ARM Cortex M7 Processor Technical Reference Manual

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ARM Cortex -M7 Processor
®

Revision r1p1

Technical Reference Manual

ARM Cortex-M7 Processor
Technical Reference Manual
Copyright © 2014, 2015 ARM. All rights reserved.
Release Information
The following changes have been made to this book.
Change history
Date

Issue

Confidentiality

Change

25 April 2014

Confidential

First release for r0p0

05 December 2014

Non-Confidential

First release for r0p2

19 March 2015

Non-Confidential

First release for r1p0

07 July 2015

Non-Confidential

First release for r1p1

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Your access to the information in this document is conditional upon your acceptance that you will not use or permit
others to use the information for the purposes of determining whether implementations infringe any third party patents.
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Copyright © 2015, ARM Limited or its affiliates. All rights reserved.
ARM Limited. Company 02557590 registered in England.
110 Fulbourn Road, Cambridge, England CB1 9NJ.

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Confidentiality Status
This document is Non-Confidential. The right to use, copy and disclose this document may be subject to license
restrictions in accordance with the terms of the agreement entered into by ARM and the party that ARM delivered this
document to.
Product Status
The information in this document is final, that is for a developed product.
Web Address
http://www.arm.com

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iii

Contents
ARM Cortex-M7 Processor Technical Reference
Manual

Preface
About this book .......................................................................................................... vii
Feedback .................................................................................................................... xi

Chapter 1

Introduction
1.1
1.2
1.3
1.4
1.5
1.6
1.7

Chapter 2

Programmers Model
2.1
2.2
2.3
2.4
2.5
2.6
2.7

Chapter 3

About the programmers model ................................................................................
Modes of operation and execution ...........................................................................
Instruction set summary ...........................................................................................
System address map ...............................................................................................
Exclusive monitor .....................................................................................................
Processor core registers ..........................................................................................
Exceptions ...............................................................................................................

2-2
2-3
2-4
2-5
2-7
2-8
2-9

System Control
3.1
3.2
3.3

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About the Cortex-M7 processor ............................................................................... 1-2
Component blocks ................................................................................................... 1-6
Interfaces ............................................................................................................... 1-11
Supported standards ............................................................................................. 1-13
Design process ...................................................................................................... 1-14
Documentation ....................................................................................................... 1-15
Product revisions ................................................................................................... 1-16

About system control ............................................................................................... 3-2
Register summary .................................................................................................... 3-3
Register descriptions ............................................................................................... 3-6

Contents

Chapter 4

Initialization
4.1

Chapter 5

Memory System
5.1
5.2
5.3
5.4
5.5
5.6
5.7
5.8

Chapter 6

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About the ITM ........................................................................................................ 12-2
ITM functional description ...................................................................................... 12-3
ITM programmers model ....................................................................................... 12-4

Fault detection and handling
13.1
13.2
13.3

Appendix A

About the DWT ...................................................................................................... 11-2
DWT functional description .................................................................................... 11-3
DWT programmers model ..................................................................................... 11-4

Instrumentation Trace Macrocell Unit
12.1
12.2
12.3

Chapter 13

About the CTI ......................................................................................................... 10-2
Cortex-M7 CTI functional description .................................................................... 10-3
CTI programmers model ........................................................................................ 10-5

Data Watchpoint and Trace Unit
11.1
11.2
11.3

Chapter 12

About debug ............................................................................................................ 9-2
About the AHBD interface ........................................................................................ 9-7
About the FPB ......................................................................................................... 9-8

Cross Trigger Interface
10.1
10.2
10.3

Chapter 11

About the FPU ......................................................................................................... 8-2
FPU functional description ....................................................................................... 8-3
FPU programmers model ........................................................................................ 8-5

Debug
9.1
9.2
9.3

Chapter 10

About the NVIC ........................................................................................................ 7-2
NVIC functional description ..................................................................................... 7-3
NVIC programmers model ....................................................................................... 7-4

Floating Point Unit
8.1
8.2
8.3

Chapter 9

About the MPU ........................................................................................................ 6-2
MPU functional description ...................................................................................... 6-3
MPU programmers model ........................................................................................ 6-4

Nested Vectored Interrupt Controller
7.1
7.2
7.3

Chapter 8

About the memory system ....................................................................................... 5-2
Fault handling .......................................................................................................... 5-3
Memory types and memory system behavior .......................................................... 5-5
AXIM interface ......................................................................................................... 5-6
AHB peripheral interface ........................................................................................ 5-22
AHB slave interface ............................................................................................... 5-30
TCM interfaces ...................................................................................................... 5-33
L1 caches .............................................................................................................. 5-37

Memory Protection Unit
6.1
6.2
6.3

Chapter 7

About Initialization .................................................................................................... 4-2

About fault detection and handling ........................................................................ 13-2
Cache RAM protection ........................................................................................... 13-3
Logic protection ..................................................................................................... 13-6

Revisions

Preface

This preface introduces the Cortex-M7 Processor Technical Reference Manual (TRM). It
contains the following sections:
•
About this book on page vii.
•
Feedback on page xi.

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Preface

About this book
This book is for the Cortex-M7 processor.
Product revision status
The rnpn identifier indicates the revision status of the product described in this manual, where:
rn
Identifies the major revision of the product.
pn
Identifies the minor revision or modification status of the product.
Intended audience
This manual is written to help system designers, system integrators, verification engineers, and
software programmers who are implementing a System-on-Chip (SoC) device based on the
Cortex-M7 processor.
Using this book
This book is organized into the following chapters:
Chapter 1 Introduction
Read this for a description of the components of the processor, and of the product
documentation.
Chapter 2 Programmers Model
Read this for a description of the processor register set, modes of operation, and
other information for programming the processor.
Chapter 3 System Control
Read this for a description of the registers and programmers model for system
control.
Chapter 4 Initialization
Read this for a description of how to initialize the processor.
Chapter 5 Memory System
Read this for a description of the processor memory system.
Chapter 6 Memory Protection Unit
Read this for a description of the Memory Protection Unit (MPU).
Chapter 7 Nested Vectored Interrupt Controller
Read this for a description of the interrupt processing and control.
Chapter 8 Floating Point Unit
Read this for a description of the Floating Point Unit (FPU).
Chapter 9 Debug
Read this for information about debugging and testing the processor.
Chapter 10 Cross Trigger Interface
Read this for information about how the Cross Trigger Interface (CTI) can be
configured.

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vii

Preface

Chapter 11 Data Watchpoint and Trace Unit
Read this for a description of the Data Watchpoint and Trace (DWT) unit.
Chapter 12 Instrumentation Trace Macrocell Unit
Read this for a description of the Instrumentation Trace Macrocell (ITM) unit.
Chapter 13 Fault detection and handling
Read this for a description about how faults are detected and handled in the
Cortex-M7 Processor.
Appendix A Revisions
Read this for a description of the technical changes between released issues of this
book.
Glossary
The ARM® Glossary is a list of terms used in ARM documentation, together with definitions for
those terms. The ARM® Glossary does not contain terms that are industry standard unless the
ARM meaning differs from the generally accepted meaning.
See ARM® Glossary, http://infocenter.arm.com/help/topic/com.arm.doc.aeg0014-/index.html.
Conventions
This book uses the conventions that are described in:
•
Typographical conventions.
•
Timing diagrams on page ix.
•
Signals on page ix.
Typographical conventions
The following table describes the typographical conventions:

Style

Purpose

italic

Introduces special terminology, denotes cross-references, and citations.

bold

Highlights interface elements, such as menu names. Denotes signal names. Also used for terms in descriptive
lists, where appropriate.

monospace

Denotes text that you can enter at the keyboard, such as commands, file and program names, and source code.

monospace

Denotes a permitted abbreviation for a command or option. You can enter the underlined text instead of the full
command or option name.

monospace italic

Denotes arguments to monospace text where the argument is to be replaced by a specific value.

monospace bold

Denotes language keywords when used outside example code.

Encloses replaceable terms for assembler syntax where they appear in code or code fragments. For example:
LDRSB , [, #]

SMALL CAPITALS

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Used in body text for a few terms that have specific technical meanings, that are defined in the ARM glossary.
For example, IMPLEMENTATION DEFINED, IMPLEMENTATION SPECIFIC, UNKNOWN, and UNPREDICTABLE.

viii

Preface

Timing diagrams
The figure named Key to timing diagram conventions explains the components used in timing
diagrams. Variations, when they occur, have clear labels. You must not assume any timing
information that is not explicit in the diagrams.
Shaded bus and signal areas are UNDEFINED, so the bus or signal can assume any value within
the shaded area at that time. The actual level is unimportant and does not affect normal
operation.
Clock
HIGH to LOW
Transient
HIGH/LOW to HIGH
Bus stable
Bus to high impedance
Bus change
High impedance to stable bus

Key to timing diagram conventions

Timing diagrams sometimes show single-bit signals as HIGH and LOW at the same time and
they look similar to the bus change shown in Key to timing diagram conventions. If a timing
diagram shows a single-bit signal in this way then its value does not affect the accompanying
description.
Signals
The signal conventions are:

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Signal level

The level of an asserted signal depends on whether the signal is
active-HIGH or active-LOW. Asserted means:
•
HIGH for active-HIGH signals.
•
LOW for active-LOW signals.

Lower-case n

At the start or end of a signal name denotes an active-LOW signal.

Preface

Additional reading
This section lists publications by ARM and by third parties.
See Infocenter, http://infocenter.arm.com, for access to ARM documentation.
See on ARM, www.arm.com/cmsis, for embedded software development resources including the
Cortex Microcontroller Software Interface Standard (CMSIS).
ARM publications
This book contains information that is specific to this product. See the following documents for
other relevant information:
•

ARM®v7-M Architecture Reference Manual (ARM DDI 0403).

•

ARM® CoreLink™ Level 2 Cache Controller L2C-310 Technical Reference Manual
(ARM DDI 0246).

•

ARM® CoreSight™ ETM-M7 Technical Reference Manual (ARM DDI 0494).

•

ARM® AMBA® AXI and ACE Protocol Specification (ARM IHI 0022).

•

ARM® AMBA® 3 AHB-Lite Protocol (v1.0) (ARM IHI 0033).

•

ARM® AMBA® 3 ATB Protocol Specification (ARM IHI 0032).

•

ARM® AMBA® 3 APB Protocol Specification (ARM IHI 0024).

•

ARM® CoreSight™ SoC-400 Technical Reference Manual (ARM DDI 0480).

•

ARM® CoreSight™ Architecture Specification (v2.0) (ARM IHI 0029).

•

ARM® Debug Interface v5 Architecture Specification (ARM IHI 0031).

•

ARM® Embedded Trace Macrocell Architecture Specification ETMv4 (ARM IHI 0064).

The following confidential books are only available to licensees:
•
ARM® Cortex®-M7 Processor Integration and Implementation Manual (ARM DII 0239).
Other publications
This section lists relevant documents published by third parties:
•
Test Access Port and Boundary-Scan Architecture, IEEE Standard 1149.1-2001 (JTAG).
•
IEEE Standard for Binary Floating-Point Arithmetic, IEEE Standard 754-2008.

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Preface

Feedback
ARM welcomes feedback on this product and its documentation.
Feedback on this product
If you have any comments or suggestions about this product, contact your supplier and give:
•
The product name.
•
The product revision or version.
•
An explanation with as much information as you can provide. Include symptoms and
diagnostic procedures if appropriate.
Feedback on content
If you have comments on content then send an e-mail to errata@arm.com. Give:
•
The title.
•
The number, ARM DDI 0489D.
•
The page numbers to which your comments apply.
•
A concise explanation of your comments.
ARM also welcomes general suggestions for additions and improvements.
Note
ARM tests the PDF only in Adobe Acrobat and Acrobat Reader, and cannot guarantee the
quality of the represented document when used with any other PDF reader.

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Chapter 1
Introduction

This chapter introduces the processor. It contains the following sections:
•
About the Cortex-M7 processor on page 1-2.
•
Component blocks on page 1-6.
•
Interfaces on page 1-11.
•
Supported standards on page 1-13.
•
Design process on page 1-14.
•
Documentation on page 1-15.
•
Product revisions on page 1-16.

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1-1

Introduction

1.1

About the Cortex-M7 processor
The Cortex-M7 processor is a highly efficient high-performance, embedded processor that
features low interrupt latency, low-cost debug, and has backwards compatibility with existing
Cortex-M profile processors. The processor has an in-order super-scalar pipeline that means
many instructions can be dual-issued, including load/load and load/store instruction pairs
because of multiple memory interfaces.
Memory interfaces that the processor supports include:
•
Tightly-Coupled Memory (TCM) interfaces.
•
Harvard instruction and data caches and AXI master (AXIM) interface.
•
Dedicated low-latency AHB-Lite peripheral (AHBP) interface.
•
AHB-Lite slave (AHBS) interface that provides DMA access to TCMs.
The processor has an optional Memory Protection Unit (MPU) that you can configure to protect
regions of memory. Error Correcting Code (ECC) functionality for error detection and
correction, is included in the data and instruction caches when implemented. The TCM
interfaces support the implementation of external ECC to provide improved reliability and to
address safety-related applications.
The Cortex-M7 processor includes optional floating-point arithmetic functionality, with support
for single and double-precision arithmetic. See Chapter 8 Floating Point Unit.
The processor is intended for high-performance, deeply embedded applications that require fast
interrupt response features.
Figure 1-1 shows the processor in a typical system.
DMAC

AHBS
Cortex-M7 processor
ITCM

Fast
Flash

DTCM

Fast
SRAM

AHBP

AXIM

AHB matrix

AHB bridge

Low latency
peripherals

GPIO

External
memory

Figure 1-1 Example Cortex-M7 system

1.1.1

Features
The main features of the Cortex-M7 processor include:

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•

An in-order issue, super-scalar pipeline with dynamic branch prediction.

•

DSP extensions.

•

The ARMv7-M Thumb® instruction set, defined in the ARM®v7-M Architecture Reference
Manual.

•

Banked Stack Pointer (SP).

•

Hardware integer divide instructions, SDIV and UDIV.

•

Handler and Thread modes.
Copyright © 2014, 2015 ARM. All rights reserved.
Non-Confidential

1-2

Introduction

1.1.2

•

Thumb and Debug states.

•

Automatic processor state saving and restoration for low-latency Interrupt Service
Routine (ISR) entry and exit.

•

Support for ARMv7-M big-endian byte-invariant or little-endian accesses.

•

Support for ARMv7-M unaligned accesses.

•

Low-latency interrupt processing achieved by:
—

A Nested Vectored Interrupt Controller (NVIC) closely integrated with the
processor.

—

Supporting exception-continuable instructions, such as LDM, LDMDB, STM, STMDB, PUSH,
POP and VLDM, VSTM, VPUSH, VPOP if the processor has the Floating Point Unit (FPU).

•

A low-cost debug solution with the optional ability to:
— Implement breakpoints.
— Implement watchpoints, tracing, and system profiling.
— Support printf() style debugging through an Instrumentation Trace Macrocell
(ITM).
— Optional Trace Port Interface Unit (TPIU).
— Optional Debug Access Port (DAP).

•

Support for an optional Embedded Trace Macrocell (ETM). See the ARM® CoreSight™
ETM-M7 Technical Reference Manual for more information.

•

A memory system, that includes an optional MPU and Harvard data and instruction cache
with ECC.

•

An optional Floating Point Unit (FPU).

•

Low-power features including architectural clock gating, sleep mode and Wake-up
Interrupt Controller (WIC).

•

Optional AXI to AHB bridge for legacy memory system support.

Interfaces
The Cortex-M7 processor has a number of external interfaces.
Figure 1-2 on page 1-4 shows the external interfaces of the Cortex-M7 processor.

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Introduction

Cortex-M7 Processor
Cross Trigger Interface

Interrupts

Debug

AHBD

Peripherals

AHBP

Memory

D0TCM
D1TCM
ITCM

DMA

AHBS

External PPB
ATB Instruction
ATB Data
ATB Instrumentation

MBIST

AXIM

Figure 1-2 Cortex-M7 processor interfaces

1.1.3

Configuration options
The Cortex-M7 processor has configurable options that you can configure during the
implementation and integration stages to match your functional requirements.
Table 1-1 shows the configurable options at build time of the processor.
Table 1-1 Implementation options

Feature

Options

Done at

Floating-point

No floating-point.

Implementation

Single-precision floating-point only.
Single-precision and double-precision floating-point.
Instruction TCM

No instruction TCM.

Integration

4KB-16MB (powers of 2).
Data TCM

No data TCM.

Integration

4KB-16MB (powers of 2). The Data TCM is split equally into two TCMs,
D0TCM, and D1TCM.
Instruction cache

No instruction cache unit (ICU)a.

Implementation

Instruction cache unit is included.
Data cache

Area optimized AXIM interface, no data cache unit (DCU)b.

Implementation

Performance optimized AXIM interface, data cache unit is included.
Instruction cache size

4KB, 8KB, 16KB, 32KB, 64KB.

Integration

Data cache size

4KB, 8KB, 16KB, 32KB, 64KB.

Integration

AHB peripheral size

64MB, 128MB, 256MB, 512MB.

Integration

ECC support on caches

No ECC on instruction cache or data cache.

Implementation

ECC on all implemented caches.

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1-4

Introduction

Table 1-1 Implementation options (continued)
Feature

Options

Done at

Protected memory regions

0 region, 8 regions, 16 regions.

Implementation

Interrupts

1-240 interrupts.

Implementation

Number bits of interrupt
priority

Between three and eight bits of interrupt priority, between 8 and 256 levels of
priority.

Implementation

Debug watchpoints and
breakpoints

Reduced set. Two data watchpoints comparators and four breakpoint comparators.

Implementation

ITM and Data Watchpoint
and Trace (DWT) trace
functionality

No ITM or DWT trace.

ETM

No ETM support.

Full set. Four data watchpoints comparators and eight breakpoint comparators.
Implementation

Complete ITM and DWT trace.
Implementation

ETM instruction trace only.
ETM instruction and data trace.
Dual-redundant processor

No dual-redundant processor.

Implementation

Dual-redundant processor included.
Reset All Registers

Only required registers that must be initialized are reset in the RTL.

Implementation

All registers are reset in the RTL excluding those in the ETM, if included.
All registers are reset in the RTL including those in the ETM, if included.
Cross Trigger Interface
(CTI)

No Cross Trigger Interface.

Wake-up Interrupt Controller
(WIC)

No Wake-up Interrupt controller.

Implementation

Cross Trigger Interface included.
Implementation

Wake-up Interrupt controller included.

a. The ICU includes an instruction cache controller.
b. The DCU includes a data cache controller.

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1-5

Introduction

1.2

Component blocks
The Cortex-M7 processor has fixed and optional component blocks. Optional components are:
•

Wake-up Interrupt Controller (WIC).

•

ITM.

•

FPU.

•

MPU.

•

Instruction cache unit.

•

Data cache unit.

•

Cross Trigger Interface (CTI).

•

ETM.

All other components are fixed.
Table 1-1 on page 1-4 shows the configurable options at implementation time of the processor.
Figure 1-3 shows the optional and fixed components of the Cortex-M7 processor.
Cortex-M7 Processor
PFU

FPB
External
PPB

‡ FPU

Interrupts

NVIC

‡ MPU

‡ CTI

Cross
Trigger
Interface

‡ ETM

ATB Data

DPU

‡ WIC

Debugger

ATB
Instruction

AHBD
DWT

Peripherals

AHBP

Memory

D0TCM
D1TCM
ITCM

‡ ITM

LSU

DMA

MBIST

Cortex-M7
Processor
ROM table

TCU

AHBS

STB

Cortex-M7
PPB ROM
table

MIU

Memory
system

‡ ICU and
I-cache RAM

ATB
Instrumentation

BIU

‡ DCU and
D-cache
RAM

‡ Optional
AXIM

Figure 1-3 Cortex-M7 functional diagram
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1-6

Introduction

The Cortex-M7 processor contains the following component blocks:
•
Data Processing Unit.
•
Prefetch Unit.
•
Load Store Unit.
•
Floating Point Unit on page 1-8.
•
Nested Vectored Interrupt Controller on page 1-8.
•
Wake-up Interrupt Controller on page 1-8.
•
Memory System on page 1-9.
•
Memory Protection Unit on page 1-9.
•
Cortex-M7 Processor and PPB ROM tables on page 1-9.
•
Cross Trigger Interface Unit on page 1-9.
•
ETM on page 1-9.
•
Debug and trace components on page 1-9.
1.2.1

Data Processing Unit
The Data Processing Unit (DPU) provides:

1.2.2

•

Parallelized integer register file with six read ports and four write ports for large-scale
dual-issue.

•

Extensive forwarding logic to minimise interlocks.

•

Two ALUs, with one ALU capable of executing SIMD operations.

•

Single MAC pipeline capable of 32x32-bit + 64-bit → 64-bit with two cycle result latency
and one MAC per cycle throughput.

•

Single divider unit with support for operand-dependent early termination.

Prefetch Unit
The Prefetch Unit (PFU) provides:

1.2.3

•

64-bit instruction fetch bandwidth.

•

4x64-bit pre-fetch queue to decouple instruction pre-fetch from DPU pipeline operation.

•

A Branch Target Address Cache (BTAC) for single-cycle turn-around of branch predictor
state and target address.

•

A static branch predictor when no BTAC is specified.

•

Forwarding of flags for early resolution of direct branches in the decoder and first
execution stages of the processor pipeline.

Load Store Unit
The Load Store Unit (LSU) provides:

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•

Dual 32-bit load channels to TCM, data cache, and AXI master (AXIM) interface for
64-bit load bandwidth and dual 32-bit load capability.

•

Single 32-bit load channel to the AHB interface.

•

Single 64-bit store channel.

1-7

Introduction

1.2.4

•

Store buffering to increase store throughput and minimize RAM contention with data and
instruction reads.

•

Separate store buffering for TCM, AHBP and AXIM for Quality of Service (QoS) and
interface-specific optimizations.

Floating Point Unit
The optional Floating Point Unit (FPU) provides:
•

Lazy floating-point context save. Automated stacking of floating-point state is delayed
until the ISR attempts to execute a floating-point instruction. This reduces the latency to
enter the ISR and removes floating-point context save for ISRs that do not use
floating-point.

•

Instructions for single-precision (C programming language float type) data-processing
operations.

•

Optional instructions for double-precision (C double type) data-processing operations.

•

Combined Multiply and Accumulate instructions for increased precision (Fused MAC).

•

Hardware support for conversion, addition, subtraction, multiplication with optional
accumulate, division, and square-root.

•

Hardware support for denormals and all IEEE Standard 754-2008 rounding modes.

•

32 32-bit single-precision registers or 16 64-bit double-precision registers.

See Chapter 8 Floating Point Unit for more information.
1.2.5

Nested Vectored Interrupt Controller
The NVIC is closely integrated with the core to achieve low-latency interrupt processing.
Features include:
•

External interrupts, configurable from 1 to 240. This is configured at implementation.

•

Configurable levels of interrupt priority from 8 to 256. Configured at implementation.

•

Dynamic reprioritization of interrupts.

•

Priority grouping. This enables selection of preempting interrupt levels and non
preempting interrupt levels.

•

Support for tail-chaining and late arrival of interrupts. This enables back-to-back interrupt
processing without the overhead of state saving and restoration between interrupts.

See Chapter 7 Nested Vectored Interrupt Controller for more information.
1.2.6

Wake-up Interrupt Controller
The optional WIC provides ultra-low power sleep mode support.
See Low power modes on page 7-3 for more information.

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1-8

Introduction

1.2.7

Memory System
The optional memory system includes:
•

A Bus Interface Unit (BIU) with a configurable AMBA 4 AXI interface that can support
a high-performance L2 memory system.

•

An extended AHB-Lite interface to support low-latency system peripherals.

•

A TCM Control Unit (TCU) with TCM interfaces that can support external ECC logic and
an AHB slave (AHBS) interface for system access to TCMs.

•

Instruction cache and data cache units, with optional Error Correction Code (ECC).

•

A Memory Built-in Self Test (MBIST) interface provided by the MBIST interface unit
(MIU). The memory system supports online MBIST, where the RAM arrays can be
accessed by the MBIST interface while the processor is running. MBIST is also supported
during production test.

See Chapter 5 Memory System for more information.
1.2.8

Store Buffer
The Store Buffer (STB) holds store operations when they have left the load/store pipeline and
have been committed by the DPU. From the STB, a store can request access to the cache RAM
in the DCU, request the BIU to initiate linefills, or request the BIU to write the data out on the
AXIM interface.
The STB can merge several store transactions into a single transaction if they are to the same
64-bit aligned address.

1.2.9

Memory Protection Unit
The optional MPU has configurable attributes for memory protection. It includes up to 16
memory regions and Sub Region Disable (SRD), enabling efficient use of memory regions. It
also has the ability to enable a background region that implements the default memory map
attributes. See Chapter 6 Memory Protection Unit for more information.

1.2.10

Cortex-M7 Processor and PPB ROM tables
The two ROM tables enable a debugger to identify and connect to CoreSight debug
components. See Chapter 9 Debug for more information.

1.2.11

Cross Trigger Interface Unit
The optional CTI enables the debug logic and ETM to interact with each other and with other
CoreSight components. See Chapter 10 Cross Trigger Interface.

1.2.12

ETM
The optional ETM provides instruction-only or instruction and data trace capabilities when
configured. See the ARM® CoreSight™ ETM-M7 Technical Reference Manual for more
information.

1.2.13

Debug and trace components
•

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Configurable Breakpoint unit (FPB) for implementing breakpoints.

1-9

Introduction

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•

Configurable Data Watchpoint and Trace (DWT) unit for implementing watchpoints, data
tracing, and system profiling.

•

Optional ITM for support of printf() style debugging, using instrumentation trace.

•

Interfaces suitable for:
—

Passing on-chip data to a Trace Port Analyzer (TPA), including Single Wire Output
(SWO) mode.

—

Debugger access to all memory and registers in the system, including access to
memory-mapped devices, access to internal core registers when the core is halted,
and access to debug control registers even when reset is asserted.

1-10

Introduction

1.3

Interfaces
The processor contains the following external interfaces:
•
AHBP interface.
•
AHBS interface.
•
AHBD interface.
•
External Private Peripheral Bus.
•
ATB interfaces.
•
TCM interface.
•
Cross Trigger interface on page 1-12.
•
MBIST interface on page 1-12.
•
AXIM interface on page 1-12.

1.3.1

AHBP interface
The AHB-Lite peripheral (AHBP) interface provides access suitable for low latency system
peripherals. It provides support for unaligned memory accesses, write buffer for buffering of
write data, and exclusive access transfers for multiprocessor systems. See AHB peripheral
interface on page 5-22 for more information.

1.3.2

AHBS interface
The AHB-Lite slave (AHBS) interface enables system access to TCMs. See AHB slave interface
on page 5-30 for more information.

1.3.3

AHBD interface
The AHB-Lite Debug (AHBD) interface provides debug access to the Cortex-M7 processor and
the complete memory map. See About the AHBD interface on page 9-7 for more information.

1.3.4

External Private Peripheral Bus
The APB External PPB (EPPB) enables access to CoreSight-compatible debug and trace
components, in the system connected to the processor.

1.3.5

ATB interfaces
The ATB interfaces output trace information used for debugging. The ATB interface is
compatible with the CoreSight architecture. See the ARM® CoreSight™ Architecture
Specification (v2.0) for more information.

1.3.6

TCM interface
The processor can have up to two TCM memory instances, Instruction TCM (ITCM) and Data
TCM (DTCM), each with a double word data width. Access to ITCM is through the ITCM
64-bit wide interface. Access to DTCM is through the D1TCM 32-bit wide interface and the
32-bit wide D0TCM interface. The DTCM accesses are split so that lower words always access
D0TCM and upper words always access D1TCM. The size of both TCM instances is
configurable, 4KB-16MB in powers of 2. See TCM interfaces on page 5-33 for more
information.

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Introduction

1.3.7

Cross Trigger interface
The processor includes an optional Cross Trigger Interface Unit which includes an interface
suitable for connection to external CoreSight components using a Cross Trigger Matrix. See
Chapter 10 Cross Trigger Interface for more information.

1.3.8

MBIST interface
The MBIST interface is used for testing the RAMs during production test. The Cortex-M7
processor also allows the RAMs to be tested using the MBIST interface during normal
execution. This is known as online MBIST.
Contact your implementation team for more information about the MBIST interface and online
MBIST.

1.3.9

AXIM interface
The AXI master (AXIM) interface provides high-performance access to an external memory
system. The AXIM interface supports use of the ARM CoreLink L2C-310 Level 2 Cache
Controller. L2C-310 Exclusive cache configuration is not supported. See AXIM interface on
page 5-6 for more information.

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Introduction

1.4

Supported standards
The processor complies with, or implements, the specifications described in:
•
ARM architecture.
•
Bus architecture.
•
Debug.
•
Embedded Trace Macrocell.
•
Floating Point Unit.
This book complements architecture reference manuals, architecture specifications, protocol
specifications, and relevant external standards. It does not duplicate information from these
sources.

1.4.1

ARM architecture
The Cortex-M7 processor implements the ARMv7E-M architecture profile. See the ARM®v7-M
Architecture Reference Manual.
The Cortex-M7 processor FPB implements the Flash Patch Breakpoint version 2 architecture
revision.

1.4.2

Bus architecture
The processor provides an:
•
External interface that is a variant of the AMBA 3 AHB-Lite protocol.
•
External interface that complies with the AMBA 4 AXI.
The processor also implements an interface for CoreSight and other debug components using
the AMBA 3 APB protocol and AMBA 3 ATB Protocol.
For more information, see:
•
The ARM® AMBA® AXI and ACE Protocol Specification.
•
The ARM® AMBA® 3 AHB-Lite Protocol (v1.0).
•
The ARM® AMBA® 3 APB Protocol Specification.
•
The ARM® AMBA® 3 ATB Protocol Specification.

1.4.3

Debug
The debug features of the processor implement the ARM debug interface architecture. See the
ARM® Debug Interface v5 Architecture Specification.

1.4.4

Embedded Trace Macrocell
When implemented, the trace features of the processor implement the ARM Embedded Trace
Macrocell (ETM)v4 architecture. See the ARM® Embedded Trace Macrocell Architecture
Specification ETMv4.

1.4.5

Floating Point Unit
Depending on your implementation, a Cortex-M7 processor with FPU can have single-precision
only or single and double-precision floating-point data processing as defined by the FPv5
architecture, that is part of the ARMv7E-M architecture. It provides floating-point computation
functionality that is compliant with the ANSI/IEEE Std 754-2008, IEEE Standard for Binary
Floating-Point Arithmetic.

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Introduction

1.5

Design process
The Cortex-M7 processor is delivered as synthesizable RTL that must go through the
implementation, integration, and programming processes before you can use it in a product.
The following definitions describe each top-level process in the design flow:
Implementation
The implementer configures and synthesizes the RTL.
Integration
The integrator connects the implemented design into a SoC. This includes
connecting it to a memory system and peripherals.
Programming
The system programmer develops the software required to configure and
initialize the processor, and tests the required application software.
Each stage in the process can be performed by a different party. Implementation and integration
choices affect the behavior and features of the processor.
For MCUs, often a single design team integrates the processor before synthesizing the complete
design. Alternatively, the team can synthesize the processor on its own or partially integrated,
to produce a macrocell that is then integrated, possibly by a separate team.
The operation of the final device depends on:
Build configuration
The implementer chooses the options that affect how the RTL source files are
pre-processed. These options usually include or exclude logic that affects one or
more of the area, maximum frequency, and features of the resulting macrocell.
Configuration inputs
The integrator configures some features of the processor by tying inputs to
specific values. These configurations affect the start-up behavior before any
software configuration is made. They can also limit the options available to the
software.
Software configuration
The programer configures the processor by programming particular values into
registers. This affects the behavior of the processor.
Note
This manual refers to implementation-defined features that are applicable to build configuration
options. Reference to a feature that is included means that the appropriate build and pin
configuration options are selected. Reference to an enabled feature means one that has also been
configured by software.

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Introduction

1.6

Documentation
The Cortex-M7 processor documentation can help you complete the top-level processes of
implementation, integration, and programming required to use the product correctly.
The Cortex-M7 processor documentation comprises a Technical Reference Manual, an
Integration and Implementation Manual, and User Guide Reference Material.
Technical Reference Manual
The Technical Reference Manual (TRM) describes the functionality and the
effects of functional options on the behavior of the Cortex-M7 processor. It is
required at all stages of the design flow. Some behavior described in the TRM
might not be relevant because of the way that the Cortex-M7 processor is
implemented and integrated. If you are programming the Cortex-M7 processor
then contact the implementer to determine:
•

The build configuration of the implementation.

•

What integration, if any, was performed before implementing the processor.

Integration and Implementation Manual
The Integration and Implementation Manual (IIM) describes:
•

The available build configuration options and related issues in selecting
them.

•

How to configure the Register Transfer Level (RTL) with the build
configuration options.

•

How to integrate the processor into a SoC. This includes a description of
the integration kit and describes the pins that the integrator must tie off to
configure the macrocell for the required integration.

•

How to implement the processor into your design. This includes
floorplanning guidelines, Memory Built-in Self Test (MBIST) and Design
for Test (DFT) information, and how to perform netlist dynamic
verification on the processor.

•

The processes to sign off the integration and implementation of the design.

The ARM product deliverables include reference scripts and information about
using them to implement your design.
Reference methodology documentation from your EDA tools vendor
complements the IIM.
The IIM is a confidential book that is only available to licensees.
User Guide Reference Material
This document provides reference material that ARM partners can configure and
include in a User Guide for an ARM Cortex-M7 processor. Typically:
•

Each chapter in this reference material might correspond to a section in the
User Guide.

•

Each top-level section in this reference material might correspond to a
chapter in the User Guide.

However, you can organize this material in any way, subject to the conditions of
the licence agreement under which ARM supplied the material.
See Additional reading on page x for more information about the books associated with the
Cortex-M7 processor.

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Introduction

1.7

Product revisions
This section describes the differences in functionality between product revisions:
r0p0

First release.

r0p1

The following changes have been made in this release:

r0p2

r1p0

r1p1

•

Updated CPUID reset value, 0x410FC271.

•

Various engineering errata fixes.

The following changes have been made in this release:
•

Updated CPUID reset value, 0x410FC272.

•

Various engineering errata fixes.

The following changes have been made in this release:
•

Updated CPUID reset value, 0x411FC270.

•

Added CTLPPBLOCK[3:0] to allow locking of registers ITCMCR,
DTCMCR, AHBPCR, VTOR to prevent unwanted updates.

•

Added ACTLR bit functions to allow low-capability AXI systems to
disable AXI reads to DEV/SO memory and disable exclusive reads/writes
to shared memory not initiated until all outstanding reads/stores on AXI are
complete.

•

Added MBISTIMPERR[2] output to MBIST interface to provide an error
when attempting to access unimplemented memory.

•

Improved handling of simultaneous AHBS and software activity relating to
the same TCM.

The following changes have been made in this release:
•

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1-16

Chapter 2
Programmers Model

This chapter describes the programmers model. It contains the following sections:
•
About the programmers model on page 2-2.
•
Modes of operation and execution on page 2-3.
•
Instruction set summary on page 2-4.
•
System address map on page 2-5.
•
Exclusive monitor on page 2-7.
•
Processor core registers on page 2-8.
•
Exceptions on page 2-9.

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Programmers Model

2.1

About the programmers model
This chapter gives an overview of the Cortex-M7 processor programmers model that describes
the implementation-defined options. In addition:
•
Chapter 3 summarizes the system control features of the programmers model.
•
Chapter 6 summarizes the MPU features of the programmers model.
•
Chapter 7 summarizes the NVIC features of the programmers model.
•
Chapter 8 summarizes the FPU features of the programmers model.
•
Chapter 9 summarizes the Debug features of the programmers model.
•
Chapter 10 summarizes the CTI features of the programmers model.
•
Chapter 11 summarizes the DWT features of the programmers model.
•
Chapter 12 summarizes the ITM features of the programmers model.

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Programmers Model

2.2

Modes of operation and execution
This section briefly describes the modes of operation and execution of the Cortex-M7 processor.
See the ARM®v7-M Architecture Reference Manual for more information.

2.2.1

Operating modes
The processor supports two modes of operation, Thread mode and Handler mode:

2.2.2

•

The processor enters Thread mode on reset, or as a result of an exception return.
Privileged and Unprivileged code can run in Thread mode.

•

The processor enters Handler mode as a result of an exception. All code is privileged in
Handler mode.

Operating states
The processor can operate in one of two operating states:

2.2.3

•

Thumb state. This is normal execution running 16-bit and 32-bit halfword-aligned Thumb
instructions.

•

Debug state. This is the state when the processor is in halting debug.

Privileged access and unprivileged User access
Code can execute as privileged or unprivileged. Unprivileged execution limits or excludes
access to some resources. Privileged execution has access to all resources. Handler mode is
always privileged. Thread mode can be privileged or unprivileged.

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Programmers Model

2.3

Instruction set summary
The processor implements the ARMv7-M instruction set and features provided by the
ARMv7E-M architecture profile. For more information about the ARMv7-M instructions, see
the ARM®v7-M Architecture Reference Manual.

2.3.1

Binary compatibility with other Cortex processors
The processor is binary compatible with the instruction sets and features implemented in other
Cortex-M profile processors. You cannot move software from the Cortex-M7 processor to:
•

The Cortex-M3 processor if it contains floating-point operations or instructions that are
part of the DSP extension, such as SADD16.

•

The Cortex-M4 processor if it contains double-precision floating-point operations.

•

The Cortex-M0 or Cortex-M0+ processors because these are implementations of the
ARMv6-M Architecture.

Code designed for the Cortex-M3 and Cortex-M4 processors is compatible with the Cortex-M7
processor as long as it does not rely on bit-banding.
To ensure a smooth transition when migrating software to the Cortex-M7 processor, ARM
recommends that code designed to operate on the Cortex-M0, M0+, M3, and M4 processors
obey the following rules and that you configure the Configuration and Control Register (CCR)
appropriately:

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Use word transfers only to access registers in the NVIC and System Control Space (SCS).

•

Treat all unused SCS registers and register fields on the processor as Do-Not-Modify.

•

Configure the following fields in the CCR:
— STKALIGN bit to 1.
— UNALIGN_TRP bit to 1.
— Leave all other bits in the CCR register at their original value.

2-4

Programmers Model

2.4

System address map
The processor contains an internal bus matrix that arbitrates the processor and external AHBD
memory accesses to both the external memory system and to the internal SCS and debug
components.
Priority is always given to the processor to ensure that any debug accesses are as non-intrusive
as possible.
Figure 2-1 shows the system address map.
0xFFFFFFFF
0xE00FFFFF
0xE00FF000
0xE00FE000
0xE0043000
0xE0042000
0xE0041000
0xE0040000

PPB ROM table
Processor ROM table
Private Peripheral Bus
CTI
ETM
Reserved (TPIU)

System
0xE0100000
Private peripheral bus - External
0xE0040000
Private peripheral bus - Internal
0xE0000000

External device 1.0GB

0xA0000000

External RAM

1.0GB

0x60000000
Peripheral

0.5GB
0x40000000

SRAM

0.5GB
0x20000000

Code

0.5GB
0x00000000

Figure 2-1 System address map

Table 2-1 shows the processor interfaces that are addressed by the different memory map
regions.
Table 2-1 Memory regions
Memory Map

Region

Code

Instruction fetches and data accesses are performed over the ITCM or AXIM interface.

SRAM

Instruction fetches and data accesses are performed over the DTCM or AXIM interface.

Peripheral

Data accesses are performed over the AHBP or AXIM interface.
Instruction fetches are performed over the AXIM interface.

External RAM

Instruction fetches and data accesses are performed over the AXIM interface.

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Programmers Model

Table 2-1 Memory regions (continued)
Memory Map

Region

External Device

Instruction fetches and data accesses are performed over the AXIM interface.

Private Peripheral Bus

Data accesses to registers associated with peripherals outside the processor are performed on the
External Private Peripheral Bus (EPPB) interface. See Private peripheral bus.
This memory region is Execute Never (XN), and so instruction fetches are prohibited. An MPU,
if present, cannot change this.

System

System segment for vendor system peripherals. Data accesses are performed over the AHBP
interface. This memory region is XN, and so instruction fetches are prohibited. An MPU, if
present, cannot change this.

See the ARM®v7-M Architecture Reference Manual for more information about the memory
model.
2.4.1

Private peripheral bus
The internal PPB interface provides access to:
•

The Instrumentation Trace Macrocell (ITM).

•

The Data Watchpoint and Trace (DWT).

•

The Breakpoint unit (FPB).

•

The SCS, including the MPU, the instruction and data cache, and the Nested Vectored
Interrupt Controller (NVIC).

•

The Processor and PPB ROM tables.

The external PPB interface provides access to:

2.4.2

•

The Embedded Trace Macrocell (ETM).

•

The Cross Trigger Interface (CTI).

•

CoreSight debug and trace components in the external system.

Unaligned accesses that cross regions
The Cortex-M7 processor supports ARMv7 unaligned accesses, and performs all accesses as
single, unaligned accesses. They are converted into two or more aligned accesses internally and
are performed on the external interfaces of the processor.
Note
All Cortex-M7 processor external accesses are aligned.
Unaligned support is only available for load/store singles (LDR, LDRH, STR, STRH). Load/store
double already supports word aligned accesses, but does not permit other unaligned accesses,
and generates a fault if this is attempted.
Unaligned accesses that cross memory map boundaries are architecturally UNPREDICTABLE. The
processor behavior is boundary dependent. Unaligned accesses are not supported to PPB space,
and so there are no boundary crossing cases for PPB accesses.

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Programmers Model

2.5

Exclusive monitor
The Cortex-M7 processor implements a local exclusive monitor. For more information about
semaphores and the local exclusive monitor see the ARM®v7-M Architecture Reference Manual.
The local monitor within the processor is constructed so that it does not hold any physical
address. Instead it treats any access as matching the address of the previous LDREX instruction.
This means that the implemented Exclusives Reservation Granule (ERG) is the entire memory
address range.

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Programmers Model

2.6

Processor core registers
The processor has the following 32-bit registers:
•
13 general-purpose registers, R0-R12.
•
Stack Pointer (SP), R13 alias of banked registers, SP_process and SP_main.
•
Link Register (LR), R14.
•
Program Counter (PC), R15.
•
Special-purpose Program Status Registers (xPSR).
For more information about the processor register set, see the ARM®v7-M Architecture
Reference Manual.

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Programmers Model

2.7

Exceptions
The processor and the NVIC prioritize and handle all exceptions. When handling exceptions:
•
All exceptions are handled in Handler mode.
•
Processor state is automatically stored to the stack on an exception, and automatically
restored from the stack at the end of the Interrupt Service Routine (ISR).
•
The vector is fetched in parallel to the state saving, enabling efficient interrupt entry.
The processor supports tail-chaining that enables back-to-back interrupts without the overhead
of state saving and restoration.
You configure the number of interrupts, and levels of interrupt priority, during implementation.
Software can choose only to enable a subset of the configured number of interrupts, and can
choose how many levels of the configured priorities to use.
Note
The EPSR.T bit supports the ARM architecture interworking model, however, as ARMv7-M
only supports execution of Thumb instructions, it must always be maintained with the value 1.
This means that all exception vectors must have bit[0] set. If bit[0] of the associated vector table
entry is set to 0 on exception entry, execution of the first instruction causes an INVSTATE
UsageFault. If this happens on a reset, this escalates to a HardFault, because UsageFault is
disabled on reset.

2.7.1

Exception handling
External read faults from either the TCM interfaces, the AXIM interface, or the AHB interfaces
generate a synchronous exception in the processor. External write faults generate an
asynchronous exception in the processor.
The processor implements advanced exception and interrupt handling, as described in the
ARM®v7-M Architecture Reference Manual.
The processor exception model has the following implementation-defined behavior in addition
to the architecturally-defined behavior:
•
Exceptions on stacking from HardFault to NMI lockup at NMI priority.
•
Exceptions on unstacking from NMI to HardFault lockup at HardFault priority.
To minimize interrupt latency, the processor can abandon the majority of multicycle instructions
that are executing when an interrupt is recognized. The only exception is a load from Device or
Strongly-ordered memory, or a shared store exclusive operation that starts on the AXI interface.
All normal memory transactions are abandoned when an interrupt is recognized.
The processor restarts any abandoned operation on return from the interrupt. The processor also
implements the Interruptible-continuable bits allowing load and store multiples to be
interruptible and continuable. In these cases the processor resumes execution of these
instructions after the last completed transfer instead of from the start. For more information on
the Interruptible-continuable bits and key limitations on when they apply, see the ARM®v7-M
Architecture Reference Manual.
Specifically, on the Cortex-M7 processor, these instructions always restart instead of continue:
•
The instruction faults.
•
The instruction is inside an If-Then (IT) block.
•
The instruction is a load multiple, has the base register in the list and has loaded the base
register.
•
The instruction is a load multiple and is subject to an ECC error.

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Chapter 3
System Control

This chapter describes the registers that program the processor. It contains the following
sections:
•
About system control on page 3-2.
•
Register summary on page 3-3.
•
Register descriptions on page 3-6.

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System Control

3.1

About system control
This chapter describes the registers that control the operation of the processor. This includes
registers in the:
•
System Control Space.
•
Access Control Space.
•
Identification Space.
•
Cache Maintenance Space.

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3-2

System Control

3.2

Register summary
Table 3-1 shows the system control registers. Registers not described in this chapter are
described in the ARM®v7-M Architecture Reference Manual.
Table 3-1 System control registers
Address

Name

Type

Reset

Description

0xE000E008

ACTLR

0x00000000

Auxiliary Control Register on page 3-6

0xE000E00C

Reserved

0xE000E010

SYST_CSR

0x00000000

SysTick Control and Status Register

0xE000E014

SYST_RVR

Unknown

SysTick Reload Value Register

0xE000E018

SYST_CVR

Unknown

SysTick Current Value Register

0xE000E01C

SYST_CALIB

-a

SysTick Calibration Value Register

0xE000ED00

CPUID

0x411FC271

CPUID Base Register on page 3-8

0xE000ED04

ICSR

RW or RO

0x00000000

Interrupt Control and State Register

0xE000ED08

VTOR

-b

Vector Table Offset Register

0xE000ED0C

AIRCR

0xFA050000c

Application Interrupt and Reset Control Register

0xE000ED10

SCR

0x00000000

System Control Register

0xE000ED14

CCR

RWd

0x00040200

Configuration and Control Register

0xE000ED18

SHPR1

0x00000000

System Handler Priority Register 1

0xE000ED1C

SHPR2

0x00000000

System Handler Priority Register 2

0xE000ED20

SHPR3

0x00000000

System Handler Priority Register 3

0xE000ED24

SHCSR

0x00000000

System Handler Control and State Register

0xE000ED28

CFSR

0x00000000

Configurable Fault Status Registerse

0xE000ED2C

HFSR

0x00000000

HardFault Status Register

0xE000ED30

DFSR

0x00000000

Debug Fault Status Register

0xE000ED34

MMFAR

Unknown

MemManage Fault Address Registerf

0xE000ED38

BFAR

Unknown

BusFault Address Registerf

0xE000ED40

ID_PFR0

0x00000030

Processor Feature Register 0

0xE000ED44

ID_PFR1

0x00000200

Processor Feature Register 1

0xE000ED48

ID_DFR0

0x00100000

Debug Feature Register 0g

0xE000ED4C

ID_AFR0

0x00000000

Auxiliary Feature Register 0

0xE000ED50

ID_MMFR0

0x00100030h

Memory Model Feature Register 0

0xE000ED54

ID_MMFR1

0x00000000

Memory Model Feature Register 1

0xE000ED58

ID_MMFR2

0x01000000

Memory Model Feature Register 2

0xE000ED5C

ID_MMFR3

0x00000000

Memory Model Feature Register 3

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System Control

Table 3-1 System control registers (continued)
Address

Name

Type

Reset

Description

0xE000ED60

ID_ISAR0

0x01101110

Instruction Set Attributes Register 0

0xE000ED64

ID_ISAR1

0x02112000

Instruction Set Attributes Register 1

0xE000ED68

ID_ISAR2

0x20232231

Instruction Set Attributes Register 2

0xE000ED6C

ID_ISAR3

0x01111131

Instruction Set Attributes Register 3

0xE000ED70

ID_ISAR4

0x01310132

Instruction Set Attributes Register 4

0xE000ED78

CLIDR

-i

Cache Level ID Register on page 3-9

0xE000ED7C

CTR

0x8303C003

Cache Type Register

0xE000ED80

CCSIDR

-j

Cache Size ID Register on page 3-10

0xE000ED84

CSSELR

UNPREDICTABLE

Cache Size Selection Register on page 3-12

0xE000ED88

CPACR

Coprocessor Access Control Register

0xE000EF00

STIR

0x00000000

Software Triggered Interrupt Register

0xE000EF50

ICIALLU

Unknown

Instruction cache invalidate all to Point of Unification
(PoU)

0xE000EF54

Reserved

0xE000EF58

ICIMVAU

Unknown

Instruction cache invalidate by address to PoU

0xE000EF5C

DCIMVAC

Unknown

Data cache invalidate by address to Point of Coherency
(PoC)

0xE000EF60

DCISW

Unknown

Data cache invalidate by set/way

0xE000EF64

DCCMVAU

Unknown

Data cache by address to PoU

0xE000EF68

DCCMVAC

Unknown

Data cache clean by address to PoC

0xE000EF6C

DCCSW

Unknown

Data cache clean by set/way

0xE000EF70

DCCIMVAC

Unknown

Data cache clean and invalidate by address to PoC

0xE000EF74

DCCISW

Unknown

Data cache clean and invalidate by set/way

0xE000EF78

BPIALL

RAZ/WI

Unknown

Not implemented

0xE000EF7C

Reserved

0xE000EF80

Reserved

0xE000EF90

CM7_ITCMCR

Unknown

0xE000EF94

CM7_DTCMCR

Unknown

Instruction and Data Tightly-Coupled Memory Control
Registers on page 3-13

0xE000EF98

CM7_AHBPCR

Unknown

AHBP Control Register on page 3-14

0xE000EF9C

CM7_CACR

Unknown

L1 Cache Control Register on page 3-15

0xE000EFA0

CM7_AHBSCR

Unknown

AHB Slave Control Register on page 3-20

0xE000EFA4

Reserved

0xE000EFA8

CM7_ABFSR

Unknown

Auxiliary Bus Fault Status Register on page 3-16

ARM DDI 0489D
ID082615

3-4

System Control

Table 3-1 System control registers (continued)
Address

Name

Type

Reset

Description

0xE000EFB0

IEBR0k

Instruction Error bank Register 0-1 on page 3-17

0xE000EFB4

IEBR1k

0xE000EFB8

DEBR0k

0xE000EFBC

DEBR1k

0xE000EFD0

PID4

0x00000004

0xE000EFD4

PID5

0x00000000

0xE000EFD8

PID6

0x00000000

0xE000EFDC

PID7

0x00000000

0xE000EFE0

PID0

-l

0xE000EFE4

PID1

0x000000B0

0xE000EFE8

PID2

0x0000000B

0xE000EFEC

PID3

0x00000000

0xE000EFF0

CID0

0x0000000D

0xE000EFF4

CID1

0x000000E0

0xE000EFF8

CID2

0x00000005

0xE000EFFC

CID3

0x000000B1

Data Error bank Register 0-1 on page 3-18

See the Component and Peripheral ID register formats in
the ARM®v7-M Architecture Reference Manual.

a. SYST_CALIB indicates the value of signal CFGSTCALIB[25:0]. See Table 3-2.
b. VTOR[31:7] indicates the value of signal INITVTOR[31:7]. VTOR[6:0] are RAZ.
c. AIRCR[15] indicates the value of signal CFGBIGEND.
d. The processor implements bit[9] of CCR, STKALIGN, as RO and has a value of 1.
e. The 32-bit CFSR comprises the status registers for the faults that have configurable priority. Software can access the combined CFSR,
or use byte or halfword accesses to access the individual registers, MemManage Status Register (MMFSR), BusFault Status Register
(BFSR), and UsageFault Status Register (UFSR). See the ARM®v7-M Architecture Reference Manual for more information.
f. BFAR and MFAR are the same physical register. Because of this, the BFARVALID and MFARVALID bits are mutually exclusive.
g. ID_DFR0 reads as 0 if no debug support is implemented.
h. The reset value depends on the values of signals CFGITCMSZ and CFGDTCMSZ.
i. The reset value depends on whether L1 cache is implemented.
j. Reset value depends on which caches are implemented and their sizes.
k. Only present if ECC is present, otherwise RAZ/WI.
l. This value is 0x00000000 for implementations without FPU or 0x0000000C for implementations with FPU.

Table 3-2 shows how signal CFGSTCALIB[25:0] is indicated in register SYST_CALIB.
Table 3-2 SYST_CALIB inputs

ARM DDI 0489D
ID082615

Bits

Name

Input

[31]

NOREF

CFGSTCALIB[25].

[30]

SKEW

CFGSTCALIB[24].

[29:24]

None. RAZ.

[23:0]

TENMS

CFGSTCALIB[23:0].

3-5

System Control

3.3

Register descriptions
This section describes the following system control registers whose implementation is specific
to this processor:
•
Auxiliary Control Register.
•
CPUID Base Register on page 3-8.
•
Cache Level ID Register on page 3-9.
•
Cache Size ID Register on page 3-10.
•
Cache Size Selection Register on page 3-12.
•
Instruction and Data Tightly-Coupled Memory Control Registers on page 3-13.
•
AHBP Control Register on page 3-14.
•
L1 Cache Control Register on page 3-15.
•
Auxiliary Bus Fault Status Register on page 3-16.
•
Instruction Error bank Register 0-1 on page 3-17.
•
Data Error bank Register 0-1 on page 3-18.
•
AHB Slave Control Register on page 3-20.

3.3.1

Auxiliary Control Register
The ACTLR characteristics are:
Purpose

Provides implementation defined configuration and control options for the
processor.

Usage Constraints There are no usage constraints.
Configurations

Available in all configurations.

Attributes

See the register summary in Table 3-1 on page 3-3.

Figure 3-1 shows the ACTLR bit assignments.
31

29 28 27 26 25

21 20

DISISSCH1

DISDYNADD
DISCRITAXIRUW
DISFPUISSOPT
Reserved

16 15 14 13 12 11 10 9
DISDI

3 2 1 0
Reserved

FPEXCODIS
DISRAMODE
DISITMATBFLUSH
DISBTACREAD
DISBTACALLOC
DISCRITAXIRUR

Reserved
DISFOLD

Figure 3-1 ACTLR bit assignments

ARM DDI 0489D
ID082615

3-6

System Control

Table 3-3 shows the ACTLR bit assignments.
Table 3-3 ACTLR bit assignments
Bits

Name

Function

[31:29]

Reserved.

[28]

DISFPUISSOPT

[27]

DISCRITAXIRUW

Disable critical AXI read-under-write:
0
Normal operation. This is backwards compatible with r0.
1
AXI reads to DEV/SO memory. Exclusive reads to shared memory are not
initiated on the AXIM AR channel until all outstanding stores on AXI are
complete.

[26]

DISDYNADD

Disables dynamic allocation of ADD and SUB instructions:
0
Normal operation. Some ADD and SUB instructions are resolved in EX1.
1
All ADD and SUB instructions are resolved in EX2.

[25:21]

DISISSCH1

0
1
[25]
[24]
[23]
[22]
[21]

Normal operation.
Instruction type might not be issued in channel 1.
VFP.
Integer MAC and MUL.
Loads to PC.
Indirect branches, but not loads to PC.
Direct branches.

[20:16]

DISDI

0
1
[20]
[19]
[18]
[17]
[16]

Normal operation.
Nothing can be dual-issued when this instruction type is in channel 0.
VFP.
Integer MAC and MUL.
Loads to PC.
Indirect branches, but not loads to PC.
Direct branches.

[15]

DISCRITAXIRUR

Disables critical AXI Read-Under-Read.
0
Normal operation.
1
An AXI read to Strongly-ordered or Device memory, or an LDREX to shared
memory, is not put on AXI if there are any outstanding reads on AXI.
Transactions on AXI cannot be interrupted. This bit might reduce the time
that these transactions are in progress and might improve worst case
interrupt latency. Performance is decreased when this bit is set.

[14]

DISBTACALLOC

0
1

Normal operation.
No new entries are allocated in Branch Target Address Cache (BTAC), but
existing entries can be updated.

[13]

DISBTACREAD

0
1

Normal operation.
BTAC is not used and only static branch prediction can occur.

[12]

DISITMATBFLUSH

Disables ITM and DWT ATB flush:
1
ITM and DWT ATB flush disabled. AFVALID is ignored and AFREADY
is held HIGH.

Normal operation.

Note
This bit is always 1 and therefore RO/WI.

ARM DDI 0489D
ID082615

3-7

System Control

Table 3-3 ACTLR bit assignments (continued)

3.3.2

Bits

Name

Function

[11]

DISRAMODE

Disables dynamic read allocate mode for Write-Back Write-Allocate memory regions:
0
Normal operation.
1
Dynamic disabled.

[10]

FPEXCODIS

Disables FPU exception outputs.
0
Normal operation.
1
FPU exception outputs are disabled.

[9:3]

Reserved.

[2]

DISFOLD

[1:0]

Reserved.

Normal operation.

CPUID Base Register
The CPUID characteristics are:
Purpose

Specifies:
•
The ID number of the processor core.
•
The version number of the processor core.
•
The implementation details of the processor core.

Usage Constraints There are no usage constraints.
Configurations

Available in all configurations.

Attributes

See the register summary in Table 3-1 on page 3-3.

Figure 3-2 shows the CPUID bit assignments.
31

24 23
IMPLEMENTER

20 19

VARIANT

16 15

1 1 1 1

4 3
PARTNO

REVISION

ARCHITECTURE

Figure 3-2 CPUID bit assignments

Table 3-4 shows the CPUID bit assignments.
Table 3-4 CPUID bit assignments
Bits

Name

[31:24]

IMPLEMENTER

Function
Indicates implementer:
ARM.

0x41

[23:20]

ARM DDI 0489D
ID082615

VARIANT

Indicates processor revision:
0x0
Revision 0.
0x1
Revision 1.

3-8

System Control

Table 3-4 CPUID bit assignments (continued)
Bits

Name

Function

[19:16]

ARCHITECTURE

Reads as 0xF.

[15:4]

PARTNO

Indicates part number:
Cortex-M7.

0xC27

[3:0]

REVISION

Indicates patch release:
Patch 0.
0x1
Patch 1.
0x2
Patch 2.
0x0

Note
See Product revisions on page 1-16 for the different Cortex-M7 procesor revisions and the
combinations of the VARIANT and REVISION bit fields used.

3.3.3

Cache Level ID Register
The CLIDR Register characteristics are:
Purpose

•

Indicates the cache levels that are implemented. Architecturally,
there can be a different number of cache levels on the instruction and
data side.

•

Captures the point-of-coherency.

•

Captures the point-of-unification.

Usage constraints The CLIDR is:
•
A read-only register.
•
Accessible in Privileged mode only.
Configurations

Available in all processor configurations.

Attributes

See the register summary in Table 3-5 on page 3-10.

Figure 3-3 shows the CLIDR bit assignments.
31 30 29

27 26

LoUU

24 23

LoC

3 2
Reserved

0
-

Reserved

Figure 3-3 CLIDR bit assignments

ARM DDI 0489D
ID082615

3-9

System Control

Table 3-5 shows the CLIDR bit assignments.
Table 3-5 CLIDR bit assignments

3.3.4

Bits

Name

Function

[31:30]

Reserved.

[29:27]

LoUU

Level of Unification Uniprocessor:
0b001
Level 2, if either cache is implemented.
0b000
Level 1, if neither instruction nor data cache is implemented.

[26:24]

LoC

Level of Coherency:
0b001
Level 2, if either cache is implemented.
0b000
Level 1, if neither instruction nor data cache is implemented.

[23:3]

Reserved.

[2:0]

Level 1 cache type:
0b001
Instruction cache is implemented.
0b010
Data cache is implemented.
0b011
Instruction and data cache are implemented.
0b000
No instruction or data cache are implemented.

Cache Size ID Register
The CCSIDR characteristics are:
Purpose

Provides information about the size and behavior of the instruction or data
cache selected by the CSSELR. Architecturally, there can be up to eight
levels of cache, containing instruction, data, or unified caches. This
processor contains L1 instruction and data caches only.

Usage constraints The CCSIDR is:
•
A read-only register.
•
Accessible in Privileged mode only.
Configurations

Available in all processor configurations.
If no instruction or data cache is configured, the corresponding CCSIDR
is RAZ.

Attributes

See the register summary in Table 3-6 on page 3-11.

Figure 3-4 shows the CCSIDR bit assignments.
31 30 29 28 27

13 12
NumSets

3 2
Associativity

LineSize

WA
RA
WB
WT

Figure 3-4 CCSIDR bit assignments

ARM DDI 0489D
ID082615

3-10

System Control

Table 3-6 shows the CCSIDR bit assignments.
Table 3-6 CCSIDR bit assignments
Bits

Name

Functiona

[31]

Indicates support available for Write-Through:
1
Write-Through support available.

[30]

Indicates support available for Write-Back:
1
Write-Back support available.

[29]

Indicates support available for read allocation:
1
Read allocation support available.

[28]

Indicates support available for write allocation:
1
Write allocation support
available.

[27:13]

NumSets

Indicates the number of sets as:
(number of sets) - 1.
Cache-size dependent.

[12:3]

Associativity

Indicates the number of ways as:
(number of ways) - 1.
0x1
Represents two instruction
caches.
0x3
Represents four data caches.

[2:0]

LineSize

Indicates the number of words in each cache line.
Represents 32 bytes.

0x1

a. See Table 3-7 for valid bit field encodings.

The LineSize field is encoded as 2 less than log(2) of the number of words in the cache line. For
example, a value of 0x0 indicates there are four words in a cache line, that is the minimum size
for the cache. A value of 0x1 indicates there are eight words in a cache line.
Table 3-7 shows the individual bit field and complete register encodings for the CCSIDR. Use
this to determine the cache size for the L1 data or instruction cache selected by the Cache Size
Selection Register (CSSELR). See Cache Size Selection Register on page 3-12.
Table 3-7 CCSIDR encodings

CSSELR

0x0

Cache

Data cache

ARM DDI 0489D
ID082615

Complete
register
encoding

NumSets

Associativity

LineSize

4KB

0xF003E019

0x001F

0x3

0x1

8KB

0xF007E019

0x003F

16KB

0xF00FE019

0x007F

32KB

0xF01FE019

0x00FF

64KB

0xF03FE019

0x01FF

Size

3-11

System Control

Table 3-7 CCSIDR encodings (continued)

CSSELR

0x1

3.3.5

Cache

Complete
register
encoding

NumSets

Associativity

LineSize

4KB

0xF007E009

0x003F

0x1

8KB

0xF00FE009

0x007F

16KB

0xF01FE009

0x00FF

32KB

0xF03FE009

0x01FF

64KB

0xF07FE009

0x03FF

Size

Instruction cache

Cache Size Selection Register
The CSSELR characteristics are:
Purpose

Holds the value that the processor uses to select the CSSELR to use.

Usage constraints The CSSELR is:
•
A read/write register.
•
Accessible in Privileged mode only.
Configurations

Available in all processor configurations.

Attributes

See the register summary in Table 3-8.

Figure 3-5 shows the CSSELR bit assignments.
31

4 3
Reserved

1 0

Level
InD

Figure 3-5 CSSELR bit assignments

Table 3-8 shows the CSSELR bit assignments.
Table 3-8 CSSELR bit assignments
Bits

Name

Function

[31:4]

Reserved.

[3:1]

Level

Identifies which cache level to select.
Level 1 cache.
This field is RAZ/WI.

0b000

[0]

ARM DDI 0489D
ID082615

InD

Selects either instruction or data cache.
0
Data cache.
1
Instruction cache.

3-12

System Control

3.3.6

Instruction and Data Tightly-Coupled Memory Control Registers
The CM7_ITCMCR and CM7_DTCMCR characteristics are:
Purpose

Controls whether an access is mapped to TCM or AXIM interface.

Usage Constraints Accessible in privileged mode only.
Configurations

Available in all configurations.

Attributes

See the register summary in Table 3-1 on page 3-3.

Figure 3-6 shows the CM7_ITCMCR and CM7_DTCMCR bit assignments.
31

7 6
Reserved

3 2 1 0
SZ
RETEN
RMW
EN

Figure 3-6 CM7_ITCMCR and CM7_DTCMCR bit assignments

Table 3-9 shows the CM7_ITCMCR and CM7_DTCMCR bit assignments.
Table 3-9 CM7_ITCMCR and CM7_DTCMCR bit assignments
Bits

Name

Type

Function

[31:7]

Reserved.

[6:3]

TCM size. Indicates the size of the relevant TCM:
No TCM implemented.
0b0011
4KB.
0b0100
8KB.
0b0101
16KB.
0b0110
32KB.
0b0111
64KB.
0b1000
128KB.
0b1001
256KB.
0b1010
512KB.
0b1011
1MB.
0b1100
2MB.
0b1101
4MB.
0b1110
8MB.
0b1111
16MB.
All other encodings are reserved. The reset value is derived from the CFGITCMSZ and CFGDTCMSZ
pins.
0b0000

ARM DDI 0489D
ID082615

3-13

System Control

Table 3-9 CM7_ITCMCR and CM7_DTCMCR bit assignments (continued)
Bits

Name

Type

Function

[2]

RETEN

Retry phase enable. When enabled the processor guarantees to honor the retry output on the
corresponding TCM interface, re-executing the instruction that performed the TCM access.
0
Retry phase disabled.
1
Retry phase enabled.
The reset value is derived from the INITRETRYEN pin. The retry functionality can be used together
with external logic to support error detection and correction in the TCM.

[1]

RMW

Read-Modify-Write (RMW) enable. Indicates that all writes to TCM, that are not the full width of the
TCM RAM, use a RMW sequence:
0
RMW disabled.
1
RMW enabled.
The reset value is derived from the INITRMWEN pin. The RMW functionality can be used together
with external logic to support error detection and correction in the TCM.

[0]

TCM enable. When a TCM is disabled all accesses are made to the AXIM interface.
0
TCM disabled.
1
TCM enabled.
The reset value is derived from the INITTCMEN pin.

3.3.7

AHBP Control Register
The CM7_AHBPCR characteristics are:
Purpose

Controls accesses to AHBP or AXIM interface.

Usage Constraints Accessible in privileged mode only.
Configurations

Available in all configurations.

Attributes

See the register summary in Table 3-1 on page 3-3.

4 3
Reserved

1 0
SZ
EN

Figure 3-7 CM7_AHBPCR bit assignments

ARM DDI 0489D
ID082615

3-14

System Control

Table 3-10 shows the CM7_AHBPCR bit assignments.
Table 3-10 CM7_AHBPCR bit assignments
Bits

Name

Type

Function

[31:4]

Reserved.

[3:1]

AHBP size:
0MB. AHBP disabled.
0b001
64MB.
0b010
128MB.
0b011
256MB.
0b100
512MB.
Other encodings are reserved. Reset values comes from the CFGAHBPSZ pins.
0b000

[0]

3.3.8

AHBP enable:
0
AHBP disabled. When disabled all accesses are made to the AXIM interface.
1
AHBP enabled.
The reset value is derived from the INITAHBPEN pins.

L1 Cache Control Register
The CM7_CACR characteristics are:
Purpose

Controls the L1 ECC and the L1 cache coherency usage model.

Usage Constraints Accessible in privileged mode only.
Configurations

Available in all configurations.

Attributes

See the register summary in Table 3-1 on page 3-3.

Figure 3-8 shows the CM7_CACR bit assignments.
31

3 2 1 0
Reserved
FORCEWT
ECCDIS
SIWT

Figure 3-8 CM7_CACR bit assignments

ARM DDI 0489D
ID082615

3-15

System Control

Table 3-11 shows the CM7_CACR bit assignments.
Table 3-11 CM7_CACR bit assignments

3.3.9

Bits

Name

Type

Function

[31:3]

Reserved, RAZ/WI.

[2]

FORCEWT

Enables Force Write-Through in the data cache:
0
Disables Force Write-Through.
1
Enables Force Write-Through. All Cacheable
memory regions are treated as Write-Through.
This bit is RAZ/WI if the data cache is excluded. If the data cache is
included the reset value of FORCEWT is 0.

[1]

ECCDIS

Enables ECC in the instruction and data cache:
0
Enables ECC in the instruction and data cache. This
is RAO/WI if both data cache and instruction cache
are excluded or if ECC is excluded.
1
Disables ECC in the instruction and data cache. This
is RAZ/WI if data cache is not configured.

[0]

SIWT

Shared cacheable-is-WT for data cache. Enables limited cache
coherency usage:
0
Normal Cacheable Shared locations are treated as
being Non-cacheable. Programmed inner
cacheability attributes are ignored. This is the
default mode of operation for Shared memory. The
data cache is transparent to software for these
locations and therefore no software maintenance is
required to maintain coherency.
1
Normal Cacheable shared locations are treated as
Write-Through. Programmed inner cacheability
attributes are ignored. All writes are globally visible.
Other memory agent updates are not visible to
Cortex-M7 processor software without suitable
cache maintenance.
Useful for heterogeneous MP-systems where, for
example, the Cortex-M7 processor is integrated on
the Accelerator Coherency Port (ACP) interface on
an MP-capable processor.
This bit is RAZ/WI when data cache is not configured.

Auxiliary Bus Fault Status Register
The CM7_ABFSR characteristics are:
Purpose

Stores information on the source of asynchronous bus faults.
In the bus-fault handler, software reads the BFSR and if an asynchronous
fault is observed, the CM7_ABFSR is read to determine which interfaces
are affected. The CM7_ABFSR must be cleared by writing any value to it.
For more information about the BFSR, see the ARMv7-M Architecture
Reference Manual.

Usage Constraints Accessible in privileged mode only. It is reset by nSYSRESET and is
cleared to 0x0 on writes of any value. The value in this register is only
defined when BFSR.IMPRECISERR is 0x1.

ARM DDI 0489D
ID082615

3-16

System Control

Configurations

Available in all configurations.

Attributes

See the register summary in Table 3-1 on page 3-3.

Figure 3-9 shows the CM7_ABFSR bit assignments.
31

10 9 8 7
Reserved

5 4 3 2 1 0

Reserved

AXIMTYPE

EPPB
AXIM
AHBP
DTCM
ITCM

Figure 3-9 CM7_ABFSR bit assignments

Table 3-12 shows the CM7_ABFSR bit assignments.
Table 3-12 CM7_ABFSR bit assignments
Bits

Name

Function

[31:10]

Reserved.

[9:8]

AXIMTYPE

Indicates the type of fault on the AXIM interface:
OKAY.
0b01
EXOKAY.
0b10
SLVERR.
0b11
DECERR.
Only valid when AXIM is 1.
0b00

3.3.10

[7:5]

Reserved.

[4]

EPPB

Asynchronous fault on EPPB interface.

[3]

AXIM

Asynchronous fault on AXIM interface.

[2]

AHBP

Asynchronous fault on AHBP interface.

[1]

DTCM

Asynchronous fault on DTCM interface.

[0]

ITCM

Asynchronous fault on ITCM interface

Instruction Error bank Register 0-1
The IEBR0-1 characteristics are:
Purpose

Stores information about the error detected in the instruction cache during
a cache lookup.

Usage Constraints Accessible in privileged mode only.
Configurations

Available if the ECC configurable option is implemented.

Attributes

See the register summary in Table 3-1 on page 3-3.

Figure 3-10 on page 3-18 shows the IEBR0-1 bit assignments.

ARM DDI 0489D
ID082615

3-17

System Control

31 30 29

18 17 16 15

2 1 0

Reserved

User-defined

RAM location

Type of error
RAM bank

Locked
Valid

Figure 3-10 IEBR0-1 bit assignments

Table 3-13 shows the IEBR0-1 bit assignments.
Table 3-13 IEBR0-1 bit assignments
Bits

Name

Type

Description

[31:30]

User-defined. Error detection logic sets this field to 0b00 on a new allocation and on powerup
reset.

[29:18]

Reserved

[17]

Type of error

Indicates the error type:
0
Correctable error.
1
Non-correctable errora.

[16]

RAM bank

Indicates which RAM bank to use:
0
Tag RAM.
1
Data RAM.

[15:2]

RAM location

Indicates the location in instruction cache RAM:
[14]
Way.
[13:4]
Index.
[3:2]
Line doubleword offset.

[1]

Locked

Indicates whether the location is locked or not locked:
0
Location is not locked and available for hardware to allocate.
1
Location is locked by software. Hardware is not allowed to allocate to this entry.
Reset by powerup reset to 0.

[0]

Valid

Indicates whether the entry is valid or not:
0
Entry is invalid.
1
Entry is valid.
Reset by powerup reset to 0.

a. Non-correctable errors are recorded when errors are found in multiple bits of the data read from the RAM. These errors result in data loss
or data corruption and therefore are non-recoverable.

3.3.11

Data Error bank Register 0-1
The DEBR0-1 characteristics are:
Purpose

Stores information about the error detected in the data cache during a
cache lookup.

Usage Constraints Accessible in privileged mode only.
Configurations

Available if the ECC configurable option is implemented.

Attributes

See the register summary in Table 3-1 on page 3-3.

Figure 3-11 on page 3-19 shows the DEBR0-1 bit assignments.
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3-18

System Control

31 30 29

18 17 16 15
Reserved

User-defined

2 1 0
RAM location

Type of error
RAM bank

Locked
Valid

Figure 3-11 DEBR0-1

Table 3-14 shows the DEBR0-1 bit assignments.
Table 3-14 DEBR0-1 bit assignments
Bits

Name

Type

Description

[31:30]

User-defined. Error detection logic sets this field to 0b00 on a new allocation and on powerup
reset.

[29:18]

Reserved.

[17]

Type of error

Indicates the error type:
0
Correctable error.
1
Non-correctable errora.

[16]

RAM bank

Indicates which RAM bank to use:
0
Tag RAM.
1
Data RAM.

[15:2]

RAM location

Indicates the data cache RAM location:
[15:14]
Way.
[13:5]
Index.
[4:2]
Line word offset.

[1]

Locked

[0]

Valid

Indicates whether the entry is valid or not:
0
Entry is invalid.
1
Entry is valid.
Reset by powerup reset to 0.

a. Non-correctable errors are recorded when errors are found in multiple bits of the data read from the RAM. These errors result in data loss
or data corruption and therefore are non-recoverable.

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3-19

System Control

3.3.12

AHB Slave Control Register
The CM7_AHBSCR characteristics are:
Purpose

Controls the priority between software and AHB slave access to TCMs.
See AHBS interface arbitration on page 5-31.

Usage Constraints Accessible in privileged mode only.
Configurations

Available in all configurations.

Attributes

See the register summary in Table 3-1 on page 3-3.

Figure 3-12 shows the CM7_AHBSCR bit assignments.
31

16 15
Reserved

2 1 0

11 10

INITCOUNT

TPRI

CTL

Figure 3-12 CM7_AHBSCR bit assignments

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3-20

System Control

Table 3-15 shows the CM7_AHBSCR bit assignments.
Table 3-15 CM7_AHBSCR bit assignments
Bits

Name

Type

Function

[31:16]

Reserved.

[15:11]

INITCOUNT

Fairness counter initialization value. Use to demote access priority of the requestor selected by
the CM7_AHBSCR.CTL field. The reset value is 0b01.

Note
•

For round-robin mode set INITCOUNT to 0b01 and CM7_AHBSCR.CTL to 0b00 or
0b01.
INITCOUNT must not be set to 0b00 because the demoted requestor then always takes
priority when contention occurs, and might cause livelock.
INITCOUNT is not used when CM7_AHBSCR.CTL is 0b11.

•
•
[10:2]

TPRI

Threshold execution priority for AHBS traffic demotion.
Priority is TPRI[7:0]. This is the same as the NVIC register encodings.
0b11111111
Priority of -1. This is the priority of the HardFault exception.
0b11111110
Priority of -2. This is the priority of the NMI exception.
0b0xxxxxxx

[1:0]

CTL

AHBS prioritization control:
0b00
AHBS access priority demoted. This is the reset value.
0b01
Software access priority demoted.
0b10
AHBS access priority demoted by initializing the fairness counter to the
CM7_AHBSCR.INITCOUNT value when the software execution priority is
higher than or equal to the threshold level programed in
CM7_AHBSCR.TPRI. When the software execution priority is below this
value, the fairness counter is initialized with 1 (round-robin).

Note
•
•

0b11

ARM DDI 0489D
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The threshold level encoding matches the NVIC encoding and uses
arithmetically larger numbers to represent lower priority.
The current execution priority of the processor is defined architecturally
and includes the effect of the PRIMASK, BASEPRI, and FAULTMASK
special-purpose registers.

AHBSPRI signal has control of access priority.

3-21

Chapter 4
Initialization

This chapter describes how to initialize the processor and which registers to access to enable
functionality before using the processor features. It contains the following section:
•

ARM DDI 0489D
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About Initialization on page 4-2.

4-1

Initialization

4.1

About Initialization
Before you run the application, you might want to:
•
Program particular values into various registers, for example, stack pointers.
•
Enable various processor features, for example, error correction.
•
Program particular values into memory, for example, the Tightly Coupled Memories
(TCMs).
Other initialization requirements are described in:
•
Initializing the MPU.
•
Initializing the FPU.
•
Initializing and enabling the L1 cache on page 4-3.
•
Disabling cache error checking and correction on page 4-4.
•
Enabling the TCM on page 4-4.
•
Preloading TCM on page 4-5.
•
Enabling the TCM retry and read-modify-write on page 4-5.
•
Enabling the AHBP interface on page 4-6
Some of the requirements for initialization are optional depending on the features implemented
in the Cortex-M7 processor.
Note
The Branch predictor is always enabled in the processor, therefore CCR.BP is RAO/WI. See
ARM®v7-M Architecture Reference Manual for more information on the Configuration and
Control register.

4.1.1

Initializing the MPU
If the processor has been implemented with a Memory Protection Unit (MPU), before you can
use it you must enable the MPU in the MPU_CTRL register. See the ARM®v7-M Architecture
Reference Manual for more information.
When setting up the MPU, and if the MPU has previously been programmed, disable unused
regions to prevent any previous region settings from affecting the new MPU setup.

4.1.2

Initializing the FPU
If the processor has been implemented with a Floating Point Unit (FPU) you must enable it
before floating point instructions can be executed. The following code is an example of how to
enable the feature.
CPACR EQU 0xE000ED88
LDR r0, =CPACR
LDR r1, [R0]
; Read CPACR
ORR r1, R1, #(0xF << 20) ; Set bits 20-23 to enable CP10 and CP11 coprocessors
STR r1, [R0]
; Write back the modified value to the CPACR
DSB
ISB

See the ARM®v7-M Architecture Reference Manual for more information.

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4-2

Initialization

Note
Floating point logic is only available with the Cortex-M7 processor with FPU.

4.1.3

Initializing and enabling the L1 cache
If the processor has been implemented with L1 data or instruction caches, they must be
invalidated before they are enabled in software, otherwise UNPREDICTABLE behavior can occur.
Invalidate the entire data cache
Software can use the following code example to invalidate the entire data cache,
if it has been included in the processor. The operation is carried out by iterating
over each line of the cache and using the DCISW register in the Private
Peripheral Bus (PPB) memory region to invalidate the line. The number of cache
ways and sets is determined by reading the CCSIDR register.

CCSIDR
CSSELR
DCISW

EQU 0xE000ED80
EQU 0xE000ED84
EQU 0xE000EF60

; Cache size ID register address
; Cache size selection register address
; Cache maintenance op address: data cache clean and invalidate by set/way

MOV r0, #0x0
LDR r11, =CSSELR
STR r0, [r11]
DSB

; CSSELR selects the cache visible in CCSIDR
; 0 = select “level 1 data cache”
;
;
; Ensure write to CSSELR before proceeding

LDR
LDR
AND
ADD

;
;
;
;

r11, =CCSIDR
r2, [r11]
r1, r2, #0x7
r7, r1, #0x4

From
Read
r1 =
r7 =

CCSIDR
data cache size information
cache line size
number of words in a cache line

UBFX r4, r2, #3, #10

; r4 = number of “ways”-1 of data cache

UBFX r2, r2, #13, #15

; r2 = number of “set”-1 of data cache

CLZ r6, r4

; calculate bit offset for “way” in DCISW

LDR r11, =DCISW

; invalidate cache by set/way

inv_loop1
MOV r1, r4
LSLS r8, r2, r7

; For each “set”
;
r1 = number of “ways”-1
;
shift “set” value to bit 5 of r8

inv_loop2
LSLS r3, r1, r6
ORRS r3, r3, r8
STR r3, [r11]
SUBS r1, r1, #0x1
BGE inv_loop2

; For each “way”
;
shift “way” value to bit 30 in r6
;
merge “way” and “set” value for DCISW
;
invalidate D-cache line
;
decrement “way”
; End for each “way”

SUBS r2, r2, #0x1
BGE inv_loop1

; Decrement “set”
; End for each “set”

DSB
ISB

; Data sync barrier after invalidate cache
; Instruction sync barrier after invalidate cache

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4-3

Initialization

Invalidate instruction cache
You can use the following code example to invalidate the entire instruction cache,
if it has been included in the processor. The operation is carried out by writing to
the ICIALLU register in the PPB memory region.
ICIALLU EQU 0xE000EF50
MOV r0, #0x0
LDR r11, =ICIALLU
STR r0, [r11]
DSB
ISB

Enabling data and instruction caches
You can use the following code example to enable the data and instruction cache
after they have been initialized. The operation is carried out by modifying the
CCR.IC and CCR.DC fields in the PPB memory region.
CCR

EQU 0xE000ED14
LDR
LDR
ORR
ORR
STR

r11, =CCR
r0, [r11]
r0, r0, #0x1:SHL:16
r0, r0, #0x1:SHL:17
r0, [r11]

; Set CCR.DC field
; Set CCR.IC field

DSB
ISB

4.1.4

Disabling cache error checking and correction
If cache error checking and correction is included in the processor it is enabled by default from
reset. The following code example can be used to disable the feature. The operation is carried
out by modifying the CM7_CACR.ECCEN bit the PPB memory region.
CM7_CACR

EQU 0xE000EF9C
LDR
LDR
BFC
STR

r11, =CM7_CACR
r0, [r11]
r0, #0x1, #0x1
r0, [r11]

; Clear CM7_CACR.ECCEN

DSB
ISB

Care must be taken when software changes the error checking fields in the CM7_CACR. If the
fields are changed when the caches contain data, ECC information in the caches might not be
correct for the new setting, resulting in unexpected errors and data loss. Therefore the fields in
the CM7_CACR must only be changed when both caches are turned off and the entire cache
must be invalidated after the change.
4.1.5

Enabling the TCM
The TCM interfaces can be enabled at reset in the system by an external signal on the processor.
If they are disabled at reset then the following code example can be used to enable both the
instruction and data TCM interfaces in software:
CM7_ITCMCR
CM7_DTCMCR

ARM DDI 0489D
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EQU 0xE000EF90
EQU 0xE000EF94

4-4

Initialization

LDR
LDR
ORR
STR

r11, =CM7_ITCMCR
r0, [r11]
r0, r0, #0x1
; Set CM7_ITCMCR.EN field
r0, [r11]

LDR
LDR
ORR
STR

r11, =CM7_DTCMCR
r0, [r11]
r0, r0, #0x1
; Set CM7_DTCMCR.EN field
r0, [r11]

DSB
ISB

4.1.6

Preloading TCM
Methods to preload TCMs include:
Memory copy with running boot code
Where boot code includes a memory copy routine that reads data from a
ROM, and writes it into the appropriate TCM, you must enable the TCM
to do this. This bootcode must be run from an address outside the TCM
region.
DMA into TCM

The System includes a DMA device that reads data from a ROM, and
writes it to the TCMs through the AHB slave interface. This method can
be used to preload the TCM so they can be used by the processor from
reset.

Using the TCM from reset
If the TCM interface is configured to enable the TCM at reset and the reset
vector address is inside the TCM memory region then the processor boots
from TCM. The system must ensure that the bootcode software is present
in the appropriate memory region before execution starts. This can be
accomplished by either initializing the memory before reset or by
transferring the data after reset using the AHB slave interface and
asserting the CPUWAIT input signal. Asserting this signal stops the
processor fetching or executing instructions after reset. When the
CPUWAIT signal is deasserted the processor starts fetching instructions
from the reset vector address in the normal way.
Note
When CPUWAIT has been deasserted to start the processor fetching,
CPUWAIT must not be asserted again except when the processor is under
processor reset or Power-on reset; that is nSYSRESET or nPORESET
asserted. The processor does not halt if the CPUWAIT is asserted while
the processor is running.

4.1.7

Enabling the TCM retry and read-modify-write
If the TCM connected to the processor supports error detection and correction then the TCM
interface must be configured to support the retry and read-modify-write features. These can be
enabled at reset in the system by external signals on the processor. If they are disabled at reset
then the following code example can be used to enable them in software:
CM7_ITCMCR
CM7_DTCMCR

ARM DDI 0489D
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EQU 0xE000EF90
EQU 0xE000EF94

4-5

Initialization

LDR
LDR
ORR
ORR
STR

r11, =CM7_ITCMCR
r0, [r11]
r0, r0, #0x1:SHL:1
r0, r0, #0x1:SHL:2
r0, [r11]

LDR
LDR
ORR
ORR
STR

r11, =CM7_DTCMCR
r0, [r11]
r0, r0, #0x1:SHL:1
r0, r0, #0x1:SHL:2
r0, [r11]

; Set CM7_ITCMCR.RMW field
; Set CM7_ITCMCR.RETEN field

; Set CM7_DTCMCR.RMW field
; Set CM7_DTCMCR.RETEN field

DSB
ISB

4.1.8

Enabling the AHBP interface
The AHBP interface can be enabled at reset in the system by an external signal on the processor.
If it is disabled at reset then the following code example can be used to enable the AHBP
interface from software:
CM7_AHBPCR

EQU 0xE000EF98

LDR
LDR
ORR
STR

r11, =CM7_AHBPCR
r0, [r11]
r0, r0, #0x1
r0, [r11]

; Set CM7_AHBPCR.EN field

DSB
ISB

ARM DDI 0489D
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4-6

Chapter 5
Memory System

This chapter describes the Cortex-M7 processor memory system. It contains the following
sections:
•
About the memory system on page 5-2.
•
Fault handling on page 5-3.
•
Memory types and memory system behavior on page 5-5.
•
AXIM interface on page 5-6.
•
AHB peripheral interface on page 5-22.
•
AHB slave interface on page 5-30.
•
TCM interfaces on page 5-33.
•
L1 caches on page 5-37.

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5-1

Memory System

5.1

About the memory system
This section provides an overview of the Cortex-M7 processor memory system.
The Cortex-M7 processor memory system can be configured during implementation and
integration. It consists of:
•
Separate optional instruction and data caches.
•
Multiple optional Tightly-Coupled Memory (TCM) areas.
•
An AHB Slave (AHBS) interface.
•
An optional Memory Protection Unit (MPU). See Chapter 6 Memory Protection Unit.
•
MBIST interface.
The cache architecture is Harvard, that is, only instructions can be fetched from the instruction
cache, and only data can be read from and written to the data cache.
In parallel with each of the caches are two areas of dedicated RAM accessible to both the
instruction and data sides. These are regions of TCM.
Instruction TCM (ITCM) uses the ITCM interface and the Data TCM (DTCM) uses two
interfaces, D0TCM and D1TCM. Cortex-M7 functional diagram on page 1-6 shows this.
The ITCM interface is 64-bits wide. The DTCM is divided into two 32-bit wide interfaces,
D0TCM and D1TCM. The upper 32-bits of data is on the D1TCM interface and the lower
32-bits of the data is on the D0TCM interface.
Memory accesses to the ITCM, required for fetching instructions and for data transfer
instructions, are performed if the address is in an enabled TCM region. Remaining instruction
accesses and remaining data accesses that are not in a peripheral interface region are looked up
in the appropriate L1 cache if they are cacheable. Accesses that are not serviced by the memory
system are passed through the AXI master (AXIM) interface or the AHBP interface to the
external memory system connected to the processor.
Both instruction and data cache RAM can be configured at implementation time to have Error
Correcting Code (ECC) to protect the data stored in the memory from errors. Each TCM
interface can support external logic to the processor to report to the processor that an error has
occurred.
The processor includes support for direct access to the TCM through the AHBS interface. The
interface provides high bandwidth for DMA traffic to the memory and can be used when the
remainder of the processor is in low-power standby mode, with the internal clock disabled.
The optional MPU handles both the instruction and data memory accesses. The MPU is
responsible for protection checking, address access permissions, and memory attributes for all
accesses. Some of these attributes can be passed through the AXIM interface or AHBP interface
to the external memory system.
The memory system includes a monitor for exclusive accesses. Exclusive load and store
instructions, for example LDREX and STREX, can be used with the appropriate memory monitoring
to provide inter-process or inter-processor synchronization and semaphores. See the ARM®v7-M
Architecture Reference Manual for more information.
The processor is designed for use in chip designs that use the AMBA 4 AXI and AMBA 3
AHB-Lite protocols.

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5-2

Memory System

5.2

Fault handling
Faults can occur on instruction fetches for the following reasons:
•
MPU MemManage.
•
External AXI slave error (SLVERR).
•
External AXI decode error (DECERR).
•
TCM external error.
•
Breakpoints, and vector capture events.
Faults can occur on data accesses for the following reasons:
•
MPU MemManage.
•
Alignment UsageFault.
•
External AXI slave error (SLVERR).
•
External AXI decode error (DECERR).
•
External AHB error from the AHBP port.
•
TCM external error.
•
Watchpoints.
Fault handling is described in:
•
Faults.
•
Usage models on page 5-4.

5.2.1

Faults
The classes of fault that can occur are:
•
MPU faults.
•
External faults.
•
Debug events on page 5-4.
•
Synchronous and asynchronous faults on page 5-4.
MPU faults
The MPU can generate a fault for various reasons. MPU faults are always synchronous, and take
priority over external faults. If an MPU fault occurs on an access that is not in the TCM, the AXI
or AHB transactions for that access are not performed.
External faults
A memory access or instruction fetch performed through the AXIM interface can generate two
different types of error response, a slave error (SLVERR) or decode error (DECERR). These
are known as external AXI errors, because they are generated by the AXI system outside the
processor.
A memory access performed through the AHBP interface can generate a single error response.
The processor manages this in the same way as a response of SLVERR from the AXI interface.
A memory or instruction fetch access performed on the TCM interface can generate a single
error response. The processor manages this in the same way as a response of SLVERR from the
AXI interface.
Synchronous faults are generated for instruction fetches and data loads. All stores generate
asynchronous faults.

ARM DDI 0489D
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5-3

Memory System

Note
An AXI slave device in the system that cannot handle exclusive transactions returns OKAY in
response to an exclusive read. This is also treated as an external error, and the processor behaves
as if the response was SLVERR.

Debug events
The debug logic in the processor can be configured to generate breakpoints or vector capture
events on instruction fetches, and watchpoints on data accesses. If the processor is
software-configured for monitor-mode debugging, a fault is taken when one of these events
occurs, or when a BKPT instruction is executed. For more information, see Chapter 9 Debug.
Synchronous and asynchronous faults
See External faults on page 5-3 for more information about the differences between
synchronous and asynchronous faults.
5.2.2

Usage models
This section describes some methods for handling errors in a system. Exactly how you program
the processor to handle faults depends on the configuration of your processor and system, and
what you are trying to achieve.
If a fault exception is taken, the fault handler reads the information in the link register, Program
Status Register (PSR) in the stack, and fault status registers to determine the type of fault. Some
types of fault are fatal to the system, and others can be fixed, and program execution resumed.
For example, an MPU background MemManage might indicate a stack overflow, and be
rectified by allocating more stack and reprogramming the MPU to reflect this. Alternatively, an
asynchronous external fault might indicate that a software error meant that a store instruction
occurred to an unmapped memory address. Such a fault is fatal to the system or process because
no information is recorded about the address the error occurred on, or the instruction that caused
the fault.
Table 5-1 shows the types of fault that are typically fatal because either the location of the error
is not recorded or the error is unrecoverable. Some faults that are marked as not fatal might turn
out to be fatal in some systems when the cause of the error has been determined. For example,
an MPU background MemManage fault might indicate a stack overflow, that can be rectified,
or it might indicate that, because of a bug, the software has accessed a nonexistent memory
location, that can be fatal. These cases can be distinguished by determining the location where
the error occurred.
Table 5-1 Types of faults

Type of fault

Conditions

Source

Synchronous

Fatal

MPU

Access not permitted by MPUa

MPU

Yes

Synchronous external

Load using external memory interface

AXIM, AHBP

Yes

Asynchronous external

Store to Normal or Device memory using external memory
interface

AXIM, AHBP

Yes

a. See the ARM®v7-M Architecture Reference Manual for more information.

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5-4

Memory System

5.3

Memory types and memory system behavior
The behavior of the memory system depends on the type attribute of the memory that is being
accessed:
•

By default, only Normal, Non-shareable memory regions can be cached in the RAMs.
Caching only takes place if the appropriate cache is enabled and the memory type is
cacheable. Shared cacheable memory regions can be cached if CACR.SIWT is set to 1.

•

The store buffer can merge any stores to Normal memory if they are not from a store
exclusive instruction accessing a memory region marked as Shared. See Store buffer on
page 5-38 for more information.

•

Only non-cached Shared exclusive transactions are marked as exclusive on the external
interface. Load and store exclusive instructions to Shared cacheable memory regions do
not result in any accesses marked as exclusive on the external interface if CACR.SIWT is
set to 1.

•

Only Normal memory is considered restartable, that is, a multi-word transfer can be
abandoned part way through because of an interrupt, to be restarted after the interrupt has
been handled. See Exception handling on page 2-9 for more information about interrupt
behavior.

•

For exclusive accesses to Non-shared memory only the internal exclusive monitor is
updated and checked. Exclusive accesses to Shared memory are checked using the
internal monitor and also, if necessary, using an external monitor using the external
memory interface AXIM or AHBP.

Table 5-2 summarizes the processor memory types and associated behavior.
Table 5-2 Memory types and associated behavior
Can be cached

Merging

Restartable

Exclusives
handled

Shared

Noa

Yes

Internal and external

Non-shared

Yes

Internal only

Shared

Internal and external

Non-shared

Internal only

Shared

Internal and external

Memory type
Normal

Device

Strongly-ordered

a. Unless CACR.SIWT is set to 1.

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5-5

Memory System

5.4

AXIM interface
This section describes the AXIM interface. The AXIM interface is a single 64-bit wide interface
that connects to a external memory system. It is used for:
•
Instruction fetches.
•
Data cache linefills and evictions.
•
Non-cacheable Normal-type memory data accesses.
•
Device and Strongly-ordered type data accesses, normally to peripherals.
The AXIM interface conforms to the AXI4 standard as described in the ARM® AMBA® AXI and
ACE Protocol Specification. Within the AXI standard, the AXIM interface uses a number of
extension signals to indicate inner memory attributes and the request source. See AXI extensions
on page 5-10.
The AXIM interface can run at the same frequency as the processor or at a lower synchronous
frequency.
Note
References in this section to an AXI slave refer to the AXI slave in the external system that is
connected to the processor AXIM interface.
The following sections describe the attributes of the AXIM interface, and provide information
about the types of burst generated:
•
AXI attributes and transactions.
•
Identifiers for AXIM interface accesses on page 5-9.
•
AXI extensions on page 5-10.
•
Memory system implications for AXI accesses on page 5-10.

5.4.1

AXI attributes and transactions
Table 5-3 shows the AXI attributes and transactions for the AXIM interface when the processor
is configured with the L1 data cache. This is for use in a native AXI system with high memory
bandwidth and supports multiple outstanding transactions, also known as a high performance
AXIM interface.
Table 5-3 High performance AXIM attributes and transactions

Attribute

Value

Description

Write issuing capability

Consisting of:
•
15 writes to Strongly-ordered or Device memory.
•
24 writes to Normal memory, that can be evictions, write bursts or single writes. A
maximum of 17 of these can be to cacheable memory and a maximum of 10 to
Non-cacheable or shareable memory.

Read issuing capability

Consisting of:
•
2 data linefills.
•
4 Non-cacheable data reads.
•
1 instruction fetch or instruction linefill.

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5-6

Memory System

Table 5-3 High performance AXIM attributes and transactions (continued)
Attribute

Value

Description

Write ID capability

Consisting of:
•
1 reserved for Strongly-ordered or Device memory.
•
1 reserved for Normal, cacheable and Non-shareable memory.
•
1 reserved for Normal, Non-cacheable or Shareable memory.
•
1 reserved for cache line evictions (Normal, cacheable, Write-Back memory).

Read ID capability

Combined issuing capability

Consisting of:
•
39 outstanding writes.
•

1 instruction fetcha.

a. The maximum issuing capability of the memory system is limited to one outstanding instruction read because all data reads are hazarded in
the BIU when the maximum number of write transactions have been issued.

Only a subset of all possible AXI transactions can be generated. These are:
•

•

For Normal, cacheable memory:
—

WRAP4 64-bit reads, for load and Write-Back Write-Allocate store linefills and
instruction linefills.

—

INCR4 64-bit writes, for evictions.

—

INCR N (N:1-4) 64-bit for write transfers, for coalesced individual Write-Through
or Write-Back, no Write-Allocate stores.

—

INCR N (N:1-4) 64-bit for read transfers, for loads when the data cache is disabled,
or for instruction fetches when the instruction cache is disabled.

For Normal, Non-cacheable memory:
—

INCR N (N:1-4) 64-bit for read transfers, for individual loads and load multiplies.

—

INCR N (N:1-4) 64-bit for write transfers, for coalesced individual stores and store
multiples.

—

INCR N (N:1-4) 64-bit for read transfers, for instruction fetches.

—

INCR 1 8-bit, 16-bit, and 32-bit exclusive reads and writes, for shared exclusives.

For Strongly-ordered or Device memory:
—

INCR 1 8-bit, 16-bit and 32-bit reads and writes, for individual load and stores.

—

INCR 1 32-bit for read transfers, load multiples.

—

INCR N (N:1-2) 32-bit for write transfers, for store multiples.

—

INCR 1 8-bit, 16-bit and 32-bit exclusive reads and writes, for shared exclusives.

•

No FIXED bursts are used.

•

Write bursts to Normal memory can use the following optimizations:
—

Entire beats with no strobes set.

—

Non-contiguous strobes per beat.

These are allowed on AXI but have implications for bridging to AHB.
For more information on IDs used for different transactions, see Identifiers for AXIM interface
accesses on page 5-9.

ARM DDI 0489D
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Memory System

Table 5-4 shows the AXI attributes and transactions for when the processor is not configured to
include the L1 data cache. That is, if you want to use it in a low-cost AXI system, or bridged to
AHB, that has a low-bandwidth memory system, like on an off-chip memory system.
Table 5-4 Area optimized AXIM attributes and transactions
Attribute

Value

Description

Write issuing capability

Consisting of:
•
15 writes to Strongly-ordered or Device memory.
•
10 writes to Normal memory.

Read issuing capability

Consisting of:
•
4 data read.
•
1 instruction fetch or instruction linefill.

Write ID capability

Consisting of:
•
1 reserved for Strongly-ordered or Device memory.
•
1 reserved for Normal memory.

Read ID capability

Combined issuing capability

Consisting of:
•
25 outstanding writes.
•

1 instruction fetcha.

a. The maximum issuing capability of the memory system is limited to one outstanding instruction read
because all data reads are hazarded in the BIU when the maximum number of write transactions have
been issued.

Only a subset of all possible AXI transactions is generated. These are:
•

For Normal memory:
—

WRAP4 64-bit read transfers, for instruction linefills where instruction cache is
included.

—

INCR N (N:1-4) 64-bit for read transfers, for individual loads and load multiplies.

—

INCR N (N:1-4) 64-bit for write transfers, for coalesced individual stores and store
multiples.

—

INCR N (N:1-4) 64-bit for read transfers, for Non-cacheable instruction fetches or
all instruction fetches with no instruction cache.

—

INCR 1 8-bit, 16-bit and 32-bit exclusive reads and writes, for shared exclusives.

•

For Strongly-ordered or Device memory:
— INCR N (N:1-2) 32-bit for read transfers, for individual loads and load multiples.
— INCR N (N:1-2) 32-bit for write transfers, for individual stores and store multiples.
— INCR 1 8-bit, 16-bit and 32-bit exclusive reads and writes, for shared exclusives.

•

No FIXED bursts are used.

•

Write bursts to Normal memory can use the following optimizations:
— Entire beats with no strobes set.
— Non-contiguous strobes per beat.
These are allowed on AXIM interface but have implications for bridging to AHB.
For more information on IDs used for different transactions, see Identifiers for AXIM
interface accesses on page 5-9.

ARM DDI 0489D
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Memory System

5.4.2

Identifiers for AXIM interface accesses
The following ID values are for read and write channels, and Write-Allocate memory accesses
on the AXIM interface:
•

•

Read channels, ARID[2:0], RID[2:0]:
0b000

Normal Non-cacheable, Device, and Strongly-ordered reads.

0b011, 0b010

Data cache line-fills.

0b100

Instruction fetches.

Write channels, AWID[1:0], WID[1:0], BID[1:0]:
0b00

Normal, Non-cacheable writes, All shared exclusive writes, for
example from STREX.

0b01

Normal cacheable writes to Write-Through and Write-Back, Non
Write-Allocate memory.

0b10

Device and Strongly-ordered writes.

0b11

Evictions to Normal cacheable Write-Back memory.

WID is not a required signal for AMBA 4 AXI. It is included for compatibility with AMBA 3
AXI systems.
5.4.3

AXI privilege information
AXI provides information about the privilege level of an access on the ARPROT and
AWPROT signals. However, when accesses might be cached or merged together, the resulting
transaction can have both privileged and user data combined. If this happens, the Cortex-M7
processor marks the transaction as privileged, even if it was initiated by a user process.
Table 5-5 shows Cortex-M7 mode and APROT values.
Table 5-5 Cortex-M7 mode and APROT values
Processor mode

Type of access

Value of APROT

Cacheable read access

Always marked as Privileged

User

Non-cacheable read access

User except for LDM, LDRD and POP when the L1 data cache is
implemented

Privileged
User

Device or Strongly-ordered
read access

User

Cacheable write access

Always marked as Privileged

User

Device or Strongly-ordered
write access

User

Normal non-cacheable write
access

Privileged, except for STREXB, STREXH, and STREX

Privileged

Privileged
User
Privileged

5.4.4

Privileged

Write response
The AXIM interface requires that the slave does not return a write response until it has received
the write address.

ARM DDI 0489D
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Memory System

Note
This write response requirement is mandatory for systems using the AMBA 4 AXI protocol. It
is also required if the Cortex-M7 processor is used with an external memory system using the
AMBA 3 AXI protocol.

5.4.5

AXI extensions
The AXIM interface uses the ARCACHE and AWCACHE AXI signals and the ARSHARE,
AWSHARE, ARINNER, and AWINNER extension signals to indicate the memory attributes
of the transfer, as returned by the MPU:
•

ARCACHE and AWCACHE of the master interface are generated from the memory
type and outer region attributes.

•

ARINNER and AWINNER are generated from the memory type and inner region
attributes.

•

ARSHARE and AWSHARE are asserted for transactions to shared memory regions.

In additional to these attribute extension signals the AXIM interface includes the following
signals:
AWMASTER and ARMASTER
Indicates the source of the memory request. When set to:

AWSPARSE

The request has been generated by software running on the
processor.

The request has been generated by a debug request on the AHB
Debug (AHBD) interface.

The AWSPARSE is part of the write address channel signal group and
indicates the burst uses sparse byte write-strobes, that is some of the beats
of the write burst do not contain data. You can use this signal to optimize
systems that bridge the AMBA 4 AXI protocol to AHB protocol.

See the ARM® AMBA® AXI and ACE Protocol Specification for valid encodings for all the
AxCACHE and AxINNER signals.
5.4.6

Memory system implications for AXI accesses
The attributes of the memory being accessed can affect an AXI access. The memory system can
cache any Normal memory address that is marked as either:
•
Cacheable, Write-Back, Read-Allocate, Write-Allocate, Non-shareable.
•
Cacheable, Write-Back, Read-Allocate only, Non-shareable.
•
Cacheable, Write-Through, Read-Allocate only, Non-shareable.
However, Device and Strongly-ordered memory is always Non-cacheable. Also, any unaligned
access to Device or Strongly-ordered memory generates alignment UsageFault and therefore
does not cause any AXI transfer. This means that the access examples given in this chapter never
show unaligned accesses to Device or Strongly-ordered memory.
Note
Memory regions marked as Non-Cacheable Normal must not be used to access read-sensitive
peripherals in a system. This is because read transactions to these regions from the processor
can be repeated multiple times if the originating load instruction is interrupted.

ARM DDI 0489D
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5-10

Memory System

5.4.7

AXIM interface transfers
The processor conforms to the ARM® AMBA® AXI and ACE Protocol Specification, but it does
not generate all the AXI transaction types that the specification permits. This section describes
the types of AXI transaction that the AXIM interface does not generate.
If you are designing an AXI slave to work only with the Cortex-M7 processor, and there are no
other AXI masters in your system, you can take advantage of these restrictions and the interface
attributes, described in Table 5-3 on page 5-6, to simplify the slave.
This section also contains tables that show some examples of the types of AXI burst that the
processor generates. However, because a particular type of transaction is not shown here does
not mean that the processor does not generate such a transaction.
Note
An AXI slave device connected to the AXIM interface must be capable of handling every kind
of transaction permitted by the ARM® AMBA® AXI and ACE Protocol Specification, except
where there is an explicit statement in this chapter that such a transaction is not generated. You
must not infer any additional restrictions from the example tables given.
Load and store instructions to Non-cacheable memory might not result in an AXI transfer
because the data might either be retrieved from, or merged into the internal store data buffers.
The exceptions to this are loads or stores to Strongly-ordered or Device memory. These always
result in AXI transfers. See Strongly-ordered and Device transactions on page 5-12.
Restrictions on AXI transfers on page 5-12 describes restrictions on the type of transfers that the
AXIM interface generates. If the processor is powered up, the buffered write response and read
data channel ready signals, BREADY and RREADY, are always asserted. They are deasserted
when the processor enters Dormant or Shutdown mode. You must not make any other
assumptions about the AXI handshaking signals, except that they conform to the ARM® AMBA®
AXI and ACE Protocol Specification.
The following sections give examples of transfers generated by the AXIM interface:
•
Restrictions on AXI transfers on page 5-12.
•
Strongly-ordered and Device transactions on page 5-12.
•
Linefills on page 5-17.
•
Cache line write-back (eviction) on page 5-17.
•
Non-cacheable reads on page 5-17.
•
Non-cacheable, Write-Back no Write-Allocate or Write-Through writes on page 5-17.
•
AXI transaction splitting on page 5-18.
•
Normal write merging on page 5-19.

ARM DDI 0489D
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Memory System

Restrictions on AXI transfers
The AXIM interface applies the following restrictions to the AXI transactions it generates:
•

A burst never transfers more than 32 bytes.

•

The burst length is never more than four transfers.

•

The maximum length of a Strongly-ordered or Device write burst is two transfers.
Strongly-ordered or Device reads are always one transfer.

•

No transaction ever crosses a 32-byte boundary in memory. See AXI transaction splitting
on page 5-18.

•

FIXED bursts are never used.

•

The write address channel always issues INCR type bursts, and never WRAP or FIXED.

•

WRAP type read bursts, see Linefills on page 5-17:
— Are used only for linefills (reads) of cacheable Normal memory.
— Always have a size of 64 bits, and a length of four transfers.
— Always have a start address that is 64-bit aligned.

•

If the transfer size is 8 bits or 16 bits then the burst length is always one transfer.

•

The transfer size is never greater than 64 bits, because it is a 64-bit AXI bus.

•

Instruction fetches, identified by ARPROT[2], are always a 64 bit transfer size, and never
locked or exclusive.

•

Transactions to Device and Strongly-ordered memory are always to addresses that are
aligned for the transfer size. See Strongly-ordered and Device transactions.

•

Exclusive accesses are always to addresses that are aligned for the transfer size.

•

Only exclusive accesses to shared memory result in exclusive accesses on the AXIM,
identified by ARLOCK and AWLOCK. Exclusive accesses to non-shared memory are
marked as non-exclusive accesses on the bus.

Strongly-ordered and Device transactions
A load or store instruction to or from Strongly-ordered or Device memory always generates AXI
transactions of the same size as implied by the instruction. All accesses using LDM, STM, LDRD, or
STRD instructions to Strongly-ordered or Device memory occur as 32-bit transfers.
LDRB

Table 5-6 shows the values of ARADDR, ARBURST, ARSIZE, and ARLEN for a LDRB from
bytes 0-7 in Strongly-ordered or Device memory.
Table 5-6 LDRB from Strongly-ordered or Device

ARM DDI 0489D
ID082615

Address[2:0]

ARADDR

ARBURST

ARSIZE

ARLEN

0x0 (byte 0)

0x00

Incr

8-bit

1 data transfer

0x1 (byte 1)

0x01

Incr

8-bit

1 data transfer

0x2 (byte 2)

0x02

Incr

8-bit

1 data transfer

0x3 (byte 3)

0x03

Incr

8-bit

1 data transfer

5-12

Memory System

Table 5-6 LDRB from Strongly-ordered or Device (continued)
Address[2:0]

ARADDR

ARBURST

ARSIZE

ARLEN

0x4 (byte 4)

0x04

Incr

8-bit

1 data transfer

0x5 (byte 5)

0x05

Incr

8-bit

1 data transfer

0x6 (byte 6)

0x06

Incr

8-bit

1 data transfer

0x7 (byte 7)

0x07

Incr

8-bit

1 data transfer

LDRH

Table 5-7 shows the values of ARADDR, ARBURST, ARSIZE, and ARLEN for a LDRH from
halfwords 0-3 in Strongly-ordered or Device memory.
Table 5-7 LDRH from Strongly-ordered or Device memory
Address[2:0]

ARADDR

ARBURST

ARSIZE

ARLEN

0x0 (halfword 0)

0x00

Incr

16-bit

1 data transfer

0x2 (halfword 1)

0x02

Incr

16-bit

1 data transfer

0x4 (halfword 2)

0x04

Incr

16-bit

1 data transfer

0x6 (halfword 3)

0x06

Incr

16-bit

1 data transfer

Note
A load of a halfword from Strongly-ordered or Device memory addresses 0x1, 0x3, 0x5, or 0x7
generates an alignment UsageFault.
LDR or LDM that transfers one register

Table 5-8 shows the values of ARADDR, ARBURST, ARSIZE, and ARLEN for a LDR or an
LDM that transfers one register (an LDM1) in Strongly-ordered or Device memory.
Table 5-8 LDR or LDM1 from Strongly-ordered or Device memory
Address[2:0]

ARADDR

ARBURST

ARSIZE

ARLEN

0x0 (word 0)

0x00

Incr

32-bit

1 data transfer

0x4 (word 1)

0x04

Incr

32-bit

1 data transfer

Note
A load of a word from Strongly-ordered or Device memory addresses 0x1, 0x2, 0x3, 0x5, 0x6, or
0x7 generates an alignment UsageFault.

ARM DDI 0489D
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Memory System

LDM that transfers two registers

Table 5-9 shows the values of ARADDR, ARBURST, ARSIZE, and ARLEN for a LDM that
transfers two registers (an LDM2) in Strongly-ordered or Device memory.
Table 5-9 LDM2, Strongly-ordered or Device memory
Address[3:0]

ARADDR

ARBURST

ARSIZE

ARLEN

0x0 (word 0)

0x00

Incr

32-bit

1 data transfer

0x04

Incr

32-bit

1 data transfer

0x04

Incr

32-bit

1 data transfer

0x08

Incr

32-bit

1 data transfer

0x08

Incr

32-bit

1 data transfer

0x0C

Incr

32-bit

1 data transfer

0x0C

Incr

32-bit

1 data transfer

0x10

Incr

32-bit

1 data transfer

0x4 (word 1)

0x8 (word 2)

0xC (word 3)

Note
A load-multiple from address 0x1, 0x2, 0x3, 0x5, 0x6, 0x7, 0x9, 0xA, 0xB, 0xD, 0xE, or 0xF generates
an alignment UsageFault.
STRB

Table 5-10 shows the values of AWADDR, AWBURST, AWSIZE, AWLEN, and WSTRB for
an STRB to Strongly-ordered or Device memory over the AXIM interface.
Table 5-10 STRB to Strongly-ordered or Device memory

ARM DDI 0489D
ID082615

Address[2:0]

AWADDR

AWBURST

AWSIZE

AWLEN

WSTRB

0x0 (byte 0)

0x00

Incr

8-bit

1 data transfer

0b00000001

0x1 (byte 1)

0x01

Incr

8-bit

1 data transfer

0b00000010

0x2 (byte 2)

0x02

Incr

8-bit

1 data transfer

0b00000100

0x3 (byte 3)

0x03

Incr

8-bit

1 data transfer

0b00001000

0x4 (byte 4)

0x04

Incr

8-bit

1 data transfer

0b00010000

0x5 (byte 5)

0x05

Incr

8-bit

1 data transfer

0b00100000

0x6 (byte 6)

0x06

Incr

8-bit

1 data transfer

0b01000000

0x7 (byte 7)

0x07

Incr

8-bit

1 data transfer

0b10000000

5-14

Memory System

STRH

Table 5-11 shows the values of AWADDR, AWBURST, AWSIZE, AWLEN, and WSTRB for
an STRH over the AXIM interface to Strongly-ordered or Device memory.
Table 5-11 STRH to Strongly-ordered or Device memory
Address[2:0]

AWADDR

AWBURST

AWSIZE

AWLEN

WSTRB

0x0 (halfword 0)

0x00

Incr

16-bit

1 data transfer

0b00000011

0x2 (halfword 1)

0x02

Incr

16-bit

1 data transfer

0b00001100

0x4 (halfword 2)

0x04

Incr

16-bit

1 data transfer

0b00110000

0x6 (halfword 3)

0x06

Incr

16-bit

1 data transfer

0b11000000

Note
A store of a halfword to Strongly-ordered or Device memory addresses 0x1, 0x3, 0x5, or 0x7
generates an alignment UsageFault.
STR or STM of one register

Table 5-12 shows the values of AWADDR, AWBURST, AWSIZE, AWLEN, and WSTRB for
an STR or an STM that transfers one register (an STM1) over the AXIM interface to Strongly-ordered
or Device memory.
Table 5-12 STR or STM1 to Strongly-ordered or Device memory
Address[2:0]

AWADDR

AWBURST

AWSIZE

AWLEN

WSTRB

0x0 (word 0)

0x00

Incr

32-bit

1 data transfer

0b00001111

0x4 (word 1)

0x04

Incr

32-bit

1 data transfer

0b11110000

Note
A store of a word to Strongly-ordered or Device memory addresses 0x1, 0x2, 0x3, 0x5, 0x6, or 0x7
generates an alignment UsageFault.
STM of five registers

Table 5-13 shows the values of AWADDR, AWBURST, AWSIZE, AWLEN, and first
WSTRB for an STM that writes five registers (an STM5) over the AXIM interface to
Strongly-ordered or Device memory.
Table 5-13 STM5 to Strongly-ordered or Device memory to word 0 or 1

ARM DDI 0489D
ID082615

Address[4:0]

AWADDR

AWBURST

AWSIZE

AWLEN

First WSTRB

0x00 (word 0)

0x00

Incr

32-bit

2 data transfer

0b00001111

0x08

Incr

32-bit

2 data transfers

0b00001111

0x10

Incr

32-bit

1 data transfer

0b00001111

5-15

Memory System

Table 5-13 STM5 to Strongly-ordered or Device memory to word 0 or 1 (continued)
Address[4:0]

AWADDR

AWBURST

AWSIZE

AWLEN

First WSTRB

0x04 (word 1)

0x04

Incr

32-bit

1 data transfer

0b11110000

0x08

Incr

32-bit

2 data transfers

0b00001111

0x10

Incr

32-bit

2 data transfers

0b00001111

Note
A store-multiple to address 0x1, 0x2, 0x3, 0x5, 0x6, or 0x7 generates an alignment UsageFault.

ARM DDI 0489D
ID082615

5-16

Memory System

Linefills
Loads and instruction fetches from Normal, cacheable memory that do not hit in the cache
generate a cache linefill when the appropriate cache is enabled. Table 5-14 shows the values of
ARADDR, ARBURST, ARSIZE, and ARLEN for cache linefills.
Table 5-14 Linefill behavior on the AXI interface
Address[4:0]a

ARADDR

ARBURST

ARSIZE

ARLEN

0x00-0x07

0x00

Wrap

64-bit

4 data transfers

0x08-0x0F

0x08

Wrap

64-bit

4 data transfers

0x10-0x17

0x10

Wrap

64-bit

4 data transfers

0x18-0x1F

0x18

Wrap

64-bit

4 data transfers

a. These are the bottom five bits of the address of the access that cause the
linefill, that is, the address of the critical word.

Cache line write-back (eviction)
When a valid and dirty cache line is evicted from the data cache, a write-back of the data must
occur. Table 5-15 shows the values of AWADDR, AWBURST, AWSIZE, and AWLEN for
cache line write-backs, over the AXIM interface.
Table 5-15 Cache line write-back
AWADDR[4:0]

AWBURST

AWSIZE

AWLEN

0x00

Incr

64-bit

4 data transfers

Non-cacheable reads
Load instructions accessing Non-cacheable Normal memory generate AXI bursts that are not
necessarily the same size or length as the instruction implies. In addition, if the data to be read
is contained in the store buffer, the instruction might not generate an AXI read transaction at all.
Non-cacheable, Write-Back no Write-Allocate or Write-Through writes
Store instructions to Non-cacheable, Write-Back no Write-Allocate Cacheable and
Write-Through Cacheable memory generate AXI bursts that are not necessarily the same size
or length as the instruction implies. The AXIM interface asserts byte-lane-strobes,
WSTRB[7:0], to ensure that only the bytes that were written by the instruction are updated.
The tables in this section give examples of the types of AXI transaction that might result from
various store instructions, accessing various addresses in Normal memory. They are provided
as examples only, and are not an exhaustive description of the AXI transactions. Depending on
the state of the processor, and the timing of the accesses, the actual bursts generated might have
a different size and length to the examples shown, even for the same instruction.
In addition, write operations to Normal memory can be merged to create more complex AXI
transactions. See Normal write merging on page 5-19 for examples.

ARM DDI 0489D
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5-17

Memory System

Table 5-16 shows possible values of AWADDR, AWBURST, AWSIZE, AWLEN, and
WSTRB for an STRH to Normal memory.
Table 5-16 STRH to Cacheable write-through or Non-cacheable Normal memory
Address[2:0]

AWADDR

AWBURST

AWSIZE

AWLEN

WSTRB

0x0 (byte 0)

0x00

Incr

64-bit

1 data transfer

0b00000011

0x1 (byte 1)

0x00

Incr

64-bit

1 data transfer

0b00000110

0x2 (byte 2)

0x00

Incr

64-bit

1 data transfer

0b00001100

0x3 (byte 3)

0x00

Incr

64-bit

1 data transfer

0b00011000

0x4 (byte 4)

0x00

Incr

64-bit

1 data transfer

0b00110000

0x5 (byte 5)

0x00

Incr

64-bit

1 data transfer

0b01100000

0x6 (byte 6)

0x00

Incr

64-bit

1 data transfer

0b11000000

0x7 (byte 7)

0x00

Incr

64-bit

1 data transfer

0b10000000

0x08

Incr

64-bit

1 data transfer

0b00000001

Table 5-17 shows possible values of AWADDR, AWBURST, AWSIZE, AWLEN, and
WSTRB for an STR that transfers one register to Normal memory through the AXIM interface.
Table 5-17 STR to Cacheable write-through or Non-cacheable Normal memory
Address[2:0]

AWADDR

AWBURST

AWSIZE

AWLEN

WSTRB

0x0 (byte 0) (word 0)

0x00

Incr

64-bit

1 data transfer

0b00001111

0x1 (byte 1)

0x00

Incr

64-bit

1 data transfer

0b00011110

0x2 (byte 2)

0x00

Incr

64-bit

1 data transfer

0b00111100

0x3 (byte 3)

0x00

Incr

64-bit

1 data transfer

0b01111000

0x4 (byte 4) (word 1)

0x00

Incr

64-bit

1 data transfer

0b11110000

0x5 (byte 5)

0x00

Incr
Incr

64-bit
64-bit

1 data transfer
1 data transfer

0b11100000

Incr
Incr

64-bit
64-bit

1 data transfer
1 data transfer

0b11000000

Incr
Incr

64-bit
64-bit

1 data transfer
1 data transfer

0b10000000

0x08
0x6 (byte 6)

0x00
0x08

0x7 (byte 5)

0x00
0x08

0b00000001

0b00000011

0b00000111

AXI transaction splitting
The processor splits AXI bursts when it accesses addresses across a cache line boundary, that
is, a 32-byte boundary. An instruction that accesses memory across one or two 32-byte
boundaries generates two or three AXI bursts respectively. The following examples show this
behavior. They are provided as examples only, and are not an exhaustive description of the AXI
transactions. Depending on the state of the processor, and the timing of the accesses, the actual
bursts generated might have a different size and length to the examples shown, even for the same
instruction.

ARM DDI 0489D
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5-18

Memory System

For example, LDMIA R10, {R0-R5} loads six words from Non-cacheable, Normal memory. The
number of AXI transactions generated by this instruction depends on the base address, R10:
•

If all six words are in the same cache line, there is a single AXI transaction. For example,
for LDMIA R10, {R0-R5} with R10 = 0x1008, the interface might generate a burst of three,
64-bit read transfers, as shown in Table 5-18.
Table 5-18 AXI transaction splitting, all six words in same cache line

•

ARADDR

ARBURST

ARSIZE

ARLEN

0x1008

Incr

64-bit

3 data transfers

If the data comes from two cache lines, then there are two AXI transactions. For example,
for LDMIA R10, {R0-R5} with R10 = 0x1010, the interface might generate one burst of two
64-bit reads, and one burst of a single 64-bit read, as shown in Table 5-19.
Table 5-19 AXI transaction splitting, data in two cache lines
ARADDR

ARBURST

ARSIZE

ARLEN

0x1010

Incr

64-bit

2 data transfers

0x1020

Incr

64-bit

1 data transfer

Table 5-20 shows possible values of ARADDR, ARBURST, ARSIZE, and ARLEN for an LDR
to Non-cacheable Normal memory that crosses a cache line boundary.
Table 5-20 Non-cacheable LDR or LDM1 crossing a cache line boundary
Address[4:0]

ARADDR

ARBURST

ARSIZE

ARLEN

0x1D (byte 29)

0x1D

Incr

32-bit

1 data transfer

0x20

Incr

32-bit

1 data transfer

0x1E

Incr

32-bit

1 data transfer

0x20

Incr

32-bit

1 data transfer

0x1F

Incr

32-bit

1 data transfer

0x20

Incr

32-bit

1 data transfer

0x1E (byte 30)

0x1F (byte 31)

Table 5-21 shows possible values of AWADDR, AWBURST, AWSIZE, AWLEN, and
WSTRB for an STRH to Non-cacheable Normal memory that crosses a cache line boundary.
Table 5-21 Non-cacheable STRH crossing a cache line boundary
Address[4:0]

AWADDR

AWBURST

AWSIZE

AWLEN

WSTRB

0x1F (byte 31)

0x18

Incr

64-bit

1 data transfer

0b10000000

0x20

Incr

64-bit

1 data transfer

0b00000001

Normal write merging
A store instruction to Non-cacheable, Write-Back no Write-Allocate Cacheable, or
Write-Through Cacheable Normal memory might not result in an AXI transfer because of the
merging of store data in the internal buffers.
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5-19

Memory System

The store buffer can detect when it contains more than one write request to the same cache line
for Write-Through Cacheable or Non-cacheable Normal memory. This means it can combine
the data from more than one instruction into a single write burst to improve the efficiency of the
AXI interface. If the AXIM receives several write requests that do not form a single contiguous
burst it can choose to output a single burst, with the WSTRB signal low for the bytes that do
not have any data.
For write accesses to Normal memory, the store can perform writes out of order, if there are no
address dependencies. It can do this to best use its ability to merge accesses.
The instruction sequence in Example 5-1 shows the merging of writes.
Example 5-1 Write merging

MOV r0, #0x4000
STRH r1, [r0, #0x18];
STR
r2, [r0, #0xC] ;
STMIA r0, {r4-r7}
;
STRB r3, [r0, #0x1D];

Store
Store
Store
Store

a halfword at 0x4018
a word at 0x400C
four words at 0x4000
a byte at 0x401D

Table 5-22 shows the values of AWADDR, AWBURST, AWSIZE, AWLEN, and WSTRB
generated if the memory at address 0x4000 is marked as Strongly-ordered or Device type
memory.
Table 5-22 AXI transactions for Strongly-ordered or Device type memory
AWADDR

AWBURST

AWSIZE

AWLEN

WSTRB

0x4018

Incr

16-bit

1 data transfer

0b00000011

0x400C

Incr

32-bit

1 data transfer

0b11110000

0x4000

Incr

32-bit

2 data transfers

0b00001111
0b11110000

0x4008

Incr

32-bit

2 data transfers

0b00001111
0b11110000

0x401D

Incr

8-bit

1 data transfer

0b00100000

In Example 5-1, each store instruction produces an AXI burst of the same size as the data written
by the instruction.
Table 5-23 shows a possible resulting transaction if the same memory is marked as
Non-cacheable Normal, or Write-Through Cacheable.
Table 5-23 AXI transactions for Non-cacheable Normal or Write-Through Cacheable
memory
AWADDR

AWBURST

AWSIZE

AWLEN

WSTRB

0x4000

Incr

64-bit

4 data transfers

0b11111111
0b11111111
0b00000000
0b00100011

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5-20

Memory System

In this example:
•

The store buffer has merged the STRB and STRH writes into one buffer entry, and therefore
a single AXI transfer, the fourth in the burst.

•

The writes, that occupy three buffer entries, have been merged into a single AXI burst of
four transfers.

•

The write generated by the STR instruction has not occurred, because it was overwritten by
the STM instruction.

•

The write transfers have occurred out of order with respect to the original program order.

The transactions shown in Table 5-23 on page 5-20 show this behavior. They are provided as
examples only, and are not an exhaustive description of the AXI transactions. Depending on the
state of the processor, and the timing of the accesses, the actual bursts generated might have a
different size and length to the examples shown, even for the same instruction.
If the same memory is marked as Write-Back Cacheable, and the addresses are allocated into a
cache line, no AXI write transactions occur until the cache line is evicted and performs a
write-back transaction. See Cache line write-back (eviction) on page 5-17.

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5-21

Memory System

5.5

AHB peripheral interface
This section describes the attributes of the AHB-Lite Peripheral (AHBP) interface, and provides
information about the types of burst generated.
The AHBP interface is a single 32-bit wide interface that connects to an external memory
system. It is used only for data access. Instruction fetches are never performed on the interface.

5.5.1

AHBP interface transfers
The AHBP interface conforms to the AHB-Lite specification, but it does not generate all the
AHB transaction types that the specification permits. This section describes the types of AHB
transaction that the AHBP interface does not generate. If you are designing an AHB slave to
work only with the Cortex-M7 processor AHBP interface, you can take advantage of these
restrictions and the interface attributes described in the following sections to simplify the slave.
This section also contains tables that show some of the types of AHB transaction that the
processor generates. However, because a particular type of transaction is not shown here does
not mean that the processor does not generate such a transaction.
Note
An AHB slave device connected to the AHBP interface must be capable of handling every kind
of transaction permitted by the AHB specification, except where there is an explicit statement
in this chapter that such a transaction is not generated. You must not infer any additional
restrictions from the example tables given.
Restrictions on AHBP interface transfers describes restrictions on the type of transfers that the
AHBP interface generates.
The following sections give examples of transfers generated by the AHBP interface:
•
Restrictions on AHBP interface transfers.
•
Strongly-ordered and Device transactions on page 5-23.
•
Normal reads on page 5-26.
•
Normal writes on page 5-27.
Restrictions on AHBP interface transfers
The AHBP interface applies the following restrictions to the AHB transactions it generates:

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•

The interface only uses one transfer and all bursts are single, that is HBURSTP[2:0] is
always SINGLE.

•

No transaction ever crosses a 4-byte boundary in memory.

•

The transfer type, that is, HTRANSP[2:0] is never BUSY or SEQUENTIAL.

•

The transfer size is never greater than 32 bits because it is a 32-bit AHB bus.

•

All transactions are data accesses, that is HPROTP[0] is always 1.

•

Transactions to Device and Strongly-ordered memory are always to addresses that are
aligned for the transfer size.

•

Exclusive accesses are always to addresses that are aligned for the transfer size.

5-22

Memory System

Strongly-ordered and Device transactions
A load or store instruction, to or from Strongly-ordered or Device memory, always generates
AHB transactions of the size implied by the instruction. All accesses using LDM, STM, LDRD, or STRD
instructions to Strongly-ordered or Device memory occur as single 32-bit transfers.
LDRB

Table 5-24 shows the values of HADDRP[1:0], HBURSTP, and HSIZEP for an LDRB from
bytes 0-3 in Strongly-ordered or Device memory.
Table 5-24 LDRB transfers
Address[1:0]

HADDRP[1:0]

HBURSTP

HSIZEP

0x0 (byte 0)

0x00

Single

8-bit

0x1 (byte 1)

0x01

Single

8-bit

0x2 (byte 2)

0x02

Single

8-bit

0x3 (byte 3)

0x03

Single

8-bit

LDRH

Table 5-25 shows the values of HADDRP[1:0], HBURSTP, and HSIZEP for an LDRH from
halfwords 0-1 in Strongly-ordered or Device memory.
Table 5-25 LDRH transfers
Address[1:0]

HADDRP[1:0]

HBURSTP

HSIZEP

0x0 (halfword 0)

0x00

Single

16-bit

0x2 (halfword 1)

0x02

Single

16-bit

Note
A load of a halfword from Strongly-ordered or Device memory addresses 0x1 or 0x3 generates
an alignment UsageFault.
LDR or LDM of one register

Table 5-26 shows the values of HADDRP[1:0], HBURSTP, and HSIZEP for an LDR or an LDM
that transfers one register, an LDM1, in Strongly-ordered or Device memory.
Table 5-26 LDR or LDM of one register
Address[1:0]

HADDRP[1:0]

HBURSTP

HSIZEP

0x0 (word 0)

0x00

Single

32-bit

Note
A load of a word from Strongly-ordered or Device memory addresses 0x1, 0x02, 0x3, 0x5, 0x06,
or 0x7 generates an alignment UsageFault.

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5-23

Memory System

LDM that transfers five registers

Table 5-27 shows the values of HADDRP[1:0], HBURSTP, and HSIZEP for an LDM that
transfers five registers, an LDM5, in Strongly-ordered or Device memory.
Table 5-27 LDM that transfers five registers
Address[1:0]

HADDRP[1:0]

HBURSTP

HSIZEP

0x0 (word 0)

0x00

Single

32-bit

0x04

Single

32-bit

0x08

Single

32-bit

0x0C

Single

32-bit

0x10

Single

32-bit

0x04

Single

32-bit

0x08

Single

32-bit

0x0C

Single

32-bit

0x10

Single

32-bit

0x14

Single

32-bit

0x4 (word 1)

Note
A load of a word from Strongly-ordered or Device memory addresses 0x1, 0x2, or 0x3 generates
an alignment UsageFault.
STRB

Table 5-28 shows the values of HADDRP[1:0], HBURSTP, and HSIZEP for an STRB from
bytes 0-3 in Strongly-ordered or Device memory.
Table 5-28 STRB transfers

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Address[1:0]

HADDRP[1:0]

HBURSTP

HSIZEP

0x0 (byte 0)

0x00

Single

8-bit

0x1 (byte 1)

0x01

Single

8-bit

0x2 (byte 2)

0x02

Single

8-bit

0x3 (byte 3)

0x03

Single

8-bit

5-24

Memory System

STRH

Table 5-29 shows the values of HADDRP[1:0], HBURSTP, and HSIZEP for an STRH from
halfwords 0-1 in Strongly-ordered or Device memory.
Table 5-29 STRH transfers
Address[1:0]

HADDRP[1:0]

HBURSTP

HSIZEP

0x0 (halfword 0)

0x00

Single

16-bit

0x2 (halfword 1)

0x02

Single

16-bit

Note
A store of a halfword to Strongly-ordered or Device memory addresses 0x1 or 0x3 generates an
alignment UsageFault.
STR of one register

Table 5-30 shows the values of HADDRP[1:0], HBURSTP, and HSIZEP for an STR that
transfers one register in Strongly-ordered or Device memory.
Table 5-30 STR of one register
Address[1:0]

HADDRP[1:0]

HBURSTP

HSIZEP

0x0 (word 0)

0x00

Single

32-bit

Note
A store of a word to Strongly-ordered or Device memory addresses 0x1, 0x2, or 0x3 generates
an alignment UsageFault.
STM of five registers

Table 5-31 shows the values of HADDRP[1:0], HBURSTP, and HSIZEP for an STM that
transfers five registers, an STM5, over the AHBP interface to Strongly-ordered or Device
memory.
Table 5-31 STM of five registers

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Address[1:0]

HADDRP[1:0]

HBURSTP

HSIZEP

0x0 (word 0)

0x00

Single

32-bit

0x04

Single

32-bit

0x08

Single

32-bit

0x0C

Single

32-bit

0x10

Single

32-bit

5-25

Memory System

Table 5-31 STM of five registers (continued)
Address[1:0]

HADDRP[1:0]

HBURSTP

HSIZEP

0x4 (word 1)

0x04

Single

32-bit

0x08

Single

32-bit

0x0C

Single

32-bit

0x10

Single

32-bit

0x14

Single

32-bit

Note
A store of a word from Strongly-ordered or Device memory addresses 0x1, 0x2, 0x3, 0x5, 0x6, or
0x7 generates an alignment UsageFault.

Normal reads
Load instructions accessing Normal memory generate AHBP interface transactions that might
not be the same size or length as the instruction implies. The tables in this section give examples
of AHBP transactions that might result from various load instructions, accessing various
addresses in Normal memory. They are examples only, and are not an exhaustive description of
the AHBP transactions.
LDRH

Table 5-32 shows possible values of HADDRP[2:0], HBURSTP, and HSIZEP for an LDRH
from bytes 0 to 3 in Normal memory.
Table 5-32 LDRH transfers in Normal memory
Address[1:0]

HADDRP[2:0]

HBURSTP

HSIZEP

0x0 (byte 0)

0x00

Single

16-bit

0x1 (byte 1)

0x00

Single

32-bit

0x2 (byte 2)

0x02

Single

16-bit

0x3 (byte 3)a

0x00

Single

32-bit

0x04

Single

32-bit

a. AHBP interface transactions do not cross a double word
boundary.

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5-26

Memory System

LDR

Table 5-33 shows possible values of HADDRP[2:0], HBURSTP, and HSIZEP for an LDR from
Normal memory.
Table 5-33 LDR transfers in Normal memory
Address[1:0]

HADDRP[2:0]

HBURSTP

HSIZEP

0x0 (byte 0)

0x0

Single

32-bit

0x1 (byte 1)

0x0

Single

32-bit

0x4

Single

32-bit

0x0

Single

32-bit

0x4

Single

32-bit

0x0

Single

32-bit

0x4

Single

32-bit

0x2 (byte 2)

0x3 (byte 3)

Normal writes
Store instructions accessing Normal memory generate AHBP interface transactions that might
not be the same size or length as the instruction implies. The tables in this section give examples
of AHBP transactions that might result from various store instructions, accessing various
addresses in Normal memory. They are examples only, and are not an exhaustive description of
the AHBP transactions.
STRH

Table 5-34 shows possible values of HADDRP[1:0], HBURSTP, and HSIZEP for an STRH
from bytes 0 to 3 in Normal memory.
Table 5-34 STRH transfers in Normal memory

ARM DDI 0489D
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Address[1:0]

HADDRP[1:0]

HBURSTP

HSIZEP

0x0 (byte 0)

0x00

Single

16-bit

0x1 (byte 1)

0x01

Single

8-bit

0x02

Single

8-bit

0x2 (byte 2)

0x02

Single

16-bit

0x3 (byte 3)

0x03

Single

8-bit

0x04

Single

8-bit

5-27

Memory System

STR or STM of one register

Table 5-35 shows possible values of HADDRP[1:0], HBURSTP, and HSIZEP for an STR to
Normal memory.
Table 5-35 STR transfers in Normal memory
Address[1:0]

HADDRP[1:0]

HBURSTP

HSIZEP

0x0 (byte 0, word 0)

0x00

Single

32-bit

0x1 (byte 1)

0x01

Single

8-bit

0x02

Single

16-bit

0x04

Single

8-bit

0x02

Single

16-bit

0x04

Single

16-bit

0x03

Single

8-bit

0x04

Single

16-bit

0x06

Single

8-bit

0x2 (byte 2)

0x3 (byte 3)

5.5.2

AHBP semaphores
The peripheral interfaces use the internal exclusive monitor of the memory system to manage
load, store and clear exclusive instructions to non-shared memory. The internal monitor checks
exclusive accesses to shared memory and also, if necessary, any external monitor using the AHB
memory interface. You can use these instructions to construct semaphores and ensure
synchronization between different processes or processors. See the ARM®v7-M Architecture
Reference Manual for more information about how these instructions work.
Only exclusive instructions to shared memory result in exclusive accesses on the AHBP.
Exclusive accesses to non-shared memory are marked as non-exclusive accesses on the bus.
The AHBP extension signals EXREQP and EXRESPP signal exclusive request and response
for shared exclusive transactions on AHBP.
AHBP exclusive accesses
This section describes the EXREQP and EXRESPP signals and the transaction properties for
AHBP exclusive accesses:
•

EXREQP is an address phase signal and is only asserted when HTRANSP indicates a
valid transaction.

•

EXRESPP is a data phase signal and is only sampled on a data phase when HREADYP
is 1.

The processor only asserts the EXREQP signal when:

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•

A load exclusive is performed to a Shared memory region on the AHBP.

•

A store exclusive is performed to a Shared memory region on the AHBP and the internal
exclusive access monitor passes. When the internal exclusive access monitor fails, no
store is performed on the AHBP.

5-28

Memory System

Table 5-36 shows the transaction properties the system must use for EXRESPP.
Table 5-36 Transaction properties
Transaction properties
Required EXRESPP
EXREQP

Load/Store

Load

0 if a system monitor is implemented that covers the access address
1 otherwise

Store

1 if a system monitor is implemented that covers the access address and the exclusive check fails
0 otherwise

Software must avoid performing exclusive accesses to shared regions of memory if no global
exclusive monitor is implemented that covers the region in question. The processor treats such
accesses as an error condition and automatically takes a BusFault exception if a load is
performed with EXREQP set to 1 and receives EXRESPP set to 1. The processor ignores
EXRESPP for accesses that:
•

Are performed with EXREQP set to 0. ARM recommends that the system drives
EXRESPP to 0 in these cases.

•

Return an error response on HRESPP.

The Cortex-M7 processor uses EXREQP and EXRESPP differently from the Cortex-M3
processor and the Cortex-M4 processor, therefore you might have to update both system
hardware and software when moving to a system using the Cortex-M7 processor.

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5-29

Memory System

5.6

AHB slave interface
The 32-bit AHB slave (AHBS) interface provides system access to the ITCM, D1TCM, and
D0TCM. It includes arbitration logic to support simultaneous system and processor TCM access
requests. The AHBS implements the AMBA 3 AHB-Lite protocol.
Writes are buffered in the processor Store Queue (SQ). The SQ also buffers software writes to
the TCM and it performs all stores in-order. Reads can be performed to the TCM out-of-order
with respect to buffered writes.
If there is a data dependency between a read and a software or AHBS buffered write, hazarding
logic stalls the read and attempts to drain the SQ until there are no longer any dependencies.
Writes continue to be performed in-order. Hazarding is performed at byte granularity.
All AHBS accesses are treated as being the same endianness as memory. No data swizzling is
performed for reads or writes.
The AHBS interface can be used when the processor is in sleep state.

5.6.1

Memory map
The memory map presented on the AHBS:
•

Is consistent with the memory map presented to software running on the processor.
Note
The TCM enable bits, defined in the ITCMCR and DTCMCR, do not affect AHBS
accesses and instead only affect software visibility of the TCMs, see Instruction and Data
Tightly-Coupled Memory Control Registers on page 3-13. AHBS accesses are handled
independently of these bits.

•

Has the additional restriction that only the TCM address range can be accessed. Any other
addresses fail.

Table 5-37 shows the AHBS memory map. Accesses to locations outside the address ranges
shown return an error response on the AHBS interface.
Table 5-37 AHBS memory map
Start
address

End address

HADDRS[2]

TCM accessed

TCM index

0x00000000

0x00000000 +

ITCM

HADDRS[n:3]a

D0TCM

HADDRS[n:3]a

D1TCM

HADDRS[n:3]a

0x20000000

0x20000000 +

0x20000000

0x20000000 +

a. The value of n depends on the configured TCM size, see TCM configuration on page 5-34.

5.6.2

Restrictions on AHBS transactions
Loopback of transactions from the AXIM or AHBP interface onto the AHBS is not supported
because it might cause deadlock.

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5-30

Memory System

Note
Loopback arrangements are unlikely to be required. The processor has higher bandwidth to
TCM than the AHBS interface. This means that software can directly transfer data to and from
TCM faster than through the AHBS interface.
This restriction does not preclude arrangements where there is an indirect relationship between
a master interface access and an AHBS access. For example, if a write from the AHBP interface
requests an external agent to perform transactions on the AHBS interface. In this case do not
introduce dependency in the system between the control access that initiates the transaction and
the transaction itself.
AHBS interface transactions are not capable of performing MPU lookups. No distinction is
made internally between unprivileged and privileged AHBS interface accesses as indicated on
HPROTS. The system is entirely responsible for providing TCM protection functionality for
AHBS interface accesses as required.
A TCM error mechanism must be used by the external TCM interface logic to indicate back to
the AHBS interface that the access was aborted. In this case, the external TCM interface logic
also mask writes and obfuscate read data. For more information on the TCM interface protocol,
see TCM interface protocol on page 5-34.
The AHBS interface reads that are aborted on the TCM interface return the read data supplied
with an error response on HRESPS. The AHBS interface writes are buffered and always return
an OK response speculatively. If a write is subsequently aborted on the TCM interface, the
AHBS raises an asynchronous abort to the system using the WABORTS signal.
The AHBS does not support exclusive or locked accesses and AHBS interface stores do not
affect the state of the internal exclusive access monitor. This makes it unsuitable for systems
requiring concurrency controls between the AHBS interface and software.
For more information on the TCM data sharing models supported between software and AHBS
interface, see System access to TCM on page 5-35.
5.6.3

AHBS interface arbitration
There are two relevant points of arbitration in the processor:
•
Accepting writes into the SQ from software and the AHBS interface.
•
Performing TCM reads from software and the AHBS interface.
The processor supports five software-configurable arbitration modes:

ARM DDI 0489D
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•

Round-robin only.

•

Reduced AHBS interface bandwidth using the fairness counter.

•

Reduced software bandwidth using the fairness counter.

•

Round-robin but AHBS interface bandwidth is reduced using the fairness counter when
execution priority is set above a defined threshold.

•

Round-robin with AHBS interface bandwidth controlled by an input signal.

5-31

Memory System

When active, the round-robin AHBS arbitration scheme has the following characteristics:
•

Any requestor, that is, software or AHBS interface, is granted access when there is no
contention. This scheme guarantees:
—

Optimal throughput for each requestor when contention is rare. In this case, the
resource usage is not evenly balanced between requestors and one requestor is more
active than the other. When contention is frequent however, the scheme used tends
towards even resource allocation between the requestors.

—

Optimal average throughput across all requestors when contention is common.

The fairness counter determines which requestor gets access, where there is contention. This
counter is decremented for each access where contention occurs, and is initialized to the
CM7_AHBSCR.INITCOUNT field value when it reaches 0. See AHB Slave Control Register
on page 3-20 for more information about how to use CM7_AHBSCR.INITCOUNT.
Some limited software configurability is provided to moderate AHBS interface bandwidth by
demoting its priority to a significantly lower level without shutting it out completely. This is
achieved by increasing the initialization value of the fairness counter that forces arbitration of
an AHBS interface access. It is also possible to invert the priority scheme to allow AHBS
interface accesses to take priority over software accesses using the fairness counter.
Typically this AHBS interface bandwidth moderation feature is expected to be used for
real-time critical code that runs in a high priority ISR. To allow individual ISRs to demote
AHBS interface traffic, a threshold execution priority (TPRI) mode is provided to enable the
processor hardware to automatically do this. See AHB Slave Control Register on page 3-20 for
more information about how to use TPRI.
Note
The processor could stop executing code if the counter initialization value is 0 and the AHBS
interface fully occupies the bandwidth of a TCM or the SQ.
The system can control the AHBS interface access priority directly using the AHBSPRI input
signal on the processor. See AHB Slave Control Register on page 3-20.

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•

Note
Improper programming might directly degrade overall system performance.

•

For the AHBS interface to accept AHBS transactions all resets must be de-asserted.

•

Changes to CM7_AHBSCR might not occur immediately because the processor must
completed existing AHBS interface traffic.

•

CM7_AHBSCR settings can be overruled and only be considered as a hint to the
processor.

5-32

Memory System

5.7

TCM interfaces
The memory system includes support for the connection of local Tightly Coupled Memory
called ITCM and DTCM. The ITCM has one 64-bit memory interface and the DTCM has two
32-bit memory interfaces, D0TCM and D1TCM, selected on bit[2] of the request address. Each
TCM interface is a physical connection on the processor that is suitable for connection to SRAM
with minimal glue logic. These ports are optimized for low-latency memory.
The TCM interfaces are designed to be connected to RAM, or RAM-like memory, that is,
Normal-type memory in the ARM architecture. The processor can issue speculative read
accesses on these interfaces. Therefore, read accesses through the TCM interfaces can be
repeated, and can access uninitialized or nonexistent memory locations. This means that the
TCM interfaces are generally not suitable for read-sensitive devices such as FIFOs. If an access
is speculative, the processor ignores any error or retry signaled for the access, see TCM interface
protocol on page 5-34.
The TCM interfaces also have a wait signal to support slow memories, see TCM interface
protocol on page 5-34.
The Prefetch Unit (PFU) can fetch instructions from any of the TCM interfaces. The Load Store
Unit (LSU) and the AHBS interface can each read and write data using any of the TCM
interfaces. Best performance is achieved if code is placed in ITCM and data in DTCM.
However, there is no functional restriction in which TCM, code and data is placed.
Each TCM interface has a fixed base address, see System address map on page 2-5.
This section describes:
•
TCM attributes and permissions.
•
TCM configuration on page 5-34.
•
TCM arbitration on page 5-34.
•
TCM interface protocol on page 5-34.
•
TCM read modify write on page 5-35.

5.7.1

TCM attributes and permissions
Accesses to the TCMs from the LSU and PFU are checked against the MPU for access
permission. Memory access attributes and permissions are not exported on this interface. Any
unaligned access to Device or Strongly Ordered memory generates an alignment UsageFault.
Reads that generate an MPU fault or alignment UsageFault are still sent to the TCM interface,
but the data is not used and the associated load instruction does not update any processor
registers, ensuring protection is maintained. Writes that generate an MPU fault or alignment
UsageFault are never broadcast on the TCM interface.
TCMs always behave as Non-cacheable Non-shared Normal memory, irrespective of the
memory type attributes defined in the MPU for a memory region containing addresses held in
the TCM. Access permissions associated with an MPU region in the TCM address space are
treated in the same way as addresses outside the TCM address space. For more information
about memory attributes, types, and permissions, see the ARM®v7-M Architecture Reference
Manual.
Note
For code portability to other ARM processors or systems, ARM recommends that TCM regions
are always defined as Normal, Non-shared memory in the MPU. This is consistent with the
default ARMv7E-M memory map attributes that apply when the MPU is either disabled or not
implemented.

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5.7.2

TCM configuration
The base address of each TCM is fixed:
•

ITCM at 0x00000000.

•

DTCM at 0x20000000.

The ITCM and DTCM occupy the lower parts of the code and data regions of the memory map
respectively, see System address map on page 2-5.
The size of each TCM is configured during integration from 4KB to 16MB in powers of two. If
a TCM is not present in a system, its size is 0KB.
The DTCM has two interfaces, D0TCM and D1TCM. This means the size of the RAM attached
to each interface is half the total size of the DTCM.
The size of the TCMs is visible to software in the TCM Control Registers, see Instruction and
Data Tightly-Coupled Memory Control Registers on page 3-13. Memory accesses to addresses
above the implemented TCM address ranges in the code and data regions of the memory map
are sent to the AXIM interface.
The ITCM and DTCM can be enabled or disabled by software using the ITCMCR.EN and
DTCMCR.EN bits. See Instruction and Data Tightly-Coupled Memory Control Registers on
page 3-13. Input configuration signals determine the values of these bits out of reset.
5.7.3

TCM arbitration
The TCU contains arbitration logic to arbitrate between TCM access requests for the LSU, PFU,
AHBS and SQ. In most cases, the LSU has the highest priority, followed by the PFU, AHBs,
and the SQ having the lowest priority.
When a higher-priority requestor is accessing a TCM, an access from a lower-priority device
stalls.
In some circumstances the SQ can have the highest priority temporarily, for example, when a
RAW hazard occurs because of a load from the same address as a store in the SQ. This ensures
that the hazard is cleared as quickly as possible allowing the load to proceed. The AHBS
interface might have the highest priority because of AHBS priority boosting, see AHBS
interface arbitration on page 5-31. If the SQ and AHBS are priority boosted at the same time,
the SQ then has the highest priority.

5.7.4

TCM interface protocol
Each TCM interface operates independently of each other, and each might perform either a read
or a write access in a particular clock cycle. In addition to the address and data signals, the TCM
interfaces also provide information about the source of an access and whether it is privileged or
not. Therefore, it is possible to determine whether an access results from an instruction fetch
from the PFU, a data access from the LSU, an SQ access, an MBIST interface access, or a DMA
transfer from the AHBS interface.
During read accesses, an external TCM memory controller can indicate that the processor must
wait one or more clock cycles before capturing the read data from the interface. The controller
can also indicate that an error occurred during a read or a write access and that the processor
must take a bus fault. The controller might, for example, use this error to indicate a privilege
violation by decoding the address, privilege indication, or access source information. For more
information about TCM errors, see Faults on page 5-3.

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If the TCM memory controller supports ECC error detection and correction it can indicate to the
processor that an access must be retried to return the corrected data. The TCM retry
functionality in the processor must be enabled to support external TCM error correction by
setting the ITCMCR.RETEN or DTCMCR.RETEN bits to 1. See Instruction and Data
Tightly-Coupled Memory Control Registers on page 3-13.
5.7.5

TCM read modify write
Read modify write can be enabled on the TCM interfaces by setting the ITCMCR.RMW or
DTCMCR.RMW bits to 1, see Instruction and Data Tightly-Coupled Memory Control Registers
on page 3-13. When enabled, the processor uses the read modify write sequence for writes that
have a data size that are less than the width of the interface. This feature is intended to be used
in systems that implement ECC in TCM.

5.7.6

Booting from TCM
The following support is available for booting volatile TCM memory that must be initialized at
reset:

5.7.7

•

The TCMs can be enabled from reset independently of software, using configuration input
signals.

•

When the CPUWAIT signal is asserted HIGH from reset, it prevents the processor
initiating its normal hardware bootup routine. This allows the TCMs to be loaded by
system hardware before the processor performs any TCM accesses. When TCM loading
is complete the signal is deasserted to allow the processor to boot up.

•

The processor AHBS port functions while CPUWAIT is asserted and services
transactions to load the TCMs initiated by system hardware. This avoids requiring
external hardware on the TCM interface for boot-time initialization.

Integration with Flash memory
When executing 32-bit instructions, the processor execution bandwidth can be as high as 64 bits
per cycle. For 16-bit instructions, it can be as high as 32 bits per cycle. The overall bandwidth
is very application specific, however, for general-purpose products, assume 64 bits per cycle is
required. The I-side memory system must sustain this bandwidth for maximum performance.
ARM recommends that if Flash is integrated on the ITCM interface, you use a system cache or
Flash accelerator to satisfy these fetch bandwidth requirements.
Alternatively, Flash can be integrated on the AXIM and the processor can be configured to
include the I-cache.

5.7.8

System access to TCM
The AHBS interface provides system access to the TCMs even when the processor is running.
Arbitration between software and AHBS accesses to the TCMs is supported without requiring
external TCM interface logic.
There is no hardware support for concurrency control between software and AHBS access to
the TCMs. In particular, software exclusive accesses to the TCMs is only subject to the internal
exclusive monitor that does not take AHBS accesses into account. This implies that the system
must not perform AHBS accesses to any regions of TCM memory that are used with software
exclusive accesses.

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However, it is possible to share data coherently between software running on the processor and
the system using the AHBS interface and with the following processor hardware guarantees:
•

Writes to the TCMs by software or AHBS are never repeated.
Note
Store multiple instructions and unaligned single stores can be repeated on exception return
and are therefore exempt from this guarantee and unsuitable for software synchronization.
The processor guarantees that no single-copy-atomic access is repeated. For more
information on atomicity, see the ARM®v7-M Architecture Reference Manual.

•

Writes to a TCM by both software and AHBS have a single point of serialization, the
TCM Store Queue. This means that when a write is observable by one master, it is
guaranteed observable by the other.

•

When a write on the AHBS interface is accepted, its data phase completes with an OK
response, the processor assumes responsibility for the coherent observation of that data
item. A read initiated by either master after the AHBS write completes, returns the
updated data.
Note
TCMs are implicitly Normal memory, and therefore write buffering is permitted. A
completed AHBS write does not imply that the write was performed on the TCM
interface, but instead that it successfully entered the Store Queue. Therefore, if all writes
are required to have been committed to memory first, the system must avoid resetting the
processor until the Store Queue has drained.

The standard message passing model for data sharing can be used. The ARM architecture
requires this model to work where coherency is supported, and is therefore portable to other
ARM processors.
Table 5-38 shows the standard message passing software protocol.
Table 5-38 Standard message passing software protocol

•

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Data generator

Data consumer

STR

LDR

DMB

LOOP until set

STR

LDR

Note
Interrupt-based synchronization on the processor is possible when the AHBS interface is
used to transfer system-generated data. In this model, an interrupt is generated when the
AHBS completes the last data transfer. The first instruction in the ISR is guaranteed to
observe any data items stored before, or on this transfer. In this case, the completion of the
last AHBS access indicates global observability, instead of having to perform a software
read of the location and waiting until it updates.
This scheme is not guaranteed to be supported on other ARM processors and you must
use it with care when you require code portability.

5-36

Memory System

5.8

L1 caches
This section describes the behavior of the optional L1 caches in the Cortex-M7 processor
memory system.
The memory system is configured during implementation and can include instruction and data
caches of varying sizes. You can configure whether each cache controller is included and, if it
is, configure the size of each cache independently. The cached instructions or data are fetched
from external memory using the AXIM interface. The cache controllers use RAMs that are
integrated into the Cortex-M7 processor during implementation.
Any access that is not for a TCM or the AHBP interface is handled by the appropriate cache
controller. If the access is to Non-shared cacheable memory, and the cache is enabled, a lookup
is performed in the cache and, if found in the cache, that is, a cache hit, the data is fetched from
or written into the cache. When the cache is not enabled and for Non-cacheable or Shared
memory the accesses are performed using the AXIM interface.
Both caches allocate a memory location to a cache line on a cache miss because of a read, that
is, all cacheable locations are Read-Allocate. In addition, the data cache can allocate on a write
access if the memory location is marked as Write-Allocate. When a cache line is allocated, the
appropriate memory is fetched into a linefill buffer by the AXIM interface before being written
to the cache. The linefill buffers always fetch the requested data first, return it, and fetch the rest
of the cache line. This enables the data read without waiting for the linefill to complete and is
known as critical word first and non-blocking behavior. If subsequent instructions require data
from the same cache line, this can also be returned when it has been fetched without waiting for
the linefill to complete, that is, the caches also support streaming. If an error is reported to the
AXIM interface for a linefill, the linefill does not update the cache RAMs.
A synchronous fault is generated if the faulting data is used by a non-speculative read in the
processor. An asynchronous fault is generated by a line-fill when an external fault occurs if write
data from an address configured as Write-Back has been merged into the line from the store
buffer. See Store buffer on page 5-38.
The data cache is four-way set-associative, the instruction cache is two-way set-associative.
Both caches use a line-length of 32-bytes. If all the cache lines in a set are valid, to allocate a
different address to the cache, the cache controller must evict a line from the cache.
Writes accesses that hit in the data cache are written into the cache RAMs. If the memory
location is marked as Write-Through, the write is also performed on the AXIM interface, so that
the data stored in the RAM remains coherent with the external memory system. If the memory
is Write-Back, the cache line is marked as dirty, and the write is only performed on the AXIM
interface when the line is evicted. When a dirty cache line is evicted, the data is passed to the
write buffer in the AXIM interface to be written to the external memory system.
The cache controllers also manage the cache maintenance operations described in Cache
maintenance operations on page 5-39.
Each cache can also be configured with ECC. If ECC is implemented and enabled, then the tags
associated with each line, and data read from the cache are checked whenever a lookup is
performed in the cache and, if possible, the data is corrected before being used in the processor.
A full description of ECC error checking and correction is beyond the scope of this document.
Contact ARM if you require more information.
For more information on the general rules about memory attributes and behavior, see the
ARM®v7-M Architecture Reference Manual.

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5.8.1

Dynamic read allocate mode
When a memory region is marked as Write-Back Write-Allocate, it normally allocates a cache
line on either a read miss or a write miss. However, there are some situations where allocating
on writes is undesirable, such as executing the C standard library memset() function to clear a
large block of memory to a known value. Writing large blocks of data like this can pollute the
cache with unnecessary data. It can also waste power and performance if a linefill must be
performed only to discard the linefill data because the entire line was subsequently written by
the memset().
To prevent this, the Cortex-M7 Bus Interface Unit (BIU) includes logic to detect when a full
cache line has been written by the core before the linefill has completed. If this situation is
detected on three consecutive linefills, it switches into dynamic read allocate mode. When in
dynamic read allocate mode, loads behave as normal and can still cause linefills, and writes still
lookup in the cache but, if they miss, they write out to external memory rather than starting a
linefill.
The BIU continues in dynamic read allocate mode until it detects either a cacheable write burst
to external memory that is not a full cache line, or there is a load to the same line as is currently
being written to external memory.
Dynamic read allocate mode can be disabled by setting the ACTLR.DISRAMODE to 1. See
Auxiliary Control Register on page 3-6.

5.8.2

Store buffer
The memory system includes a store buffer to hold data before it is written to the cache RAMs
or passed to the AXIM interface. The store buffer has four entries. Each entry can contain up to
64 bits of data and a 32-bit address. All write requests from the data-side that are not to a TCM
or the AHBP interface are stored in the store buffer.
Store buffer merging
The store buffer has merging capabilities. If a previous write access has updated an entry, other
write accesses on the same line can merge into this entry. Merging is only possible for stores to
Normal memory.
Merging is possible between several entries that can be linked together if the data inside the
different entries belong to the same cache line.
No merging occurs for writes to Strongly-ordered or Device memory. The processor
automatically drains the store buffer as necessary before performing Strongly-ordered or Device
reads.
Store buffer behavior
The store buffer directs write requests to the following blocks:
•

Cache controller for cacheable write hits:
The store buffer sends a cache lookup to check that the cache hits in the specified line, and
if so, the store buffer merges its data into the cache when the entry is drained.

•

AXIM interface:
—

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For Non-cacheable, Write-Through Cacheable, Write-Back no Write-Allocate
Cacheable stores that miss in the data cache, a write access is performed on the
AXIM interface.

5-38

Memory System

—

For Write-Back, Write-Allocate stores that miss in the data cache, a linefill is started
using either of the two linefill buffers. When the linefill data is returned from the
external memory system, the data in the store buffer is merged into the linefill buffer
and subsequently written into the cache.

Store buffer draining
A store buffer entry is drained if:
•

All bytes in the entry have been written. This might result from merging.

•

The entry can be merged into a linefill buffer.

•

The entry contains a store to Device or Strongly-ordered memory.

•

The entry is Non-cacheable or Write-Through and has been waiting for merge data for too
long.

The store buffer is completely drained when:
•
An explicit drain request is done for:
— Cache maintenance operations.
— A DMB or DSB instruction.
— An exclusive store to Shared memory.
•
The store buffer is full or likely to become full.
The store buffer is drained of all stores to Strongly-ordered or Device memory before a load is
performed from Strongly-ordered or Device memory.
5.8.3

Cache maintenance operations
All cache maintenance operations are executed by writing to registers in the memory-mapped
System Control Space (SCS) region of the internal PPB memory space. The operations
supported for the data cache are:
•
Invalidate by address.
•
Invalidate by Set/Way combination.
•
Clean by address.
•
Clean by Set/Way combination.
•
Clean and Invalidate by address.
•
Clean and Invalidate by Set/Way combination.
The operations supported for the instruction cache are:
•
Invalidate all.
•
Invalidate by address.
For more information see ARM®v7-M Architecture Reference Manual.

5.8.4

Cache interaction with memory system
After you enable or disable the instruction cache, you must issue an ISB instruction to flush the
pipeline. This ensures that all subsequent instruction fetches see the effect of enabling or
disabling the instruction cache.
After reset, you must invalidate each cache before enabling it.
When disabling the data cache, you must clean the entire cache to ensure that any dirty data is
flushed to external memory.

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Memory System

Before enabling the data cache, you must invalidate the entire data cache because external
memory might have changed from when the cache was disabled.
Before enabling the instruction cache, you must invalidate the entire instruction cache if
external memory might have changed since the cache was disabled.
See Chapter 4 Initialization for example code suitable for initializing and enabling the
instruction and data caches.

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Chapter 6
Memory Protection Unit

This chapter describes the Memory Protection Unit (MPU). It contains the following sections:
•
About the MPU on page 6-2.
•
MPU functional description on page 6-3.
•
MPU programmers model on page 6-4.

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Memory Protection Unit

6.1

About the MPU
The MPU is an optional component for memory protection. The processor supports the standard
ARMv7 Protected Memory System Architecture model. The MPU provides full support for:
•

Eight or sixteen protection regions.

•

Overlapping protection regions, with ascending region priority:
15
Highest priority, when 16 regions are implemented.
7
Highest priority, when 8 regions are implemented.
0
Lowest priority.

•

Access permissions.

•

Exporting memory attributes to the system.

MPU mismatches and permission violations invoke the programmable-priority MemManage
fault handler. See the ARM®v7-M Architecture Reference Manual for more information.
You can use the MPU to:
•
Enforce privilege rules.
•
Separate processes.
•
Enforce access rules.

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Memory Protection Unit

6.2

MPU functional description
The access permission bits, TEX, C, B, AP, and XN, of the Region Attributes and Size Register,
MPU_RASR, control access to the corresponding memory region. If an access is made to an
area of memory without the required permissions, a MemManage fault is raised. For more
information, see the ARM®v7-M Architecture Reference Manual.

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Memory Protection Unit

6.3

MPU programmers model
Table 6-1 shows the MPU registers. These registers are described in the ARM®v7-M
Architecture Reference Manual.
Table 6-1 MPU registers
Address

Name

Type

Reset

Description

0xE000ED90

MPU_TYPE

0x00000800a

MPU Type Register

0xE000ED94

MPU_CTRL

0x00000000

MPU Control Register

0xE000ED98

MPU_RNR

Unknown

MPU Region Number Register

0xE000ED9C

MPU_RBAR

Unknown

MPU Region Base Address Register

0xE000EDA0

MPU_RASR

Unknown

MPU Region Attribute and Size Register

0xE000EDA4

MPU_RBAR_A1

Unknown

MPU alias registers

0xE000EDA8

MPU_RASR_A1

Unknown

0xE000EDAC

MPU_RBAR_A2

Unknown

0xE000EDB0

MPU_RASR_A2

Unknown

0xE000EDB4

MPU_RBAR_A3

Unknown

0xE000EDB8

MPU_RASR_A3

Unknown

a. The reset value depends on the number of regions implemented:
0x00000000

0 regions.

0x00000800

8 regions.

0x00001000

16 regions.

Note
The MPU registers support aligned word accesses only. Byte and halfword accesses are
UNPREDICTABLE.

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Chapter 7
Nested Vectored Interrupt Controller

This chapter describes the Nested Vectored Interrupt Controller (NVIC). It contains the
following sections:
•
About the NVIC on page 7-2.
•
NVIC functional description on page 7-3.
•
NVIC programmers model on page 7-4.

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Nested Vectored Interrupt Controller

7.1

About the NVIC
The NVIC provides configurable interrupt handling abilities to the processor. It:
•
Facilitates low-latency exception and interrupt handling.
•
Controls power management.

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Nested Vectored Interrupt Controller

7.2

NVIC functional description
The NVIC supports up to 240 interrupts each with up to 256 levels of priority. You can change
the priority of an interrupt dynamically. The NVIC and the processor core interface are closely
coupled, to enable low-latency interrupt processing and efficient processing of late arriving
interrupts. The NVIC maintains knowledge of the stacked, or nested, interrupts to enable
tail-chaining of interrupts.
You can only fully access the NVIC from privileged mode, but you can cause interrupts to enter
a pending state in user mode if you enable the Configuration and Control Register. Any other
user mode access causes a bus fault.
You can access all NVIC registers using only word accesses. For more information on NVIC
registers accessibility and their usage constraints, see the ARM®v7-M Architecture Reference
Manual.
Processor exception handling is described in Exceptions on page 2-9.

7.2.1

Low power modes
Your implementation can include a Wake-up Interrupt Controller (WIC). This enables the
processor and NVIC to be put into a very low-power sleep mode leaving the WIC to identify
and prioritize interrupts. When the WIC is used, you must enable SLEEPDEEP in the System
Control Register.
The processor fully implements the Wait For Interrupt (WFI), Wait For Event (WFE), and the Send
Event (SEV) instructions. In addition, the processor also supports the use of SLEEPONEXIT, that
causes the processor core to enter sleep mode when it returns from an exception handler to
Thread mode. See the ARM®v7-M Architecture Reference Manual for more information.

7.2.2

Level versus pulse interrupts
The processor supports both level and pulse interrupts. A level interrupt is held asserted until it
is cleared by the ISR accessing the device. A pulse interrupt is a variant of an edge model. You
must ensure that the pulse is sampled on the rising edge of the processor clock, FCLK, instead
of being asynchronous.
For level interrupts, if the signal is not deasserted before the return from the interrupt routine,
the interrupt again enters the pending state and re-activates. This is particularly useful for FIFO
and buffer-based devices because it ensures that they drain either by a single ISR or by repeated
invocations, with no extra work. This means that the device holds the signal in assert until the
device is empty.
A pulse interrupt can be reasserted during the ISR so that the interrupt can be in the pending
state and active at the same time. If another pulse arrives while the interrupt is still pending, the
interrupt remains pending and the ISR runs only once.
Pulse interrupts are mostly used for external signals and for rate or repeat signals.

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Nested Vectored Interrupt Controller

7.3

NVIC programmers model
This section describes the NVIC registers whose implementation is specific to this processor.
Other registers are described in the ARM®v7-M Architecture Reference Manual. Table 7-1
shows the NVIC registers.
Table 7-1 NVIC registers

7.3.1

Address

Name

Type

Reset

Description

0xE000E004

ICTR

Interrupt Controller Type Register

0xE000E100-0xE000E11C

NVIC_ISER0-NVIC_ISER7

0x00000000

Interrupt Set-Enable Registers

0xE000E180-0xE000E19C

NVIC_ICER0-NVIC_ICER7

0x00000000

Interrupt Clear-Enable Registers

0xE000E200-0xE000E21C

NVIC_ISPR0-NVIC_ISPR7

0x00000000

Interrupt Set-Pending Registers

0xE000E280-0xE000E29C

NVIC_ICPR0-NVIC_ICPR7

0x00000000

Interrupt Clear-Pending Registers

0xE000E300-0xE000E31C

NVIC_IABR0-NVIC_IABR7

0x00000000

Interrupt Active Bit Register

0xE000E400-0xE000E4EC

NVIC_IPR0-NVIC_IPR59

0x00000000

Interrupt Priority Register

Interrupt Controller Type Register
The ICTR characteristics are:
Purpose

Shows the number of interrupt lines that the NVIC supports.

Usage Constraints There are no usage constraints.
Configurations

Available in all configurations.

Attributes

See the register summary in Table 7-1.

Figure 7-1 shows the ICTR bit assignments.
31

4 3

Reserved

INTLINESNUM

Figure 7-1 ICTR bit assignments

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Nested Vectored Interrupt Controller

Table 7-2 shows the ICTR bit assignments.
Table 7-2 ICTR bit assignments
Bits

Name

Function

[31:4]

Reserved.

[3:0]

INTLINESNUM

Total number of interrupt lines in groups of 32:
0-32.
0b0001
33-64.
0b0010
65-96.
0b0011
97-128.
0b0100
129-160.
0b0101
161-192.
0b0110
193-224.
0b0111
225-256a.
0b0000

a. The processor supports a maximum of 240 external interrupts.

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7-5

Chapter 8
Floating Point Unit

This chapter describes the Floating Point Unit (FPU). It contains the following sections:
•
About the FPU on page 8-2.
•
FPU functional description on page 8-3.
•
FPU programmers model on page 8-5.

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Floating Point Unit

8.1

About the FPU
The Cortex-M7 processor with FPU is an implementation of the single-precision and
double-precision variant of the ARMv7-M Architecture with Floating-Point Extension (FPv5).
The FPv5 extensions features are:
•

Addition of double-precision operand support for existing data processing instructions in
FPv4-SP-D16-M.

•

Some new instructions for both double and single-precision operands.

•

16 double-precision registers. This is the same as for FPv4 and there are no additional
registers.

•

Software-enable control for single-precision and double-precision support using CPACR.

•

Double-precision and single-precision support, when both are implemented, cannot be
enabled independently of one another.

•

Identical load/store instruction support to FPv4 extensions that already includes support
for 64-bit data types.

Table 8-1 shows the ISA supported for the different configurations of the Cortex-M7 processor.
Table 8-1 Cortex-M7 ISA Support
Configuration

ISA supported

Processor with no floating-point

v7E-M

Processor with single-precision floating-point

v7E-M + FPv5-SP-D16-M

Processor with single-precision and double-precision floating-point

v7E-M + FPv5-DP-D16-M

It provides floating-point computation functionality that is compliant with the ANSI/IEEE Std
754-2008, IEEE Standard for Binary Floating-Point Arithmetic, referred to as the IEEE 754
standard.

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Floating Point Unit

8.2

FPU functional description
This section describes the operations and that the FPU supports and what exceptions the FPU
generates.
The FPU fully supports single-precision and double-precision add, subtract, multiply, divide,
multiply and accumulate, and square root operations. It also provides conversions between
fixed-point and floating-point data formats, and floating-point constant instructions.
The FPU provides an extension register file containing 32 single-precision registers. These can
be viewed as:
•
Sixteen 64-bit doubleword registers, D0-D15.
•
Thirty-two 32-bit single-word registers, S0-S31.
•
A combination of registers from these views.
For more information about the FPU, see the ARM®v7-M Architecture Reference Manual.
This section contains the following:
•
Modes of operation.
•
Compliance with the IEEE 754 standard on page 8-4.
•
Exceptions on page 8-4.
The modes of operation are controlled using the Floating-Point Status and Control Register,
FPSCR. For more information about the FPSCR see the ARMv7-M Architecture Reference
Manual.

8.2.1

Modes of operation
The FPU provides three modes of operation to accommodate a variety of applications:
•
Full-compliance mode.
•
Flush-to-zero mode.
•
Default NaN mode.
Full-compliance mode
In full-compliance mode, the FPU processes all operations according to the IEEE 754 standard
in hardware.
Flush-to-zero mode
Setting the FPSCR.FZ bit enables flush-to-zero mode. In this mode, the FPU treats all
subnormal input operands of arithmetic operations as zeros in the operation. Exceptions that
result from a zero operand are signaled appropriately. VABS, VNEG, and VMOV are not considered
arithmetic operations and are not affected by flush-to-zero mode. A result that is tiny, as
described in the IEEE 754 standard, where the destination precision is smaller in magnitude than
the minimum normal value before rounding, is replaced with a zero. The FPSCR.IDC bit
indicates when an input flush occurs. The FPSCR.UFC bit indicates when a result flush occurs.
Default NaN mode
Setting the FPSCR.DN bit enables default NaN mode. In this mode, the result of any arithmetic
data processing operation that involves an input NaN, or that generates a NaN result, returns the
default NaN. Propagation of the fraction bits is maintained only by VABS, VNEG, and VMOV
operations. All other arithmetic operations ignore any information in the fraction bits of an input
NaN.

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8-3

Floating Point Unit

8.2.2

Compliance with the IEEE 754 standard
When Default NaN (DN) and Flush-to-Zero (FZ) modes are disabled, FPv5 functionality is
compliant with the IEEE 754 standard in hardware. No support code is required to achieve this
compliance.
See the ARM®v7-M Architecture Reference Manual for information about FP architecture
compliance with the IEEE 754 standard.

8.2.3

Exceptions
The FPU sets the cumulative exception status flag in the FPSCR register as required for each
instruction, in accordance with the FPv5 architecture. The FPU does not support exception
traps. The processor also has six output pins, FPIXC, FPUFC, FPOFC, FPDZC, FPIDC, and
FPIOC, that each reflect the status of one of the cumulative exception flags.
The processor can reduce the exception latency by using lazy stacking. This means that the
processor reserves space on the stack for the FP state, but does not save that state information
to the stack until it is required to do so. See the ARM®v7-M Architecture Reference Manual for
more information.

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8-4

Floating Point Unit

8.3

FPU programmers model
Table 8-2 shows the floating-point system registers in the Cortex-M7 processor with FPU, when
implemented. These registers are described in the ARM®v7-M Architecture Reference Manual.
Table 8-2 Floating-point system registers
Address

Name

Type

Reset

Description

0xE000EF34

FPCCR

0xC0000000

Context Control Register

0xE000EF38

FPCAR

Context Address Register

0xE000EF3C

FPDSCR

0x00000000

Default Status Control Register

0xE000EF40

MVFR0

0x10110021a

Media and VFP Feature Register 0

0x10110221b
0xE000EF44

MVFR1

0x11000011a

Media and VFP Feature Register 1

0x12000011b
0xE000EF48

MVFR2

0x00000040

Media and VFP Feature Register 2

a. Single-precision only FPU.
b. Single-precision and double-precision FPU.

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8-5

Chapter 9
Debug

This chapter describes how to debug and test software running on the processor. It contains the
following sections:
•
About debug on page 9-2.
•
About the AHBD interface on page 9-7.
•
About the FPB on page 9-8.

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9-1

Debug

9.1

About debug
Cortex-M7 debug functionality includes processor halt, single-step, processor core register
access, Vector Catch, unlimited software breakpoints, and full system memory access. See the
ARM®v7-M Architecture Reference Manual for more information. The processor also includes
support for hardware breakpoints and watchpoints configured during implementation:
•
A breakpoint unit supporting four to eight instruction comparators.
•
A watchpoint unit supporting two or four watchpoints.
For processors that implement debug, ARM recommends that a debugger identify and connect
to the debug components using the CoreSight debug infrastructure.
Figure 9-1 shows the recommended flow that a debugger can follow to discover the components
in the CoreSight debug infrastructure. In this case a debugger reads the peripheral and
component ID registers for each CoreSight component in the CoreSight system.
CoreSight debug port
CoreSight access port
Base pointer

Redirection from the
‡ System ROM table, if implemented
Cortex-M7 Processor ROM table
CoreSight ID
Pointers

Cortex-M7 PPB ROM
table
CoreSight ID

‡ ETM

‡ CTI

CoreSight ID

Pointers

ETM control

CTI control

System control space

Data watchpoint unit

Breakpoint unit

CoreSight ID

Cortex-M7 CPUID

Watchpoint control

Breakpoint control

Debug control

‡ Instrumentation
trace macrocell unit
CoreSight ID
Instrumentation
trace control

‡ Optional component

Figure 9-1 CoreSight discovery

To identify the Cortex-M7 processor within the CoreSight system, ARM recommends that a
debugger perform the following actions:
1.

ARM DDI 0489D
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Locate and identify the Cortex-M7 Processor ROM table using its CoreSight
identification. See Table 9-2 on page 9-4 for more information.

9-2

Debug

Follow the pointer in the Cortex-M7 Processor ROM table to the Cortex-M7 PPB ROM
table. From the PPB ROM table pointers the following components can be identified:
a.
System Control Space (SCS).
b.
Breakpoint unit (FPB).
c.
Data Watchpoint and Trace unit (DWT).
d.
Instrumentation Trace Macrocell unit (IMT).
See Table 9-4 on page 9-5 for more information.

When a debugger identifies the SCS from its CoreSight identification, it can identify the
processor and its revision number from the CPUID register in the SCS at address 0xE000ED00.
A debugger cannot rely on the Cortex-M7 Processor ROM table being the first ROM table
encountered. One or more system ROM tables are required between the access port and the
processor ROM table if other CoreSight components are in the system. If a system ROM table
is present, this can include a unique identifier for the implementation.
9.1.1

Cortex-M7 Processor ROM table identification and entries
Table 9-1 shows the processor ROM table identification registers and values for debugger
detection. This permits debuggers to identify the processor.
Table 9-1 Cortex-M7 Processor ROM table identification values
Address

Value

Description

0xE00FEFD0

Peripheral ID4

0x00000004

0xE00FEFD4

Peripheral ID5

0x00000000

Component and Peripheral ID register formats in the
ARM®v7-M Architecture Reference Manual

0xE00FEFD8

Peripheral ID6

0x00000000

0xE00FEFDC

Peripheral ID7

0x00000000

0xE00FEFE0

Peripheral ID0

0x000000C8

0xE00FEFE4

Peripheral ID1

0x000000B4

0xE00FEFE8

Peripheral ID2

0x0000000B

0xE00FEFEC

Peripheral ID3

0x00000000

0xE00FEFF0

Component ID0

0x0000000D

0xE00FEFF4

Component ID1

0x00000010

0xE00FEFF8

Component ID2

0x00000005

0xE00FEFFC

Component ID3

0x000000B1

These values for the Peripheral ID registers identify this as the Cortex-M7 Processor ROM
table. The Component ID registers identify this as a CoreSight ROM table.
Note
The Cortex-M7 Processor ROM table only supports word-size transactions.

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9-3

Debug

Table 9-2 shows the CoreSight components that the Cortex-M7 Processor ROM table points to.
Table 9-2 Cortex-M7 Processor ROM table components
Address

Component

Value

Description

0xE00FE000

Cortex-M7 PPB ROM Table

0x00001003

See Cortex-M7 PPB ROM table identification and entries

0xE00FE004

ETM

0xFFF43003a

See the ARM® CoreSight™ ETM-M7 Technical Reference Manual

0xE00FE008

CTI

0xFFF44003b

See Chapter 10 Cross Trigger Interface

0xE00FE00C

Reserved

0x1FF02002

See the ARM® CoreSight™ Architecture Specification (v2.0)

0xE00FE010

End marker

0x00000000

0xE00FEFCC

SYSTEM ACCESS

0x00000001

a. Reads as 0xFFF43002 if the ETM is not implemented.
b. Reads as 0xFFF44002 if the CTI is not implemented.

The Cortex-M7 Processor ROM table entries point to the debug components of the processor.
The offset for each entry is the offset of that component from the ROM table base address,
0xE00FE000.
See the ARM® CoreSight™ Architecture Specification (v2.0) for more information about the
ROM table ID and component registers, and access types.
9.1.2

Cortex-M7 PPB ROM table identification and entries
Table 9-3 shows the Cortex-M7 PPB ROM table identification registers and values for debugger
detection. This permits debuggers to identify the CoreSight components on the PPB in the
processor and their debug capabilities.
Table 9-3 Cortex-M7 PPB ROM table identification values

ARM DDI 0489D
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Address

Value

Description

0xE00FFFD0

Peripheral ID4

0x00000004

0xE00FFFD4

Peripheral ID5

0x00000000

Component and Peripheral ID register formats in the
ARM®v7-M Architecture Reference Manual

0xE00FFFD8

Peripheral ID6

0x00000000

0xE00FFFDC

Peripheral ID7

0x00000000

0xE00FFFE0

Peripheral ID0

0x000000C7

0xE00FFFE4

Peripheral ID1

0x000000B4

0xE00FFFE8

Peripheral ID2

0x0000000B

0xE00FFFEC

Peripheral ID3

0x00000000

0xE00FFFF0

Component ID0

0x0000000D

0xE00FFFF4

Component ID1

0x00000010

0xE00FFFF8

Component ID2

0x00000005

0xE00FFFFC

Component ID3

0x000000B1

9-4

Debug

These values for the Peripheral ID registers identify this as the Cortex-M7 PPB ROM table. The
Component ID registers identify this as a CoreSight ROM table.
Note
The Cortex-M7 PPB ROM table only supports word size transactions.
Table 9-4 shows the CoreSight components that the Cortex-M7 PPB ROM table points to. The
values depend on the implemented debug configuration.
Table 9-4 Cortex-M7 PPB ROM table components
Address

Component

Value

Description

0xE00FF000

SCS

0xFFF0F003

See System Control Space.

0xE00FF004

DWT

0xFFF02003

See Table 11-1 on page 11-4.

0xE00FF008

FPB

0xFFF03003

See Table 9-7 on page 9-8.

0xE00FF00C

ITM

0xFFF01003a

See Table 12-1 on page 12-4.

0xE00FF010

Reserved (TPIU)

0xFFF41002

Not present, TPIU not implemented inside
Cortex-M7.

0xE00FF014

Reserved (ETM)

0xFFF42002

Not present, ETM is referenced by the
Cortex-M7 Processor ROM table. See
Cortex-M7 Processor ROM table identification
and entries on page 9-3.

0xE00FF018

End marker

0x00000000

0xE00FFFCC

SYSTEM ACCESS

0x00000001

See DAP accessible ROM table in the ARM®v7-M
Architecture Reference Manual.

a. Reads as 0xFFF01002 if the ITM is not implemented.

The Cortex-M7 PPB ROM table entries point to the debug components of the processor. The
offset for each entry is the offset of that component from the ROM table base address,
0xE00FF000.
See the ARM®v7-M Architecture Reference Manual and the ARM® CoreSight™ Architecture
Specification (v2.0) for more information about the ROM table ID and component registers, and
their addresses and access types.
9.1.3

System Control Space
The processor provides debug through registers in the SCS. See:
•
Debug register summary on page 9-6.
•
System address map on page 2-5.

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9-5

Debug

SCS CoreSight identification
Table 9-5 shows the SCS CoreSight identification registers and values for debugger detection.
Final debugger identification of the Cortex-M7 processor is through the CPUID register in the
SCS. See CPUID Base Register on page 3-8.
Table 9-5 SCS identification values
Address

Value

Description

0xE000EFD0

Peripheral ID4

0x00000004

0xE000EFD4

Peripheral ID5

0x00000000

Component and Peripheral ID register formats in
the ARM®v7-M Architecture Reference Manual

0xE000EFD8

Peripheral ID6

0x00000000

0xE000EFDC

Peripheral ID7

0x00000000

0xE000EFE0

Peripheral ID0

0x0000000Ca

0xE000EFE4

Peripheral ID1

0x000000B0

0xE000EFE8

Peripheral ID2

0x0000000B

0xE000EFEC

Peripheral ID3

0x00000000

0xE000EFF0

Component ID0

0x0000000D

0xE000EFF4

Component ID1

0x000000E0

0xE000EFF8

Component ID2

0x00000005

0xE000EFFC

Component ID3

0x000000B1

a. 0x0000000C SCS identification value for implementations without FPU.

See the ARM®v7-M Architecture Reference Manual and the ARM® CoreSight™ Architecture
Specification (v2.0) for more information about the ROM table ID and component registers, and
their addresses and access types.
9.1.4

Debug register summary
Table 9-6 shows the debug registers. Each of these registers is 32 bits wide and is described in
the ARM®v7-M Architecture Reference Manual.
Table 9-6 Debug registers
Address

Name

Type

Reset

Description

0xE000ED30

DFSR

0x00000000a

Debug Fault Status Register

0xE000EDF0

DHCSR

0x00000000

Debug Halting Control and Status Register

0xE000EDF4

DCRSR

Debug Core Register Selector Register

0xE000EDF8

DCRDR

Debug Core Register Data Register

0xE000EDFC

DEMCR

0x00000000

Debug Exception and Monitor Control Register

a. Power-on reset only.

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9-6

Debug

9.2

About the AHBD interface
The 32-bit AHB debug (AHBD) interface implements the AMBA 3 AHB-Lite protocol.
It can be used with a CoreSight AHB-AP to provide debugger access to:
•

All processor control and debug resources.

•

A view of memory that is consistent with that observed by load/store instructions acting
on the processor.

AHBD interface accesses are only in little-endian format. The processor ensures data is
presented in the correct big- or little-endian format to the system. This is transparent to the
debugger.

•

ARM DDI 0489D
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Note
The instruction cache is not accessible to a debugger. Therefore debugger accesses to
cacheable, executable regions of memory might not be coherent with the instructions
visible to the instruction side of the processor.
The data cache must be enabled by setting the CCR.DC to 1 to read and write data to the
cache. If CCR.DC is set to 0, all debug requests to memory regions outside the TCM and
peripheral address space, access only the external memory on AXIM even if the debug
request is marked as cacheable on the AHBD interface.

9-7

Debug

9.3

About the FPB
The FPB implements hardware breakpoints.
The FPB can be configured during implementation to provide either four or eight instruction
comparators. You can configure each comparator individually to return a BKPT instruction to the
processor on a match, to provide hardware breakpoint capability.
The FPB does not support Flash patching. The FP_REMAP register is not implemented and is
RAZ/WI.

9.3.1

FPB functional description
The FPB contains both a global enable and individual enables for each of the comparators
implemented. If the comparison for an entry matches, the address is remapped to a BKPT
instruction if that feature is enabled.
If the FPB supports only four breakpoints then only comparators 0-3 are used, and comparators
4-7 are implemented as RAZ/WI.

9.3.2

FPB programmers model
Table 9-7 shows the FPB registers. Depending on the implementation of your processor, some
of these registers might not be present. Any register that is configured as not present reads as
zero.
Table 9-7 FPB register summary
Address

Name

Type

Reset

Description

0xE0002000

FP_CTRL

0x10000040a

FlashPatch Control Register

0x10000080b

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0xE0002004

FP_REMAP

RAZ/WI

Not implemented

0xE0002008

FP_COMP0

0b00000000c

FlashPatch Comparator Register0

0xE000200C

FP_COMP1

0b00000000

FlashPatch Comparator Register1

0xE0002010

FP_COMP2

0b00000000

FlashPatch Comparator Register2

0xE0002014

FP_COMP3

0b00000000

FlashPatch Comparator Register3

0xE0002018

FP_COMP4

0b00000000

FlashPatch Comparator Register4

0xE000201C

FP_COMP5

0b00000000

FlashPatch Comparator Register5

0xE0002020

FP_COMP6

0b00000000

FlashPatch Comparator Register6

0xE0002024

FP_COMP7

0b00000000

FlashPatch Comparator Register7

0xE0000FB0

FP_LAR

FlashPatch Lock Access Register

0xE0000FB4

FP_LSR

Unknown

FlashPatch Lock Status Register

9-8

Debug

Table 9-7 FPB register summary (continued)
Address

Name

Type

Reset

Description

0xE0002FD0

PID4

0x00000004

Peripheral identification registers

0xE0002FD4

PID5

0x00000000

0xE0002FD8

PID6

0x00000000

0xE0002FDC

PID7

0x00000000

0xE0002FE0

PID0

0x0000000E

0xE0002FE4

PID1

0x000000B0

0xE0002FE8

PID2

0x0000000B

0xE0002FEC

PID3

0x00000000

0xE0002FF0

CID0

0x0000000D

0xE0002FF4

CID1

0x000000E0

0xE0002FF8

CID2

0x00000005

0xE0002FFC

CID3

0x000000B1

Component identification registers

a. If four instruction comparators are implemented.
b. If eight instruction comparators are implemented.
c. For FP_COMP0 to FP_COMP7, bit 0 is reset to 0. Other bits in these registers are not reset.

All FPB registers are described in the ARM®v7-M Architecture Reference Manual.

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9-9

Chapter 10
Cross Trigger Interface

This chapter describes the Cortex-M7 Cross Trigger Interface (CTI). It contains the following
sections:
•
About the CTI on page 10-2.
•
Cortex-M7 CTI functional description on page 10-3.
•
CTI programmers model on page 10-5.

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10-1

Cross Trigger Interface

10.1

About the CTI
If implemented, the CTI enables the debug logic and ETM to interact with each other and with
other CoreSight components. This is called cross triggering. For example, you can configure the
CTI to generate an interrupt when the ETM trigger event occurs.

ARM DDI 0489D
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10-2

Cross Trigger Interface

10.2

Cortex-M7 CTI functional description
The Cortex-M7 CTI is connected to a number of trigger inputs and trigger outputs. Figure 10-1
shows the debug system components and the available trigger inputs and trigger outputs.
External debug request
Debug request
External restart request
Restart request

Processor

Interrupt requests

CTI

Processor halted
DWT comparator outputs
ETM event outputs

ETM
ETM event inputs

Figure 10-1 Debug system components

Table 10-1 shows how the CTI trigger inputs are connected to the Cortex-M7 processor.
Table 10-1 Trigger signals to the CTI
Signal

Description

Connection

Acknowledge, handshake

CTITRIGIN[7]

ETM Event Output 3

ETM to CTI

Pulsed

CTITRIGIN[6]

ETM Event Output 2

CTITRIGIN[5]

ETM Event Output 1

CTITRIGIN[4]

ETM Event Output 0

CTITRIGIN[3]

DWT Comparator Output 2

CTITRIGIN[2]

DWT Comparator Output 1

CTITRIGIN[1]

DWT Comparator Output 0

CTITRIGIN[0]

Processor Halted

Processor to CTI

Table 10-2 shows how the CTI trigger outputs are connected to the processor and ETM.
Table 10-2 Trigger signals from the CTI
Signal

Description

Connection

Acknowledge, handshake

CTITRIGOUT[7]

Processor Restart

CTI to Processor

Processor Restarted

CTITRIGOUT[6]

ETM Event Input 3

CTI to ETM

Pulsed

CTITRIGOUT[5]

ETM Event Input 2

Pulsed

CTITRIGOUT[4]

ETM Event Input 1

Pulsed

CTITRIGOUT[3]

ETM Event Input 0

Pulsed

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10-3

Cross Trigger Interface

Table 10-2 Trigger signals from the CTI (continued)
Signal

Description

Connection

Acknowledge, handshake

CTITRIGOUT[2]

Interrupt request 1

CTI to system

Acknowledged by writing to the CTIINTACK register in ISR

CTITRIGOUT[1]

Interrupt request 0

CTITRIGOUT[0]

Processor debug request

CTI to processor

Acknowledged by the debugger writing to the CTIINTACK
register

•

ARM DDI 0489D
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Note
After the processor is halted using CTI Trigger Output 0, the Processor Debug Request
signal remains asserted. The debugger must write to CTIINTACK to clear the halting
request before restarting the processor.
After asserting an interrupt using the CTI Trigger Output 1 or 2, the Interrupt Service
Routine (ISR) must clear the interrupt request by writing to the CTI Interrupt
Acknowledge, CTIINTACK.

10-4

Cross Trigger Interface

10.3

CTI programmers model
Table 10-3 shows the CTI programmable registers. See the ARM® CoreSight™ SoC-400
Technical Reference Manual for register descriptions.
Table 10-3 CTI register summary

ARM DDI 0489D
ID082615

Address
offset

Type

Reset
value

Description

0x000

CTICONTROL

0x00000000

CTI Control Register

0x010

CTIINTACK

0x00000000

CTI Interrupt Acknowledge Register

0x014

CTIAPPSET

0x00000000

CTI Application Trigger Set Register

0x018

CTIAPPCLEAR

0x00000000

CTI Application Trigger Clear Register

0x01C

CTIAPPPULSE

0x00000000

CTI Application Pulse Register

0x020-0x03C

CTIINEN[7:0]

0x00000000

CTI Trigger to Channel Enable Registers

0x0A0-0x0BC

CTIOUTEN[7:0]

0x00000000

CTI Channel to Trigger Enable Registers

0x130

CTITRIGINSTATUS

0x00000000

CTI Trigger In Status Register

0x134

CTITRIGOUTSTATUS

0x00000000

CTI Trigger Out Status Register

0x138

CTICHINSTATUS

0x00000000

CTI Channel In Status Register

0x140

CTIGATE

0x00000000

Enable CTI Channel Gate register

0x144

ASICCTL

0x00000000

External Multiplexer Control register

0xEDC

ITCHINACK

0x00000000

Integration Test Channel Input
Acknowledge register

0xEE0

ITTRIGINACK

0x00000000

Integration Test Trigger Input Acknowledge
register

0xEE4

ITCHOUT

0x00000000

Integration Test Channel Output register

0xEE8

ITTRIGOUT

0x00000000

Integration Test Trigger Output register

0xEEC

ITCHOUTACK

0x00000000

Integration Test Channel Output
Acknowledge register

0xEF0

ITTRIGOUTACK

0x00000000

Integration Test Trigger Output
Acknowledge register

0xEF4

ITCHIN

0x00000000

Integration Test Channel Input register

0xEF8

ITTRIGIN

0x00000000

Integration Test Trigger Input register

0xF00

ITCTRL

0x00000000

Integration Mode Control register

0xFA0

CLAIMSET

0x0000000F

Claim Tag Set register

0xFA4

CLAIMCLR

0x00000000

Claim Tag Clear register

0xFB0

LAR

0x00000000

Lock Access Register

0xFB4

LSR

0x00000003

Lock Status Register

0xFB8

AUTHSTATUS

0x00000005

Authentication Status register

0xFC8

DEVID

0x00040800

Device Configuration register

10-5

Cross Trigger Interface

Table 10-3 CTI register summary (continued)

ARM DDI 0489D
ID082615

Address
offset

Type

Reset
value

Description

0xFCC

DEVTYPE

0x00000014

Device Type Identifier register

0xFD0

PIDR4

0x00000004

Peripheral ID4 Register

0xFD4

Reserved

0xFD8

Reserved

0xFDC

Reserved

0xFE0

PIDR0

0x00000006

Peripheral ID0 Register

0xFE4

PIDR1

0x000000B9

Peripheral ID1 Register

0xFE8

PIDR2

0x0000004B

Peripheral ID2 Register

0xFEC

PIDR3

0x00000000

Peripheral ID3 Register

0xFF0

CIDR0

0x0000000D

Component ID0 Register

0xFF4

CIDR1

0x00000090

Component ID1 Register

0xFF8

CIDR2

0x00000005

Component ID2 Register

0xFFC

CIDR3

0x000000B1

Component ID3 Register

10-6

Chapter 11
Data Watchpoint and Trace Unit

This chapter describes the Data Watchpoint and Trace (DWT) unit. It contains the following
sections:
•
About the DWT on page 11-2.
•
DWT functional description on page 11-3.
•
DWT programmers model on page 11-4.

ARM DDI 0489D
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11-1

Data Watchpoint and Trace Unit

11.1

About the DWT
The DWT is a debug unit that provides watchpoints and system profiling for the processor. Data
tracing is also available if the processor has been implemented with DWT and ITM trace. See
Chapter 12 Instrumentation Trace Macrocell Unit for details about the ITM.

ARM DDI 0489D
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11-2

Data Watchpoint and Trace Unit

11.2

DWT functional description
A full DWT contains four comparators that you can configure as:
•
A hardware watchpoint.
•
An ETM trigger.
•
A PC sampler event trigger.
•
A data address sampler event trigger.
The first comparator, DWT_COMP0, can also compare against the clock cycle counter,
CYCCNT. You can also use the second comparator, DWT_COMP1, as a data comparator.
A reduced DWT contains two comparators that you can use as a watchpoint or as a trigger. The
comparators support data matching.
The DWT if present contains counters for:
•
Clock cycles, CYCCNT.
•
Folded instructions.
•
Load Store Unit (LSU) operations.
•
Sleep cycles.
•
CPI, that is all instruction cycles except for the first cycle.
•
Interrupt overhead.
Note
An event is generated each time a counter overflows.
You can configure the DWT to generate PC samples at defined intervals, and to generate
interrupt event information.
The DWT provides periodic requests for protocol synchronization to the ITM.

ARM DDI 0489D
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11-3

Data Watchpoint and Trace Unit

11.3

DWT programmers model
Table 11-1 shows the DWT registers. Depending on the implementation of your processor, some
of these registers might not be present. Any register that is configured as not present reads as
zero.
Table 11-1 DWT register summary

ARM DDI 0489D
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Address

Name

Type

Reset

Description

0xE0001000

DWT_CTRL

See a

Control Register

0xE0001004

DWT_CYCCNT

0x00000000

Cycle Count Register

0xE0001008

DWT_CPICNT

CPI Count Register

0xE000100C

DWT_EXCCNT

Exception Overhead Count Register

0xE0001010

DWT_SLEEPCNT

Sleep Count Register

0xE0001014

DWT_LSUCNT

LSU Count Register

0xE0001018

DWT_FOLDCNT

Folded-instruction Count Register

0xE000101C

DWT_PCSR

Program Counter Sample Register

0xE0001020

DWT_COMP0

Comparator Register 0

0xE0001024

DWT_MASK0

Mask Register 0

0xE0001028

DWT_FUNCTION0

0x00000000

Function Register 0

0xE0001030

DWT_COMP1

Comparator Register 1

0xE0001034

DWT_MASK1

Mask Register1

0xE0001038

DWT_FUNCTION1

0x00000000b

Function Register 1

0xE0001040

DWT_COMP2

Comparator Register 2

0xE0001044

DWT_MASK2

Mask Register 2

0xE0001048

DWT_FUNCTION2

0x00000000

Function Register 2

0xE0001050

DWT_COMP3

Comparator Register 3

0xE0001054

DWT_MASK3

Mask Register 3

0xE0001058

DWT_FUNCTION3

0x00000000

Function Register 3

0xE0000FB0

DWT_LAR

Lock Access Register

0xE0000FB4

DWT_LSR

Unknown

Lock Status Register

11-4

Data Watchpoint and Trace Unit

Table 11-1 DWT register summary (continued)
Address

Name

Type

Reset

Description

0xE0001FD0

PID4

0x00000004

Peripheral identification registers

0xE0001FD4

PID5

0x00000000

0xE0001FD8

PID6

0x00000000

0xE0001FDC

PID7

0x00000000

0xE0001FE0

PID0

0x00000002

0xE0001FE4

PID1

0x000000B0

0xE0001FE8

PID2

0x0000000B

0xE0001FEC

PID3

0x00000000

0xE0001FF0

CID0

0x0000000D

0xE0001FF4

CID1

0x000000E0

0xE0001FF8

CID2

0x00000005

0xE0001FFC

CID3

0x000000B1

Component identification registers

a. Possible reset values are:
0x40000000 for full DWT, with trace.
0x48000000 for full DWT, without trace.
0x20000000 for reduced DWT, with trace.
0x28000000 for reduced DWT, without trace.

b. If the processor is configured for minimal debug, the DWT_FUNCTION1[9] is always RAZ.
If the processor is configured for full debug, the DWT_FUNCTION1[9] is always RA0.
All other bits in the DWT_FUNCTION1 register are reset to zero.

DWT registers are described in the ARM®v7-M Architecture Reference Manual.

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•

Note
Cycle matching functionality is only available in comparator 0.

•

Data matching functionality is only available in comparator 1.

•

Data value is only sampled for accesses that do not produce an MPU or bus fault. The PC
is sampled irrespective of any faults. The PC is only sampled for the first address of a
burst.

•

The FUNCTION field in the DWT_FUNCTION1 register is overridden for comparators
given by DATAVADDR0 and DATAVADDR1 if DATAVMATCH is also set in
DWT_FUNCTION1. The comparators given by DATAVADDR0 and DATAVADDR1 can
then only perform address comparator matches for comparator 1 data matches.

•

ARM does not recommend PC match for watchpoints because watchpoints are
asynchronous to the event that causes them. It mainly guards and triggers the ETM.

11-5

Chapter 12
Instrumentation Trace Macrocell Unit

This chapter describes the Instrumentation Trace Macrocell (ITM) unit. It contains the
following sections:
•
About the ITM on page 12-2.
•
ITM functional description on page 12-3.
•
ITM programmers model on page 12-4.

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Instrumentation Trace Macrocell Unit

12.1

About the ITM
The ITM is a an optional application-driven trace source that supports printf() style debugging
to trace operating system and application events, and generates diagnostic system information.

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Instrumentation Trace Macrocell Unit

12.2

ITM functional description
The ITM generates trace information as packets. There are four sources that can generate
packets. If multiple sources generate packets at the same time, the ITM arbitrates the order that
packets are output. The four sources in decreasing order of priority are:
Software trace

Software can write directly to ITM stimulus registers to generate packets.

Hardware trace

The DWT generates these packets, and the ITM outputs them.

Time stamping

Timestamps are generated relative to packets. The ITM contains a 21-bit
counter to generate the timestamp. The processor clock output clocks the
counter.

Global system timestamping
Timestamps can optionally be generated using a system-wide 64-bit count
value. The same count value is used for inserting timestamps in the ETM
trace stream, permitting coarse-grain correlation.

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Instrumentation Trace Macrocell Unit

12.3

ITM programmers model
Table 12-1 shows the ITM registers whose implementation is specific to this processor. Other
registers are described in the ARM®v7-M Architecture Reference Manual.
Depending on the implementation of your processor, the ITM registers might not be present.
Any register that is configured as not present reads as zero.

•
•

Note
You must enable TRCENA of the Debug Exception and Monitor Control Register before
you program or use the ITM.
If the ITM stream requires synchronization packets, you must configure the
synchronization packet rate in the DWT.

Table 12-1 ITM register summary
Address

Name

Type

Reset

Description

0xE0000000-

ITM_STIM0- ITM_STIM31

Stimulus Port Registers 0-31

0xE0000E00

ITM_TER

0x00000000

Trace Enable Register

0xE0000E40

ITM_TPR

0x00000000

ITM Trace Privilege Register on page 12-5

0xE0000E80

ITM_TCR

0x00000000

Trace Control Register

0xE0000EF0

ITM_ITATRDY

Unknown

Integration Mode: Read ATB Ready

0xE0000EF8

ITM_ITATVAL

Integration Mode: Write ATB Valid

0xE0000F00

ITM_TCTRL

0x00000000

Integration Mode Control Register

0xE0000FB0

ITM_LAR

Lock Access Register

0xE0000FB4

ITM_LSR

Unknown

Lock Status Register

0xE0000FD0

PID4

0x00000004

Peripheral identification registers

0xE0000FD4

PID5

0x00000000

0xE0000FD8

PID6

0x00000000

0xE0000FDC

PID7

0x00000000

0xE0000FE0

PID0

0x00000001

0xE0000FE4

PID1

0x000000B0

0xE0000FE8

PID2

0x0000000B

0xE0000FEC

PID3

0x00000000

0xE0000FF0

CID0

0x0000000D

0xE0000FF4

CID1

0x000000E0

0xE0000FF8

CID2

0x00000005

0xE0000FFC

CID3

0x000000B1

0xE000007C

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Component identification registers

12-4

Instrumentation Trace Macrocell Unit

Note
ITM registers are fully accessible in privileged mode. In user mode, all registers can be read,
but only the Stimulus Registers and Trace Enable Registers can be written, and only when the
corresponding Trace Privilege Register bit is set. Invalid user mode writes to the ITM registers
are discarded.

12.3.1

ITM Trace Privilege Register
The ITM_TPR characteristics are:
Purpose

Enables an operating system to control the stimulus ports that are
accessible by user code.

Usage constraints You can only write to this register in privileged mode.
Configurations

This register is available if the ITM is configured in your implementation.

Attributes

See Table 12-1 on page 12-4.

Figure 12-1 shows the ITM_TPR bit assignments.
31

4 3

Reserved
PRIVMASK

Figure 12-1 ITM_TPR bit assignments

Table 12-2 shows the ITM_TPR bit assignments.
Table 12-2 ITM_TPR bit assignments

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Bits

Name

Function

[31:4]

Reserved.

[3:0]

PRIVMASK

Bit mask to enable tracing on ITM stimulus ports:
Bit[0]
Stimulus ports [7:0].
Bit[1]
Stimulus ports [15:8].
Bit[2]
Stimulus ports [23:16].
Bit[3]
Stimulus ports [31:24].

12-5

Chapter 13
Fault detection and handling

This chapter describes the fault detection and handling features of the Cortex-M7 processor. It
contains the following sections:
•
About fault detection and handling on page 13-2.
•
Cache RAM protection on page 13-3.
•
Logic protection on page 13-6.

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Fault detection and handling

13.1

About fault detection and handling
The Cortex-M7 processor fault detection and handling features:
•
Report any detected error to the system.
•
Correct any detected and correctable error.
When the system-on-chip reports a failure, the logging and status must provide all the required
information to identify the source of the failure. The intention is to detect and correct the errors
as much as possible, and identify them to the system.
For Error Correcting Code (ECC) on RAM, all errors explicitly seen must be reported, so that
the error propagation is minimized.

13.1.1

RAM and logic protection
The processor protects memories and logic in two different ways.
•

The RAMs are protected with ECC.

•

The logic of the individual processors is protected by duplication with diagnostic
compare. This is known as redundant logic in a lock-step implementation.

These are independent, and can be used separately.
The processor uses Single Error Correction and Double Error Detection (SEC-DED) ECCs to
detect and correct errors in the RAMs. A finite number of hard, that is, permanent errors can be
detected and corrected with continued normal operation using dedicated error registers.
13.1.2

Analysis of errors
A monitor external to the processor is responsible for analyzing the notified error and marking
the corrupted entries as reusable if it has been proven to be a soft error. This analysis can be
performed by reading and writing the RAM directly through the processor MBIST interface.

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Fault detection and handling

13.2

Cache RAM protection
The following sections describe RAM protection:
•
Protection method.
•
RAM protection summary on page 13-4.
•
ECC codes on page 13-4.
•
RAM configuration on page 13-5.
•
Performance impact on page 13-5.

13.2.1

Protection method
The following sections describe how RAM errors are managed:
•
Detecting errors.
•
Recovering from errors.
•
Handling permanent errors.
•
Error bank register behavior on page 13-4.
Detecting errors
The Cortex-M7 processor uses ECC to detect errors in the cache RAMs.
Recovering from errors
The Cortex-M7 processor can recover from a RAM error detected in the cache by using clean
and invalidate and retry. When an error is detected, as shown in Table 13-1 on page 13-4, the
corresponding index/way is cleaned and invalidated. When the clean and invalidate operation
completed, the requester retries its access. The ECC can also be used to correct single-bit errors
in the RAM.
Instruction cache
In the instruction cache, lines are always clean so that invalidating the line is
sufficient. The retried access then fetches the correct value from external
memory.
Data cache
In the data cache, the cache line can be dirty. The correction of the RAM contents
is done as part of the clean and invalidate operation for caches. This takes place
in the write buffer and the corrected data is written back to external memory. The
retried access then reads the correct value from external memory. If the data
cannot be corrected then the error is non-recoverable.
Handling permanent errors
Permanent errors are handled as follows:
General behavior
If hard, or permanent, errors occur on the RAMs, the clean, invalidate and retry
scheme might cause a deadlock, and the access is continuously replayed. To
prevent this, error bank registers are provided to mask the faulty locations as
unusable and invalid. There are two banks for each side of the memory system.
When an error is detected, the location is pushed in the bank, masking the
corresponding valid bit of the location when reading and when allocating a new

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13-3

Fault detection and handling

line. The line is therefore no longer used unless the entry is reset. Because of
implementation details, there is a short period of time when the line is still seen
by the system, but is removed from the allocation pool.
The depth of the error bank determines how many errors can be supported by the
system. When this limit is reached, the system might livelock. The processor
provides information to the system indicating the number of corrupted locations
to monitor the error bank status before it becomes full. This is a condition that can
cause a potential deadlock. This information is reported on several pins signaling
the use of the error bank, that is, showing if the error bank is empty or at least one
error has been encountered.
Error bank register behavior
Both the instruction and data side use the same algorithm to select the bank to update:

13.2.2

•

If there is a non-valid, unlocked bank then it is always allocated in preference to a valid
bank.

•

If both banks are valid, or both banks are non-valid, and both are not locked then a
round-robin counter updated on each allocation selects the bank to fill.

•

If there is one locked bank then the other bank is always allocated, whether or not it is
already valid.

•

If both banks are locked then no allocation takes place.

RAM protection summary
Table 13-1 shows how the different types of RAM are protected.
Table 13-1 RAM protection summary

RAM type

Protection

Recoverable error

Non-recoverable error

Hard error support

Data tag RAM

SEC-DED ECC

Error seen as single bit
errors

Error seen as a multiple bit
error

Up to two hard errors

Data cache data RAM

SEC-DED ECC

Error seen as single bit
errors

Error seen as a multiple bit
error on dirty lines

Instruction tag RAM

SEC-DED ECC

Any error, single or
double, on the tag or
valid bit stored in the
RAM

Nonea

Instruction cache data RAM

SEC-DED ECC

Any error on the data
stored in the RAM

Nonea

a. The instruction cache is never dirty so cache RAM errors are always recoverable by invalidating the cache and retrying the instruction.

13.2.3

ECC codes
When implemented, the instruction and data caches have:
•
Separate 32-bit ECC codes with seven check bits, one for:
— Instruction cache tag RAM, that is RAM index, tag value, outer attributes and valid
bit.
— Data cache data RAM.

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Fault detection and handling

—

•
13.2.4

Data cache data tag RAM, that is the RAM index, tag value, outer attributes, valid
bit and dirty bit.
A 64-bit ECC code with eight check bits for the instruction cache data RAM.

RAM configuration
Table 13-2 shows the RAM configuration with or without ECC when the processor is
implemented with 4KB instruction and data cache.
Table 13-2 RAM configuration with or without ECC

13.2.5

RAM

Storage for a RAM
set without ECC

Storage for a RAM
set with ECC

Data tag RAM

4x26 bits

4x(26+7) bits

Data data RAM

8x32 bits

8x(32+7) bits

Instruction tag RAM

4x22 bits

4x(22+7) bits

Instruction data RAM

4x64 bits

4x(64+8) bits

Performance impact
In an error-free system, the major performance impact is the cost of the read-modify-write
scheme for non-full stores in the data side. If a store buffer slot does not contain at least a full
32-bit word, it must read the word to be able to compute the check bits. This can occur because
software only writes to an area of memory with byte or halfword store instructions. The data can
then be written in the RAM. This additional read can have a negative impact on performance
because it prevents the slot from being used for another write.
The buffering and outstanding capabilities of the memory system mask part of the additional
read, and it is negligible for most codes. However, ARM recommends that you use as few
cacheable STRB and STRH instructions as possible to reduce the performance impact.
Note
There might be a frequency impact because XOR trees are added on the data returned from the
RAMs.

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Fault detection and handling

13.3

Logic protection
The processor logic can be protected by a duplicate, redundant, processor, that is the exact copy
of the first processor. Both processors share the same RAMs protected with ECC and the same
input pins. The second processor is delayed by two clock cycles so that this redundant system
can detect glitches in the inputs.
The outputs of the two processors are compared on each cycle to detect any error. The outputs
of the first processor are delayed so they can be synchronized with the second processor. This
mechanism relies on the fact that any error occurring in the processor is eventually visible on
the outputs of the processor, or is inherently a safe failure.
On detection of an error in one processor, both processors are reset before executing a code
sequence, to put them in the same initial state. They can then restart execution from a previously
taken snapshot.
The processor provides a template of the logic required for the comparison of the two
processors.

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13-6

Appendix A
Revisions

This appendix describes the technical changes between released issues of this book.
Table A-1 Issue A
Change

Location

Affects

First release

Table A-2 Differences between issue A and issue B
Change

Location

Affects

ARM®v7-M Architecture Reference Manual, issue E.b,
defines Flash Patch Breakpoint version 2

ARM architecture on page 1-13

r0p2
onwards

Prefix CM7_ added to register names ITCMCR,
DTCMCR, CACR, AHBSCR, ABFSR and AHBPCR

r0p2

Cortex-M7 processor features clarified

Features on page 1-2

All revisions

Implementation options table updated

Table 1-1 on page 1-4

All revisions

Data Process Unit changed to Data Processing Unit

Data Processing Unit on page 1-7

All revisions

Single MAC pipeline description clarified

Data Processing Unit on page 1-7

All revisions

Prefetch Unit features clarified

Prefetch Unit on page 1-7

All revisions

ETM block description clarified

Cross Trigger Interface Unit on page 1-9

All revisions

TCM interface description clarified

TCM interface on page 1-11

All revisions

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A-1

Revisions

Table A-2 Differences between issue A and issue B (continued)
Change

Location

Affects

MBIST interface description clarified

MBIST interface on page 1-12

All revisions

Binary compatibility with other Cortex processors
section updated

Binary compatibility with other Cortex processors on
page 2-4

All revisions

Exclusive monitor description clarified

Exclusive monitor on page 2-7

All revisions

Private peripheral bus section updated

Private peripheral bus on page 2-6

All revisions

Exception handling section updated

Exception handling on page 2-9

All revisions

System control registers table updated

Table 3-1 on page 3-3

r0p2

Added ACTLR field descriptions for new system
dependent optimization modes

Auxiliary Control Register on page 3-6

r0p2

CPUID.REVISION function updated

Table 3-4 on page 3-8

r0p2

CLIDR bit assignments table updated

Table 3-5 on page 3-10

r0p2

CCSIDR bit assignments figure clarified

CCSIDR bit assignments on page 3-10

All revisions

CCSIDR.Associativity function updated

Table 3-6 on page 3-11

r0p2

AHBP Control Register clarified

AHBP Control Register on page 3-14

All revisions

CACR[1] name and function updated

Table 3-11 on page 3-16

r0p2

CACR[0] function updated

Table 3-11 on page 3-16

All revisions

Changed RAZ to RAO in Note

About Initialization on page 4-2

All revisions

Note clarified

Preloading TCM on page 4-5

All revisions

Changed AHBP peripheral interface to AHBP
interface

About the memory system on page 5-2

All revisions

Changed AHBP peripheral port to AHBP port

Fault handling on page 5-3

All revisions

Write ID capability description clarified

Table 5-3 on page 5-6

All revisions

ARADDR value for address 0x1D updated

Table 5-20 on page 5-19

All revisions

TCM attributes and permissions section updated

TCM attributes and permissions on page 5-33

r0p1 and
r0p2

Store buffer behavior clarified

Store buffer on page 5-38

All revisions

Low power modes section updated

Low power modes on page 7-3

All revisions

Processor ROM table identification values addresses
updated

Table 9-1 on page 9-3

All revisions

Processor ROM table components table updated

Table 9-2 on page 9-4

All revisions

FPB register summary table updated

Table 9-7 on page 9-8

All revisions

DWT register summary table updated

Table 11-1 on page 11-4

All revisions

Error bank register behavior section added

Protection method on page 13-3

All revisions

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A-2

Revisions

Table A-3 Differences between issue B and issue C
Change

Location

Affects

Bullet list updated

About the Cortex-M7 processor on page 1-2

r1p0

Features updated

Features on page 1-2

r1p0

Memory system section updated

Memory System on page 1-9

r1p0

Store Buffer section added

Store Buffer on page 1-9

All revisions

CPUID reset value updated

Table 3-1 on page 3-3

r1p0

ACTLR bit functions updated

Table 3-3 on page 3-7

All revisions

CPUID.VARIANT and CPUID.REVISION
functions updated

Table 3-4 on page 3-8

r1p0

CSSELR bit assignments table updated

Table 3-8 on page 3-12

All revisions

AHB slave interface section updated

AHB slave interface on page 5-30

r1p0

Memory map section added

Memory map on page 5-30

r1p0

Restrictions on AHBS transactions section updated

Restrictions on AHBS transactions on page 5-30

r1p0

AHBS interface arbitration section updated

AHBS interface arbitration on page 5-31

r1p0

TCM interfaces section updated

TCM interfaces on page 5-33

r1p0

Note added

TCM attributes and permissions on page 5-33

r1p0

TCM configuration section updated

TCM configuration on page 5-34

r1p0

TCM arbitration section updated

TCM arbitration on page 5-34

r1p0

TCM interface protocol section updated

TCM interface protocol on page 5-34

r1p0

TCM read modify write section added

TCM read modify write on page 5-35

r1p0

Booting from TCM section added

Booting from TCM on page 5-35

r1p0

Integration with Flash memory section added

Integration with Flash memory on page 5-35

r1p0

System access to TCM section added

System access to TCM on page 5-35

r1p0

Table A-4 Differences between issue C and issue D
Change

Location

Affects

Updated note about the ARM architecture interworking model

Exceptions on page 2-9

All revisions

CPUID.VARIANT and CPUID.REVISION functions updated

Table 3-1 on page 3-3

r1p1

Added a note to the CPUID register description

CPUID Base Register on page 3-8

All revisions

Invalidate the entire data cache description updated

Initializing and enabling the L1 cache on page 4-3

All revisions

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A-3

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Title                           : ARM Cortex-M7 Processor Technical Reference Manual
Creator                         : ARM Limited
Description                     : ARM Cortex-M7 Technical Reference Manual(TRM).This guide contains documentation for the Cortex-M7 processor, the programmers model, instruction set, registers, memory map, floating point, multimedia, trace and debug support. Components include ETM,MPU, NVIC, FPB,  DWT, ITM, AHB, TPIU, FPU, AXI.
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Page Count                      : 151
Subject                         : ARM Cortex-M7 Technical Reference Manual(TRM).This guide contains documentation for the Cortex-M7 processor, the programmers model, instruction set, registers, memory map, floating point, multimedia, trace and debug support. Components include ETM,MPU, NVIC, FPB,  DWT, ITM, AHB, TPIU, FPU, AXI.
Author                          : ARM Limited
Keywords                        : Cortex-M, Cortex-M7

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