vAddr)
if error then
EXCVADDR ← vAddr
Exception (LoadStoreErrorCause)
else
m1 ← if half0 then MR[0||x]31..16 else MR[0||x]15..0
m2 ← if half1 then MR[1||y]31..16 else MR[1||y]15..0
ACC ← ACC + (m11524||m1) × (m21524||m2)
AR[s] ← vAddr
MR[w] ← mem32
endif
Exceptions
Memory Load Group (see page 244)
MULL Multiply Low
450 Xtensa Instruction Set Architecture (ISA) Reference Manual
Instruction Word (RRR)
Required Configuration Option
32-bit Integer Multiply Option (See Section 4.3.5 on page 58)
Assembler Syntax
MULL ar, as, at
Description
MULL performs a 32-bit multiplication of the contents of address registers as and at,
and writes the least significant 32 bits of the product to address register ar. Because the
least significant product bits are unaffected by the multiplicand and multiplier sign, MULL
is useful for both signed and unsigned multiplication.
Operation
AR[r] ← AR[s] × AR[t]
Exceptions
EveryInstR Group (see page 244)
23 20 19 16 15 12 11 8 7 4 3 0
10000010 r s t 0000
444444
Signed Multiply/Subtract MULS.AA.*
Xtensa Instruction Set Architecture (ISA) Reference Manual 451
Instruction Word (RRR)
Required Configuration Option
MAC16 Option (See Section 4.3.7 on page 60)
Assembler Syntax
MULS.AA.* as, at
Where * expands as follows:
MULS.AA.LL - for (half=0)
MULS.AA.HL - for (half=1)
MULS.AA.LH - for (half=2)
MULS.AA.HH - for (half=3)
Description
MULS.AA.* performs a two’s complement multiply of half of each of the address regis-
ters as and at, producing a 32-bit result. The result is sign-extended to 40 bits and
subtracted from the contents of the MAC16 accumulator.
Operation
m1 ← if half0 then AR[s]31..16 else AR[s]15..0
m2 ← if half1 then AR[t]31..16 else AR[t]15..0
ACC ← ACC − (m11524||m1) × (m21524||m2)
Exceptions
EveryInstR Group (see page 244)
23 20 19 16 15 12 11 8 7 4 3 0
011111 half 0 0 0 0 s t 0 1 0 0
444444
MULS.AD.* Signed Multiply/Subtract
452 Xtensa Instruction Set Architecture (ISA) Reference Manual
Instruction Word (RRR)
Required Configuration Option
MAC16 Option (See Section 4.3.7 on page 60)
Assembler Syntax
MULS.AD.* as, my
Where * expands as follows:
MULS.AD.LL - for (half=0)
MULS.AD.HL - for (half=1)
MULS.AD.LH - for (half=2)
MULS.AD.HH - for (half=3)
Description
MULS.AD.* performs a two’s complement multiply of half of address register as and
half of MAC16 register my, producing a 32-bit result. The result is sign-extended to 40
bits and subtracted from the contents of the MAC16 accumulator. The my operand can
designate either MAC16 register m2 or m3.
Operation
m1 ← if half0 then AR[s]31..16 else AR[s]15..0
m2 ← if half1 then MR[1||y]31..16 else MR[1||y]15..0
ACC ← ACC − (m11524||m1) × (m21524||m2)
Exceptions
EveryInstR Group (see page 244)
23 20 19 16 15 12 11 8 7 4 3 0
001111 half 0000 s 0y000100
444444
Signed Multiply/Subtract MULS.DA.*
Xtensa Instruction Set Architecture (ISA) Reference Manual 453
Instruction Word (RRR)
Required Configuration Option
MAC16 Option (See Section 4.3.7 on page 60)
Assembler Syntax
MULS.DA.* mx, at
Where * expands as follows:
MULS.DA.LL - for (half=0)
MULS.DA.HL - for (half=1)
MULS.DA.LH - for (half=2)
MULS.DA.HH - for (half=3)
Description
MULS.DA.* performs a two’s complement multiply of half of MAC16 register mx and half
of address register at, producing a 32-bit result. The result is sign-extended to 40 bits
and subtracted from the contents of the MAC16 accumulator. The mx operand can
designate either MAC16 register m0 or m1.
Operation
m1 ← if half0 then MR[0||x]31..16 else MR[0||x]15..0
m2 ← if half1 then AR[t]31..16 else AR[t]15..0
ACC ← ACC − (m11524||m1) × (m21524||m2)
Exceptions
EveryInstR Group (see page 244)
23 20 19 16 15 12 11 8 7 4 3 0
011011 half 0x000000 t 0100
444444
MULS.DD.* Signed Multiply/Subtract
454 Xtensa Instruction Set Architecture (ISA) Reference Manual
Instruction Word (RRR)
Required Configuration Option
MAC16 Option (See Section 4.3.7 on page 60)
Assembler Syntax
MULS.DD.* mx, my
Where * expands as follows:
MULS.DD.LL - for (half=0)
MULS.DD.HL - for (half=1)
MULS.DD.LH - for (half=2)
MULS.DD.HH - for (half=3)
Description
MULS.DD.* performs a two’s complement multiply of half of each of MAC16 registers
mx and my, producing a 32-bit result. The result is sign-extended to 40 bits and subtract-
ed from the contents of the MAC16 accumulator. The mx operand can designate either
MAC16 register m0 or m1. The my operand can designate either MAC16 register m2 or
m3.
Operation
m1 ← if half0 then MR[0||x]31..16 else MR[0||x]15..0
m2 ← if half1 then MR[1||y]31..16 else MR[1||y]15..0
ACC ← ACC − (m11524||m1) × (m21524||m2)
Exceptions
EveryInst Group (see page 244)
23 20 19 16 15 12 11 8 7 4 3 0
001011 half 0x0000000y000100
444444
Multiply Signed High MULSH
Xtensa Instruction Set Architecture (ISA) Reference Manual 455
Instruction Word (RRR)
Required Configuration Option
32-bit Integer Multiply Option (See Section 4.3.5 on page 58)
Assembler Syntax
MULSH ar, as, at
Description
MULSH performs a 32-bit two’s complement multiplication of the contents of address reg-
isters as and at and writes the most significant 32 bits of the product to address register
ar.
Operation
tp ← (AR[s]3132||AR[s]) × (AR[t]3132||AR[t])
AR[r] ← tp63..32
Exceptions
EveryInstR Group (see page 244)
23 20 19 16 15 12 11 8 7 4 3 0
10110010 r s t 0000
444444
MULUH Multiply Unsigned High
456 Xtensa Instruction Set Architecture (ISA) Reference Manual
Instruction Word (RRR)
Required Configuration Option
32-bit Integer Multiply Option (See Section 4.3.5 on page 58)
Assembler Syntax
MULUH ar, as, at
Description
MULUH performs an unsigned multiplication of the contents of address registers as and
at, and writes the most significant 32 bits of the product to address register ar.
Operation
tp ← (032||AR[s]) × (032||AR[t])
AR[r] ← tp63..32
Exceptions
EveryInstR Group (see page 244)
23 20 19 16 15 12 11 8 7 4 3 0
10100010 r s t 0000
444444
Negate NEG
Xtensa Instruction Set Architecture (ISA) Reference Manual 457
Instruction Word (RRR)
Required Configuration Option
Core Architecture (See Section 4.2 on page 50)
Assembler Syntax
NEG ar, at
Description
NEG calculates the two’s complement negation of the contents of address register at
and writes it to address register ar. Arithmetic overflow is not detected.
Operation
AR[r] ← 0 − AR[t]
Exceptions
EveryInstR Group (see page 244)
23 20 19 16 15 12 11 8 7 4 3 0
01100000 r 0000 t 0000
444444
NEG.S Negate Single
458 Xtensa Instruction Set Architecture (ISA) Reference Manual
Instruction Word (RRR)
Required Configuration Option
Floating-Point Coprocessor Option (See Section 4.3.11 on page 67)
Assembler Syntax
NEG.S fr, fs
Description
NEG.S negates the single-precision value of the contents of floating-point register fs
and writes the result to floating-point register fr.
Operation
FR[r] ← −s FR[s]
Exceptions
EveryInst Group (see page 244)
GenExcep(Coprocessor0Disabled) if Coprocessor Option
23 20 19 16 15 12 11 8 7 4 3 0
11111010 r s 01100000
444444
No-Operation NOP
Xtensa Instruction Set Architecture (ISA) Reference Manual 459
Instruction Word (RRR)
Required Configuration Option
Core Architecture (See Section 4.2 on page 50)
Assembler Syntax
NOP
Description
This instruction performs no operation. It is typically used for instruction alignment. NOP
is a 24-bit instruction. For a 16-bit version, see NOP.N.
Assembler Note
The assembler may convert NOP instructions to NOP.N when the Code Density Option is
enabled. Prefixing the NOP instruction with an underscore (_NOP) disables this optimiza-
tion and forces the assembler to generate the wide form of the instruction.
Operation
none
Exceptions
EveryInst Group (see page 244)
Implementation Notes
In some implementations NOP is not an instruction but only an assembler macro that
uses the instruction “OR An, An, An” (with An a convenient register).
23 20 19 16 15 12 11 8 7 4 3 0
000000000010000011110000
444444
NOP.N Narrow No-Operation
460 Xtensa Instruction Set Architecture (ISA) Reference Manual
Instruction Word (RRRN)
Required Configuration Option
Code Density Option (See Section 4.3.1 on page 53)
Assembler Syntax
NOP.N
Description
This instruction performs no operation. It is typically used for instruction alignment.
NOP.N is a 16-bit instruction. For a 24-bit version, see NOP.
Assembler Note
The assembler may convert NOP.N instructions to NOP. Prefixing the NOP.N instruction
with an underscore (_NOP.N) disables this optimization and forces the assembler to
generate the narrow form of the instruction.
Operation
none
Exceptions
EveryInst Group (see page 244)
15 12 11 8 7 4 3 0
1111000000111101
4444
Normalization Shift Amount NSA
Xtensa Instruction Set Architecture (ISA) Reference Manual 461
Instruction Word (RRR)
Required Configuration Option
Miscellaneous Operations Option (See Section 4.3.8 on page 62)
Assembler Syntax
NSA at, as
Description
NSA calculates the left shift amount that will normalize the twos complement contents of
address register as and writes this amount (in the range 0 to 31) to address register at.
If as contains 0 or -1, NSA returns 31. Using SSL and SLL to shift as left by the NSA
result yields the smallest value for which bits 31 and 30 differ unless as contains 0.
Operation
sign ← AR[s]31
if AR[s]30..0 = sign31 then
AR[t] ← 31
else
b4 ← AR[s]30..16 = sign15
t3 ← if b4 then AR[s]15..0 else AR[s]31..16
b3 ← t315..8 = sign8
t2 ← if b3 then t37..0 else t315..8
b2 ← t37..4 = sign4
t1 ← if b2 then t23..0 else t27..4
b1 ← t33..2 = sign2
b0 ← if b1 then t11 = sign else t13 = sign
AR[t] ← 027||((b4||b3||b2||b1||b0) − 1)
endif
Exceptions
EveryInstR Group (see page 244)
23 20 19 16 15 12 11 8 7 4 3 0
010000001110 s t 0000
444444
NSAU Normalization Shift Amount Unsigned
462 Xtensa Instruction Set Architecture (ISA) Reference Manual
Instruction Word (RRR)
Required Configuration Option
Miscellaneous Operations Option (See Section 4.3.8 on page 62)
Assembler Syntax
NSAU at, as
Description
NSAU calculates the left shift amount that will normalize the unsigned contents of
address register as and writes this amount (in the range 0 to 32) to address register at.
If as contains 0, NSAU returns 32. Using SSL and SLL to shift as left by the NSAU result
yields the smallest value for which bit 31 is set, unless as contains 0.
Operation
if AR[s] = 032 then
AR[t] ← 32
else
b4 ← AR[s]31..16 = 016
t3 ← if b4 then AR[s]15..0 else AR[s]31..16
b3 ← t315..8 = 08
t2 ← if b3 then t37..0 else t315..8
b2 ← t27..4 = 04
t1 ← if b2 then t23..0 else t27..4
b1 ← t13..2 = 02
b0 ← if b1 then t11 = 0 else t13 = 0
AR[t] ← 027||b4||b3||b2||b1||b0
endif
Exceptions
EveryInstR Group (see page 244)
23 20 19 16 15 12 11 8 7 4 3 0
010000001111 s t 0000
444444
Compare Single Equal OEQ.S
Xtensa Instruction Set Architecture (ISA) Reference Manual 463
Instruction Word (RRR)
Required Configuration Option
Floating-Point Coprocessor Option (See Section 4.3.11 on page 67)
Assembler Syntax
OEQ.S br, fs, ft
Description
OEQ.S compares the contents of floating-point registers fs and ft for IEEE754 equality.
If the values are ordered and equal then Boolean register br is set to 1, otherwise br is
set to 0. IEEE754 specifies that +0 and −0 compare as equal. IEEE754 floating-point
values are ordered if neither is a NaN.
Operation
BRr ← not isNaN(FR[s]) and not isNaN(FR[t])
and (FR[s] =s FR[t])
Exceptions
EveryInst Group (see page 244)
GenExcep(Coprocessor0Disabled) if Coprocessor Option
23 20 19 16 15 12 11 8 7 4 3 0
00101011 r s t 0000
444444
OLE.S Compare Single Ord & Less Than or Equal
464 Xtensa Instruction Set Architecture (ISA) Reference Manual
Instruction Word (RRR)
Required Configuration Option
Floating-Point Coprocessor Option (See Section 4.3.11 on page 67)
Assembler Syntax
OLE.S br, fs, ft
Description
OLE.S compares the contents of floating-point registers fs and ft. If the contents of fs
are ordered with, and less than or equal to the contents of ft, then Boolean register br
is set to 1, otherwise br is set to 0. According to IEEE754, +0 and −0 compare as equal.
IEEE754 floating-point values are ordered if neither is a NaN.
Operation
BRr ← not isNaN(FR[s]) and not isNaN(FR[t])
and (FR[s] ≤s FR[t])
Exceptions
EveryInst Group (see page 244)
GenExcep(Coprocessor0Disabled) if Coprocessor Option
23 20 19 16 15 12 11 8 7 4 3 0
01101011 r s t 0000
444444
Compare Single Ordered and Less Than OLT.S
Xtensa Instruction Set Architecture (ISA) Reference Manual 465
Instruction Word (RRR)
Required Configuration Option
Floating-Point Coprocessor Option (See Section 4.3.11 on page 67)
Assembler Syntax
OLT.S br, fs, ft
Description
OLT.S compares the contents of floating-point registers fs and ft. If the contents of fs
are ordered with and less than the contents of ft then Boolean register br is set to 1,
otherwise br is set to 0. According to IEEE754, +0 and −0 compare as equal. IEEE754
floating-point values are ordered if neither is a NaN.
Operation
BRr ← not isNaN(FR[s]) and not isNaN(FR[t])
and (FR[s] <s FR[t])
Exceptions
EveryInst Group (see page 244)
GenExcep(Coprocessor0Disabled) if Coprocessor Option
23 20 19 16 15 12 11 8 7 4 3 0
01001011 r s t 0000
444444
OR Bitwise Logical Or
466 Xtensa Instruction Set Architecture (ISA) Reference Manual
Instruction Word (RRR)
Required Configuration Option
Core Architecture (See Section 4.2 on page 50)
Assembler Syntax
OR ar, as, at
Description
OR calculates the bitwise logical or of address registers as and at. The result is written
to address register ar.
Operation
AR[r] ← AR[s] or AR[t]
Exceptions
EveryInstR Group (see page 244)
23 20 19 16 15 12 11 8 7 4 3 0
00100000 r s t 0000
444444
Boolean Or ORB
Xtensa Instruction Set Architecture (ISA) Reference Manual 467
Instruction Word (RRR)
Required Configuration Option
Boolean Option (See Section 4.3.10 on page 65)
Assembler Syntax
ORB br, bs, bt
Description
ORB performs the logical or of Boolean registers bs and bt, and writes the result to
Boolean register br.
When the sense of one of the source Booleans is inverted (0 → true, 1 → false), use
ORBC. When the sense of both of the source Booleans is inverted, use ANDB and an
inverted test of the result.
Operation
BRr ← BRs or BRt
Exceptions
EveryInst Group (see page 244)
23 20 19 16 15 12 11 8 7 4 3 0
00100010 r s t 0000
444444
ORBC Boolean Or with Complement
468 Xtensa Instruction Set Architecture (ISA) Reference Manual
Instruction Word (RRR)
Required Configuration Option
Boolean Option (See Section 4.3.10 on page 65)
Assembler Syntax
ORBC br, bs, bt
Description
ORBC performs the logical or of Boolean register bs with the logical complement of
Boolean register bt and writes the result to Boolean register br.
Operation
BRr ← BRs or not BRt
Exceptions
EveryInst Group (see page 244)
23 20 19 16 15 12 11 8 7 4 3 0
00110010 r s t 0000
444444
Probe Data TLB PDTLB
Xtensa Instruction Set Architecture (ISA) Reference Manual 469
Instruction Word (RRR)
Required Configuration Option
Region Translation Option (page 156) or the MMU Option (page 158)
Assembler Syntax
PDTLB at, as
Description
PDTLB searches the data TLB for an entry that translates the virtual address in address
register as and writes the way and index of that entry to address register at. If no entry
matches, zero is written to the hit bit of at. The value written to at is implementation-
specific, but in all implementations a value with the hit bit set is suitable as an input to
the IDTLB or WDTLB instructions. See Section 4.6 on page 138 for information on the re-
sult register formats for specific memory protection and translation options.
PDTLB is a privileged instruction.
Operation
if CRING ≠ 0 then
Exception (PrivilegedInstructionCause)
else
(match, vpn, ei, wi) ← ProbeDataTLB(AR[s])
if match > 1 then
EXCVADDR ← AR[s]
Exception (LoadStoreTLBMultiHit)
else
AR[t] ← PackDataTLBEntrySpec(match, vpn, ei, wi)
endif
endif
Exceptions
EveryInstR Group (see page 244)
GenExcep(LoadStoreTLBMultiHitCause) if Region Protection Option or MMU Option
GenExcep(PrivilegedCause) if Exception Option
23 20 19 16 15 12 11 8 7 4 3 0
010100001101 s t 0000
444444
PITLB Probe Instruction TLB
470 Xtensa Instruction Set Architecture (ISA) Reference Manual
Instruction Word (RRR)
Required Configuration Option
Region Translation Option (page 156) or the MMU Option (page 158)
Assembler Syntax
PITLB at, as
Description
PITLB searches the Instruction TLB for an entry that translates the virtual address in
address register as and writes the way and index of that entry to address register at. If
no entry matches, zero is written to the hit bit of at. The value written to at is implemen-
tation-specific, but in all implementations a value with the hit bit set is suitable as an in-
put to the IITLB or WITLB instructions. See Section 4.6 on page 138 for information on
the result register formats for specific memory protection and translation options.
PITLB is a privileged instruction.
Operation
if CRING ≠ 0 then
Exception (PrivilegedInstructionCause)
else
(match, vpn, ei, wi) ← ProbeInstTLB(AR[s])
if match > 1 then
EXCVADDR ← AR[s]
Exception (InstructionFetchTLBMultiHit)
else
AR[t] ← PackInstTLBEntrySpec(match, vpn, ei, wi)
endif
endif
Exceptions
EveryInstR Group (see page 244)
GenExcep(PrivilegedCause) if Exception Option
23 20 19 16 15 12 11 8 7 4 3 0
010100000101 s t 0000
444444
Quotient Signed QUOS
Xtensa Instruction Set Architecture (ISA) Reference Manual 471
Instruction Word (RRR)
Required Configuration Option
32-bit Integer Divide Option (See Section 4.3.6 on page 59)
Assembler Syntax
QUOS ar, as, at
Description
QUOS performs a 32-bit two’s complement division of the contents of address register as
by the contents of address register at and writes the quotient to address register ar.
The ambiguity which exists when either address register as or address register at is
negative is resolved by requiring the product of the quotient and address register at to
be smaller in absolute value than the address register as. If the contents of address reg-
ister at are zero, QUOS raises an Integer Divide by Zero exception instead of writing a
result. Overflow (-2147483648 divided by -1) is not detected.
Operation
if AR[t] = 032 then
Exception (IntegerDivideByZero)
else
AR[r] ← AR[s] quo AR[t]
endif
Exceptions
EveryInstR Group (see page 244)
GenExcep(IntegerDivideByZeroCause) if 32-bit Integer Divide Option
23 20 19 16 15 12 11 8 7 4 3 0
11010010 r s t 0000
444444
QUOU Quotient Unsigned
472 Xtensa Instruction Set Architecture (ISA) Reference Manual
Instruction Word (RRR)
Required Configuration Option
32-bit Integer Divide Option (See Section 4.3.6 on page 59)
Assembler Syntax
QUOU ar, as, at
Description
QUOU performs a 32-bit unsigned division of the contents of address register as by the
contents of address register at and writes the quotient to address register ar. If the con-
tents of address register at are zero, QUOU raises an Integer Divide by Zero exception
instead of writing a result.
Operation
if AR[t] = 032 then
Exception (IntegerDivideByZero)
else
tq ← (0||AR[s]) quo (0||AR[t])
AR[r] ← tq31..0
endif
Exceptions
EveryInstR Group (see page 244)
GenExcep(IntegerDivideByZeroCause) if 32-bit Integer Divide Option
23 20 19 16 15 12 11 8 7 4 3 0
11000010 r s t 0000
444444
Read Data TLB Entry Virtual RDTLB0
Xtensa Instruction Set Architecture (ISA) Reference Manual 473
Instruction Word (RRR)
Required Configuration Option
Region Translation Option (page 156) or the MMU Option (page 158)
Assembler Syntax
RDTLB0 at, as
Description
RDTLB0 reads the data TLB entry specified by the contents of address register as and
writes the Virtual Page Number (VPN) and address space ID (ASID) to address register
at. See Section 4.6 on page 138 for information on the address and result register for-
mats for specific memory protection and translation options.
RDTLB0 is a privileged instruction.
Operation
AR[t] ← RDTLB0(AR[s])
Exceptions
EveryInstR Group (see page 244)
GenExcep(PrivilegedCause) if Exception Option
23 20 19 16 15 12 11 8 7 4 3 0
010100001011 s t 0000
444444
RDTLB1 Read Data TLB Entry Translation
474 Xtensa Instruction Set Architecture (ISA) Reference Manual
Instruction Word (RRR)
Required Configuration Option
Region Translation Option (page 156) or the MMU Option (page 158)
Assembler Syntax
RDTLB1 at, as
Description
RDTLB1 reads the data TLB entry specified by the contents of address register as and
writes the Physical Page Number (PPN) and cache attribute (CA) to address register
at. See Section 4.6 on page 138 for information on the address and result register for-
mats for specific memory protection and translation options.
RDTLB1 is a privileged instruction.
Operation
AR[t] ← RDTLB1(AR[s])
Exceptions
EveryInstR Group (see page 244)
GenExcep(PrivilegedCause) if Exception Option
23 20 19 16 15 12 11 8 7 4 3 0
010100001111 s t 0000
444444
Remainder Signed REMS
Xtensa Instruction Set Architecture (ISA) Reference Manual 475
Instruction Word (RRR)
Required Configuration Option
32-bit Integer Divide Option (See Section 4.3.6 on page 59)
Assembler Syntax
REMS ar, as, at
Description
REMS performs a 32-bit two’s complement division of the contents of address register as
by the contents of address register at and writes the remainder to address register ar.
The ambiguity which exists when either address register as or address register at is
negative is resolved by requiring the remainder to have the same sign as address regis-
ter as. If the contents of address register at are zero, REMS raises an Integer Divide by
Zero exception instead of writing a result.
Operation
if AR[t] = 032 then
Exception (IntegerDivideByZero)
else
AR[r] ← AR[s] rem AR[t]
endif
Exceptions
EveryInstR Group (see page 244)
GenExcep(IntegerDivideByZeroCause) if 32-bit Integer Divide Option
23 20 19 16 15 12 11 8 7 4 3 0
11110010 r s t 0000
444444
REMU Remainder Unsigned
476 Xtensa Instruction Set Architecture (ISA) Reference Manual
Instruction Word (RRR)
Required Configuration Option
32-bit Integer Divide Option (See Section 4.3.6 on page 59)
Assembler Syntax
REMU ar, as, at
Description
REMU performs a 32-bit unsigned division of the contents of address register as by the
contents of address register at and writes the remainder to address register ar. If the
contents of address register at are zero, REMU raises an Integer Divide by Zero excep-
tion instead of writing a result.
Operation
if AR[t] = 032 then
Exception (IntegerDivideByZero)
else
tr ← (0||AR[s]) rem (0||AR[t])
AR[r] ← tr31..0
endif
Exceptions
EveryInstR Group (see page 244)
GenExcep(IntegerDivideByZeroCause) if 32-bit Integer Divide Option
23 20 19 16 15 12 11 8 7 4 3 0
11100010 r s t 0000
444444
Read External Register RER
Xtensa Instruction Set Architecture (ISA) Reference Manual 477
Instruction Word (RRR)
Required Configuration Option
Core Architecture (See Section 4.2 on page 50)
Assembler Syntax
RER at, as
Description
RER reads one of a set of "External Registers". It is in some ways similar to the RSR.*
instruction except that the registers being read are not defined by the Xtensa ISA and
are conceptually outside the processor core. They are read through processor ports.
Address register as is used to determine which register is to be read and the result is
placed in address register at. When no External Register is addressed by the value in
address register as, the result in address register at is undefined. The entire address
space is reserved for use by Tensilica. RER and WER are managed by the processor core
so that the requests appear on the processor ports in program order. External logic is re-
sponsible for extending that order to the registers themselves.
RER is a privileged instruction.
Operation
if CRING ≠ 0 then
Exception (PrivilegedInstructionCause)
else
Read External Register as defined outside the processor.
endif
Exceptions
EveryInstR Group (see page 244)
GenExcep(PrivilegedCause) if Exception Option
23 20 19 16 15 12 11 8 7 4 3 0
010000000110 s t 0000
444444
RET Non-Windowed Return
478 Xtensa Instruction Set Architecture (ISA) Reference Manual
Instruction Word (CALLX)
Required Configuration Option
Core Architecture (See Section 4.2 on page 50)
Assembler Syntax
RET
Description
RET returns from a routine called by CALL0 or CALLX0. It is equivalent to the instruction
JX A0
RET exists as a separate instruction because some Xtensa ISA implementations may
realize performance advantages from treating this operation as a special case.
Assembler Note
The assembler may convert RET instructions to RET.N when the Code Density Option is
enabled. Prefixing the RET instruction with an underscore (_RET) disables this optimiza-
tion and forces the assembler to generate the wide form of the instruction.
Operation
nextPC ← AR[0]
Exceptions
EveryInst Group (see page 244)
23 20 19 16 15 12 11 876543 0
000000000000000010000000
4 4 4 4 2 2 4
Narrow Non-Windowed Return RET.N
Xtensa Instruction Set Architecture (ISA) Reference Manual 479
Instruction Word (RRRN)
Required Configuration Option
Code Density Option (See Section 4.3.1 on page 53)
Assembler Syntax
RET.N
Description
RET.N is the same as RET in a 16-bit encoding. RET returns from a routine called by
CALL0 or CALLX0.
Assembler Note
The assembler may convert RET.N instructions to RET. Prefixing the RET.N instruction
with an underscore (_RET.N) disables this optimization and forces the assembler to
generate the narrow form of the instruction.
Operation
nextPC ← AR[0]
Exceptions
EveryInst Group (see page 244)
15 12 11 8 7 4 3 0
1111000000001101
4444
RETW Windowed Return
480 Xtensa Instruction Set Architecture (ISA) Reference Manual
Instruction Word (CALLX)
Required Configuration Option
Windowed Register Option (See Section 4.7.1 on page 180)
Assembler Syntax
RETW
Description
RETW returns from a subroutine called by CALL4, CALL8, CALL12, CALLX4, CALLX8, or
CALLX12, and that had ENTRY as its first instruction.
RETW uses bits 29..0 of address register a0 as the low 30 bits of the return address
and bits 31..30 of the address of the RETW as the high two bits of the return address.
Bits 31..30 of a0 are used as the caller’s window increment.
RETW subtracts the window increment from WindowBase to return to the caller’s regis-
ters. It then checks the WindowStart bit for this WindowBase. If it is set, then the
caller’s registers still reside in the register file, and RETW completes by clearing its own
WindowStart bit and jumping to the return address. If the WindowStart bit is clear,
then the caller’s registers have been stored into the stack, so RETW signals one of win-
dow underflow’s 4, 8, or 12, based on the size of the caller’s window increment. The un-
derflow handler is invoked with WindowBase decremented, a minor exception to the
rule that instructions aborted by an exception have no side effects to the operating state
of the processor. The processor stores the previous value of WindowBase in PS.OWB so
that it can be restored by RFWU.
The window underflow handler is expected to restore the caller’s registers, set the
caller’s WindowStart bit, and then return (see RFWU) to re-execute the RETW, which
will then complete.
The operation of this instruction is undefined if AR[0]31..30 is 02, if PS.WOE is 0, if
PS.EXCM is 1, or if the first set bit among [WindowStartWindowBase-1,
WindowStartWindowBase-2, WindowStartWindowBase-3] is anything other than
WindowStartWindowBase-n, where n is AR[0]31..30. (If none of the three bits is set, an
23 20 19 16 15 12 11 876543 0
000000000000000010010000
4 4 4 4 2 2 4
Windowed Return RETW
Xtensa Instruction Set Architecture (ISA) Reference Manual 481
underflow exception will be raised as described above, but if the wrong first one is set,
the state is not legal.) Some implementations raise an illegal instruction exception in
these cases as a debugging aid.
Assembler Note
The assembler may convert RETW instructions to RETW.N when the Code Density
Option is enabled. Prefixing the RETW instruction with an underscore (_RETW) disables
this optimization and forces the assembler to generate the wide form of the instruction.
Operation
n ← AR[0]31..30
nextPC ← PC31..30||AR[0]29..0
owb ← WindowBase
m ← if WindowStartWindowBase-4’b0001 then 2’b01
elsif WindowStartWindowBase-4’b0010 then 2’b10
elsif WindowStartWindowBase-4’b0011 then 2’b11
else 2’b00
if n=2’b00 | (m≠2’b00 & m≠n) | PS.WOE=0 | PS.EXCM=1 then
-- undefined operation
-- may raise illegal instruction exception
else
WindowBase ← WindowBase − (02||n)
if WindowStartWindowBase ≠ 0 then
WindowStartowb ← 0
else
-- Underflow exception
PS.EXCM ← 1
EPC[1] ← PC
PS.OWB ← owb
nextPC ← if n = 2'b01 then WindowUnderflow4
else if n = 2'b10 then WindowUnderflow8
else WindowUnderflow12
endif
endif
Exceptions
EveryInst Group (see page 244)
WindowUnderExcep if Windowed Register Option
RETW.N Narrow Windowed Return
482 Xtensa Instruction Set Architecture (ISA) Reference Manual
Instruction Word (RRRN)
Required Configuration Option
Code Density Option (See Section 4.3.1 on page 53) and Windowed Register Option
(See Section 4.7.1 on page 180)
Assembler Syntax
RETW.N
Description
RETW.N is the same as RETW in a 16-bit encoding.
Assembler Note
The assembler may convert RETW.N instructions to RETW. Prefixing the RETW.N instruc-
tion with an underscore (_RETW.N) disables this optimization and forces the assembler
to generate the narrow form of the instruction.
Operation
n ← AR[0]31..30
nextPC ← PC31..30||AR[0]29..0
owb ← WindowBase
m ← if WindowStartWindowBase-4’b0001 then 2’b01
elsif WindowStartWindowBase-4’b0010 then 2’b10
elsif WindowStartWindowBase-4’b0011 then 2’b11
else 2’b00
if n=2’b00 | (m≠2’b00 & m≠n) | PS.WOE=0 | PS.EXCM=1 then
-- undefined operation
-- may raise illegal instruction exception
else
WindowBase ← WindowBase − (02||n)
if WindowStartWindowBase ≠ 0 then
WindowStartowb ← 0
else
-- Underflow exception
PS.EXCM ← 1
EPC[1] ← PC
15 12 11 8 7 4 3 0
1111000000011101
4444
Narrow Windowed Return RETW.N
Xtensa Instruction Set Architecture (ISA) Reference Manual 483
PS.OWB ← owb
nextPC ← if n = 2'b01 then WindowUnderflow4
else if n = 2'b10 then WindowUnderflow8
else WindowUnderflow12
endif
endif
Exceptions
EveryInst Group (see page 244)
WindowUnderExcep if Windowed Register Option
RFDD Return from Debug and Dispatch
484 Xtensa Instruction Set Architecture (ISA) Reference Manual
Instruction Word (RRR)
Required Configuration Option
Debug Option (See Section 4.7.6 on page 197) and OCD, Implementation-Specific
Assembler Syntax
RFDD
Description
This instruction is used only in On-Chip Debug Mode and exists only in some implemen-
tations. It is an illegal instruction when the processor is not in On-Chip Debug Mode.
See the Tensilica On-Chip Debugging Guide for a description of its operation.
Exceptions
EveryInst Group (see page 244)
GenExcep(IllegalInstructionCause) if Exception Option
23 20 19 16 15 12 11 8 7 4 3 0
111100011110000s000010000
444444
Return from Double Exception RFDE
Xtensa Instruction Set Architecture (ISA) Reference Manual 485
Instruction Word (RRR)
Required Configuration Option
Exception Option (See Section 4.4.1 on page 82)
Assembler Syntax
RFDE
Description
RFDE returns from an exception that went to the double exception vector (that is, an ex-
ception raised while the processor was executing with PS.EXCM set). It is similar to RFE,
but PS.EXCM is not cleared, and DEPC, if it exists, is used instead of EPC[1]. RFDE sim-
ply jumps to the exception PC. PS.UM and PS.WOE are left unchanged.
RFDE is a privileged instruction.
Operation
if CRING ≠ 0 then
Exception (PrivilegedInstructionCause)
elsif NDEPC=1 then
nextPC ¨ DEPC
else
nextPC ← EPC[1]
endif
Exceptions
EveryInst Group (see page 244)
GenExcep(PrivilegedCause) if Exception Option
23 20 19 16 15 12 11 8 7 4 3 0
000000000011001000000000
444444
RFDO Return from Debug Operation
486 Xtensa Instruction Set Architecture (ISA) Reference Manual
Instruction Word (RRR)
Required Configuration Option
Debug Option (See Section 4.7.6 on page 197) and OCD, Implementation-Specific
Assembler Syntax
RFDO
Description
This instruction is used only in On-Chip Debug Mode and exists only in some implemen-
tations. It is an illegal instruction when the processor is not in On-Chip Debug Mode.
See the Tensilica On-Chip Debugging Guide for a description of its operation.
Exceptions
EveryInst Group (see page 244)
GenExcep(IllegalInstructionCause) if Exception Option
23 20 19 16 15 12 11 8 7 4 3 0
111100011110000000000000
444444
Return from Exception RFE
Xtensa Instruction Set Architecture (ISA) Reference Manual 487
Instruction Word (RRR)
Required Configuration Option
Exception Option (See Section 4.4.1 on page 82)
Assembler Syntax
RFE
Description
RFE returns from either the UserExceptionVector or the KernelExceptionVector. RFE
sets PS.EXCM back to 0, and then jumps to the address in EPC[1]. PS.UM and PS.WOE
are left unchanged.
RFE is a privileged instruction.
Operation
if CRING ≠ 0 then
Exception (PrivilegedInstructionCause)
else
PS.EXCM ← 0
nextPC ← EPC[1]
endif
Exceptions
EveryInst Group (see page 244)
GenExcep(PrivilegedCause) if Exception Option
23 20 19 16 15 12 11 8 7 4 3 0
000000000011000000000000
444444
RFI Return from High-Priority Interrupt
488 Xtensa Instruction Set Architecture (ISA) Reference Manual
Instruction Word (RRR)
Required Configuration Option
High-Priority Interrupt Option (See Section 4.4.5 on page 106)
Assembler Syntax
RFI 0..15
Description
RFI returns from a high-priority interrupt. It restores the PS from EPS[level] and
jumps to the address in EPC[level]. Level is given as a constant 2..(NLEVEL+NNMI)
in the instruction word. The operation of this opcode when level is 0 or 1 or greater than
(NLEVEL+NNMI) is undefined.
RFI is a privileged instruction.
Operation
if CRING ≠ 0 then
Exception (PrivilegedInstructionCause)
else
nextPC ← EPC[level]
PS ← EPS[level]
endif
Exceptions
EveryInst Group (see page 244)
GenExcep(PrivilegedCause) if Exception Option
23 20 19 16 15 12 11 8 7 4 3 0
000000000011 level 00010000
444444
Return from Memory Error RFME
Xtensa Instruction Set Architecture (ISA) Reference Manual 489
Instruction Word (RRR)
Required Configuration Option
Memory ECC/Parity Option (See Section 4.5.14 on page 128)
Assembler Syntax
RFME
Description
RFME returns from a memory error exception. It restores the PS from MEPS and jumps to
the address in MEPC. In addition, the MEME bit of the MESR register is cleared.
RFME is a privileged instruction.
Operation
if CRING ≠ 0 then
Exception (PrivilegedInstructionCause)
else
nextPC ← MEPC
PS ← MEPS
MESR.MEME ← 0
endif
Exceptions
EveryInst Group (see page 244)
GenExcep(PrivilegedCause) if Exception Option
23 20 19 16 15 12 11 8 7 4 3 0
000000000011000000100000
444444
RFR Move FR to AR
490 Xtensa Instruction Set Architecture (ISA) Reference Manual
Instruction Word (RRR)
Required Configuration Option
Floating-Point Coprocessor Option (See Section 4.3.11 on page 67)
Assembler Syntax
RFR ar, fs
Description
RFR moves the contents of floating-point register fs to address register ar. The move is
non-arithmetic; no floating-point exceptions are raised.
Operation
AR[r] ← FR[s]
Exceptions
EveryInstR Group (see page 244)
GenExcep(Coprocessor0Disabled) if Coprocessor Option
23 20 19 16 15 12 11 8 7 4 3 0
11111010 r s 01000000
444444
Return from User-Mode Exception RFUE
Xtensa Instruction Set Architecture (ISA) Reference Manual 491
Instruction Word (RRR)
Required Configuration Option
Exception Option (Xtensa Exception Architecture 1 Only)
Assembler Syntax
RFUE
Description
RFUE exists only in Xtensa Exception Architecture 1 (see Section A.2 “Xtensa Exception
Architecture 1” on page 611). It is an illegal instruction in current Xtensa implementa-
tions.
Exceptions
EveryInst Group (see page 244)
GenExcep(IllegalInstructionCause) if Exception Option
23 20 19 16 15 12 11 8 7 4 3 0
000000000011000100000000
444444
RFWO Return from Window Overflow
492 Xtensa Instruction Set Architecture (ISA) Reference Manual
Instruction Word (RRR)
Required Configuration Option
Windowed Register Option (See Section 4.7.1 on page 180)
Assembler Syntax
RFWO
Description
RFWO returns from an exception that went to one of the three window overflow vectors. It
sets PS.EXCM back to 0, clears the WindowStart bit of the registers that were spilled,
restores WindowBase from PS.OWB, and then jumps to the address in EPC[1]. PS.UM
is left unchanged.
RFWO is a privileged instruction.
Operation
if CRING ≠ 0 then
Exception (PrivilegedInstructionCause)
else
PS.EXCM ← 0
nextPC ← EPC[1]
WindowStartWindowBase ← 0
WindowBase ← PS.OWB
endif
Exceptions
EveryInst Group (see page 244)
GenExcep(PrivilegedCause) if Exception Option
23 20 19 16 15 12 11 8 7 4 3 0
000000000011010000000000
444444
Return From Window Underflow RFWU
Xtensa Instruction Set Architecture (ISA) Reference Manual 493
Instruction Word (RRR)
Required Configuration Option
Windowed Register Option (See Section 4.7.1 on page 180)
Assembler Syntax
RFWU
Description
RFWU returns from an exception that went to one of the three window underflow vectors.
It sets PS.EXCM back to 0, sets the WindowStart bit of the registers that were reload-
ed, restores WindowBase from PS.OWB, and then jumps to the address in EPC[1].
PS.UM is left unchanged.
RFWU is a privileged instruction.
Operation
if CRING ≠ 0 then
Exception (PrivilegedInstructionCause)
else
PS.EXCM ← 0
nextPC ← EPC[1]
WindowStartWindowBase ← 1
WindowBase ← PS.OWB
endif
Exceptions
EveryInst Group (see page 244)
GenExcep(PrivilegedCause) if Exception Option
23 20 19 16 15 12 11 8 7 4 3 0
000000000011010100000000
444444
RITLB0 Read Instruction TLB Entry Virtual
494 Xtensa Instruction Set Architecture (ISA) Reference Manual
Instruction Word (RRR)
Required Configuration Option
Region Translation Option (page 156) or the MMU Option (page 158)
Assembler Syntax
RITLB0 at, as
Description
RITLB0 reads the instruction TLB entry specified by the contents of address register as
and writes the Virtual Page Number (VPN) and address space ID (ASID) to address reg-
ister at. See Section 4.6 on page 138 for information on the address and result register
formats for specific memory protection and translation options.
RITLB0 is a privileged instruction.
Operation
AR[t] ← RITLB0(AR[s])
Exceptions
EveryInstR Group (see page 244)
GenExcep(PrivilegedCause) if Exception Option
23 20 19 16 15 12 11 8 7 4 3 0
010100000011 s t 0000
444444
Read Instruction TLB Entry Translation RITLB1
Xtensa Instruction Set Architecture (ISA) Reference Manual 495
Instruction Word (RRR)
Required Configuration Option
Region Translation Option (page 156) or the MMU Option (page 158)
Assembler Syntax
RITLB1 at, as
Description
RITLB1 reads the instruction TLB entry specified by the contents of address register as
and writes the Physical Page Number (PPN) and cache attribute (CA) to address regis-
ter at. See Section 4.6 on page 138 for information on the address and result register
formats for specific memory protection and translation options.
RITLB1 is a privileged instruction.
Operation
AR[t] ← RITLB1(AR[s])
Exceptions
EveryInstR Group (see page 244)
GenExcep(PrivilegedCause) if Exception Option
23 20 19 16 15 12 11 8 7 4 3 0
010100000111 s t 0000
444444
ROTW Rotate Window
496 Xtensa Instruction Set Architecture (ISA) Reference Manual
Instruction Word (RRR)
Required Configuration Option
Windowed Register Option (See Section 4.7.1 on page 180)
Assembler Syntax
ROTW -8..7
Description
ROTW adds a constant to WindowBase, thereby moving the current window into the
register file. ROTW is intended for use in exception handlers and context switch code.
ROTW is a privileged instruction.
Operation
if CRING ≠ 0 then
Exception (PrivilegedInstructionCause)
else
WindowBase ← WindowBase + imm4
endif
Exceptions
EveryInst Group (see page 244)
GenExcep(PrivilegedCause) if Exception Option
23 20 19 16 15 12 11 8 7 4 3 0
0100000010000000 imm4 0000
444444
Round Single to Fixed ROUND.S
Xtensa Instruction Set Architecture (ISA) Reference Manual 497
Instruction Word (RRR)
Required Configuration Option
Floating-Point Coprocessor Option (See Section 4.3.11 on page 67)
Assembler Syntax
ROUND.S ar, fs, 0..15
Description
ROUND.S converts the contents of floating-point register fs from single-precision to
signed integer format, rounding toward the nearest. The single-precision value is first
scaled by a power of two constant value encoded in the t field, with 0..15 representing
1.0, 2.0, 4.0, …, 32768.0. The scaling allows for a fixed point notation where the binary
point is at the right end of the integer for t=0 and moves to the left as t increases until
for t=15 there are 15 fractional bits represented in the fixed point number. For positive
overflow (value ≥ 32'h7fffffff), positive infinity, or NaN, 32'h7fffffff is
returned; for negative overflow (value ≤ 32'h80000000) or negative infinity,
32'h80000000 is returned. The result is written to address register ar.
Operation
AR[r] ← rounds(FR[s] ×s pows(2.0,t))
Exceptions
EveryInstR Group (see page 244)
GenExcep(Coprocessor0Disabled) if Coprocessor Option
23 20 19 16 15 12 11 8 7 4 3 0
10001010 r s t 0000
444444
RSIL Read and Set Interrupt Level
498 Xtensa Instruction Set Architecture (ISA) Reference Manual
Instruction Word (RRR)
Required Configuration Option
Interrupt Option (See Section 4.4.4 on page 100)
Assembler Syntax
RSIL at, 0..15
Description
RSIL first reads the PS Special Register (described in Table 4–63 on page 87, PS Reg-
ister Fields), writes this value to address register at, and then sets PS.INTLEVEL to a
constant in the range 0..15 encoded in the instruction word. Interrupts at and below the
PS.INTLEVEL level are disabled.
A WSR.PS or XSR.PS followed by an RSIL should be separated with an ESYNC to guar-
antee the value written is read back.
On some Xtensa ISA implementations the latency of RSIL is greater than one cycle,
and so it is advantageous to schedule uses of the RSIL result later.
RSIL is typically used as follows:
RSIL a2, newlevel
code to be executed at newlevel
WSR.PS a2
The instruction following the RSIL is guaranteed to be executed at the new interrupt
level specified in PS.INTLEVEL, therefore it is not necessary to insert one of the SYNC
instructions to force the interrupt level change to take effect.
RSIL is a privileged instruction.
Operation
if CRING ≠ 0 then
Exception (PrivilegedInstructionCause)
else
AR[t] ← PS
23 20 19 16 15 12 11 8 7 4 3 0
000000000110 imm4 t 0000
444444
Read and Set Interrupt Level RSIL
Xtensa Instruction Set Architecture (ISA) Reference Manual 499
PS.INTLEVEL ← s
endif
Exceptions
EveryInstR Group (see page 244)
GenExcep(PrivilegedCause) if Exception Option
RSR.* Read Special Register
500 Xtensa Instruction Set Architecture (ISA) Reference Manual
Instruction Word (RSR)
Required Configuration Option
Core Architecture (See Section 4.2 on page 50)
Assembler Syntax
RSR.* at
RSR at, *
RSR at, 0..255
Description
RSR.* reads the Special Registers that are described in Section 3.8.10 “Processor Con-
trol Instructions” on page 45. See Section 5.3 on page 208 for more detailed information
on the operation of this instruction for each Special Register.
The contents of the Special Register designated by the 8-bit sr field of the instruction
word are written to address register at. The name of the Special Register is used in
place of the ‘*’ in the assembler syntax above and the translation is made to the 8-bit sr
field by the assembler.
RSR is an assembler macro for RSR.* that provides compatibility with the older versions
of the instruction containing either the name or the number of the Special Register.
A WSR.* followed by an RSR.* to the same register should be separated with ESYNC to
guarantee the value written is read back. On some Xtensa ISA implementations, the la-
tency of RSR.* is greater than one cycle, and so it is advantageous to schedule other
instructions before instructions that use the RSR.* result.
RSR.* with Special Register numbers ≥ 64 is privileged. An RSR.* for an unconfigured
register generally will raise an illegal instruction exception.
Operation
sr ← if msbFirst then s||r else r||s
if sr ≥ 64 and CRING ≠ 0 then
23 20 19 16 15 8 7 4 3 0
00000011 sr t 0000
4 4 8 4 4
Read Special Register RSR.*
Xtensa Instruction Set Architecture (ISA) Reference Manual 501
Exception (PrivilegedInstructionCause)
else
see the Tables in Section 5.3 on page 208
endif
Exceptions
EveryInstR Group (see page 244)
GenExcep(IllegalInstructionCause) if Exception Option
GenExcep(PrivilegedCause) if Exception Option
RSYNC Register Read Synchronize
502 Xtensa Instruction Set Architecture (ISA) Reference Manual
Instruction Word (RRR)
Required Configuration Option
Core Architecture (See Section 4.2 on page 50)
Assembler Syntax
RSYNC
Description
RSYNC waits for all previously fetched WSR.* instructions to be performed before inter-
preting the register fields of the next instruction. This operation is also performed as part
of ISYNC. ESYNC and DSYNC are performed as part of this instruction.
This instruction is appropriate after WSR.WindowBase, WSR.WindowStart, WSR.PS,
WSR.CPENABLE, or WSR.EPS* instructions before using their results. See the Special
Register Tables in Section 5.3 on page 208 for a complete description of the uses of the
RSYNC instruction.
Because the instruction execution pipeline is implementation-specific, the operation sec-
tion below specifies only a call to the implementation’s rsync function.
Operation
rsync()
Exceptions
EveryInst Group (see page 244)
23 20 19 16 15 12 11 8 7 4 3 0
000000000010000000010000
444444
Read User Register RUR.*
Xtensa Instruction Set Architecture (ISA) Reference Manual 503
Instruction Word (RRR)
Required Configuration Option
No Option - instructions created from the TIE language (See Section 4.3.9.2 “Coproces-
sor Context Switch” on page 64)
Assembler Syntax
RUR.* ar
RUR ar, *
Description
RUR.* reads TIE state that has been grouped into 32-bit quantities by the TIE
user_register statement. The name in the user_register statement replaces the
“*” in the instruction name and causes the correct register number to be placed in the st
field of the encoded instruction. The contents of the TIE user_register designated by
the 8-bit number 16*s+t are written to address register ar. Here s and t are the
numbers corresponding to the respective fields of the instruction word.
RUR is an assembler macro for RUR.*, which provides compatibility with the older
version of the instruction.
Operation
AR[r] ← user_register[st]
Exceptions
EveryInstR Group (see page 244)
GenExcep(Coprocessor*Disabled) if Coprocessor Option
23 20 19 16 15 12 11 8 7 4 3 0
11100011 r s t 0000
444444
S8I Store 8-bit
504 Xtensa Instruction Set Architecture (ISA) Reference Manual
Instruction Word
(RRI8)
Required Configuration Option
Core Architecture (See Section 4.2 on page 50)
Assembler Syntax
S8I at, as, 0..255
Description
S8I is an 8-bit store from address register at to memory. It forms a virtual address by
adding the contents of address register as and an 8-bit zero-extended constant value
encoded in the instruction word. Therefore, the offset has a range from 0 to 255. Eight
bits (1 byte) from the least significant quarter of address register at are written to mem-
ory at the physical address.
If the Region Translation Option (page 156) or the MMU Option (page 158)is enabled,
the virtual address is translated to the physical address. If not, the physical address is
identical to the virtual address. If the translation or memory reference encounters an
error (for example, protection violation or non-existent memory), the processor raises
one of several exceptions (see Section 4.4.1.5 on page 89).
Operation
vAddr ← AR[s] + (024||imm8)
Store8 (vAddr, AR[t]7..0)
Exceptions
Memory Group (see page 244)
GenExcep(StoreProhibitedCause) if Region Protection Option or MMU Option
DebugExcep(DBREAK) if Debug Option
23 16 15 12 11 8 7 4 3 0
imm8 0 1 0 0 s t 0 0 1 0
8 4444
Store 16-bit S16I
Xtensa Instruction Set Architecture (ISA) Reference Manual 505
Instruction Word
(RRI8)
Required Configuration Option
Core Architecture (See Section 4.2 on page 50)
Assembler Syntax
S16I at, as, 0..510
Description
S16I is a 16-bit store from address register at to memory. It forms a virtual address by
adding the contents of address register as and an 8-bit zero-extended constant value
encoded in the instruction word shifted left by one. Therefore, the offset can specify mul-
tiples of two from zero to 510. Sixteen bits (two bytes) from the least significant half of
the register are written to memory at the physical address.
If the Region Translation Option (page 156) or the MMU Option (page 158) is enabled,
the virtual address is translated to the physical address. If not, the physical address is
identical to the virtual address. If the translation or memory reference encounters an
error (for example, protection violation or non-existent memory), the processor raises
one of several exceptions (see Section 4.4.1.5 on page 89).
Without the Unaligned Exception Option (page 99), the least significant bit of the
address is ignored. A reference to an odd address produces the same result as a refer-
ence to the address, minus one. With the Unaligned Exception Option, such an access
raises an exception.
Assembler Note
To form a virtual address, S16I calculates the sum of address register as and the imm8
field of the instruction word times two. Therefore, the machine-code offset is in terms of
16-bit (2 byte) units. However, the assembler expects a byte offset and encodes this into
the instruction by dividing by two.
Operation
vAddr ← AR[s] + (023||imm8||0)
Store16 (vAddr, AR[t]15..0)
Exceptions
Memory Store Group (see page 245)
23 16 15 12 11 8 7 4 3 0
imm8 0 1 0 1 s t 0 0 1 0
8 4444
S32C1I Store 32-bit Compare Conditional
506 Xtensa Instruction Set Architecture (ISA) Reference Manual
Instruction Word
(RRI8)
Required Configuration Option
Conditional Store Option (See Section 4.3.13 on page 77)
Assembler Syntax
S32C1I at, as, 0..1020
Description
S32C1I is a conditional store instruction intended for updating synchronization variables
in memory shared between multiple processors. It may also be used to atomically up-
date variables shared between different interrupt levels or other pairs of processes on a
single processor. S32C1I attempts to store the contents of address register at to the
virtual address formed by adding the contents of address register as and an 8-bit zero-
extended constant value encoded in the instruction word shifted left by two. If the old
contents of memory at the physical address equals the contents of the SCOMPARE1 Spe-
cial Register, the new data is written; otherwise the memory is left unchanged. In either
case, the value read from the location is written to address register at. The memory
read, compare, and write may take place in the processor or the memory system, de-
pending on the Xtensa ISA implementation, as long as these operations exclude other
writes to this location. See Section 4.3.13 “Conditional Store Option” on page 77 for
more information on where the atomic operation takes place.
From a memory ordering point of view, the atomic pair of accesses has the characteris-
tics of both an acquire and a release. That is, the atomic pair of accesses does not begin
until all previous loads, stores, acquires, and releases have performed. The atomic pair
must perform before any following load, store, acquire, or release may begin.
If the Region Translation Option (page 156) or the MMU Option (page 158)is enabled,
the virtual address is translated to the physical address. If not, the physical address is
identical to the virtual address. If the translation or memory reference encounters an
error (for example, protection violation or non-existent memory), the processor raises
one of several exceptions (see Section 4.4.1.5 on page 89).
23 16 15 12 11 8 7 4 3 0
imm8 1 1 1 0 s t 0 0 1 0
8 4444
Store 32-bit Compare Conditional S32C1I
Xtensa Instruction Set Architecture (ISA) Reference Manual 507
Without the Unaligned Exception Option (page 99), the two least significant bits of the
address are ignored. A reference to an address that is not 0 mod 4 produces the same
result as a reference to the address with the least significant bits cleared. With the Un-
aligned Exception Option, such an access raises an exception.
S32C1I does both a load and a store when the store is successful. However, memory
protection tests check for store capability and the instruction may raise a
StoreProhibitedCause exception, but will never raise a LoadProhibited Cause exception.
Assembler Note
To form a virtual address, S32C1I calculates the sum of address register as and the
imm8 field of the instruction word times four. Therefore, the machine-code offset is in
terms of 32-bit (4 byte) units. However, the assembler expects a byte offset and encodes
this into the instruction by dividing by four.
Operation
vAddr ← AR[s] + (022||imm8||02)
(mem32, error) ← Store32C1 (vAddr, AR[t], SCOMPARE1)
if error then
EXCVADDR ← vAddr
Exception (LoadStoreError)
else
AR[t] ← mem32
endif
Exceptions
Memory Store Group (see page 245)
S32E Store 32-bit for Window Exceptions
508 Xtensa Instruction Set Architecture (ISA) Reference Manual
Instruction Word (RRI4)
Required Configuration Option
Windowed Register Option (See Section 4.7.1 on page 180)
Assembler Syntax
S32E at, as, -64..-4
Description
S32E is a 32-bit store instruction similar to S32I, but with semantics required by window
overflow and window underflow exception handlers. In particular, memory access check-
ing is done with PS.RING instead of CRING, and the offset used to form the virtual ad-
dress is a 4-bit one-extended immediate. Therefore, the offset can specify multiples of
four from -64 to -4. In configurations without the MMU Option, there is no PS.RING and
S32E is similar to S32I with a negative offset.
If the Region Translation Option (page 156) or the MMU Option (page 158) is enabled,
the virtual address is translated to the physical address. If not, the physical address is
identical to the virtual address. If the translation or memory reference encounters an
error (for example, protection violation or non-existent memory), the processor raises
one of several exceptions (see Section 4.4.1.5 on page 89).
Without the Unaligned Exception Option (page 99), the two least significant bits of the
address are ignored. A reference to an address that is not 0 mod 4 produces the same
result as a reference to the address with the least significant bits cleared. With the Un-
aligned Exception Option, such an access raises an exception.
S32E is a privileged instruction.
Assembler Note
To form a virtual address, S32E calculates the sum of address register as and the r field
of the instruction word times four (and one extended). Therefore, the machine-code
offset is in terms of 32-bit (4 byte) units. However, the assembler expects a byte offset
and encodes this into the instruction by dividing by four.
23 20 19 16 15 12 11 8 7 4 3 0
01001001 r s t 0000
444444
Store 32-bit for Window Exceptions S32E
Xtensa Instruction Set Architecture (ISA) Reference Manual 509
Operation
if CRING ≠ 0 then
Exception (PrivilegedInstructionCause)
else
vAddr ← AR[s] + (126||r||02)
ring ← if MMU Option then PS.RING else 0
Store32Ring (vAddr, AR[t], ring)
endif
Exceptions
Memory Store Group (see page 245)
GenExcep(PrivilegedCause) if Exception Option
S32I Store 32-bit
510 Xtensa Instruction Set Architecture (ISA) Reference Manual
Instruction Word
(RRI8)
Required Configuration Option
Core Architecture (See Section 4.2 on page 50)
Assembler Syntax
S32I at, as, 0..1020
Description
S32I is a 32-bit store from address register at to memory. It forms a virtual address by
adding the contents of address register as and an 8-bit zero-extended constant value
encoded in the instruction word shifted left by two. Therefore, the offset can specify mul-
tiples of four from zero to 1020. The data to be stored is taken from the contents of ad-
dress register at and written to memory at the physical address.
If the Region Translation Option (page 156) or the MMU Option (page 158) is enabled,
the virtual address is translated to the physical address. If not, the physical address is
identical to the virtual address. If the translation or memory reference encounters an er-
ror (for example, protection violation or non-existent memory), the processor raises one
of several exceptions (see Section 4.4.1.5 on page 89).
Without the Unaligned Exception Option (page 99), the two least significant bits of the
address are ignored. A reference to an address that is not 0 mod 4 produces the same
result as a reference to the address with the least significant bits cleared. With the Un-
aligned Exception Option, such an access raises an exception.
S32I is one of only a few memory reference instructions that can access instruction
RAM.
Assembler Note
The assembler may convert S32I instructions to S32I.N when the Code Density
Option is enabled and the imm8 operand falls within the available range. Prefixing the
S32I instruction with an underscore (_S32I) disables this optimization and forces the
assembler to generate the wide form of the instruction.
23 16 15 12 11 8 7 4 3 0
imm8 0 1 1 0 s t 0 0 1 0
8 4444
Store 32-bit S32I
Xtensa Instruction Set Architecture (ISA) Reference Manual 511
To form a virtual address, S32I calculates the sum of address register as and the imm8
field of the instruction word times four. Therefore, the machine-code offset is in terms of
32-bit (4 byte) units. However, the assembler expects a byte offset and encodes this into
the instruction by dividing by four.
Operation
vAddr ← AR[s] + (022||imm8||02)
Store32 (vAddr, AR[t])
Exceptions
Memory Store Group (see page 245)
S32I.N Narrow Store 32-bit
512 Xtensa Instruction Set Architecture (ISA) Reference Manual
Instruction Word (RRRN)
Required Configuration Option
Code Density Option (See Section 4.3.1 on page 53)
Assembler Syntax
S32I.N at, as, 0..60
Description
S32I.N is similar to S32I, but has a 16-bit encoding and supports a smaller range of
offset values encoded in the instruction word.
S32I.N is a 32-bit store to memory. It forms a virtual address by adding the contents of
address register as and an 4-bit zero-extended constant value encoded in the instruc-
tion word shifted left by two. Therefore, the offset can specify multiples of four from zero
to 60. The data to be stored is taken from the contents of address register at and written
to memory at the physical address.
S32I.N is one of only a few memory reference instructions that can access instruction
RAM.
If the Region Translation Option (page 156) or the MMU Option (page 158)is enabled,
the virtual address is translated to the physical address. If not, the physical address is
identical to the virtual address. If the translation or memory reference encounters an
error (for example, protection violation or non-existent memory), the processor raises
one of several exceptions (see Section 4.4.1.5 on page 89).
Without the Unaligned Exception Option (page 99), the two least significant bits of the
address are ignored. A reference to an address that is not 0 mod 4 produces the same
result as a reference to the address with the least significant bits cleared. With the Un-
aligned Exception Options, such an access raises an exception.
15 12 11 8 7 4 3 0
imm4 s t 1 0 0 1
4444
Narrow Store 32-bit S32I.N
Xtensa Instruction Set Architecture (ISA) Reference Manual 513
Assembler Note
The assembler may convert S32I.N instructions to S32I. Prefixing the S32I.N instruc-
tion with an underscore (_S32I.N) disables this optimization and forces the assembler
to generate the narrow form of the instruction.
To form a virtual address, S32I.N calculates the sum of address register as and the
imm4 field of the instruction word times four. Therefore, the machine-code offset is in
terms of 32-bit (4 byte) units. However, the assembler expects a byte offset and encodes
this into the instruction by dividing by four.
Operation
vAddr ← AR[s] + (026||imm4||02)
Store32 (vAddr, AR[t])
Exceptions
Memory Store Group (see page 245)
S32RI Store 32-bit Release
514 Xtensa Instruction Set Architecture (ISA) Reference Manual
Instruction Word
(RRI8)
Required Configuration Option
Multiprocessor Synchronization Option (See Section 4.3.12 on page 74)
Assembler Syntax
S32RI at, as, 0..1020
Description
S32RI is a store barrier and 32-bit store from address register at to memory. S32RI
stores to synchronization variables, which signals that previously written data is
“released” for consumption by readers of the synchronization variable. This store will not
perform until all previous loads, stores, acquires, and releases have performed. This
ensures that any loads of the synchronization variable that see the new value will also
find all previously written data available as well.
S32RI forms a virtual address by adding the contents of address register as and an
8-bit zero-extended constant value encoded in the instruction word shifted left by two.
Therefore, the offset can specify multiples of four from zero to 1020. S32RI waits for
previous loads, stores, acquires, and releases to be performed, and then the data to be
stored is taken from the contents of address register at and written to memory at the
physical address. Because the method of waiting is implementation dependent, this is
indicated in the operation section below by the implementation function release.
If the Region Translation Option (page 156) or the MMU Option (page 158) is enabled,
the virtual address is translated to the physical address. If not, the physical address is
identical to the virtual address. If the translation or memory reference encounters an
error (for example, protection violation or non-existent memory), the processor raises
one of several exceptions (see Section 4.4.1.5 on page 89).
Without theUnaligned Exception Option (page 99), the two least significant bits of the
address are ignored. A reference to an address that is not 0 mod 4 produces the same
result as a reference to the address with the least significant bits cleared. With the Un-
aligned Exception Option, such an access raises an exception.
23 16 15 12 11 8 7 4 3 0
imm8 1 1 1 1 s t 0 0 1 0
8 4444
Store 32-bit Release S32RI
Xtensa Instruction Set Architecture (ISA) Reference Manual 515
Assembler Note
To form a virtual address, S32RI calculates the sum of address register as and the
imm8 field of the instruction word times four. Therefore, the machine-code offset is in
terms of 32-bit (4 byte) units. However, the assembler expects a byte offset and encodes
this into the instruction by dividing by four.
Operation
vAddr ← AR[s] + (022||imm8||02)
release()
Store32 (vAddr, AR[t])
Exceptions
Memory Store Group (see page 245)
SDCT Store Data Cache Tag
516 Xtensa Instruction Set Architecture (ISA) Reference Manual
Instruction Word (RRR)
Required Configuration Option
Data Cache Test Option (See Section 4.5.6 on page 121)
Assembler Syntax
SDCT at, as
Description
SDCT is not part of the Xtensa Instruction Set Architecture, but is instead specific to an
implementation. That is, it may not exist in all implementations of the Xtensa ISA.
SDCT is intended for writing the RAM array that implements the data cache tags as part
of manufacturing test.
SDCT uses the contents of address register as to select a line in the data cache and
writes the contents of address register at to the tag associated with that line. The value
written from at is described under Cache Tag Format in Section 4.5.1.2 on page 112.
SDCT is a privileged instruction.
Operation
if CRING ≠ 0 then
Exception (PrivilegedInstructionCause)
else
index ← AR[s]dih..dil
DataCacheTag[index] ← AR[t]
endif
Exceptions
EveryInstR Group (see page 244)
GenExcep(PrivilegedCause) if Exception Option
MemoryErrorException if Memory ECC/Parity Option
23 20 19 16 15 12 11 8 7 4 3 0
111100011001 s t 0000
444444
Store Data Cache Tag SDCT
Xtensa Instruction Set Architecture (ISA) Reference Manual 517
Implementation Notes
x ← ceil(log2(DataCacheBytes))
y ← log2(DataCacheBytes ÷ DataCacheWayCount)
z ← log2(DataCacheLineBytes)
The cache line specified by index AR[s]x-1..z in a direct-mapped cache or way
AR[s]x-1..y and index AR[s]y-1..z in a set-associative cache is the chosen line. If the
specified cache way is not valid (the fourth way of a three way cache), the instruction
does nothing.
SEXT Sign Extend
518 Xtensa Instruction Set Architecture (ISA) Reference Manual
Instruction Word (RRR)
Required Configuration Option
Miscellaneous Operations Option (See Section 4.3.8 on page 62)
Assembler Syntax
SEXT ar, as, 7..22
Description
SEXT takes the contents of address register as and replicates the bit specified by its
immediate operand (in the range 7 to 22) to the high bits and writes the result to address
register ar. The input can be thought of as an imm+1 bit value with the high bits irrele-
vant and this instruction produces the 32-bit sign-extension of this value.
Assembler Note
The immediate values accepted by the assembler are 7 to 22. The assembler encodes
these in the t field of the instruction using 0 to 15.
Operation
b ← t+7
AR[r] ← AR[s]b31−b||AR[s]b..0
Exceptions
EveryInstR Group (see page 244)
23 20 19 16 15 12 11 8 7 4 3 0
00100011 r s t 0000
444444
Store Instruction Cache Tag SICT
Xtensa Instruction Set Architecture (ISA) Reference Manual 519
Instruction Word (RRR)
Required Configuration Option
Instruction Cache Test Option (See Section 4.5.3 on page 116)
Assembler Syntax
SICT at, as
Description
SICT is not part of the Xtensa Instruction Set Architecture, but is instead specific to an
implementation. That is, it may not exist in all implementations of the Xtensa ISA.
SICT is intended for writing the RAM array that implements the instruction cache tags as
part of manufacturing test.
SICT uses the contents of address register as to select a line in the instruction cache,
and writes the contents of address register at to the tag associated with that line. The
value written from at is described under Cache Tag Format in Section 4.5.1.2 on
page 112.
SICT is a privileged instruction.
Operation
if CRING ≠ 0 then
Exception (PrivilegedInstructionCause)
else
index ← AR[s]iih..iil
InstCacheTag[index] ← AR[t]
endif
Exceptions
EveryInstR Group (see page 244)
GenExcep(PrivilegedCause) if Exception Option
MemoryErrorException if Memory ECC/Parity Option
23 20 19 16 15 12 11 8 7 4 3 0
111100010001 s t 0000
444444
SICT Store Instruction Cache Tag
520 Xtensa Instruction Set Architecture (ISA) Reference Manual
Implementation Notes
x ← ceil(log2(InstCacheBytes))
y ← log2(InstCacheBytes ÷ InstCacheWayCount)
z ← log2(InstCacheLineBytes)
The cache line specified by index AR[s]x-1..z in a direct-mapped cache or way
AR[s]x-1..y and index AR[s]y-1..z in a set-associative cache is the chosen line. If the
specified cache way is not valid (the fourth way of a three way cache), the instruction
does nothing.
Store Instruction Cache Word SICW
Xtensa Instruction Set Architecture (ISA) Reference Manual 521
Instruction Word (RRR)
Required Configuration Option
Instruction Cache Test Option (See Section 4.5.3 on page 116)
Assembler Syntax
SICW at, as
Description
SICW is not part of the Xtensa Instruction Set Architecture, but is instead specific to an
implementation. That is, it may not exist in all implementations of the Xtensa ISA.
SICW is intended for writing the RAM array that implements the instruction cache as part
of manufacturing tests.
SICW uses the contents of address register as to select a line in the instruction cache,
and writes the contents of address register at to the data associated with that line.
SICW is a privileged instruction.
Operation
if CRING ≠ 0 then
Exception (PrivilegedInstructionCause)
else
index ← AR[s]iih..iiw
InstCacheData [index] ← AR[t]
endif
Exceptions
EveryInstR Group (see page 244)
GenExcep(PrivilegedCause) if Exception Option
MemoryErrorException if Memory ECC/Parity Option
23 20 19 16 15 12 11 8 7 4 3 0
111100010011 s t 0000
444444
SICW Store Instruction Cache Word
522 Xtensa Instruction Set Architecture (ISA) Reference Manual
Implementation Notes
x ← ceil(log2(InstCacheBytes))
y ← log2(InstCacheBytes ÷ InstCacheWayCount)
z ← log2(InstCacheLineBytes)
The cache line specified by index AR[s]x-1..z in a direct-mapped cache or way
AR[s]x-1..y and index AR[s]y-1..z in a set-associative cache is the chosen line. If the
specified cache way is not valid (the fourth way of a three way cache), the instruction
does nothing. Within the cache line, AR[s]z-1..2 is used to determine which 32-bit
quantity within the line is written.
The width of the instruction cache RAM may be more than 32 bits depending on the con-
figuration. In that case, some implementations may write the same data replicated
enough times to fill the entire width of the RAM.
Simulator Call SIMCALL
Xtensa Instruction Set Architecture (ISA) Reference Manual 523
Instruction Word (RRR)
Required Configuration Option
Xtensa Instruction Set Simulator only — illegal in hardware
Assembler Syntax
SIMCALL
Description
SIMCALL is not implemented by any Xtensa processor. Processors raise an illegal
instruction exception for this opcode. It is implemented by the Xtensa Instruction Set
Simulator only to allow simulated programs to request services of the simulator host
processor. See the Xtensa Instruction Set Simulator (ISS) User’s Guide.
The value in address register a2 is the request code. Most codes request host system
call services while others are used for special purposes such as debugging. Arguments
needed by host system calls will be found in a3, a4, and a5 and a return code will be
stored to a2 and an error number to a3.
Operation
See the Xtensa Instruction Set Simulator (ISS) User’s Guide.
Exceptions
EveryInst Group (see page 244)
GenExcep(IllegalInstructionCause) if Exception Option
23 20 19 16 15 12 11 8 7 4 3 0
000000000101000100000000
444444
SLL Shift Left Logical
524 Xtensa Instruction Set Architecture (ISA) Reference Manual
Instruction Word (RRR)
Required Configuration Option
Core Architecture (See Section 4.2 on page 50)
Assembler Syntax
SLL ar, as
Description
SLL shifts the contents of address register as left by the number of bit positions speci-
fied (as 32 minus number of bit positions) in the SAR (shift amount register) and writes
the result to address register ar. Typically the SSL or SSA8L instructions are used to
specify the left shift amount by loading SAR with 32-shift. This transformation allows
SLL to be implemented in the SRC funnel shifter (which only shifts right), using the SLL
data as the most significant 32 bits and zero as the least significant 32 bits. Note the
result of SLL is undefined if SAR > 32.
Operation
sa ← SAR5..0
AR[r] ← (AR[s]||032)31+sa..sa
Exceptions
EveryInstR Group (see page 244)
23 20 19 16 15 12 11 8 7 4 3 0
10100001 r s 00000000
444444
Shift Left Logical Immediate SLLI
Xtensa Instruction Set Architecture (ISA) Reference Manual 525
Instruction Word (RRR)
Required Configuration Option
Core Architecture (See Section 4.2 on page 50)
Assembler Syntax
SLLI ar, as, 1..31
Description
SLLI shifts the contents of address register as left by a constant amount in the range
1..31 encoded in the instruction. The shift amount sa field is split, with bits 3..0 in bits
7..4 of the instruction word and bit 4 in bit 20 of the instruction word. The shift amount is
encoded as 32−shift. When the sa field is 0, the result of this instruction is undefined.
Assembler Note
The shift amount is specified in the assembly language as the number of bit positions to
shift left. The assembler performs the 32-shift calculation when it assembles the in-
struction word. When the immediate operand evaluates to zero, the assembler converts
this instruction to an OR instruction to effect a register-to-register move. To disable this
transformation, prefix the mnemonic with an underscore (_SLLI). If imm evaluates to
zero when the mnemonic has the underscore prefix, the assembler will emit an error.
Operation
AR[r] ← (AR[s]||032)31+sa..sa
Exceptions
EveryInstR Group (see page 244)
23 20 19 16 15 12 11 8 7 4 3 0
000sa40 0 0 1 r s sa3..0 0000
444444
SRA Shift Right Arithmetic
526 Xtensa Instruction Set Architecture (ISA) Reference Manual
Instruction Word (RRR)
Required Configuration Option
Core Architecture (See Section 4.2 on page 50)
Assembler Syntax
SRA ar, at
Description
SRA arithmetically shifts the contents of address register at right, inserting the sign of
at on the left, by the number of bit positions specified by SAR (shift amount register) and
writes the result to address register ar. Typically the SSR or SSA8B instructions are used
to load SAR with the shift amount from an address register. Note the result of SRA is un-
defined if SAR > 32.
Operation
sa ← SAR5..0
AR[r] ← ((AR[t]31)32||AR[t])31+sa..sa
Exceptions
EveryInstR Group (see page 244)
23 20 19 16 15 12 11 8 7 4 3 0
10110001 r 0000 t 0000
444444
Shift Right Arithmetic Immediate SRAI
Xtensa Instruction Set Architecture (ISA) Reference Manual 527
Instruction Word (RRR)
Required Configuration Option
Core Architecture (See Section 4.2 on page 50)
Assembler Syntax
SRAI ar, at, 0..31
Description
SRAI arithmetically shifts the contents of address register at right, inserting the sign of
at on the left, by a constant amount encoded in the instruction word in the range 0..31.
The shift amount sa field is split, with bits 3..0 in bits 11..8 of the instruction word,
and bit 4 in bit 20 of the instruction word.
Operation
AR[r] ← ((AR[t]31)32||AR[t])31+sa..sa
Exceptions
EveryInstR Group (see page 244)
23 20 19 16 15 12 11 8 7 4 3 0
001sa40001 r sa3..0 t 0000
444444
SRC Shift Right Combined
528 Xtensa Instruction Set Architecture (ISA) Reference Manual
Instruction Word (RRR)
Required Configuration Option
Core Architecture (See Section 4.2 on page 50)
Assembler Syntax
SRC ar, as, at
Description
SRC performs a right shift of the concatenation of address registers as and at by the
shift amount in SAR. The least significant 32 bits of the shift result are written to address
register ar. A shift with a wider input than output is called a funnel shift. SRC directly per-
forms right funnel shifts. Left funnel shifts are done by swapping the high and low oper-
ands to SRC and setting SAR to 32 minus the shift amount. The SSL and SSA8B instruc-
tions directly implement such SAR settings. Note the result of SRC is undefined if SAR >
32.
Operation
sa ← SAR5..0
AR[r] ← (AR[s]||AR[t])31+sa..sa
Exceptions
EveryInstR Group (see page 244)
23 20 19 16 15 12 11 8 7 4 3 0
10000001 r s t 0000
444444
Shift Right Logical SRL
Xtensa Instruction Set Architecture (ISA) Reference Manual 529
Instruction Word (RRR)
Required Configuration Option
Core Architecture (See Section 4.2 on page 50)
Assembler Syntax
SRL ar, at
Description
SRL shifts the contents of address register at right, inserting zeros on the left, by the
number of bits specified by SAR (shift amount register) and writes the result to address
register ar. Typically the SSR or SSA8B instructions are used to load SAR with the shift
amount from an address register. Note the result of SRL is undefined if SAR > 32.
Operation
sa ← SAR5..0
AR[r] ← (032||AR[t])31+sa..sa
Exceptions
EveryInstR Group (see page 244)
23 20 19 16 15 12 11 8 7 4 3 0
10010001 r 0000 t 0000
444444
SRLI Shift Right Logical Immediate
530 Xtensa Instruction Set Architecture (ISA) Reference Manual
Instruction Word (RRR)
Required Configuration Option
Core Architecture (See Section 4.2 on page 50)
Assembler Syntax
SRLI ar, at, 0..15
Description
SRLI shifts the contents of address register at right, inserting zeros on the left, by a
constant amount encoded in the instruction word in the range 0..15. There is no SRLI
for shifts ≥ 16. EXTUI replaces these shifts.
Assembler Note
The assembler converts SRLI instructions with a shift amount ≥ 16 into EXTUI. Prefixing
the SRLI instruction with an underscore (_SRLI) disables this replacement and forces
the assembler to generate an error.
Operation
AR[r] ← (032||AR[t])31+sa..sa
Exceptions
EveryInstR Group (see page 244)
23 20 19 16 15 12 11 8 7 4 3 0
01000001 r sa t 0000
444444
Set Shift Amount for BE Byte Shift SSA8B
Xtensa Instruction Set Architecture (ISA) Reference Manual 531
Instruction Word (RRR)
Required Configuration Option
Core Architecture (See Section 4.2 on page 50)
Assembler Syntax
SSA8B as
Description
SSA8B sets the shift amount register (SAR) for a left shift by multiples of eight (for exam-
ple, for big-endian (BE) byte alignment). The left shift amount is the two least significant
bits of address register as multiplied by eight. Thirty-two minus this amount is written to
SAR. Using 32 minus the left shift amount causes a funnel right shift and swapped high
and low input operands to perform a left shift. SSA8B is similar to SSL, except the shift
amount is multiplied by eight.
SSA8B is typically used to set up for an SRC instruction to shift bytes. It may be used with
big-endian byte ordering to extract a 32-bit value from a non-aligned byte address.
Operation
SAR ← 32 − (0||AR[s]1..0||03)
Exceptions
EveryInstR Group (see page 244)
23 20 19 16 15 12 11 8 7 4 3 0
010000000011 s 00000000
444444
SSA8L Set Shift Amount for LE Byte Shift
532 Xtensa Instruction Set Architecture (ISA) Reference Manual
Instruction Word (RRR)
Required Configuration Option
Core Architecture (See Section 4.2 on page 50)
Assembler Syntax
SSA8L as
Description
SSA8L sets the shift amount register (SAR) for a right shift by multiples of eight (for ex-
ample, for little-endian (LE) byte alignment). The right shift amount is the two least sig-
nificant bits of address register as multiplied by eight, and is written to SAR. SSA8L is
similar to SSR, except the shift amount is multiplied by eight.
SSA8L is typically used to set up for an SRC instruction to shift bytes. It may be used with
little-endian byte ordering to extract a 32-bit value from a non-aligned byte address.
Operation
SAR ← 0||AR[s]1..0||03
Exceptions
EveryInstR Group (see page 244)
23 20 19 16 15 12 11 8 7 4 3 0
010000000010 s 00000000
444444
Set Shift Amount Immediate SSAI
Xtensa Instruction Set Architecture (ISA) Reference Manual 533
Instruction Word (RRR)
Required Configuration Option
Core Architecture (See Section 4.2 on page 50)
Assembler Syntax
SSAI 0..31
Description
SSAI sets the shift amount register (SAR) to a constant. The shift amount sa field is split,
with bits 3..0 in bits 11..8 of the instruction word, and bit 4 in bit 4 of the instruction
word. Because immediate forms exist of most shifts (SLLI, SRLI, SRAI), this is primari-
ly useful to set the shift amount for SRC.
Operation
SAR ← 0||sa
Exceptions
EveryInst Group (see page 244)
23 20 19 16 15 12 11 8 7 4 3 0
010000000100 sa3..0 000sa40000
444444
SSI Store Single Immediate
534 Xtensa Instruction Set Architecture (ISA) Reference Manual
Instruction Word
(RRI8)
Required Configuration Option
Floating-Point Coprocessor Option (See Section 4.3.11 on page 67)
Assembler Syntax
SSI ft, as, 0..1020
Description
SSI is a 32-bit store from floating-point register ft to memory. It forms a virtual address
by adding the contents of address register as and an 8-bit zero-extended constant value
encoded in the instruction word shifted left by two. Therefore, the offset can specify mul-
tiples of four from zero to 1020. The data to be stored is taken from the contents of float-
ing-point register ft and written to memory at the physical address.
If the Region Translation Option (page 156) or the MMU Option (page 158) is enabled,
the virtual address is translated to the physical address. If not, the physical address is
identical to the virtual address. If the translation or memory reference encounters an
error (for example, protection violation or non-existent memory), the processor raises
one of several exceptions (see Section 4.4.1.5 on page 89).
Without the Unaligned Exception Option (page 99), the two least significant bits of the
address are ignored. A reference to an address that is not 0 mod 4 produces the same
result as a reference to the address with the least significant bits cleared. With the Un-
aligned Exception Option, such an access raises an exception.
Assembler Note
To form a virtual address, SSI calculates the sum of address register as and the imm8
field of the instruction word times four. Therefore, the machine-code offset is in terms of
32-bit (4 byte) units. However, the assembler expects a byte offset and encodes this into
the instruction by dividing by four.
Operation
vAddr ← AR[s] + (022||imm8||02)
Store32 (vAddr, FR[t])
23 16 15 12 11 8 7 4 3 0
imm8 0 1 0 0 s t 0 0 1 1
8 4444
Store Single Immediate SSI
Xtensa Instruction Set Architecture (ISA) Reference Manual 535
Exceptions
Memory Store Group (see page 245)
GenExcep(Coprocessor0Disabled) if Coprocessor Option
SSIU Store Single Immediate with Update
536 Xtensa Instruction Set Architecture (ISA) Reference Manual
Instruction Word
(RRI8)
Required Configuration Option
Floating-Point Coprocessor Option (See Section 4.3.11 on page 67)
Assembler Syntax
SSIU ft, as, 0..1020
Description
SSIU is a 32-bit store from floating-point register ft to memory with base address regis-
ter update. It forms a virtual address by adding the contents of address register as and
an 8-bit zero-extended constant value encoded in the instruction word shifted left by two.
Therefore, the offset can specify multiples of four from zero to 1020. The data to be
stored is taken from the contents of floating-point register ft and written to memory at
the physical address. The virtual address is written back to address register as.
If the Region Translation Option (page 156) or the MMU Option (page 158) is enabled,
the virtual address is translated to the physical address. If not, the physical address is
identical to the virtual address. If the translation or memory reference encounters an
error (for example, protection violation or non-existent memory), the processor raises
one of several exceptions (see Section 4.4.1.5 on page 89).
Without the Unaligned Exception Option (page 99), the two least significant bits of the
address are ignored. A reference to an address that is not 0 mod 4 produces the same
result as a reference to the address with the least significant bits cleared. With the Un-
aligned Exception Option, such an access raises an exception.
Assembler Note
To form a virtual address, SSIU calculates the sum of address register as and the imm8
field of the instruction word times four. Therefore, the machine-code offset is in terms of
32-bit (4 byte) units. However, the assembler expects a byte offset and encodes this into
the instruction by dividing by four.
Operation
vAddr ← AR[s] + (022||imm8||02)
23 16 15 12 11 8 7 4 3 0
imm8 1 1 0 0 s t 0 0 1 1
8 4444
Store Single Immediate with Update SSIU
Xtensa Instruction Set Architecture (ISA) Reference Manual 537
Store32 (vAddr, FR[t])
AR[s] ← vAddr
Exceptions
Memory Store Group (see page 245)
GenExcep(Coprocessor0Disabled) if Coprocessor Option
SSL Set Shift Amount for Left Shift
538 Xtensa Instruction Set Architecture (ISA) Reference Manual
Instruction Word (RRR)
Required Configuration Option
Core Architecture (See Section 4.2 on page 50)
Assembler Syntax
SSL as
Description
SSL sets the shift amount register (SAR) for a left shift (for example, SLL). The left shift
amount is the 5 least significant bits of address register as. 32 minus this amount is writ-
ten to SAR. Using 32 minus the left shift amount causes a right funnel shift, and swapped
high and low input operands to perform a left shift.
Operation
sa ← AR[s]4..0
SAR ← 32 − (0||sa)
Exceptions
EveryInstR Group (see page 244)
23 20 19 16 15 12 11 8 7 4 3 0
010000000001 s 00000000
444444
Set Shift Amount for Right Shift SSR
Xtensa Instruction Set Architecture (ISA) Reference Manual 539
Instruction Word (RRR)
Required Configuration Option
Core Architecture (See Section 4.2 on page 50)
Assembler Syntax
SSR as
Description
SSR sets the shift amount register (SAR) for a right shift (for example, SRL, SRA, or SRC).
The least significant five bits of address register as are written to SAR. The most signifi-
cant bit of SAR is cleared. This instruction is similar to a WSR.SAR, but differs in that only
AR[s]4..0 is used, instead of AR[s]5..0.
Operation
sa ← AR[s]4..0
SAR ← 0||sa
Exceptions
EveryInstR Group (see page 244)
23 20 19 16 15 12 11 8 7 4 3 0
010000000000 s 00000000
444444
SSX Store Single Indexed
540 Xtensa Instruction Set Architecture (ISA) Reference Manual
Instruction Word (RRR)
Required Configuration Option
Floating-Point Coprocessor Option (See Section 4.3.11 on page 67)
Assembler Syntax
SSX fr, as, at
Description
SSX is a 32-bit store from floating-point register ft to memory. It forms a virtual address
by adding the contents of address register as and the contents of address register at.
The data to be stored is taken from the contents of floating-point register fr and written
to memory at the physical address.
If the Region Translation Option (page 156) or the MMU Option (page 158)is enabled,
the virtual address is translated to the physical address. If not, the physical address is
identical to the virtual address. If the translation or memory reference encounters an
error (for example, protection violation or non-existent memory), the processor raises
one of several exceptions (see Section 4.4.1.5 on page 89).
Without the Unaligned Exception Option (page 99), the two least significant bits of the
address are ignored. A reference to an address that is not 0 mod 4 produces the same
result as a reference to the address with the least significant bits cleared. With the Un-
aligned Exception Option, such an access raises an exception.
Operation
vAddr ← AR[s] + (AR[t])
Store32 (vAddr, FR[r])
Exceptions
Memory Store Group (see page 245)
GenExcep(Coprocessor0Disabled) if Coprocessor Option
23 20 19 16 15 12 11 8 7 4 3 0
01001000 r s t 0000
444444
Store Single Indexed with Update SSXU
Xtensa Instruction Set Architecture (ISA) Reference Manual 541
Instruction Word (RRR)
Required Configuration Option
Floating-Point Coprocessor Option (See Section 4.3.11 on page 67)
Assembler Syntax
SSXU fr, as, at
Description
SSXU is a 32-bit store from floating-point register ft to memory with base address regis-
ter update. It forms a virtual address by adding the contents of address register as and
the contents of address register at. The data to be stored is taken from the contents of
floating-point register fr and written to memory at the physical address. The virtual ad-
dress is written back to address register as.
If the Region Translation Option (page 156) or the MMU Option (page 158)is enabled,
the virtual address is translated to the physical address. If not, the physical address is
identical to the virtual address. If the translation or memory reference encounters an
error (for example, protection violation or non-existent memory), the processor raises
one of several exceptions (see Section 4.4.1.5 on page 89).
Without the Unaligned Exception Option (page 99), the two least significant bits of the
address are ignored. A reference to an address that is not 0 mod 4 produces the same
result as a reference to the address with the least significant bits cleared. With the Un-
aligned Exception Option, such an access raises an exception.
Operation
vAddr ← AR[s] + (AR[t])
Store32 (vAddr, FR[r])
AR[s] ← vAddr
Exceptions
Memory Store Group (see page 245)
GenExcep(Coprocessor0Disabled) if Coprocessor Option
23 20 19 16 15 12 11 8 7 4 3 0
01011000 r s t 0000
444444
SUB Subtract
542 Xtensa Instruction Set Architecture (ISA) Reference Manual
Instruction Word (RRR)
Required Configuration Option
Core Architecture (See Section 4.2 on page 50)
Assembler Syntax
SUB ar, as, at
Description
SUB calculates the two’s complement 32-bit difference of address registers as and at.
The low 32 bits of the difference are written to address register ar. Arithmetic overflow is
not detected.
Operation
AR[r] ← AR[s] − AR[t]
Exceptions
EveryInstR Group (see page 244)
23 20 19 16 15 12 11 8 7 4 3 0
11000000 r s t 0000
444444
Subtract Single SUB.S
Xtensa Instruction Set Architecture (ISA) Reference Manual 543
Instruction Word (RRR)
Required Configuration Option
Floating-Point Coprocessor Option (See Section 4.3.11 on page 67)
Assembler Syntax
SUB.S fr, fs, ft
Description
SUB.S computes the IEEE754 single-precision difference of the contents of floating-
point registers fs and ft and writes the result to floating-point register fr.
Operation
FR[r] ← FR[s] −s FR[t]
Exceptions
EveryInst Group (see page 244)
GenExcep(Coprocessor0Disabled) if Coprocessor Option
23 20 19 16 15 12 11 8 7 4 3 0
00011010 r s t 0000
444444
SUBX2 Subtract with Shift by 1
544 Xtensa Instruction Set Architecture (ISA) Reference Manual
Instruction Word (RRR)
Required Configuration Option
Core Architecture (See Section 4.2 on page 50)
Assembler Syntax
SUBX2 ar, as, at
Description
SUBX2 calculates the two’s complement 32-bit difference of address register as shifted
left by 1 bit and address register at. The low 32 bits of the difference are written to
address register ar. Arithmetic overflow is not detected.
SUBX2 is frequently used as part of sequences to multiply by small constants.
Operation
AR[r] ← (AR[s]30..0||0) − AR[t]
Exceptions
EveryInstR Group (see page 244)
23 20 19 16 15 12 11 8 7 4 3 0
11010000 r s t 0000
444444
Subtract with Shift by 2 SUBX4
Xtensa Instruction Set Architecture (ISA) Reference Manual 545
Instruction Word (RRR)
Required Configuration Option
Core Architecture (See Section 4.2 on page 50)
Assembler Syntax
SUBX4 ar, as, at
Description
SUBX4 calculates the two’s complement 32-bit difference of address register as shifted
left by two bits and address register at. The low 32 bits of the difference are written to
address register ar. Arithmetic overflow is not detected.
SUBX4 is frequently used as part of sequences to multiply by small constants.
Operation
AR[r] ← (AR[s]29..0||02) − AR[t]
Exceptions
EveryInstR Group (see page 244)
23 20 19 16 15 12 11 8 7 4 3 0
11100000 r s t 0000
444444
SUBX8 Subtract with Shift by 3
546 Xtensa Instruction Set Architecture (ISA) Reference Manual
Instruction Word (RRR)
Required Configuration Option
Core Architecture (See Section 4.2 on page 50)
Assembler Syntax
SUBX8 ar, as, at
Description
SUBX8 calculates the two’s complement 32-bit difference of address register as shifted
left by three bits and address register at. The low 32 bits of the difference are written to
address register ar. Arithmetic overflow is not detected.
SUBX8 is frequently used as part of sequences to multiply by small constants.
Operation
AR[r] ← (AR[s]28..0||03) − AR[t]
Exceptions
EveryInstR Group (see page 244)
23 20 19 16 15 12 11 8 7 4 3 0
11110000 r s t 0000
444444
System Call SYSCALL
Xtensa Instruction Set Architecture (ISA) Reference Manual 547
Instruction Word (RRR)
Required Configuration Option
Exception Option (See Section 4.4.1 on page 82)
Assembler Syntax
SYSCALL
Description
When executed, the SYSCALL instruction raises a system-call exception, redirecting ex-
ecution to an exception vector (see Section 4.4.1 on page 82). Therefore, SYSCALL in-
structions never complete. EPC[1] contains the address of the SYSCALL and ICOUNT is
not incremented. The system call handler should add 3 to EPC[1] before returning from
the exception to continue execution.
The program may pass parameters to the system-call handler in the registers. There are
no bits in SYSCALL instruction reserved for this purpose. See Section 8.2.2 “System
Calls” on page 597 for a description of software conventions for system call parameters.
Operation
Exception (SyscallCause)
Exceptions
EveryInst Group (see page 244)
GenExcep(SyscallCause) if Exception Option
23 20 19 16 15 12 11 8 7 4 3 0
000000000101000000000000
444444
TRUNC.S Truncate Single to Fixed
548 Xtensa Instruction Set Architecture (ISA) Reference Manual
Instruction Word (RRR)
Required Configuration Option
Floating-Point Coprocessor Option (See Section 4.3.11 on page 67)
Assembler Syntax
TRUNC.S ar, fs, 0..15
Description
TRUNC.S converts the contents of floating-point register fs from single-precision to
signed integer format, rounding toward 0. The single-precision value is first scaled by a
power of two constant value encoded in the t field, with 0..15 representing 1.0, 2.0, 4.0,
…, 32768.0. The scaling allows for a fixed point notation where the binary point is at the
right end of the integer for t=0, and moves to the left as t increases until for t=15 there
are 15 fractional bits represented in the fixed point number. For positive overflow (value
≥ 32'h7fffffff), positive infinity, or NaN, 32'h7fffffff is returned; for negative
overflow (value ≤ 32'h80000000) or negative infinity, 32'h80000000 is returned. The
result is written to address register ar.
Operation
AR[r] ← truncs(FR[s] ×s pows(2.0,t))
Exceptions
EveryInstR Group (see page 244)
GenExcep(Coprocessor0Disabled) if Coprocessor Option
23 20 19 16 15 12 11 8 7 4 3 0
10011010 r s t 0000
444444
Compare Single Unordered or Equal UEQ.S
Xtensa Instruction Set Architecture (ISA) Reference Manual 549
Instruction Word (RRR)
Required Configuration Option
Floating-Point Coprocessor Option (See Section 4.3.11 on page 67)
Assembler Syntax
UEQ.S br, fs, ft
Description
UEQ.S compares the contents of floating-point registers fs and ft. If the values are
equal or unordered then Boolean register br is set to 1, otherwise br is set to 0. Accord-
ing to IEEE754, +0 and −0 compare as equal. IEEE754 floating-point values are
unordered if either of them is a NaN.
Operation
BRr ← isNaN(FR[s]) or isNaN(FR[t]) or (FR[s] =s FR[t])
Exceptions
EveryInst Group (see page 244)
GenExcep(Coprocessor0Disabled) if Coprocessor Option
23 20 19 16 15 12 11 8 7 4 3 0
00111011 r s t 0000
444444
UFLOAT.S Convert Unsigned Fixed to Single
550 Xtensa Instruction Set Architecture (ISA) Reference Manual
Instruction Word (RRR)
Required Configuration Option
Floating-Point Coprocessor Option (See Section 4.3.11 on page 67)
Assembler Syntax
UFLOAT.S fr, as, 0..15
Description
UFLOAT.S converts the contents of address register as from unsigned integer to single-
precision format, rounding according to the current rounding mode. The converted inte-
ger value is then scaled by a power of two constant value encoded in the t field, with
0..15 representing 1.0, 0.5, 0.25, …, 1.0÷s32768.0. The scaling allows for a fixed point
notation where the binary point is at the right end of the integer for t=0, and moves to
the left as t increases until for t=15 there are 15 fractional bits represented in the fixed
point number. The result is written to floating-point register fr.
Operation
FR[r] ← ufloats(AR[s]) ×s pows(2.0,-t))
Exceptions
EveryInstR Group (see page 244)
GenExcep(Coprocessor0Disabled) if Coprocessor Option
23 20 19 16 15 12 11 8 7 4 3 0
11011010 r s t 0000
444444
Compare Single Unord or Less Than or Equal ULE.S
Xtensa Instruction Set Architecture (ISA) Reference Manual 551
Instruction Word (RRR)
Required Configuration Option
Floating-Point Coprocessor Option (See Section 4.3.11 on page 67)
Assembler Syntax
ULE.S br, fs, ft
Description
ULE.S compares the contents of floating-point registers fs and ft. If the contents of fs
are less than or equal to or unordered with the contents of ft, then Boolean register br
is set to 1, otherwise br is set to 0. IEEE754 specifies that +0 and −0 compare as equal.
IEEE754 floating-point values are unordered if either of them is a NaN.
Operation
BRr ← isNaN(FR[s]) or isNaN(FR[t]) or (FR[s] ≤s FR[t])
Exceptions
EveryInst Group (see page 244)
GenExcep(Coprocessor0Disabled) if Coprocessor Option
23 20 19 16 15 12 11 8 7 4 3 0
01111011 r s t 0000
444444
ULT.S Compare Single Unordered or Less Than
552 Xtensa Instruction Set Architecture (ISA) Reference Manual
Instruction Word (RRR)
Required Configuration Option
Floating-Point Coprocessor Option (See Section 4.3.11 on page 67)
Assembler Syntax
ULT.S br, fs, ft
Description
ULT.S compares the contents of floating-point registers fs and ft. If the contents of fs
are less than or unordered with the contents of ft, then Boolean register br is set to 1,
otherwise br is set to 0. IEEE754 specifies that +0 and −0 compare as equal. IEEE754
floating-point values are unordered if either of them is a NaN.
Operation
BRr ← isNaN(FR[s]) or isNaN(FR[t]) or (FR[s] <s FR[t])
Exceptions
EveryInst Group (see page 244)
GenExcep(Coprocessor0Disabled) if Coprocessor Option
23 20 19 16 15 12 11 8 7 4 3 0
01011011 r s t 0000
444444
Unsigned Multiply UMUL.AA.*
Xtensa Instruction Set Architecture (ISA) Reference Manual 553
Instruction Word (RRR)
Required Configuration Option
MAC16 Option (See Section 4.3.7 on page 60)
Assembler Syntax
UMUL.AA.* as, at
Where * expands as follows:
UMUL.AA.LL - for (half=0)
UMUL.AA.HL - for (half=1)
UMUL.AA.LH - for (half=2)
UMUL.AA.HH - for (half=3)
Description
UMUL.AA.* performs an unsigned multiply of half of each of the address registers as
and at, producing a 32-bit result. The result is zero-extended to 40 bits and written to
the MAC16 accumulator.
Operation
m1 ← if half0 then AR[s]31..16 else AR[s]15..0
m2 ← if half1 then AR[t]31..16 else AR[t]15..0
ACC ← (024||m1) × (024||m2)
Exceptions
EveryInstR Group (see page 244)
23 20 19 16 15 12 11 8 7 4 3 0
011100 half 0 0 0 0 s t 0 1 0 0
444444
UN.S Compare Single Unordered
554 Xtensa Instruction Set Architecture (ISA) Reference Manual
Instruction Word (RRR)
Required Configuration Option
Floating-Point Coprocessor Option (See Section 4.3.11 on page 67)
Assembler Syntax
UN.S br, fs, ft
Description
UN.S sets Boolean register br to 1 if the contents of either floating-point register fs or
ft is a IEEE754 NaN; otherwise br is set to 0.
Operation
BRr ← isNaN(FR[s]) or isNaN(FR[t])
Exceptions
EveryInst Group (see page 244)
GenExcep(Coprocessor0Disabled) if Coprocessor Option
23 20 19 16 15 12 11 8 7 4 3 0
00011011 r s t 0000
444444
Truncate Single to Fixed Unsigned UTRUNC.S
Xtensa Instruction Set Architecture (ISA) Reference Manual 555
Instruction Word (RRR)
Required Configuration Option
Floating-Point Coprocessor Option (See Section 4.3.11 on page 67)
Assembler Syntax
UTRUNC.S ar, fs, 0..15
Description
UTRUNC.S converts the contents of floating-point register fs from single-precision to
unsigned integer format, rounding toward 0. The single-precision value is first scaled by
a power of two constant value encoded in the t field, with 0..15 representing 1.0, 2.0,
4.0, …, 32768.0. The scaling allows for a fixed point notation where the binary point is at
the right end of the integer for t=0, and moves to the left as t increases until for t=15
there are 15 fractional bits represented in the fixed point number. For positive overflow
(value ≥ 32'hffffffff), positive infinity, or NaN, 32'hffffffff is returned; for neg-
ative numbers or negative infinity, 32'h80000000 is returned. The result is written to
address register ar.
Operation
AR[r] ← utruncs(FR[s] ×s pows(2.0,t))
Exceptions
EveryInstR Group (see page 244)
GenExcep(Coprocessor0Disabled) if Coprocessor Option
23 20 19 16 15 12 11 8 7 4 3 0
11101010 r s t 0000
444444
WAITI Wait for Interrupt
556 Xtensa Instruction Set Architecture (ISA) Reference Manual
Instruction Word (RRR)
Required Configuration Option
Interrupt Option (See Section 4.4.4 on page 100)
Assembler Syntax
WAITI 0..15
Description
WAITI sets the interrupt level in PS.INTLEVEL to imm4 and then, on some Xtensa ISA
implementations, suspends processor operation until an interrupt occurs. WAITI is typi-
cally used in an idle loop to reduce power consumption. CCOUNT continues to increment
during suspended operation, and a CCOMPARE interrupt will wake the processor.
When an interrupt is taken during suspended operation, EPC[i] will have the address
of the instruction following WAITI. An implementation is not required to enter suspended
operation and may leave suspended operation and continue execution at the following
instruction at any time. Usually, therefore, the WAITI instruction should be within a loop.
The combination of setting the interrupt level and suspending operation avoids a race
condition where an interrupt between the interrupt level setting and the suspension of
operation would be ignored until a second interrupt occurred.
WAITI is a privileged instruction.
Operation
if CRING ≠ 0 then
Exception (PrivilegedInstructionCause)
else
PS.INTLEVEL ← imm4
endif
Exceptions
EveryInst Group (see page 244)
GenExcep(PrivilegedCause) if Exception Option
23 20 19 16 15 12 11 8 7 4 3 0
000000000111 imm4 00000000
444444
Write Data TLB Entry WDTLB
Xtensa Instruction Set Architecture (ISA) Reference Manual 557
Instruction Word (RRR)
Required Configuration Option
Region Translation Option (page 156) or the MMU Option (page 158)
Assembler Syntax
WDTLB at, as
Description
WDTLB uses the contents of address register as to specify a data TLB entry and writes
the contents of address register at into that entry. See Section 4.6 on page 138 for in-
formation on the address and result register formats for specific memory protection and
translation options. The point at which the data TLB write is effected is implementation-
specific. Any translation that would be affected by this write before the execution of a
DSYNC instruction is therefore undefined.
WDTLB is a privileged instruction.
Operation
if CRING ≠ 0 then
Exception (PrivilegedInstructionCause)
else
(vpn, ei, wi) ← SplitDataTLBEntrySpec(AR[s])
(ppn, sr, ring, ca) ← SplitDataEntry(wi, AR[t])
DataTLB[wi][ei].ASID ← ASID(ring)
DataTLB[wi][ei].VPN ← vpn
DataTLB[wi][ei].PPN ← ppn
DataTLB[wi][ei].SR ← sr
DataTLB[wi][ei].CA ← ca
endif
Exceptions
EveryInstR Group (see page 244)
GenExcep(PrivilegedCause) if Exception Option
23 20 19 16 15 12 11 8 7 4 3 0
010100001110 s t 0000
444444
WER Write External Register
558 Xtensa Instruction Set Architecture (ISA) Reference Manual
Instruction Word (RRR)
Required Configuration Option
Core Architecture (See Section 4.2 on page 50)
Assembler Syntax
WER at, as
Description
WER writes one of a set of "External Registers". It is in some ways similar to the WSR.*
instruction except that the registers being written are not defined by the Xtensa ISA and
are conceptually outside the processor core. They are written through processor ports.
Address register as is used to determine which register is to be written and address reg-
ister at provides the write data. When no External Register is addressed by the value in
address register as, no write occurs. The entire address space is reserved for use by
Tensilica. RER and WER are managed by the processor core so that the requests appear
on the processor ports in program order. External logic is responsible for extending that
order to the registers themselves.
WER is a privileged instruction.
Operation
if CRING ≠ 0 then
Exception (PrivilegedInstructionCause)
else
Write External Register as defined outside the processor.
endif
Exceptions
EveryInstR Group (see page 244)
GenExcep(PrivilegedCause) if Exception Option
23 20 19 16 15 12 11 8 7 4 3 0
010000000111 s t 0000
444444
Move AR to FR WFR
Xtensa Instruction Set Architecture (ISA) Reference Manual 559
Instruction Word (RRR)
Required Configuration Option
Floating-Point Coprocessor Option (See Section 4.3.11 on page 67)
Assembler Syntax
WFR fr, as
Description
WFR moves the contents of address register as to floating-point register fr. The move is
non-arithmetic; no floating-point exceptions are raised.
Operation
FR[r] ← AR[s]
Exceptions
EveryInstR Group (see page 244)
GenExcep(Coprocessor0Disabled) if Coprocessor Option
23 20 19 16 15 12 11 8 7 4 3 0
11111010 r s 01010000
444444
WITLB Write Instruction TLB Entry
560 Xtensa Instruction Set Architecture (ISA) Reference Manual
Instruction Word (RRR)
Required Configuration Option
Region Translation Option (page 156) or the MMU Option (page 158)
Assembler Syntax
WITLB at, as
Description
WITLB uses the contents of address register as to specify an instruction TLB entry and
writes the contents of address register at into that entry. See Section 4.6 on page 138
for information on the address and result register formats for specific memory protection
and translation options. The point at which the instruction TLB write is effected is imple-
mentation-specific. Any translation that would be affected by this write before the execu-
tion of an ISYNC instruction is therefore undefined.
WITLB is a privileged instruction.
Operation
if CRING ≠ 0 then
Exception (PrivilegedInstructionCause)
else
(vpn, ei, wi) ← SplitInstTLBEntrySpec(AR[s])
(ppn, sr, ring, ca) ← SplitInstEntry(wi, AR[t])
InstTLB[wi][ei].ASID ← ASID(ring)
InstTLB[wi][ei].VPN ← vpn
InstTLB[wi][ei].PPN ← ppn
InstTLB[wi][ei].SR ← sr
InstTLB[wi][ei].CA ← ca
endif
Exceptions
EveryInstR Group (see page 244)
GenExcep(PrivilegedCause) if Exception Option
23 20 19 16 15 12 11 8 7 4 3 0
010100000110 s t 0000
444444
Write Special Register WSR.*
Xtensa Instruction Set Architecture (ISA) Reference Manual 561
Instruction Word (RSR)
Required Configuration Option
Core Architecture (See Section 4.2 on page 50)
Assembler Syntax
WSR.* at
WSR at, *
WSR at, 0..255
Description
WSR.* writes the special registers that are described in Section 3.8.10 “Processor Con-
trol Instructions” on page 45. See Section 5.3 on page 208 for more detailed information
on the operation of this instruction for each Special Register.
The contents of address register at are written to the special register designated by the
8-bit sr field of the instruction word. The name of the Special Register is used in place
of the ‘*’ in the assembler syntax above and the translation is made to the 8-bit sr field
by the assembler.
WSR is an assembler macro for WSR.* that provides compatibility with the older versions
of the instruction containing either the name or the number of the Special Register.
The point at which WSR.* to certain registers affects subsequent instructions is not al-
ways defined (SAR and ACC are exceptions). In these cases, the Special Register Tables
in Section 5.3 on page 208 explain how to ensure the effects are seen by a particular
point in the instruction stream (typically involving the use of one of the ISYNC, RSYNC,
ESYNC, or DSYNC instructions). A WSR.* followed by an RSR.* to the same register
should be separated with an ESYNC to guarantee the value written is read back. A
WSR.PS followed by RSIL also requires an ESYNC.
WSR.* with Special Register numbers ≥ 64 is privileged. A WSR.* for an unconfigured
register generally will raise an illegal instruction exception.
23 20 19 16 15 8 7 4 3 0
00010011 sr t 0000
4 4 8 4 4
WSR.* Write Special Register
562 Xtensa Instruction Set Architecture (ISA) Reference Manual
Operation
sr ← if msbFirst then s||r else r||s
if sr ≥ 64 and CRING ≠ 0 then
Exception (PrivilegedInstructionCause)
else
see the Special Register Tables in Section 5.3 on page 208
endif
Exceptions
EveryInstR Group (see page 244)
GenExcep(IllegalInstructionCause) if Exception Option
GenExcep(PrivilegedCause) if Exception Option
Write User Register WUR.*
Xtensa Instruction Set Architecture (ISA) Reference Manual 563
Instruction Word (RSR)
Required Configuration Option
No Option - instructions created from the TIE language (See Section 4.3.9.2 “Coproces-
sor Context Switch” on page 64)
Assembler Syntax
WUR.* at
WUR at,*
Description
WUR.* writes TIE state that has been grouped into 32-bit quantities by the TIE
user_register statement. The name in the user_register statement replaces the
“*” in the instruction name and causes the correct register number to be placed in the st
field of the encoded instruction. The contents of address register at are written to the
TIE user_register designated by the 8-bit sr field of the instruction word.
WUR is an assembler macro for WUR.* that provides compatibility with the older version
of the instruction.
Operation
user_register[sr] ← AR[t]
Exceptions
EveryInstR Group (see page 244)
GenExcep(Coprocessor*Disabled) if Coprocessor Option
23 20 19 16 15 8 7 4 3 0
11110011 sr t 0000
4 4 8 4 4
XOR Bitwise Logical Exclusive Or
564 Xtensa Instruction Set Architecture (ISA) Reference Manual
Instruction Word (RRR)
Required Configuration Option
Core Architecture (See Section 4.2 on page 50)
Assembler Syntax
XOR ar, as, at
Description
XOR calculates the bitwise logical exclusive or of address registers as and at. The
result is written to address register ar.
Operation
AR[r] ← AR[s] xor AR[t]
Exceptions
EveryInstR Group (see page 244)
23 20 19 16 15 12 11 8 7 4 3 0
00110000 r s t 0000
444444
Boolean Exclusive Or XORB
Xtensa Instruction Set Architecture (ISA) Reference Manual 565
Instruction Word (RRR)
Required Configuration Option
Boolean Option (See Section 4.3.10 on page 65)
Assembler Syntax
XORB br, bs, bt
Description
XORB performs the logical exclusive or of Boolean registers bs and bt and writes the
result to Boolean register br.
When the sense of one of the source Booleans is inverted (0 → true, 1 → false), use an
inverted test of the result. When the sense of both of the source Booleans is inverted,
use a non-inverted test of the result.
Operation
BRr ← BRs xor BRt
Exceptions
EveryInstR Group (see page 244)
23 20 19 16 15 12 11 8 7 4 3 0
01000010 r s t 0000
444444
XSR.* Exchange Special Register
566 Xtensa Instruction Set Architecture (ISA) Reference Manual
Instruction Word (RSR)
Required Configuration Option
Core Architecture (See Section 4.2 on page 50) (added in T1040)
Assembler Syntax
XSR.* at
XSR at, *
XSR at, 0..255
Description
XSR.* simultaneously reads and writes the special registers that are described in
Section 3.8.10 “Processor Control Instructions” on page 45. See Section 5.3 on
page 208 for more detailed information on the operation of this instruction for each
Special Register.
The contents of address register at and the Special Register designated by the immedi-
ate in the 8-bit sr field of the instruction word are both read. The read address register
value is then written to the Special Register, and the read Special Register value is writ-
ten to at. The name of the Special Register is used in place of the ‘*’ in the assembler
syntax above and the translation is made to the 8-bit sr field by the assembler.
XSR is an assembler macro for XSR.*, which provides compatibility with the older ver-
sions of the instruction containing either the name or the number of the Special Register.
The point at which XSR.* to certain registers affects subsequent instructions is not al-
ways defined (SAR and ACC are exceptions). In these cases, the Special Register Tables
in Section 5.3 on page 208 explain how to ensure the effects are seen by a particular
point in the instruction stream (typically involving the use of one of the ISYNC, RSYNC,
ESYNC, or DSYNC instructions). An XSR.* followed by an RSR.* to the same register
should be separated with an ESYNC to guarantee the value written is read back. An
XSR.PS followed by RSIL also requires an ESYNC. In general, the restrictions on XSR.*
include the union of the restrictions of the corresponding RSR.* and WSR.*.
23 20 19 16 15 8 7 4 3 0
01100001 sr t 0000
4 4 8 4 4
Xtensa Instruction Set Architecture (ISA) Reference Manual 567
XSR.* with Special Register numbers ≥ 64 is privileged. An XSR.* for an unconfigured
register generally will raise an illegal instruction exception.
Operation
sr ← if msbFirst then s||r else r||s
if sr ≥ 64 and CRING ≠ 0 then
Exception (PrivilegedInstructionCause)
else
t0 ← AR[t]
t1 ← see RSR frame of the Tables in Section 5.3 on page 208
see WSR frame of the Tables in Section 5.3 on page 208 ← t0
AR[t] ← t1
endif
Exceptions
EveryInstR Group (see page 244)
GenExcep(IllegalInstructionCause) if Exception Option
GenExcep(PrivilegedCause) if Exception Option
568 Xtensa Instruction Set Architecture (ISA) Reference Manual
Chapter 7. Instruction Formats and Opcodes
Xtensa Instruction Set Architecture (ISA) Reference Manual 569
7. Instruction Formats and Opcodes
7.1 Formats
The following sections show the named opcode formats for instruction encodings. The
field names in these formats are used in the opcode tables in Section 7.3.1. The format
names are used throughout this document. Each chart shows both big-endian and little-
endian encodings with bits numbered appropriately for that endianness. The vertical
bars in the formats indicate the points at which the opcode is separated, reversed in or-
der, and reassembled to arrive at the opposite endianness format.
7.1.1 RRR
7.1.2 RRI4
0 3 4 7 8 11 12 15 16 19 20 23
Big End. op0 t s r op1 op2
444444
23 20 19 16 15 12 11 8 7 4 3 0
Little End. op2 op1 r s t op0
444444
0 3 4 7 8 11 12 15 16 19 20 23
Big End. op0 t s r op1 imm4
444444
23 20 19 16 15 12 11 8 7 4 3 0
Little End. imm4 op1 r s t op0
444444
Chapter 7. Instruction Formats and Opcodes
570 Xtensa Instruction Set Architecture (ISA) Reference Manual
7.1.3 RRI8
7.1.4 RI16
7.1.5 RSR
0 3 4 7 8 11 12 15 16 23
Big End. op0 t s r imm8
4444 8
23 16 15 12 11 8 7 4 3 0
Little End. imm8 r s t op0
8 4444
0 3 4 7 8 23
Big End. op0 timm16
4 4 16
23 8 7 4 3 0
Little End. imm16 top0
16 4 4
0 3 4 7 8 15 16 19 20 23
Big End. op0 trs op1 op2
4 4 8 4 4
23 20 19 16 15 7 4 3 0
Little End. op2 op1 rs top0
4 4 8 4 4
Chapter 7. Instruction Formats and Opcodes
Xtensa Instruction Set Architecture (ISA) Reference Manual 571
7.1.6 CALL
7.1.7 CALLX
7.1.8 BRI8
0 3456 23
Big End. op0 noffset
4 2 18
23 6543 0
Little End. offset nop0
18 2 4
0 345678 11 12 15 16 19 20 23
Big End. op0 n m s r op1 op2
4 2 2 4 4 4 4
23 20 19 16 15 12 11 8 7 4 3 0
Little End. op2 op1 r s m n op0
4 4 4 4 2 2 4
0 345678 11 12 15 16 23
Big End. op0 n m s r imm8
4 2 2 4 4 8
23 16 15 12 11 8 7 4 3 0
Little End. imm8 r s m n op0
8 4 4 2 2 4
Chapter 7. Instruction Formats and Opcodes
572 Xtensa Instruction Set Architecture (ISA) Reference Manual
7.1.9 BRI12
7.1.10 RRRN
7.1.11 RI7
0 345678 11 12 23
Big End. op0 n m s imm12
4 2 2 4 12
23 12 11 8 7 4 3 0
Little End. imm12 s m n op0
12 4 2 2 4
0 3 4 7 8 11 12 15
Big End. op0 t s r
4444
15 12 11 8 7 4 3 0
Little End. r s t op0
4444
0 3 4 7 8 11 12 15
Big End. op0 iimm76..4 simm73..0
4444
15 12 11 8 7 6 4 3 0
Little End. imm73..0 s i imm76..4 op0
4444
Chapter 7. Instruction Formats and Opcodes
Xtensa Instruction Set Architecture (ISA) Reference Manual 573
7.1.12 RI6
7.2 Instruction Fields
0 3 4 7 8 11 12 15
Big End. op0 i z imm65..4 simm63..0
4444
15 12 11 876543 0
Little End. imm63..0 s i z imm65..4 op0
4444
Table 7–191. Uses Of Instruction Fields
Field Definition
op0 Major opcode
op1 4-bit sub-opcode for 24-bit instructions
op2 4-bit sub-opcode for 24-bit instructions
rAR target (result), BR target (result),
4-bit immediate,
4-bit sub-opcode
sAR source, BR source
AR target
tAR target, BR target,
AR source, BR source,
4-bit sub-opcode
nRegister window increment,
2-bit sub-opcode,
n||00 is used as a AR target on CALLn/CALLXn
m2-bit sub-opcode
i1-bit sub-opcode
z1-bit sub-opcode
imm6 6-bit immediate (PC-relative offset)
imm7 7-bit immediate (for MOVI.N)
imm8 8-bit immediate
Chapter 7. Instruction Formats and Opcodes
574 Xtensa Instruction Set Architecture (ISA) Reference Manual
7.3 Opcode Encodings
The following tables show the instruction-field bit values assigned to specific opcodes.
The following special notation is used:
The table titles tell the name of the parent opcode and what table the parent is in,
the formats for instructions in this table, and in parentheses at the end, what fields
still vary for items listed in this table. In the upper left corner of the table is the field
decoded in the table. Below it and to the right are templates which the field matches
for the corresponding row or column.
Non-italic opcodes are instructions. These have page numbers where the corre-
sponding instruction is described in more detail.
Italics opcodes are not instructions, but are parents to other opcodes. These have
table numbers that show further decode into instructions or other parents to other
opcodes.
Some entries have further conditions after them such as (s=0), which means that the
s field must be zero. All other opcodes are illegal; therefore another table seems
unnecessary.
The bit-range of opcodes that use more than one table entry is delimited by vertical
bars.
imm12 12-bit immediate
imm16 16-bit immediate
offset 18-bit PC-relative offset
Table 7–191. Uses Of Instruction Fields
(continued)
Field Definition
Chapter 7. Instruction Formats and Opcodes
Xtensa Instruction Set Architecture (ISA) Reference Manual 575
Subscripts on opcodes indicate the architectural option(s) in which the opcode is
implemented. The subscripts and their associated architectural options are:
- C—Instruction Cache or Data Cache Options
- D—MAC16 Option
- F—Floating-Point Coprocessor Option
- I—32-Bit Integer Multiply/Divide Option
- L—Instruction or Data Cache Index Lock Option
- M—MMU Option
- N—Code Density (Narrow instructions) Option
- P—Coprocessor Option
- S—Speculation Option
- U—Miscellaneous Operations Option
- W—Windowed Registers Option
- X—Exception or Interrupt Options
- Y—Multiprocessor Synchronization Option
7.3.1 Opcode Maps
Table 7–192. Whole Opcode Space
op0 xx00 xx01 xx10 xx11
00xx
QRST — Table 7–193 L32R — page 382 LSAI — Table 7–216 LSCIP — Tab le 7–220
01xx
MAC16D — Table 7–221 CALLN — Table 7–232 SI — Ta b l e 7–233 B — Ta b l e 7–238
10xx
L32I.NN — page 380 S32I.NN — page 512 ADD.NN — page 249 ADDI.NN — page 252
11xx
ST2N — Table 7–239 ST3N — Table 7–240 reserved reserved
Table 7–193. QRST (from Table 7–192) Formats RRR, CALLX, and RSR (t, s, r, op2 vary)
op1 xx00 xx01 xx10 xx11
00xx
RST0 — Ta b l e 7–194 RST1 — Ta b l e 7–205 RST2 — Ta b le 7–209 RST3 — Ta b l e 7–210
01xx
EXTUI — page 344 CUST0 — Section 7.3.2 CUST1 — Section 7.3.2
10xx
LSCXP — Table 7–211 LSC4 — Table 7–212 FP0F — Table 7–213 FP1F — Table 7–215
11xx
reserved reserved reserved reserved
Chapter 7. Instruction Formats and Opcodes
576 Xtensa Instruction Set Architecture (ISA) Reference Manual
Table 7–194. RST0 (from Table 7–193) Formats RRR and CALLX (t, s, r vary)
op2 xx00 xx01 xx10 xx11
00xx
ST0 — Ta b l e 7–195 AND — page 259 OR — page 466 XOR — page 564
01xx
ST1 — Ta b l e 7–202 TLB — Ta b le 7–203 RT0 — Ta b l e 7–204 reserved
10xx
ADD — page 248 ADDX2 — page 254 ADDX4 — page 255 ADDX8 — page 256
11xx
SUB — page 542 SUBX2 — page 544 SUBX4 — page 545 SUBX8 — page 546
Table 7–195. ST0 (from Table 7–194 Formats RRR and CALLX (t, s vary)
rxx00 xx01 xx10 xx11
00xx
SNM0 — Table 7–196 MOVSPW — page 427 SYNC — Ta ble 7–199 RFEIX — Table 7–200
01xx
BREAKX — page 293 SYSCALLX — page 547 (s,t=0) RSILX — page 498 WAITIX — page 556 (t=0)
10xx
ANY4P — page 262 ALL4P — page 257 ANY8P — page 263 ALL8P — page 258
11xx
reserved reserved reserved reserved
Table 7–196. SNM0 (from Table 7–195) Format CALLX (n, s vary)
m00 01 10 11
ILL — page 358 (s,n=0) reserved JR — Ta b l e 7–197 CALLX — Ta b l e 7–198
Table 7–197. JR (from Table 7–196) Format CALLX (s varies)
n00 01 10 11
RET — page 478 (s=0) RETWW — page 480 (s=0) JX — page 368 reserved
Table 7–198. CALLX (from Table 7–196) Format CALLX (s varies)
n00 01 10 11
CALLX0 — page 304 CALLX4W — page 305 CALLX8W — page 307 CALLX12W — page 309
Table 7–199. SYNC (from Table 7–195) Format RRR (s varies)
txx00 xx01 xx10 xx11
00xx
ISYNC — page 364 (s=0) RSYNC — page 502 (s=0) ESYNC — page 342 (s=0) DSYNC — page 339 (s=0)
01xx
reserved reserved reserved reserved
10xx
EXCW — page 343 (s=0) reserved reserved reserved
11xx
MEMW — page 409 (s=0) EXTW — page 345 (s=0) reserved reserved
Chapter 7. Instruction Formats and Opcodes
Xtensa Instruction Set Architecture (ISA) Reference Manual 577
Table 7–200. RFEI (from Table 7–195) Format RRR (s varies)
txx00 xx01 xx10 xx11
00xx
RFETX — Table 7–201 RFIX — page 488 RFME — page 489 (s=0) reserved
01xx
reserved reserved reserved reserved
10xx
reserved reserved reserved reserved
11xx
reserved reserved reserved reserved
Table 7–201. RFET (from Table 7–200) Format RRR (no bits vary)
sxx00 xx01 xx10 xx11
00xx
RFEX — page 487 RFUEX — page 491 RFDEX — page 485 reserved
01xx
RFWOW — page 492 RFWUW — page 493 reserved reserved
10xx
reserved reserved reserved reserved
11xx
reserved reserved reserved reserved
Table 7–202. ST1 (from Table 7–194) Format RRR (t, s vary)
rxx00 xx01 xx10 xx11
00xx
SSR — page 539 (t=0) SSL — page 538 (t=0) SSA8L — page 532 (t=0) SSA8B — page 531 (t=0)
01xx
SSAI — page 533 (t=0) reserved RER — page 477 WER — page 558
10xx
ROTWW — page 496 (s=0) reserved reserved reserved
11xx
reserved reserved NSAU — page 461 NSAUU — page 462
Table 7–203. TLB (from Table 7–194) Format RRR (t, s vary)
rxx00 xx01 xx10 xx11
00xx
reserved reserved reserved RITLB0 — page 494
01xx
IITLB — page 355 (t=0) PITLB — page 470 WITLB — page 560 RITLB1 — page 495
10xx
reserved reserved reserved RDTLB0 — page 473
11xx
IDTLB — page 348 (t=0) PDTLB — page 469 WDTLB — page 557 RDTLB1 — page 474
Chapter 7. Instruction Formats and Opcodes
578 Xtensa Instruction Set Architecture (ISA) Reference Manual
Table 7–204. RT0 (from Table 7–194) Format RRR (t, r vary)
sxx00 xx01 xx10 xx11
00xx
NEG — page 457 ABS — page 246 reserved reserved
01xx
reserved reserved reserved reserved
10xx
reserved reserved reserved reserved
11xx
reserved reserved reserved reserved
Table 7–205. RST1 (from Table 7–193) Format RRR (t, s, r vary)
op2 xx00 xx01 xx10 xx11
00xx
SLLI — page 525 SRAI — page 527
01xx
SRLI — page 530 reserved XSR — page 566 ACCER — Ta b l e 7–206
10xx
SRC — page 528 SRL — page 529 (s=0) SLL — page 524 (t=0) SRA — page 526 (s=0)
11xx
MUL16U — page 437 MUL16S — page 436 reserved IMP — Table 7–207
Table 7–206. ACCER (from Table 7–205) Format RRR (t, s vary)
op2 xx00 xx01 xx10 xx11
00xx
RER — page 477
01xx
10xx
WER — page 558
11xx
Table 7–207. IMP (from Table 7–205) Format RRR (t, s vary) (Section 7.3.3)
rxx00 xx01 xx10 xx11
00xx
LICT — page 388 SICT — page 519 LICW — page 390 SICW — page 521
01xx
reserved reserved reserved reserved
10xx
LDCT — page 384 SDCT — page 516 reserved reserved
11xx
reserved reserved RFDX — Ta b l e 7–208 reserved
Chapter 7. Instruction Formats and Opcodes
Xtensa Instruction Set Architecture (ISA) Reference Manual 579
Table 7–208. RFDX (from Table 7–207) Format RRR (s varies)
txx00 xx01 xx10 xx11
00xx
RFDO — page 486 (s=0) RFDD — page 484 (s=0,1) reserved reserved
01xx
reserved reserved reserved reserved
10xx
reserved reserved reserved reserved
11xx
reserved reserved reserved reserved
Table 7–209. RST2 (from Table 7–193) Format RRR (t, s, r vary)
op2 xx00 xx01 xx10 xx11
00xx
ANDBP — page 260 ANDBCP — page 261 ORBP — page 467 ORBCP — page 468
01xx
XORBP — page 565 reserved reserved reserved
10xx
MULLI — page 450 reserved MULUHI — page 456 MULSHI — page 455
11xx
QUOUI — page 472 QUOSI — page 471 REMUI — page 476 REMSI — page 475
Table 7–210. RST3 (from Table 7–193) Formats RRR and RSR (t, s, r vary)
op2 xx00 xx01 xx10 xx11
00xx
RSR — page 500 WSR — page 561 SEXTU — page 518 CLAMPSU — page 312
01xx
MINU — page 410 MAXU — page 407 MINUU — page 411 MAXUU — page 408
10xx
MOVEQZ — page 415 MOVNEZ — page 425 MOVLTZ — page 423 MOVGEZ — page 419
11xx
MOVFP — page 417 MOVTP — page 428 RUR — page 503 WUR — page 563
Table 7–211. LSCX (from Table 7–193) Format RRR (t, s, r vary)
op2 xx00 xx01 xx10 xx11
00xx
LSXF — page 402 LSXUF — page 404 reserved reserved
01xx
SSXF — page 540 SSXUF — page 534 reserved reserved
10xx
reserved reserved reserved reserved
11xx
reserved reserved reserved reserved
Chapter 7. Instruction Formats and Opcodes
580 Xtensa Instruction Set Architecture (ISA) Reference Manual
Table 7–212. LSC4 (from Table 7–193) Format RRI4 (t, s, r vary)
op2 xx00 xx01 xx10 xx11
00xx
L32E — page 376 reserved reserved reserved
01xx
S32E — page 508 reserved reserved reserved
10xx
reserved reserved reserved reserved
11xx
reserved reserved reserved reserved
Table 7–213. FP0 (from Table 7–193) Format RRR (t, s, r vary)
op2 xx00 xx01 xx10 xx11
00xx
ADD.SF — page 250 SUB.SF — page 543 MUL.SF — page 435 reserved
01xx
MADD.SF — page 406 MSUB.SF — page 430 reserved reserved
10xx
ROUND.SF — page 497 TRUNC.SF — page 548 FLOOR.SF — page 347 CEIL.SF — page 311
11xx
FLOAT.SF — page 346 UFLOAT.SF — page 550 UTRUNC.SF — page 555 FP1OPF — Table 7–214
Table 7–214. FP1OP (from Table 7–213) Format RRR (s, r vary)
txx00 xx01 xx10 xx11
00xx
MOV.SF — page 414 ABS.SF — page 247 reserved reserved
01xx
RFRF — page 490 WFRF — page 559 NEG.SF — page 458 reserved
10xx
reserved reserved reserved reserved
11xx
reserved reserved reserved reserved
Table 7–215. FP1 (from Table 7–193) Format RRR (t, s, r vary)
op2 xx00 xx01 xx10 xx11
00xx
reserved UN.SF — page 554 OEQ.SF — page 463 UEQ.SF — page 549
01xx
OLT.SF — page 465 ULT.SF — page 552 OLE.SF — page 464 ULE.SF — page 551
10xx
MOVEQZ.SF — page 416 MOVNEZ.SF — page 426 MOVLTZ.SF — page 424 MOVGEZ.SF — page 420
11xx
MOVF.SF — page 418 MOVT.SF — page 429 reserved reserved
Chapter 7. Instruction Formats and Opcodes
Xtensa Instruction Set Architecture (ISA) Reference Manual 581
Table 7–216. LSAI (from Table 7–192) Formats RRI8 and RRI4 (t, s, imm8 vary)
rxx00 xx01 xx10 xx11
00xx
L8UI — page 369 L16UI — page 372 L32I — page 378 reserved
01xx
S8I — page 504 S16I — page 505 S32I — page 510 CACHEC — Table 7–217
10xx
reserved L16SI — page 370 MOVI — page 421 L32AIY — page 374
11xx
ADDI — page 251 ADDMI — page 253 S32C1IY — page 506 S32RIY — page 514
Table 7–217. CACHE (from Table 7–216) Formats RRI8 and RRI4 (s, imm8 vary)
txx00 xx01 xx10 xx11
00xx
DPFRC — page 331 DPFWC — page 335 DPFROC — page 333 DPFWOC — page 337
01xx
DHWBC — page 317 DHWBIC — page 319 DHIC — page 313 DIIC — page 321
10xx
DCEC — Tab le 7–218 reserved reserved reserved
11xx
IPFC — page 360 ICEC — Table 7–219 IHIC — page 349 IIIC — page 353
Table 7–218. DCE (from Table 7–217) Format RRI4 (s, imm4 vary)
op1 xx00 xx01 xx10 xx11
00xx
DPFLL — page 329 reserved DHUL — page 315 DIUL — page 323
01xx
DIWBC — page 325 DIWBIC — page 327 reserved reserved
10xx
reserved reserved reserved reserved
11xx
reserved reserved reserved reserved
Table 7–219. ICE (from Table 7–217) Format RRI4 (s, imm4 vary)
op1 xx00 xx01 xx10 xx11
00xx
IPFLL — page 362 reserved IHUL — page 351 IIUL — page 356
01xx
reserved reserved reserved reserved
10xx
reserved reserved reserved reserved
11xx
reserved reserved reserved reserved
Chapter 7. Instruction Formats and Opcodes
582 Xtensa Instruction Set Architecture (ISA) Reference Manual
Table 7–220. LSCI (from Table 7–192) Format RRI8 (t, s, imm8 vary)
rxx00 xx01 xx10 xx11
00xx
LSIF — page 398 reserved reserved reserved
01xx
SSIF — page 534 reserved reserved reserved
10xx
LSIUF — page 400 reserved reserved reserved
11xx
SSIUF — page 536 reserved reserved reserved
Table 7–221. MAC16 (from Table 7–192) Format RRR (t, s, r, op1 vary)
op2 xx00 xx01 xx10 xx11
00xx
MACID — Table 7–222 MACCD — Table 7–226 MACDD — Tabl e 7–224 MACAD — Ta b l e 7–225
01xx
MACIA — Tab le 7–223 MACCA — Ta b l e 7–227 MACDA — Ta b l e 7–228 MACAA — Table 7–229
10xx
MACI — Table 7–230 MACC — Table 7–231 reserved reserved
11xx
reserved reserved reserved reserved
Table 7–222. MACID (from Table 7–221) Format RRR (t, s, r vary)
op1 xx00 xx01 xx10 xx11
00xx
reserved reserved reserved reserved
01xx
reserved reserved reserved reserved
10xx
MULA.DD.LL.LDINC —
page 448
MULA.DD.HL.LDINC —
page 448
MULA.DD.LH.LDINC —
page 448
MULA.DD.HH.LDINC —
page 448
11xx
reserved reserved reserved reserved
Table 7–223. MACIA (from Table 7–221) Format RRR (t, s, r vary)
op1 xx00 xx01 xx10 xx11
00xx
reserved reserved reserved reserved
01xx
reserved reserved reserved reserved
10xx
MULA.DA.LL.LDINC —
page 443
MULA.DA.HL.LDINC —
page 443
MULA.DA.LH.LDINC —
page 443
MULA.DA.HH.LDINC —
page 443
11xx
reserved reserved reserved reserved
Chapter 7. Instruction Formats and Opcodes
Xtensa Instruction Set Architecture (ISA) Reference Manual 583
Table 7–224. MACDD (from Table 7–221) Format RRR (t, s, r vary)
op1 xx00 xx01 xx10 xx11
00xx
reserved reserved reserved reserved
01xx
MUL.DD.LL — page 434 MUL.DD.HL — page 434 MUL.DD.LH — page 434 MUL.DD.HH — page 434
10xx
MULA.DD.LL — page 445 MULA.DD.HL — page 445 MULA.DD.LH — page 445 MULA.DD.HH — page 445
11xx
MULS.DD.LL — page 454 MULS.DD.HL — page 454 MULS.DD.LH — page 454 MULS.DD.HH — page 454
Table 7–225. MACAD (from Table 7–221) Format RRR (t, s, r vary)
op1 xx00 xx01 xx10 xx11
00xx
reserved reserved reserved reserved
01xx
MUL.AD.LL — page 432 MUL.AD.HL — page 432 MUL.AD.LH — page 432 MUL.AD.HH — page 432
10xx
MULA.AD.LL — page 439 MULA.AD.HL — page 439 MULA.AD.LH — page 439 MULA.AD.HH — page 439
11xx
MULS.AD.LL — page 452 MULS.AD.HL — page 452 MULS.AD.LH — page 452 MULS.AD.HH — page 452
Table 7–226. MACCD (from Table 7–221) Format RRR (t, s, r vary)
op1 xx00 xx01 xx10 xx11
00xx
reserved reserved reserved reserved
01xx
reserved reserved reserved reserved
10xx
MULA.DD.LL.LDDEC —
page 446
MULA.DD.HL.LDDEC —
page 446
MULA.DD.LH.LDDEC —
page 446
MULA.DD.HH.LDDEC —
page 446
11xx
reserved reserved reserved reserved
Table 7–227. MACCA (from Table 7–221) Format RRR (t, s, r vary)
op1 xx00 xx01 xx10 xx11
00xx
reserved reserved reserved reserved
01xx
reserved reserved reserved reserved
10xx
MULA.DA.LL.LDDEC —
page 441
MULA.DA.HL.LDDEC —
page 441
MULA.DA.LH.LDDEC —
page 441
MULA.DA.HH.LDDEC —
page 441
11xx
reserved reserved reserved reserved
Chapter 7. Instruction Formats and Opcodes
584 Xtensa Instruction Set Architecture (ISA) Reference Manual
Table 7–228. MACDA (from Table 7–221) Format RRR (t, s, r vary)
op1 xx00 xx01 xx10 xx11
00xx
reserved reserved reserved reserved
01xx
MUL.DA.LL — page 433 MUL.DA.HL — page 433 MUL.DA.LH — page 433 MUL.DA.HH — page 433
10xx
MULA.DA.LL — page 440 MULA.DA.HL — page 440 MULA.DA.LH — page 440 MULA.DA.HH — page 440
11xx
MULS.DA.LL — page 453 MULS.DA.HL — page 453 MULS.DA.LH — page 453 MULS.DA.HH — page 453
Table 7–229. MACAA (from Table 7–221) Format RRR (t, s, r vary)
op1 xx00 xx01 xx10 xx11
00xx
UMUL.AA.LL — page 553 UMUL.AA.HL — page 553 UMUL.AA.LH — page 553 UMUL.AA.HH — page 553
01xx
MUL.AA.LL — page 431 MUL.AA.HL — page 431 MUL.AA.LH — page 431 MUL.AA.HH — page 431
10xx
MULA.AA.LL — page 438 MULA.AA.HL — page 438 MULA.AA.LH — page 438 MULA.AA.HH — page 438
11xx
MULS.AA.LL — page 451 MULS.AA.HL — page 451 MULS.AA.LH — page 451 MULS.AA.HH — page 451
Table 7–230. MACI (from Table 7–221) Format RRR (t, s, r vary)
op1 xx00 xx01 xx10 xx11
00xx
LDINC — page 387 (t=0) reserved reserved reserved
01xx
reserved reserved reserved reserved
10xx
reserved reserved reserved reserved
11xx
reserved reserved reserved reserved
Table 7–231. MACC (from Table 7–221) Format RRR (t, s, r vary)
op1 xx00 xx01 xx10 xx11
00xx
LDDEC — page 386 (t=0) reserved reserved reserved
01xx
reserved reserved reserved reserved
10xx
reserved reserved reserved reserved
11xx
reserved reserved reserved reserved
Table 7–232. CALLN (from Table 7–192) Format CALL (offset varies)
n00 01 10 11
CALL0 — page 297 CALL4 — page 298 CALL8 — page 300 CALL12 — page 302
Chapter 7. Instruction Formats and Opcodes
Xtensa Instruction Set Architecture (ISA) Reference Manual 585
Table 7–233. SI (from Table 7–192) Formats CALL, BRI8 and BRI12(offset varies)
n00 01 10 11
J — page 366 BZ — Ta b l e 7–234 BI0 — Ta b l e 7–235 BI1 — Ta b l e 7–236
Table 7–234. BZ (from Table 7–233) Format BRI12 (s, imm12 vary)
m00 01 10 11
BEQZ — page 274 BNEZ — page 290 BLTZ — page 286 BGEZ — page 281
Table 7–235. BI0 (from Table 7–233) Format BRI8 (s, r, imm8 vary)
m00 01 10 11
BEQI — page 273 BNEI — page 289 BLTI — page 283 BGEI — page 278
Table 7–236. BI1 (from Table 7–233) Formats BRI8 and BRI12 (s, r, imm8 vary)
m00 01 10 11
ENTRYW — page 340 B1 — Table 7–237 BLTUI — page 285 BGEUI — page 280
Table 7–237. B1 (from Table 7–236) Format BRI8 (s, imm8 vary)
rxx00 xx01 xx10 xx11
00xx
BFP — page 276 BTP — page 296 reserved reserved
01xx
reserved reserved reserved reserved
10xx
LOOP — page 392 LOOPNEZ — page 396 LOOPGTZ — page 394 reserved
11xx
reserved reserved reserved reserved
Table 7–238. B (from Table 7–192) Format RRI8 (t, s, imm8 vary)
rxx00 xx01 xx10 xx11
00xx
BNONE — page 292 BEQ — page 272 BLT — page 282 BLTU — page 284
01xx
BALL — page 264 BBC — page 266 BBCI — page 267
10xx
BANY — page 265 BNE — page 288 BGE — page 277 BGEU — page 279
11xx
BNALL — page 287 BBS — page 269 BBSI — page 270
Chapter 7. Instruction Formats and Opcodes
586 Xtensa Instruction Set Architecture (ISA) Reference Manual
7.3.2 CUST0 and CUST1 Opcode Encodings
CUST0 and CUST1 opcode encodings shown in Table 7–193 are permanently reserved
for designer-defined opcodes. In the future, customers who use these spaces exclusive-
ly for their own designer-defined opcodes will be able to add new Tensilica-defined op-
tions without changing their opcodes or binary executables.
7.3.3 Cache-Option Opcode Encodings (Implementation-Specific)
The encodings for the r field sub-opcodes of the IMP family of opcodes, which are im-
plementation-specific Cache-Option opcodes, are shown in Table 7–207. The IMP fami-
ly of opcodes is reserved for these implementation-specific instructions. For a descrip-
tion of these instructions, see Chapter 6.
Table 7–239. ST2 (from Table 7–192) Formats RI7 and RI6 (s, r vary)
txx00 xx01 xx10 xx11
00xx
MOVI.NN — page 422
01xx
10xx
BEQZ.NN — page 275
11xx
BNEZ.NN — page 291
Table 7–240. ST3 (from Table 7–192) Format RRRN (t, s vary)
rxx00 xx01 xx10 xx11
00xx
MOV.NN — page 413 reserved reserved reserved
01xx
reserved reserved reserved reserved
10xx
reserved reserved reserved reserved
11xx
reserved reserved reserved S3 — Table 7–241 (s=0)
Table 7–241. S3 (from Table 7–240) Format RRRN (no fields vary)
txx00 xx01 xx10 xx11
00xx
RET.NN — page 479 RETW.NWN — page 482 BREAK.NN — page 295 NOP.NN — page 460
01xx
reserved reserved ILL.NN — page 359 reserved
10xx
reserved reserved reserved reserved
11xx
reserved reserved reserved reserved
Chapter 8. Using the Xtensa Architecture
Xtensa Instruction Set Architecture (ISA) Reference Manual 587
8. Using the Xtensa Architecture
This chapter describes Tensilica’s software tool support of the Xtensa ISA and the con-
ventions used by software.
8.1 The Windowed Register and CALL0 ABIs
The Xtensa ISA supports two different application binary interfaces (ABIs). The win-
dowed register ABI works with the Windowed Register Option and is the default ABI.
The CALL0 ABI can be used with any Xtensa processor. It does not make use of register
windows, so it typically has slightly worse performance and code size than the win-
dowed register ABI.
These two ABIs share much in common and diverge mostly in the areas of stack frame
layout and general-purpose register usage. The basic data type sizes and alignments
are identical, and the argument passing and return value conventions are nearly the
same.
8.1.1 Windowed Register Usage and Stack Layout
Table 8–242 shows the general-purpose register usage for the windowed register ABI.
Registers a0 and a1 are reserved for the return address and stack pointer, respectively.
They must always contain those values, because they are used for stack unwinding in
debuggers and exception handling. Incoming arguments are stored in registers a2
through a7. The location of outgoing arguments depends on the window size.
The stack frame layout for the windowed register ABI is shown in Figure 8–53. The stack
grows down, from high to low addresses. The stack pointer (SP) must be aligned to 16-
byte boundaries. A stack-frame pointer (FP) may (but is not required to) be allocated in
register a7. For example, it may be needed when the routine contains a call to alloca.
If a frame pointer is used, its value is equal to the original stack pointer (immediately af-
ter entry to the function), before any alloca space allocation.
Table 8–242. Windowed Register Usage
Register Use
a0 Return address
a1 (sp) Stack pointer
a2 – a7 Incoming arguments
a7 Callee’s stack-frame pointer (optional)
Chapter 8. Using the Xtensa Architecture
588 Xtensa Instruction Set Architecture (ISA) Reference Manual
The register-spill overflow area is equal to N–4 words, where N can be 4, 8, or 12 as de-
termined by the largest CALLN or CALLXN in the function. For details, see “Windowed
Procedure-Call Protocol” on page 187.
The stack pointer SP should only be modified by ENTRY and MOVSP instructions. If some
other instruction modifies SP, any values in the register-spill area will not be moved. An
exception to this rule is when setting the initial stack pointer for a new stack, where the
register-spill area is guaranteed to be empty and where MOVSP cannot safely be used.
Figure 8–53. Stack Frame for the Windowed Register ABI
alloca Space
Space for Outgoing
Arguments
Local Variables
Register-Spill Overflow
(0 to 8 words)
After CallBefore Call
Space for Arguments
Register-Spill Area
(4 words)
Register-Spill Area
(4 words)
SP
SP
High
Memory
Low
Memory
Chapter 8. Using the Xtensa Architecture
Xtensa Instruction Set Architecture (ISA) Reference Manual 589
8.1.2 CALL0 Register Usage and Stack Layout
Table 8–243 shows the general-purpose register usage for the CALL0 ABI. The stack
pointer in register a1 and registers a12–a15 are callee-saved, but the rest of the regis-
ters are caller-saved. Register a0 holds the return address upon entry to a function, but
unlike the windowed register ABI, it is not reserved for this purpose and may hold other
values after the return address has been saved. Function arguments are passed in reg-
isters a2 through a7.
The stack frame layout for the CALL0 ABI is the same as for the windowed register ABI,
except without the reserved register-spill areas. (Registers will need to be saved to the
stack, but there is no convention for where in the frame to place that storage.) Like the
windowed register ABI, the stack grows down and the stack pointer must be aligned to
16-byte boundaries. The optional stack-frame pointer is also used in the same way, but
it is placed in register a15 with the CALL0 ABI.
8.1.3 Data Types and Alignment
Table 8–244 shows the data-type sizes and their alignment. The maximum alignment for
user-defined types is 16 bytes.
Table 8–243. CALL0 Register Usage
Register Use
a0 Return Address
a1 (sp) Stack Pointer (callee-saved)
a2 – a7 Function Arguments
a8 Static Chain (see Section 8.1.8)
a12 – a15 Callee-saved
a15 Stack-Frame Pointer (optional)
Table 8–244. Data Types and Alignment
Data Type Size and Alignment
char11 byte
short 2 bytes
int 4 bytes
long 4 bytes
long long 8 bytes
float 4 bytes
1. The char type is unsigned by default for Xtensa processors.
2. The xtbool types are only available if the Boolean registers are included in the processor configuration. See “Boolean Option” on page 65 for
information about the Boolean registers.
Chapter 8. Using the Xtensa Architecture
590 Xtensa Instruction Set Architecture (ISA) Reference Manual
8.1.4 Argument Passing
Arguments are passed in both registers and memory. In general, the first six words of ar-
guments go in the AR register file, and any remaining arguments go on the stack. For a
CALLN instruction (where N is 0 for the CALL0 ABI, or where N is 4, 8, or 12 for the win-
dowed register ABI) the caller places the first arguments in registers AR[N+2] through
AR[N+7]. (Note that this implies that CALL12 can only be used when there are two
words of arguments or less; only AR[N+2] and AR[N+3] can be used when N=12.) The
callee receives these arguments in AR[2] through AR[7].
If there are more than six words of arguments, the additional arguments are stored on
the stack beginning at the caller’s stack pointer and at increasingly positive offsets from
the stack pointer. That is, the caller stores the seventh argument word (after the first six
words in registers) at [sp + 0], the eighth word at [sp + 4], and so on. The callee can ac-
cess these arguments in memory beginning at [sp + FRAMESIZE], where FRAMESIZE
is the size of the callee’s stack frame.
All arguments consist of an integral number of 4-byte words. Thus, the minimum argu-
ment size is one word. Integer values smaller than a word (that is, char and short) are
stored in the least significant portion of the argument word, with the upper bits set to
zero for unsigned values or sign-extended for signed values.
When a value larger than 4 bytes is passed in registers, the ordering of the words is the
same as the byte ordering. With little endian ordering, the least significant word goes in
the first register. With big endian ordering, the most significant word comes first.
double 8 bytes
long double 8 bytes
pointer 4 bytes
xtbool21 byte
xtbool221 byte
xtbool421 byte
xtbool821 byte
xtbool1622 bytes
user-defined types user-defined
Table 8–244. Data Types and Alignment
(continued)
Data Type Size and Alignment
1. The char type is unsigned by default for Xtensa processors.
2. The xtbool types are only available if the Boolean registers are included in the processor configuration. See “Boolean Option” on page 65 for
information about the Boolean registers.
Chapter 8. Using the Xtensa Architecture
Xtensa Instruction Set Architecture (ISA) Reference Manual 591
Each argument must be passed entirely in registers or entirely on the stack; an argu-
ment cannot be split with some words in registers and the remainder on the stack. If an
argument does not fit entirely in the remaining unused registers, it is passed on the
stack and those registers remain unused.
Arguments must be properly aligned. If the type of the argument requires 4-byte or less
alignment, this requirement has no effect; all arguments have at least 4-byte alignment
anyway. If an argument requires 8-byte alignment and is passed in registers, the first
word must be in an even-numbered register. This sometimes requires leaving an odd-
numbered register unused. Similarly, if an argument requires 16-byte alignment and is
passed in registers, the first word must be in the first argument register (AR[N+2]); oth-
erwise, it is passed on the stack. If an argument is passed in memory, the memory loca-
tion must have the alignment required by the argument type.
Structures and other aggregate types are passed by value. The preceding rules apply to
structures in the same way as scalars. If a structure is small enough to be passed in reg-
isters, the words of the structure are placed in registers according to their order in mem-
ory. A variable-sized structure is always passed on the stack and any remaining argu-
ment registers go unused. If the size of a structure is not an integral number of words,
padding is inserted at one end of the structure. For structures smaller than a word, the
padding is always in the most-significant part of the word. A structure larger than a word
is padded in the last bytes of the last argument word, so that the structure is contiguous
when the registers are stored to consecutive words of memory.
Values of user-defined TIE types cannot be passed as arguments. (That is, they cannot
be arguments of procedure calls; they may still be used as arguments of certain intrinsic
functions and macros that do not correspond to real procedure calls.)
8.1.5 Return Values
Values of four words or less are returned in registers. The callee places the return value
in registers beginning with AR[2] and continuing up to (and including) AR[5], depending
on the size of the value. For a CALLN instruction (where N is 0 for the CALL0 ABI, or
where N is 4, 8, or 12 for the windowed register ABI) the caller receives these values in
registers AR[N+2] through AR[N+5]. (Note that, as with arguments, this limits the use of
CALL12 instructions. A CALL12 instruction can only be used when the return value is
two words or less; only AR[N+2] and AR[N+3] can be used when N=12.)
Return values smaller than a word are stored in the least-significant part of AR[2], with
the upper bits set to zero for unsigned values or sign-extended for signed values.
Values larger than four words are returned by invisible reference. The caller passes a
pointer as an invisible first argument and the callee stores the return value in the memo-
ry referenced by the pointer. The memory allocated by the caller must have the appropri-
ate size and alignment for the return value.
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Even though values of user-defined types cannot be passed as arguments, they are al-
lowed as return values. If a procedure returns such a value, it is stored in the first regis-
ter of the register file associated with that user-defined type.
8.1.6 Variable Arguments
Variable argument lists are handled in the same way as other arguments. There is no
change to the calling convention for functions with variable argument lists.
8.1.7 Other Register Conventions
In addition to the general-purpose AR register file, Xtensa processors may contain a va-
riety of other register files, special registers, and TIE states (which may be mapped to
user registers). The conventions for saving and restoring these registers across function
calls vary. Some are caller-saved, which means that a function does not need to save
those registers to the stack before modifying them, because it can assume that the call-
er has already saved them. For callee-saved registers, the responsibility is reversed and
the callee function must save the original values of the registers that it modifies. Some
other registers are global — any changes to their values persist across function calls —
and for some others, the usage conventions are not specified.
Unless otherwise specified, the default convention is that all registers are caller-saved.
The exceptions are:
When using the CALL0 ABI, several of the AR registers are callee-saved (see
Table 8–243 on page 589).
No convention is specified for the use of TIE states — the programmer can decide
how to use TIE states. If you are using TIE states together with cooperative (non-
preemptive) context switching, be careful that your use of TIE states matches the
assumptions of the operating system. The operating system may assume that TIE
states need not be saved when a context switch primitive is invoked; that is, it may
assume that TIE states are caller-saved.
The following special registers and user registers are global: LITBASE,
THREADPTR, and FCR. These registers are used for special purposes and typically
keep the same values across function calls.
As a consequence of the LOOP special registers (LBEG, LEND, and LCOUNT) being call-
er-saved, the LOOP instructions should not be used for loops containing function calls.
Doing so would require saving and restoring the LOOP registers around the call, which
would overwhelm the advantage of the LOOP instructions.
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8.1.8 Nested Functions
Some languages (including C with a GCC extension) allow nested functions. A function
A nested inside another function B must be able to access the local variables of both A
and B. Implementing this requires that when B calls A, it must somehow pass to A infor-
mation to allow locating B’s stack frame. Some implementations of nested functions use
a data structure known as a “display” for this purpose. GCC uses the simpler alternative
of passing a “static chain” as an invisible argument to the nested function. The static
chain is simply a pointer to the caller’s stack frame. This approach is preferable to using
a display as long as functions are not deeply nested.
Because nested functions may be called indirectly through pointers, the caller may not
be able to detect when it is calling a nested function. Therefore, the invisible static chain
argument must be passed in a reserved location where it does not interfere with the oth-
er arguments. For the CALL0 ABI, the static chain is passed in register a8. For the win-
dowed register ABI, there are no registers available to hold the static chain, and the
stack locations at positive offsets from SP are all used for passing normal arguments.
The solution is to store the static chain on the stack at a negative offset from the caller’s
stack pointer. The first four words below SP are reserved as a register save area, so the
static chain is passed in the fifth word below SP. That is, the caller places the static chain
in memory at [SP–20], and the callee reads it from [SP + FRAMESIZE – 20] where
FRAMESIZE is the size of the callee’s stack frame.
When the address of a nested function is stored into a pointer, the compiler actually
emits code to dynamically create a small piece of executable code known as a “trampo-
line”, and the pointer is set to reference the trampoline. When an indirect call is made
through the pointer, the trampoline code sets the value of the static chain and then
transfers control to the nested function. The trampoline code is allocated on the stack —
this implies that it must be possible to execute code stored in the region of memory hold-
ing the stack. For example, when using nested functions that have their addresses
taken, the stack cannot be located in a separate data memory.
This positioning of the static chain for the windowed register ABI has an implication for
exception handlers. If an exception occurs after the static chain has been written but
before the ENTRY instruction in the callee, the contents of memory from [SP–20] through
[SP–1] must be preserved by the handler. Because of the register overflow save area,
the contents of memory from [SP–16] to [SP–1] must be preserved regardless, so the
presence of the static chain simply adds one more word of memory that must be pre-
served.
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8.1.9 Stack Initialization
Creating and initializing a stack for a new thread requires:
reserving some memory,
setting up the initial stack frame,
setting the stack pointer to the initial frame, and
setting the initial return address (in register a0) to zero.
If the initial procedure executed by the thread does not store any data in the initial stack
frame, and if all the call instructions in the initial procedure use the CALL0 ABI or a win-
dow size of four, then the initial stack frame can be empty and requires no setup. The
default C runtime initialization code meets these conditions, so that the stack can be ini-
tialized simply by setting the stack pointer to the high end of the reserved memory.
If the thread begins with some other code that may execute a CALL8 or CALL12 instruc-
tion or that requires storage on the stack, the initial frame must be constructed before
jumping to the initial procedure. The size of the initial frame is equal to the sum of the lo-
cal storage requirements and the extra save area. The stack pointer should be initialized
to the high end of the reserved memory less the size of the initial frame. Furthermore,
assuming the thread begins executing with only the current register window loaded, the
base save area at (sp – 16) must be initialized as if it had been written by a window
overflow. Specifically, the stack pointer value stored at (sp – 12) must be set to the high
end of the reserved stack area plus 16 bytes. This allows subsequent window overflows
to locate the extra save area in the initial stack frame.
The return address register (a0) for the first procedure on the stack must be explicitly
set to zero. This is used to mark the top of the stack for use by stack unwinding code.
The following code is an example of how the stack may be initialized to allow CALL8 (but
not CALL12) in the initial thread:
movi a0, 0
movi sp, stackbase + stacksize - 16
addi a4, sp, 32 // point 16 past extra save area
s32e a4, sp, -12 // access to extra save area
call8 firstfunction
The following code is an example of how the stack may be initialized to allow CALL12
and “loc” bytes of locals and parameters in the initial thread (loc is a multiple of 16):
movi a0, 0
movi sp, stackbase + stacksize - loc - 32
addi a4, sp, loc + 48 // point 16 past extra save area
s32e a4, sp, -12 // access to extra save area
call12 firstfunction
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8.2 Other Conventions
This section describes the usage conventions other than the Xtensa application binary
interface (ABI).
8.2.1 Break Instruction Operands
The break (24-bit) instruction has two immediate 4-bit operands, and the break.n
(narrow, 16-bit) instruction has one immediate 4-bit operand. These operands (informal-
ly called “break codes” in this section) can be used to convey relevant information to the
debug exception handler. Their exact meaning is a matter of convention. However,
some of the tools and software (debuggers, OS ports, and so forth) used with Xtensa
cores necessarily make use of the break instructions, so some conventions had to be
established. The conventions that have been adopted are described in this section.
Half of the break codes are reserved for use by software provided by Tensilica and its
partners, leaving the remaining half for “user-defined” purposes. Note that making use of
user-defined break codes usually requires special OS or monitor support, or at least
having control of the debug exception handler (or of the external OCD software when
OCD mode is enabled). Break code allocations are described in Table 8–245.
Break codes have been allocated for a number of planted breakpoints (breakpoints that
replace some arbitrary pre-existing instruction, usually under control of a debugger or
related software, and usually temporarily) and coded breakpoints (breakpoints explicitly
coded in the assembly source).
Planted breakpoints have a narrow (16-bit) and a wide (24-bit) version. Because 24-bit
instructions exist in all Xtensa processors, instructions 24-bits or wider may be replaced
with a 24-bit BREAK instruction. With the density option, the narrow version (BREAK.N)
must generally be used when replacing an existing narrow instruction. Otherwise a wide
break instruction would overwrite two sequential instructions, the second of which could
be the (now corrupted) target of a branch. Note that without the density option, only the
wide form of the break instruction can be used because the narrow version does not
exist.
A number of coded breakpoints have been defined to provide a means of making vari-
ous exceptions (that is, illegal instructions, load/store errors, and so forth) visible to the
debugger, which does not otherwise see these types of exceptions through the debug
exception vector. These breakpoints necessarily require support from the OS (or RTOS).
They are typically invoked by the OS for those exceptions and interrupts that neither the
OS nor the application handles, thus providing an opportunity for a debugger (if one is
active) to catch the condition. If the OS has its own mechanism for handling unregis-
tered exceptions and interrupts, the relevant coded breakpoint is normally invoked be-
fore this mechanism (there often is no well-defined “after”). Thus, it is very important that
the debug exception handler treat the coded breakpoint as a no-op if no debugger is ac-
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tive, to let the OS follow its default course of action. By convention, any break 1,x in-
struction must be skipped and ignored if no debugger is active. If the debug exception
handler (or OCD software if OCD mode is enabled) detects the presence of a debugger,
it will transfer control to the debugger. Otherwise, it must immediately resume execution
at the instruction following the break (which requires incrementing EPC[DEBUGLEVEL]
by two for break.n or by three for break), in effect making the break a no-op.
Another essential requirement for break 1,0 through break 1,5 is that the OS in-
voke these coded breakpoints in exactly the same context (core state) as when the ex-
ception was entered (except, necessarily, for PC and EXCSAVEn). This allows the de-
bugger to know the exact state of the core at the time the exception (or interrupt)
occurred, without requiring any OS dependency. For example, when detecting an un-
handled level-1 user exception, the OS has typically saved (in EXCSAVE1 and possibly
memory) and modified only a few address registers; these registers must all be restored
prior to executing the break 1,1 instruction. The debug exception handler can then ex-
amine all registers as they were when the user exception occurred, including examining
EXCCAUSE to determine which exception occurred, and so forth. Similarly, following a
break 1,2 it can resolve which interrupt occurred using EPS[DEBUGLEVEL].INTLEV-
EL.
Coded breakpoints can always use the wide (24-bit) form of the break instruction, so
they were not allocated from the limited number of narrow break instructions.
Table 8–245. Breakpoint Instruction Operand Conventions
Breakpoint Instruction Type Description
break 0,0 planted
Breakpoints set by host debugger for debugging programs.
These break instruction appear in code as a result of one of the
following actions:
The debugger can request the monitor to write the breakpoint
instruction into the code.
The debugger can explicitly write this instruction into the code.
break 0,1 planted
Breakpoints set by the monitor or OCD software for its own
purposes. For example, xmon uses this breakpoint to detect and
intercept UART interrupts. Ideally the presence of these breaks
in the code is hidden from the debugger.
break 0,2 to 0,15 (undefined) Reserved (Tensilica)
break 1,0 coded Signals an unhandled level 1 kernel exception
break 1,1 coded Signals an unhandled level 1 user exception
break 1,2 coded Signals an unhandled high-priority interrupt
break 1,3 coded Signals an unhandled window overflow or underflow exception
(unlikely to be invoked)
break 1,4 coded Signals an unhandled double exception
break 1,5 coded Signals an unhandled memory error exception
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8.2.2 System Calls
The details of system calls are inherently dependent on the operating system, but there
are a few conventions that apply to all systems. The SYSCALL instruction has no imme-
diate operands, so the system call parameters are passed in registers. Each operating
system is free to define its own register usage for system call parameters, with the ex-
ception that the system call request code must always be in register a2.
The system call request code 0 must be defined for all systems that use the windowed
register ABI. (If the Xtensa processor configuration uses the CALL0 ABI, system call 0
need not be implemented.) The purpose of system call 0 is to flush the register windows
to the stack. It is often useful to have a portable and reasonably efficient means of flush-
ing register windows, such as when walking up the stack to find an exception handler.
This system call provides an easy way to flush the register windows on all systems.
In general, each operating system can define its own conventions for which general-pur-
pose registers may be modified by a system call, including which registers will hold any
return values or error codes. For system call 0 in particular, no return value is expected
and each operating system must guarantee that no general-purpose registers other than
a2 will be modified. The value in a2 upon return from system call 0 depends on the oper-
ating system.
break 1,6 to 1,13 coded Reserved (Tensilica)
break 1,14 coded
Issue a request through the debugger. Any use of this break
instruction is debugger-specific. For example, certain versions of
GDB use this to implement target initiated host I/O.
break 1,15 coded
Transfer control to debugger if present. This is typically inserted
manually in the code for debugging purposes, or to signal critical
events that should cause entry into the debugger if one is active,
but be ignored otherwise.
break 2,x to 7,x (undefined) Reserved (Tensilica)
break 8,x to 15,x (undefined) User-defined
break.n 0 planted Same as break 0,0, but can also replace narrow (16-bit)
instructions.
break.n 1 planted Same as break 0,1, but can also replace narrow (16-bit)
instructions.
break.n 2 to 7(undefined) Reserved (Tensilica)
break.n 8 to 15 (undefined) User-defined
Table 8–245. Breakpoint Instruction Operand Conventions
(continued)
Breakpoint Instruction Type Description
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8.3 Assembly Code
This section describes various things of interest to the assembly language writer, includ-
ing some examples.
8.3.1 Assembler Replacements and the Underscore Form
Machine code generated by the assembler may include opcode replacements for certain
assembler opcodes. For example:
The assembler can turn ADD into ADD.N, or ADDI into ADDI.N, and so forth when
the density option is enabled.
The assembler substitutes a different instruction when an operand is out of range.
For example, it turns MOVI into L32R when the immediate is outside the range
-2048 to 2047.
By default, the assembler handles branches that won’t reach. For example, writing:
beq a1, a2, label
might actually generate:
bne a1, a2, .L1
j label
.L1:
if label is too far to reach with a simple beq instruction.
These transformations can be disabled by prefixing the instruction name with an under-
score (for example,_ADD) and with pseudo-ops. The assembler directives.begin and
.end with no-transform can also be used to enable and disable these transforma-
tions. See the GNU Assembler User’s Guide for more detail.
8.3.2 Instruction Idioms
Table 8–246 specifies the preferred instruction idioms for common operations. These
idioms are specified using only core instructions; in some cases substituting density
instructions would be appropriate.
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Table 8–246. Instruction Idioms
Operation Preferred Idiom
AR[x] ← AR[y]
or ax, ay, ay
(generated by the MOV assembler macro)
(or if present, use 16-bit option MOV.N)
AR[x] ← not AR[y] movi at, -1
xor ax, ay, at
AR[x] ← AR[y] and not AR[z] and at, ay, az
xor ax, ay, at
AR[x] ← imm32 l32r ax, literalpooloffset
AR[x] ← AR[y] << AR[z] ssl az
sll ax, ay
AR[x] ← AR[y] >>u AR[z] ssr az
srl ax, ay
AR[x] ← AR[y] >>s AR[z] ssr az
sra ax, ay
AR[x] ← rot(AR[y], AR[z]) ssa az
src ax, ay, ay
AR[x] ← byteswap(AR[y])
ssai 8
srli ax, ay, 16
src ax, ax, ay
src ax, ax, ax
src ax, ay, ax
if AR[x] ≤ AR[y] goto L bge ay, ax, L
if AR[x] > AR[y] goto L blt ay, ax, L
if AR[x] ≤ imm goto L blti ax, imm+1, L
if AR[x] > imm goto L bgei ax, imm+1, L
AR[x] ← AR[y] ≠ AR[z]
movi at, 1
xor ax, ay, az
movnez ax, at, ax
AR[x] ← AR[y] = AR[z]
movi ax, 1
bne ay, az, L
movi ax, 0
L:
AR[x] ← AR[y] ≠ 0
movi at, 1
movi ax, 0
movnez ax, at, ay
AR[x] ← AR[y] = 0
movi at, 1
movi ax, 0
moveqz ax, at, ay
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8.3.3 Example: A FIR Filter with MAC16 Option
With the MAC16 Option, a portion of a real FIR filter might be:
input[next] = sample;// put sample into history array
acc = 0x4000; // for rounding
for (i = 0; i < n; i += 1) {
acc += input[i > next ? next-i+n : next-i] * coeff[i];
}
output[next] = acc >> 15;
next = next == N-1 ? 0 : next+1;
The read of the accumulator and shift is done as follows:
rsr a6, acclo // read 40-bit ACC
rsr a7, acchi // ...
ssai 15 // convert back to fractional 16
src a2, a7, a6 // bit form
clampsa2, a2, 15 // clamp to 16 bits
64-bit add
(x ← y + z)
add ax0, ay0, az0
add ax1, ay1, az1
bgeu ax0, az0, L1
addi ax1, ax1, 1
L1:
64-bit subtract
(x ← y − z)
sub ax0, ay0, az0
sub ax1, ay1, az1
bgeu ay0, az0, L
addi ax1, ax1, -1
L:
64-bit compare and branch
if x < y goto L
blt ax1, ay1, L
bne ax1, ay1, L1
bltu ax0, ay0, L
L1:
64-bit multiply
(x ← y × z)
mull ax0, ay0, az0
muluh ax1, ay0, az0
mull t, ay0, az1
add ax1, ax1, t
mull t, ay1, az0
add ax1, ax1, t
BR[x] ← BR[y] orb bx, by, by
BR[x] ← 0 xorb bx, b0, b0
BR[x] ← 1 orbc bx, b0, b0
Table 8–246. Instruction Idioms
(continued)
Operation Preferred Idiom
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To simplify the coding, change the preceding to store data in the input array backward
so that the array references are all increments instead of decrements. Now convert it
into two loops to avoid the circular addressing:
input[next] = in;
acc = 0x4000;
j = 0;
for (i = next; i < N; i += 1, j += 1) {
acc += input[i] * coeff[j];
}
for (i = 0; i < next; i += 1, j += 1) {
acc += input[i] * coeff[j];
}
next = next == 0 ? N-1 : next-1;
and then implement the loops with two calls to an assembler subroutine:
mac16_dot (N - next, &input[next], &coeff[0]);
mac16_dot (next, &input[0], &coeff[N - next]);
The MAC16 assembler for mac16_dot is:
// FIR Filter using MAC16
// Copyright 1999 Tensilica Inc.
// These coded instructions, statements, and computer programs are
// Confidential Proprietary Information of Tensilica Inc. and may not
be
// disclosed to third parties or copied in any form, in whole or in
part,
// without the prior written consent of Tensilica Inc.
// Exports
.global mac16_set_acc
.global mac16_acc
.global mac16_dot
// Use defines to make the code below less endian-specific
#if __XTENSA_EL__
# define MULA00 mula.dd.ll
# define MULA22 mula.dd.hh
# define MULA02 mula.dd.lh
# define MULA20 mula.dd.hl
# define MULA00L mula.dd.ll.ldinc
# define MULA22L mula.dd.hh.ldinc
# define MULA02L mula.dd.lh.ldinc
# define MULA20L mula.dd.hl.ldinc
# define BBCI(_r,_b,_l) bbci _r, _b, _l
# define BBSI(_r,_b,_l) bbsi _r, _b, _l
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#endif
#if __XTENSA_EB__
# define MULA00 mula.dd.hh
# define MULA22 mula.dd.ll
# define MULA02 mula.dd.hl
# define MULA20 mula.dd.lh
# define MULA00L mula.dd.hh.ldinc
# define MULA22L mula.dd.ll.ldinc
# define MULA02L mula.dd.hl.ldinc
# define MULA20L mula.dd.lh.ldinc
# define BBCI(_r,_b,_l) bbci _r, 31-(_b), _l
# define BBSI(_r,_b,_l) bbsi _r, 31-(_b), _l
#endif
#include <machine/specreg.h>
.text
// void mac16_set_acc(int hi, int lo)
.align4
mac16_set_acc:
entrysp, 16
wsr a2, ACCHI
wsr a3, ACCLO
retw
// int mac16_acc(int shift)
.align4
mac16_acc:
entrysp, 16
ssr a2
rsr a2, ACCHI
rsr a3, ACCLO
src a2, a2, a3
retw
// int mac16_dot (int n, int16* a, int16* b)
.align4
mac16_dot:
entrysp, 16
// a2: n
// a3: a[]
// a4: b[]
blti a2, 1, .sameret// if n <= 0, nothing to do
addi a3, a3, -4// compensate for pre-increment
addi a4, a4, -4// compensate for pre-increment
xor a5, a3, a4// check if vectors have same alignment
BBSI(a5, 1, .diffalign)
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.samealign:// vectors have same alignment
BBCI(a3, 1, .samewordalign)
ldincm0, a3 // a[0]
addi a3, a3, -2// undo overincrement, leave *a word-aligned
ldincm2, a4 // b[0]
addi a4, a4, -2// undo overincrement, leave *b word-aligned
MULA22m0, m2 // add product of misaligned first values
addi a2, a2, -1// finished one iteration
.samewordalign:// a[0] is word-aligned, b[0] is word-aligned
srli a5, a2, 2 // will do 4 MACs per inner loop iteration
beqz a5, .samemod4check// not even wind-up or wind-down
addi a5, a5, -1// (n/4)-1 inner loop iterations
// (1 iteration done in wind-up/wind-down)
// wind up
ldincm0, a3 // m0 = a[1]:a[0]
ldincm2, a4 // m2 = b[1]:b[0]
ldincm1, a3 // m1 = a[3]:a[2]
MULA00Lm3, a4, m0, m2// m3 = b[3]:b[2]; acc += a[0]*b[0]
loopneza5, .sameloopend
.sameloop:// for i = 4; i < N-3; i += 4
MULA22Lm0, a3, m0, m2// m0 = a[i+1]:a[i+0]; acc += a[i-4+1]:b[i-
4+1]
MULA00Lm2, a4, m1, m3// m2 = b[i+1]:b[i+0]; acc += a[i-4+2]:b[i-
4+2]
MULA22Lm1, a3, m1, m3// m1 = a[i+3]:a[i+2]; acc += a[i-4+3]:b[i-
4+3]
MULA00Lm3, a4, m0, m2// m3 = b[i+3]:b[i+2]; acc += a[i+0]*b[i+0]
.sameloopend:
// wind down
MULA22m0, m2 // acc += a[i+1]*b[i+1]
MULA00m1, m3 // acc += a[i+2]*b[i+2]
MULA22m1, m3 // acc += a[i+3]*b[i+3]
.samemod4check:
BBCI(a2, 1, .samemod2check)
// count is 2 mod 4
ldincm0, a3 // m0 = a[i+5]:a[i+4]
ldincm2, a4 // m2 = b[i+5]:b[i+5]
MULA00m0, m2 // acc += a[i+4]*b[i+4]
MULA22m0, m2 // acc += a[i+5]*b[i+5]
.samemod2check:
BBCI(a2, 0, .sameret)
// count is 1 mod 2
ldincm0, a3 // m0 = a[i+7]:a[i+6]
ldincm2, a4 // m2 = b[i+7]:b[i+6]
MULA00m0, m2 // acc += a[i+6]*b[i+6]
.sameret:
retw
.diffalign:// vectors have different alignment
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BBCI(a3, 1, .diffwordalign)
// a[0] is misaligned, b[0] is aligned
ldincm0, a3 // a[0]
addi a3, a3, -2// undo overincrement, leave *a word-aligned
ldincm2, a4 // b[0]
addi a4, a4, -2// undo overincrement, leave *b misaligned
MULA20m0, m2 // add product of first values
addi a2, a2, -1// finished one iteration
.diffwordalign: // a[0] is now aligned, b[0] is misaligned
srli a5, a2, 2 // will do 4 MACs per inner loop iteration
ldincm3, a4 // m3 = b[0]:b[-1]
beqz a5, .diffmod4check// not even wind-up or wind-down
addi a5, a5, -1// (n/4)-1 inner loop iterations
// (1 iteration done in wind-up/wind-down)
// wind up
ldincm0, a3 // m0 = a[1]:a[0]
ldincm2, a4 // m2 = b[2]:b[1]
MULA02Lm1, a3, m0, m3// m1 = a[3]:a[2]; acc += a[0] * b[0]
MULA20Lm3, a4, m0, m2// m3 = b[4]:b[3]; acc += a[1] * b[1]
loopneza5, .diffloopend
.diffloop:// for i = 4; i < N-3; i += 4
MULA02Lm0, a3, m1, m2// m0 = a[i+1]:a[i+0]; acc += a[i-4+2]*b[i-
4+2]
MULA20Lm2, a4, m1, m3// m2 = b[i+2]:b[i+1]; acc += a[i-4+3]*b[i-
4+3]
MULA02Lm1, a3, m0, m3// m1 = a[i+3]:a[i+2]; acc += a[i+0]*b[i+0]
MULA20Lm3, a4, m0, m2// m3 = b[i+4]:b[i+3]; acc += a[i+1]*b[i+1]
.diffloopend:
// wind down
MULA02m1, m2 // acc += a[i+2] * b[i+2]
MULA20m1, m3 // acc += a[i+3] * b[i+3]
.diffmod4check:
BBCI(a2, 1, .diffmod2check)
// count is 2 mod 4
ldincm0, a3 // m0 = a[i+5]:a[i+4]
MULA02m0, m3 // acc += a[i+4] * b[i+4]
ldincm3, a4 // m3 = b[i+6]:b[i+5]
MULA20m0, m3 // acc += a[i+5] * b[i+5]
.diffmod2check:
BBCI(a2, 0, .diffret)
// count is 1 mod 2
ldincm0, a3 // m0 = a[i+7]:a[i+6]
MULA02m0, m3 // acc += a[i+6] * b[i+6]
.diffret:
retw
Chapter 8. Using the Xtensa Architecture
Xtensa Instruction Set Architecture (ISA) Reference Manual 605
8.4 Performance
This book describes the Xtensa Instruction Set Architecture (ISA) but is not the refer-
ence for performance. The ISA is defined independently of its various implementations,
so that software that targets the ISA will run on any its implementations. The ISA in-
cludes features that are not required by some of its implementations, but which will be
important to include in software written today if it is to work on future implementations
(for example, using MEMW, EXTW, and EXCW). While correct software must adhere to the
ISA and not to the specifics of any of its implementations, it is sometimes important to
know the details of an implementation for performance reasons, such as scheduling in-
structions to avoid pipeline delays. This chapter provides an overview of performance
modeling.
8.4.1 Processor Performance Terminology and Modeling
It is important to have a model of processor performance for both code generation and
simulation. However, the interactions of multiple instructions in a processor pipeline can
be complex. It is common to simplify and describe pipeline and cache performance sep-
arately even though they may interact, because the information is used in different stag-
es of compilation or coding. We adopt this approach, and then separately describe some
of the interactions. It is also common to describe the pipelining of instructions with laten-
cy (the time an instruction takes to produce its result after it receives its inputs) and
throughput (the time an instruction delays other instructions independent of operand de-
pendencies) numbers, but this cannot accommodate some situations. Therefore, we
adopt a slightly more complicated, but more accurate model. This model focuses on pre-
dicting when one instruction issues relative to other instructions. An instruction issues
when all of its data inputs are available and all the necessary hardware functional units
are available for it. Issue is the point at which computation of the instruction’s results
begins.
Instead of using a per-instruction latency number, instructions are modeled as taking
their operands in various pipeline stage numbers, and producing results in various pipe-
line stage numbers. When instruction IA writes (or defines) X (either an explicit operand
or implicit state register) and instruction IB reads (or uses) X, then instruction IB de-
pends on IA.1 If instruction IA defines X in stage SA (at the end of the stage), and in-
struction IB uses X in stage SB (at the beginning of the stage), then instruction IB can is-
sue no earlier than D = max(SA − SB + 1, 0) cycles after IA issued. This is illustrated in
Figure 8–54. If the processor reaches IB earlier than D cycles after IA, it generally de-
lays IB’s issue into the pipeline until D cycles have elapsed. When the processor delays
an instruction because of a pipeline interaction, it is called an “interlock.” For a few spe-
cial dependencies (primarily those involving the special registers controlling exceptions,
1. This situation is called a “read after write” dependency. Other possible operand dependencies familiar to coders are “write after write” and “write after
read.”
Chapter 8. Using the Xtensa Architecture
606 Xtensa Instruction Set Architecture (ISA) Reference Manual
interrupts, and memory management) the processor does not interlock. These situations
are called “hazards.” For correct operation, code generation must insert xSYNC instruc-
tions to avoid hazards by delaying the dependent instruction. The xSYNC series of in-
structions is designed to accomplish this delay in an implementation-independent man-
ner.
When an instruction is described as making one of its values available at the end of
some stage, this refers to when the computation is complete, and not necessarily the
time that the actual processor state is written. It is usual to delay the state write until at
least the point at which the instruction is committed (that is, cannot be aborted by its
own or an earlier instruction’s exception). In some implementations the state write is de-
layed still further to satisfy resource constraints. However, the delay in writing the actual
processor state is usually invisible; most processors will detect the use of an operand
that has been produced by one instruction and is being used by another even though the
processor state has not been written, and forward the required value from one pipeline
stage to the other. This operation is called bypass.
Instructions may be delayed in a pipeline for reasons other than operand dependencies.
The most common situation is for two or more instructions to require a particular piece of
the processor’s hardware (called a “functional unit”) to execute. If there are fewer copies
of the unit than instructions that need to use the unit in a given cycle, the processor must
delay some of the instructions to prevent the instructions from interfering with each oth-
er. For example, a processor may have only one read port for its data cache. If instruc-
tion IC uses this read port in its stage 4 and instruction ID uses the read port in its stage
3, then it would not be possible to issue IC in cycle 10 and ID in cycle 11, because they
would both need to use the data cache read port in cycle 14. Typically, the processor
would delay ID’s issue into the pipeline by one cycle to avoid conflict with IC.
Modern processor pipeline design tends to avoid the use of functional units in varying
pipeline stages by different instructions and to fully pipeline functional unit logic. This
means that most instructions would conflict with each other on a shared functional unit
only if they issued in the same cycle. However, there are usually still a small number of
cases in which a functional unit is used for several cycles. For example, floating-point or
integer division may iterate for several cycles in a single piece of hardware. In this case,
once a divide has started, it is not possible to start another divide until the first has left
the iterative hardware. This is illustrated in Figure 8–55.
Chapter 8. Using the Xtensa Architecture
Xtensa Instruction Set Architecture (ISA) Reference Manual 607
Figure 8–54. Instruction Operand Dependency Interlock
Figure 8–55. Functional Unit Interlock
Cycle T+0T+1T+2T+3T+4T+5T+6
IA A0 A1 A2 A3
IB attempted B0 B1 B2 B3
IB attempted B0 B1 B2 B3
IB issued B0 B1 B2 B3
value for X defined (3)
value for X needed (1) but not available
value for X needed (1) bypassed from IA
bypass of X from IA to IB
IA issues in cycle T+0, IB issues in cycle T+0+max(3−1+1,0) = T+3
Cycle T+0T+1T+2T+3T+4T+5T+6
IA A0 A1 A2 A3
IB attempted B0 B1 B2 B3
IB issued B0 B1 B2 B3
Two cycle use of a functional unit
Functional unit needed for 3 cycles but not available
Functional unit available after instruction is delayed
IB tries to issue at T+1 and reserve the unit in T+2..T+4, but is blocked by IA’s T+2 reservation
IB is retried and issues in cycle T+2, thereby avoiding IA’s reservations
IA issues at T+0 and reserves the functional unit in cycles T+1 and T+2
Chapter 8. Using the Xtensa Architecture
608 Xtensa Instruction Set Architecture (ISA) Reference Manual
8.4.2 Xtensa Processor Family
Many implementations of the Xtensa processor use a 5-stage pipeline capable of exe-
cuting at most one instruction per cycle. The pipeline stages are described in
Table 8–247. The first stage, I, is partially decoupled from the next, R, and R is partially
decoupled from the last three stages, E, M, and W, which operate in lock-step. If an inter-
lock condition is detected in the R stage, then in the next cycle the instruction is retried in
R and a no-op is sent on to the E stage. If an instruction is held in R, then the word
fetched in I is captured in a buffer.
The three primary implications of the Xtensa pipeline are shown in Figure 8–56.
Instructions that depend on an ALU result can execute with no delay because their
result is available at the end of E and is needed at the beginning of E by the depen-
dent instruction.
Instructions that depend on load instruction results must issue two cycles after the
load because the load result is available at the end of its M stage and is needed at
the beginning of E by the dependent instruction. For best performance, code gener-
ation should put an independent instruction in between the load and any instruction
that uses the load result.
Finally, the branch decision occurs in E, and for taken branches must affect the I
stage of the target fetch, and so there are two fetched fall-through instructions that
are killed on taken branches.
Table 8–247. Xtensa Pipeline
Name Description
I
Instruction cache/RAM/ROM access
Instruction cache tag comparison
Instruction alignment
R
AR register file read
Instruction decode, interlocking, and bypass
Instruction cache miss recognition
E
Execution of most ALU-type instructions (ADD, SUB, etc.)
Virtual address generation for load and store instructions
Branch decision and address selection
M
Data cache/RAM/ROM access for load and store instructions
Data cache tag comparison
Data cache miss recognition
Load data alignment
WState writes (e.g. AR register file write)
Chapter 8. Using the Xtensa Architecture
Xtensa Instruction Set Architecture (ISA) Reference Manual 609
The base processor uses 32-bit aligned fetches from the instruction cache/RAM/ROM.
Processors with instructions larger than 32 bits in size use fetches big enough to fetch at
least one instruction per cycle. If the target of a branch is an instruction that crosses a
fetch boundary, then two fetches will be required before the entire instruction is avail-
able, and so the target instruction will begin three cycles after the branch instead of two.
For best performance, code generation should align 24-bit targets of frequently taken
branches on 0 or 1 mod 4 byte boundaries, and 16-bit targets on 0, 1, or 2 mod 4 byte
boundaries.
The processor avoids overflowing its write buffer by interlocking in the R stage on stores
when the write buffer is full or might become full from stores in the E and M stages.
Figure 8–56. Xtensa Pipeline Effects
Refer to a specific Xtensa processor data book for detailed descriptions of processor
performance and tables of pipeline stages where operands are used and defined.
Cycle T+0T+1T+2T+3T+4T+5T+6T+7
From0 (ALU) IREMW
From1 (Load) IREMW
From2 IREMW
From3 (Branch) IREMW
From4 (killed by taken branch) IREM
From5 (killed by taken branch) IRE
To0 IR
Load to use
Taken branch delay
ALU to use
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610 Xtensa Instruction Set Architecture (ISA) Reference Manual
Appendix A. Differences Between Old and Current Hardware
Xtensa Instruction Set Architecture (ISA) Reference Manual 611
A. Differences Between Old and Current Hardware
A.1 Added Instructions
Instructions have been added to the instruction set at various points. Most have been
added as a part of new options, but a few have been added to existing options. Table 9-
248 shows instructions added to existing options along with the first implementation in
which they were added.
A.2 Xtensa Exception Architecture 1
As is described in Section 4.4.1, there are two variants of the Exception Option. Xtensa
Exception Architecture 1 (XEA1) is no longer available for new hardware and this sec-
tion describes the differences between it and Xtensa Exception Architecture 2 (XEA2),
which is described in the option chapter in Section 4.4.1.
The biggest difference between the two is that where XEA2 has a bit, PS.EXCM, that
causes certain effects in the hardware that are useful on entering and leaving excep-
tions and interrupts, XEA1 has that functionality bundled into the setting of the
PS.INTLEVEL field. There is no provision for either ring protection or double exceptions
in XEA1.
The following subsections describe the differences in more detail.
Table 9-248. Instructions Added
Instruction First Implementation Containing the Instruction
DIWB T1050
DIWBI T1050
EXTW RA-2004.1
NOP (actual instruction rather than assembly macro) RA-2004.1
RER RC-2009.0
WER RC-2009.0
XSR T1040
Appendix A. Differences Between Old and Current Hardware
612 Xtensa Instruction Set Architecture (ISA) Reference Manual
A.2.1 Differences in the PS Register
The following fields of the PS register (see page 87) are different in XEA1:
There is no PS.EXCM field in XEA1
There is no PS.RING field in XEA1
PS.INTLEVEL always exists in XEA1 (added by the Exception Option) instead of
appearing with the Interrupt Option. In this case CINTLEVEL is 0 for normal opera-
tion and 1 when executing in an exception handler.
Some of the functions surrounding the fields of the PS register are also different from
later behavior (see Section 4.4.1.3). In XEA1:
CEXCM ← PS.INTLEVEL ≠ 0
CRING ← 0
CINTLEVEL ← PS.INTLEVEL
CWOE ← PS.WOE
CLOOPENABLE ← 1
In XEA1, there is no architectural provision to take an instruction related exception when
CINTLEVEL is greater than zero, but in actual hardware delivered it was possible to do
under carefully controlled situations.
In XEA1, the PS register is reset to the value 028||14, which is different from what is giv-
en in Section 3.6 for XEA2.
A.2.2 Exception Semantics
Instead of the semantics shown in Section 4.4.1.10, exceptions have the following se-
mantics in Xtensa Exception Architecture 1 (XEA1):
procedure Exception(cause)
EPC[1] ← PC
PS.INTLEVEL ← 1
n ← if WindowStartWindowBase+1 then 2’b01
else if WindowStartWindowBase+2 then 2’b10
else if WindowStartWindowBase+3 then 2’b11
else 2’b00
if PS.UM then
EXCCAUSE ← cause
nextPC ← UserExceptionVector
PS.UM ← 0
PS.WOE ← 0
elseif n ≠ 2’b00 then
PS.OWB ← WindowBase
PS.WOE ← 0
Appendix A. Differences Between Old and Current Hardware
Xtensa Instruction Set Architecture (ISA) Reference Manual 613
m ← WindowBase + (2'b00||n)
nextPC ← if WindowStartm+1 then WindowOverflow4
else if WindowStartm+2 then WindowOverflow8
else WindowOverflow12
WindowBase ← m
else
EXCCAUSE ← cause
nextPC ← KernelExceptionVector
-- note PS.WOE left unchanged
-- note PS.UM is already 0
endif
endprocedure Exception
The intent of the window checks in Xtensa Exception Architecture 1 is to allow the kernel
exception handler to use CALLX12 without taking an exception. This allows the handler
to “save” 12 registers using the windowed-register mechanism instead of using 12 loads
and 12 stores. This results in low-overhead kernel exceptions. When the window over-
flow exception is invoked instead of the requested exception, the RFWO from the handler
will attempt to re-execute the instruction that caused the original exception, and this time
the kernel exception handler will be invoked. This feature has proved difficult to use in
operating systems.
User vector mode exceptions work differently because it is usually necessary to switch
stacks when going from the program stack to the exception stack, and this involves stor-
ing all windows to the program stack.
Instead of the semantics shown in Section 4.7.1.3, window checks have the following
semantics in Xtensa Exception Architecture 1 (XEA1):
procedure WindowCheck (wr, ws, wt)
n ← if (wr ≠ 2'b00 or ws ≠ 2'b00 or wt ≠ 2'b00)
and WindowStartWindowBase+1 then 2’b01
else if (wr1 or ws1 or wt1)
and WindowStartWindowBase+2 then 2’b10
else if (wr = 2'b11 or ws = 2'b11 or wt = 2'b11)
and WindowStartWindowBase+3 then 2’b11
else 2’b00
if CWOE = 1 and n ≠ 2’b00 then
PS.OWB ← WindowBase
m ← WindowBase + (2'b00||n)
PS.WOE ← 0
PS.INTLEVEL ← 1
EPC[1] ← PC
nextPC ← if WindowStartm+1 then WindowOverflow4
else if WindowStartm+2 then WindowOverflow8
else WindowOverflow12
WindowBase ← m
endif
endprocedure WindowCheck
Appendix A. Differences Between Old and Current Hardware
614 Xtensa Instruction Set Architecture (ISA) Reference Manual
A.2.3 Checking ICOUNT
The procedure for taking an ICOUNT interrupt is different from the one given in
Section 4.7.6.8. Instead of setting PS.EXCM, it clears PS.WOE and PS.UM as shown
here:
procedure checkIcount ()
if CINTLEVEL < ICOUNTLEVEL then
if ICOUNT ≠ -1 then
ICOUNT ← ICOUNT + 1
elseif CINTLEVEL < DEBUGLEVEL then
EPC[DEBUGLEVEL] ← PC
EPS[DEBUGLEVEL] ← PS
DEBUGCAUSE ← 1
PC ← InterruptVector[DEBUGLEVEL]
PS.WOE ← 0
PS.UM ← 0
PS.INTLEVEL ← DEBUGLEVEL
endif
endif
endprocedure checkIcount
A.2.4 The
BREAK
and
BREAK.N
Instructions
In XEA1 the BREAK and BREAK.N instructions do not affect PS.EXCM, since it does not
exist, but set PS.UM ← 0 and PS.WOE ← 0 instead.
A.2.5 The
RETW
and
RETW.N
Instructions
In XEA1 the RETW and RETW.N instructions are not affected by and do not affect PS.EX-
CM, since it does not exist. In the underflow case, before setting
EPC[1] ← PC, these instructions set PS.WOE ← 0 and PS.INTLEVEL ← 1 instead.
A.2.6 The
RFDE
Instruction
There is no RFDE instruction in XEA1.
A.2.7 The
RFE
Instruction
In XEA1 the RFE instruction does not affect PS.EXCM, since it does not exist, but sets
PS.INTLEVEL ← 0 instead. In XEA1, it is used only to return from exceptions that went
to the kernel exception vector.
Appendix A. Differences Between Old and Current Hardware
Xtensa Instruction Set Architecture (ISA) Reference Manual 615
A.2.8 The
RFUE
Instruction
XEA1 supports the RFUE instruction, which is nearly identical to the RFE instruction but
sets PS.UM ← 1 and PS.WOE ← 1 in addition. A partial description is given in
Chapter 6, page 243. The following instruction entry shows the RFUE instruction that is
not fully described in Chapter 6. Note that an ESYNC instruction needs to be used be-
tween a WSR/XSR.EPC1 and an RFUE instruction.
Instruction Word
Required Configuration Option:
Exception Option (Xtensa Exception Architecture 1 Only)
Assembler Syntax
RFUE
Description
RFUE exists only in Xtensa Exception Architecture 1. It is an illegal instruction in Xtensa
Exception Architecture 2 and above.
RFUE returns from an exception that went to the UserExceptionVector (that is, a
non-window synchronous exception or level-1 interrupt that occurred while the proces-
sor was executing with PS.UM set). It sets PS.UM back to 1, clears PS.INTLEVEL back
to 0, sets PS.WOE back to 1, and then jumps to the address in EPC[1].
RFUE is a privileged instruction.
Operation
if CRING ≠ 0 then
Exception (PrivilegedInstructionCause)
else
PS.UM ← 1
PS.INTLEVEL ← 0
PS.WOE ← 1
nextPC ← EPC[1]
endif
23 0
000000000011000100000000
24
Appendix A. Differences Between Old and Current Hardware
616 Xtensa Instruction Set Architecture (ISA) Reference Manual
Exceptions
EveryInst Group (see page 244)
GenExcep(IllegalInstructionCause) if Exception Option
A.2.9 The
RFWO
and
RFWU
Instructions
In XEA1 the RFWO and RFWU instructions do not affect PS.EXCM, since it does not exist,
but set PS.INTLEVEL ← 0 and PS.WOE ← 1 instead.
A.2.10 Exception Virtual Address Register
The exception virtual address register, EXCVADDR, does not exist in XEA1. There are no
memory management tables to refill and so it is not absolutely necessary. On other
memory exceptions, system software must decode the instruction to determine the
memory address involved if it wishes to know.
A.2.11 Double Exceptions
There is never a DEPC register in XEA1. Double exceptions are not generally recover-
able in XEA1 and often not detectable.
A.2.12 Use of the RSIL Instruction
The RSIL instruction is typically used for executing a region of code at a new level:
RSIL a2, newlevel
code to be executed at newlevel
WSR a2, PS
In XEA2, the atomicity of the RSIL instruction is a convenience, but in XEA1 it is
required to avoid race conditions that have to do with the fact that returning from
exceptions sets PS.INTLEVEL to zero.
A.2.13 Writeback Cache
No writeback data cache is available in XEA1.
Appendix A. Differences Between Old and Current Hardware
Xtensa Instruction Set Architecture (ISA) Reference Manual 617
A.2.14 The Cache Attribute Register
In XEA1, the Options for Memory Protection and Translation in Section 4.6 and the cor-
responding TLB management instructions are not available. Instead, functionality similar
to the Region Protection Option described in Section 4.6.3 is available through the
cache attribute register. Table 9-249 shows the cache attribute register and its addition
as a Special Register.
The following table shows the Cache Attribute Special Register as it is implemented in
XEA1 and described as current Special Registers are described in Chapter 5.
The single register controls protection for all of memory and for both instruction and data
fetches. As shown in Figure 9-57, the register consists of eight 4-bit attribute fields. For
any memory access, one of the attrn (attribute) fields is chosen for both instruction
and data accesses by the following algorithm:
b ← vAddr31..29
cacheattr ← CACHEATTR(b||2'b11)..(b||2'b00)
Table 9-249. Cache Attribute Register
Register
Mnemonic Quantity Width
(bits) Register Name R/W
Special
Register
Number
1
CACHEATTR 132 Cache attribute R/W 98
1. Registers with a Special Register assignment are read and/or written with the RSR, WSR, and XSR instructions. See Table 5–127 on
page 205.
Table 9-250. Cache Attribute Special Register
SR# Name Description Reset Value
98 CACHEATTR Cache Attribute Register 32’h22222222
Option Count Bits Privileged? XSR Legal?
Exception Option Architecture 1 132 Yes
WSR Function RSR Function
CACHEATTR ← AR[t] AR[t] ← CACHEATTR
Other Changes to the Register Other Effects of the Register
Any instruction/data address translation
Instruction
⇒ xSYNC ⇒
Instruction
WSR/XSR CACHEATTR ⇒ ESYNC ⇒ RSR/XSR CACHEATTR
WSR/XSR CACHEATTR ⇒ ISYNC ⇒ Any Instruction address translation that depends on new value
WSR/XSR CACHEATTR ⇒ DSYNC ⇒ Any data address translation that depends on the change
Appendix A. Differences Between Old and Current Hardware
618 Xtensa Instruction Set Architecture (ISA) Reference Manual
This allows the cache attributes to be separately specified for each 512MB of address
space, just as with the attributes in the Region Protection Option described in
Section 4.6.3. And as with that option, no translation of addresses is done.
Figure 9-57. CACHEATTR Register
The resulting attribute is interpreted for both cache and local memory accesses as de-
scribed in Section 4.6.3.3, except that writeback caches are not available. It is in this
sense that the Region Protection Option is upward compatible with XEA1.
After changing the attribute of a region by WSR to CACHEATTR, the operation of instruc-
tion fetch from that region is undefined until an ISYNC instruction is executed. Thus soft-
ware should not change the cache attribute of the region containing the current PC.
After changing the attribute of a region by WSR to CACHEATTR, the operation of loads
from and stores to that region are undefined until a DSYNC instruction is executed.
The processor sets every region of CACHEATTR to bypass (4'b0010) on processor
reset.
The following pseudocode describes the accessing of the CACHEATTR register.
function fcadecode (ca)-- cacheattr decode for fetch
if not (ca = 4'd1 or ca = 4'd2 or ca = 4'd3 or ca = 4'd4) then
fcadecode ← undefined8||1
else
usehit ← ca = 4'd1 or ca = 4'd3 or ca = 4'd4
allocate ← ca = 4'd1 or ca = 4'd3 or ca = 4'd4
writethru ← undefined
isolate ← undefined
guard ← 0
coherent ← 0
prefetch ← 0
streaming ← 0
fcadecode ← streaming||prefetch||coherent||guard
||isolate||writethru||allocate||usehit||0
endif
endfunction fcadecode
function lcadecode (ca)-- cacheattr decode for load
if ca > 4'd4 and ca ≠ 4'd14 then
lcadecode ← undefined8||1
31 28 27 24 23 20 19 16 15 12 11 8 7 4 3 0
attr7 attr6 attr5 attr4 attr3 attr2 attr1 attr0
44444444
Appendix A. Differences Between Old and Current Hardware
Xtensa Instruction Set Architecture (ISA) Reference Manual 619
else
usehit ← ca ≠ 4'd2
allocate ← ca = 4'd1 or ca = 4'd3 or ca = 4'd4
writethru ← undefined
isolate ← ca = 4'd14
guard ← 0
coherent ← 0
prefetch ← 0
streaming ← 0
lcadecode ← streaming||prefetch||coherent||guard
||isolate||writethru||allocate||usehit||0
endif
endfunction lcadecode
function scadecode (ca)-- cacheattr decode for store
if ca > 4'd4 and ca ≠ 4'd14 then
scadecode ← undefined8||1
else
usehit ← undefined
allocate ← ca = 4'd3 or ca = 4'd4
writethru ← ca < 4'd4
isolate ← ca = 4'd14
guard ← 0
coherent ← 0
prefetch ← 0
streaming ← 0
scadecode ← streaming||prefetch||coherent||guard
||isolate||writethru||allocate||usehit||0
endif
endfunction scadecode
A.3 New Exception Cause Values
Beginning with the RB-2006.0 release, the EXCCAUSE register, as indicated in
Table 4–64 on page 89, can, in limited cases have different values than it did before
that. In particular, exceptions which used to result in EXCCAUSE code 2 (Instruction-
FetchErrorCause) are now split into three values. EXCCAUSE code 2 (Instruction-
FetchErrorCause) now covers only those errors occuring inside the Xtensa processor.
EXCCAUSE code 12 (InstrPIFDataErrorCause) now covers data errors on the PIF for
Instruction fetch and EXCCAUSE code 14 (InstrPIFAddrErrorCause) now covers ad-
dress errors on the PIF for Instruction fetch. Similarly, exceptions which used to result in
EXCCAUSE code 3 (LoadStoreErrorCause) are now split into three values. EXCCAUSE
code 3 (LoadStoreErrorCause) now covers only those errors occuring inside the Xtensa
processor. EXCCAUSE code 13 (LoadStorePIFDataErrorCause) now covers data errors
on the PIF for Load/Store and EXCCAUSE code 15 (LoadStorePIFAddrErrorCause) now
covers address errors on the PIF for Load/Store.
Appendix A. Differences Between Old and Current Hardware
620 Xtensa Instruction Set Architecture (ISA) Reference Manual
This change was made to make it easier to separate errors caused by the system from
errors caused by the Xtensa processor itself during debugging. If exception code is up-
graded so that exceptions with EXCCAUSE set to values 12-15 are routed to the code
that handled EXCCAUSE 2 and 3 as appropriate, then the previous functionality is re-
tained.
A.4 ICOUNTLEVEL
The ICOUNTLEVEL Special Register is undefined after reset instead of 4’hF, beginning
with the RA-2004.1 release. This change should not cause any difficulty as the behavior
is the same after reset since PS.INTLEVEL is 4’hF.
A.5 MMU Option Memory Attributes
As described in Section 4.6.5.10, T1050 used different MMU Option Memory Attributes.
System software may use the subset of attributes (1, 3, 5, 7, 12, 13, and 14) that have
not changed to support all Xtensa processors.
The specific differences for T1050 were:
In Table 4–109 on page 178, rows with Attribute 0, 2, 4, 6, 8, and 10 were equivalent
to the row with Attribute 12 in the table.
In Ta bl e 4–109 on page 178, the row with Attribute 15 was equivalent to the row with
Attribute 7, for the Data MMU but to the row with Attribute 12 for the Instruction
MMU.
In Ta bl e 4–109 on page 178 for Data Loads when writeback caches are not present,
rows with Attributes 9 and 11 were called “No Allocate” instead of “Cached” and the
column labeled “Fill Load”) contained “no” for instead of “yes”.
A.6 Special Register Read and Write
Before the RA-2004.1 release, Special Registers were read and written with the RSR,
WSR, and XSR instructions. Each of these instructions takes one operand to indicate the
Special Register that was the source or destination of the instruction, and another oper-
and to indicate the AR register used as the other operand.
Beginning with the RA-2004.1 release, this trio of instructions was replaced with an indi-
vidual trio of instructions for each Special Register. For example, the new instructions for
accessing the LBEG register are called RSR.LBEG, WSR.LBEG, and XSR.LBEG. The new
Appendix A. Differences Between Old and Current Hardware
Xtensa Instruction Set Architecture (ISA) Reference Manual 621
instructions take only one operand, which is the AR register. The old version of the in-
structions continues to be supported as an assembler macro that translates to the new
ones.
The old trio of instructions was legal whether or not the Special Register accessed was
defined in the particular implementation and, therefore, never produced an illegal in-
struction exception. Each of the new, much larger set of instructions is associated with a
particular Special Register, and therefore is legal only if the associated register is de-
fined. Each of the trio of instructions for an undefined register raises an illegal instruction
exception when execution is attempted.
Rather than list several hundred individual instructions, Chapter 6 lists the instructions
as RSR.*, WSR.*, and XSR.* and references the list of Special Registers in Chapter 5.
A.7 MMU Modification
In the RC.2009.0 release and after, the IVARWAY56 and DVARWAY56 parameters in
Table 4–105 on page 159 must both be "Variable" whereas before that they must both
be "Fixed". The functional operation of the MMU with the parameters set to Fixed may
be emulated when the parameters are set to Variable. In other words, the function of the
earlier MMU can be emulated by the later one.
A.8 Reduction of SYNC Instruction Requirements
For the T1050 release and releases before it, there were additional SYNC instruction re-
quirements not listed in Section 5.3 on page 208. These additional SYNC instruction re-
quirements are listed in Table 9–251, by subsection and in the same format used in
Section 5.3. If these SYNC instructions are inserted in later releases where they are not
needed, the code will still function correctly.
Table 9–251. T1050 Additional SYNC Requirements
Instruction
⇒
xSYNC
⇒
Instruction
Section 5.3.2 on page 212
WSR/XSR LBEG ⇒ ESYNC ⇒ RSR/XSR LBEG
WSR/XSR LEND ⇒ ESYNC ⇒ RSR/XSR LEND
Section 5.3.3 on page 213
WSR/XSR ACCLO ⇒ ESYNC ⇒ RSR/XSR ACCLO
WSR/XSR ACCHI ⇒ ESYNC ⇒ RSR/XSR ACCHI
WSR/XSR M0..3 ⇒ ESYNC ⇒ RSR/XSR M0..3
WSR/XSR M0..3 ⇒ ESYNC ⇒ MAC16 Option instructions
Appendix A. Differences Between Old and Current Hardware
622 Xtensa Instruction Set Architecture (ISA) Reference Manual
Section 5.3.4 on page 215
WSR/XSR SAR ⇒ ESYNC ⇒ RSR/XSR SAR
WSR/XSR SAR ⇒ ESYNC ⇒ SLL/SRL/SRA/SRC
WSR/XSR BR ⇒ ESYNC ⇒ RSR/XSR BR
WSR/XSR BR ⇒ ESYNC ⇒ Listed instruction use of BR
Instruction setting of BR ⇒ ESYNC ⇒ RSR/XSR BR
WSR/XSR LITBASE ⇒ ESYNC ⇒ RSR/XSR LITBASE
WSR/XSR SCOMPARE1 ⇒ ESYNC ⇒ RSR/XSR SCOMPARE1
Section 5.3.5 on page 216
WSR/XSR PS ⇒ ESYNC ⇒ RSR/XSR PS
WSR/XSR PS ⇒ RSYNC ⇒ CALL4/8/12, CALLX4/8/12
WSR/XSR PS ⇒ RSYNC ⇒ RFI/RFDD/RFDO/RFE/RFWO/RFWU/RSIL/WAITI
WSR/XSR PS.INTLEVEL ⇒ RSYNC ⇒ RSIL
WSR/XSR PS.UM ⇒ ESYNC ⇒ RSIL
WSR/XSR PS.RING ⇒ RSYNC ⇒ Privileged instruction exception
WSR/XSR PS.OWB ⇒ RSYNC ⇒ RFWO/RFWU
WSR/XSR PS.OWB ⇒ RSYNC ⇒ RSIL
WSR/XSR PS.CALLINC ⇒ RSYNC ⇒ ENTRY/RSIL
WSR/XSR PS.WOE ⇒ RSYNC ⇒ RSIL
Section 5.3.6 on page 221
WSR/XSR WINDOWBASE ⇒ ESYNC ⇒ RSR/XSR WINDOWBASE
WSR/XSR WINDOWSTART ⇒ ESYNC ⇒ RSR/XSR WINDOWSTART
Section 5.3.7 on page 221
WSR/XSR PTEVADDR ⇒ ESYNC ⇒ RSR/XSR PTEVADDR
WSR/XSR EXCVADDR ⇒ ESYNC ⇒ RSR/XSR PTEVADDR
WSR/XSR RASID ⇒ ESYNC ⇒ RSR/XSR RASID
WSR/XSR ITLBCFG ⇒ ESYNC ⇒ RSR/XSR ITLBCFG
WSR/XSR DTLBCFG ⇒ ESYNC ⇒ RSR/XSR DTLBCFG
Section 5.3.8 on page 223
WSR/XSR EXCCAUSE ⇒ ESYNC ⇒ RSR/XSR EXCCAUSE
WSR/XSR EXCVADDR ⇒ ESYNC ⇒ RSR/XSR EXCVADDR
WSR/XSR EXCVADDR ⇒ ESYNC ⇒ RSR/XSR PTEVADDR
Table 9–251. T1050 Additional SYNC Requirements
Appendix A. Differences Between Old and Current Hardware
Xtensa Instruction Set Architecture (ISA) Reference Manual 623
Section 5.3.9 on page 226
WSR/XSR EPC1 ⇒ ESYNC ⇒ RSR/XSR EPC1
WSR/XSR EPC1 ⇒ ESYNC ⇒ RFE/RFWO/RFWU
WSR/XSR EPC2..7 ⇒ ESYNC ⇒ RSR/XSR EPC2..7
WSR/XSR EPC2..7 ⇒ ESYNC ⇒ RFI 2..7 (to the level of the EPC changed)
WSR/XSR DEPC ⇒ ESYNC ⇒ RSR/XSR DEPC
WSR/XSR DEPC ⇒ ESYNC ⇒ RFDE
WSR/XSR MEPC ⇒ (none) ⇒ RSR/XSR MEPC
WSR/XSR MEPC ⇒ (none) ⇒ RFME
WSR/XSR EPS2..7 ⇒ ESYNC ⇒ RSR/XSR EPS2..7
WSR/XSR EPS2..7 ⇒ RSYNC ⇒ RFI 2..7 (to the level of the EPS changed)
WSR/XSR EXCSAVE1 ⇒ ESYNC ⇒ RSR/XSR EXCSAVE1
WSR/XSR EXCSAVE2..7 ⇒ ESYNC ⇒ RSR/XSR EXCSAVE2..7 (to the same register)
WSR/XSR MESAVE ⇒ (none) ⇒ RSR/XSR MESAVE
Section 5.3.11 on page 231
WSR/XSR ICOUNTLEVEL ⇒ ESYNC ⇒ RSR/XSR ICOUNTLEVEL
WSR/XSR CCOMPARE0..2 ⇒ ESYNC ⇒ RSR/XSR CCOMPARE0..2
Section 5.3.12 on page 233
WSR/XSR IBREAKENABLE ⇒ ESYNC ⇒ RSR/XSR IBREAKENABLE
WSR/XSR IBREAKA0..1 ⇒ ESYNC ⇒ RSR/XSR IBREAKA0..1
WSR/XSR DBREAKC0..1 ⇒ ESYNC ⇒ RSR/XSR DBREAKC0..1
WSR/XSR DBREAKA0..1 ⇒ ESYNC ⇒ RSR/XSR DBREAKA0..1
Section 5.3.13 on page 235
WSR/XSR MISC0..3 ⇒ ESYNC ⇒ RSR/XSR MISC0..3
WSR/XSR CPENABLE ⇒ ESYNC ⇒ RSR/XSR CPENABLE
WSR/XSR CPENABLE ⇒ RSYNC ⇒ Any coprocessor instruction if its enable bit was changed
Table 9–251. T1050 Additional SYNC Requirements
Appendix A. Differences Between Old and Current Hardware
624 Xtensa Instruction Set Architecture (ISA) Reference Manual
Index
Xtensa Instruction Set Architecture (ISA) Reference Manual 625
Index
Numerics
16-bit instructions
code density option .................................... 53
16-bit Integer Multiply Option......................... 57
benefit for DSP algorithms .........................57
32-bit Integer Divide Option ........................... 59
32-bit Integer Multiply Option......................... 58
A
ABI
CALL0 ...................................................... 587
Windowed Register.................................. 587
Access rights, checking ............................... 148
Accessing
memory ............................................144, 145
peripherals ............................................... 165
ACCHI special register........................... 61, 214
ACCLO special register........................... 61, 214
Adding
architectural enhancements ......................... 1
bus interface ............................................ 194
caches to processor................................. 111
exceptions and interrupts........................... 82
instructions for data cache ....................... 121
memory to processor ............................... 111
new instructions to instruction set .............. 53
Additional register files ................................ 240
Address
register file .................................................24
space, and protection fields ..................... 150
translation, virtual-to-physical................... 139
Address Registers (AR).......................... 24, 208
Addressing
format for TLB ..........152, 157, 167, 169, 172
modes ........................................................ 28
Alignment................................................. 98, 99
and data formats ........................................26
and data types ......................................... 589
AllocaCause ....................................... 89, 181
Application Binary Interface (ABI)........ 180, 587
Application-specific processors, creating....... 13
AR Register File ....................................... 8, 208
Architectural
enhancements, adding................................. 1
state of an Xtensa machine ..................... 205
Architecture
enhancements, adding.................................1
exceptions and interrupts ...........................32
load instructions .........................................33
memory ......................................................27
memory ordering ........................................39
processor control instructions ....................45
processor-configuration parameters ..........23
registers .....................................................24
reset state ..................................................32
store instructions ........................................36
Argument passing, ABI ................................590
Arithmetic instructions....................................43
Assembler opcodes .....................................598
Assembly code ............................................598
ATOMCTL
register fields..............................................81
ATOMCTL special register.......................78, 237
Atomic memory accesses..............................77
Attaching hardware to processor pipeline....127
Attribute .......................................................144
Attributes, overview of .................................144
Auto-refill......................................................141
PTE format ...............................................174
TLB ways .................................................174
B
Backward-traceable call stacks ...................191
Battery-operated systems, Xtensa ISA..........11
Big-endian
byte ordering ..............................................18
fetch semantics ..........................................31
notation ......................................................17
opcode formats ........................................569
Bit and byte order, notation............................17
Bitwise logical instructions .............................44
Boolean Option ..............................................65
Boolean registers...........................................65
BR special register .................................65, 215
Branching.......................................................65
Break codes, reserved.................................595
Break instruction operands ..........................595
Breakpoint
coded .......................................................595
instruction operand conventions ..............596
Index
626 Xtensa Instruction Set Architecture (ISA) Reference Manual
planted......................................................595
special registers........................................233
using.........................................................199
BRI12
opcode format ..........................................572
BRI8
opcode format ..........................................571
Bus interface used by memory accesses.....194
Bypass
access to peripherals................................165
definition ...................................................606
operation for instructions ..........................606
Bypass Attribute...........................................144
Byte ordering..................................................18
C
Cache
adding to processor..................................111
bypass memory accesses ........................194
changing data...........................................241
data ..........................................................118
directing access to....................................150
dirty bit......................................................121
index...........................................................27
Instruction.................................................115
local memories .........................................240
locking ..............................................117, 122
misses for cacheable addresses ..............194
processor’s interpretation of addresses......27
reading and writing the data of .................116
reading and writing the tag of ...........116, 121
tag ..............................................................27
tag format .................................................112
terminology...............................................112
testing data cache ....................................121
testing instruction cache...........................116
Cache Attribute ............................................144
Cached access to peripherals......................165
Cache-Option opcode encodings.................586
CALL
opcode format ..........................................571
Call and Return instructions .................180, 208
Call stacks, backward-traceable ..................191
CALL, Windowed Register Option ...............186
CALL0 ABI ...................................................587
argument passing.....................................590
nested functions .......................................593
other register conventions ........................592
register use...............................................589
return values.............................................591
stack frame .............................................. 589
stack initialization..................................... 594
variable arguments .................................. 592
CALLX
opcode format.......................................... 571
Case, and notation ........................................ 20
CCOMPARE special register.......................... 233
CCOMPARE0..2 special register ................. 111
CCOUNT special register ...................... 111, 232
Changing
cache data ............................................... 241
instruction memory .................................. 240
Checking
access rights............................................ 148
Choosing the TLB ....................................... 146
CINTLEVEL current variable 88, 102, 105, 108,
110, 199, 201, 203
Clamping ....................................................... 62
Clock counting and comparison .................. 111
CLOOPENABLE current variable............... 56, 89
Code density ................................................. 10
Code Density Option ............................... 10, 53
Code size, reducing ........................ 10, 53, 180
Coded breakpoints ...................................... 595
debugger ................................................. 595
exceptions ............................................... 595
Conditional branch instructions ..................... 40
Conditional Store Option ............................... 77
Configurability ............................................. 4, 7
Configuration parameters
NDREFILLENTRIES ................ 166, 168, 172
NIREFILLENTRIES ................ 166, 168, 172
Configuration variables
DataCacheBytes .................................. 119
DataCacheLineBytes.......................... 119
DataCacheWayCount ............................ 119
DataRAMBytes....................................... 126
DataRAMPAddr....................................... 126
DataROMBytes....................................... 127
DataROMPAddr....................................... 127
DEBUGLEVEL ........................................... 197
DivAlgorithm......................................... 59
EXCMLEVEL ............... 88, 107, 108, 109, 197
InstCacheBytes .................................. 115
InstCacheLineBytes.......................... 115
InstCacheWayCount ............................ 115
InstRAMBytes....................................... 124
InstRAMPAddr....................................... 124
InstROMBytes....................................... 125
Index
Xtensa Instruction Set Architecture (ISA) Reference Manual 627
InstROMPAddr ....................................... 125
InstructionCLAMPS .............................. 62
InstructionMINMAX .............................. 62
InstructionNSA..................................... 62
InstructionSEXT................................... 62
INTTYPE ..................................................101
LEVEL ...................................................... 107
LEVEL1 ....................................................101
msbFirst..................................................50
Mul32High................................................ 59
MulAlgorithm ......................................... 59
NAREG ...................................................... 181
NCOMPARE................................................ 110
NDBREAK ..................................................197
NDEPC ..................................................83, 92
NDREFILLENTRIES................................. 159
NIBREAK ..................................................197
NINTERRUPT ........................................... 101
NIREFILLENTRIES................................. 159
NLEVEL ....................................................107
NMISC ...................................................... 195
NNMI ........................................................ 107
SZICOUNT................................................ 197
TIMERINT0..2 ....................................... 110
XLMIBytes.............................................. 127
XLMIPAddr.............................................. 127
Configuration, processor ............................... 13
Configuring, MMU Option ............................ 192
Consistency, memory .............................. 39, 74
Context switch ............................................... 64
Controlling
exceptions and interrupts........................... 82
ordering of memory references ..................76
Coprocessor
extensions .................................................... 9
registers ..................................................... 24
Coprocessor Option....................................... 63
Coprocessor#DisabledCause........... 64, 91
Core architecture
data formats and alignment ....................... 26
exceptions and interrupts........................... 32
instructions ................................................. 51
load instructions .........................................33
memory ...................................................... 27
memory ordering........................................ 39
overview ..................................................... 23
processor configurations............................50
processor control instructions ....................45
processor state ..........................................51
processor-configuration parameters ..........23
registers .....................................................24
reset state ..................................................32
store instructions ........................................36
Core ISA ............................................10, 11, 23
CPENABLE special register ....................64, 236
CRING current variable ...88, 90, 142, 143, 144,
148, 159, 171
CUST0 and CUST1 Opcode encodings ........586
CWOE current variable ............................89, 185
D
Data Cache
tag format .................................................112
Data cache
tag of the ..................................................121
tag RAM format, dirty bit ..........................121
Data Cache Index Lock Option....................122
Data Cache Option ......................................118
Data Cache Test Option ..............................121
Data format
and alignment.............................................26
IxTLB ......................................................173
PxTLB ......................................153, 158, 172
RxTLBn ............................153, 158, 170, 171
WxTLB ......................................153, 157, 168
Data Local Memory......................................126
Data RAM Option.........................................126
Data ROM Option ........................................126
Data TLB..............................................139, 147
Data types......................................................14
and alignment...........................................589
Data-address breakpoint registers...............199
DataCacheBytes.......................................119
DataCacheLineBytes ..............................119
DataCacheWayCount ................................119
DataRAMBytes ...........................................126
DataRAMPAddr ...........................................126
DataROMBytes ...........................................127
DataROMPAddr ...........................................127
DBREAKA0..1 special register ............198, 235
DBREAKC0..1 special register ............198, 234
DDR special register .............................198, 236
Debug
exceptions ................................................201
interrupts, Debug Option ..........................203
registers, Debug Option ...........................202
supervisor executing on processor ..........203
Debug Data Register (DDR) ........................203
Debug exception handler .............................595
Index
628 Xtensa Instruction Set Architecture (ISA) Reference Manual
Debug Option...............................................197
instruction counting...................................201
DEBUGCAUSE register...................................198
DEBUGCAUSE special register ..............198, 226
Debugger
coded breakpoints ....................................595
executing on remote host .........................203
Debugging
facilitating .................................................142
visibility, ICOUNTLEVEL register ..............201
DEBUGLEVEL................................................197
exception ..................................................199
setting.......................................................201
Definitions
Notations ................................................... xix
Terms ........................................................ xix
Delaying dependent instruction....................606
Demand paging............................................145
hardware ..................................................158
Density option ..............................................595
DEPC special register .............................84, 227
Design flow, Xtensa .......................................15
Designers, Xtensa Processor Generator .......13
Determining if store succeeded, S32C1I.......78
Development and verification tools ..................5
Devices ........................................................127
Digital Signal Processing, see DSP
Direct memory access to local memories ....194
DivAlgorithm .............................................59
Divide .............................................................59
Double Exception Prog Counter (DEPC) regis-
ter ...................................................................92
DoubleExceptionVector........83, 85, 86, 89
DSP................................................................54
16-bit integer multiply option.......................57
for more than 16 bits of precision ...............67
multiply-accumulate....................................60
DSYNC instruction, TLB entries.....................239
DTLB entries, processor state......................239
DTLBCFG register and MMU Option.............162
DTLBCFG special register.....................160, 223
E
ECC .............................................................128
ENTRY
instruction, moving register window..........184
Windowed Register Option.......................186
EPC1 special register .............................84, 226
EPC2..7 special register.....107, 226, 227, 228
EPS2..7 special register.....................107, 227
Example, FIR Filter with MAC16 Option ..... 600
EXCCAUSE special register.................... 84, 224
Exception
cause priority list........................................ 96
cause register ............................................ 89
cause, numerical list .................................. 89
exception groups ..................................... 243
semantics ............................................ 93, 96
state special registers.............................. 226
support special registers.......................... 223
vector....................................................... 144
wait (EXCW) .............................................. 343
Exception Option........................................... 82
Double Exception Prog Counter (DEPC)
register....................................................... 92
exception causes....................................... 89
Exception Prog Counter (EPC) register..... 91
Exception Save Register ........................... 92
exception semantics ............................ 93, 96
Exception Virtual Address (EXCVADDR).... 91,
137
kernel vector mode .................................... 93
operating modes........................................ 93
Program State (PS) register....................... 87
user vector mode....................................... 93
Exception Prog Counter (EPC) register ........ 91
Exception Save Register ............................... 92
Exception vector
list of vectors........................................ 94, 95
DoubleExceptionVector ..................... 83
Exception Registers................................... 95
Information Registers ................................ 94
InterruptVector2..7........................ 107
KernelExceptionVector ..................... 83
ResetVector..................................... 83, 85
UserExceptionVector.......................... 83
WindowOverflow12 .............................. 181
WindowOverflow4 ................................ 181
WindowOverflow8 ................................ 181
WindowUnderflow12 ............................ 181
WindowUnderflow4 .............................. 181
WindowUnderflow8 .............................. 181
Exception Virtual Address register ........ 91, 137
Exceptions and interrupts.............................. 32
adding and controlling ............................... 82
priority of.................................................... 96
Exchange Special Register (XSR.SAR)......... 26
Exclusive access with S32C1I instruction .... 78
EXCMLEVEL................... 88, 107, 108, 109, 197
Index
Xtensa Instruction Set Architecture (ISA) Reference Manual 629
EXCSAVE1 special register ....................84, 228
EXCSAVE2..7 special register.... 107, 228, 229
EXCVADDR special register84, 91, 137, 224, 225
Expressions, and notational forms................. 19
Extended L32R Option .................................. 56
Literal Base (LITBASE) register.................57
Extensibility......................................................4
of Xtensa ISA ............................................... 8
Extensions
coprocessor ................................................. 9
instruction..................................................... 9
register file ...................................................9
state ............................................................. 9
EXTW instruction............................................. 39
F
FCR user register ......................................... 239
Fetch semantics
big-endian .................................................. 31
little-endian................................................. 29
Fields, instruction...................................21, 573
FLIX (Flexible Length Instruction Extensions)14
Floating-Point Coprocessor Option................ 67
data formats ............................................... 26
high-end audio processing......................... 23
processor state ........................................ 205
Floating-point Coprocessor Option
exceptions .................................................. 71
instructions ................................................. 71
representation ............................................ 69
state ........................................................... 69
Flushing register windows ...........................597
Format of PTEs ........................................... 174
Formats for accessing TLB entries .............. 152
FSR user register ......................................... 239
Functions, nested ........................................ 593
Funnel shifts ..................................................25
G
General Registers........................................ 208
General registers ......................... 208, 587, 589
Generating interrupts from counters ............ 110
Guarded Attribute ........................................ 144
H
Handling register window underflow ............ 192
Hardware
attaching into processor pipeline ............. 127
interlocking of instructions........................ 241
Hazards, definition ....................................... 606
High Priority Interrupt Option ....................... 106
checking for interrupts..............................109
interrupt process ......................................108
specifying high-priority interrupts .............108
HIgh-priority interrupt process .....................108
I
IBREAKA0..1 special register ............198, 234
IBREAKENABLE special register..........198, 233
ICOUNT register, Debug Option...................201
ICOUNT special register.......................198, 231
ICOUNTLEVEL register, for debugging ........201
ICOUNTLEVEL special register ............198, 232
Identification of Processors..........................196
IEEE754.........................................................67
IllegalInstructionCause ...............83, 89
Implementation
of core ISA .................................................23
pipeline.......................................................12
Improving
performance for large sys memories........175
program performance...............................180
speed and code density ...........................208
system reliability.......................................142
Index from Virtual Page Number (VPN).......173
Initializing a stack.........................................594
InstCacheBytes.......................................115
InstCacheLineBytes ..............................115
InstCacheWayCount ................................115
InstFetchPrivilegeCause .............90, 159
InstFetchProhibitedCause ...90, 151, 159
InstRAMBytes ...........................................124
InstRAMPAddr ...........................................124
InstROMBytes ...........................................125
InstROMPAddr ...........................................125
InstrPIFAddrErrorCause .......90, 195, 619
InstrPIFDataErrorCause .......90, 195, 619
Instruction ......................................................13
cache........................................................115
caches, ISYNC instruction........................240
counting, Debug Option ...........................201
extensions ....................................................9
fetch ...........................................................29
fields...................................................21, 573
formats .....................................................569
idioms.......................................................598
issue definition .........................................605
issuing relative to other instructions .........605
memory, ISYNC instruction ......................240
operand dependency interlock .................607
RAM or ROM............................................124
Index
630 Xtensa Instruction Set Architecture (ISA) Reference Manual
Ram or ROM ............................................125
TLB...................................................139, 147
Instruction Cache
tag format .................................................112
Instruction Cache Index Lock Option ...........117
Instruction Cache Option..............................115
Instruction cache tag and data .....................116
Instruction Cache Test Option......................116
Instruction Extension (TIE) language ...............9
Instruction Local Memory .....................124, 125
Instruction operands, BREAK........................595
Instruction Set Architecture (ISA), Xtensa........5
Instruction set, adding new instructions .........53
InstructionCLAMPS ..................................62
Instruction-description expressions................19
InstructionFetchErrorCause .83, 89, 619
InstructionMINMAX ..................................62
InstructionNSA.........................................62
Instructions
accessing user registers...........................237
arithmetic....................................................43
bitwise logical .............................................44
BREAK.......................................................595
bypass operation ......................................606
conditional branch ......................................40
delaying dependent instruction.................606
EXTW...........................................................39
general registers.......................................208
interlocking of in hardware........................241
jump and call ..............................................40
load.............................................................33
MEMW...........................................................39
move...........................................................42
narrow ......................................................595
need for synch instructions.......................240
pipeline stage numbers ............................605
processor control........................................45
shift.............................................................44
store ...........................................................36
summary.....................................................33
SYSCALL ..................................................597
xSYNC.........................................................45
InstructionSEXT.......................................62
InstTLBMissCause.............................90, 159
InstTLBMultiHitCause ....................90, 159
INTCLEAR special register...................102, 230
Integer Divide .................................................59
Integer Multiply...................................57, 58, 60
IntegerDivideByZeroCause .............60, 90
INTENABLE special register................ 102, 231
Interlock, definition ...................................... 605
Internal Instruction Memory......................... 124
Interrupt
High-Level Language .............................. 108
Interrupt Option ........................................... 100
Level-1 interrupt process ......................... 105
specifying interrupts................................. 102
Interrupt process, Level-1 ........................... 105
INTERRUPT special register........ 102, 229, 230
Interrupt special registers............................ 229
Interrupts
and exceptions .......................................... 32
and exceptions, priority of.......................... 96
checking for ............................................. 109
generating from counters......................... 110
specifying................................................. 102
InterruptVector2..7 ............... 86, 87, 107
INTTYPE ..................................................... 101
Invalid Attribute ........................................... 144
ISA and shifts ................................................ 25
Isolate Attribute ........................................... 144
ISYNC instruction
instruction caches.................................... 240
instruction memory .................................. 240
TLB entries .............................................. 239
ITLB entries................................................. 205
processor state ........................................ 239
ITLBCFG register and MMU Option............ 162
ITLBCFG special register .................... 160, 223
IxTLB data format ...................................... 173
J
Jump and call instructions............................. 40
K
Kernel vector mode ....................................... 93
Kernel/user privilege levels ......................... 142
KernelExceptionVector ....... 83, 85, 86, 89
L
L32R Option
easing access to literal data ...................... 56
Large memories in systems ........................ 175
Latency
lowering with XLMI Option....................... 127
pipelining of instructions .......................... 605
LBEG special register ............................ 55, 212
LCOUNT special register ................................ 55
LEND special register ............................ 55, 213
LEVEL ......................................................... 107
Index
Xtensa Instruction Set Architecture (ISA) Reference Manual 631
LEVEL1........................................................ 101
Level-1 Interrupt .......................................... 100
Level-1 interrupt process ............................. 105
Level1InterruptCause.................... 89, 101
Levels
of decreasing privilege, rings ................... 142
of privilege................................................ 142
List of
registers ................................................... 205
special registers ....................................... 209
user registers ...................................237, 238
LITBASE special register .............. 57, 216, 382
Literal Base (LITBASE) register .................... 57
Literal, L32R ................................................ 382
Little-endian
byte ordering ..............................................18
fetch semantics .......................................... 29
notation ...................................................... 17
opcode format .......................................... 569
Load instructions ........................................... 33
Loading
PTE from memory.................................... 141
synch variable using L32AI....................... 76
LoadProhibitedCause.............. 90, 151, 160
LoadStoreAlignmentCause ............. 90, 100
LoadStoreErrorCause................ 83, 89, 619
LoadStorePIFAddrErrorCause90, 195, 619
LoadStorePIFDataErrorCause90, 195, 619
LoadStorePrivilegeCause ............. 90, 160
LoadStoreTLBMissCause ................. 90, 159
LoadStoreTLBMultiHitCause......... 90, 160
Local Memories ........................................... 123
Local memories and cache.......................... 240
Local memory, directing access to .............. 148
Locking Cache Lines ........................... 117, 122
Lookup in the TLB ....................................... 147
Loop Option ........................................... 54, 208
LOOP special registers ................................. 212
Lowering latency with XLMI Option ............. 127
Low-Latency Devices .................................. 127
Low-Latency Memories................................ 123
M
M0..3 special register........................... 61, 214
MAC16 Option ............................................... 60
for integer filters ......................................... 23
MAC16 special registers............................... 213
Managing physical registers ........................ 183
Maximum instruction...................................... 62
Medium-Priority Interrupts ........................... 109
Memory........................................................123
accessing .................................144, 145, 154
adding to processor..................................111
addressing..................................................27
addressing modes......................................28
attributes ..................................................154
attributes for MMU Option ................175, 620
attributes for Region Translation Option ..158
big-endian fetch semantics ........................31
directing access to ...................................148
EXTW instruction .........................................39
instruction fetch ..........................................29
internal .....................................124, 125, 126
little-endian fetch semantics .......................29
management special registers .................221
map, MMU Option ....................................164
MEMW instruction .........................................39
ordering ......................................................39
ordering and S32C1I instruction................81
program counter.........................................29
protection, options for...............................138
protection, overview .................................142
translation, overview of ............................139
Xtensa ISA .................................................27
Memory access
ordering ......................................................74
requirements ..............................................75
Memory alignment ...................................98, 99
Memory consistency ......................................74
Memory Integrity Option ..............................128
Memory Management ..................150, 156, 158
Memory Management Unit ..........................158
Memory ordering
EXTW.........................................................345
MEMW.........................................................409
Memory ordering and synchronization
L32AI ......................................................374
S32RI ......................................................514
Memory-based page table ...........................158
MemoryErrorVector ..................................86
MEMW instruction.............................................39
Minimizing implementation cost.....................10
Minimum
instruction...................................................62
MISC0..3 special register ..................196, 236
Miscellaneous Operations Option..................62
Miscellaneous Special Registers Option ....195,
196
MMID special register ...........................204, 235
Index
632 Xtensa Instruction Set Architecture (ISA) Reference Manual
MMU Option...........................27, 142, 158, 239
configuration issue....................................192
ITLBCFG register .....................................162
memory attributes for........................175, 620
memory map.............................................164
operating semantics .................................178
PTEVADDR register ...................................161
Ring ASID (RASID) register......................161
structure of TLBs ......................................163
Move instructions ...........................................42
MOVI instruction .............................................42
Moving register window................................184
MR special register..................................61, 214
msbFirst......................................................50
Mul32High....................................................59
MulAlgorithm .............................................59
Multiply...............................................57, 58, 60
Multiply-accumulate .......................................60
Multiprocessor................................................39
Multiprocessor Synchronization Option....39, 74
Multi-stepping...............................................201
Mutex .............................................................77
Mutex and synchronization, S32C1I ...........506
N
NAREG ..........................................................181
Narrow instruction ........................................595
NCOMPARE....................................................110
NDBREAK ......................................................197
NDEPC ......................................................83, 92
NDREFILLENTRIES.....................................159
Nested functions, ABI...................................593
Nested privileges with sharing .....................143
NIBREAK ......................................................197
NINTERRUPT................................................101
NIREFILLENTRIES.....................................159
NLEVEL ........................................................107
NMISC ..........................................................195
NNMI ............................................................107
No-allocate Attribute.....................................144
Non-Maskable Interrupt........................100, 106
Non-privileged special register set .................26
Normalization .................................................62
Notation
big-endian...................................................17
bit and byte order .......................................17
case............................................................20
expressions ................................................19
instruction fields..........................................21
little-endian .................................................17
statements ................................................. 21
unsigned semantics................................... 20
NREFILLENTRIES config ........... 166, 168, 172
O
Opcode encodings
Cache-Option .......................................... 586
CUST0 and CUST1 ................................... 586
tables of values........................................ 574
Opcode formats
big-endian................................................ 569
BRI12....................................................... 572
BRI8......................................................... 571
CALL........................................................ 571
CALLX ..................................................... 571
little-endian .............................................. 569
RI16 ......................................................... 570
RI6 ........................................................... 573
RI7 ........................................................... 572
RRI4 ........................................................ 569
RRI8 ........................................................ 570
RRR......................................................... 569
RRRN ...................................................... 572
RSR ......................................................... 570
Opcode maps .............................................. 575
Opcode space for extensions........................ 50
Opcodes...................................................... 569
assembler ................................................ 598
Operand dependency interlock, instruction .607
Operation ...................................................... 13
semantics, MMU Option .......................... 178
Options
16-bit Integer Multiply ................................ 57
32-bit Integer Divide .................................. 59
32-bit Integer Multiply ................................ 58
Boolean ..................................................... 65
Code Density ............................................. 53
Conditional Store ....................................... 77
Coprocessor .............................................. 63
Data Cache.............................................. 118
Data Cache Index Lock ........................... 122
Data Cache Test...................................... 121
Data RAM ................................................ 126
Data ROM................................................ 126
Debug ...................................................... 197
Exception................................................... 82
Extended L32R.......................................... 56
Floating-Point Coprocessor ....................... 67
High Priority Interrupt............................... 106
Instruction Cache..................................... 115
Index
Xtensa Instruction Set Architecture (ISA) Reference Manual 633
Instruction Cache Index Lock................... 117
Instruction Cache Test ............................. 116
Instruction RAM ....................................... 124
Instruction ROM .......................................125
Interrupt.................................................... 100
Loop ........................................................... 54
MAC16 ....................................................... 60
Memory Integrity (Parity and ECC) ..........128
Miscellaneous Operations.......................... 62
Miscellaneous Special Registers .....195, 196
MMU ........................................................ 158
Multiprocessor Synchronization .................74
Processor ID ............................................ 196
Processor Interface.................................. 194
Region Protection .................................... 150
Region Translation................................... 156
Timer Interrupt ......................................... 110
Trace Port ................................................203
Unaligned Exception ............................98, 99
Windowed Register.................................. 180
XLMI (Xtensa Local Memory Interface).... 127
Ordering memory accesses........................... 74
Overflow
and program stack ...................................192
exceptions ................................................ 187
P
Page Table Entry (PTE) .............. 141, 144, 174
format....................................................... 174
Page table, memory-based ......................... 158
Paging, demand paging............................... 145
Parity ........................................................... 128
Passing
arguments ................................................ 590
Performance
latency...................................................... 605
pipeline..................................................... 605
terminology and modeling........................ 605
throughput ................................................ 605
Xtensa ISA ......................................... 11, 605
Peripherals, access to ................................. 165
Physical Page Number (PPN) .... 156, 167, 170,
174
Physical registers, managing....................... 183
PIF, directing access to ............................... 150
Pipeline
performance ............................................. 605
schedule..................................................... 14
stage numbers .........................................605
Pipelines, Xtensa ISA .................................... 12
Planted breakpoints .....................................595
density option ...........................................595
narrow version..........................................595
Power savings and low power, WAITI ........556
Previous version, changes from ..................xxiii
PRID special register ...........................197, 235
Priority of exceptions and interrupts ..............96
Privilege levels.............................................142
kernel/users..............................................142
levels of decreasing .................................142
PrivilegedCause ..............................90, 159
Privileges, nested with sharing ....................143
Procedure Call .............................................180
Procedure-call protocol ................................187
Processor
configuration...............................................13
configuration parameters ...........................23
control instructions .....................................45
performance terminology and modeling ...605
Xtensa processor family...........................608
Processor Generator, Xtensa ........................13
Processor ID Option ....................................196
Processor Interface Option ..........................194
Processor state
alphabetical list of processor state ...........205
additional register files .............................240
caches and local memories......................240
general registers ......................................208
instruction caches ....................................240
instruction memory...................................240
list of registers ..........................................205
list of special registers..............................209
list of user registers ..........................237, 238
Program Counter (PC) ..............................208
special registers .......................................208
TLB entries...............................................239
user registers ...........................................237
Processor Status special register ................216
Processor synchronization
Multiprocessor Synchronization Option......74
Program counter ............................................29
Program Counter (PC)..................................208
Program performance, increasing ...............180
Program State (PS) register ...........................87
Protection field for regions ...........................150
Protocol, windowed procedure-call..............187
Prototypes......................................................14
PS special register .................................84, 217
PS.CALLINC special register ..............182, 220
Index
634 Xtensa Instruction Set Architecture (ISA) Reference Manual
PS.EXCM special register...............................84
PS.INTLEVEL special register ....101, 217, 218
PS.OWB special register .......................182, 220
PS.RING special register.....................160, 219
PS.UM special register ...........................84, 219
PS.WOE special register .......................182, 220
PTE, assigning capabilities to attr. field .......145
PTEVADDR register and MMU Option...........161
PTEVADDR special register...................160, 222
PxTLB data format .......................153, 158, 172
Q
Queues, defining ............................................14
R
RAM option features ....................................123
RASID register and MMU Option .................161
RASID special register .........................160, 222
RCW transaction............................................79
Read Special Register (RSR.SAR).................26
Readable scratch registers ..........................195
Reading
special registers..................................26, 211
user registers............................................237
Real Time Trace...........................................203
Reducing
code size ......................................10, 53, 180
system cost.................................................11
Region Protection Option ...............27, 150, 205
Region Translation Option ...........................156
Regions, protection fields for........................150
Register
file extensions...............................................9
files and processor state...........................205
window underflow handling ......................192
windowing special registers......................221
Register files
additional ..................................................240
defining.......................................................14
Register windows
flushing .....................................................597
Xtensa ISA ...............................................180
Registers
alphabetical list of all registers..................205
see also Special Registers
address register file ....................................24
Address Registers (AR) ..............................24
breakpoint special registers......................233
coprocessor registers .................................24
core architecture.........................................24
exception state special registers ............. 226
exception support special registers ......... 223
Exchange Special Register (XSR.SAR) ..... 26
general..................................................... 208
interrupt special registers ........................ 229
LOOP special registers ............................. 212
MAC16 special registers........................... 213
memory management special registers... 221
non-privileged special register set ............. 26
other privileged special registers ............. 235
other unprivileged special registers ......... 215
processor status special register ............. 216
Read Special Register (RSR.SAR) ............ 26
reading and writing special ........................ 26
register windowing special registers ........ 221
SAR special register ................................. 215
special and processor state..................... 205
timing special registers ............................ 231
use in ABI ........................................ 587, 589
user and processor state ......................... 205
Write Special Register (RSR.SAR)............. 26
Register-window underflow ......................... 192
Release Consistency .................................... 75
Release consistency ............................... 39, 74
Requirements for memory access ................ 75
Reserved break codes ................................ 595
Reset state .................................................... 32
ResetVector......................................... 83, 85
Return values, ABI ...................................... 591
RETW, Windowed Register Option............... 186
RI16
opcode format.......................................... 570
RI6
opcode format.......................................... 573
RI7
opcode format.......................................... 572
Rings, levels of decreasing privilege ........... 142
ROM option features ................................... 123
RRI4
opcode format.......................................... 569
RRI8
opcode format.......................................... 570
RRR
opcode format.......................................... 569
RRRN
opcode format.......................................... 572
RSR............................................................. 620
opcode format.......................................... 570
RxTLBn data format ............ 153, 158, 170, 171
Index
Xtensa Instruction Set Architecture (ISA) Reference Manual 635
S
S32C1I instruction
and exclusive access ................................. 78
and memory ordering.................................81
ATOMCTL Register......................................80
use models................................................. 79
SAR special register ..................................... 215
Saturation of integer values........................... 62
Schedule of Pipeline ...................................... 14
SCOMPARE1 special register .................. 78, 216
Scratch registers.......................................... 196
Scratch registers readable and writable ...... 195
Self-modifying code, unsupported ............... 240
Shift Amount Register (SAR).......................... 25
Shift instructions ...................................... 25, 44
Sign Extension............................................... 62
Single-instruction shifts.................................. 25
Single-stepping ............................................201
Software Interrupt ........................................ 100
Special Registers.................................208, 620
Special registers .......................................... 205
numerical list of special registers ............. 209
reading and writing................................... 211
ACCHI ................................................ 61, 214
ACCLO ................................................ 61, 214
ATOMCTL ............................................ 78, 237
BR.......................................................65, 215
CCOMPARE................................................ 233
CCOMPARE0..2 ....................................... 111
CCOUNT ............................................ 111, 232
CPENABLE.......................................... 64, 236
DBREAKA0..1 ................................. 198, 235
DBREAKC0..1 ................................. 198, 234
DDR................................................... 198, 236
DEBUGCAUSE ................................... 198, 226
DEPC ..................................................84, 227
DTLBCFG .......................................... 160, 223
EPC1 ..................................................84, 226
EPC2..7 .......................... 107, 226, 227, 228
EPS2..7 .......................................... 107, 227
EXCCAUSE.......................................... 84, 224
EXCSAVE1.......................................... 84, 228
EXCSAVE2..7 .........................107, 228, 229
EXCVADDR.................................. 84, 224, 225
IBREAKA0..1 ................................. 198, 234
IBREAKENABLE ............................... 198, 233
ICOUNT ............................................ 198, 231
ICOUNTLEVEL ................................. 198, 232
INTCLEAR........................................ 102, 230
INTENABLE......................................102, 231
INTERRUPT..............................102, 229, 230
ITLBCFG ..........................................160, 223
LBEG...................................................55, 212
LCOUNT ......................................................55
LEND...................................................55, 213
LITBASE ....................................57, 216, 382
M0..3 ................................................61, 214
MISC0..3 ........................................196, 236
MMID.................................................204, 235
MR.......................................................61, 214
PRID.................................................197, 235
PS.......................................................84, 217
PS.CALLINC....................................182, 220
PS.EXCM ....................................................84
PS.INTLEVEL .........................101, 217, 218
PS.OWB ............................................182, 220
PS.RING ..........................................160, 219
PS.UM ................................................84, 219
PS.WOE ............................................182, 220
PTEVADDR ........................................160, 222
RASID ..............................................160, 222
SAR...........................................................215
SCOMPARE1........................................78, 216
THREADPTR..............................................196
VECBASE ....................................................99
WindowBase....................................181, 221
WindowStart .................................181, 221
Specifying
high-priority interrupts ..............................108
interrupts ..................................................102
Stack............................................................180
frame ................................................587, 589
initialization, ABI.......................................594
pointer (SP) ..............................................587
State
see also Registers
additional register files .............................240
caches and local memories......................240
defining new ...............................................14
extensions ....................................................9
general registers ......................................208
list of all registers .....................................205
list of special registers..............................209
list of user registers ..........................237, 238
Program Counter (PC) ..............................208
special registers .......................................208
TLB entries...............................................239
user registers ...........................................237
Index
636 Xtensa Instruction Set Architecture (ISA) Reference Manual
Statements, and notational forms ..................21
Stopping executing prog being debugged....203
Store instructions ...........................................36
StoreProhibitedCause ............91, 151, 160
Storing synch variable with S32RI.................76
Structure of TLBs, MMU Option ...................163
Summary of instructions.................................33
Synchronization........................................74, 77
Synchronization between processors
Multiprocessor Synchronization Option......74
synchronization instruction
DSYNC.......................................................339
ESYNC.......................................................342
ISYNC.......................................................364
RSYNC.......................................................502
Synchronization instructions, need for .........240
Synchronization variables
loading with L32AI.....................................76
storing with S32RI......................................76
Synchronizing special register writes .............45
SYSCALL instruction.....................................597
SyscallCause .......................................83, 89
System
calls ..........................................................597
cost, reducing .............................................11
reliability, improving..................................142
System Bus..................................................194
Systems with large memories ......................175
SZICOUNT....................................................197
T
Tag of the data cache ..................................121
Tag of the instruction cache.........................116
Tensilica ...........................................................9
Instruction Extension (TIE) language .........13
overview .......................................................1
product features ...........................................1
Testing data cache.......................................121
Testing instruction cache .............................116
THREADPTR special register ........................196
THREADPTR user register.............................238
Throughput, pipelining of instructions ..........605
Timer ............................................................100
Timer Interrupt Option..................................110
clock counting and comparison ................111
TIMERINT0..2 ...........................................110
Timing special register .................................231
TLB
addressing format.....152, 157, 167, 169, 172
choosing ...................................................146
data TLB .................................................. 147
formats for accessing entries................... 152
instruction TLB......................................... 147
lookup ...................................................... 147
memory attributes.................................... 154
Physical Page Number (PPN) ................. 167
structure of, MMU Option ........................ 163
translation hardware ................................ 139
Virtual Page Number (VPN) .................... 166
TLB entries
DSYNC instruction .................................... 239
ISYNC instruction .................................... 239
processor state ................................ 205, 239
Tools, development and verification................ 5
Trace Port Option........................................ 203
Tracing Processor Activity........................... 203
Translation
hardware.................................................. 139
options for................................................ 138
virtual-to-physical..................................... 139
U
Unaligned Exception Option.............. 25, 98, 99
Underflow
and program stack................................... 192
exceptions ............................................... 187
Unsigned semantics ...................................... 20
User exception, examining all registers ...... 596
User registers.............................................. 205
numerical list of user registers................. 237
FCR .......................................................... 239
FSR .......................................................... 239
list of ........................................................ 238
processor state ........................................ 237
reading and writing .................................. 237
THREADPTR ............................................. 238
User vector mode.................................. 93, 144
User/kernel privilege levels ......................... 142
User-defined break codes ........................... 595
UserExceptionVector ........... 83, 85, 86, 89
Using Xtensa architecture
assembly code......................................... 598
CALL0 ABI............................................... 587
conventions other than ABI ..................... 595
instruction idioms..................................... 598
system calls ............................................. 597
Windowed Register ABI........................... 587
V
Variable arguments, ABI ............................. 592
Index
Xtensa Instruction Set Architecture (ISA) Reference Manual 637
VECBASE special register .............................. 99
Vector, exception......................................... 144
Verification and development tools.................. 5
Virtual Page Number (VPN)................. 166, 170
index ........................................................ 173
Virtual-to-physical
address translation................................... 139
translation ................................................ 156
W
Window overflow
and program stack ...................................192
exceptions ................................................ 187
Window underflow
and program stack ...................................192
exceptions ................................................ 187
WindowBase special register .............. 181, 221
Windowed procedure-call protocol .............. 187
Windowed Register ABI............................... 587
argument passing .................................... 590
nested functions....................................... 593
other register conventions........................ 592
register use .............................................. 587
return values ............................................ 591
stack frame .............................................. 587
stack iniitialization ....................................594
variable arguments .................................. 592
Windowed Register Option .............. 24, 29, 180
Application Binary Interface (ABI) ............ 587
managing physical registers..................... 183
register usage .......................................... 188
Windowed registers and call
RETW ........................................................ 480
RETW.N ....................................................482
WindowOverflow12 ............................ 86, 181
WindowOverflow4 .............................. 86, 181
WindowOverflow8 .............................. 86, 181
WindowStart special register............ 181, 221
WindowUnderflow12 .......................... 86, 181
WindowUnderflow4 ............................ 86, 181
WindowUnderflow8 ............................ 86, 181
Writable Physical Page Numbers (PPNs).... 156
Writable scratch registers ............................ 195
Write Special Register (WSR.SAR)................. 26
Write-through Attribute ................................ 144
Writing
special registers ................................. 26, 211
user registers ........................................... 237
WSR ............................................................ 620
WxTLB data format....................... 153, 157, 168
X
XLMI Option.................................................127
XLMIBytes .................................................127
XLMIPAddr .................................................127
XSR .............................................................620
xSYNC instructions.........................................45
Xtensa
Application Binary Interface (ABI) ............587
architectural state.....................................205
battery-operated systems...........................11
design flow .................................................15
extensibility of...............................................8
memory order semantics............................39
performance ...............................................11
pipelines .....................................................12
processor family .......................................608
Processor Generator..................................13
self-mofiying code ............................240, 364
T1050 pipeline..........................................608
Xtensa Exception Architecture 2
Disabled loops............................................56
Xtensa Instruction Set Architecture (ISA) ........5
Xtensa instructions, general registers..........208
Xtensa ISA
configurability ...............................................7
enhancements to performance ..................11
memory ......................................................27
performance .............................................605
register windows ......................................180
using.........................................................587
Z
Zero-overhead loops......................................54
disabled for exceptions ..............................56
LOOP.........................................................392
LOOPGTZ ..................................................394
LOOPNEZ ..................................................396
restrictions..................................................55
Index
638 Xtensa Instruction Set Architecture (ISA) Reference Manual

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