Avr Libc User Manual

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avr-libc
2.0.0
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CONTENTS i
Contents
1 AVR Libc 1
1.1 Introduction ............................... 1
1.2 General information about this library ................. 1
1.3 Supported Devices ........................... 2
1.4 avr-libc License ............................. 12
2 Toolchain Overview 13
2.1 Introduction ............................... 13
2.2 FSF and GNU .............................. 13
2.3 GCC ................................... 14
2.4 GNU Binutils .............................. 14
2.5 avr-libc ................................. 16
2.6 Building Software ............................ 16
2.7 AVRDUDE ............................... 16
2.8 GDB / Insight / DDD .......................... 16
2.9 AVaRICE ................................ 17
2.10 SimulAVR ................................ 17
2.11 Utilities ................................. 17
2.12 Toolchain Distributions (Distros) .................... 17
2.13 Open Source ............................... 17
3 Memory Areas and Using malloc() 18
3.1 Introduction ............................... 18
3.2 Internal vs. external RAM ....................... 19
3.3 Tunables for malloc() .......................... 19
3.4 Implementation details ......................... 21
4 Memory Sections 22
4.1 The .text Section ............................ 23
4.2 The .data Section ............................ 23
4.3 The .bss Section ............................. 23
4.4 The .eeprom Section .......................... 23
4.5 The .noinit Section ........................... 23
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CONTENTS ii
4.6 The .initN Sections ........................... 24
4.7 The .finiN Sections ........................... 25
4.8 The .note.gnu.avr.deviceinfo Section .................. 26
4.9 Using Sections in Assembler Code ................... 27
4.10 Using Sections in C Code ........................ 27
5 Data in Program Space 28
5.1 Introduction ............................... 28
5.2 A Note On const ............................ 28
5.3 Storing and Retrieving Data in the Program Space ........... 29
5.4 Storing and Retrieving Strings in the Program Space ......... 30
5.5 Caveats ................................. 32
6 avr-libc and assembler programs 32
6.1 Introduction ............................... 32
6.2 Invoking the compiler .......................... 33
6.3 Example program ............................ 33
6.4 Pseudo-ops and operators ........................ 37
7 Inline Assembler Cookbook 38
7.1 GCC asm Statement ........................... 39
7.2 Assembler Code ............................. 40
7.3 Input and Output Operands ....................... 41
7.4 Clobbers ................................. 45
7.5 Assembler Macros ........................... 47
7.6 C Stub Functions ............................ 48
7.7 C Names Used in Assembler Code ................... 49
7.8 Links .................................. 49
8 How to Build a Library 50
8.1 Introduction ............................... 50
8.2 How the Linker Works ......................... 50
8.3 How to Design a Library ........................ 50
8.4 Creating a Library ............................ 51
8.5 Using a Library ............................. 52
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CONTENTS iii
9 Benchmarks 52
9.1 A few of libc functions. ......................... 53
9.2 Math functions. ............................. 54
10 Porting From IAR to AVR GCC 55
10.1 Introduction ............................... 55
10.2 Registers ................................ 56
10.3 Interrupt Service Routines (ISRs) .................... 56
10.4 Intrinsic Routines ............................ 57
10.5 Flash Variables ............................. 57
10.6 Non-Returning main() ......................... 58
10.7 Locking Registers ............................ 59
11 Frequently Asked Questions 59
11.1 FAQ Index ................................ 59
11.2 My program doesn’t recognize a variable updated within an interrupt
routine .................................. 61
11.3 I get "undefined reference to..." for functions like "sin()" ....... 61
11.4 How to permanently bind a variable to a register? ........... 62
11.5 How to modify MCUCR or WDTCR early? .............. 62
11.6 What is all this _BV() stuff about? ................... 63
11.7 Can I use C++ on the AVR? ...................... 63
11.8 Shouldn’t I initialize all my variables? ................. 64
11.9 Why do some 16-bit timer registers sometimes get trashed? ...... 65
11.10How do I use a #define’d constant in an asm statement? ........ 65
11.11Why does the PC randomly jump around when single-stepping through
my program in avr-gdb? ........................ 66
11.12How do I trace an assembler file in avr-gdb? .............. 67
11.13How do I pass an IO port as a parameter to a function? ........ 68
11.14What registers are used by the C compiler? .............. 70
11.15How do I put an array of strings completely in ROM? ......... 71
11.16How to use external RAM? ....................... 73
11.17Which -O flag to use? .......................... 74
11.18How do I relocate code to a fixed address? ............... 74
11.19My UART is generating nonsense! My ATmega128 keeps crashing!
Port F is completely broken! ...................... 75
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CONTENTS iv
11.20Why do all my "foo...bar" strings eat up the SRAM? ......... 75
11.21Why does the compiler compile an 8-bit operation that uses bitwise
operators into a 16-bit operation in assembly? ............. 76
11.22How to detect RAM memory and variable overlap problems? ..... 77
11.23Is it really impossible to program the ATtinyXX in C? ......... 77
11.24What is this "clock skew detected" message? .............. 77
11.25Why are (many) interrupt flags cleared by writing a logical 1? . . . . 78
11.26Why have "programmed" fuses the bit value 0? ............ 79
11.27Which AVR-specific assembler operators are available? ........ 79
11.28Why are interrupts re-enabled in the middle of writing the stack pointer? 79
11.29Why are there five different linker scripts? ............... 80
11.30How to add a raw binary image to linker output? ............ 80
11.31How do I perform a software reset of the AVR? ............ 81
11.32I am using floating point math. Why is the compiled code so big? Why
does my code not work? ........................ 82
11.33What pitfalls exist when writing reentrant code? ............ 82
11.34Why are some addresses of the EEPROM corrupted (usually address
zero)? .................................. 85
11.35Why is my baud rate wrong? ...................... 86
11.36On a device with more than 128 KiB of flash, how to make function
pointers work? ............................. 86
11.37Why is assigning ports in a "chain" a bad idea? ............ 86
12 Building and Installing the GNU Tool Chain 87
12.1 Building and Installing under Linux, FreeBSD, and Others ...... 87
12.2 Required Tools ............................. 88
12.3 Optional Tools .............................. 88
12.4 GNU Binutils for the AVR target .................... 89
12.5 GCC for the AVR target ......................... 90
12.6 AVR LibC ................................ 90
12.7 AVRDUDE ............................... 91
12.8 GDB for the AVR target ........................ 91
12.9 SimulAVR ................................ 92
12.10AVaRICE ................................ 92
12.11Building and Installing under Windows ................ 93
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12.12Tools Required for Building the Toolchain for Windows ........ 93
12.13Building the Toolchain for Windows .................. 96
13 Using the GNU tools 101
13.1 Options for the C compiler avr-gcc ................... 101
13.1.1 Machine-specific options for the AVR ............. 101
13.1.2 Selected general compiler options ............... 110
13.2 Options for the assembler avr-as .................... 111
13.2.1 Machine-specific assembler options .............. 111
13.2.2 Examples for assembler options passed through the C compiler 112
13.3 Controlling the linker avr-ld ...................... 113
13.3.1 Selected linker options ..................... 113
13.3.2 Passing linker options from the C compiler .......... 114
14 Compiler optimization 115
14.1 Problems with reordering code ..................... 115
15 Using the avrdude program 117
16 Release Numbering and Methodology 119
16.1 Release Version Numbering Scheme .................. 119
16.2 Releasing AVR Libc .......................... 119
16.2.1 Creating an SVN branch .................... 119
16.2.2 Making a release ........................ 120
17 Acknowledgments 122
18 Todo List 123
19 Deprecated List 123
20 Module Index 124
20.1 Modules ................................. 124
21 Data Structure Index 126
21.1 Data Structures ............................. 126
22 File Index 126
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CONTENTS vi
22.1 File List ................................. 126
23 Module Documentation 128
23.1 <alloca.h>: Allocate space in the stack ................ 128
23.1.1 Detailed Description ...................... 128
23.1.2 Function Documentation .................... 128
23.2 <assert.h>: Diagnostics ........................ 129
23.2.1 Detailed Description ...................... 129
23.2.2 Define Documentation ..................... 129
23.3 <ctype.h>: Character Operations ................... 130
23.3.1 Detailed Description ...................... 130
23.3.2 Function Documentation .................... 131
23.4 <errno.h>: System Errors ....................... 132
23.4.1 Detailed Description ...................... 133
23.4.2 Define Documentation ..................... 133
23.4.3 Variable Documentation .................... 133
23.5 <inttypes.h>: Integer Type conversions ................ 133
23.5.1 Detailed Description ...................... 136
23.5.2 Define Documentation ..................... 137
23.5.3 Typedef Documentation .................... 147
23.6 <math.h>: Mathematics ........................ 147
23.6.1 Detailed Description ...................... 149
23.6.2 Define Documentation ..................... 149
23.6.3 Function Documentation .................... 154
23.7 <setjmp.h>: Non-local goto ...................... 160
23.7.1 Detailed Description ...................... 160
23.7.2 Function Documentation .................... 161
23.8 <stdint.h>: Standard Integer Types .................. 162
23.8.1 Detailed Description ...................... 165
23.8.2 Define Documentation ..................... 165
23.8.3 Typedef Documentation .................... 171
23.9 <stdio.h>: Standard IO facilities .................... 174
23.9.1 Detailed Description ...................... 175
23.9.2 Define Documentation ..................... 178
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23.9.3 Typedef Documentation .................... 181
23.9.4 Function Documentation .................... 181
23.10<stdlib.h>: General utilities ...................... 192
23.10.1 Detailed Description ...................... 193
23.10.2 Define Documentation ..................... 193
23.10.3 Typedef Documentation .................... 194
23.10.4 Function Documentation .................... 194
23.10.5 Variable Documentation .................... 202
23.11<string.h>: Strings ........................... 203
23.11.1 Detailed Description ...................... 204
23.11.2 Define Documentation ..................... 204
23.11.3 Function Documentation .................... 204
23.12<time.h>: Time ............................ 216
23.12.1 Detailed Description ...................... 217
23.12.2 Define Documentation ..................... 218
23.12.3 Typedef Documentation .................... 219
23.12.4 Enumeration Type Documentation ............... 219
23.12.5 Function Documentation .................... 220
23.13<avr/boot.h>: Bootloader Support Utilities .............. 225
23.13.1 Detailed Description ...................... 225
23.13.2 Define Documentation ..................... 227
23.14<avr/cpufunc.h>: Special AVR CPU functions ............ 231
23.14.1 Detailed Description ...................... 232
23.14.2 Define Documentation ..................... 232
23.14.3 Function Documentation .................... 232
23.15<avr/eeprom.h>: EEPROM handling ................. 232
23.15.1 Detailed Description ...................... 233
23.15.2 Define Documentation ..................... 234
23.15.3 Function Documentation .................... 235
23.16<avr/fuse.h>: Fuse Support ...................... 237
23.17<avr/interrupt.h>: Interrupts ...................... 240
23.17.1 Detailed Description ...................... 240
23.17.2 Define Documentation ..................... 257
23.18<avr/io.h>: AVR device-specific IO definitions ............ 260
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23.18.1 Detailed Description ...................... 260
23.18.2 Define Documentation ..................... 261
23.19<avr/lock.h>: Lockbit Support ..................... 261
23.20<avr/pgmspace.h>: Program Space Utilities ............. 264
23.20.1 Detailed Description ...................... 266
23.20.2 Define Documentation ..................... 266
23.20.3 Typedef Documentation .................... 270
23.20.4 Function Documentation .................... 274
23.21<avr/power.h>: Power Reduction Management ............ 288
23.21.1 Detailed Description ...................... 288
23.21.2 Function Documentation .................... 291
23.22Additional notes from <avr/sfr_defs.h>................ 292
23.23<avr/sfr_defs.h>: Special function registers .............. 293
23.23.1 Detailed Description ...................... 293
23.23.2 Define Documentation ..................... 294
23.24<avr/signature.h>: Signature Support ................. 295
23.25<avr/sleep.h>: Power Management and Sleep Modes ......... 296
23.25.1 Detailed Description ...................... 296
23.25.2 Function Documentation .................... 297
23.26<avr/version.h>: avr-libc version macros ............... 298
23.26.1 Detailed Description ...................... 298
23.26.2 Define Documentation ..................... 299
23.27<avr/wdt.h>: Watchdog timer handling ................ 299
23.27.1 Detailed Description ...................... 300
23.27.2 Define Documentation ..................... 301
23.27.3 Function Documentation .................... 303
23.28<util/atomic.h>Atomically and Non-Atomically Executed Code Blocks303
23.28.1 Detailed Description ...................... 303
23.28.2 Define Documentation ..................... 305
23.29<util/crc16.h>: CRC Computations .................. 306
23.29.1 Detailed Description ...................... 306
23.29.2 Function Documentation .................... 307
23.30<util/delay.h>: Convenience functions for busy-wait delay loops . . . 310
23.30.1 Detailed Description ...................... 310
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23.30.2 Define Documentation ..................... 311
23.30.3 Function Documentation .................... 311
23.31<util/delay_basic.h>: Basic busy-wait delay loops .......... 313
23.31.1 Detailed Description ...................... 313
23.31.2 Function Documentation .................... 313
23.32<util/parity.h>: Parity bit generation .................. 314
23.32.1 Detailed Description ...................... 314
23.32.2 Define Documentation ..................... 314
23.33<util/setbaud.h>: Helper macros for baud rate calculations ...... 314
23.33.1 Detailed Description ...................... 315
23.33.2 Define Documentation ..................... 316
23.34<util/twi.h>: TWI bit mask definitions ................ 317
23.34.1 Detailed Description ...................... 318
23.34.2 Define Documentation ..................... 318
23.35<compat/deprecated.h>: Deprecated items .............. 321
23.35.1 Detailed Description ...................... 322
23.35.2 Define Documentation ..................... 322
23.35.3 Function Documentation .................... 324
23.36<compat/ina90.h>: Compatibility with IAR EWB 3.x ........ 324
23.37Demo projects .............................. 325
23.37.1 Detailed Description ...................... 325
23.38Combining C and assembly source files ................ 326
23.38.1 Hardware setup ......................... 326
23.38.2 A code walkthrough ...................... 327
23.38.3 The source code ........................ 329
23.39A simple project ............................. 329
23.39.1 The Project ........................... 329
23.39.2 The Source Code ........................ 331
23.39.3 Compiling and Linking ..................... 333
23.39.4 Examining the Object File ................... 333
23.39.5 Linker Map Files ........................ 338
23.39.6 Generating Intel Hex Files ................... 340
23.39.7 Letting Make Build the Project ................. 341
23.39.8 Reference to the source code .................. 343
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23.40A more sophisticated project ...................... 343
23.40.1 Hardware setup ......................... 344
23.40.2 Functional overview ...................... 347
23.40.3 A code walkthrough ...................... 347
23.40.4 The source code ........................ 350
23.41Using the standard IO facilities ..................... 350
23.41.1 Hardware setup ......................... 350
23.41.2 Functional overview ...................... 352
23.41.3 A code walkthrough ...................... 352
23.41.4 The source code ........................ 357
23.42Example using the two-wire interface (TWI) .............. 357
23.42.1 Introduction into TWI ..................... 358
23.42.2 The TWI example project ................... 358
23.42.3 The Source Code ........................ 358
24 Data Structure Documentation 362
24.1 div_t Struct Reference ......................... 362
24.1.1 Detailed Description ...................... 362
24.1.2 Field Documentation ...................... 362
24.2 ldiv_t Struct Reference ......................... 363
24.2.1 Detailed Description ...................... 363
24.2.2 Field Documentation ...................... 363
24.3 tm Struct Reference ........................... 363
24.3.1 Detailed Description ...................... 363
24.3.2 Field Documentation ...................... 364
24.4 week_date Struct Reference ...................... 365
24.4.1 Detailed Description ...................... 365
24.4.2 Field Documentation ...................... 365
25 File Documentation 365
25.1 assert.h File Reference ......................... 365
25.1.1 Detailed Description ...................... 366
25.2 atoi.S File Reference .......................... 366
25.2.1 Detailed Description ...................... 366
25.3 atol.S File Reference .......................... 366
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25.3.1 Detailed Description ...................... 366
25.4 atomic.h File Reference ......................... 366
25.4.1 Detailed Description ...................... 366
25.5 boot.h File Reference .......................... 366
25.5.1 Detailed Description ...................... 367
25.6 cpufunc.h File Reference ........................ 367
25.6.1 Detailed Description ...................... 367
25.7 crc16.h File Reference ......................... 367
25.7.1 Detailed Description ...................... 367
25.8 ctype.h File Reference ......................... 367
25.8.1 Detailed Description ...................... 368
25.9 delay.h File Reference ......................... 368
25.9.1 Detailed Description ...................... 368
25.10delay_basic.h File Reference ...................... 368
25.10.1 Detailed Description ...................... 368
25.11errno.h File Reference ......................... 368
25.11.1 Detailed Description ...................... 369
25.12fdevopen.c File Reference ....................... 369
25.12.1 Detailed Description ...................... 369
25.13fuse.h File Reference .......................... 369
25.13.1 Detailed Description ...................... 369
25.14interrupt.h File Reference ........................ 369
25.14.1 Detailed Description ...................... 370
25.15inttypes.h File Reference ........................ 370
25.15.1 Detailed Description ...................... 372
25.16io.h File Reference ........................... 372
25.16.1 Detailed Description ...................... 372
25.17lock.h File Reference .......................... 372
25.17.1 Detailed Description ...................... 372
25.18math.h File Reference .......................... 372
25.18.1 Detailed Description ...................... 375
25.19parity.h File Reference ......................... 375
25.19.1 Detailed Description ...................... 375
25.20pgmspace.h File Reference ....................... 375
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1 AVR Libc 1
25.20.1 Detailed Description ...................... 377
25.21power.h File Reference ......................... 377
25.21.1 Detailed Description ...................... 377
25.21.2 Define Documentation ..................... 377
25.22setbaud.h File Reference ........................ 378
25.22.1 Detailed Description ...................... 378
25.23setjmp.h File Reference ......................... 378
25.23.1 Detailed Description ...................... 378
25.24signature.h File Reference ....................... 378
25.24.1 Detailed Description ...................... 378
25.25sleep.h File Reference .......................... 378
25.25.1 Detailed Description ...................... 378
25.26stdint.h File Reference ......................... 378
25.26.1 Detailed Description ...................... 381
25.27stdio.h File Reference .......................... 381
25.27.1 Detailed Description ...................... 383
25.28stdlib.h File Reference ......................... 383
25.28.1 Detailed Description ...................... 384
25.29string.h File Reference ......................... 384
25.29.1 Detailed Description ...................... 385
25.30time.h File Reference .......................... 385
25.30.1 Detailed Description ...................... 387
25.31twi.h File Reference ........................... 387
25.31.1 Detailed Description ...................... 388
25.32wdt.h File Reference .......................... 388
25.32.1 Detailed Description ...................... 388
1 AVR Libc
1.1 Introduction
The latest version of this document is always available from
http://savannah.nongnu.org/projects/avr-libc/
The AVR Libc package provides a subset of the standard C library for Atmel AVR
8-bit RISC microcontrollers. In addition, the library provides the basic
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1.2 General information about this library 2
startup code needed by most applications.
There is a wealth of information in this document which goes beyond simply describ-
ing the interfaces and routines provided by the library. We hope that this document
provides enough information to get a new AVR developer up to speed quickly using
the freely available development tools: binutils, gcc avr-libc and many others.
If you find yourself stuck on a problem which this document doesn’t quite address, you
may wish to post a message to the avr-gcc mailing list. Most of the developers of the
AVR binutils and gcc ports in addition to the devleopers of avr-libc subscribe to the
list, so you will usually be able to get your problem resolved. You can subscribe to the
list at http://lists.nongnu.org/mailman/listinfo/avr-gcc-list
. Before posting to the list, you might want to try reading the Frequently Asked Ques-
tions chapter of this document.
Note
If you think you’ve found a bug, or have a suggestion for an improvement, ei-
ther in this documentation or in the library itself, please use the bug tracker at
https://savannah.nongnu.org/bugs/?group=avr-libc to ensure
the issue won’t be forgotten.
1.2 General information about this library
In general, it has been the goal to stick as best as possible to established standards
while implementing this library. Commonly, this refers to the C library as described by
the ANSI X3.159-1989 and ISO/IEC 9899:1990 ("ANSI-C") standard, as well as parts
of their successor ISO/IEC 9899:1999 ("C99"). Some additions have been inspired by
other standards like IEEE Std 1003.1-1988 ("POSIX.1"), while other extensions are
purely AVR-specific (like the entire program-space string interface).
Unless otherwise noted, functions of this library are not guaranteed to be reentrant. In
particular, any functions that store local state are known to be non-reentrant, as well
as functions that manipulate IO registers like the EEPROM access routines. If these
functions are used within both standard and interrupt contexts undefined behaviour will
result. See the FAQ for a more detailed discussion.
1.3 Supported Devices
The following is a list of AVR devices currently supported by the library. Note that
actual support for some newer devices depends on the ability of the compiler/assembler
to support these devices at library compile-time.
megaAVR Devices:
• atmega103
• atmega128
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1.3 Supported Devices 3
• atmega128a
• atmega1280
• atmega1281
• atmega1284
• atmega1284p
• atmega16
• atmega161
• atmega162
• atmega163
• atmega164a
• atmega164p
• atmega164pa
• atmega165
• atmega165a
• atmega165p
• atmega165pa
• atmega168
• atmega168a
• atmega168p
• atmega168pa
• atmega168pb
• atmega16a
• atmega2560
• atmega2561
• atmega32
• atmega32a
• atmega323
• atmega324a
• atmega324p
• atmega324pa
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1.3 Supported Devices 4
• atmega325
• atmega325a
• atmega325p
• atmega325pa
• atmega3250
• atmega3250a
• atmega3250p
• atmega3250pa
• atmega328
• atmega328p
• atmega48
• atmega48a
• atmega48pa
• atmega48pb
• atmega48p
• atmega64
• atmega64a
• atmega640
• atmega644
• atmega644a
• atmega644p
• atmega644pa
• atmega645
• atmega645a
• atmega645p
• atmega6450
• atmega6450a
• atmega6450p
• atmega8
• atmega8a
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1.3 Supported Devices 5
• atmega88
• atmega88a
• atmega88p
• atmega88pa
• atmega88pb
• atmega8515
• atmega8535
tinyAVR Devices:
• attiny4
• attiny5
• attiny10
• attiny11 [1]
• attiny12 [1]
• attiny13
• attiny13a
• attiny15 [1]
• attiny20
• attiny22
• attiny24
• attiny24a
• attiny25
• attiny26
• attiny261
• attiny261a
• attiny28 [1]
• attiny2313
• attiny2313a
• attiny40
• attiny4313
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1.3 Supported Devices 6
• attiny43u
• attiny44
• attiny44a
• attiny441
• attiny45
• attiny461
• attiny461a
• attiny48
• attiny828
• attiny84
• attiny84a
• attiny841
• attiny85
• attiny861
• attiny861a
• attiny87
• attiny88
• attiny1634
Automotive AVR Devices:
• atmega16m1
• atmega32c1
• atmega32m1
• atmega64c1
• atmega64m1
• attiny167
• ata5505
• ata5272
• ata5702m322
• ata5782
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1.3 Supported Devices 7
• ata5790
• ata5790n
• ata5791
• ata5795
• ata5831
• ata6612c
• ata6613c
• ata6614q
• ata6616c
• ata6617c
• ata664251
• ata8210
• ata8510
CAN AVR Devices:
• at90can32
• at90can64
• at90can128
LCD AVR Devices:
• atmega169
• atmega169a
• atmega169p
• atmega169pa
• atmega329
• atmega329a
• atmega329p
• atmega329pa
• atmega3290
• atmega3290a
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1.3 Supported Devices 8
• atmega3290p
• atmega3290pa
• atmega649
• atmega649a
• atmega6490
• atmega6490a
• atmega6490p
• atmega649p
Lighting AVR Devices:
• at90pwm1
• at90pwm2
• at90pwm2b
• at90pwm216
• at90pwm3
• at90pwm3b
• at90pwm316
• at90pwm161
• at90pwm81
Smart Battery AVR Devices:
• atmega8hva
• atmega16hva
• atmega16hva2
• atmega16hvb
• atmega16hvbrevb
• atmega32hvb
• atmega32hvbrevb
• atmega64hve
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1.3 Supported Devices 9
• atmega64hve2
• atmega406
USB AVR Devices:
• at90usb82
• at90usb162
• at90usb646
• at90usb647
• at90usb1286
• at90usb1287
• atmega8u2
• atmega16u2
• atmega16u4
• atmega32u2
• atmega32u4
• atmega32u6
XMEGA Devices:
• atxmega8e5
• atxmega16a4
• atxmega16a4u
• atxmega16c4
• atxmega16d4
• atxmega16e5
• atxmega32a4
• atxmega32a4u
• atxmega32c3
• atxmega32c4
• atxmega32d3
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1.3 Supported Devices 10
• atxmega32d4
• atxmega32e5
• atxmega64a1
• atxmega64a1u
• atxmega64a3
• atxmega64a3u
• atxmega64a4u
• atxmega64b1
• atxmega64b3
• atxmega64c3
• atxmega64d3
• atxmega64d4
• atxmega128a1
• atxmega128a1u
• atxmega128a3
• atxmega128a3u
• atxmega128a4u
• atxmega128b1
• atxmega128b3
• atxmega128c3
• atxmega128d3
• atxmega128d4
• atxmega192a3
• atxmega192a3u
• atxmega192c3
• atxmega192d3
• atxmega256a3
• atxmega256a3u
• atxmega256a3b
• atxmega256a3bu
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1.3 Supported Devices 11
• atxmega256c3
• atxmega256d3
• atxmega384c3
• atxmega384d3
Wireless AVR devices:
• atmega644rfr2
• atmega64rfr2
• atmega128rfa1
• atmega1284rfr2
• atmega128rfr2
• atmega2564rfr2
• atmega256rfr2
Miscellaneous Devices:
• at94K [2]
• at76c711 [3]
• at43usb320
• at43usb355
• at86rf401
• at90scr100
• ata6285
• ata6286
• ata6289
• m3000 [4]
Classic AVR Devices:
• at90s1200 [1]
• at90s2313
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1.4 avr-libc License 12
• at90s2323
• at90s2333
• at90s2343
• at90s4414
• at90s4433
• at90s4434
• at90s8515
• at90c8534
• at90s8535
Note
[1] Assembly only. There is no direct support for these devices to be programmed
in C since they do not have a RAM based stack. Still, it could be possible to
program them in C, see the FAQ for an option.
Note
[2] The at94K devices are a combination of FPGA and AVR microcontroller.
[TRoth-2002/11/12: Not sure of the level of support for these. More information
would be welcomed.]
Note
[3] The at76c711 is a USB to fast serial interface bridge chip using an AVR core.
Note
[4] The m3000 is a motor controller AVR ASIC from Intelligent Motion Systems
(IMS) / Schneider Electric.
1.4 avr-libc License
avr-libc can be freely used and redistributed, provided the following license conditions
are met.
Portions of avr-libc are Copyright (c) 1999-2016
Werner Boellmann,
Dean Camera,
Pieter Conradie,
Brian Dean,
Keith Gudger,
Wouter van Gulik,
Bjoern Haase,
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1.4 avr-libc License 13
Steinar Haugen,
Peter Jansen,
Reinhard Jessich,
Magnus Johansson,
Harald Kipp,
Carlos Lamas,
Cliff Lawson,
Artur Lipowski,
Marek Michalkiewicz,
Todd C. Miller,
Rich Neswold,
Colin O’Flynn,
Bob Paddock,
Andrey Pashchenko,
Reiner Patommel,
Florin-Viorel Petrov,
Alexander Popov,
Michael Rickman,
Theodore A. Roth,
Juergen Schilling,
Philip Soeberg,
Anatoly Sokolov,
Nils Kristian Strom,
Michael Stumpf,
Stefan Swanepoel,
Helmut Wallner,
Eric B. Weddington,
Joerg Wunsch,
Dmitry Xmelkov,
Atmel Corporation,
egnite Software GmbH,
The Regents of the University of California.
All rights reserved.
Redistribution and use in source and binary forms, with or without
modification, are permitted provided that the following conditions are met:
*Redistributions of source code must retain the above copyright
notice, this list of conditions and the following disclaimer.
*Redistributions in binary form must reproduce the above copyright
notice, this list of conditions and the following disclaimer in
the documentation and/or other materials provided with the
distribution.
*Neither the name of the copyright holders nor the names of
contributors may be used to endorse or promote products derived
from this software without specific prior written permission.
THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE
LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
POSSIBILITY OF SUCH DAMAGE.
Generated on Wed Jul 25 09:38:10 2018 for avr-libc by Doxygen
2 Toolchain Overview 14
2 Toolchain Overview
2.1 Introduction
Welcome to the open source software development toolset for the Atmel AVR!
There is not a single tool that provides everything needed to develop software for the
AVR. It takes many tools working together. Collectively, the group of tools are called a
toolset, or commonly a toolchain, as the tools are chained together to produce the final
executable application for the AVR microcontroller.
The following sections provide an overview of all of these tools. You may be used
to cross-compilers that provide everything with a GUI front-end, and not know what
goes on "underneath the hood". You may be coming from a desktop or server computer
background and not used to embedded systems. Or you may be just learning about the
most common software development toolchain available on Unix and Linux systems.
Hopefully the following overview will be helpful in putting everything in perspective.
2.2 FSF and GNU
According to its website, "the Free Software Foundation (FSF), established in 1985, is
dedicated to promoting computer users’ rights to use, study, copy, modify, and redis-
tribute computer programs. The FSF promotes the development and use of free soft-
ware, particularly the GNU operating system, used widely in its GNU/Linux variant."
The FSF remains the primary sponsor of the GNU project.
The GNU Project was launched in 1984 to develop a complete Unix-like operating
system which is free software: the GNU system. GNU is a recursive acronym for
»GNU’s Not Unix«; it is pronounced guh-noo, approximately like canoe.
One of the main projects of the GNU system is the GNU Compiler Collection, or GCC,
and its sister project, GNU Binutils. These two open source projects provide a foun-
dation for a software development toolchain. Note that these projects were designed to
originally run on Unix-like systems.
2.3 GCC
GCC stands for GNU Compiler Collection. GCC is highly flexible compiler system. It
has different compiler front-ends for different languages. It has many back-ends that
generate assembly code for many different processors and host operating systems. All
share a common "middle-end", containing the generic parts of the compiler, including
a lot of optimizations.
In GCC, a host system is the system (processor/OS) that the compiler runs on. A
target system is the system that the compiler compiles code for. And, a build system
is the system that the compiler is built (from source code) on. If a compiler has the
same system for host and for target, it is known as a native compiler. If a compiler
has different systems for host and target, it is known as a cross-compiler. (And if all
three, build,host, and target systems are different, it is known as a Canadian cross
compiler, but we won’t discuss that here.) When GCC is built to execute on a host
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2.4 GNU Binutils 15
system such as FreeBSD, Linux, or Windows, and it is built to generate code for the
AVR microcontroller target, then it is a cross compiler, and this version of GCC is
commonly known as "AVR GCC". In documentation, or discussion, AVR GCC is
used when referring to GCC targeting specifically the AVR, or something that is AVR
specific about GCC. The term "GCC" is usually used to refer to something generic
about GCC, or about GCC as a whole.
GCC is different from most other compilers. GCC focuses on translating a high-level
language to the target assembly only. AVR GCC has three available compilers for the
AVR: C language, C++, and Ada. The compiler itself does not assemble or link the
final code.
GCC is also known as a "driver" program, in that it knows about, and drives other
programs seamlessly to create the final output. The assembler, and the linker are part
of another open source project called GNU Binutils. GCC knows how to drive the
GNU assembler (gas) to assemble the output of the compiler. GCC knows how to drive
the GNU linker (ld) to link all of the object modules into a final executable.
The two projects, GCC and Binutils, are very much interrelated and many of the same
volunteers work on both open source projects.
When GCC is built for the AVR target, the actual program names are prefixed with
"avr-". So the actual executable name for AVR GCC is: avr-gcc. The name "avr-gcc"
is used in documentation and discussion when referring to the program itself and not
just the whole AVR GCC system.
See the GCC Web Site and GCC User Manual for more information about GCC.
2.4 GNU Binutils
The name GNU Binutils stands for "Binary Utilities". It contains the GNU assembler
(gas), and the GNU linker (ld), but also contains many other utilities that work with
binary files that are created as part of the software development toolchain.
Again, when these tools are built for the AVR target, the actual program names are
prefixed with "avr-". For example, the assembler program name, for a native assembler
is "as" (even though in documentation the GNU assembler is commonly referred to as
"gas"). But when built for an AVR target, it becomes "avr-as". Below is a list of the
programs that are included in Binutils:
avr-as
The Assembler.
avr-ld
The Linker.
avr-ar
Create, modify, and extract from libraries (archives).
avr-ranlib
Generate index to library (archive) contents.
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2.5 avr-libc 16
avr-objcopy
Copy and translate object files to different formats.
avr-objdump
Display information from object files including disassembly.
avr-size
List section sizes and total size.
avr-nm
List symbols from object files.
avr-strings
List printable strings from files.
avr-strip
Discard symbols from files.
avr-readelf
Display the contents of ELF format files.
avr-addr2line
Convert addresses to file and line.
avr-c++filt
Filter to demangle encoded C++ symbols.
2.5 avr-libc
GCC and Binutils provides a lot of the tools to develop software, but there is one critical
component that they do not provide: a Standard C Library.
There are different open source projects that provide a Standard C Library depending
upon your system time, whether for a native compiler (GNU Libc), for some other
embedded system (newlib), or for some versions of Linux (uCLibc). The open source
AVR toolchain has its own Standard C Library project: avr-libc.
AVR-Libc provides many of the same functions found in a regular Standard C Library
and many additional library functions that is specific to an AVR. Some of the Standard
C Library functions that are commonly used on a PC environment have limitations or
additional issues that a user needs to be aware of when used on an embedded system.
AVR-Libc also contains the most documentation about the whole AVR toolchain.
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2.6 Building Software 17
2.6 Building Software
Even though GCC, Binutils, and avr-libc are the core projects that are used to build
software for the AVR, there is another piece of software that ties it all together: Make.
GNU Make is a program that makes things, and mainly software. Make interprets and
executes a Makefile that is written for a project. A Makefile contains dependency rules,
showing which output files are dependent upon which input files, and instructions on
how to build output files from input files.
Some distributions of the toolchains, and other AVR tools such as MFile, contain a
Makefile template written for the AVR toolchain and AVR applications that you can
copy and modify for your application.
See the GNU Make User Manual for more information.
2.7 AVRDUDE
After creating your software, you’ll want to program your device. You can do this by
using the program AVRDUDE which can interface with various hardware devices to
program your processor.
AVRDUDE is a very flexible package. All the information about AVR processors
and various hardware programmers is stored in a text database. This database can be
modified by any user to add new hardware or to add an AVR processor if it is not
already listed.
2.8 GDB / Insight / DDD
The GNU Debugger (GDB) is a command-line debugger that can be used with the rest
of the AVR toolchain. Insight is GDB plus a GUI written in Tcl/Tk. Both GDB and
Insight are configured for the AVR and the main executables are prefixed with the target
name: avr-gdb, and avr-insight. There is also a "text mode" GUI for GDB: avr-gdbtui.
DDD (Data Display Debugger) is another popular GUI front end to GDB, available on
Unix and Linux systems.
2.9 AVaRICE
AVaRICE is a back-end program to AVR GDB and interfaces to the Atmel JTAG In-
Circuit Emulator (ICE), to provide emulation capabilities.
2.10 SimulAVR
SimulAVR is an AVR simulator used as a back-end with AVR GDB.
2.11 Utilities
There are also other optional utilities available that may be useful to add to your toolset.
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2.12 Toolchain Distributions (Distros) 18
SRecord is a collection of powerful tools for manipulating EPROM load files. It
reads and writes numerous EPROM file formats, and can perform many different ma-
nipulations.
MFile is a simple Makefile generator is meant as an aid to quickly customize a Make-
file to use for your AVR application.
2.12 Toolchain Distributions (Distros)
All of the various open source projects that comprise the entire toolchain are normally
distributed as source code. It is left up to the user to build the tool application from its
source code. This can be a very daunting task to any potential user of these tools.
Luckily there are people who help out in this area. Volunteers take the time to build the
application from source code on particular host platforms and sometimes packaging
the tools for convenient installation by the end user. These packages contain the binary
executables of the tools, pre-made and ready to use. These packages are known as
"distributions" of the AVR toolchain, or by a more shortened name, "distros".
AVR toolchain distros are available on FreeBSD, Windows, Mac OS X, and certain
flavors of Linux.
2.13 Open Source
All of these tools, from the original source code in the multitude of projects, to the
various distros, are put together by many, many volunteers. All of these projects could
always use more help from other people who are willing to volunteer some of their time.
There are many different ways to help, for people with varying skill levels, abilities,
and available time.
You can help to answer questions in mailing lists such as the avr-gcc-list, or on forums
at the AVR Freaks website. This helps many people new to the open source AVR tools.
If you think you found a bug in any of the tools, it is always a big help to submit a good
bug report to the proper project. A good bug report always helps other volunteers to
analyze the problem and to get it fixed for future versions of the software.
You can also help to fix bugs in various software projects, or to add desirable new
features.
Volunteers are always welcome! :-)
3 Memory Areas and Using malloc()
3.1 Introduction
Many of the devices that are possible targets of avr-libc have a minimal amount of
RAM. The smallest parts supported by the C environment come with 128 bytes of
RAM. This needs to be shared between initialized and uninitialized variables (sections
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3.1 Introduction 19
.data and .bss), the dynamic memory allocator, and the stack that is used for calling
subroutines and storing local (automatic) variables.
Also, unlike larger architectures, there is no hardware-supported memory management
which could help in separating the mentioned RAM regions from being overwritten by
each other.
The standard RAM layout is to place .data variables first, from the beginning of the
internal RAM, followed by .bss. The stack is started from the top of internal RAM,
growing downwards. The so-called "heap" available for the dynamic memory allocator
will be placed beyond the end of .bss. Thus, there’s no risk that dynamic memory will
ever collide with the RAM variables (unless there were bugs in the implementation of
the allocator). There is still a risk that the heap and stack could collide if there are large
requirements for either dynamic memory or stack space. The former can even happen
if the allocations aren’t all that large but dynamic memory allocations get fragmented
over time such that new requests don’t quite fit into the "holes" of previously freed
regions. Large stack space requirements can arise in a C function containing large
and/or numerous local variables or when recursively calling function.
Note
The pictures shown in this document represent typical situations where the RAM
locations refer to an ATmega128. The memory addresses used are not displayed
in a linear scale.
!
__bss_end
__data_end == __bss_start
__data_start
RAMENDSP
*(__malloc_heap_start) == __heap_start
*(__brkval) (<= *SP − *(__malloc_margin))
variables
.data
variables
.bss
0x10FF
0x0100
heap stack
on−board RAM external RAM
0x1100
0xFFFF
Figure 1: RAM map of a device with internal RAM
On a simple device like a microcontroller it is a challenge to implement a dynamic
memory allocator that is simple enough so the code size requirements will remain low,
yet powerful enough to avoid unnecessary memory fragmentation and to get it all done
with reasonably few CPU cycles. Microcontrollers are often low on space and also run
at much lower speeds than the typical PC these days.
The memory allocator implemented in avr-libc tries to cope with all of these con-
straints, and offers some tuning options that can be used if there are more resources
available than in the default configuration.
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3.2 Internal vs. external RAM 20
3.2 Internal vs. external RAM
Obviously, the constraints are much harder to satisfy in the default configuration where
only internal RAM is available. Extreme care must be taken to avoid a stack-heap
collision, both by making sure functions aren’t nesting too deeply, and don’t require
too much stack space for local variables, as well as by being cautious with allocating
too much dynamic memory.
If external RAM is available, it is strongly recommended to move the heap into the ex-
ternal RAM, regardless of whether or not the variables from the .data and .bss sections
are also going to be located there. The stack should always be kept in internal RAM.
Some devices even require this, and in general, internal RAM can be accessed faster
since no extra wait states are required. When using dynamic memory allocation and
stack and heap are separated in distinct memory areas, this is the safest way to avoid a
stack-heap collision.
3.3 Tunables for malloc()
There are a number of variables that can be tuned to adapt the behavior of malloc()
to the expected requirements and constraints of the application. Any changes to these
tunables should be made before the very first call to malloc(). Note that some library
functions might also use dynamic memory (notably those from the <stdio.h>: Stan-
dard IO facilities), so make sure the changes will be done early enough in the startup
sequence.
The variables __malloc_heap_start and __malloc_heap_end can be used
to restrict the malloc() function to a certain memory region. These variables are stati-
cally initialized to point to __heap_start and __heap_end, respectively, where
__heap_start is filled in by the linker to point just beyond .bss, and __heap_end
is set to 0 which makes malloc() assume the heap is below the stack.
If the heap is going to be moved to external RAM, __malloc_heap_end must be
adjusted accordingly. This can either be done at run-time, by writing directly to this
variable, or it can be done automatically at link-time, by adjusting the value of the
symbol __heap_end.
The following example shows a linker command to relocate the entire .data and .bss
segments, and the heap to location 0x1100 in external RAM. The heap will extend up
to address 0xffff.
avr-gcc ... -Wl,--section-start,.data=0x801100,--defsym=__heap_end=0x80ffff ...
Note
See explanation for offset 0x800000. See the chapter about using gcc for the -Wl
options.
The ld (linker) user manual states that using -Tdata=<x>is equivalent to using
--section-start,.data=<x>. However, you have to use --section-start as above be-
cause the GCC frontend also sets the -Tdata option for all MCU types where the
SRAM doesn’t start at 0x800060. Thus, the linker is being faced with two -Tdata
options. Sarting with binutils 2.16, the linker changed the preference, and picks
the "wrong" option in this situation.
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3.3 Tunables for malloc() 21
SP
RAMEND
__bss_end
__data_end == __bss_start
__data_start
*(__malloc_heap_end) == __heap_end
*(__malloc_heap_start) == __heap_start
*(__brkval)
variables
.data
variables
.bss
heap
external RAM
0x10FF
0x0100
stack
on−board RAM
0x1100
0xFFFF
Figure 2: Internal RAM: stack only, external RAM: variables and heap
If dynamic memory should be placed in external RAM, while keeping the variables in
internal RAM, something like the following could be used. Note that for demonstration
purposes, the assignment of the various regions has not been made adjacent in this
example, so there are "holes" below and above the heap in external RAM that remain
completely unaccessible by regular variables or dynamic memory allocations (shown
in light bisque color in the picture below).
avr-gcc ... -Wl,--defsym=__heap_start=0x802000,--defsym=__heap_end=0x803fff ...
SP
RAMEND
__bss_end
__data_end == __bss_start
__data_start
*(__malloc_heap_end) == __heap_end
*(__brkval)
*(__malloc_heap_start) == __heap_start
0x10FF
0x0100
stack
on−board RAM
0x1100
0xFFFF
.data
variablesvariables
.bss
heap
0x2000
external RAM
0x3FFF
Figure 3: Internal RAM: variables and stack, external RAM: heap
If __malloc_heap_end is 0, the allocator attempts to detect the bottom of stack
in order to prevent a stack-heap collision when extending the actual size of the heap
to gain more space for dynamic memory. It will not try to go beyond the current
stack limit, decreased by __malloc_margin bytes. Thus, all possible stack frames
of interrupt routines that could interrupt the current function, plus all further nested
function calls must not require more stack space, or they will risk colliding with the
data segment.
The default value of __malloc_margin is set to 32.
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3.4 Implementation details 22
3.4 Implementation details
Dynamic memory allocation requests will be returned with a two-byte header
prepended that records the size of the allocation. This is later used by free(). The
returned address points just beyond that header. Thus, if the application accidentally
writes before the returned memory region, the internal consistency of the memory al-
locator is compromised.
The implementation maintains a simple freelist that accounts for memory blocks that
have been returned in previous calls to free(). Note that all of this memory is considered
to be successfully added to the heap already, so no further checks against stack-heap
collisions are done when recycling memory from the freelist.
The freelist itself is not maintained as a separate data structure, but rather by modifying
the contents of the freed memory to contain pointers chaining the pieces together. That
way, no additional memory is reqired to maintain this list except for a variable that
keeps track of the lowest memory segment available for reallocation. Since both, a
chain pointer and the size of the chunk need to be recorded in each chunk, the minimum
chunk size on the freelist is four bytes.
When allocating memory, first the freelist is walked to see if it could satisfy the request.
If there’s a chunk available on the freelist that will fit the request exactly, it will be
taken, disconnected from the freelist, and returned to the caller. If no exact match could
be found, the closest match that would just satisfy the request will be used. The chunk
will normally be split up into one to be returned to the caller, and another (smaller)
one that will remain on the freelist. In case this chunk was only up to two bytes larger
than the request, the request will simply be altered internally to also account for these
additional bytes since no separate freelist entry could be split off in that case.
If nothing could be found on the freelist, heap extension is attempted. This is where
__malloc_margin will be considered if the heap is operating below the stack, or
where __malloc_heap_end will be verified otherwise.
If the remaining memory is insufficient to satisfy the request, NULL will eventually be
returned to the caller.
When calling free(), a new freelist entry will be prepared. An attempt is then made to
aggregate the new entry with possible adjacent entries, yielding a single larger entry
available for further allocations. That way, the potential for heap fragmentation is
hopefully reduced. When deallocating the topmost chunk of memory, the size of the
heap is reduced.
A call to realloc() first determines whether the operation is about to grow or shrink the
current allocation. When shrinking, the case is easy: the existing chunk is split, and the
tail of the region that is no longer to be used is passed to the standard free() function for
insertion into the freelist. Checks are first made whether the tail chunk is large enough
to hold a chunk of its own at all, otherwise realloc() will simply do nothing, and return
the original region.
When growing the region, it is first checked whether the existing allocation can be ex-
tended in-place. If so, this is done, and the original pointer is returned without copying
any data contents. As a side-effect, this check will also record the size of the largest
chunk on the freelist.
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4 Memory Sections 23
If the region cannot be extended in-place, but the old chunk is at the top of heap, and
the above freelist walk did not reveal a large enough chunk on the freelist to satisfy
the new request, an attempt is made to quickly extend this topmost chunk (and thus
the heap), so no need arises to copy over the existing data. If there’s no more space
available in the heap (same check is done as in malloc()), the entire request will fail.
Otherwise, malloc() will be called with the new request size, the existing data will be
copied over, and free() will be called on the old region.
4 Memory Sections
Remarks
Need to list all the sections which are available to the avr.
Weak Bindings
FIXME: need to discuss the .weak directive.
The following describes the various sections available.
4.1 The .text Section
The .text section contains the actual machine instructions which make up your program.
This section is further subdivided by the .initN and .finiN sections dicussed below.
Note
The avr-size program (part of binutils), coming from a Unix background,
doesn’t account for the .data initialization space added to the .text section, so in
order to know how much flash the final program will consume, one needs to add
the values for both, .text and .data (but not .bss), while the amount of pre-allocated
SRAM is the sum of .data and .bss.
4.2 The .data Section
This section contains static data which was defined in your code. Things like the fol-
lowing would end up in .data:
char err_str[] = "Your program has died a horrible death!";
struct point pt = { 1, 1 };
It is possible to tell the linker the SRAM address of the beginning of the .data section.
This is accomplished by adding -Wl,-Tdata,addr to the avr-gcc command
used to the link your program. Not that addr must be offset by adding 0x800000
the to real SRAM address so that the linker knows that the address is in the SRAM
memory space. Thus, if you want the .data section to start at 0x1100, pass 0x801100
at the address to the linker. [offset explained]
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4.3 The .bss Section 24
Note
When using malloc() in the application (which could even happen inside library
calls), additional adjustments are required.
4.3 The .bss Section
Uninitialized global or static variables end up in the .bss section.
4.4 The .eeprom Section
This is where eeprom variables are stored.
4.5 The .noinit Section
This sections is a part of the .bss section. What makes the .noinit section special is that
variables which are defined as such:
int foo __attribute__ ((section (".noinit")));
will not be initialized to zero during startup as would normal .bss data.
Only uninitialized variables can be placed in the .noinit section. Thus, the following
code will cause avr-gcc to issue an error:
int bar __attribute__ ((section (".noinit"))) = 0xaa;
It is possible to tell the linker explicitly where to place the .noinit section by adding
-Wl,--section-start=.noinit=0x802000 to the avr-gcc command line
at the linking stage. For example, suppose you wish to place the .noinit section at
SRAM address 0x2000:
$ avr-gcc ... -Wl,--section-start=.noinit=0x802000 ...
Note
Because of the Harvard architecture of the AVR devices, you must manually add
0x800000 to the address you pass to the linker as the start of the section. Oth-
erwise, the linker thinks you want to put the .noinit section into the .text section
instead of .data/.bss and will complain.
Alternatively, you can write your own linker script to automate this. [FIXME: need an
example or ref to dox for writing linker scripts.]
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4.6 The .initN Sections 25
4.6 The .initN Sections
These sections are used to define the startup code from reset up through the start of
main(). These all are subparts of the .text section.
The purpose of these sections is to allow for more specific placement of code within
your program.
Note
Sometimes, it is convenient to think of the .initN and .finiN sections as functions,
but in reality they are just symbolic names which tell the linker where to stick a
chunk of code which is not a function. Notice that the examples for asm and Ccan
not be called as functions and should not be jumped into.
The .initN sections are executed in order from 0 to 9.
.init0:
Weakly bound to __init(). If user defines __init(), it will be jumped into immedi-
ately after a reset.
.init1:
Unused. User definable.
.init2:
In C programs, weakly bound to initialize the stack, and to clear __zero_reg__
(r1).
.init3:
Unused. User definable.
.init4:
For devices with >64 KB of ROM, .init4 defines the code which takes care of copying
the contents of .data from the flash to SRAM. For all other devices, this code as well
as the code to zero out the .bss section is loaded from libgcc.a.
.init5:
Unused. User definable.
.init6:
Unused for C programs, but used for constructors in C++ programs.
.init7:
Unused. User definable.
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4.7 The .finiN Sections 26
.init8:
Unused. User definable.
.init9:
Jumps into main().
4.7 The .finiN Sections
These sections are used to define the exit code executed after return from main() or a
call to exit(). These all are subparts of the .text section.
The .finiN sections are executed in descending order from 9 to 0.
.finit9:
Unused. User definable. This is effectively where _exit() starts.
.fini8:
Unused. User definable.
.fini7:
Unused. User definable.
.fini6:
Unused for C programs, but used for destructors in C++ programs.
.fini5:
Unused. User definable.
.fini4:
Unused. User definable.
.fini3:
Unused. User definable.
.fini2:
Unused. User definable.
.fini1:
Unused. User definable.
.fini0:
Goes into an infinite loop after program termination and completion of any _exit()
code (execution of code in the .fini9 ->.fini1 sections).
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4.8 The .note.gnu.avr.deviceinfo Section 27
4.8 The .note.gnu.avr.deviceinfo Section
This section contains device specific information picked up from the device
header file and compiler builtin macros. The layout conforms to the stan-
dard ELF note section layout (http://docs.oracle.com/cd/E23824_-
01/html/819-0690/chapter6-18048.html).
The section contents are laid out as below.
#define __NOTE_NAME_LEN 4
struct __note_gnu_avr_deviceinfo
{
struct
{
uint32_t namesz; /*= __NOTE_NAME_LEN */
uint32_t descsz; /*= size of avr_desc */
uint32_t type; /*= 1 - no other AVR note types exist */
char note_name[__NOTE_NAME_LEN]; /*= "AVR\0" */
}
note_header;
struct
{
uint32_t flash_start;
uint32_t flash_size;
uint32_t sram_start;
uint32_t sram_size;
uint32_t eeprom_start;
uint32_t eeprom_size;
uint32_t offset_table_size;
uint32_t offset_table[1]; /*Offset table containing byte offsets into
string table that immediately follows it.
index 0: Device name byte offset
*/
char str_table [2 +
strlen(__AVR_DEVICE_NAME__)]; /*Standard ELF string table.
index 0 : NULL
index 1 : Device name
index 2 : NULL
*/
}
avr_desc;
};
4.9 Using Sections in Assembler Code
Example:
#include <avr/io.h>
.section .init1,"ax",@progbits
ldi r0, 0xff
out _SFR_IO_ADDR(PORTB), r0
out _SFR_IO_ADDR(DDRB), r0
Note
The ,"ax",@progbits tells the assembler that the section is allocatable ("a"),
executable ("x") and contains data ("@progbits"). For more detailed information
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4.10 Using Sections in C Code 28
on the .section directive, see the gas user manual.
4.10 Using Sections in C Code
Example:
#include <avr/io.h>
void my_init_portb (void) __attribute__ ((naked)) \
__attribute__ ((section (".init3")))
__attribute__ ((used));
void
my_init_portb (void)
{
PORTB = 0xff;
DDRB = 0xff;
}
Note
Section .init3 is used in this example, as this ensures the inernal __zero_reg_-
_has already been set up. The code generated by the compiler might blindly
rely on __zero_reg__ being really 0. __attribute__ ((used)) tells
the compiler that code must be generated for this function even if it appears that
the function is not referenced - this is necessary to prevent compiler optimizations
(like LTO) from eliminating the function.
5 Data in Program Space
5.1 Introduction
So you have some constant data and you’re running out of room to store it? Many
AVRs have limited amount of RAM in which to store data, but may have more Flash
space available. The AVR is a Harvard architecture processor, where Flash is used for
the program, RAM is used for data, and they each have separate address spaces. It is
a challenge to get constant data to be stored in the Program Space, and to retrieve that
data to use it in the AVR application.
The problem is exacerbated by the fact that the C Language was not designed for
Harvard architectures, it was designed for Von Neumann architectures where code and
data exist in the same address space. This means that any compiler for a Harvard
architecture processor, like the AVR, has to use other means to operate with separate
address spaces.
Some compilers use non-standard C language keywords, or they extend the standard
syntax in ways that are non-standard. The AVR toolset takes a different approach.
GCC has a special keyword, __attribute__ that is used to attach different at-
tributes to things such as function declarations, variables, and types. This keyword is
followed by an attribute specification in double parentheses. In AVR GCC, there is a
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5.2 A Note On const 29
special attribute called progmem. This attribute is use on data declarations, and tells
the compiler to place the data in the Program Memory (Flash).
AVR-Libc provides a simple macro PROGMEM that is defined as the attribute syn-
tax of GCC with the progmem attribute. This macro was created as a convenience
to the end user, as we will see below. The PROGMEM macro is defined in the
<avr/pgmspace.h>system header file.
It is difficult to modify GCC to create new extensions to the C language syntax, so
instead, avr-libc has created macros to retrieve the data from the Program Space. These
macros are also found in the <avr/pgmspace.h>system header file.
5.2 A Note On const
Many users bring up the idea of using C’s keyword const as a means of declaring
data to be in Program Space. Doing this would be an abuse of the intended meaning of
the const keyword.
const is used to tell the compiler that the data is to be "read-only". It is used to help
make it easier for the compiler to make certain transformations, or to help the compiler
check for incorrect usage of those variables.
For example, the const keyword is commonly used in many functions as a modifier on
the parameter type. This tells the compiler that the function will only use the parameter
as read-only and will not modify the contents of the parameter variable.
const was intended for uses such as this, not as a means to identify where the data
should be stored. If it were used as a means to define data storage, then it loses its
correct meaning (changes its semantics) in other situations such as in the function pa-
rameter example.
5.3 Storing and Retrieving Data in the Program Space
Let’s say you have some global data:
unsigned char mydata[11][10] =
{
{0x00,0x01,0x02,0x03,0x04,0x05,0x06,0x07,0x08,0x09},
{0x0A,0x0B,0x0C,0x0D,0x0E,0x0F,0x10,0x11,0x12,0x13},
{0x14,0x15,0x16,0x17,0x18,0x19,0x1A,0x1B,0x1C,0x1D},
{0x1E,0x1F,0x20,0x21,0x22,0x23,0x24,0x25,0x26,0x27},
{0x28,0x29,0x2A,0x2B,0x2C,0x2D,0x2E,0x2F,0x30,0x31},
{0x32,0x33,0x34,0x35,0x36,0x37,0x38,0x39,0x3A,0x3B},
{0x3C,0x3D,0x3E,0x3F,0x40,0x41,0x42,0x43,0x44,0x45},
{0x46,0x47,0x48,0x49,0x4A,0x4B,0x4C,0x4D,0x4E,0x4F},
{0x50,0x51,0x52,0x53,0x54,0x55,0x56,0x57,0x58,0x59},
{0x5A,0x5B,0x5C,0x5D,0x5E,0x5F,0x60,0x61,0x62,0x63},
{0x64,0x65,0x66,0x67,0x68,0x69,0x6A,0x6B,0x6C,0x6D}
};
and later in your code you access this data in a function and store a single byte into a
variable like so:
byte = mydata[i][j];
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5.3 Storing and Retrieving Data in the Program Space 30
Now you want to store your data in Program Memory. Use the PROGMEM macro found
in <avr/pgmspace.h>and put it after the declaration of the variable, but before
the initializer, like so:
#include <avr/pgmspace.h>
.
.
.
const unsigned char mydata[11][10] PROGMEM =
{
{0x00,0x01,0x02,0x03,0x04,0x05,0x06,0x07,0x08,0x09},
{0x0A,0x0B,0x0C,0x0D,0x0E,0x0F,0x10,0x11,0x12,0x13},
{0x14,0x15,0x16,0x17,0x18,0x19,0x1A,0x1B,0x1C,0x1D},
{0x1E,0x1F,0x20,0x21,0x22,0x23,0x24,0x25,0x26,0x27},
{0x28,0x29,0x2A,0x2B,0x2C,0x2D,0x2E,0x2F,0x30,0x31},
{0x32,0x33,0x34,0x35,0x36,0x37,0x38,0x39,0x3A,0x3B},
{0x3C,0x3D,0x3E,0x3F,0x40,0x41,0x42,0x43,0x44,0x45},
{0x46,0x47,0x48,0x49,0x4A,0x4B,0x4C,0x4D,0x4E,0x4F},
{0x50,0x51,0x52,0x53,0x54,0x55,0x56,0x57,0x58,0x59},
{0x5A,0x5B,0x5C,0x5D,0x5E,0x5F,0x60,0x61,0x62,0x63},
{0x64,0x65,0x66,0x67,0x68,0x69,0x6A,0x6B,0x6C,0x6D}
};
That’s it! Now your data is in the Program Space. You can compile, link, and check
the map file to verify that mydata is placed in the correct section.
Now that your data resides in the Program Space, your code to access (read) the data
will no longer work. The code that gets generated will retrieve the data that is located
at the address of the mydata array, plus offsets indexed by the iand jvariables.
However, the final address that is calculated where to the retrieve the data points to
the Data Space! Not the Program Space where the data is actually located. It is likely
that you will be retrieving some garbage. The problem is that AVR GCC does not
intrinsically know that the data resides in the Program Space.
The solution is fairly simple. The "rule of thumb" for accessing data stored in the
Program Space is to access the data as you normally would (as if the variable is stored
in Data Space), like so:
byte = mydata[i][j];
then take the address of the data:
byte = &(mydata[i][j]);
then use the appropriate pgm_read_∗macro, and the address of your data becomes
the parameter to that macro:
byte = pgm_read_byte(&(mydata[i][j]));
The pgm_read_∗macros take an address that points to the Program Space, and re-
trieves the data that is stored at that address. This is why you take the address of the
offset into the array. This address becomes the parameter to the macro so it can gen-
erate the correct code to retrieve the data from the Program Space. There are different
pgm_read_∗macros to read different sizes of data at the address given.
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5.4 Storing and Retrieving Strings in the Program Space 31
5.4 Storing and Retrieving Strings in the Program Space
Now that you can successfully store and retrieve simple data from Program Space you
want to store and retrive strings from Program Space. And specifically you want to
store and array of strings to Program Space. So you start off with your array, like so:
char *string_table[] =
{
"String 1",
"String 2",
"String 3",
"String 4",
"String 5"
};
and then you add your PROGMEM macro to the end of the declaration:
char *string_table[] PROGMEM =
{
"String 1",
"String 2",
"String 3",
"String 4",
"String 5"
};
Right? WRONG!
Unfortunately, with GCC attributes, they affect only the declaration that they are at-
tached to. So in this case, we successfully put the string_table variable, the array
itself, in the Program Space. This DOES NOT put the actual strings themselves into
Program Space. At this point, the strings are still in the Data Space, which is probably
not what you want.
In order to put the strings in Program Space, you have to have explicit declarations for
each string, and put each string in Program Space:
const char string_1[] PROGMEM = "String 1";
const char string_2[] PROGMEM = "String 2";
const char string_3[] PROGMEM = "String 3";
const char string_4[] PROGMEM = "String 4";
const char string_5[] PROGMEM = "String 5";
Then use the new symbols in your table, like so:
PGM_P const string_table[] PROGMEM =
{
string_1,
string_2,
string_3,
string_4,
string_5
};
Now this has the effect of putting string_table in Program Space, where
string_table is an array of pointers to characters (strings), where each pointer
is a pointer to the Program Space, where each string is also stored.
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5.5 Caveats 32
The PGM_P type above is also a macro that defined as a pointer to a character in the
Program Space.
Retrieving the strings are a different matter. You probably don’t want to pull the string
out of Program Space, byte by byte, using the pgm_read_byte() macro. There are
other functions declared in the <avr/pgmspace.h>header file that work with strings
that are stored in the Program Space.
For example if you want to copy the string from Program Space to a buffer in RAM
(like an automatic variable inside a function, that is allocated on the stack), you can do
this:
void foo(void)
{
char buffer[10];
for (unsigned char i = 0; i < 5; i++)
{
strcpy_P(buffer, (PGM_P)pgm_read_word(&(string_table[i])));
// Display buffer on LCD.
}
return;
}
Here, the string_table array is stored in Program Space, so we access it normally,
as if were stored in Data Space, then take the address of the location we want to access,
and use the address as a parameter to pgm_read_word. We use the pgm_read_-
word macro to read the string pointer out of the string_table array. Remember
that a pointer is 16-bits, or word size. The pgm_read_word macro will return a 16-
bit unsigned integer. We then have to typecast it as a true pointer to program memory,
PGM_P. This pointer is an address in Program Space pointing to the string that we
want to copy. This pointer is then used as a parameter to the function strcpy_P. The
function strcpy_P is just like the regular strcpy function, except that it copies a
string from Program Space (the second parameter) to a buffer in the Data Space (the
first parameter).
There are many string functions available that work with strings located in Program
Space. All of these special string functions have a suffix of _P in the function name,
and are declared in the <avr/pgmspace.h>header file.
5.5 Caveats
The macros and functions used to retrieve data from the Program Space have to gen-
erate some extra code in order to actually load the data from the Program Space. This
incurs some extra overhead in terms of code space (extra opcodes) and execution time.
Usually, both the space and time overhead is minimal compared to the space savings
of putting data in Program Space. But you should be aware of this so you can mini-
mize the number of calls within a single function that gets the same piece of data from
Program Space. It is always instructive to look at the resulting disassembly from the
compiler.
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6 avr-libc and assembler programs 33
6 avr-libc and assembler programs
6.1 Introduction
There might be several reasons to write code for AVR microcontrollers using plain
assembler source code. Among them are:
• Code for devices that do not have RAM and are thus not supported by the C
compiler.
• Code for very time-critical applications.
• Special tweaks that cannot be done in C.
Usually, all but the first could probably be done easily using the inline assembler facility
of the compiler.
Although avr-libc is primarily targeted to support programming AVR microcontrollers
using the C (and C++) language, there’s limited support for direct assembler usage as
well. The benefits of it are:
• Use of the C preprocessor and thus the ability to use the same symbolic constants
that are available to C programs, as well as a flexible macro concept that can use
any valid C identifier as a macro (whereas the assembler’s macro concept is
basically targeted to use a macro in place of an assembler instruction).
• Use of the runtime framework like automatically assigning interrupt vectors. For
devices that have RAM, initializing the RAM variables can also be utilized.
6.2 Invoking the compiler
For the purpose described in this document, the assembler and linker are usually not
invoked manually, but rather using the C compiler frontend (avr-gcc) that in turn
will call the assembler and linker as required.
This approach has the following advantages:
• There is basically only one program to be called directly, avr-gcc, regardless
of the actual source language used.
• The invokation of the C preprocessor will be automatic, and will include the
appropriate options to locate required include files in the filesystem.
• The invokation of the linker will be automatic, and will include the appropri-
ate options to locate additional libraries as well as the application start-up code
(crtXXX.o) and linker script.
Note that the invokation of the C preprocessor will be automatic when the filename
provided for the assembler file ends in .S (the capital letter "s"). This would even apply
to operating systems that use case-insensitive filesystems since the actual decision is
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6.3 Example program 34
made based on the case of the filename suffix given on the command-line, not based on
the actual filename from the file system.
As an alternative to using .S, the suffix .sx is recognized for this purpose (starting
with GCC 4.3.0). This is primarily meant to be compatible with other compiler envi-
ronments that have been providing this variant before in order to cope with operating
systems where filenames are case-insensitive (and, with some versions of make that
could not distinguish between .s and .S on such systems).
Alternatively, the language can explicitly be specified using the -x
assembler-with-cpp option.
6.3 Example program
The following annotated example features a simple 100 kHz square wave generator
using an AT90S1200 clocked with a 10.7 MHz crystal. Pin PD6 will be used for the
square wave output.
#include <avr/io.h> ; Note [1]
work = 16 ; Note [2]
tmp = 17
inttmp = 19
intsav = 0
SQUARE = PD6 ; Note [3]
; Note [4]:
tmconst= 10700000 / 200000 ; 100 kHz => 200000 edges/s
fuzz= 8 ; # clocks in ISR until TCNT0 is set
.section .text
.global main ; Note [5]
main:
rcall ioinit
1:
rjmp 1b ; Note [6]
.global TIMER0_OVF_vect ; Note [7]
TIMER0_OVF_vect:
ldi inttmp, 256 - tmconst + fuzz
out _SFR_IO_ADDR(TCNT0), inttmp ; Note [8]
in intsav, _SFR_IO_ADDR(SREG) ; Note [9]
sbic _SFR_IO_ADDR(PORTD), SQUARE
rjmp 1f
sbi _SFR_IO_ADDR(PORTD), SQUARE
rjmp 2f
1: cbi _SFR_IO_ADDR(PORTD), SQUARE
2:
out _SFR_IO_ADDR(SREG), intsav
reti
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6.3 Example program 35
ioinit:
sbi _SFR_IO_ADDR(DDRD), SQUARE
ldi work, _BV(TOIE0)
out _SFR_IO_ADDR(TIMSK), work
ldi work, _BV(CS00) ; tmr0: CK/1
out _SFR_IO_ADDR(TCCR0), work
ldi work, 256 - tmconst
out _SFR_IO_ADDR(TCNT0), work
sei
ret
.global __vector_default ; Note [10]
__vector_default:
reti
.end
Note [1]
As in C programs, this includes the central processor-specific file containing the IO port
definitions for the device. Note that not all include files can be included into assembler
sources.
Note [2]
Assignment of registers to symbolic names used locally. Another option would be to
use a C preprocessor macro instead:
#define work 16
Note [3]
Our bit number for the square wave output. Note that the right-hand side consists of a
CPP macro which will be substituted by its value (6 in this case) before actually being
passed to the assembler.
Note [4]
The assembler uses integer operations in the host-defined integer size (32 bits or longer)
when evaluating expressions. This is in contrast to the C compiler that uses the C type
int by default in order to calculate constant integer expressions.
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6.3 Example program 36
In order to get a 100 kHz output, we need to toggle the PD6 line 200000 times per
second. Since we use timer 0 without any prescaling options in order to get the de-
sired frequency and accuracy, we already run into serious timing considerations: while
accepting and processing the timer overflow interrupt, the timer already continues to
count. When pre-loading the TCCNT0 register, we therefore have to account for the
number of clock cycles required for interrupt acknowledge and for the instructions to
reload TCCNT0 (4 clock cycles for interrupt acknowledge, 2 cycles for the jump from
the interrupt vector, 2 cycles for the 2 instructions that reload TCCNT0). This is what
the constant fuzz is for.
Note [5]
External functions need to be declared to be .global. main is the application entry
point that will be jumped to from the ininitalization routine in crts1200.o.
Note [6]
The main loop is just a single jump back to itself. Square wave generation itself is
completely handled by the timer 0 overflow interrupt service. A sleep instruction
(using idle mode) could be used as well, but probably would not conserve much energy
anyway since the interrupt service is executed quite frequently.
Note [7]
Interrupt functions can get the usual names that are also available to C programs. The
linker will then put them into the appropriate interrupt vector slots. Note that they must
be declared .global in order to be acceptable for this purpose. This will only work if
<avr/io.h>has been included. Note that the assembler or linker have no chance
to check the correct spelling of an interrupt function, so it should be double-checked.
(When analyzing the resulting object file using avr-objdump or avr-nm, a name
like __vector_Nshould appear, with Nbeing a small integer number.)
Note [8]
As explained in the section about special function registers, the actual IO port address
should be obtained using the macro _SFR_IO_ADDR. (The AT90S1200 does not have
RAM thus the memory-mapped approach to access the IO registers is not available. It
would be slower than using in /out instructions anyway.)
Since the operation to reload TCCNT0 is time-critical, it is even performed before
saving SREG. Obviously, this requires that the instructions involved would not change
any of the flag bits in SREG.
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6.4 Pseudo-ops and operators 37
Note [9]
Interrupt routines must not clobber the global CPU state. Thus, it is usually necessary
to save at least the state of the flag bits in SREG. (Note that this serves as an example
here only since actually, all the following instructions would not modify SREG either,
but that’s not commonly the case.)
Also, it must be made sure that registers used inside the interrupt routine do not conflict
with those used outside. In the case of a RAM-less device like the AT90S1200, this can
only be done by agreeing on a set of registers to be used exclusively inside the interrupt
routine; there would not be any other chance to "save" a register anywhere.
If the interrupt routine is to be linked together with C modules, care must be taken
to follow the register usage guidelines imposed by the C compiler. Also, any register
modified inside the interrupt sevice needs to be saved, usually on the stack.
Note [10]
As explained in Interrupts, a global "catch-all" interrupt handler that gets all unassigned
interrupt vectors can be installed using the name __vector_default. This must
be .global, and obviously, should end in a reti instruction. (By default, a jump to
location 0 would be implied instead.)
6.4 Pseudo-ops and operators
The available pseudo-ops in the assembler are described in the GNU assembler (gas)
manual. The manual can be found online as part of the current binutils release under
http://sources.redhat.com/binutils/.
As gas comes from a Unix origin, its pseudo-op and overall assembler syntax is slightly
different than the one being used by other assemblers. Numeric constants follow the C
notation (prefix 0x for hexadecimal constants), expressions use a C-like syntax.
Some common pseudo-ops include:
• .byte allocates single byte constants
• .ascii allocates a non-terminated string of characters
• .asciz allocates a \0-terminated string of characters (C string)
• .data switches to the .data section (initialized RAM variables)
• .text switches to the .text section (code and ROM constants)
• .set declares a symbol as a constant expression (identical to .equ)
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7 Inline Assembler Cookbook 38
• .global (or .globl) declares a public symbol that is visible to the linker (e. g.
function entry point, global variable)
• .extern declares a symbol to be externally defined; this is effectively a comment
only, as gas treats all undefined symbols it encounters as globally undefined any-
way
Note that .org is available in gas as well, but is a fairly pointless pseudo-op in an as-
sembler environment that uses relocatable object files, as it is the linker that determines
the final position of some object in ROM or RAM.
Along with the architecture-independent standard operators, there are some AVR-
specific operators available which are unfortunately not yet described in the official
documentation. The most notable operators are:
•lo8 Takes the least significant 8 bits of a 16-bit integer
•hi8 Takes the most significant 8 bits of a 16-bit integer
•pm Takes a program-memory (ROM) address, and converts it into a RAM ad-
dress. This implies a division by 2 as the AVR handles ROM addresses as 16-bit
words (e.g. in an IJMP or ICALL instruction), and can also handle relocatable
symbols on the right-hand side.
Example:
ldi r24, lo8(pm(somefunc))
ldi r25, hi8(pm(somefunc))
call something
This passes the address of function somefunc as the first parameter to function
something.
7 Inline Assembler Cookbook
AVR-GCC
Inline Assembler Cookbook
About this Document
The GNU C compiler for Atmel AVR RISC processors offers, to embed assembly
language code into C programs. This cool feature may be used for manually optimizing
time critical parts of the software or to use specific processor instruction, which are not
available in the C language.
Because of a lack of documentation, especially for the AVR version of the compiler, it
may take some time to figure out the implementation details by studying the compiler
and assembler source code. There are also a few sample programs available in the net.
Hopefully this document will help to increase their number.
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7.1 GCC asm Statement 39
It’s assumed, that you are familiar with writing AVR assembler programs, because this
is not an AVR assembler programming tutorial. It’s not a C language tutorial either.
Note that this document does not cover file written completely in assembler language,
refer to avr-libc and assembler programs for this.
Copyright (C) 2001-2002 by egnite Software GmbH
Permission is granted to copy and distribute verbatim copies of this manual provided
that the copyright notice and this permission notice are preserved on all copies. Permis-
sion is granted to copy and distribute modified versions of this manual provided that
the entire resulting derived work is distributed under the terms of a permission notice
identical to this one.
This document describes version 3.3 of the compiler. There may be some parts, which
hadn’t been completely understood by the author himself and not all samples had been
tested so far. Because the author is German and not familiar with the English language,
there are definitely some typos and syntax errors in the text. As a programmer the
author knows, that a wrong documentation sometimes might be worse than none. Any-
way, he decided to offer his little knowledge to the public, in the hope to get enough
response to improve this document. Feel free to contact the author via e-mail. For the
latest release check http://www.ethernut.de/.
Herne, 17th of May 2002 Harald Kipp harald.kipp-at-egnite.de
Note
As of 26th of July 2002, this document has been merged into the
documentation for avr-libc. The latest version is now available at
http://savannah.nongnu.org/projects/avr-libc/.
7.1 GCC asm Statement
Let’s start with a simple example of reading a value from port D:
asm("in %0, %1" : "=r" (value) : "I" (_SFR_IO_ADDR(PORTD)) );
Each asm statement is devided by colons into (up to) four parts:
1. The assembler instructions, defined as a single string constant:
"in %0, %1"
2. A list of output operands, separated by commas. Our example uses just one:
"=r" (value)
3. A comma separated list of input operands. Again our example uses one operand
only:
"I" (_SFR_IO_ADDR(PORTD))
4. Clobbered registers, left empty in our example.
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7.1 GCC asm Statement 40
You can write assembler instructions in much the same way as you would write assem-
bler programs. However, registers and constants are used in a different way if they refer
to expressions of your C program. The connection between registers and C operands is
specified in the second and third part of the asm instruction, the list of input and output
operands, respectively. The general form is
asm(code : output operand list : input operand list [: clobber list]);
In the code section, operands are referenced by a percent sign followed by a single digit.
0refers to the first 1to the second operand and so forth. From the above example:
0refers to "=r" (value) and
1refers to "I" (_SFR_IO_ADDR(PORTD)).
This may still look a little odd now, but the syntax of an operand list will be explained
soon. Let us first examine the part of a compiler listing which may have been generated
from our example:
lds r24,value
/*#APP */
in r24, 12
/*#NOAPP */
sts value,r24
The comments have been added by the compiler to inform the assembler that the in-
cluded code was not generated by the compilation of C statements, but by inline as-
sembler statements. The compiler selected register r24 for storage of the value read
from PORTD. The compiler could have selected any other register, though. It may not
explicitely load or store the value and it may even decide not to include your assembler
code at all. All these decisions are part of the compiler’s optimization strategy. For
example, if you never use the variable value in the remaining part of the C program,
the compiler will most likely remove your code unless you switched off optimization.
To avoid this, you can add the volatile attribute to the asm statement:
asm volatile("in %0, %1" : "=r" (value) : "I" (_SFR_IO_ADDR(PORTD)));
Alternatively, operands can be given names. The name is prepended in brackets to the
constraints in the operand list, and references to the named operand use the bracketed
name instead of a number after the % sign. Thus, the above example could also be
written as
asm("in %[retval], %[port]" :
[retval] "=r" (value) :
[port] "I" (_SFR_IO_ADDR(PORTD)) );
The last part of the asm instruction, the clobber list, is mainly used to tell the compiler
about modifications done by the assembler code. This part may be omitted, all other
parts are required, but may be left empty. If your assembler routine won’t use any
input or output operand, two colons must still follow the assembler code string. A
good example is a simple statement to disable interrupts:
asm volatile("cli"::);
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7.2 Assembler Code 41
7.2 Assembler Code
You can use the same assembler instruction mnemonics as you’d use with any other
AVR assembler. And you can write as many assembler statements into one code string
as you like and your flash memory is able to hold.
Note
The available assembler directives vary from one assembler to another.
To make it more readable, you should put each statement on a seperate line:
asm volatile("nop\n\t"
"nop\n\t"
"nop\n\t"
"nop\n\t"
::);
The linefeed and tab characters will make the assembler listing generated by the com-
piler more readable. It may look a bit odd for the first time, but that’s the way the
compiler creates it’s own assembler code.
You may also make use of some special registers.
Symbol Register
__SREG__ Status register at address 0x3F
__SP_H__ Stack pointer high byte at address 0x3E
__SP_L__ Stack pointer low byte at address 0x3D
__tmp_reg__ Register r0, used for temporary storage
__zero_reg__ Register r1, always zero
Register r0 may be freely used by your assembler code and need not be restored at
the end of your code. It’s a good idea to use __tmp_reg__ and __zero_reg__
instead of r0 or r1, just in case a new compiler version changes the register usage
definitions.
7.3 Input and Output Operands
Each input and output operand is described by a constraint string followed by a C
expression in parantheses. AVR-GCC 3.3 knows the following constraint characters:
Note
The most up-to-date and detailed information on contraints for the avr can be found
in the gcc manual.
The xregister is r27:r26, the yregister is r29:r28, and the zregister is
r31:r30
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7.3 Input and Output Operands 42
Constraint Used for Range
a Simple upper registers r16 to r23
b Base pointer registers
pairs
y, z
d Upper register r16 to r31
e Pointer register pairs x, y, z
q Stack pointer register SPH:SPL
r Any register r0 to r31
t Temporary register r0
w Special upper register
pairs
r24, r26, r28, r30
x Pointer register pair X x (r27:r26)
y Pointer register pair Y y (r29:r28)
z Pointer register pair Z z (r31:r30)
G Floating point constant 0.0
I 6-bit positive integer
constant
0 to 63
J 6-bit negative integer
constant
-63 to 0
K Integer constant 2
L Integer constant 0
l Lower registers r0 to r15
M 8-bit integer constant 0 to 255
N Integer constant -1
O Integer constant 8, 16, 24
P Integer constant 1
Q (GCC >= 4.2.x) A
memory address based
on Y or Z pointer with
displacement.
R (GCC >= 4.3.x) Integer
constant.
-6 to 5
The selection of the proper contraint depends on the range of the constants or registers,
which must be acceptable to the AVR instruction they are used with. The C compiler
doesn’t check any line of your assembler code. But it is able to check the constraint
against your C expression. However, if you specify the wrong constraints, then the
compiler may silently pass wrong code to the assembler. And, of course, the assembler
will fail with some cryptic output or internal errors. For example, if you specify the
constraint "r" and you are using this register with an "ori" instruction in your as-
sembler code, then the compiler may select any register. This will fail, if the compiler
chooses r2 to r15. (It will never choose r0 or r1, because these are uses for special
purposes.) That’s why the correct constraint in that case is "d". On the other hand, if
you use the constraint "M", the compiler will make sure that you don’t pass anything
else but an 8-bit value. Later on we will see how to pass multibyte expression results
to the assembler code.
The following table shows all AVR assembler mnemonics which require operands, and
the related contraints. Because of the improper constraint definitions in version 3.3,
they aren’t strict enough. There is, for example, no constraint, which restricts integer
constants to the range 0 to 7 for bit set and bit clear operations.
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7.3 Input and Output Operands 43
Mnemonic Constraints Mnemonic Constraints
adc r,r add r,r
adiw w,I and r,r
andi d,M asr r
bclr I bld r,I
brbc I,label brbs I,label
bset I bst r,I
cbi I,I cbr d,I
com r cp r,r
cpc r,r cpi d,M
cpse r,r dec r
elpm t,z eor r,r
in r,I inc r
ld r,e ldd r,b
ldi d,M lds r,label
lpm t,z lsl r
lsr r mov r,r
movw r,r mul r,r
neg r or r,r
ori d,M out I,r
pop r push r
rol r ror r
sbc r,r sbci d,M
sbi I,I sbic I,I
sbiw w,I sbr d,M
sbrc r,I sbrs r,I
ser d st e,r
std b,r sts label,r
sub r,r subi d,M
swap r
Constraint characters may be prepended by a single constraint modifier. Contraints
without a modifier specify read-only operands. Modifiers are:
Modifier Specifies
= Write-only operand, usually used for all
output operands.
+ Read-write operand
& Register should be used for output only
Output operands must be write-only and the C expression result must be an lvalue,
which means that the operands must be valid on the left side of assignments. Note,
that the compiler will not check if the operands are of reasonable type for the kind of
operation used in the assembler instructions.
Input operands are, you guessed it, read-only. But what if you need the same operand
for input and output? As stated above, read-write operands are not supported in inline
assembler code. But there is another solution. For input operators it is possible to use
a single digit in the constraint string. Using digit n tells the compiler to use the same
register as for the n-th operand, starting with zero. Here is an example:
asm volatile("swap %0" : "=r" (value) : "0" (value));
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7.3 Input and Output Operands 44
This statement will swap the nibbles of an 8-bit variable named value. Constraint "0"
tells the compiler, to use the same input register as for the first operand. Note however,
that this doesn’t automatically imply the reverse case. The compiler may choose the
same registers for input and output, even if not told to do so. This is not a problem in
most cases, but may be fatal if the output operator is modified by the assembler code
before the input operator is used. In the situation where your code depends on different
registers used for input and output operands, you must add the &constraint modifier to
your output operand. The following example demonstrates this problem:
asm volatile("in %0,%1" "\n\t"
"out %1, %2" "\n\t"
: "=&r" (input)
: "I" (_SFR_IO_ADDR(port)), "r" (output)
);
In this example an input value is read from a port and then an output value is written to
the same port. If the compiler would have choosen the same register for input and out-
put, then the output value would have been destroyed on the first assembler instruction.
Fortunately, this example uses the &constraint modifier to instruct the compiler not to
select any register for the output value, which is used for any of the input operands.
Back to swapping. Here is the code to swap high and low byte of a 16-bit value:
asm volatile("mov __tmp_reg__, %A0" "\n\t"
"mov %A0, %B0" "\n\t"
"mov %B0, __tmp_reg__" "\n\t"
: "=r" (value)
: "0" (value)
);
First you will notice the usage of register __tmp_reg__, which we listed among
other special registers in the Assembler Code section. You can use this register without
saving its contents. Completely new are those letters Aand Bin %A0 and %B0. In fact
they refer to two different 8-bit registers, both containing a part of value.
Another example to swap bytes of a 32-bit value:
asm volatile("mov __tmp_reg__, %A0" "\n\t"
"mov %A0, %D0" "\n\t"
"mov %D0, __tmp_reg__" "\n\t"
"mov __tmp_reg__, %B0" "\n\t"
"mov %B0, %C0" "\n\t"
"mov %C0, __tmp_reg__" "\n\t"
: "=r" (value)
: "0" (value)
);
Instead of listing the same operand as both, input and output operand, it can also be
declared as a read-write operand. This must be applied to an output operand, and the
respective input operand list remains empty:
asm volatile("mov __tmp_reg__, %A0" "\n\t"
"mov %A0, %D0" "\n\t"
"mov %D0, __tmp_reg__" "\n\t"
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7.4 Clobbers 45
"mov __tmp_reg__, %B0" "\n\t"
"mov %B0, %C0" "\n\t"
"mov %C0, __tmp_reg__" "\n\t"
: "+r" (value));
If operands do not fit into a single register, the compiler will automatically assign
enough registers to hold the entire operand. In the assembler code you use %A0 to refer
to the lowest byte of the first operand, %A1 to the lowest byte of the second operand
and so on. The next byte of the first operand will be %B0, the next byte %C0 and so on.
This also implies, that it is often neccessary to cast the type of an input operand to the
desired size.
A final problem may arise while using pointer register pairs. If you define an input
operand
"e" (ptr)
and the compiler selects register Z(r30:r31), then
%A0 refers to r30 and
%B0 refers to r31.
But both versions will fail during the assembly stage of the compiler, if you explicitely
need Z, like in
ld r24,Z
If you write
ld r24, %a0
with a lower case afollowing the percent sign, then the compiler will create the proper
assembler line.
7.4 Clobbers
As stated previously, the last part of the asm statement, the list of clobbers, may be
omitted, including the colon seperator. However, if you are using registers, which
had not been passed as operands, you need to inform the compiler about this. The
following example will do an atomic increment. It increments an 8-bit value pointed
to by a pointer variable in one go, without being interrupted by an interrupt routine
or another thread in a multithreaded environment. Note, that we must use a pointer,
because the incremented value needs to be stored before interrupts are enabled.
asm volatile(
"cli" "\n\t"
"ld r24, %a0" "\n\t"
"inc r24" "\n\t"
"st %a0, r24" "\n\t"
"sei" "\n\t"
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7.4 Clobbers 46
:
: "e" (ptr)
: "r24"
);
The compiler might produce the following code:
cli
ld r24, Z
inc r24
st Z, r24
sei
One easy solution to avoid clobbering register r24 is, to make use of the special tem-
porary register __tmp_reg__ defined by the compiler.
asm volatile(
"cli" "\n\t"
"ld __tmp_reg__, %a0" "\n\t"
"inc __tmp_reg__" "\n\t"
"st %a0, __tmp_reg__" "\n\t"
"sei" "\n\t"
:
: "e" (ptr)
);
The compiler is prepared to reload this register next time it uses it. Another problem
with the above code is, that it should not be called in code sections, where interrupts
are disabled and should be kept disabled, because it will enable interrupts at the end.
We may store the current status, but then we need another register. Again we can solve
this without clobbering a fixed, but let the compiler select it. This could be done with
the help of a local C variable.
{
uint8_t s;
asm volatile(
"in %0, __SREG__" "\n\t"
"cli" "\n\t"
"ld __tmp_reg__, %a1" "\n\t"
"inc __tmp_reg__" "\n\t"
"st %a1, __tmp_reg__" "\n\t"
"out __SREG__, %0" "\n\t"
: "=&r" (s)
: "e" (ptr)
);
}
Now every thing seems correct, but it isn’t really. The assembler code modifies the
variable, that ptr points to. The compiler will not recognize this and may keep its
value in any of the other registers. Not only does the compiler work with the wrong
value, but the assembler code does too. The C program may have modified the value
too, but the compiler didn’t update the memory location for optimization reasons. The
worst thing you can do in this case is:
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7.5 Assembler Macros 47
{
uint8_t s;
asm volatile(
"in %0, __SREG__" "\n\t"
"cli" "\n\t"
"ld __tmp_reg__, %a1" "\n\t"
"inc __tmp_reg__" "\n\t"
"st %a1, __tmp_reg__" "\n\t"
"out __SREG__, %0" "\n\t"
: "=&r" (s)
: "e" (ptr)
: "memory"
);
}
The special clobber "memory" informs the compiler that the assembler code may mod-
ify any memory location. It forces the compiler to update all variables for which the
contents are currently held in a register before executing the assembler code. And of
course, everything has to be reloaded again after this code.
In most situations, a much better solution would be to declare the pointer destination
itself volatile:
volatile uint8_t *ptr;
This way, the compiler expects the value pointed to by ptr to be changed and will
load it whenever used and store it whenever modified.
Situations in which you need clobbers are very rare. In most cases there will be better
ways. Clobbered registers will force the compiler to store their values before and reload
them after your assembler code. Avoiding clobbers gives the compiler more freedom
while optimizing your code.
7.5 Assembler Macros
In order to reuse your assembler language parts, it is useful to define them as macros
and put them into include files. AVR Libc comes with a bunch of them, which could be
found in the directory avr/include. Using such include files may produce compiler
warnings, if they are used in modules, which are compiled in strict ANSI mode. To
avoid that, you can write __asm__ instead of asm and __volatile__ instead of
volatile. These are equivalent aliases.
Another problem with reused macros arises if you are using labels. In such
cases you may make use of the special pattern =, which is replaced by a unique
number on each asm statement. The following code had been taken from
avr/include/iomacros.h:
#define loop_until_bit_is_clear(port,bit) \
__asm__ __volatile__ ( \
"L_%=: " "sbic %0, %1" "\n\t" \
"rjmp L_%=" \
: /*no outputs */
: "I" (_SFR_IO_ADDR(port)),
"I" (bit)
)
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7.6 C Stub Functions 48
When used for the first time, L_= may be translated to L_1404, the next usage might
create L_1405 or whatever. In any case, the labels became unique too.
Another option is to use Unix-assembler style numeric labels. They are explained in
How do I trace an assembler file in avr-gdb?. The above example would then look like:
#define loop_until_bit_is_clear(port,bit)
__asm__ __volatile__ (
"1: " "sbic %0, %1" "\n\t"
"rjmp 1b"
: /*no outputs */
: "I" (_SFR_IO_ADDR(port)),
"I" (bit)
)
7.6 C Stub Functions
Macro definitions will include the same assembler code whenever they are referenced.
This may not be acceptable for larger routines. In this case you may define a C stub
function, containing nothing other than your assembler code.
void delay(uint8_t ms)
{
uint16_t cnt;
asm volatile (
"\n"
"L_dl1%=:" "\n\t"
"mov %A0, %A2" "\n\t"
"mov %B0, %B2" "\n"
"L_dl2%=:" "\n\t"
"sbiw %A0, 1" "\n\t"
"brne L_dl2%=" "\n\t"
"dec %1" "\n\t"
"brne L_dl1%=" "\n\t"
: "=&w" (cnt)
: "r" (ms), "r" (delay_count)
);
}
The purpose of this function is to delay the program execution by a specified number
of milliseconds using a counting loop. The global 16 bit variable delay_count must
contain the CPU clock frequency in Hertz divided by 4000 and must have been set
before calling this routine for the first time. As described in the clobber section, the
routine uses a local variable to hold a temporary value.
Another use for a local variable is a return value. The following function returns a 16
bit value read from two successive port addresses.
uint16_t inw(uint8_t port)
{
uint16_t result;
asm volatile (
"in %A0,%1" "\n\t"
"in %B0,(%1) + 1"
: "=r" (result)
: "I" (_SFR_IO_ADDR(port))
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7.7 C Names Used in Assembler Code 49
);
return result;
}
Note
inw() is supplied by avr-libc.
7.7 C Names Used in Assembler Code
By default AVR-GCC uses the same symbolic names of functions or variables in C and
assembler code. You can specify a different name for the assembler code by using a
special form of the asm statement:
unsigned long value asm("clock") = 3686400;
This statement instructs the compiler to use the symbol name clock rather than value.
This makes sense only for external or static variables, because local variables do not
have symbolic names in the assembler code. However, local variables may be held in
registers.
With AVR-GCC you can specify the use of a specific register:
void Count(void)
{
register unsigned char counter asm("r3");
... some code...
asm volatile("clr r3");
... more code...
}
The assembler instruction, "clr r3", will clear the variable counter. AVR-GCC will
not completely reserve the specified register. If the optimizer recognizes that the vari-
able will not be referenced any longer, the register may be re-used. But the compiler
is not able to check wether this register usage conflicts with any predefined register. If
you reserve too many registers in this way, the compiler may even run out of registers
during code generation.
In order to change the name of a function, you need a prototype declaration, because
the compiler will not accept the asm keyword in the function definition:
extern long Calc(void) asm ("CALCULATE");
Calling the function Calc() will create assembler instructions to call the function
CALCULATE.
7.8 Links
For a more thorough discussion of inline assembly usage, see the gcc user
manual. The latest version of the gcc manual is always available here:
http://gcc.gnu.org/onlinedocs/
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8 How to Build a Library 50
8 How to Build a Library
8.1 Introduction
So you keep reusing the same functions that you created over and over? Tired of cut and
paste going from one project to the next? Would you like to reduce your maintenance
overhead? Then you’re ready to create your own library! Code reuse is a very laudable
goal. With some upfront investment, you can save time and energy on future projects
by having ready-to-go libraries. This chapter describes some background information,
design considerations, and practical knowledge that you will need to create and use
your own libraries.
8.2 How the Linker Works
The compiler compiles a single high-level language file (C language, for example) into
a single object module file. The linker (ld) can only work with object modules to link
them together. Object modules are the smallest unit that the linker works with.
Typically, on the linker command line, you will specify a set of object modules (that
has been previously compiled) and then a list of libraries, including the Standard C
Library. The linker takes the set of object modules that you specify on the command
line and links them together. Afterwards there will probably be a set of "undefined
references". A reference is essentially a function call. An undefined reference is a
function call, with no defined function to match the call.
The linker will then go through the libraries, in order, to match the undefined references
with function definitions that are found in the libraries. If it finds the function that
matches the call, the linker will then link in the object module in which the function is
located. This part is important: the linker links in THE ENTIRE OBJECT MODULE in
which the function is located. Remember, the linker knows nothing about the functions
internal to an object module, other than symbol names (such as function names). The
smallest unit the linker works with is object modules.
When there are no more undefined references, the linker has linked everything and is
done and outputs the final application.
8.3 How to Design a Library
How the linker behaves is very important in designing a library. Ideally, you want to
design a library where only the functions that are called are the only functions to be
linked into the final application. This helps keep the code size to a minimum. In order
to do this, with the way the linker works, is to only write one function per code module.
This will compile to one function per object module. This is usually a very different
way of doing things than writing an application!
There are always exceptions to the rule. There are generally two cases where you
would want to have more than one function per object module.
The first is when you have very complementary functions that it doesn’t make much
sense to split them up. For example, malloc() and free(). If someone is going to use
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8.4 Creating a Library 51
malloc(), they will very likely be using free() (or at least should be using free()). In this
case, it makes more sense to aggregate those two functions in the same object module.
The second case is when you want to have an Interrupt Service Routine (ISR) in your
library that you want to link in. The problem in this case is that the linker looks for
unresolved references and tries to resolve them with code in libraries. A reference is
the same as a function call. But with ISRs, there is no function call to initiate the ISR.
The ISR is placed in the Interrupt Vector Table (IVT), hence no call, no reference,
and no linking in of the ISR. In order to do this, you have to trick the linker in a way.
Aggregate the ISR, with another function in the same object module, but have the other
function be something that is required for the user to call in order to use the ISR, like
perhaps an initialization function for the subsystem, or perhaps a function that enables
the ISR in the first place.
8.4 Creating a Library
The librarian program is called ar (for "archiver") and is found in the GNU Binutils
project. This program will have been built for the AVR target and will therefore be
named avr-ar.
The job of the librarian program is simple: aggregate a list of object modules into a
single library (archive) and create an index for the linker to use. The name that you
create for the library filename must follow a specific pattern: libname.a. The name part
is the unique part of the filename that you create. It makes it easier if the name part
relates to what the library is about. This name part must be prefixed by "lib", and it
must have a file extension of .a, for "archive". The reason for the special form of the
filename is for how the library gets used by the toolchain, as we will see later on.
Note
The filename is case-sensitive. Use a lowercase "lib" prefix, and a lowercase ".a"
as the file extension.
The command line is fairly simple:
avr-ar rcs <library name> <list of object modules>
The rcommand switch tells the program to insert the object modules into the archive
with replacement. The ccommand line switch tells the program to create the archive.
And the scommand line switch tells the program to write an object-file index into the
archive, or update an existing one. This last switch is very important as it helps the
linker to find what it needs to do its job.
Note
The command line switches are case sensitive! There are uppercase switches that
have completely different actions.
MFile and the WinAVR distribution contain a Makefile Template that includes the
necessary command lines to build a library. You will have to manually modify the
template to switch it over to build a library instead of an application.
See the GNU Binutils manual for more information on the ar program.
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8.5 Using a Library 52
8.5 Using a Library
To use a library, use the -l switch on your linker command line. The string immedi-
ately following the -l is the unique part of the library filename that the linker will link
in. For example, if you use:
-lm
this will expand to the library filename:
libm.a
which happens to be the math library included in avr-libc.
If you use this on your linker command line:
-lprintf_flt
then the linker will look for a library called:
libprintf_flt.a
This is why naming your library is so important when you create it!
The linker will search libraries in the order that they appear on the command line.
Whichever function is found first that matches the undefined reference, it will be linked
in.
There are also command line switches that tell GCC which directory to look in (-L)
for the libraries that are specified to be linke in with -l.
See the GNU Binutils manual for more information on the GNU linker (ld) program.
9 Benchmarks
The results below can only give a rough estimate of the resources necessary for using
certain library functions. There is a number of factors which can both increase or
reduce the effort required:
• Expenses for preparation of operands and their stack are not considered.
• In the table, the size includes all additional functions (for example, function to
multiply two integers) but they are only linked from the library.
• Expenses of time of performance of some functions essentially depend on param-
eters of a call, for example, qsort() is recursive, and sprintf() receives parameters
in a stack.
• Different versions of the compiler can give a significant difference in code size
and execution time. For example, the dtostre() function, compiled with avr-gcc
3.4.6, requires 930 bytes. After transition to avr-gcc 4.2.3, the size become 1088
bytes.
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9.1 A few of libc functions. 53
9.1 A few of libc functions.
Avr-gcc version is 4.7.1
The size of function is given in view of all picked up functions. By default Avr-libc
is compiled with -mcall-prologues option. In brackets the size without taking
into account modules of a prologue and an epilogue is resulted. Both of the size can
coincide, if function does not cause a prologue/epilogue.
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9.2 Math functions. 54
Function Units Avr2 Avr25 Avr4
atoi ("12345") Flash bytes
Stack bytes
MCU clocks
82 (82)
2
155
78 (78)
2
149
74 (74)
2
149
atol ("12345") Flash bytes
Stack bytes
MCU clocks
122 (122)
2
221
118 (118)
2
219
118 (118)
2
219
dtostre (1.2345,
s, 6, 0)
Flash bytes
Stack bytes
MCU clocks
1116 (1004)
17
1247
1048 (938)
17
1105
1048 (938)
17
1105
dtostrf (1.2345,
15, 6, s)
Flash bytes
Stack bytes
MCU clocks
1616 (1616)
38
1634
1508 (1508)
38
1462
1508 (1508)
38
1462
itoa (12345, s,
10)
Flash bytes
Stack bytes
MCU clocks
110 (110)
2
879
102 (102)
2
875
102 (102)
2
875
ltoa (12345L, s,
10)
Flash bytes
Stack bytes
MCU clocks
134 (134)
2
1597
126 (126)
2
1593
126 (126)
2
1593
malloc (1) Flash bytes
Stack bytes
MCU clocks
768 (712)
6
215
714 (660)
6
201
714 (660)
6
201
realloc ((void
∗)0, 1)
Flash bytes
Stack bytes
MCU clocks
1284 (1172)
18
305
1174 (1064)
18
286
1174 (1064)
18
286
qsort (s,
sizeof(s), 1, cmp)
Flash bytes
Stack bytes
MCU clocks
1252 (1140)
42
21996
1022 (912)
42
19905
1028 (918)
42
17541
sprintf_min (s,
"%d", 12345)
Flash bytes
Stack bytes
MCU clocks
1224 (1112)
53
1841
1092 (982)
53
1694
1088 (978)
53
1689
sprintf (s, "%d",
12345)
Flash bytes
Stack bytes
MCU clocks
1614 (1502)
58
1647
1476 (1366)
58
1552
1454 (1344)
58
1547
sprintf_flt (s,
"%e", 1.2345)
Flash bytes
Stack bytes
MCU clocks
3228 (3116)
67
2573
2990 (2880)
67
2311
2968 (2858)
67
2311
sscanf_min
("12345", "%d",
&i)
Flash bytes
Stack bytes
MCU clocks
1532 (1420)
55
1607
1328 (1218)
55
1446
1328 (1218)
55
1446
sscanf ("12345",
"%d", &i)
Flash bytes
Stack bytes
MCU clocks
2008 (1896)
55
1610
1748 (1638)
55
1449
1748 (1638)
55
1449
sscanf
("point,color",
"%[a-z]", s)
Flash bytes
Stack bytes
MCU clocks
2008 (1896)
86
3067
1748 (1638)
86
2806
1748 (1638)
86
2806
sscanf_flt
("1.2345", "%e",
&x)
Flash bytes
Stack bytes
MCU clocks
3464 (3352)
71
2497
3086 (2976)
71
2281
3070 (2960)
71
2078
strtod ("1.2345",
&p)
Flash bytes
Stack bytes
MCU clocks
1632 (1520)
20
1235
1536 (1426)
20
1177
1480 (1480)
21
1124
strtol ("12345",
&p, 0)
Flash bytes
Stack bytes
MCU clocks
918 (806)
22
956
834 (724)
22
891
792 (792)
28
794
9.2 Math functions.
The table contains the number of MCU clocks to calculate a function with a given
argument(s). The main reason of a big difference between Avr2 and Avr4 is a hardware
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10 Porting From IAR to AVR GCC 55
multiplication.
Function Avr2 Avr4
__addsf3 (1.234, 5.678) 113 108
__mulsf3 (1.234, 5.678) 375 138
__divsf3 (1.234, 5.678) 466 465
acos (0.54321) 4411 2455
asin (0.54321) 4517 2556
atan (0.54321) 4710 2271
atan2 (1.234, 5.678) 5270 2857
cbrt (1.2345) 2684 2555
ceil (1.2345) 177 177
cos (1.2345) 3387 1671
cosh (1.2345) 4922 2979
exp (1.2345) 4708 2765
fdim (5.678, 1.234) 111 111
floor (1.2345) 180 180
fmax (1.234, 5.678) 39 37
fmin (1.234, 5.678) 35 35
fmod (5.678, 1.234) 131 131
frexp (1.2345, 0) 42 41
hypot (1.234, 5.678) 1341 866
ldexp (1.2345, 6) 42 42
log (1.2345) 4142 2134
log10 (1.2345) 4498 2260
modf (1.2345, 0) 433 429
pow (1.234, 5.678) 9293 5047
round (1.2345) 150 150
sin (1.2345) 3353 1653
sinh (1.2345) 4946 3003
sqrt (1.2345) 494 492
tan (1.2345) 4381 2426
tanh (1.2345) 5126 3173
trunc (1.2345) 178 178
10 Porting From IAR to AVR GCC
10.1 Introduction
C language was designed to be a portable language. There two main types of port-
ing activities: porting an application to a different platform (OS and/or processor),
and porting to a different compiler. Porting to a different compiler can be exacerbated
when the application is an embedded system. For example, the C language Standard,
strangely, does not specify a standard for declaring and defining Interrupt Service Rou-
tines (ISRs). Different compilers have different ways of defining registers, some of
which use non-standard language constructs.
This chapter describes some methods and pointers on porting an AVR application built
with the IAR compiler to the GNU toolchain (AVR GCC). Note that this may not be
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10.2 Registers 56
an exhaustive list.
10.2 Registers
IO header files contain identifiers for all the register names and bit names for a par-
ticular processor. IAR has individual header files for each processor and they must be
included when registers are being used in the code. For example:
#include <iom169.h>
Note
IAR does not always use the same register names or bit names that are used in the
AVR datasheet.
AVR GCC also has individual IO header files for each processor. However, the ac-
tual processor type is specified as a command line flag to the compiler. (Using the
-mmcu=processor flag.) This is usually done in the Makefile. This allows you to
specify only a single header file for any processor type:
#include <avr/io.h>
Note
The forward slash in the <avr/io.h>file name that is used to separate subdirecto-
ries can be used on Windows distributions of the toolchain and is the recommended
method of including this file.
The compiler knows the processor type and through the single header file above, it can
pull in and include the correct individual IO header file. This has the advantage that you
only have to specify one generic header file, and you can easily port your application
to another processor type without having to change every file to include the new IO
header file.
The AVR toolchain tries to adhere to the exact names of the registers and names of
the bits found in the AVR datasheet. There may be some descrepencies between the
register names found in the IAR IO header files and the AVR GCC IO header files.
10.3 Interrupt Service Routines (ISRs)
As mentioned above, the C language Standard, strangely, does not specify a standard
way of declaring and defining an ISR. Hence, every compiler seems to have their own
special way of doing so.
IAR declares an ISR like so:
#pragma vector=TIMER0_OVF_vect
__interrupt void MotorPWMBottom()
{
// code
}
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10.4 Intrinsic Routines 57
In AVR GCC, you declare an ISR like so:
ISR(PCINT1_vect)
{
//code
}
AVR GCC uses the ISR macro to define an ISR. This macro requries the header file:
#include <avr/interrupt.h>
The names of the various interrupt vectors are found in the individual processor IO
header files that you must include with <avr/io.h>.
Note
The names of the interrupt vectors in AVR GCC has been changed to match the
names of the vectors in IAR. This significantly helps in porting applications from
IAR to AVR GCC.
10.4 Intrinsic Routines
IAR has a number of intrinsic routine such as
__enable_interrupts() __disable_interrupts() __watchdog_-
reset()
These intrinsic functions compile to specific AVR opcodes (SEI, CLI, WDR).
There are equivalent macros that are used in AVR GCC, however they are not located
in a single include file.
AVR GCC has sei() for __enable_interrupts(), and cli()
for __disable_interrupts(). Both of these macros are located in
<avr/interrupt.h>.
AVR GCC has the macro wdt_reset() in place of __watchdog_reset().
However, there is a whole Watchdog Timer API available in AVR GCC that can be
found in <avr/wdt.h>.
10.5 Flash Variables
The C language was not designed for Harvard architecture processors with separate
memory spaces. This means that there are various non-standard ways to define a vari-
able whose data resides in the Program Memory (Flash).
IAR uses a non-standard keyword to declare a variable in Program Memory:
__flash int mydata[] = ....
AVR GCC uses Variable Attributes to achieve the same effect:
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10.6 Non-Returning main() 58
int mydata[] __attribute__((progmem))
Note
See the GCC User Manual for more information about Variable Attributes.
avr-libc provides a convenience macro for the Variable Attribute:
#include <avr/pgmspace.h>
.
.
.
int mydata[] PROGMEM = ....
Note
The PROGMEM macro expands to the Variable Attribute of progmem. This
macro requires that you include <avr/pgmspace.h>. This is the canonical
method for defining a variable in Program Space.
To read back flash data, use the pgm_read_∗() macros defined in
<avr/pgmspace.h>. All Program Memory handling macros are defined
there.
There is also a way to create a method to define variables in Program Memory that is
common between the two compilers (IAR and AVR GCC). Create a header file that has
these definitions:
#if defined(__ICCAVR__) // IAR C Compiler
#define FLASH_DECLARE(x) __flash x
#endif
#if defined(__GNUC__) // GNU Compiler
#define FLASH_DECLARE(x) x __attribute__((__progmem__))
#endif
This code snippet checks for the IAR compiler or for the GCC compiler and defines a
macro FLASH_DECLARE(x) that will declare a variable in Program Memory using
the appropriate method based on the compiler that is being used. Then you would used
it like so:
FLASH_DECLARE(int mydata[] = ...);
10.6 Non-Returning main()
To declare main() to be a non-returning function in IAR, it is done like this:
__C_task void main(void)
{
// code
}
To do the equivalent in AVR GCC, do this:
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10.7 Locking Registers 59
void main(void) __attribute__((noreturn));
void main(void)
{
//...
}
Note
See the GCC User Manual for more information on Function Attributes.
In AVR GCC, a prototype for main() is required so you can declare the function at-
tribute to specify that the main() function is of type "noreturn". Then, define main() as
normal. Note that the return type for main() is now void.
10.7 Locking Registers
The IAR compiler allows a user to lock general registers from r15 and down by using
compiler options and this keyword syntax:
__regvar __no_init volatile unsigned int filteredTimeSinceCommutation @14;
This line locks r14 for use only when explicitly referenced in your code thorugh the var
name "filteredTimeSinceCommutation". This means that the compiler cannot dispose
of it at its own will.
To do this in AVR GCC, do this:
register unsigned char counter asm("r3");
Typically, it should be possible to use r2 through r15 that way.
Note
Do not reserve r0 or r1 as these are used internally by the compiler for a temporary
register and for a zero value.
Locking registers is not recommended in AVR GCC as it removes this register
from the control of the compiler, which may make code generation worse. Use at
your own risk.
11 Frequently Asked Questions
11.1 FAQ Index
1. My program doesn’t recognize a variable updated within an interrupt routine
2. I get "undefined reference to..." for functions like "sin()"
3. How to permanently bind a variable to a register?
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11.1 FAQ Index 60
4. How to modify MCUCR or WDTCR early?
5. What is all this _BV() stuff about?
6. Can I use C++ on the AVR?
7. Shouldn’t I initialize all my variables?
8. Why do some 16-bit timer registers sometimes get trashed?
9. How do I use a #define’d constant in an asm statement?
10. Why does the PC randomly jump around when single-stepping through my pro-
gram in avr-gdb?
11. How do I trace an assembler file in avr-gdb?
12. How do I pass an IO port as a parameter to a function?
13. What registers are used by the C compiler?
14. How do I put an array of strings completely in ROM?
15. How to use external RAM?
16. Which -O flag to use?
17. How do I relocate code to a fixed address?
18. My UART is generating nonsense! My ATmega128 keeps crashing! Port F is
completely broken!
19. Why do all my "foo...bar" strings eat up the SRAM?
20. Why does the compiler compile an 8-bit operation that uses bitwise operators
into a 16-bit operation in assembly?
21. How to detect RAM memory and variable overlap problems?
22. Is it really impossible to program the ATtinyXX in C?
23. What is this "clock skew detected" message?
24. Why are (many) interrupt flags cleared by writing a logical 1?
25. Why have "programmed" fuses the bit value 0?
26. Which AVR-specific assembler operators are available?
27. Why are interrupts re-enabled in the middle of writing the stack pointer?
28. Why are there five different linker scripts?
29. How to add a raw binary image to linker output?
30. How do I perform a software reset of the AVR?
31. I am using floating point math. Why is the compiled code so big? Why does my
code not work?
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11.2 My program doesn’t recognize a variable updated within an interrupt
routine 61
32. What pitfalls exist when writing reentrant code?
33. Why are some addresses of the EEPROM corrupted (usually address zero)?
34. Why is my baud rate wrong?
35. On a device with more than 128 KiB of flash, how to make function pointers
work?
36. Why is assigning ports in a "chain" a bad idea?
11.2 My program doesn’t recognize a variable updated within an
interrupt routine
When using the optimizer, in a loop like the following one:
uint8_t flag;
...
ISR(SOME_vect) {
flag = 1;
}
...
while (flag == 0) {
...
}
the compiler will typically access flag only once, and optimize further accesses com-
pletely away, since its code path analysis shows that nothing inside the loop could
change the value of flag anyway. To tell the compiler that this variable could be
changed outside the scope of its code path analysis (e. g. from within an interrupt
routine), the variable needs to be declared like:
volatile uint8_t flag;
Back to FAQ Index.
11.3 I get "undefined reference to..." for functions like "sin()"
In order to access the mathematical functions that are declared in <math.h>, the
linker needs to be told to also link the mathematical library, libm.a.
Typically, system libraries like libm.a are given to the final C compiler command
line that performs the linking step by adding a flag -lm at the end. (That is, the initial
lib and the filename suffix from the library are written immediately after a -l flag. So
for a libfoo.a library, -lfoo needs to be provided.) This will make the linker
search the library in a path known to the system.
An alternative would be to specify the full path to the libm.a file at the same place
on the command line, i. e. after all the object files (∗.o). However, since this re-
quires knowledge of where the build system will exactly find those library files, this is
deprecated for system libraries.
Back to FAQ Index.
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11.4 How to permanently bind a variable to a register? 62
11.4 How to permanently bind a variable to a register?
This can be done with
register unsigned char counter asm("r3");
Typically, it should be safe to use r2 through r7 that way.
Registers r8 through r15 can be used for argument passing by the compiler in case
many or long arguments are being passed to callees. If this is not the case throughout
the entire application, these registers could be used for register variables as well.
Extreme care should be taken that the entire application is compiled with a consistent
set of register-allocated variables, including possibly used library functions.
See C Names Used in Assembler Code for more details.
Back to FAQ Index.
11.5 How to modify MCUCR or WDTCR early?
The method of early initialization (MCUCR,WDTCR or anything else) is different (and
more flexible) in the current version. Basically, write a small assembler file which
looks like this:
;; begin xram.S
#include <avr/io.h>
.section .init1,"ax",@progbits
ldi r16,_BV(SRE) | _BV(SRW)
out _SFR_IO_ADDR(MCUCR),r16
;; end xram.S
Assemble it, link the resulting xram.o with other files in your program, and this piece
of code will be inserted in initialization code, which is run right after reset. See the
linker script for comments about the new .initNsections (which one to use, etc.).
The advantage of this method is that you can insert any initialization code you want
(just remember that this is very early startup -- no stack and no __zero_reg__ yet),
and no program memory space is wasted if this feature is not used.
There should be no need to modify linker scripts anymore, except for some very spe-
cial cases. It is best to leave __stack at its default value (end of internal SRAM
-- faster, and required on some devices like ATmega161 because of errata), and add
-Wl,-Tdata,0x801100 to start the data section above the stack.
For more information on using sections, see Memory Sections. There is also an ex-
ample for Using Sections in C Code. Note that in C code, any such function would
preferably be placed into section .init3 as the code in .init2 ensures the internal register
__zero_reg__ is already cleared.
Back to FAQ Index.
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11.6 What is all this _BV() stuff about? 63
11.6 What is all this _BV() stuff about?
When performing low-level output work, which is a very central point in microcon-
troller programming, it is quite common that a particular bit needs to be set or cleared
in some IO register. While the device documentation provides mnemonic names for
the various bits in the IO registers, and the AVR device-specific IO definitions reflect
these names in definitions for numerical constants, a way is needed to convert a bit
number (usually within a byte register) into a byte value that can be assigned directly
to the register. However, sometimes the direct bit numbers are needed as well (e. g. in
an SBI() instruction), so the definitions cannot usefully be made as byte values in the
first place.
So in order to access a particular bit number as a byte value, use the _BV() macro.
Of course, the implementation of this macro is just the usual bit shift (which is done
by the compiler anyway, thus doesn’t impose any run-time penalty), so the following
applies:
_BV(3) => 1 << 3 => 0x08
However, using the macro often makes the program better readable.
"BV" stands for "bit value", in case someone might ask you. :-)
Example: clock timer 2 with full IO clock (CS2x= 0b001), toggle OC2 output on
compare match (COM2x= 0b01), and clear timer on compare match (CTC2 = 1). Make
OC2 (PD7) an output.
TCCR2 = _BV(COM20)|_BV(CTC2)|_BV(CS20);
DDRD = _BV(PD7);
Back to FAQ Index.
11.7 Can I use C++ on the AVR?
Basically yes, C++ is supported (assuming your compiler has been configured and
compiled to support it, of course). Source files ending in .cc, .cpp or .C will automati-
cally cause the compiler frontend to invoke the C++ compiler. Alternatively, the C++
compiler could be explicitly called by the name avr-c++.
However, there’s currently no support for libstdc++, the standard support library
needed for a complete C++ implementation. This imposes a number of restrictions on
the C++ programs that can be compiled. Among them are:
• Obviously, none of the C++ related standard functions, classes, and template
classes are available.
• The operators new and delete are not implemented, attempting to use them
will cause the linker to complain about undefined external references. (This
could perhaps be fixed.)
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11.8 Shouldn’t I initialize all my variables? 64
• Some of the supplied include files are not C++ safe, i. e. they need to be wrapped
into
extern "C" { . . . }
(This could certainly be fixed, too.)
• Exceptions are not supported. Since exceptions are enabled by default in the
C++ frontend, they explicitly need to be turned off using -fno-exceptions
in the compiler options. Failing this, the linker will complain about an undefined
external reference to __gxx_personality_sj0.
Constructors and destructors are supported though, including global ones.
When programming C++ in space- and runtime-sensitive environments like microcon-
trollers, extra care should be taken to avoid unwanted side effects of the C++ calling
conventions like implied copy constructors that could be called upon function invo-
cation etc. These things could easily add up into a considerable amount of time and
program memory wasted. Thus, casual inspection of the generated assembler code
(using the -S compiler option) seems to be warranted.
Back to FAQ Index.
11.8 Shouldn’t I initialize all my variables?
Global and static variables are guaranteed to be initialized to 0 by the C standard.
avr-gcc does this by placing the appropriate code into section .init4 (see The .initN
Sections). With respect to the standard, this sentence is somewhat simplified (because
the standard allows for machines where the actual bit pattern used differs from all bits
being 0), but for the AVR target, in general, all integer-type variables are set to 0, all
pointers to a NULL pointer, and all floating-point variables to 0.0.
As long as these variables are not initialized (i. e. they don’t have an equal sign and
an initialization expression to the right within the definition of the variable), they go
into the .bss section of the file. This section simply records the size of the variable,
but otherwise doesn’t consume space, neither within the object file nor within flash
memory. (Of course, being a variable, it will consume space in the target’s SRAM.)
In contrast, global and static variables that have an initializer go into the .data section
of the file. This will cause them to consume space in the object file (in order to record
the initializing value), and in the flash ROM of the target device. The latter is needed
since the flash ROM is the only way that the compiler can tell the target device the
value this variable is going to be initialized to.
Now if some programmer "wants to make doubly sure" their variables really get a 0
at program startup, and adds an initializer just containing 0 on the right-hand side,
they waste space. While this waste of space applies to virtually any platform C is
implemented on, it’s usually not noticeable on larger machines like PCs, while the
waste of flash ROM storage can be very painful on a small microcontroller like the
AVR.
So in general, variables should only be explicitly initialized if the initial value is non-
zero.
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11.9 Why do some 16-bit timer registers sometimes get trashed? 65
Note
Recent versions of GCC are now smart enough to detect this situation, and revert
variables that are explicitly initialized to 0 to the .bss section. Still, other compilers
might not do that optimization, and as the C standard guarantees the initialization,
it is safe to rely on it.
Back to FAQ Index.
11.9 Why do some 16-bit timer registers sometimes get trashed?
Some of the timer-related 16-bit IO registers use a temporary register (called TEMP in
the Atmel datasheet) to guarantee an atomic access to the register despite the fact that
two separate 8-bit IO transfers are required to actually move the data. Typically, this
includes access to the current timer/counter value register (TCNTn), the input capture
register (ICRn), and write access to the output compare registers (OCRnM). Refer to
the actual datasheet for each device’s set of registers that involves the TEMP register.
When accessing one of the registers that use TEMP from the main application, and
possibly any other one from within an interrupt routine, care must be taken that no
access from within an interrupt context could clobber the TEMP register data of an
in-progress transaction that has just started elsewhere.
To protect interrupt routines against other interrupt routines, it’s usually best to use the
ISR() macro when declaring the interrupt function, and to ensure that interrupts are still
disabled when accessing those 16-bit timer registers.
Within the main program, access to those registers could be encapsulated in calls to the
cli() and sei() macros. If the status of the global interrupt flag before accessing one of
those registers is uncertain, something like the following example code can be used.
uint16_t
read_timer1(void)
{
uint8_t sreg;
uint16_t val;
sreg = SREG;
cli();
val = TCNT1;
SREG = sreg;
return val;
}
Back to FAQ Index.
11.10 How do I use a #define’d constant in an asm statement?
So you tried this:
asm volatile("sbi 0x18,0x07;");
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11.11 Why does the PC randomly jump around when single-stepping through
my program in avr-gdb? 66
Which works. When you do the same thing but replace the address of the port by its
macro name, like this:
asm volatile("sbi PORTB,0x07;");
you get a compilation error: "Error: constant value required".
PORTB is a precompiler definition included in the processor specific file included in
avr/io.h. As you may know, the precompiler will not touch strings and PORTB,
instead of 0x18, gets passed to the assembler. One way to avoid this problem is:
asm volatile("sbi %0, 0x07" : "I" (_SFR_IO_ADDR(PORTB)):);
Note
For C programs, rather use the standard C bit operators instead, so the above would
be expressed as PORTB |= (1 << 7). The optimizer will take care to trans-
form this into a single SBI instruction, assuming the operands allow for this.
Back to FAQ Index.
11.11 Why does the PC randomly jump around when single-
stepping through my program in avr-gdb?
When compiling a program with both optimization (-O) and debug information (-g)
which is fortunately possible in avr-gcc, the code watched in the debugger is opti-
mized code. While it is not guaranteed, very often this code runs with the exact same
optimizations as it would run without the -g switch.
This can have unwanted side effects. Since the compiler is free to reorder code ex-
ecution as long as the semantics do not change, code is often rearranged in order to
make it possible to use a single branch instruction for conditional operations. Branch
instructions can only cover a short range for the target PC (-63 through +64 words from
the current PC). If a branch instruction cannot be used directly, the compiler needs to
work around it by combining a skip instruction together with a relative jump (rjmp)
instruction, which will need one additional word of ROM.
Another side effect of optimization is that variable usage is restricted to the area of code
where it is actually used. So if a variable was placed in a register at the beginning of
some function, this same register can be re-used later on if the compiler notices that the
first variable is no longer used inside that function, even though the variable is still in
lexical scope. When trying to examine the variable in avr-gdb, the displayed result
will then look garbled.
So in order to avoid these side effects, optimization can be turned off while debugging.
However, some of these optimizations might also have the side effect of uncovering
bugs that would otherwise not be obvious, so it must be noted that turning off opti-
mization can easily change the bug pattern. In most cases, you are better off leaving
optimizations enabled while debugging.
Back to FAQ Index.
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11.12 How do I trace an assembler file in avr-gdb? 67
11.12 How do I trace an assembler file in avr-gdb?
When using the -g compiler option, avr-gcc only generates line number and other
debug information for C (and C++) files that pass the compiler. Functions that don’t
have line number information will be completely skipped by a single step command
in gdb. This includes functions linked from a standard library, but by default also
functions defined in an assembler source file, since the -g compiler switch does not
apply to the assembler.
So in order to debug an assembler input file (possibly one that has to be passed through
the C preprocessor), it’s the assembler that needs to be told to include line-number
information into the output file. (Other debug information like data types and variable
allocation cannot be generated, since unlike a compiler, the assembler basically doesn’t
know about this.) This is done using the (GNU) assembler option --gstabs.
Example:
$ avr-as -mmcu=atmega128 --gstabs -o foo.o foo.s
When the assembler is not called directly but through the C compiler frontend
(either implicitly by passing a source file ending in .S, or explicitly using -x
assembler-with-cpp), the compiler frontend needs to be told to pass the
--gstabs option down to the assembler. This is done using -Wa,--gstabs.
Please take care to only pass this option when compiling an assembler input file. Oth-
erwise, the assembler code that results from the C compilation stage will also get line
number information, which confuses the debugger.
Note
You can also use -Wa,-gstabs since the compiler will add the extra ’-’ for
you.
Example:
$ EXTRA_OPTS="-Wall -mmcu=atmega128 -x assembler-with-cpp"
$ avr-gcc -Wa,--gstabs ${EXTRA_OPTS} -c -o foo.o foo.S
Also note that the debugger might get confused when entering a piece of code that has
a non-local label before, since it then takes this label as the name of a new function that
appears to have been entered. Thus, the best practice to avoid this confusion is to only
use non-local labels when declaring a new function, and restrict anything else to local
labels. Local labels consist just of a number only. References to these labels consist
of the number, followed by the letter bfor a backward reference, or ffor a forward
reference. These local labels may be re-used within the source file, references will pick
the closest label with the same number and given direction.
Example:
myfunc: push r16
push r17
push r18
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11.13 How do I pass an IO port as a parameter to a function? 68
push YL
push YH
...
eor r16, r16 ; start loop
ldi YL, lo8(sometable)
ldi YH, hi8(sometable)
rjmp 2f ; jump to loop test at end
1: ld r17, Y+ ; loop continues here
...
breq 1f ; return from myfunc prematurely
...
inc r16
2: cmp r16, r18
brlo 1b ; jump back to top of loop
1: pop YH
pop YL
pop r18
pop r17
pop r16
ret
Back to FAQ Index.
11.13 How do I pass an IO port as a parameter to a function?
Consider this example code:
#include <inttypes.h>
#include <avr/io.h>
void
set_bits_func_wrong (volatile uint8_t port, uint8_t mask)
{
port |= mask;
}
void
set_bits_func_correct (volatile uint8_t *port, uint8_t mask)
{
*port |= mask;
}
#define set_bits_macro(port,mask) ((port) |= (mask))
int main (void)
{
set_bits_func_wrong (PORTB, 0xaa);
set_bits_func_correct (&PORTB, 0x55);
set_bits_macro (PORTB, 0xf0);
return (0);
}
The first function will generate object code which is not even close to what is intended.
The major problem arises when the function is called. When the compiler sees this call,
it will actually pass the value of the PORTB register (using an IN instruction), instead
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11.13 How do I pass an IO port as a parameter to a function? 69
of passing the address of PORTB (e.g. memory mapped io addr of 0x38, io port 0x18
for the mega128). This is seen clearly when looking at the disassembly of the call:
set_bits_func_wrong (PORTB, 0xaa);
10a: 6a ea ldi r22, 0xAA ; 170
10c: 88 b3 in r24, 0x18 ; 24
10e: 0e 94 65 00 call 0xca
So, the function, once called, only sees the value of the port register and knows nothing
about which port it came from. At this point, whatever object code is generated for
the function by the compiler is irrelevant. The interested reader can examine the full
disassembly to see that the function’s body is completely fubar.
The second function shows how to pass (by reference) the memory mapped address of
the io port to the function so that you can read and write to it in the function. Here’s
the object code generated for the function call:
set_bits_func_correct (&PORTB, 0x55);
112: 65 e5 ldi r22, 0x55 ; 85
114: 88 e3 ldi r24, 0x38 ; 56
116: 90 e0 ldi r25, 0x00 ; 0
118: 0e 94 7c 00 call 0xf8
You can clearly see that 0x0038 is correctly passed for the address of the io port.
Looking at the disassembled object code for the body of the function, we can see that
the function is indeed performing the operation we intended:
void
set_bits_func_correct (volatile uint8_t *port, uint8_t mask)
{
f8: fc 01 movw r30, r24
*port |= mask;
fa: 80 81 ld r24, Z
fc: 86 2b or r24, r22
fe: 80 83 st Z, r24
}
100: 08 95 ret
Notice that we are accessing the io port via the LD and ST instructions.
The port parameter must be volatile to avoid a compiler warning.
Note
Because of the nature of the IN and OUT assembly instructions, they can not be
used inside the function when passing the port in this way. Readers interested in
the details should consult the Instruction Set datasheet.
Finally we come to the macro version of the operation. In this contrived example, the
macro is the most efficient method with respect to both execution speed and code size:
set_bits_macro (PORTB, 0xf0);
11c: 88 b3 in r24, 0x18 ; 24
11e: 80 6f ori r24, 0xF0 ; 240
120: 88 bb out 0x18, r24 ; 24
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11.14 What registers are used by the C compiler? 70
Of course, in a real application, you might be doing a lot more in your function which
uses a passed by reference io port address and thus the use of a function over a macro
could save you some code space, but still at a cost of execution speed.
Care should be taken when such an indirect port access is going to one of the 16-bit
IO registers where the order of write access is critical (like some timer registers). All
versions of avr-gcc up to 3.3 will generate instructions that use the wrong access order
in this situation (since with normal memory operands where the order doesn’t matter,
this sometimes yields shorter code).
See http://mail.nongnu.org/archive/html/avr-libc-dev/2003-01/msg00044.html
for a possible workaround.
avr-gcc versions after 3.3 have been fixed in a way where this optimization will be
disabled if the respective pointer variable is declared to be volatile, so the correct
behaviour for 16-bit IO ports can be forced that way.
Back to FAQ Index.
11.14 What registers are used by the C compiler?
•Data types:
char is 8 bits, int is 16 bits, long is 32 bits, long long is 64 bits, float and
double are 32 bits (this is the only supported floating point format), pointers
are 16 bits (function pointers are word addresses, to allow addressing up to 128K
program memory space). There is a -mint8 option (see Options for the C
compiler avr-gcc) to make int 8 bits, but that is not supported by avr-libc and
violates C standards (int must be at least 16 bits). It may be removed in a future
release.
•Call-used registers (r18-r27, r30-r31):
May be allocated by gcc for local data. You may use them freely in assembler
subroutines. Calling C subroutines can clobber any of them - the caller is re-
sponsible for saving and restoring.
•Call-saved registers (r2-r17, r28-r29):
May be allocated by gcc for local data. Calling C subroutines leaves them un-
changed. Assembler subroutines are responsible for saving and restoring these
registers, if changed. r29:r28 (Y pointer) is used as a frame pointer (points to
local data on stack) if necessary. The requirement for the callee to save/preserve
the contents of these registers even applies in situations where the compiler as-
signs them for argument passing.
•Fixed registers (r0, r1):
Never allocated by gcc for local data, but often used for fixed purposes:
r0 - temporary register, can be clobbered by any C code (except interrupt handlers
which save it), may be used to remember something for a while within one piece of
assembler code
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11.15 How do I put an array of strings completely in ROM? 71
r1 - assumed to be always zero in any C code, may be used to remember something for
a while within one piece of assembler code, but must then be cleared after use (clr
r1). This includes any use of the [f]mul[s[u]] instructions, which return their
result in r1:r0. Interrupt handlers save and clear r1 on entry, and restore r1 on exit (in
case it was non-zero).
•Function call conventions:
Arguments - allocated left to right, r25 to r8. All arguments are aligned to start in
even-numbered registers (odd-sized arguments, including char, have one free
register above them). This allows making better use of the movw instruction on
the enhanced core.
If too many, those that don’t fit are passed on the stack.
Return values: 8-bit in r24 (not r25!), 16-bit in r25:r24, up to 32 bits in r22-r25, up to
64 bits in r18-r25. 8-bit return values are zero/sign-extended to 16 bits by the called
function (unsigned char is more efficient than signed char - just clr r25).
Arguments to functions with variable argument lists (printf etc.) are all passed on stack,
and char is extended to int.
Warning
There was no such alignment before 2000-07-01, including the old patches for
gcc-2.95.2. Check your old assembler subroutines, and adjust them accordingly.
Back to FAQ Index.
11.15 How do I put an array of strings completely in ROM?
There are times when you may need an array of strings which will never be modified.
In this case, you don’t want to waste ram storing the constant strings. The most obvious
(and incorrect) thing to do is this:
#include <avr/pgmspace.h>
PGM_P array[2] PROGMEM = {
"Foo",
"Bar"
};
int main (void)
{
char buf[32];
strcpy_P (buf, array[1]);
return 0;
}
The result is not what you want though. What you end up with is the array stored in
ROM, while the individual strings end up in RAM (in the .data section).
To work around this, you need to do something like this:
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11.15 How do I put an array of strings completely in ROM? 72
#include <avr/pgmspace.h>
const char foo[] PROGMEM = "Foo";
const char bar[] PROGMEM = "Bar";
PGM_P array[2] PROGMEM = {
foo,
bar
};
int main (void)
{
char buf[32];
PGM_P p;
int i;
memcpy_P(&p, &array[i], sizeof(PGM_P));
strcpy_P(buf, p);
return 0;
}
Looking at the disassembly of the resulting object file we see that array is in flash as
such:
00000026 <array>:
26: 2e 00 .word 0x002e ; ????
28: 2a 00 .word 0x002a ; ????
0000002a <bar>:
2a: 42 61 72 00 Bar.
0000002e <foo>:
2e: 46 6f 6f 00 Foo.
foo is at addr 0x002e.
bar is at addr 0x002a.
array is at addr 0x0026.
Then in main we see this:
memcpy_P(&p, &array[i], sizeof(PGM_P));
70: 66 0f add r22, r22
72: 77 1f adc r23, r23
74: 6a 5d subi r22, 0xDA ; 218
76: 7f 4f sbci r23, 0xFF ; 255
78: 42 e0 ldi r20, 0x02 ; 2
7a: 50 e0 ldi r21, 0x00 ; 0
7c: ce 01 movw r24, r28
7e: 81 96 adiw r24, 0x21 ; 33
80: 08 d0 rcall .+16 ; 0x92
This code reads the pointer to the desired string from the ROM table array into a
register pair.
The value of i(in r22:r23) is doubled to accommodate for the word offset required to
access array[], then the address of array (0x26) is added, by subtracting the negated
address (0xffda). The address of variable pis computed by adding its offset within the
stack frame (33) to the Y pointer register, and memcpy_P is called.
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11.16 How to use external RAM? 73
strcpy_P(buf, p);
82: 69 a1 ldd r22, Y+33 ; 0x21
84: 7a a1 ldd r23, Y+34 ; 0x22
86: ce 01 movw r24, r28
88: 01 96 adiw r24, 0x01 ; 1
8a: 0c d0 rcall .+24 ; 0xa4
This will finally copy the ROM string into the local buffer buf.
Variable p(located at Y+33) is read, and passed together with the address of buf (Y+1)
to strcpy_P. This will copy the string from ROM to buf.
Note that when using a compile-time constant index, omitting the first step (reading
the pointer from ROM via memcpy_P) usually remains unnoticed, since the compiler
would then optimize the code for accessing array at compile-time.
Back to FAQ Index.
11.16 How to use external RAM?
Well, there is no universal answer to this question; it depends on what the external
RAM is going to be used for.
Basically, the bit SRE (SRAM enable) in the MCUCR register needs to be set in order
to enable the external memory interface. Depending on the device to be used, and
the application details, further registers affecting the external memory operation like
XMCRA and XMCRB, and/or further bits in MCUCR might be configured. Refer to the
datasheet for details.
If the external RAM is going to be used to store the variables from the C program
(i. e., the .data and/or .bss segment) in that memory area, it is essential to set up the
external memory interface early during the device initialization so the initialization of
these variable will take place. Refer to How to modify MCUCR or WDTCR early? for
a description how to do this using few lines of assembler code, or to the chapter about
memory sections for an example written in C.
The explanation of malloc() contains a discussion about the use of internal RAM vs.
external RAM in particular with respect to the various possible locations of the heap
(area reserved for malloc()). It also explains the linker command-line options that are
required to move the memory regions away from their respective standard locations in
internal RAM.
Finally, if the application simply wants to use the additional RAM for private data
storage kept outside the domain of the C compiler (e. g. through a char ∗variable
initialized directly to a particular address), it would be sufficient to defer the initial-
ization of the external RAM interface to the beginning of main(), so no tweaking of
the .init3 section is necessary. The same applies if only the heap is going to be located
there, since the application start-up code does not affect the heap.
It is not recommended to locate the stack in external RAM. In general, accessing exter-
nal RAM is slower than internal RAM, and errata of some AVR devices even prevent
this configuration from working properly at all.
Back to FAQ Index.
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11.17 Which -O flag to use? 74
11.17 Which -O flag to use?
There’s a common misconception that larger numbers behind the -O option might auto-
matically cause "better" optimization. First, there’s no universal definition for "better",
with optimization often being a speed vs. code size trade off. See the detailed discus-
sion for which option affects which part of the code generation.
A test case was run on an ATmega128 to judge the effect of compiling the library itself
using different optimization levels. The following table lists the results. The test case
consisted of around 2 KB of strings to sort. Test #1 used qsort() using the standard
library strcmp(), test #2 used a function that sorted the strings by their size (thus had
two calls to strlen() per invocation).
When comparing the resulting code size, it should be noted that a floating point version
of fvprintf() was linked into the binary (in order to print out the time elapsed) which
is entirely not affected by the different optimization levels, and added about 2.5 KB to
the code.
Optimization
flags
Size of .text Time for test #1 Time for test #2
-O3 6898 903 µs 19.7 ms
-O2 6666 972 µs 20.1 ms
-Os 6618 955 µs 20.1 ms
-Os
-mcall-prologues
6474 972 µs 20.1 ms
(The difference between 955 µs and 972 µs was just a single timer-tick, so take this
with a grain of salt.)
So generally, it seems -Os -mcall-prologues is the most universal "best" opti-
mization level. Only applications that need to get the last few percent of speed benefit
from using -O3.
Back to FAQ Index.
11.18 How do I relocate code to a fixed address?
First, the code should be put into a new named section. This is done with a section
attribute:
__attribute__ ((section (".bootloader")))
In this example, .bootloader is the name of the new section. This attribute needs to be
placed after the prototype of any function to force the function into the new section.
void boot(void) __attribute__ ((section (".bootloader")));
To relocate the section to a fixed address the linker flag --section-start is used.
This option can be passed to the linker using the -Wl compiler option:
-Wl,--section-start=.bootloader=0x1E000
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11.19 My UART is generating nonsense! My ATmega128 keeps crashing! Port
F is completely broken! 75
The name after section-start is the name of the section to be relocated. The number
after the section name is the beginning address of the named section.
Back to FAQ Index.
11.19 My UART is generating nonsense! My ATmega128 keeps
crashing! Port F is completely broken!
Well, certain odd problems arise out of the situation that the AVR devices as shipped
by Atmel often come with a default fuse bit configuration that doesn’t match the user’s
expectations. Here is a list of things to care for:
• All devices that have an internal RC oscillator ship with the fuse enabled that
causes the device to run off this oscillator, instead of an external crystal. This
often remains unnoticed until the first attempt is made to use something critical
in timing, like UART communication.
• The ATmega128 ships with the fuse enabled that turns this device into AT-
mega103 compatibility mode. This means that some ports are not fully usable,
and in particular that the internal SRAM is located at lower addresses. Since by
default, the stack is located at the top of internal SRAM, a program compiled for
an ATmega128 running on such a device will immediately crash upon the first
function call (or rather, upon the first function return).
• Devices with a JTAG interface have the JTAGEN fuse programmed by default.
This will make the respective port pins that are used for the JTAG interface un-
available for regular IO.
Back to FAQ Index.
11.20 Why do all my "foo...bar" strings eat up the SRAM?
By default, all strings are handled as all other initialized variables: they occupy RAM
(even though the compiler might warn you when it detects write attempts to these RAM
locations), and occupy the same amount of flash ROM so they can be initialized to the
actual string by startup code. The compiler can optimize multiple identical strings into
a single one, but obviously only for one compilation unit (i. e., a single C source file).
That way, any string literal will be a valid argument to any C function that expects a
const char ∗argument.
Of course, this is going to waste a lot of SRAM. In Program Space String Utilities, a
method is described how such constant data can be moved out to flash ROM. How-
ever, a constant string located in flash ROM is no longer a valid argument to pass to a
function that expects a const char ∗-type string, since the AVR processor needs
the special instruction LPM to access these strings. Thus, separate functions are needed
that take this into account. Many of the standard C library functions have equivalents
available where one of the string arguments can be located in flash ROM. Private func-
tions in the applications need to handle this, too. For example, the following can be
used to implement simple debugging messages that will be sent through a UART:
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11.21 Why does the compiler compile an 8-bit operation that uses bitwise
operators into a 16-bit operation in assembly? 76
#include <inttypes.h>
#include <avr/io.h>
#include <avr/pgmspace.h>
int
uart_putchar(char c)
{
if (c == ’\n’)
uart_putchar(’\r’);
loop_until_bit_is_set(USR, UDRE);
UDR = c;
return 0; /*so it could be used for fdevopen(), too */
}
void
debug_P(const char *addr)
{
char c;
while ((c = pgm_read_byte(addr++)))
uart_putchar(c);
}
int
main(void)
{
ioinit(); /*initialize UART, ... */
debug_P(PSTR("foo was here\n"));
return 0;
}
Note
By convention, the suffix _P to the function name is used as an indication that
this function is going to accept a "program-space string". Note also the use of the
PSTR() macro.
Back to FAQ Index.
11.21 Why does the compiler compile an 8-bit operation that uses
bitwise operators into a 16-bit operation in assembly?
Bitwise operations in Standard C will automatically promote their operands to an int,
which is (by default) 16 bits in avr-gcc.
To work around this use typecasts on the operands, including literals, to declare that
the values are to be 8 bit operands.
This may be especially important when clearing a bit:
var &= ~mask; /*wrong way! */
The bitwise "not" operator (∼) will also promote the value in mask to an int. To keep
it an 8-bit value, typecast before the "not" operator:
var &= (unsigned char)~mask;
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11.22 How to detect RAM memory and variable overlap problems? 77
Back to FAQ Index.
11.22 How to detect RAM memory and variable overlap prob-
lems?
You can simply run avr-nm on your output (ELF) file. Run it with the -n option, and
it will sort the symbols numerically (by default, they are sorted alphabetically).
Look for the symbol _end, that’s the first address in RAM that is not allocated by
a variable. (avr-gcc internally adds 0x800000 to all data/bss variable addresses, so
please ignore this offset.) Then, the run-time initialization code initializes the stack
pointer (by default) to point to the last available address in (internal) SRAM. Thus, the
region between _end and the end of SRAM is what is available for stack. (If your
application uses malloc(), which e. g. also can happen inside printf(), the heap for
dynamic memory is also located there. See Memory Areas and Using malloc().)
The amount of stack required for your application cannot be determined that easily.
For example, if you recursively call a function and forget to break that recursion, the
amount of stack required is infinite. :-) You can look at the generated assembler code
(avr-gcc ... -S), there’s a comment in each generated assembler file that tells
you the frame size for each generated function. That’s the amount of stack required for
this function, you have to add up that for all functions where you know that the calls
could be nested.
Back to FAQ Index.
11.23 Is it really impossible to program the ATtinyXX in C?
While some small AVRs are not directly supported by the C compiler since they do not
have a RAM-based stack (and some do not even have RAM at all), it is possible anyway
to use the general-purpose registers as a RAM replacement since they are mapped into
the data memory region.
Bruce D. Lightner wrote an excellent description of how to do this, and offers this
together with a toolkit on his web page:
http://lightner.net/avr/ATtinyAvrGcc.html
Back to FAQ Index.
11.24 What is this "clock skew detected" message?
It’s a known problem of the MS-DOS FAT file system. Since the FAT file system has
only a granularity of 2 seconds for maintaining a file’s timestamp, and it seems that
some MS-DOS derivative (Win9x) perhaps rounds up the current time to the next sec-
ond when calculating the timestamp of an updated file in case the current time cannot
be represented in FAT’s terms, this causes a situation where make sees a "file coming
from the future".
Since all make decisions are based on file timestamps, and their dependencies, make
warns about this situation.
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11.25 Why are (many) interrupt flags cleared by writing a logical 1? 78
Solution: don’t use inferior file systems / operating systems. Neither Unix file systems
nor HPFS (aka NTFS) do experience that problem.
Workaround: after saving the file, wait a second before starting make. Or simply
ignore the warning. If you are paranoid, execute a make clean all to make sure
everything gets rebuilt.
In networked environments where the files are accessed from a file server, this message
can also happen if the file server’s clock differs too much from the network client’s
clock. In this case, the solution is to use a proper time keeping protocol on both sys-
tems, like NTP. As a workaround, synchronize the client’s clock frequently with the
server’s clock.
Back to FAQ Index.
11.25 Why are (many) interrupt flags cleared by writing a logical
1?
Usually, each interrupt has its own interrupt flag bit in some control register, indicating
the specified interrupt condition has been met by representing a logical 1 in the respec-
tive bit position. When working with interrupt handlers, this interrupt flag bit usually
gets cleared automatically in the course of processing the interrupt, sometimes by just
calling the handler at all, sometimes (e. g. for the U[S]ART) by reading a particular
hardware register that will normally happen anyway when processing the interrupt.
From the hardware’s point of view, an interrupt is asserted as long as the respective bit
is set, while global interrupts are enabled. Thus, it is essential to have the bit cleared
before interrupts get re-enabled again (which usually happens when returning from an
interrupt handler).
Only few subsystems require an explicit action to clear the interrupt request when using
interrupt handlers. (The notable exception is the TWI interface, where clearing the
interrupt indicates to proceed with the TWI bus hardware handshake, so it’s never done
automatically.)
However, if no normal interrupt handlers are to be used, or in order to make extra
sure any pending interrupt gets cleared before re-activating global interrupts (e. g.
an external edge-triggered one), it can be necessary to explicitly clear the respective
hardware interrupt bit by software. This is usually done by writing a logical 1 into this
bit position. This seems to be illogical at first, the bit position already carries a logical
1 when reading it, so why does writing a logical 1 to it clear the interrupt bit?
The solution is simple: writing a logical 1 to it requires only a single OUT instruction,
and it is clear that only this single interrupt request bit will be cleared. There is no need
to perform a read-modify-write cycle (like, an SBI instruction), since all bits in these
control registers are interrupt bits, and writing a logical 0 to the remaining bits (as it
is done by the simple OUT instruction) will not alter them, so there is no risk of any
race condition that might accidentally clear another interrupt request bit. So instead of
writing
TIFR |= _BV(TOV0); /*wrong! */
simply use
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11.26 Why have "programmed" fuses the bit value 0? 79
TIFR = _BV(TOV0);
Back to FAQ Index.
11.26 Why have "programmed" fuses the bit value 0?
Basically, fuses are just a bit in a special EEPROM area. For technical reasons, erased
E[E]PROM cells have all bits set to the value 1, so unprogrammed fuses also have a
logical 1. Conversely, programmed fuse cells read out as bit value 0.
Back to FAQ Index.
11.27 Which AVR-specific assembler operators are available?
See Pseudo-ops and operators.
Back to FAQ Index.
11.28 Why are interrupts re-enabled in the middle of writing the
stack pointer?
When setting up space for local variables on the stack, the compiler generates code like
this:
/*prologue: frame size=20 */
push r28
push r29
in r28,__SP_L__
in r29,__SP_H__
sbiw r28,20
in __tmp_reg__,__SREG__
cli
out __SP_H__,r29
out __SREG__,__tmp_reg__
out __SP_L__,r28
/*prologue end (size=10) */
It reads the current stack pointer value, decrements it by the required amount of bytes,
then disables interrupts, writes back the high part of the stack pointer, writes back
the saved SREG (which will eventually re-enable interrupts if they have been enabled
before), and finally writes the low part of the stack pointer.
At the first glance, there’s a race between restoring SREG, and writing SPL. However,
after enabling interrupts (either explicitly by setting the Iflag, or by restoring it as part
of the entire SREG), the AVR hardware executes (at least) the next instruction still with
interrupts disabled, so the write to SPL is guaranteed to be executed with interrupts
disabled still. Thus, the emitted sequence ensures interrupts will be disabled only for
the minimum time required to guarantee the integrity of this operation.
Back to FAQ Index.
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11.29 Why are there five different linker scripts? 80
11.29 Why are there five different linker scripts?
From a comment in the source code:
Which one of the five linker script files is actually used depends on command line
options given to ld.
A .x script file is the default script A .xr script is for linking without relocation (-r flag)
A .xu script is like .xr but ∗do∗create constructors (-Ur flag) A .xn script is for linking
with -n flag (mix text and data on same page). A .xbn script is for linking with -N flag
(mix text and data on same page).
Back to FAQ Index.
11.30 How to add a raw binary image to linker output?
The GNU linker avr-ld cannot handle binary data directly. However, there’s a com-
panion tool called avr-objcopy. This is already known from the output side: it’s
used to extract the contents of the linked ELF file into an Intel Hex load file.
avr-objcopy can create a relocatable object file from arbitrary binary input, like
avr-objcopy -I binary -O elf32-avr foo.bin foo.o
This will create a file named foo.o, with the contents of foo.bin. The contents
will default to section .data, and two symbols will be created named _binary_-
foo_bin_start and _binary_foo_bin_end. These symbols can be referred
to inside a C source to access these data.
If the goal is to have those data go to flash ROM (similar to having used the PROGMEM
attribute in C source code), the sections have to be renamed while copying, and it’s also
useful to set the section flags:
avr-objcopy --rename-section .data=.progmem.data,contents,alloc,load,readonly,dat
a -I binary -O elf32-avr foo.bin foo.o
Note that all this could be conveniently wired into a Makefile, so whenever foo.bin
changes, it will trigger the recreation of foo.o, and a subsequent relink of the final
ELF file.
Below are two Makefile fragments that provide rules to convert a .txt file to an object
file, and to convert a .bin file to an object file:
$(OBJDIR)/%.o : %.txt
@echo Converting $<
@cp $(<) $(*).tmp
@echo -n 0 | tr 0 ’\000’ >> $(*).tmp
@$(OBJCOPY) -I binary -O elf32-avr \
--rename-section .data=.progmem.data,contents,alloc,load,readonly,data \
--redefine-sym _binary_$*_tmp_start=$*\
--redefine-sym _binary_$*_tmp_end=$*_end \
--redefine-sym _binary_$*_tmp_size=$*_size_sym \
$(*).tmp $(@)
@echo "extern const char" $(*)"[] PROGMEM;" > $(*).h
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11.31 How do I perform a software reset of the AVR? 81
@echo "extern const char" $(*)_end"[] PROGMEM;" >> $(*).h
@echo "extern const char" $(*)_size_sym"[];" >> $(*).h
@echo "#define $(*)_size ((int)$(*)_size_sym)" >> $(*).h
@rm $(*).tmp
$(OBJDIR)/%.o : %.bin
@echo Converting $<
@$(OBJCOPY) -I binary -O elf32-avr \
--rename-section .data=.progmem.data,contents,alloc,load,readonly,data \
--redefine-sym _binary_$*_bin_start=$*\
--redefine-sym _binary_$*_bin_end=$*_end \
--redefine-sym _binary_$*_bin_size=$*_size_sym \
$(<) $(@)
@echo "extern const char" $(*)"[] PROGMEM;" > $(*).h
@echo "extern const char" $(*)_end"[] PROGMEM;" >> $(*).h
@echo "extern const char" $(*)_size_sym"[];" >> $(*).h
@echo "#define $(*)_size ((int)$(*)_size_sym)" >> $(*).h
Back to FAQ Index.
11.31 How do I perform a software reset of the AVR?
The canonical way to perform a software reset of non-XMega AVR’s is to use the
watchdog timer. Enable the watchdog timer to the shortest timeout setting, then go into
an infinite, do-nothing loop. The watchdog will then reset the processor.
XMega parts have a specific bit RST_SWRST_bm in the RST.CTRL register, that gen-
erates a hardware reset. RST_SWRST_bm is protected by the XMega Configuration
Change Protection system.
The reason why using the watchdog timer or RST_SWRST_bm is preferable over jump-
ing to the reset vector, is that when the watchdog or RST_SWRST_bm resets the AVR,
the registers will be reset to their known, default settings. Whereas jumping to the reset
vector will leave the registers in their previous state, which is generally not a good idea.
CAUTION! Older AVRs will have the watchdog timer disabled on a reset. For these
older AVRs, doing a soft reset by enabling the watchdog is easy, as the watchdog will
then be disabled after the reset. On newer AVRs, once the watchdog is enabled, then it
stays enabled, even after a reset! For these newer AVRs a function needs to be added
to the .init3 section (i.e. during the startup code, before main()) to disable the watchdog
early enough so it does not continually reset the AVR.
Here is some example code that creates a macro that can be called to perform a soft
reset:
#include <avr/wdt.h>
...
#define soft_reset() \
do \
{ \
wdt_enable(WDTO_15MS); \
for(;;) \
{ \
} \
} while(0)
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11.32 I am using floating point math. Why is the compiled code so big? Why
does my code not work? 82
For newer AVRs (such as the ATmega1281) also add this function to your code to then
disable the watchdog after a reset (e.g., after a soft reset):
#include <avr/wdt.h>
...
// Function Pototype
void wdt_init(void) __attribute__((naked)) __attribute__((section(".init3")));
...
// Function Implementation
void wdt_init(void)
{
MCUSR = 0;
wdt_disable();
return;
}
Back to FAQ Index.
11.32 I am using floating point math. Why is the compiled code so
big? Why does my code not work?
You are not linking in the math library from AVR-LibC. GCC has a library that is used
for floating point operations, but it is not optimized for the AVR, and so it generates big
code, or it could be incorrect. This can happen even when you are not using any floating
point math functions from the Standard C library, but you are just doing floating point
math operations.
When you link in the math library from AVR-LibC, those routines get replaced by
hand-optimized AVR assembly and it produces much smaller code.
See I get "undefined reference to..." for functions like "sin()" for more details on how
to link in the math library.
Back to FAQ Index.
11.33 What pitfalls exist when writing reentrant code?
Reentrant code means the ability for a piece of code to be called simultaneously from
two or more threads. Attention to re-enterability is needed when using a multi-tasking
operating system, or when using interrupts since an interrupt is really a temporary
thread.
The code generated natively by gcc is reentrant. But, only some of the libraries in
avr-libc are explicitly reentrant, and some are known not to be reentrant. In general,
any library call that reads and writes global variables (including I/O registers) is not
reentrant. This is because more than one thread could read or write the same storage at
the same time, unaware that other threads are doing the same, and create inconsistent
and/or erroneous results.
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11.33 What pitfalls exist when writing reentrant code? 83
A library call that is known not to be reentrant will work if it is used only within one
thread and no other thread makes use of a library call that shares common storage with
it.
Below is a table of library calls with known issues.
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11.33 What pitfalls exist when writing reentrant code? 84
Library call Reentrant Issue Workaround/Alterna-
tive
rand(),random() Uses global variables to
keep state information.
Use special reentrant
versions: rand_r(),
random_r().
strtod(),strtol(),strtoul() Uses the global variable
errno to return
success/failure.
Ignore errno, or protect
calls with cli()/sei() or
ATOMIC_BLOCK() if
the application can
tolerate it. Or use
sccanf() or sccanf_P() if
possible.
malloc(),realloc(),
calloc(),free()
Uses the stack pointer
and global variables to
allocate and free
memory.
Protect calls with
cli()/sei() or
ATOMIC_BLOCK() if
the application can
tolerate it. If using an
OS, use the OS provided
memory allocator since
the OS is likely
modifying the stack
pointer anyway.
fdevopen(),fclose() Uses calloc() and free(). Protect calls with
cli()/sei() or
ATOMIC_BLOCK() if
the application can
tolerate it. Or use
fdev_setup_stream() or
FDEV_SETUP_-
STREAM().
Note: fclose() will only
call free() if the stream
has been opened with
fdevopen().
eeprom_∗(), boot_∗() Accesses I/O registers. Protect calls with
cli()/sei(),
ATOMIC_BLOCK(), or
use OS locking.
pgm_∗_far() Accesses I/O register
RAMPZ.
Starting with GCC 4.3,
RAMPZ is automatically
saved for ISRs, so
nothing further is needed
if only using interrupts.
Some OSes may
automatically preserve
RAMPZ during context
switching. Check the OS
documentation before
assuming it does.
Otherwise, protect calls
with cli()/sei(),
ATOMIC_BLOCK(), or
use explicit OS locking.
printf(),printf_P(),
vprintf(), vprintf_P(),
puts(),puts_P()
Alters flags and character
count in global FILE
stdout.
Use only in one thread.
Or if returned character
count is unimportant, do
not use the ∗_P versions.
Note: Formatting to a
string output, e.g.
sprintf(),sprintf_P(),
snprintf(),snprintf_P(),
vsprintf(),vsprintf_P(),
vsnprintf(),
vsnprintf_P(), is thread
safe. The formatted
string could then be
followed by an fwrite()
which simply calls the
lower layer to send the
string.
fprintf(),fprintf_P(),
vfprintf(),vfprintf_P(),
fputs(),fputs_P()
Alters flags and character
count in the FILE
argument. Problems can
occur if a global FILE is
used from multiple
threads.
Assign each thread its
own FILE for output. Or
if returned character
count is unimportant, do
not use the ∗_P versions.
assert() Contains an embedded
fprintf(). See above for
fprintf().
See above for fprintf().
clearerr() Alters flags in the FILE
argument.
Assign each thread its
own FILE for output.
getchar(),gets() Alters flags, character
count, and unget buffer
in global FILE stdin.
Use only in one thread.
∗∗∗
fgetc(),ungetc(),fgets(),
scanf(),scanf_P(),
fscanf(),fscanf_P(),
vscanf(),vfscanf(),
vfscanf_P(),fread()
Alters flags, character
count, and unget buffer
in the FILE argument.
Assign each thread its
own FILE for input. ∗∗∗
Note: Scanning from a
string, e.g. sscanf() and
sscanf_P(), are thread
safe.
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11.34 Why are some addresses of the EEPROM corrupted (usually address
zero)? 85
Note
It’s not clear one would ever want to do character input simultaneously from more
than one thread anyway, but these entries are included for completeness.
An effort will be made to keep this table up to date if any new issues are discovered or
introduced.
Back to FAQ Index.
11.34 Why are some addresses of the EEPROM corrupted (usually
address zero)?
The two most common reason for EEPROM corruption is either writing to the EEP-
ROM beyond the datasheet endurance specification, or resetting the AVR while an
EEPROM write is in progress.
EEPROM writes can take up to tens of milliseconds to complete. So that the CPU
is not tied up for that long of time, an internal state-machine handles EEPROM write
requests. The EEPROM state-machine expects to have all of the EEPROM registers
setup, then an EEPROM write request to start the process. Once the EEPROM state-
machine has started, changing EEPROM related registers during an EEPROM write
is guaranteed to corrupt the EEPROM write process. The datasheet always shows the
proper way to tell when a write is in progress, so that the registers are not changed by
the user’s program. The EEPROM state-machine will always complete the write in
progress unless power is removed from the device.
As with all EEPROM technology, if power fails during an EEPROM write the state of
the byte being written is undefined.
In older generation AVRs the EEPROM Address Register (EEAR) is initialized to zero
on reset, be it from Brown Out Detect, Watchdog or the Reset Pin. If an EEPROM
write has just started at the time of the reset, the write will be completed, but now
at address zero instead of the requested address. If the reset occurs later in the write
process both the requested address and address zero may be corrupted.
To distinguish which AVRs may exhibit the corrupt of address zero while a write is
in process during a reset, look at the "initial value" section for the EEPROM Address
Register. If EEAR shows the initial value as 0x00 or 0x0000, then address zero and
possibly the one being written will be corrupted. Newer parts show the initial value as
"undefined", these will not corrupt address zero during a reset (unless it was address
zero that was being written).
EEPROMs have limited write endurance. The datasheet specifies the number of EEP-
ROM writes that are guaranteed to function across the full temperature specification of
the AVR, for a given byte. A read should always be performed before a write, to see
if the value in the EEPROM actually needs to be written, so not to cause unnecessary
EEPROM wear.
The failure mechanism for an overwritten byte is generally one of "stuck" bits, i. e. a
bit will stay at a one or zero state regardless of the byte written. Also a write followed
by a read may return the correct data, but the data will change with the passage of time,
due the EEPROM’s inability to hold a charge from the excessive write wear.
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11.35 Why is my baud rate wrong? 86
Back to FAQ Index.
11.35 Why is my baud rate wrong?
Some AVR datasheets give the following formula for calculating baud rates:
(F_CPU/(UART_BAUD_RATE*16L)-1)
Unfortunately that formula does not work with all combinations of clock speeds and
baud rates due to integer truncation during the division operator.
When doing integer division it is usually better to round to the nearest integer, rather
than to the lowest. To do this add 0.5 (i. e. half the value of the denominator) to the
numerator before the division, resulting in the formula:
((F_CPU + UART_BAUD_RATE *8L) / (UART_BAUD_RATE *16L) - 1)
This is also the way it is implemented in <util/setbaud.h>: Helper macros for baud
rate calculations.
Back to FAQ Index.
11.36 On a device with more than 128 KiB of flash, how to make
function pointers work?
Function pointers beyond the "magical" 128 KiB barrier(s) on larger devices are sup-
posed to be resolved through so-called trampolines by the linker, so the actual pointers
used in the code can remain 16 bits wide.
In order for this to work, the option -mrelax must be given on the compiler
command-line that is used to link the final ELF file. (Older compilers did not im-
plement this option for the AVR, use -Wl,--relax instead.)
Back to FAQ Index.
11.37 Why is assigning ports in a "chain" a bad idea?
Suppose a number of IO port registers should get the value 0xff assigned. Conve-
niently, it is implemented like this:
DDRB = DDRD = 0xff;
According to the rules of the C language, this causes 0xff to be assigned to DDRD,
then DDRD is read back, and the value is assigned to DDRB. The compiler stands no
chance to optimize the readback away, as an IO port register is declared "volatile".
Thus, chaining that kind of IO port assignments would better be avoided, using explicit
assignments instead:
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12 Building and Installing the GNU Tool Chain 87
DDRB = 0xff;
DDRD = 0xff;
Even worse ist this, e. g. on an ATmega1281:
DDRA = DDRB = DDRC = DDRD = DDRE = DDRF = DDRG = 0xff;
The same happens as outlined above. However, when reading back register DDRG, this
register only implements 6 out of the 8 bits, so the two topmost (unimplemented) bits
read back as 0! Consequently, all remaining DDRxregisters get assigned the value 0x3f,
which does not match the intention of the developer in any way.
Back to FAQ Index.
12 Building and Installing the GNU Tool Chain
This chapter shows how to build and install, from source code, a complete develop-
ment environment for the AVR processors using the GNU toolset. There are two main
sections, one for Linux, FreeBSD, and other Unix-like operating systems, and another
section for Windows.
12.1 Building and Installing under Linux, FreeBSD, and Others
The default behaviour for most of these tools is to install every thing under the
/usr/local directory. In order to keep the AVR tools separate from the base
system, it is usually better to install everything into /usr/local/avr. If the
/usr/local/avr directory does not exist, you should create it before trying to
install anything. You will need root access to install there. If you don’t have root
access to the system, you can alternatively install in your home directory, for exam-
ple, in $HOME/local/avr. Where you install is a completely arbitrary decision, but
should be consistent for all the tools.
You specify the installation directory by using the --prefix=dir option with the
configure script. It is important to install all the AVR tools in the same directory
or some of the tools will not work correctly. To ensure consistency and simplify the
discussion, we will use $PREFIX to refer to whatever directory you wish to install in.
You can set this as an environment variable if you wish as such (using a Bourne-like
shell):
$ PREFIX=$HOME/local/avr
$ export PREFIX
Note
Be sure that you have your PATH environment variable set to search the direc-
tory you install everything in before you start installing anything. For example, if
you use --prefix=$PREFIX, you must have $PREFIX/bin in your exported
PATH. As such:
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12.2 Required Tools 88
$ PATH=$PATH:$PREFIX/bin
$ export PATH
Warning
If you have CC set to anything other than avr-gcc in your environment, this will
cause the configure script to fail. It is best to not have CC set at all.
Note
It is usually the best to use the latest released version of each of the tools.
12.2 Required Tools
•GNU Binutils
http://sources.redhat.com/binutils/
Installation
•GCC
http://gcc.gnu.org/
Installation
•AVR LibC
http://savannah.gnu.org/projects/avr-libc/
Installation
12.3 Optional Tools
You can develop programs for AVR devices without the following tools. They may or
may not be of use for you.
•AVRDUDE
http://savannah.nongnu.org/projects/avrdude/
Installation
Usage Notes
•GDB
http://sources.redhat.com/gdb/
Installation
•SimulAVR
http://savannah.gnu.org/projects/simulavr/
Installation
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12.4 GNU Binutils for the AVR target 89
•AVaRICE
http://avarice.sourceforge.net/
Installation
12.4 GNU Binutils for the AVR target
The binutils package provides all the low-level utilities needed in building and ma-
nipulating object files. Once installed, your environment will have an AVR assembler
(avr-as), linker (avr-ld), and librarian (avr-ar and avr-ranlib). In addi-
tion, you get tools which extract data from object files (avr-objcopy), dissassem-
ble object file information (avr-objdump), and strip information from object files
(avr-strip). Before we can build the C compiler, these tools need to be in place.
Download and unpack the source files:
$ bunzip2 -c binutils-<version>.tar.bz2 | tar xf -
$ cd binutils-<version>
Note
Replace <version>with the version of the package you downloaded.
If you obtained a gzip compressed file (.gz), use gunzip instead of bunzip2.
It is usually a good idea to configure and build binutils in a subdirectory so as not
to pollute the source with the compiled files. This is recommended by the binutils
developers.
$ mkdir obj-avr
$ cd obj-avr
The next step is to configure and build the tools. This is done by supplying arguments
to the configure script that enable the AVR-specific options.
$ ../configure --prefix=$PREFIX --target=avr --disable-nls
If you don’t specify the --prefix option, the tools will get installed in the
/usr/local hierarchy (i.e. the binaries will get installed in /usr/local/bin,
the info pages get installed in /usr/local/info, etc.) Since these tools are chang-
ing frequently, It is preferrable to put them in a location that is easily removed.
When configure is run, it generates a lot of messages while it determines what
is available on your operating system. When it finishes, it will have created several
Makefiles that are custom tailored to your platform. At this point, you can build the
project.
$ make
Note
BSD users should note that the project’s Makefile uses GNU make syntax.
This means FreeBSD users may need to build the tools by using gmake.
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12.5 GCC for the AVR target 90
If the tools compiled cleanly, you’re ready to install them. If you specified a destination
that isn’t owned by your account, you’ll need root access to install them. To install:
$ make install
You should now have the programs from binutils installed into $PREFIX/bin. Don’t
forget to set your PATH environment variable before going to build avr-gcc.
12.5 GCC for the AVR target
Warning
You must install avr-binutils and make sure your path is set properly before in-
stalling avr-gcc.
The steps to build avr-gcc are essentially same as for binutils:
$ bunzip2 -c gcc-<version>.tar.bz2 | tar xf -
$ cd gcc-<version>
$ mkdir obj-avr
$ cd obj-avr
$ ../configure --prefix=$PREFIX --target=avr --enable-languages=c,c++ \
--disable-nls --disable-libssp --with-dwarf2
$ make
$ make install
To save your self some download time, you can alternatively download only the
gcc-core-<version>.tar.bz2 and gcc-c++-<version>.tar.bz2
parts of the gcc. Also, if you don’t need C++ support, you only need the core part
and should only enable the C language support. (Starting with GCC 4.7 releases, these
split files are no longer available though.)
Note
Early versions of these tools did not support C++.
The stdc++ libs are not included with C++ for AVR due to the size limitations of
the devices.
12.6 AVR LibC
Warning
You must install avr-binutils,avr-gcc and make sure your path is set properly be-
fore installing avr-libc.
Note
If you have obtained the latest avr-libc from cvs, you will have to run the
bootstrap script before using either of the build methods described below.
To build and install avr-libc:
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12.7 AVRDUDE 91
$ gunzip -c avr-libc-<version>.tar.gz | tar xf -
$ cd avr-libc-<version>
$ ./configure --prefix=$PREFIX --build=‘./config.guess‘ --host=avr
$ make
$ make install
Optionally, generation of debug information can be requested with:
$ gunzip -c avr-libc-<version>.tar.gz | tar xf -
$ cd avr-libc-<version>
$ ./configure --prefix=$PREFIX --build=‘./config.guess‘ --host=avr \
--with-debug-info=DEBUG_INFO
$ make
$ make install
where DEBUG_INFO can be one of stabs,dwarf-2, or dwarf-4.
The default is to not generate any debug information, which is suitable for binary dis-
tributions of avr-libc, where the user does not have the source code installed the debug
information would refer to.
12.7 AVRDUDE
Note
It has been ported to windows (via MinGW or cygwin), Linux and Solaris. Other
Unix systems should be trivial to port to.
avrdude is part of the FreeBSD ports system. To install it, simply do the following:
# cd /usr/ports/devel/avrdude
# make install
Note
Installation into the default location usually requires root permissions. However,
running the program only requires access permissions to the appropriate ppi(4)
device.
Building and installing on other systems should use the configure system, as such:
$ gunzip -c avrdude-<version>.tar.gz | tar xf -
$ cd avrdude-<version>
$ mkdir obj-avr
$ cd obj-avr
$ ../configure --prefix=$PREFIX
$ make
$ make install
12.8 GDB for the AVR target
GDB also uses the configure system, so to build and install:
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12.9 SimulAVR 92
$ bunzip2 -c gdb-<version>.tar.bz2 | tar xf -
$ cd gdb-<version>
$ mkdir obj-avr
$ cd obj-avr
$ ../configure --prefix=$PREFIX --target=avr
$ make
$ make install
Note
If you are planning on using avr-gdb, you will probably want to install either
simulavr or avarice since avr-gdb needs one of these to run as a a remote target
backend.
12.9 SimulAVR
SimulAVR also uses the configure system, so to build and install:
$ gunzip -c simulavr-<version>.tar.gz | tar xf -
$ cd simulavr-<version>
$ mkdir obj-avr
$ cd obj-avr
$ ../configure --prefix=$PREFIX
$ make
$ make install
Note
You might want to have already installed avr-binutils,avr-gcc and avr-libc if you
want to have the test programs built in the simulavr source.
12.10 AVaRICE
Note
These install notes are not applicable to avarice-1.5 or older. You probably don’t
want to use anything that old anyways since there have been many improvements
and bug fixes since the 1.5 release.
AVaRICE also uses the configure system, so to build and install:
$ gunzip -c avarice-<version>.tar.gz | tar xf -
$ cd avarice-<version>
$ mkdir obj-avr
$ cd obj-avr
$ ../configure --prefix=$PREFIX
$ make
$ make install
Note
AVaRICE uses the BFD library for accessing various binary file formats. You
may need to tell the configure script where to find the lib and headers for the link
to work. This is usually done by invoking the configure script like this (Replace
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12.11 Building and Installing under Windows 93
<hdr_path>with the path to the bfd.h file on your system. Replace <lib_-
path>with the path to libbfd.a on your system.):
$ CPPFLAGS=-I<hdr_path> LDFLAGS=-L<lib_path> ../configure --prefix=$PREFIX
12.11 Building and Installing under Windows
Building and installing the toolchain under Windows requires more effort because all
of the tools required for building, and the programs themselves, are mainly designed
for running under a POSIX environment such as Unix and Linux. Windows does not
natively provide such an environment.
There are two projects available that provide such an environment, Cygwin and
MinGW. There are advantages and disadvantages to both. Cygwin provides a very
complete POSIX environment that allows one to build many Linux based tools from
source with very little or no source modifications. However, POSIX functionality is
provided in the form of a DLL that is linked to the application. This DLL has to be
redistributed with your application and there are issues if the Cygwin DLL already
exists on the installation system and different versions of the DLL. On the other hand,
MinGW can compile code as native Win32 applications. However, this means that pro-
grams designed for Unix and Linux (i.e. that use POSIX functionality) will not compile
as MinGW does not provide that POSIX layer for you. Therefore most programs that
compile on both types of host systems, usually must provide some sort of abstraction
layer to allow an application to be built cross-platform.
MinGW does provide somewhat of a POSIX environment, called MSYS, that al-
lows you to build Unix and Linux applications as they woud normally do, with a
configure step and a make step. Cygwin also provides such an environment. This
means that building the AVR toolchain is very similar to how it is built in Linux, de-
scribed above. The main differences are in what the PATH environment variable gets
set to, pathname differences, and the tools that are required to build the projects under
Windows. We’ll take a look at the tools next.
12.12 Tools Required for Building the Toolchain for Windows
These are the tools that are currently used to build an AVR tool chain. This list may
change, either the version of the tools, or the tools themselves, as improvements are
made.
•MinGW
Download the MinGW Automated Installer, 20100909 (or later)
<http://sourceforge.net/projects/mingw/files/Automated%20MinGW%20Installer/mingw-get-inst/mingw-get-inst-20100909/mingw-get-inst-20100909.exe/download>
–Run mingw-get-inst-20100909.exe
–In the installation wizard, keep the default values and press the "Next" but-
ton for all installer pages except for the pages explicitly listed below.
–In the installer page "Repository Catalogues", select the "Download latest
repository catalogues" radio button, and press the "Next" button
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12.12 Tools Required for Building the Toolchain for Windows 94
–In the installer page "License Agreement", select the "I accept the agree-
ment" radio button, and press the "Next" button
–In the installer page "Select Components", be sure to select these items:
*C compiler (default checked)
*C++ compiler
*Ada compiler
*MinGW Developer Toolkit (which includes "MSYS Basic System").
–Install.
•Install Cygwin
–Install everything, all users, UNIX line endings. This will take a ∗long∗
time. A fat internet pipe is highly recommended. It is also recommended
that you download all to a directory first, and then install from that directory
to your machine.
Note
GMP, MPFR, and MPC are required to build GCC.
GMP is a prequisite for building MPFR. Build GMP first.
MPFR is a prerequisite for building MPC. Build MPFR second.
•Build GMP for MinGW
–Latest Version
–<http://gmplib.org/>
–Build script:
./configure 2>&1 | tee gmp-configure.log
make 2>&1 | tee gmp-make.log
make check 2>&1 | tee gmp-make-check.log
make install 2>&1 | tee gmp-make-install.log
–GMP headers will be installed under /usr/local/include and library installed
under /usr/local/lib.
•Build MPFR for MinGW
–Latest Version
–<http://www.mpfr.org/>
–Build script:
./configure --with-gmp=/usr/local --disable-shared 2>&1 | tee mpfr-configure.log
make 2>&1 | tee mpfr-make.log
make check 2>&1 | tee mpfr-make-check.log
make install 2>&1 | tee mpfr-make-install.log
–MPFR headers will be installed under /usr/local/include and library in-
stalled under /usr/local/lib.
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12.12 Tools Required for Building the Toolchain for Windows 95
•Build MPC for MinGW
–Latest Version
–<http://www.multiprecision.org/>
–Build script:
./configure --with-gmp=/usr/local --with-mpfr=/usr/local --disable-shared 2>&1 | tee mpfr-configure.log
make 2>&1 | tee mpfr-make.log
make check 2>&1 | tee mpfr-make-check.log
make install 2>&1 | tee mpfr-make-install.log
–MPFR headers will be installed under /usr/local/include and library in-
stalled under /usr/local/lib.
Note
Doxygen is required to build AVR-LibC documentation.
•Install Doxygen
–Version 1.7.2
–<http://www.stack.nl/∼dimitri/doxygen/>
–Download and install.
NetPBM is required to build graphics in the AVR-LibC documentation.
•Install NetPBM
–Version 10.27.0
–From the GNUWin32 project: <http://gnuwin32.sourceforge.net/packages.html>
–Download and install.
fig2dev is required to build graphics in the AVR-LibC documentation.
•Install fig2dev
–Version 3.2 patchlevel 5c
–From WinFig 4.62: <http://www.schmidt-web-berlin.de/winfig/>
–Download the zip file version of WinFig
–Unzip the download file and install fig2dev.exe in a location of your
choice, somewhere in the PATH.
–You may have to unzip and install related DLL files for fig2dev. In the
version above, you have to install QtCore4.dll and QtGui4.dll.
MikTeX is required to build various documentation.
•Install MiKTeX
–Version 2.9
–<http://miktex.org/>
–Download and install.
Ghostscript is required to build various documentation.
•Install Ghostscript
–Version 9.00
–<http://www.ghostscript.com>
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12.13 Building the Toolchain for Windows 96
–Download and install.
–In the \bin subdirectory of the installaion, copy gswin32c.exe to gs.exe.
• Set the TEMP and TMP environment variables to c:\temp or to the short file-
name version. This helps to avoid NTVDM errors during building.
12.13 Building the Toolchain for Windows
All directories in the PATH enviornment variable should be specified using their short
filename (8.3) version. This will also help to avoid NTVDM errors during building.
These short filenames can be specific to each machine.
Build the tools below in MinGW/MSYS.
•Binutils
–Open source code pacakge and patch as necessary.
–Configure and build in a directory outside of the source code tree.
–Set PATH, in order:
*<MikTex executables>
*<ghostscript executables>
*/usr/local/bin
*/usr/bin
*/bin
*/mingw/bin
*c:/cygwin/bin
*<install directory>/bin
–Configure
CFLAGS=-D__USE_MINGW_ACCESS \
../$archivedir/configure \
--prefix=$installdir \
--target=avr \
--disable-nls \
--enable-doc \
--datadir=$installdir/doc/binutils \
--with-gmp=/usr/local \
--with-mpfr=/usr/local \
2>&1 | tee binutils-configure.log
–Make
make all html install install-html 2>&1 | tee binutils-make.log
–Manually change documentation location.
•GCC
–Open source code pacakge and patch as necessary.
–Configure and build in a directory outside of the source code tree.
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12.13 Building the Toolchain for Windows 97
–Set PATH, in order:
*<MikTex executables>
*<ghostscript executables>
*/usr/local/bin
*/usr/bin
*/bin
*/mingw/bin
*c:/cygwin/bin
*<install directory>/bin
–Configure
LDFLAGS=’-L /usr/local/lib -R /usr/local/lib’ \
CFLAGS=’-D__USE_MINGW_ACCESS’ \
../gcc-$version/configure \
--with-gmp=/usr/local \
--with-mpfr=/usr/local \
--with-mpc=/usr/local \
--prefix=$installdir \
--target=$target \
--enable-languages=c,c++ \
--with-dwarf2 \
--enable-doc \
--with-docdir=$installdir/doc/$project \
--disable-shared \
--disable-libada \
--disable-libssp \
2>&1 | tee $project-configure.log
–Make
make all html install 2>&1 | tee $package-make.log
•avr-libc
–Open source code package.
–Configure and build at the top of the source code tree.
–Set PATH, in order:
*/usr/local/bin
*/mingw/bin
*/bin
*<MikTex executables>
*<install directory>/bin
*<Doxygen executables>
*<NetPBM executables>
*<fig2dev executable>
*<Ghostscript executables>
*c:/cygwin/bin
–Configure
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12.13 Building the Toolchain for Windows 98
./configure \
--host=avr \
--prefix=$installdir \
--enable-doc \
--disable-versioned-doc \
--enable-html-doc \
--enable-xml-doc \
--enable-pdf-doc \
--enable-man-doc \
--mandir=$installdir/man \
--datadir=$installdir \
2>&1 | tee $package-configure.log
–Make
make all install 2>&1 | tee $package-make.log
–Manually change location of man page documentation.
–Move the examples to the top level of the install tree.
–Convert line endings in examples to Windows line endings.
–Convert line endings in header files to Windows line endings.
•AVRDUDE
–Open source code package.
–Configure and build at the top of the source code tree.
–Set PATH, in order:
*<MikTex executables>
*/usr/local/bin
*/usr/bin
*/bin
*/mingw/bin
*c:/cygwin/bin
*<install directory>/bin
–Set location of LibUSB headers and libraries
export CPPFLAGS="-I../../libusb-win32-device-bin-$libusb_version/include"
export CFLAGS="-I../../libusb-win32-device-bin-$libusb_version/include"
export LDFLAGS="-L../../libusb-win32-device-bin-$libusb_version/lib/gcc"
–Configure
./configure \
--prefix=$installdir \
--datadir=$installdir \
--sysconfdir=$installdir/bin \
--enable-doc \
--disable-versioned-doc \
2>&1 | tee $package-configure.log
–Make
make -k all install 2>&1 | tee $package-make.log
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12.13 Building the Toolchain for Windows 99
–Convert line endings in avrdude config file to Windows line endings.
–Delete backup copy of avrdude config file in install directory if exists.
•Insight/GDB
–Open source code pacakge and patch as necessary.
–Configure and build in a directory outside of the source code tree.
–Set PATH, in order:
*<MikTex executables>
*/usr/local/bin
*/usr/bin
*/bin
*/mingw/bin
*c:/cygwin/bin
*<install directory>/bin
–Configure
CFLAGS=-D__USE_MINGW_ACCESS \
LDFLAGS=’-static’ \
../$archivedir/configure \
--prefix=$installdir \
--target=avr \
--with-gmp=/usr/local \
--with-mpfr=/usr/local \
--enable-doc \
2>&1 | tee insight-configure.log
–Make
make all install 2>&1 | tee $package-make.log
•SRecord
–Open source code package.
–Configure and build at the top of the source code tree.
–Set PATH, in order:
*<MikTex executables>
*/usr/local/bin
*/usr/bin
*/bin
*/mingw/bin
*c:/cygwin/bin
*<install directory>/bin
–Configure
./configure \
--prefix=$installdir \
--infodir=$installdir/info \
--mandir=$installdir/man \
2>&1 | tee $package-configure.log
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12.13 Building the Toolchain for Windows 100
–Make
make all install 2>&1 | tee $package-make.log
Build the tools below in Cygwin.
•AVaRICE
–Open source code package.
–Configure and build in a directory outside of the source code tree.
–Set PATH, in order:
*<MikTex executables>
*/usr/local/bin
*/usr/bin
*/bin
*<install directory>/bin
–Set location of LibUSB headers and libraries
export CPPFLAGS=-I$startdir/libusb-win32-device-bin-$libusb_version/include
export CFLAGS=-I$startdir/libusb-win32-device-bin-$libusb_version/include
export LDFLAGS="-static -L$startdir/libusb-win32-device-bin-$libusb_version/lib/gcc "
–Configure
../$archivedir/configure \
--prefix=$installdir \
--datadir=$installdir/doc \
--mandir=$installdir/man \
--infodir=$installdir/info \
2>&1 | tee avarice-configure.log
–Make
make all install 2>&1 | tee avarice-make.log
•SimulAVR
–Open source code package.
–Configure and build in a directory outside of the source code tree.
–Set PATH, in order:
*<MikTex executables>
*/usr/local/bin
*/usr/bin
*/bin
*<install directory>/bin
–Configure
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13 Using the GNU tools 101
export LDFLAGS="-static"
../$archivedir/configure \
--prefix=$installdir \
--datadir=$installdir \
--disable-tests \
--disable-versioned-doc \
2>&1 | tee simulavr-configure.log
–Make
make -k all install 2>&1 | tee simulavr-make.log
make pdf install-pdf 2>&1 | tee simulavr-pdf-make.log
13 Using the GNU tools
This is a short summary of the AVR-specific aspects of using the GNU tools. Normally,
the generic documentation of these tools is fairly large and maintained in texinfo
files. Command-line options are explained in detail in the manual page.
13.1 Options for the C compiler avr-gcc
13.1.1 Machine-specific options for the AVR
The following machine-specific options are recognized by the C compiler frontend. In
addition to the preprocessor macros indicated in the tables below, the preprocessor will
define the macros __AVR and __AVR__ (to the value 1) when compiling for an AVR
target. The macro AVR will be defined as well when using the standard levels gnu89
(default) and gnu99 but not with c89 and c99.
•-mmcu=architecture
Compile code for architecture. Currently known architectures are
Architecture PBSMacros PBSDescription
avr1 PBS__AVR_ARCH__=1
__AVR_ASM_ONLY__
__AVR_2_BYTE_PC__ [2]
PBSSimple CPU core,
only assembler support
avr2 PBS__AVR_ARCH__=2
__AVR_2_BYTE_PC__ [2]
PBS"Classic" CPU core,
up to 8 KB of ROM
avr25 [1] PBS__AVR_ARCH__=25
__AVR_HAVE_MOVW__ [1]
__AVR_HAVE_LPMX__ [1]
__AVR_2_BYTE_PC__ [2]
PBS"Classic" CPU
core with ’MOVW’
and ’LPM Rx, Z[+]’
instruction, up to 8 KB
of ROM
avr3 PBS__AVR_ARCH__=3
__AVR_MEGA__ [5]
__AVR_HAVE_JMP_CALL__ [4]
__AVR_2_BYTE_PC__ [2]
PBS"Classic" CPU core,
16 KB to 64 KB of ROM
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13.1 Options for the C compiler avr-gcc 102
avr31 PBS__AVR_ARCH__=31
__AVR_MEGA__ [5]
__AVR_HAVE_JMP_CALL__ [4]
__AVR_HAVE_RAMPZ__ [4]
__AVR_HAVE_ELPM__ [4]
__AVR_2_BYTE_PC__ [2]
PBS"Classic" CPU core,
128 KB of ROM
avr35 [3] PBS__AVR_ARCH__=35
__AVR_MEGA__ [5]
__AVR_HAVE_JMP_CALL__ [4]
__AVR_HAVE_MOVW__ [1]
__AVR_HAVE_LPMX__ [1]
__AVR_2_BYTE_PC__ [2]
PBS"Classic" CPU
core with ’MOVW’
and ’LPM Rx, Z[+]’
instruction, 16 KB to 64
KB of ROM
avr4 PBS__AVR_ARCH__=4
__AVR_ENHANCED__ [5]
__AVR_HAVE_MOVW__ [1]
__AVR_HAVE_LPMX__ [1]
__AVR_HAVE_MUL__ [1]
__AVR_2_BYTE_PC__ [2]
PBS"Enhanced" CPU
core, up to 8 KB of
ROM
avr5 PBS__AVR_ARCH__=5
__AVR_MEGA__ [5]
__AVR_ENHANCED__ [5]
__AVR_HAVE_JMP_CALL__ [4]
__AVR_HAVE_MOVW__ [1]
__AVR_HAVE_LPMX__ [1]
__AVR_HAVE_MUL__ [1]
__AVR_2_BYTE_PC__ [2]
PBS"Enhanced" CPU
core, 16 KB to 64 KB of
ROM
avr51 PBS__AVR_ARCH__=51
__AVR_MEGA__ [5]
__AVR_ENHANCED__ [5]
__AVR_HAVE_JMP_CALL__ [4]
__AVR_HAVE_MOVW__ [1]
__AVR_HAVE_LPMX__ [1]
__AVR_HAVE_MUL__ [1]
__AVR_HAVE_RAMPZ__ [4]
__AVR_HAVE_ELPM__ [4]
__AVR_HAVE_ELPMX__ [4]
__AVR_2_BYTE_PC__ [2]
PBS"Enhanced" CPU
core, 128 KB of ROM
avr6 [2] PBS__AVR_ARCH__=6
__AVR_MEGA__ [5]
__AVR_ENHANCED__ [5]
__AVR_HAVE_JMP_CALL__ [4]
__AVR_HAVE_MOVW__ [1]
__AVR_HAVE_LPMX__ [1]
__AVR_HAVE_MUL__ [1]
__AVR_HAVE_RAMPZ__ [4]
__AVR_HAVE_ELPM__ [4]
__AVR_HAVE_ELPMX__ [4]
__AVR_3_BYTE_PC__ [2]
PBS"Enhanced" CPU
core, 256 KB of ROM
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13.1 Options for the C compiler avr-gcc 103
[1] New in GCC 4.2
[2] Unofficial patch for GCC 4.1
[3] New in GCC 4.2.3
[4] New in GCC 4.3
[5] Obsolete.
By default, code is generated for the avr2 architecture.
Note that when only using -mmcu=architecture but no -mmcu=MCU type, including
the file <avr/io.h>cannot work since it cannot decide which device’s definitions
to select.
•-mmcu=MCU type
The following MCU types are currently understood by avr-gcc. The table matches
them against the corresponding avr-gcc architecture name, and shows the preprocessor
symbol declared by the -mmcu option.
Architecture MCU name Macro
avr1 at90s1200 __AVR_AT90S1200__
avr1 attiny11 __AVR_ATtiny11__
avr1 attiny12 __AVR_ATtiny12__
avr1 attiny15 __AVR_ATtiny15__
avr1 attiny28 __AVR_ATtiny28__
avr2 at90s2313 __AVR_AT90S2313__
avr2 at90s2323 __AVR_AT90S2323__
avr2 at90s2333 __AVR_AT90S2333__
avr2 at90s2343 __AVR_AT90S2343__
avr2 attiny22 __AVR_ATtiny22__
avr2 attiny26 __AVR_ATtiny26__
avr2 at90s4414 __AVR_AT90S4414__
avr2 at90s4433 __AVR_AT90S4433__
avr2 at90s4434 __AVR_AT90S4434__
avr2 at90s8515 __AVR_AT90S8515__
avr2 at90c8534 __AVR_AT90C8534__
avr2 at90s8535 __AVR_AT90S8535__
avr2/avr25 [1] at86rf401 __AVR_AT86RF401__
avr2/avr25 [1] ata5272 __AVR_ATA5272__
avr2/avr25 [1] ata6616c __AVR_ATA6616C__
avr2/avr25 [1] attiny13 __AVR_ATtiny13__
avr2/avr25 [1] attiny13a __AVR_ATtiny13A__
avr2/avr25 [1] attiny2313 __AVR_ATtiny2313__
avr2/avr25 [1] attiny2313a __AVR_ATtiny2313A__
avr2/avr25 [1] attiny24 __AVR_ATtiny24__
avr2/avr25 [1] attiny24a __AVR_ATtiny24A__
avr2/avr25 [1] attiny25 __AVR_ATtiny25__
avr2/avr25 [1] attiny261 __AVR_ATtiny261__
avr2/avr25 [1] attiny261a __AVR_ATtiny261A__
avr2/avr25 [1] attiny4313 __AVR_ATtiny4313__
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13.1 Options for the C compiler avr-gcc 104
avr2/avr25 [1] attiny43u __AVR_ATtiny43U__
avr2/avr25 [1] attiny44 __AVR_ATtiny44__
avr2/avr25 [1] attiny44a __AVR_ATtiny44A__
avr2/avr25 [1] attiny441 __AVR_ATtiny441__
avr2/avr25 [1] attiny45 __AVR_ATtiny45__
avr2/avr25 [1] attiny461 __AVR_ATtiny461__
avr2/avr25 [1] attiny461a __AVR_ATtiny461A__
avr2/avr25 [1] attiny48 __AVR_ATtiny48__
avr2/avr25 [1] attiny828 __AVR_ATtiny828__
avr2/avr25 [1] attiny84 __AVR_ATtiny84__
avr2/avr25 [1] attiny84a __AVR_ATtiny84A__
avr2/avr25 [1] attiny841 __AVR_ATtiny841__
avr2/avr25 [1] attiny85 __AVR_ATtiny85__
avr2/avr25 [1] attiny861 __AVR_ATtiny861__
avr2/avr25 [1] attiny861a __AVR_ATtiny861A__
avr2/avr25 [1] attiny87 __AVR_ATtiny87__
avr2/avr25 [1] attiny88 __AVR_ATtiny88__
avr3 atmega603 __AVR_ATmega603__
avr3 at43usb355 __AVR_AT43USB355__
avr3/avr31 [3] atmega103 __AVR_ATmega103__
avr3/avr31 [3] at43usb320 __AVR_AT43USB320__
avr3/avr35 [2] at90usb82 __AVR_AT90USB82__
avr3/avr35 [2] at90usb162 __AVR_AT90USB162__
avr3/avr35 [2] ata5505 __AVR_ATA5505__
avr3/avr35 [2] ata6617c __AVR_ATA6617C__
avr3/avr35 [2] ata664251 __AVR_ATA664251__
avr3/avr35 [2] atmega8u2 __AVR_ATmega8U2__
avr3/avr35 [2] atmega16u2 __AVR_ATmega16U2__
avr3/avr35 [2] atmega32u2 __AVR_ATmega32U2__
avr3/avr35 [2] attiny167 __AVR_ATtiny167__
avr3/avr35 [2] attiny1634 __AVR_ATtiny1634__
avr3 at76c711 __AVR_AT76C711__
avr4 ata6285 __AVR_ATA6285__
avr4 ata6286 __AVR_ATA6286__
avr4 ata6289 __AVR_ATA6289__
avr4 ata6612c __AVR_ATA6612C__
avr4 atmega48 __AVR_ATmega48__
avr4 atmega48a __AVR_ATmega48A__
avr4 atmega48pa __AVR_ATmega48PA__
avr4 atmega48pb __AVR_ATmega48PB__
avr4 atmega48p __AVR_ATmega48P__
avr4 atmega8 __AVR_ATmega8__
avr4 atmega8a __AVR_ATmega8A__
avr4 atmega8515 __AVR_ATmega8515__
avr4 atmega8535 __AVR_ATmega8535__
avr4 atmega88 __AVR_ATmega88__
avr4 atmega88a __AVR_ATmega88A__
avr4 atmega88p __AVR_ATmega88P__
avr4 atmega88pa __AVR_ATmega88PA__
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13.1 Options for the C compiler avr-gcc 105
avr4 atmega88pb __AVR_ATmega88PB__
avr4 atmega8hva __AVR_ATmega8HVA__
avr4 at90pwm1 __AVR_AT90PWM1__
avr4 at90pwm2 __AVR_AT90PWM2__
avr4 at90pwm2b __AVR_AT90PWM2B__
avr4 at90pwm3 __AVR_AT90PWM3__
avr4 at90pwm3b __AVR_AT90PWM3B__
avr4 at90pwm81 __AVR_AT90PWM81__
avr5 at90can32 __AVR_AT90CAN32__
avr5 at90can64 __AVR_AT90CAN64__
avr5 at90pwm161 __AVR_AT90PWM161__
avr5 at90pwm216 __AVR_AT90PWM216__
avr5 at90pwm316 __AVR_AT90PWM316__
avr5 at90scr100 __AVR_AT90SCR100__
avr5 at90usb646 __AVR_AT90USB646__
avr5 at90usb647 __AVR_AT90USB647__
avr5 at94k __AVR_AT94K__
avr5 atmega16 __AVR_ATmega16__
avr5 ata5702m322 __AVR_ATA5702M322__
avr5 ata5782 __AVR_ATA5782__
avr5 ata5790 __AVR_ATA5790__
avr5 ata5790n __AVR_ATA5790N__
avr5 ata5791 __AVR_ATA5791__
avr5 ata5795 __AVR_ATA5795__
avr5 ata5831 __AVR_ATA5831__
avr5 ata6613c __AVR_ATA6613C__
avr5 ata6614q __AVR_ATA6614Q__
avr5 ata8210 __AVR_ATA8210__
avr5 ata8510 __AVR_ATA8510__
avr5 atmega161 __AVR_ATmega161__
avr5 atmega162 __AVR_ATmega162__
avr5 atmega163 __AVR_ATmega163__
avr5 atmega164a __AVR_ATmega164A__
avr5 atmega164p __AVR_ATmega164P__
avr5 atmega164pa __AVR_ATmega164PA__
avr5 atmega165 __AVR_ATmega165__
avr5 atmega165a __AVR_ATmega165A__
avr5 atmega165p __AVR_ATmega165P__
avr5 atmega165pa __AVR_ATmega165PA__
avr5 atmega168 __AVR_ATmega168__
avr5 atmega168a __AVR_ATmega168A__
avr5 atmega168p __AVR_ATmega168P__
avr5 atmega168pa __AVR_ATmega168PA__
avr5 atmega168pb __AVR_ATmega168PB__
avr5 atmega169 __AVR_ATmega169__
avr5 atmega169a __AVR_ATmega169A__
avr5 atmega169p __AVR_ATmega169P__
avr5 atmega169pa __AVR_ATmega169PA__
avr5 atmega16a __AVR_ATmega16A__
avr5 atmega16hva __AVR_ATmega16HVA__
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13.1 Options for the C compiler avr-gcc 106
avr5 atmega16hva2 __AVR_ATmega16HVA2__
avr5 atmega16hvb __AVR_ATmega16HVB__
avr5 atmega16hvbrevb __AVR_ATmega16HVBREVB__
avr5 atmega16m1 __AVR_ATmega16M1__
avr5 atmega16u4 __AVR_ATmega16U4__
avr5 atmega32 __AVR_ATmega32__
avr5 atmega32a __AVR_ATmega32A__
avr5 atmega323 __AVR_ATmega323__
avr5 atmega324a __AVR_ATmega324A__
avr5 atmega324p __AVR_ATmega324P__
avr5 atmega324pa __AVR_ATmega324PA__
avr5 atmega325 __AVR_ATmega325__
avr5 atmega325a __AVR_ATmega325A__
avr5 atmega325p __AVR_ATmega325P__
avr5 atmega325pa __AVR_ATmega325PA__
avr5 atmega3250 __AVR_ATmega3250__
avr5 atmega3250a __AVR_ATmega3250A__
avr5 atmega3250p __AVR_ATmega3250P__
avr5 atmega3250pa __AVR_ATmega3250PA__
avr5 atmega328 __AVR_ATmega328__
avr5 atmega328p __AVR_ATmega328P__
avr5 atmega329 __AVR_ATmega329__
avr5 atmega329a __AVR_ATmega329A__
avr5 atmega329p __AVR_ATmega329P__
avr5 atmega329pa __AVR_ATmega329PA__
avr5 atmega3290 __AVR_ATmega3290__
avr5 atmega3290a __AVR_ATmega3290A__
avr5 atmega3290p __AVR_ATmega3290P__
avr5 atmega3290pa __AVR_ATmega3290PA__
avr5 atmega32c1 __AVR_ATmega32C1__
avr5 atmega32hvb __AVR_ATmega32HVB__
avr5 atmega32hvbrevb __AVR_ATmega32HVBREVB__
avr5 atmega32m1 __AVR_ATmega32M1__
avr5 atmega32u4 __AVR_ATmega32U4__
avr5 atmega32u6 __AVR_ATmega32U6__
avr5 atmega406 __AVR_ATmega406__
avr5 atmega644rfr2 __AVR_ATmega644RFR2__
avr5 atmega64rfr2 __AVR_ATmega64RFR2__
avr5 atmega64 __AVR_ATmega64__
avr5 atmega64a __AVR_ATmega64A__
avr5 atmega640 __AVR_ATmega640__
avr5 atmega644 __AVR_ATmega644__
avr5 atmega644a __AVR_ATmega644A__
avr5 atmega644p __AVR_ATmega644P__
avr5 atmega644pa __AVR_ATmega644PA__
avr5 atmega645 __AVR_ATmega645__
avr5 atmega645a __AVR_ATmega645A__
avr5 atmega645p __AVR_ATmega645P__
avr5 atmega6450 __AVR_ATmega6450__
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13.1 Options for the C compiler avr-gcc 107
avr5 atmega6450a __AVR_ATmega6450A__
avr5 atmega6450p __AVR_ATmega6450P__
avr5 atmega649 __AVR_ATmega649__
avr5 atmega649a __AVR_ATmega649A__
avr5 atmega6490 __AVR_ATmega6490__
avr5 atmega6490a __AVR_ATmega6490A__
avr5 atmega6490p __AVR_ATmega6490P__
avr5 atmega649p __AVR_ATmega649P__
avr5 atmega64c1 __AVR_ATmega64C1__
avr5 atmega64hve __AVR_ATmega64HVE__
avr5 atmega64hve2 __AVR_ATmega64HVE2__
avr5 atmega64m1 __AVR_ATmega64M1__
avr5 m3000 __AVR_M3000__
avr5/avr51 [3] at90can128 __AVR_AT90CAN128__
avr5/avr51 [3] at90usb1286 __AVR_AT90USB1286__
avr5/avr51 [3] at90usb1287 __AVR_AT90USB1287__
avr5/avr51 [3] atmega128 __AVR_ATmega128__
avr5/avr51 [3] atmega128a __AVR_ATmega128A__
avr5/avr51 [3] atmega1280 __AVR_ATmega1280__
avr5/avr51 [3] atmega1281 __AVR_ATmega1281__
avr5/avr51 [3] atmega1284 __AVR_ATmega1284__
avr5/avr51 [3] atmega1284p __AVR_ATmega1284P__
avr5/avr51 [3] atmega1284rfr2 __AVR_ATmega1284RFR2__
avr5/avr51 [3] atmega128rfr2 __AVR_ATmega128RFR2__
avr6 atmega2560 __AVR_ATmega2560__
avr6 atmega2561 __AVR_ATmega2561__
avr6 atmega2564rfr2 __AVR_ATmega2564RFR2__
avr6 atmega256rfr2 __AVR_ATmega256RFR2__
avrxmega2 atxmega8e5 __AVR_ATxmega8E5__
avrxmega2 atxmega16a4 __AVR_ATxmega16A4__
avrxmega2 atxmega16a4u __AVR_ATxmega16A4U__
avrxmega2 atxmega16c4 __AVR_ATxmega16C4__
avrxmega2 atxmega16d4 __AVR_ATxmega16D4__
avrxmega2 atxmega16e5 __AVR_ATxmega16E5__
avrxmega2 atxmega32a4 __AVR_ATxmega32A4__
avrxmega2 atxmega32a4u __AVR_ATxmega32A4U__
avrxmega2 atxmega32c3 __AVR_ATxmega32C3__
avrxmega2 atxmega32c4 __AVR_ATxmega32C4__
avrxmega2 atxmega32d3 __AVR_ATxmega32D3__
avrxmega2 atxmega32d4 __AVR_ATxmega32D4__
avrxmega2 atxmega32e5 __AVR_ATxmega32E5__
avrxmega4 atxmega64a3 __AVR_ATxmega64A3__
avrxmega4 atxmega64a3u __AVR_ATxmega64A3U__
avrxmega4 atxmega64a4u __AVR_ATxmega64A4U__
avrxmega4 atxmega64b1 __AVR_ATxmega64B1__
avrxmega4 atxmega64b3 __AVR_ATxmega64B3__
avrxmega4 atxmega64c3 __AVR_ATxmega64C3__
avrxmega4 atxmega64d3 __AVR_ATxmega64D3__
avrxmega4 atxmega64d4 __AVR_ATxmega64D4__
avrxmega5 atxmega64a1 __AVR_ATxmega64A1__
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13.1 Options for the C compiler avr-gcc 108
avrxmega5 atxmega64a1u __AVR_ATxmega64A1U__
avrxmega6 atxmega128a3 __AVR_ATxmega128A3__
avrxmega6 atxmega128a3u __AVR_ATxmega128A3U__
avrxmega6 atxmega128b1 __AVR_ATxmega128B1__
avrxmega6 atxmega128b3 __AVR_ATxmega128B3__
avrxmega6 atxmega128c3 __AVR_ATxmega128C3__
avrxmega6 atxmega128d3 __AVR_ATxmega128D3__
avrxmega6 atxmega128d4 __AVR_ATxmega128D4__
avrxmega6 atxmega192a3 __AVR_ATxmega192A3__
avrxmega6 atxmega192a3u __AVR_ATxmega192A3U__
avrxmega6 atxmega192c3 __AVR_ATxmega192C3__
avrxmega6 atxmega192d3 __AVR_ATxmega192D3__
avrxmega6 atxmega256a3 __AVR_ATxmega256A3__
avrxmega6 atxmega256a3u __AVR_ATxmega256A3U__
avrxmega6 atxmega256a3b __AVR_ATxmega256A3B__
avrxmega6 atxmega256a3bu __AVR_ATxmega256A3BU__
avrxmega6 atxmega256c3 __AVR_ATxmega256C3__
avrxmega6 atxmega256d3 __AVR_ATxmega256D3__
avrxmega6 atxmega384c3 __AVR_ATxmega384C3__
avrxmega6 atxmega384d3 __AVR_ATxmega384D3__
avrxmega7 atxmega128a1 __AVR_ATxmega128A1__
avrxmega7 atxmega128a1u __AVR_ATxmega128A1U__
avrxmega7 atxmega128a4u __AVR_ATxmega128A4U__
avrtiny10 attiny4 __AVR_ATtiny4__
avrtiny10 attiny5 __AVR_ATtiny5__
avrtiny10 attiny9 __AVR_ATtiny9__
avrtiny10 attiny10 __AVR_ATtiny10__
avrtiny10 attiny20 __AVR_ATtiny20__
avrtiny10 attiny40 __AVR_ATtiny40__
[1] ’avr25’ architecture is new in GCC 4.2
[2] ’avr35’ architecture is new in GCC 4.2.3
[3] ’avr31’ and ’avr51’ architectures is new in GCC 4.3
•-morder1
•-morder2
Change the order of register assignment. The default is
r24, r25, r18, r19, r20, r21, r22, r23, r30, r31, r26, r27, r28, r29, r17, r16, r15, r14, r13,
r12, r11, r10, r9, r8, r7, r6, r5, r4, r3, r2, r0, r1
Order 1 uses
r18, r19, r20, r21, r22, r23, r24, r25, r30, r31, r26, r27, r28, r29, r17, r16, r15, r14, r13,
r12, r11, r10, r9, r8, r7, r6, r5, r4, r3, r2, r0, r1
Order 2 uses
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13.1 Options for the C compiler avr-gcc 109
r25, r24, r23, r22, r21, r20, r19, r18, r30, r31, r26, r27, r28, r29, r17, r16, r15, r14, r13,
r12, r11, r10, r9, r8, r7, r6, r5, r4, r3, r2, r1, r0
•-mint8
Assume int to be an 8-bit integer. Note that this is not really supported by
avr-libc, so it should normally not be used. The default is to use 16-bit integers.
•-mno-interrupts
Generates code that changes the stack pointer without disabling interrupts. Normally,
the state of the status register SREG is saved in a temporary register, interrupts are
disabled while changing the stack pointer, and SREG is restored.
Specifying this option will define the preprocessor macro __NO_INTERRUPTS__ to
the value 1.
•-mcall-prologues
Use subroutines for function prologue/epilogue. For complex functions that use many
registers (that needs to be saved/restored on function entry/exit), this saves some space
at the cost of a slightly increased execution time.
•-mtiny-stack
Change only the low 8 bits of the stack pointer.
•-mno-tablejump
Deprecated, use -fno-jump-tables instead.
•-mshort-calls
Use rjmp/rcall (limited range) on >8K devices. On avr2 and avr4 architec-
tures (less than 8 KB or flash memory), this is always the case. On avr3 and avr5
architectures, calls and jumps to targets outside the current function will by default use
jmp/call instructions that can cover the entire address range, but that require more
flash ROM and execution time.
•-mrtl
Dump the internal compilation result called "RTL" into comments in the generated
assembler code. Used for debugging avr-gcc.
•-msize
Dump the address, size, and relative cost of each statement into comments in the gen-
erated assembler code. Used for debugging avr-gcc.
•-mdeb
Generate lots of debugging information to stderr.
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13.1 Options for the C compiler avr-gcc 110
13.1.2 Selected general compiler options
The following general gcc options might be of some interest to AVR users.
•-On
Optimization level n. Increasing nis meant to optimize more, an optimization level of
0 means no optimization at all, which is the default if no -O option is present. The
special option -Os is meant to turn on all -O2 optimizations that are not expected to
increase code size.
Note that at -O3, gcc attempts to inline all "simple" functions. For the AVR target,
this will normally constitute a large pessimization due to the code increasement. The
only other optimization turned on with -O3 is -frename-registers, which could
rather be enabled manually instead.
A simple -O option is equivalent to -O1.
Note also that turning off all optimizations will prevent some warnings from being
issued since the generation of those warnings depends on code analysis steps that are
only performed when optimizing (unreachable code, unused variables).
See also the appropriate FAQ entry for issues regarding debugging optimized code.
•-Wa,assembler-options
•-Wl,linker-options
Pass the listed options to the assembler, or linker, respectively.
•-g
Generate debugging information that can be used by avr-gdb.
•-ffreestanding
Assume a "freestanding" environment as per the C standard. This turns off automatic
builtin functions (though they can still be reached by prepending __builtin_ to
the actual function name). It also makes the compiler not complain when main()
is declared with a void return type which makes some sense in a microcontroller
environment where the application cannot meaningfully provide a return value to its
environment (in most cases, main() won’t even return anyway). However, this also
turns off all optimizations normally done by the compiler which assume that functions
known by a certain name behave as described by the standard. E. g., applying the
function strlen() to a literal string will normally cause the compiler to immediately
replace that call by the actual length of the string, while with -ffreestanding, it
will always call strlen() at run-time.
•-funsigned-char
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13.2 Options for the assembler avr-as 111
Make any unqualfied char type an unsigned char. Without this option, they default to
a signed char.
•-funsigned-bitfields
Make any unqualified bitfield type unsigned. By default, they are signed.
•-fshort-enums
Allocate to an enum type only as many bytes as it needs for the declared range of
possible values. Specifically, the enum type will be equivalent to the smallest integer
type which has enough room.
•-fpack-struct
Pack all structure members together without holes.
•-fno-jump-tables
Do not generate tablejump instructions. By default, jump tables can be used to op-
timize switch statements. When turned off, sequences of compare statements are
used instead. Jump tables are usually faster to execute on average, but in particular for
switch statements, where most of the jumps would go to the default label, they might
waste a bit of flash memory.
NOTE: The tablejump instructions use the LPM assembler instruction for access to
jump tables. Always use -fno-jump-tables switch, if compiling a bootloader for
devices with more than 64 KB of code memory.
13.2 Options for the assembler avr-as
13.2.1 Machine-specific assembler options
•-mmcu=architecture
•-mmcu=MCU name
avr-as understands the same -mmcu= options as avr-gcc. By default, avr2 is assumed,
but this can be altered by using the appropriate .arch pseudo-instruction inside the
assembler source file.
•-mall-opcodes
Turns off opcode checking for the actual MCU type, and allows any possible AVR
opcode to be assembled.
•-mno-skip-bug
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13.2 Options for the assembler avr-as 112
Don’t emit a warning when trying to skip a 2-word instruction with a
CPSE/SBIC/SBIS/SBRC/SBRS instruction. Early AVR devices suffered from a
hardware bug where these instructions could not be properly skipped.
•-mno-wrap
For RJMP/RCALL instructions, don’t allow the target address to wrap around for de-
vices that have more than 8 KB of memory.
•--gstabs
Generate .stabs debugging symbols for assembler source lines. This enables avr-gdb
to trace through assembler source files. This option must not be used when assembling
sources that have been generated by the C compiler; these files already contain the
appropriate line number information from the C source files.
•-a[cdhlmns=file]
Turn on the assembler listing. The sub-options are:
•comit false conditionals
•domit debugging directives
•hinclude high-level source
•linclude assembly
•minclude macro expansions
•nomit forms processing
•sinclude symbols
•=file set the name of the listing file
The various sub-options can be combined into a single -a option list; =file must be the
last one in that case.
13.2.2 Examples for assembler options passed through the C compiler
Remember that assembler options can be passed from the C compiler frontend using
-Wa (see above), so in order to include the C source code into the assembler listing in
file foo.lst, when compiling foo.c, the following compiler command-line can be
used:
$ avr-gcc -c -O foo.c -o foo.o -Wa,-ahls=foo.lst
In order to pass an assembler file through the C preprocessor first, and have the assem-
bler generate line number debugging information for it, the following command can be
used:
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13.3 Controlling the linker avr-ld 113
$ avr-gcc -c -x assembler-with-cpp -o foo.o foo.S -Wa,--gstabs
Note that on Unix systems that have case-distinguishing file systems, specifying a file
name with the suffix .S (upper-case letter S) will make the compiler automatically
assume -x assembler-with-cpp, while using .s would pass the file directly to
the assembler (no preprocessing done).
13.3 Controlling the linker avr-ld
13.3.1 Selected linker options
While there are no machine-specific options for avr-ld, a number of the standard op-
tions might be of interest to AVR users.
•-lname
Locate the archive library named libname.a, and use it to resolve currently
unresolved symbols from it. The library is searched along a path that con-
sists of builtin pathname entries that have been specified at compile time (e. g.
/usr/local/avr/lib on Unix systems), possibly extended by pathname entries
as specified by -L options (that must precede the -l options on the command-line).
•-Lpath
Additional location to look for archive libraries requested by -l options.
•--defsym symbol=expr
Define a global symbol symbol using expr as the value.
•-M
Print a linker map to stdout.
•-Map mapfile
Print a linker map to mapfile.
•--cref
Output a cross reference table to the map file (in case -Map is also present), or to
stdout.
•--section-start sectionname=org
Start section sectionname at absolute address org.
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13.3 Controlling the linker avr-ld 114
•-Tbss org
•-Tdata org
•-Ttext org
Start the bss,data, or text section at org, respectively.
•-T scriptfile
Use scriptfile as the linker script, replacing the default linker script. De-
fault linker scripts are stored in a system-specific location (e. g. under
/usr/local/avr/lib/ldscripts on Unix systems), and consist of the AVR
architecture name (avr2 through avr5) with the suffix .x appended. They describe how
the various memory sections will be linked together.
13.3.2 Passing linker options from the C compiler
By default, all unknown non-option arguments on the avr-gcc command-line (i. e.,
all filename arguments that don’t have a suffix that is handled by avr-gcc) are passed
straight to the linker. Thus, all files ending in .o (object files) and .a (object libraries)
are provided to the linker.
System libraries are usually not passed by their explicit filename but rather using the
-l option which uses an abbreviated form of the archive filename (see above). avr-
libc ships two system libraries, libc.a, and libm.a. While the standard library
libc.a will always be searched for unresolved references when the linker is started
using the C compiler frontend (i. e., there’s always at least one implied -lc option),
the mathematics library libm.a needs to be explicitly requested using -lm. See also
the entry in the FAQ explaining this.
Conventionally, Makefiles use the make macro LDLIBS to keep track of -l (and
possibly -L) options that should only be appended to the C compiler command-line
when linking the final binary. In contrast, the macro LDFLAGS is used to store other
command-line options to the C compiler that should be passed as options during the
linking stage. The difference is that options are placed early on the command-line,
while libraries are put at the end since they are to be used to resolve global symbols
that are still unresolved at this point.
Specific linker flags can be passed from the C compiler command-line using the -Wl
compiler option, see above. This option requires that there be no spaces in the appended
linker option, while some of the linker options above (like -Map or --defsym) would
require a space. In these situations, the space can be replaced by an equal sign as
well. For example, the following command-line can be used to compile foo.c into an
executable, and also produce a link map that contains a cross-reference list in the file
foo.map:
$ avr-gcc -O -o foo.out -Wl,-Map=foo.map -Wl,--cref foo.c
Alternatively, a comma as a placeholder will be replaced by a space before passing the
option to the linker. So for a device with external SRAM, the following command-line
would cause the linker to place the data segment at address 0x2000 in the SRAM:
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14 Compiler optimization 115
$ avr-gcc -mmcu=atmega128 -o foo.out -Wl,-Tdata,0x802000
See the explanation of the data section for why 0x800000 needs to be added to the
actual value. Note that the stack will still remain in internal RAM, through the symbol
__stack that is provided by the run-time startup code. This is probably a good idea
anyway (since internal RAM access is faster), and even required for some early devices
that had hardware bugs preventing them from using a stack in external RAM. Note
also that the heap for malloc() will still be placed after all the variables in the data
section, so in this situation, no stack/heap collision can occur.
In order to relocate the stack from its default location at the top of interns RAM, the
value of the symbol __stack can be changed on the linker command-line. As the
linker is typically called from the compiler frontend, this can be achieved using a com-
piler option like
-Wl,--defsym=__stack=0x8003ff
The above will make the code use stack space from RAM address 0x3ff downwards.
The amount of stack space available then depends on the bottom address of internal
RAM for a particular device. It is the responsibility of the application to ensure the
stack does not grow out of bounds, as well as to arrange for the stack to not collide
with variable allocations made by the compiler (sections .data and .bss).
14 Compiler optimization
14.1 Problems with reordering code
Author
Jan Waclawek
Programs contain sequences of statements, and a naive compiler would execute them
exactly in the order as they are written. But an optimizing compiler is free to re-
order the statements - or even parts of them - if the resulting "net effect" is the same.
The "measure" of the "net effect" is what the standard calls "side effects", and is ac-
complished exclusively through accesses (reads and writes) to variables qualified as
volatile. So, as long as all volatile reads and writes are to the same addresses and
in the same order (and writes write the same values), the program is correct, regard-
less of other operations in it. (One important point to note here is, that time duration
between consecutive volatile accesses is not considered at all.)
Unfortunately, there are also operations which are not covered by volatile accesses.
An example of this in avr-gcc/avr-libc are the cli() and sei() macros defined in
<avr/interrupt.h>, which convert directly to the respective assembler mnemonics
through the __asm__() statement. These don’t constitute a variable access at all,
not even volatile, so the compiler is free to move them around. Although there is
a "volatile" qualifier which can be attached to the __asm__() statement, its effect on
(re)ordering is not clear from the documentation (and is more likely only to prevent
complete removal by the optimiser), as it (among other) states:
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14.1 Problems with reordering code 116
Note that even a volatile asm instruction can be moved relative to other code, including
across jump instructions. [...] Similarly, you can’t expect a sequence of volatile asm
instructions to remain perfectly consecutive.
See also
http://gcc.gnu.org/onlinedocs/gcc-4.3.4/gcc/Extended-Asm.html
There is another mechanism which can be used to achieve something similar: memory
barriers. This is accomplished through adding a special "memory" clobber to the inline
asm statement, and ensures that all variables are flushed from registers to memory
before the statement, and then re-read after the statement. The purpose of memory
barriers is slightly different than to enforce code ordering: it is supposed to ensure that
there are no variables "cached" in registers, so that it is safe to change the content of
registers e.g. when switching context in a multitasking OS (on "big" processors with
out-of-order execution they also imply usage of special instructions which force the
processor into "in-order" state (this is not the case of AVRs)).
However, memory barrier works well in ensuring that all volatile accesses before and
after the barrier occur in the given order with respect to the barrier. However, it does
not ensure the compiler moving non-volatile-related statements across the barrier. Peter
Dannegger provided a nice example of this effect:
#define cli() __asm volatile( "cli" ::: "memory" )
#define sei() __asm volatile( "sei" ::: "memory" )
unsigned int ivar;
void test2( unsigned int val )
{
val = 65535U / val;
cli();
ivar = val;
sei();
}
compiles with optimisations switched on (-Os) to
00000112 <test2>:
112: bc 01 movw r22, r24
114: f8 94 cli
116: 8f ef ldi r24, 0xFF ; 255
118: 9f ef ldi r25, 0xFF ; 255
11a: 0e 94 96 00 call 0x12c ; 0x12c <__udivmodhi4>
11e: 70 93 01 02 sts 0x0201, r23
122: 60 93 00 02 sts 0x0200, r22
126: 78 94 sei
128: 08 95 ret
where the potentially slow division is moved across cli(), resulting in interrupts to be
disabled longer than intended. Note, that the volatile access occurs in order with respect
to cli() or sei(); so the "net effect" required by the standard is achieved as intended, it
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15 Using the avrdude program 117
is "only" the timing which is off. However, for most of embedded applications, timing
is an important, sometimes critical factor.
See also
https://www.mikrocontroller.net/topic/65923
Unfortunately, at the moment, in avr-gcc (nor in the C standard), there is no mecha-
nism to enforce complete match of written and executed code ordering - except maybe
of switching the optimization completely off (-O0), or writing all the critical code in
assembly.
To sum it up:
• memory barriers ensure proper ordering of volatile accesses
• memory barriers don’t ensure statements with no volatile accesses to be re-
ordered across the barrier
15 Using the avrdude program
Note
This section was contributed by Brian Dean [ bsd@bsdhome.com ].
The avrdude program was previously called avrprog. The name was changed to
avoid confusion with the avrprog program that Atmel ships with AvrStudio.
avrdude is a program that is used to update or read the flash and EEPROM memories
of Atmel AVR microcontrollers on FreeBSD Unix. It supports the Atmel serial pro-
gramming protocol using the PC’s parallel port and can upload either a raw binary file
or an Intel Hex format file. It can also be used in an interactive mode to individually
update EEPROM cells, fuse bits, and/or lock bits (if their access is supported by the
Atmel serial programming protocol.) The main flash instruction memory of the AVR
can also be programmed in interactive mode, however this is not very useful because
one can only turn bits off. The only way to turn flash bits on is to erase the entire
memory (using avrdude’s -e option).
avrdude is part of the FreeBSD ports system. To install it, simply do the following:
# cd /usr/ports/devel/avrdude
# make install
Once installed, avrdude can program processors using the contents of the .hex file
specified on the command line. In this example, the file main.hex is burned into the
flash memory:
# avrdude -p 2313 -e -m flash -i main.hex
avrdude: AVR device initialized and ready to accept instructions
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15 Using the avrdude program 118
avrdude: Device signature = 0x1e9101
avrdude: erasing chip
avrdude: done.
avrdude: reading input file "main.hex"
avrdude: input file main.hex auto detected as Intel Hex
avrdude: writing flash:
1749 0x00
avrdude: 1750 bytes of flash written
avrdude: verifying flash memory against main.hex:
avrdude: reading on-chip flash data:
1749 0x00
avrdude: verifying ...
avrdude: 1750 bytes of flash verified
avrdude done. Thank you.
The -p 2313 option lets avrdude know that we are operating on an AT90S2313
chip. This option specifies the device id and is matched up with the device of the same
id in avrdude’s configuration file ( /usr/local/etc/avrdude.conf ). To list
valid parts, specify the -v option. The -e option instructs avrdude to perform a
chip-erase before programming; this is almost always necessary before programming
the flash. The -m flash option indicates that we want to upload data into the flash
memory, while -i main.hex specifies the name of the input file.
The EEPROM is uploaded in the same way, the only difference is that you would use
-m eeprom instead of -m flash.
To use interactive mode, use the -t option:
# avrdude -p 2313 -t
avrdude: AVR device initialized and ready to accept instructions
avrdude: Device signature = 0x1e9101
avrdude>
The ’?’ command displays a list of valid
commands:
avrdude> ?
>>> ?
Valid commands:
dump : dump memory : dump <memtype> <addr> <N-Bytes>
read : alias for dump
write : write memory : write <memtype> <addr> <b1> <b2> ... <bN>
erase : perform a chip erase
sig : display device signature bytes
part : display the current part information
send : send a raw command : send <b1> <b2> <b3> <b4>
help : help
? : help
quit : quit
Use the ’part’ command to display valid memory types for use with the
’dump’ and ’write’ commands.
avrdude>
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16 Release Numbering and Methodology 119
16 Release Numbering and Methodology
16.1 Release Version Numbering Scheme
Release numbers consist of three parts, a major number, a minor number, and a revision
number, each separated by a dot.
The major number is currently 2, to indicate the multilib layout has been adapted to
the fairly different one used starting with AVR-GCC version 5. Nevertheless, it is still
believed to be generally API-compatible with release versions 1.x.
In the past (up to 1.6.x), even minor numbers have been used to indicate "stable" re-
leases, and odd minor numbers have been reserved for development branches/versions.
As the latter has never really been used, and maintaining a stable branch that eventually
became effectively the same as the development version has proven to be just a cum-
bersome and tedious job, this scheme has given up in early 2010, so starting with 1.7.0,
every minor number will be used. Minor numbers will be bumped upon judgement of
the development team, whenever it seems appropriate, but at least in cases where some
API was changed.
Starting with version 1.4.0, a file <avr/version.h>indicates the library version of an
installed library tree.
16.2 Releasing AVR Libc
The information in this section is only relevant to AVR Libc developers and can be
ignored by end users.
Note
In what follows, I assume you know how to use SVN and how to checkout multiple
source trees in a single directory without having them clobber each other. If you
don’t know how to do this, you probably shouldn’t be making releases or cutting
branches.
16.2.1 Creating an SVN branch
The following steps should be taken to cut a branch in SVN (assuming $username is
set to your savannah username):
1. Check out a fresh source tree from SVN trunk.
2. Update the NEWS file with pending release number and commit to SVN trunk:
Change Changes since avr-libc-<last_release>:to Changes in avr-libc-<this_-
relelase>.
3. Set the branch-point tag (setting <major>and <minor>accordingly):
svn copy svn+ssh://$username@svn.savannah.nongnu.org/avr-libc/trunk
svn+ssh://$username@svn.savannah.nongnu.org/avr-libc/tags/avr-libc-<major>_-
<minor>-branchpoint
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16.2 Releasing AVR Libc 120
4. Create the branch:
svn copy svn+ssh://$username@svn.savannah.nongnu.org/avr-libc/trunk
svn+ssh://$username@svn.savannah.nongnu.org/avr-libc/branches/avr-libc-<major>_-
<minor>-branch
5. Update the package version in configure.ac and commit configure.ac to SVN
trunk:
Change minor number to next odd value.
6. Update the NEWS file and commit to SVN trunk:
Add Changes since avr-libc-<this_release>:
7. Check out a new tree for the branch:
svn co svn+ssh://$username@svn.savannah.nongnu.org/avr-libc/branches/avr-libc-<major>_-
<minor>-branch
8. Update the package version in configure.ac and commit configure.ac to SVN
branch:
Change the patch number to 90 to denote that this now a branch leading up to a
release. Be sure to leave the <date>part of the version.
9. Bring the build system up to date by running bootstrap and configure.
10. Perform a ’make distcheck’ and make sure it succeeds. This will create the
snapshot source tarball. This should be considered the first release candidate.
11. Upload the snapshot tarball to savannah.
12. Update the bug tracker interface on Savannah: Bugs —>Edit field values —>
Release / Fixed Release
13. Announce the branch and the branch tag to the avr-libc-dev list so other devel-
opers can checkout the branch.
16.2.2 Making a release
A stable release will only be done on a branch, not from the SVN trunk.
The following steps should be taken when making a release:
1. Make sure the source tree you are working from is on the correct branch:
svn switch svn+ssh://$username@svn.savannah.nongnu.org/avr-libc/branches/avr-libc-<major>_-
<minor>-branch
2. Update the package version in configure.ac and commit it to SVN.
3. Update the gnu tool chain version requirements in the README and commit to
SVN.
4. Update the ChangeLog file to note the release and commit to SVN on the branch:
Add Released avr-libc-<this_release>.
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16.2 Releasing AVR Libc 121
5. Update the NEWS file with pending release number and commit to SVN:
Change Changes since avr-libc-<last_release>:to Changes in avr-libc-<this_-
relelase>:.
6. Bring the build system up to date by running bootstrap and configure.
7. Perform a ’make distcheck’ and make sure it succeeds. This will create the
source tarball.
8. Tag the release:
svn copy . svn+ssh://$username@svn.savannah.nongnu.org/avr-libc/tags/avr-libc-<major>_-
<minor>_<patch>-release
or
svn copy svn+ssh://$username@svn.savannah.nongnu.org/avr-libc/branches/avr-libc-<major>_-
<minor>-branch svn+ssh://$username@svn.savannah.nongnu.org/avr-libc/tags/avr-libc-<major>_-
<minor>_<patch>-release
9. Upload the tarball to savannah.
10. Update the NEWS file, and commit to SVN:
Add Changes since avr-libc-<major>_<minor>_<patch>:
11. Update the bug tracker interface on Savannah: Bugs —>Edit field values —>
Release / Fixed Release
12. Generate the latest documentation and upload to savannah.
13. Announce the release.
The following hypothetical diagram should help clarify version and branch relation-
ships.
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17 Acknowledgments 122
cvs tag −b avr−libc−1_0−branch
cvs tag avr−libc−1_0−branchpoint
set version to 1.1.0.<date>
set version to 0.90.90.<date>
set version to 1.0
cvs tag avr−libc−1_0−release
1.2 Branch1.0 BranchHEAD
set version to 1.0.0.<date>
cvs tag avr−libc−1_2−branchpoint
cvs tag avr−libc−2.0−branchpoint
cvs tag −b avr−libc−1_2−branch
set version to 1.3.0.<date>
set version to 2.1.0.<date>
set version to 1.1.90.<date>
set version to 1.0.1
set version to 1.2
cvs tag avr−libc−1_2−release
cvs tag avr−libc−1_0_1−release
Figure 4: Release tree
17 Acknowledgments
This document tries to tie together the labors of a large group of people. Without
these individuals’ efforts, we wouldn’t have a terrific, free set of tools to develop AVR
projects. We all owe thanks to:
• The GCC Team, which produced a very capable set of development tools for an
amazing number of platforms and processors.
• Denis Chertykov [ denisc@overta.ru ] for making the AVR-specific
changes to the GNU tools.
• Denis Chertykov and Marek Michalkiewicz [ marekm@linux.org.pl ] for
developing the standard libraries and startup code for AVR-GCC.
• Uros Platise for developing the AVR programmer tool, uisp.
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18 Todo List 123
• Joerg Wunsch [ joerg@FreeBSD.ORG ] for adding all the AVR development
tools to the FreeBSD [ http://www.freebsd.org ] ports tree and for pro-
viding the basics for the demo project.
• Brian Dean [ bsd@bsdhome.com ] for developing avrdude (an alternative to
uisp) and for contributing documentation which describes how to use it. Avr-
dude was previously called avrprog.
• Eric Weddington [ eweddington@cso.atmel.com ] for maintaining the
WinAVR package and thus making the continued improvements to the open
source AVR toolchain available to many users.
• Rich Neswold for writing the original avr-tools document (which he graciously
allowed to be merged into this document) and his improvements to the demo
project.
• Theodore A. Roth for having been a long-time maintainer of many of the tools
(AVR-Libc, the AVR port of GDB,AVaRICE,uisp,avrdude).
• All the people who currently maintain the tools, and/or have submitted sugges-
tions, patches and bug reports. (See the AUTHORS files of the various tools.)
• And lastly, all the users who use the software. If nobody used the software, we
would probably not be very motivated to continue to develop it. Keep those bug
reports coming. ;-)
18 Todo List
Group avr_boot From email with Marek: On smaller devices (all except AT-
mega64/128), __SPM_REG is in the I/O space, accessible with the shorter "in"
and "out" instructions - since the boot loader has a limited size, this could be an
important optimization.
19 Deprecated List
Global cbi(port, bit)
Global enable_external_int(mask)
Global inb(port)
Global inp(port)
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20 Module Index 124
Global INTERRUPT(signame)
Global ISR_ALIAS(vector, target_vector) For new code, the use of ISR(..., ISR_-
ALIASOF(...)) is recommended.
Global outb(port, val)
Global outp(val, port)
Global sbi(port, bit)
Global SIGNAL(vector) Do not use SIGNAL() in new code. Use ISR() instead.
Global timer_enable_int(unsigned char ints)
20 Module Index
20.1 Modules
Here is a list of all modules:
<alloca.h>: Allocate space in the stack 128
<assert.h>: Diagnostics 129
<ctype.h>: Character Operations 130
<errno.h>: System Errors 132
<inttypes.h>: Integer Type conversions 133
<math.h>: Mathematics 147
<setjmp.h>: Non-local goto 160
<stdint.h>: Standard Integer Types 162
<stdio.h>: Standard IO facilities 174
<stdlib.h>: General utilities 192
<string.h>: Strings 203
<time.h>: Time 216
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20.1 Modules 125
<avr/boot.h>: Bootloader Support Utilities 225
<avr/cpufunc.h>: Special AVR CPU functions 231
<avr/eeprom.h>: EEPROM handling 232
<avr/fuse.h>: Fuse Support 237
<avr/interrupt.h>: Interrupts 240
<avr/io.h>: AVR device-specific IO definitions 260
<avr/lock.h>: Lockbit Support 261
<avr/pgmspace.h>: Program Space Utilities 264
<avr/power.h>: Power Reduction Management 288
<avr/sfr_defs.h>: Special function registers 293
Additional notes from <avr/sfr_defs.h>292
<avr/signature.h>: Signature Support 295
<avr/sleep.h>: Power Management and Sleep Modes 296
<avr/version.h>: avr-libc version macros 298
<avr/wdt.h>: Watchdog timer handling 299
<util/atomic.h>Atomically and Non-Atomically Executed Code Blocks 303
<util/crc16.h>: CRC Computations 306
<util/delay.h>: Convenience functions for busy-wait delay loops 310
<util/delay_basic.h>: Basic busy-wait delay loops 313
<util/parity.h>: Parity bit generation 314
<util/setbaud.h>: Helper macros for baud rate calculations 314
<util/twi.h>: TWI bit mask definitions 317
<compat/deprecated.h>: Deprecated items 321
<compat/ina90.h>: Compatibility with IAR EWB 3.x 324
Demo projects 325
Combining C and assembly source files 326
A simple project 329
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21 Data Structure Index 126
A more sophisticated project 343
Using the standard IO facilities 350
Example using the two-wire interface (TWI) 357
21 Data Structure Index
21.1 Data Structures
Here are the data structures with brief descriptions:
div_t 362
ldiv_t 363
tm 363
week_date 365
22 File Index
22.1 File List
Here is a list of all documented files with brief descriptions:
alloca.h ??
assert.h 365
atoi.S 366
atol.S 366
atomic.h 366
boot.h 366
cpufunc.h 367
crc16.h 367
ctype.h 367
defines.h ??
delay.h 368
delay_basic.h 368
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22.1 File List 127
deprecated.h ??
dtoa_conv.h ??
eedef.h ??
eeprom.h ??
ephemera_common.h ??
errno.h 368
eu_dst.h ??
fdevopen.c 369
fuse.h 369
hd44780.h ??
ina90.h ??
interrupt.h 369
inttypes.h 370
io.h 372
iocompat.h ??
lcd.h ??
lock.h 372
math.h 372
parity.h 375
pgmspace.h 375
portpins.h ??
power.h 377
project.h ??
setbaud.h 378
setjmp.h 378
sfr_defs.h ??
signal.h ??
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23 Module Documentation 128
signature.h 378
sleep.h 378
stdint.h 378
stdio.h 381
stdio_private.h ??
stdlib.h 383
stdlib_private.h ??
string.h 384
time.h 385
util/twi.h 387
compat/twi.h ??
uart.h ??
usa_dst.h ??
version.h ??
wdt.h 388
xmega.h ??
xtoa_fast.h ??
23 Module Documentation
23.1 <alloca.h>: Allocate space in the stack
Functions
• void ∗alloca (size_t __size)
23.1.1 Detailed Description
23.1.2 Function Documentation
23.1.2.1 void∗alloca (size_t __size)
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23.2 <assert.h>: Diagnostics 129
Allocate __size bytes of space in the stack frame of the caller.
This temporary space is automatically freed when the function that called alloca() re-
turns to its caller. Avr-libc defines the alloca() as a macro, which is translated into the
inlined __builtin_alloca() function. The fact that the code is inlined, means
that it is impossible to take the address of this function, or to change its behaviour by
linking with a different library.
Returns
alloca() returns a pointer to the beginning of the allocated space. If the allocation
causes stack overflow, program behaviour is undefined.
Warning
Avoid use alloca() inside the list of arguments of a function call.
23.2 <assert.h>: Diagnostics
Defines
• #define assert(expression)
23.2.1 Detailed Description
#include <assert.h>
This header file defines a debugging aid.
As there is no standard error output stream available for many applications using this
library, the generation of a printable error message is not enabled by default. These
messages will only be generated if the application defines the macro
__ASSERT_USE_STDERR
before including the <assert.h>header file. By default, only abort() will be called
to halt the application.
23.2.2 Define Documentation
23.2.2.1 #define assert(expression)
Parameters
expression Expression to test for.
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23.3 <ctype.h>: Character Operations 130
The assert() macro tests the given expression and if it is false, the calling process is
terminated. A diagnostic message is written to stderr and the function abort() is called,
effectively terminating the program.
If expression is true, the assert() macro does nothing.
The assert() macro may be removed at compile time by defining NDEBUG as a macro
(e.g., by using the compiler option -DNDEBUG).
23.3 <ctype.h>: Character Operations
Character classification routines
These functions perform character classification. They return true or false status de-
pending whether the character passed to the function falls into the function’s classifi-
cation (i.e. isdigit() returns true if its argument is any value ’0’ though ’9’, inclusive).
If the input is not an unsigned char value, all of this function return false.
• int isalnum (int __c)
• int isalpha (int __c)
• int isascii (int __c)
• int isblank (int __c)
• int iscntrl (int __c)
• int isdigit (int __c)
• int isgraph (int __c)
• int islower (int __c)
• int isprint (int __c)
• int ispunct (int __c)
• int isspace (int __c)
• int isupper (int __c)
• int isxdigit (int __c)
Character convertion routines
This realization permits all possible values of integer argument. The toascii() function
clears all highest bits. The tolower() and toupper() functions return an input argument
as is, if it is not an unsigned char value.
• int toascii (int __c)
• int tolower (int __c)
• int toupper (int __c)
23.3.1 Detailed Description
These functions perform various operations on characters.
#include <ctype.h>
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23.3 <ctype.h>: Character Operations 131
23.3.2 Function Documentation
23.3.2.1 int isalnum (int __c)
Checks for an alphanumeric character. It is equivalent to (isalpha(c) ||
isdigit(c)).
23.3.2.2 int isalpha (int __c)
Checks for an alphabetic character. It is equivalent to (isupper(c) ||
islower(c)).
23.3.2.3 int isascii (int __c)
Checks whether cis a 7-bit unsigned char value that fits into the ASCII character set.
23.3.2.4 int isblank (int __c)
Checks for a blank character, that is, a space or a tab.
23.3.2.5 int iscntrl (int __c)
Checks for a control character.
23.3.2.6 int isdigit (int __c)
Checks for a digit (0 through 9).
23.3.2.7 int isgraph (int __c)
Checks for any printable character except space.
23.3.2.8 int islower (int __c)
Checks for a lower-case character.
23.3.2.9 int isprint (int __c)
Checks for any printable character including space.
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23.4 <errno.h>: System Errors 132
23.3.2.10 int ispunct (int __c)
Checks for any printable character which is not a space or an alphanumeric character.
23.3.2.11 int isspace (int __c)
Checks for white-space characters. For the avr-libc library, these are:
space, form-feed (’\f’), newline (’\n’), carriage return (’\r’), horizontal tab (’\t’), and
vertical tab (’\v’).
23.3.2.12 int isupper (int __c)
Checks for an uppercase letter.
23.3.2.13 int isxdigit (int __c)
Checks for a hexadecimal digits, i.e. one of 0 1 2 3 4 5 6 7 8 9 a b c d e f A B C D E
F.
23.3.2.14 int toascii (int __c)
Converts cto a 7-bit unsigned char value that fits into the ASCII character set, by
clearing the high-order bits.
Warning
Many people will be unhappy if you use this function. This function will convert
accented letters into random characters.
23.3.2.15 int tolower (int __c)
Converts the letter cto lower case, if possible.
23.3.2.16 int toupper (int __c)
Converts the letter cto upper case, if possible.
23.4 <errno.h>: System Errors
Defines
• #define EDOM 33
• #define ERANGE 34
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23.5 <inttypes.h>: Integer Type conversions 133
Variables
• int errno
23.4.1 Detailed Description
#include <errno.h>
Some functions in the library set the global variable errno when an error occurs. The
file, <errno.h>, provides symbolic names for various error codes.
23.4.2 Define Documentation
23.4.2.1 #define EDOM 33
Domain error.
23.4.2.2 #define ERANGE 34
Range error.
23.4.3 Variable Documentation
23.4.3.1 int errno
Error code for last error encountered by library.
The variable errno holds the last error code encountered by a library function. This
variable must be cleared by the user prior to calling a library function.
Warning
The errno global variable is not safe to use in a threaded or multi-task system. A
race condition can occur if a task is interrupted between the call which sets error
and when the task examines errno. If another task changes errno during this
time, the result will be incorrect for the interrupted task.
23.5 <inttypes.h>: Integer Type conversions
Far pointers for memory access >64K
• typedef int32_t int_farptr_t
• typedef uint32_t uint_farptr_t
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23.5 <inttypes.h>: Integer Type conversions 134
macros for printf and scanf format specifiers
For C++, these are only included if __STDC_LIMIT_MACROS is defined before in-
cluding <inttypes.h>.
• #define PRId8 "d"
• #define PRIdLEAST8 "d"
• #define PRIdFAST8 "d"
• #define PRIi8 "i"
• #define PRIiLEAST8 "i"
• #define PRIiFAST8 "i"
• #define PRId16 "d"
• #define PRIdLEAST16 "d"
• #define PRIdFAST16 "d"
• #define PRIi16 "i"
• #define PRIiLEAST16 "i"
• #define PRIiFAST16 "i"
• #define PRId32 "ld"
• #define PRIdLEAST32 "ld"
• #define PRIdFAST32 "ld"
• #define PRIi32 "li"
• #define PRIiLEAST32 "li"
• #define PRIiFAST32 "li"
• #define PRIdPTR PRId16
• #define PRIiPTR PRIi16
• #define PRIo8 "o"
• #define PRIoLEAST8 "o"
• #define PRIoFAST8 "o"
• #define PRIu8 "u"
• #define PRIuLEAST8 "u"
• #define PRIuFAST8 "u"
• #define PRIx8 "x"
• #define PRIxLEAST8 "x"
• #define PRIxFAST8 "x"
• #define PRIX8 "X"
• #define PRIXLEAST8 "X"
• #define PRIXFAST8 "X"
• #define PRIo16 "o"
• #define PRIoLEAST16 "o"
• #define PRIoFAST16 "o"
• #define PRIu16 "u"
• #define PRIuLEAST16 "u"
• #define PRIuFAST16 "u"
• #define PRIx16 "x"
• #define PRIxLEAST16 "x"
• #define PRIxFAST16 "x"
• #define PRIX16 "X"
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23.5 <inttypes.h>: Integer Type conversions 135
• #define PRIXLEAST16 "X"
• #define PRIXFAST16 "X"
• #define PRIo32 "lo"
• #define PRIoLEAST32 "lo"
• #define PRIoFAST32 "lo"
• #define PRIu32 "lu"
• #define PRIuLEAST32 "lu"
• #define PRIuFAST32 "lu"
• #define PRIx32 "lx"
• #define PRIxLEAST32 "lx"
• #define PRIxFAST32 "lx"
• #define PRIX32 "lX"
• #define PRIXLEAST32 "lX"
• #define PRIXFAST32 "lX"
• #define PRIoPTR PRIo16
• #define PRIuPTR PRIu16
• #define PRIxPTR PRIx16
• #define PRIXPTR PRIX16
• #define SCNd8 "hhd"
• #define SCNdLEAST8 "hhd"
• #define SCNdFAST8 "hhd"
• #define SCNi8 "hhi"
• #define SCNiLEAST8 "hhi"
• #define SCNiFAST8 "hhi"
• #define SCNd16 "d"
• #define SCNdLEAST16 "d"
• #define SCNdFAST16 "d"
• #define SCNi16 "i"
• #define SCNiLEAST16 "i"
• #define SCNiFAST16 "i"
• #define SCNd32 "ld"
• #define SCNdLEAST32 "ld"
• #define SCNdFAST32 "ld"
• #define SCNi32 "li"
• #define SCNiLEAST32 "li"
• #define SCNiFAST32 "li"
• #define SCNdPTR SCNd16
• #define SCNiPTR SCNi16
• #define SCNo8 "hho"
• #define SCNoLEAST8 "hho"
• #define SCNoFAST8 "hho"
• #define SCNu8 "hhu"
• #define SCNuLEAST8 "hhu"
• #define SCNuFAST8 "hhu"
• #define SCNx8 "hhx"
• #define SCNxLEAST8 "hhx"
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23.5 <inttypes.h>: Integer Type conversions 136
• #define SCNxFAST8 "hhx"
• #define SCNo16 "o"
• #define SCNoLEAST16 "o"
• #define SCNoFAST16 "o"
• #define SCNu16 "u"
• #define SCNuLEAST16 "u"
• #define SCNuFAST16 "u"
• #define SCNx16 "x"
• #define SCNxLEAST16 "x"
• #define SCNxFAST16 "x"
• #define SCNo32 "lo"
• #define SCNoLEAST32 "lo"
• #define SCNoFAST32 "lo"
• #define SCNu32 "lu"
• #define SCNuLEAST32 "lu"
• #define SCNuFAST32 "lu"
• #define SCNx32 "lx"
• #define SCNxLEAST32 "lx"
• #define SCNxFAST32 "lx"
• #define SCNoPTR SCNo16
• #define SCNuPTR SCNu16
• #define SCNxPTR SCNx16
23.5.1 Detailed Description
#include <inttypes.h>
This header file includes the exact-width integer definitions from <stdint.h>, and
extends them with additional facilities provided by the implementation.
Currently, the extensions include two additional integer types that could hold a "far"
pointer (i.e. a code pointer that can address more than 64 KB), as well as standard
names for all printf and scanf formatting options that are supported by the <stdio.h>:
Standard IO facilities. As the library does not support the full range of conversion
specifiers from ISO 9899:1999, only those conversions that are actually implemented
will be listed here.
The idea behind these conversion macros is that, for each of the types defined by
<stdint.h>, a macro will be supplied that portably allows formatting an object of that
type in printf() or scanf() operations. Example:
#include <inttypes.h>
uint8_t smallval;
int32_t longval;
...
printf("The hexadecimal value of smallval is %" PRIx8
", the decimal value of longval is %" PRId32 ".\n",
smallval, longval);
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23.5 <inttypes.h>: Integer Type conversions 137
23.5.2 Define Documentation
23.5.2.1 #define PRId16 "d"
decimal printf format for int16_t
23.5.2.2 #define PRId32 "ld"
decimal printf format for int32_t
23.5.2.3 #define PRId8 "d"
decimal printf format for int8_t
23.5.2.4 #define PRIdFAST16 "d"
decimal printf format for int_fast16_t
23.5.2.5 #define PRIdFAST32 "ld"
decimal printf format for int_fast32_t
23.5.2.6 #define PRIdFAST8 "d"
decimal printf format for int_fast8_t
23.5.2.7 #define PRIdLEAST16 "d"
decimal printf format for int_least16_t
23.5.2.8 #define PRIdLEAST32 "ld"
decimal printf format for int_least32_t
23.5.2.9 #define PRIdLEAST8 "d"
decimal printf format for int_least8_t
23.5.2.10 #define PRIdPTR PRId16
decimal printf format for intptr_t
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23.5 <inttypes.h>: Integer Type conversions 138
23.5.2.11 #define PRIi16 "i"
integer printf format for int16_t
23.5.2.12 #define PRIi32 "li"
integer printf format for int32_t
23.5.2.13 #define PRIi8 "i"
integer printf format for int8_t
23.5.2.14 #define PRIiFAST16 "i"
integer printf format for int_fast16_t
23.5.2.15 #define PRIiFAST32 "li"
integer printf format for int_fast32_t
23.5.2.16 #define PRIiFAST8 "i"
integer printf format for int_fast8_t
23.5.2.17 #define PRIiLEAST16 "i"
integer printf format for int_least16_t
23.5.2.18 #define PRIiLEAST32 "li"
integer printf format for int_least32_t
23.5.2.19 #define PRIiLEAST8 "i"
integer printf format for int_least8_t
23.5.2.20 #define PRIiPTR PRIi16
integer printf format for intptr_t
23.5.2.21 #define PRIo16 "o"
octal printf format for uint16_t
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23.5 <inttypes.h>: Integer Type conversions 139
23.5.2.22 #define PRIo32 "lo"
octal printf format for uint32_t
23.5.2.23 #define PRIo8 "o"
octal printf format for uint8_t
23.5.2.24 #define PRIoFAST16 "o"
octal printf format for uint_fast16_t
23.5.2.25 #define PRIoFAST32 "lo"
octal printf format for uint_fast32_t
23.5.2.26 #define PRIoFAST8 "o"
octal printf format for uint_fast8_t
23.5.2.27 #define PRIoLEAST16 "o"
octal printf format for uint_least16_t
23.5.2.28 #define PRIoLEAST32 "lo"
octal printf format for uint_least32_t
23.5.2.29 #define PRIoLEAST8 "o"
octal printf format for uint_least8_t
23.5.2.30 #define PRIoPTR PRIo16
octal printf format for uintptr_t
23.5.2.31 #define PRIu16 "u"
decimal printf format for uint16_t
23.5.2.32 #define PRIu32 "lu"
decimal printf format for uint32_t
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23.5 <inttypes.h>: Integer Type conversions 140
23.5.2.33 #define PRIu8 "u"
decimal printf format for uint8_t
23.5.2.34 #define PRIuFAST16 "u"
decimal printf format for uint_fast16_t
23.5.2.35 #define PRIuFAST32 "lu"
decimal printf format for uint_fast32_t
23.5.2.36 #define PRIuFAST8 "u"
decimal printf format for uint_fast8_t
23.5.2.37 #define PRIuLEAST16 "u"
decimal printf format for uint_least16_t
23.5.2.38 #define PRIuLEAST32 "lu"
decimal printf format for uint_least32_t
23.5.2.39 #define PRIuLEAST8 "u"
decimal printf format for uint_least8_t
23.5.2.40 #define PRIuPTR PRIu16
decimal printf format for uintptr_t
23.5.2.41 #define PRIX16 "X"
uppercase hexadecimal printf format for uint16_t
23.5.2.42 #define PRIx16 "x"
hexadecimal printf format for uint16_t
23.5.2.43 #define PRIX32 "lX"
uppercase hexadecimal printf format for uint32_t
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23.5 <inttypes.h>: Integer Type conversions 141
23.5.2.44 #define PRIx32 "lx"
hexadecimal printf format for uint32_t
23.5.2.45 #define PRIX8 "X"
uppercase hexadecimal printf format for uint8_t
23.5.2.46 #define PRIx8 "x"
hexadecimal printf format for uint8_t
23.5.2.47 #define PRIXFAST16 "X"
uppercase hexadecimal printf format for uint_fast16_t
23.5.2.48 #define PRIxFAST16 "x"
hexadecimal printf format for uint_fast16_t
23.5.2.49 #define PRIXFAST32 "lX"
uppercase hexadecimal printf format for uint_fast32_t
23.5.2.50 #define PRIxFAST32 "lx"
hexadecimal printf format for uint_fast32_t
23.5.2.51 #define PRIXFAST8 "X"
uppercase hexadecimal printf format for uint_fast8_t
23.5.2.52 #define PRIxFAST8 "x"
hexadecimal printf format for uint_fast8_t
23.5.2.53 #define PRIXLEAST16 "X"
uppercase hexadecimal printf format for uint_least16_t
23.5.2.54 #define PRIxLEAST16 "x"
hexadecimal printf format for uint_least16_t
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23.5 <inttypes.h>: Integer Type conversions 142
23.5.2.55 #define PRIXLEAST32 "lX"
uppercase hexadecimal printf format for uint_least32_t
23.5.2.56 #define PRIxLEAST32 "lx"
hexadecimal printf format for uint_least32_t
23.5.2.57 #define PRIXLEAST8 "X"
uppercase hexadecimal printf format for uint_least8_t
23.5.2.58 #define PRIxLEAST8 "x"
hexadecimal printf format for uint_least8_t
23.5.2.59 #define PRIXPTR PRIX16
uppercase hexadecimal printf format for uintptr_t
23.5.2.60 #define PRIxPTR PRIx16
hexadecimal printf format for uintptr_t
23.5.2.61 #define SCNd16 "d"
decimal scanf format for int16_t
23.5.2.62 #define SCNd32 "ld"
decimal scanf format for int32_t
23.5.2.63 #define SCNd8 "hhd"
decimal scanf format for int8_t
23.5.2.64 #define SCNdFAST16 "d"
decimal scanf format for int_fast16_t
23.5.2.65 #define SCNdFAST32 "ld"
decimal scanf format for int_fast32_t
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23.5 <inttypes.h>: Integer Type conversions 143
23.5.2.66 #define SCNdFAST8 "hhd"
decimal scanf format for int_fast8_t
23.5.2.67 #define SCNdLEAST16 "d"
decimal scanf format for int_least16_t
23.5.2.68 #define SCNdLEAST32 "ld"
decimal scanf format for int_least32_t
23.5.2.69 #define SCNdLEAST8 "hhd"
decimal scanf format for int_least8_t
23.5.2.70 #define SCNdPTR SCNd16
decimal scanf format for intptr_t
23.5.2.71 #define SCNi16 "i"
generic-integer scanf format for int16_t
23.5.2.72 #define SCNi32 "li"
generic-integer scanf format for int32_t
23.5.2.73 #define SCNi8 "hhi"
generic-integer scanf format for int8_t
23.5.2.74 #define SCNiFAST16 "i"
generic-integer scanf format for int_fast16_t
23.5.2.75 #define SCNiFAST32 "li"
generic-integer scanf format for int_fast32_t
23.5.2.76 #define SCNiFAST8 "hhi"
generic-integer scanf format for int_fast8_t
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23.5 <inttypes.h>: Integer Type conversions 144
23.5.2.77 #define SCNiLEAST16 "i"
generic-integer scanf format for int_least16_t
23.5.2.78 #define SCNiLEAST32 "li"
generic-integer scanf format for int_least32_t
23.5.2.79 #define SCNiLEAST8 "hhi"
generic-integer scanf format for int_least8_t
23.5.2.80 #define SCNiPTR SCNi16
generic-integer scanf format for intptr_t
23.5.2.81 #define SCNo16 "o"
octal scanf format for uint16_t
23.5.2.82 #define SCNo32 "lo"
octal scanf format for uint32_t
23.5.2.83 #define SCNo8 "hho"
octal scanf format for uint8_t
23.5.2.84 #define SCNoFAST16 "o"
octal scanf format for uint_fast16_t
23.5.2.85 #define SCNoFAST32 "lo"
octal scanf format for uint_fast32_t
23.5.2.86 #define SCNoFAST8 "hho"
octal scanf format for uint_fast8_t
23.5.2.87 #define SCNoLEAST16 "o"
octal scanf format for uint_least16_t
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23.5 <inttypes.h>: Integer Type conversions 145
23.5.2.88 #define SCNoLEAST32 "lo"
octal scanf format for uint_least32_t
23.5.2.89 #define SCNoLEAST8 "hho"
octal scanf format for uint_least8_t
23.5.2.90 #define SCNoPTR SCNo16
octal scanf format for uintptr_t
23.5.2.91 #define SCNu16 "u"
decimal scanf format for uint16_t
23.5.2.92 #define SCNu32 "lu"
decimal scanf format for uint32_t
23.5.2.93 #define SCNu8 "hhu"
decimal scanf format for uint8_t
23.5.2.94 #define SCNuFAST16 "u"
decimal scanf format for uint_fast16_t
23.5.2.95 #define SCNuFAST32 "lu"
decimal scanf format for uint_fast32_t
23.5.2.96 #define SCNuFAST8 "hhu"
decimal scanf format for uint_fast8_t
23.5.2.97 #define SCNuLEAST16 "u"
decimal scanf format for uint_least16_t
23.5.2.98 #define SCNuLEAST32 "lu"
decimal scanf format for uint_least32_t
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23.5 <inttypes.h>: Integer Type conversions 146
23.5.2.99 #define SCNuLEAST8 "hhu"
decimal scanf format for uint_least8_t
23.5.2.100 #define SCNuPTR SCNu16
decimal scanf format for uintptr_t
23.5.2.101 #define SCNx16 "x"
hexadecimal scanf format for uint16_t
23.5.2.102 #define SCNx32 "lx"
hexadecimal scanf format for uint32_t
23.5.2.103 #define SCNx8 "hhx"
hexadecimal scanf format for uint8_t
23.5.2.104 #define SCNxFAST16 "x"
hexadecimal scanf format for uint_fast16_t
23.5.2.105 #define SCNxFAST32 "lx"
hexadecimal scanf format for uint_fast32_t
23.5.2.106 #define SCNxFAST8 "hhx"
hexadecimal scanf format for uint_fast8_t
23.5.2.107 #define SCNxLEAST16 "x"
hexadecimal scanf format for uint_least16_t
23.5.2.108 #define SCNxLEAST32 "lx"
hexadecimal scanf format for uint_least32_t
23.5.2.109 #define SCNxLEAST8 "hhx"
hexadecimal scanf format for uint_least8_t
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23.6 <math.h>: Mathematics 147
23.5.2.110 #define SCNxPTR SCNx16
hexadecimal scanf format for uintptr_t
23.5.3 Typedef Documentation
23.5.3.1 typedef int32_t int_farptr_t
signed integer type that can hold a pointer >64 KB
23.5.3.2 typedef uint32_t uint_farptr_t
unsigned integer type that can hold a pointer >64 KB
23.6 <math.h>: Mathematics
Defines
• #define M_E 2.7182818284590452354
• #define M_LOG2E 1.4426950408889634074
• #define M_LOG10E 0.43429448190325182765
• #define M_LN2 0.69314718055994530942
• #define M_LN10 2.30258509299404568402
• #define M_PI 3.14159265358979323846
• #define M_PI_2 1.57079632679489661923
• #define M_PI_4 0.78539816339744830962
• #define M_1_PI 0.31830988618379067154
• #define M_2_PI 0.63661977236758134308
• #define M_2_SQRTPI 1.12837916709551257390
• #define M_SQRT2 1.41421356237309504880
• #define M_SQRT1_2 0.70710678118654752440
• #define NAN __builtin_nan("")
• #define INFINITY __builtin_inf()
• #define cosf cos
• #define sinf sin
• #define tanf tan
• #define fabsf fabs
• #define fmodf fmod
• #define cbrtf cbrt
• #define hypotf hypot
• #define squaref square
• #define floorf floor
• #define ceilf ceil
• #define frexpf frexp
• #define ldexpf ldexp
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23.6 <math.h>: Mathematics 148
• #define expf exp
• #define coshf cosh
• #define sinhf sinh
• #define tanhf tanh
• #define acosf acos
• #define asinf asin
• #define atanf atan
• #define atan2f atan2
• #define logf log
• #define log10f log10
• #define powf pow
• #define isnanf isnan
• #define isinff isinf
• #define isfinitef isfinite
• #define copysignf copysign
• #define signbitf signbit
• #define fdimf fdim
• #define fmaf fma
• #define fmaxf fmax
• #define fminf fmin
• #define truncf trunc
• #define roundf round
• #define lroundf lround
• #define lrintf lrint
Functions
• double cos (double __x)
• double sin (double __x)
• double tan (double __x)
• double fabs (double __x)
• double fmod (double __x, double __y)
• double modf (double __x, double ∗__iptr)
• float modff (float __x, float ∗__iptr)
• double sqrt (double __x)
• float sqrtf (float)
• double cbrt (double __x)
• double hypot (double __x, double __y)
• double square (double __x)
• double floor (double __x)
• double ceil (double __x)
• double frexp (double __x, int ∗__pexp)
• double ldexp (double __x, int __exp)
• double exp (double __x)
• double cosh (double __x)
• double sinh (double __x)
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23.6 <math.h>: Mathematics 149
• double tanh (double __x)
• double acos (double __x)
• double asin (double __x)
• double atan (double __x)
• double atan2 (double __y, double __x)
• double log (double __x)
• double log10 (double __x)
• double pow (double __x, double __y)
• int isnan (double __x)
• int isinf (double __x)
• static int isfinite (double __x)
• static double copysign (double __x, double __y)
• int signbit (double __x)
• double fdim (double __x, double __y)
• double fma (double __x, double __y, double __z)
• double fmax (double __x, double __y)
• double fmin (double __x, double __y)
• double trunc (double __x)
• double round (double __x)
• long lround (double __x)
• long lrint (double __x)
23.6.1 Detailed Description
#include <math.h>
This header file declares basic mathematics constants and functions.
Notes:
• In order to access the functions declared herein, it is usually also required to
additionally link against the library libm.a. See also the related FAQ entry.
• Math functions do not raise exceptions and do not change the errno vari-
able. Therefore the majority of them are declared with const attribute, for
better optimization by GCC.
23.6.2 Define Documentation
23.6.2.1 #define acosf acos
The alias for acos().
23.6.2.2 #define asinf asin
The alias for asin().
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23.6 <math.h>: Mathematics 150
23.6.2.3 #define atan2f atan2
The alias for atan2().
23.6.2.4 #define atanf atan
The alias for atan().
23.6.2.5 #define cbrtf cbrt
The alias for cbrt().
23.6.2.6 #define ceilf ceil
The alias for ceil().
23.6.2.7 #define copysignf copysign
The alias for copysign().
23.6.2.8 #define cosf cos
The alias for cos().
23.6.2.9 #define coshf cosh
The alias for cosh().
23.6.2.10 #define expf exp
The alias for exp().
23.6.2.11 #define fabsf fabs
The alias for fabs().
23.6.2.12 #define fdimf fdim
The alias for fdim().
23.6.2.13 #define floorf floor
The alias for floor().
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23.6 <math.h>: Mathematics 151
23.6.2.14 #define fmaf fma
The alias for fma().
23.6.2.15 #define fmaxf fmax
The alias for fmax().
23.6.2.16 #define fminf fmin
The alias for fmin().
23.6.2.17 #define fmodf fmod
The alias for fmod().
23.6.2.18 #define frexpf frexp
The alias for frexp().
23.6.2.19 #define hypotf hypot
The alias for hypot().
23.6.2.20 #define INFINITY __builtin_inf()
INFINITY constant.
23.6.2.21 #define isfinitef isfinite
The alias for isfinite().
23.6.2.22 #define isinff isinf
The alias for isinf().
23.6.2.23 #define isnanf isnan
The alias for isnan().
23.6.2.24 #define ldexpf ldexp
The alias for ldexp().
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23.6 <math.h>: Mathematics 152
23.6.2.25 #define log10f log10
The alias for log10().
23.6.2.26 #define logf log
The alias for log().
23.6.2.27 #define lrintf lrint
The alias for lrint().
23.6.2.28 #define lroundf lround
The alias for lround().
23.6.2.29 #define M_1_PI 0.31830988618379067154
The constant 1/pi.
23.6.2.30 #define M_2_PI 0.63661977236758134308
The constant 2/pi.
23.6.2.31 #define M_2_SQRTPI 1.12837916709551257390
The constant 2/sqrt(pi).
23.6.2.32 #define M_E 2.7182818284590452354
The constant e.
23.6.2.33 #define M_LN10 2.30258509299404568402
The natural logarithm of the 10.
23.6.2.34 #define M_LN2 0.69314718055994530942
The natural logarithm of the 2.
23.6.2.35 #define M_LOG10E 0.43429448190325182765
The logarithm of the eto base 10.
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23.6 <math.h>: Mathematics 153
23.6.2.36 #define M_LOG2E 1.4426950408889634074
The logarithm of the eto base 2.
23.6.2.37 #define M_PI 3.14159265358979323846
The constant pi.
23.6.2.38 #define M_PI_2 1.57079632679489661923
The constant pi/2.
23.6.2.39 #define M_PI_4 0.78539816339744830962
The constant pi/4.
23.6.2.40 #define M_SQRT1_2 0.70710678118654752440
The constant 1/sqrt(2).
23.6.2.41 #define M_SQRT2 1.41421356237309504880
The square root of 2.
23.6.2.42 #define NAN __builtin_nan("")
NAN constant.
23.6.2.43 #define powf pow
The alias for pow().
23.6.2.44 #define roundf round
The alias for round().
23.6.2.45 #define signbitf signbit
The alias for signbit().
23.6.2.46 #define sinf sin
The alias for sin().
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23.6 <math.h>: Mathematics 154
23.6.2.47 #define sinhf sinh
The alias for sinh().
23.6.2.48 #define squaref square
The alias for square().
23.6.2.49 #define tanf tan
The alias for tan().
23.6.2.50 #define tanhf tanh
The alias for tanh().
23.6.2.51 #define truncf trunc
The alias for trunc().
23.6.3 Function Documentation
23.6.3.1 double acos (double __x)
The acos() function computes the principal value of the arc cosine of __x. The
returned value is in the range [0, pi] radians. A domain error occurs for arguments not
in the range [-1, +1].
23.6.3.2 double asin (double __x)
The asin() function computes the principal value of the arc sine of
__x. The returned value is in the range [-pi/2, pi/2] radians. A domain error occurs for
arguments not in the range [-1, +1].
23.6.3.3 double atan (double __x)
The atan() function computes the principal value of the arc tangent of __x. The
returned value is in the range [-pi/2, pi/2] radians.
23.6.3.4 double atan2 (double __y, double __x)
The atan2() function computes the principal value of the arc tangent of __y
/ __x, using the signs of both arguments to determine the quadrant of the return value.
The returned value is in the range [-pi, +pi] radians.
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23.6 <math.h>: Mathematics 155
23.6.3.5 double cbrt (double __x)
The cbrt() function returns the cube root of __x.
23.6.3.6 double ceil (double __x)
The ceil() function returns the smallest integral value greater than or equal to __x,
expressed as a floating-point number.
23.6.3.7 static double copysign (double __x, double __y)[static]
The copysign() function returns __x but with the sign of __y. They work even if __x
or __y are NaN or zero.
23.6.3.8 double cos (double __x)
The cos() function returns the cosine of __x, measured in radians.
23.6.3.9 double cosh (double __x)
The cosh() function returns the hyperbolic cosine of __x.
23.6.3.10 double exp (double __x)
The exp() function returns the exponential value of __x.
23.6.3.11 double fabs (double __x)
The fabs() function computes the absolute value of a floating-point number __x.
23.6.3.12 double fdim (double __x, double __y)
The fdim() function returns max(__x - __y, 0). If __x or __y or both are NaN, NaN is
returned.
23.6.3.13 double floor (double __x)
The floor() function returns the largest integral value less than or equal to __x,
expressed as a floating-point number.
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23.6 <math.h>: Mathematics 156
23.6.3.14 double fma (double __x, double __y, double __z)
The fma() function performs floating-point multiply-add. This is the operation (__x ∗
__y) + __z, but the intermediate result is not rounded to the destination type. This can
sometimes improve the precision of a calculation.
23.6.3.15 double fmax (double __x, double __y)
The fmax() function returns the greater of the two values __x and __y. If an argument
is NaN, the other argument is returned. If both arguments are NaN, NaN is returned.
23.6.3.16 double fmin (double __x, double __y)
The fmin() function returns the lesser of the two values __x and __y. If an argument
is NaN, the other argument is returned. If both arguments are NaN, NaN is returned.
23.6.3.17 double fmod (double __x, double __y)
The function fmod() returns the floating-point remainder of __x / __y.
23.6.3.18 double frexp (double __x, int ∗__pexp)
The frexp() function breaks a floating-point number into a normalized fraction and an
integral power of 2. It stores the integer in the int object pointed to by __pexp.
If __x is a normal float point number, the frexp() function returns the value v, such that
vhas a magnitude in the interval [1/2, 1) or zero, and __x equals vtimes 2 raised to
the power __pexp. If __x is zero, both parts of the result are zero. If __x is not a finite
number, the frexp() returns __x as is and stores 0 by __pexp.
Note
This implementation permits a zero pointer as a directive to skip a storing the
exponent.
23.6.3.19 double hypot (double __x, double __y)
The hypot() function returns sqrt(__x∗__x + __y∗__y). This
is the length of the hypotenuse of a right triangle with sides of length __x and __y, or
the distance of the point (__x,__y) from the origin. Using this function instead of the
direct formula is wise, since the error is much smaller. No underflow with small __x
and __y. No overflow if result is in range.
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23.6 <math.h>: Mathematics 157
23.6.3.20 static int isfinite (double __x)[static]
The isfinite() function returns a nonzero value if __x is finite: not plus or minus
infinity, and not NaN.
23.6.3.21 int isinf (double __x)
The function isinf() returns 1 if the argument __x is positive infinity, -1 if __x is
negative infinity, and 0 otherwise.
Note
The GCC 4.3 can replace this function with inline code that returns the 1 value for
both infinities (gcc bug #35509).
23.6.3.22 int isnan (double __x)
The function isnan() returns 1 if the argument __x represents a "not-a-number" (NaN)
object, otherwise 0.
23.6.3.23 double ldexp (double __x, int __exp)
The ldexp() function multiplies a floating-point number by an integral power of 2. It
returns the value of __x times 2 raised to the power __exp.
23.6.3.24 double log (double __x)
The log() function returns the natural logarithm of argument __x.
23.6.3.25 double log10 (double __x)
The log10() function returns the logarithm of argument __x to base 10.
23.6.3.26 long lrint (double __x)
The lrint() function rounds __x to the nearest
integer, rounding the halfway cases to the even integer direction. (That is both 1.5 and
2.5 values are rounded to 2). This function is similar to rint() function, but it differs in
type of return value and in that an overflow is possible.
Returns
The rounded long integer value. If __x is not a finite number or an overflow was,
this realization returns the LONG_MIN value (0x80000000).
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23.6 <math.h>: Mathematics 158
23.6.3.27 long lround (double __x)
The lround() function rounds __x to the nearest integer, but rounds
halfway cases away from zero (instead of to the nearest even integer). This function is
similar to round() function, but it differs in type of return value and in that an overflow
is possible.
Returns
The rounded long integer value. If __x is not a finite number or an overflow was,
this realization returns the LONG_MIN value (0x80000000).
23.6.3.28 double modf (double __x, double ∗__iptr)
The modf() function breaks the argument __x into integral and fractional parts,
each of which has the same sign as the argument. It stores the integral part as a double
in the object pointed to by __iptr.
The modf() function returns the signed fractional part of __x.
Note
This implementation skips writing by zero pointer. However, the GCC 4.3 can
replace this function with inline code that does not permit to use NULL address
for the avoiding of storing.
23.6.3.29 float modff (float __x, float ∗__iptr)
An alias for modf().
23.6.3.30 double pow (double __x, double __y)
The function pow() returns the value of __x to the exponent __y.
23.6.3.31 double round (double __x)
The round() function rounds __x to the nearest integer, but rounds halfway cases
away from zero (instead of to the nearest even integer). Overflow is impossible.
Returns
The rounded value. If __x is an integral or infinite, __x itself is returned. If __x is
NaN, then NaN is returned.
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23.6 <math.h>: Mathematics 159
23.6.3.32 int signbit (double __x)
The signbit() function returns a nonzero value if the value of __x has its sign bit set.
This is not the same as ‘__x <0.0’, because IEEE 754 floating point allows zero to be
signed. The comparison ‘-0.0 <0.0’ is false, but ‘signbit (-0.0)’ will return a nonzero
value.
23.6.3.33 double sin (double __x)
The sin() function returns the sine of __x, measured in radians.
23.6.3.34 double sinh (double __x)
The sinh() function returns the hyperbolic sine of __x.
23.6.3.35 double sqrt (double __x)
The sqrt() function returns the non-negative square root of __x.
23.6.3.36 float sqrtf (float)
An alias for sqrt().
23.6.3.37 double square (double __x)
The function square() returns __x ∗__x.
Note
This function does not belong to the C standard definition.
23.6.3.38 double tan (double __x)
The tan() function returns the tangent of __x, measured in radians.
23.6.3.39 double tanh (double __x)
The tanh() function returns the hyperbolic tangent of __x.
23.6.3.40 double trunc (double __x)
The trunc() function rounds __x to the nearest integer not larger in absolute value.
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23.7 <setjmp.h>: Non-local goto 160
23.7 <setjmp.h>: Non-local goto
Functions
• int setjmp (jmp_buf __jmpb)
• void longjmp (jmp_buf __jmpb, int __ret) __ATTR_NORETURN__
23.7.1 Detailed Description
While the C language has the dreaded goto statement, it can only be used to jump to
a label in the same (local) function. In order to jump directly to another (non-local)
function, the C library provides the setjmp() and longjmp() functions. setjmp() and
longjmp() are useful for dealing with errors and interrupts encountered in a low-level
subroutine of a program.
Note
setjmp() and longjmp() make programs hard to understand and maintain. If possi-
ble, an alternative should be used.
longjmp() can destroy changes made to global register variables (see How to per-
manently bind a variable to a register?).
For a very detailed discussion of setjmp()/longjmp(), see Chapter 7 of Advanced Pro-
gramming in the UNIX Environment, by W. Richard Stevens.
Example:
#include <setjmp.h>
jmp_buf env;
int main (void)
{
if (setjmp (env))
{
... handle error ...
}
while (1)
{
... main processing loop which calls foo() some where ...
}
}
...
void foo (void)
{
... blah, blah, blah ...
if (err)
{
longjmp (env, 1);
}
}
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23.7 <setjmp.h>: Non-local goto 161
23.7.2 Function Documentation
23.7.2.1 void longjmp (jmp_buf __jmpb, int __ret)
Non-local jump to a saved stack context.
#include <setjmp.h>
longjmp() restores the environment saved by the last call of setjmp() with the corre-
sponding __jmpb argument. After longjmp() is completed, program execution contin-
ues as if the corresponding call of setjmp() had just returned the value __ret.
Note
longjmp() cannot cause 0 to be returned. If longjmp() is invoked with a second
argument of 0, 1 will be returned instead.
Parameters
__jmpb Information saved by a previous call to setjmp().
__ret Value to return to the caller of setjmp().
Returns
This function never returns.
23.7.2.2 int setjmp (jmp_buf __jmpb)
Save stack context for non-local goto.
#include <setjmp.h>
setjmp() saves the stack context/environment in __jmpb for later use by longjmp(). The
stack context will be invalidated if the function which called setjmp() returns.
Parameters
__jmpb Variable of type jmp_buf which holds the stack information such that
the environment can be restored.
Returns
setjmp() returns 0 if returning directly, and non-zero when returning from
longjmp() using the saved context.
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23.8 <stdint.h>: Standard Integer Types 162
23.8 <stdint.h>: Standard Integer Types
Exact-width integer types
Integer types having exactly the specified width
• typedef signed char int8_t
• typedef unsigned char uint8_t
• typedef signed int int16_t
• typedef unsigned int uint16_t
• typedef signed long int int32_t
• typedef unsigned long int uint32_t
• typedef signed long long int int64_t
• typedef unsigned long long int uint64_t
Integer types capable of holding object pointers
These allow you to declare variables of the same size as a pointer.
• typedef int16_t intptr_t
• typedef uint16_t uintptr_t
Minimum-width integer types
Integer types having at least the specified width
• typedef int8_t int_least8_t
• typedef uint8_t uint_least8_t
• typedef int16_t int_least16_t
• typedef uint16_t uint_least16_t
• typedef int32_t int_least32_t
• typedef uint32_t uint_least32_t
• typedef int64_t int_least64_t
• typedef uint64_t uint_least64_t
Fastest minimum-width integer types
Integer types being usually fastest having at least the specified width
• typedef int8_t int_fast8_t
• typedef uint8_t uint_fast8_t
• typedef int16_t int_fast16_t
• typedef uint16_t uint_fast16_t
• typedef int32_t int_fast32_t
• typedef uint32_t uint_fast32_t
• typedef int64_t int_fast64_t
• typedef uint64_t uint_fast64_t
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23.8 <stdint.h>: Standard Integer Types 163
Greatest-width integer types
Types designating integer data capable of representing any value of any integer type in
the corresponding signed or unsigned category
• typedef int64_t intmax_t
• typedef uint64_t uintmax_t
Limits of specified-width integer types
C++ implementations should define these macros only when __STDC_LIMIT_-
MACROS is defined before <stdint.h>is included
• #define INT8_MAX 0x7f
• #define INT8_MIN (-INT8_MAX - 1)
• #define UINT8_MAX (INT8_MAX ∗2 + 1)
• #define INT16_MAX 0x7fff
• #define INT16_MIN (-INT16_MAX - 1)
• #define UINT16_MAX (__CONCAT(INT16_MAX, U) ∗2U + 1U)
• #define INT32_MAX 0x7fffffffL
• #define INT32_MIN (-INT32_MAX - 1L)
• #define UINT32_MAX (__CONCAT(INT32_MAX, U) ∗2UL + 1UL)
• #define INT64_MAX 0x7fffffffffffffffLL
• #define INT64_MIN (-INT64_MAX - 1LL)
• #define UINT64_MAX (__CONCAT(INT64_MAX, U) ∗2ULL + 1ULL)
Limits of minimum-width integer types
• #define INT_LEAST8_MAX INT8_MAX
• #define INT_LEAST8_MIN INT8_MIN
• #define UINT_LEAST8_MAX UINT8_MAX
• #define INT_LEAST16_MAX INT16_MAX
• #define INT_LEAST16_MIN INT16_MIN
• #define UINT_LEAST16_MAX UINT16_MAX
• #define INT_LEAST32_MAX INT32_MAX
• #define INT_LEAST32_MIN INT32_MIN
• #define UINT_LEAST32_MAX UINT32_MAX
• #define INT_LEAST64_MAX INT64_MAX
• #define INT_LEAST64_MIN INT64_MIN
• #define UINT_LEAST64_MAX UINT64_MAX
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23.8 <stdint.h>: Standard Integer Types 164
Limits of fastest minimum-width integer types
• #define INT_FAST8_MAX INT8_MAX
• #define INT_FAST8_MIN INT8_MIN
• #define UINT_FAST8_MAX UINT8_MAX
• #define INT_FAST16_MAX INT16_MAX
• #define INT_FAST16_MIN INT16_MIN
• #define UINT_FAST16_MAX UINT16_MAX
• #define INT_FAST32_MAX INT32_MAX
• #define INT_FAST32_MIN INT32_MIN
• #define UINT_FAST32_MAX UINT32_MAX
• #define INT_FAST64_MAX INT64_MAX
• #define INT_FAST64_MIN INT64_MIN
• #define UINT_FAST64_MAX UINT64_MAX
Limits of integer types capable of holding object pointers
• #define INTPTR_MAX INT16_MAX
• #define INTPTR_MIN INT16_MIN
• #define UINTPTR_MAX UINT16_MAX
Limits of greatest-width integer types
• #define INTMAX_MAX INT64_MAX
• #define INTMAX_MIN INT64_MIN
• #define UINTMAX_MAX UINT64_MAX
Limits of other integer types
C++ implementations should define these macros only when __STDC_LIMIT_-
MACROS is defined before <stdint.h>is included
• #define PTRDIFF_MAX INT16_MAX
• #define PTRDIFF_MIN INT16_MIN
• #define SIG_ATOMIC_MAX INT8_MAX
• #define SIG_ATOMIC_MIN INT8_MIN
• #define SIZE_MAX UINT16_MAX
• #define WCHAR_MAX __WCHAR_MAX__
• #define WCHAR_MIN __WCHAR_MIN__
• #define WINT_MAX __WINT_MAX__
• #define WINT_MIN __WINT_MIN__
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23.8 <stdint.h>: Standard Integer Types 165
Macros for integer constants
C++ implementations should define these macros only when __STDC_CONSTANT_-
MACROS is defined before <stdint.h>is included.
These definitions are valid for integer constants without suffix and for macros defined
as integer constant without suffix
• #define INT8_C(value) ((int8_t) value)
• #define UINT8_C(value) ((uint8_t) __CONCAT(value, U))
• #define INT16_C(value) value
• #define UINT16_C(value) __CONCAT(value, U)
• #define INT32_C(value) __CONCAT(value, L)
• #define UINT32_C(value) __CONCAT(value, UL)
• #define INT64_C(value) __CONCAT(value, LL)
• #define UINT64_C(value) __CONCAT(value, ULL)
• #define INTMAX_C(value) __CONCAT(value, LL)
• #define UINTMAX_C(value) __CONCAT(value, ULL)
23.8.1 Detailed Description
#include <stdint.h>
Use [u]intN_t if you need exactly N bits.
Since these typedefs are mandated by the C99 standard, they are preferred over rolling
your own typedefs.
23.8.2 Define Documentation
23.8.2.1 #define INT16_C(value) value
define a constant of type int16_t
23.8.2.2 #define INT16_MAX 0x7fff
largest positive value an int16_t can hold.
23.8.2.3 #define INT16_MIN (-INT16_MAX - 1)
smallest negative value an int16_t can hold.
23.8.2.4 #define INT32_C(value) __CONCAT(value, L)
define a constant of type int32_t
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23.8 <stdint.h>: Standard Integer Types 166
23.8.2.5 #define INT32_MAX 0x7fffffffL
largest positive value an int32_t can hold.
23.8.2.6 #define INT32_MIN (-INT32_MAX - 1L)
smallest negative value an int32_t can hold.
23.8.2.7 #define INT64_C(value) __CONCAT(value, LL)
define a constant of type int64_t
23.8.2.8 #define INT64_MAX 0x7fffffffffffffffLL
largest positive value an int64_t can hold.
23.8.2.9 #define INT64_MIN (-INT64_MAX - 1LL)
smallest negative value an int64_t can hold.
23.8.2.10 #define INT8_C(value) ((int8_t) value)
define a constant of type int8_t
23.8.2.11 #define INT8_MAX 0x7f
largest positive value an int8_t can hold.
23.8.2.12 #define INT8_MIN (-INT8_MAX - 1)
smallest negative value an int8_t can hold.
23.8.2.13 #define INT_FAST16_MAX INT16_MAX
largest positive value an int_fast16_t can hold.
23.8.2.14 #define INT_FAST16_MIN INT16_MIN
smallest negative value an int_fast16_t can hold.
23.8.2.15 #define INT_FAST32_MAX INT32_MAX
largest positive value an int_fast32_t can hold.
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23.8 <stdint.h>: Standard Integer Types 167
23.8.2.16 #define INT_FAST32_MIN INT32_MIN
smallest negative value an int_fast32_t can hold.
23.8.2.17 #define INT_FAST64_MAX INT64_MAX
largest positive value an int_fast64_t can hold.
23.8.2.18 #define INT_FAST64_MIN INT64_MIN
smallest negative value an int_fast64_t can hold.
23.8.2.19 #define INT_FAST8_MAX INT8_MAX
largest positive value an int_fast8_t can hold.
23.8.2.20 #define INT_FAST8_MIN INT8_MIN
smallest negative value an int_fast8_t can hold.
23.8.2.21 #define INT_LEAST16_MAX INT16_MAX
largest positive value an int_least16_t can hold.
23.8.2.22 #define INT_LEAST16_MIN INT16_MIN
smallest negative value an int_least16_t can hold.
23.8.2.23 #define INT_LEAST32_MAX INT32_MAX
largest positive value an int_least32_t can hold.
23.8.2.24 #define INT_LEAST32_MIN INT32_MIN
smallest negative value an int_least32_t can hold.
23.8.2.25 #define INT_LEAST64_MAX INT64_MAX
largest positive value an int_least64_t can hold.
23.8.2.26 #define INT_LEAST64_MIN INT64_MIN
smallest negative value an int_least64_t can hold.
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23.8 <stdint.h>: Standard Integer Types 168
23.8.2.27 #define INT_LEAST8_MAX INT8_MAX
largest positive value an int_least8_t can hold.
23.8.2.28 #define INT_LEAST8_MIN INT8_MIN
smallest negative value an int_least8_t can hold.
23.8.2.29 #define INTMAX_C(value) __CONCAT(value, LL)
define a constant of type intmax_t
23.8.2.30 #define INTMAX_MAX INT64_MAX
largest positive value an intmax_t can hold.
23.8.2.31 #define INTMAX_MIN INT64_MIN
smallest negative value an intmax_t can hold.
23.8.2.32 #define INTPTR_MAX INT16_MAX
largest positive value an intptr_t can hold.
23.8.2.33 #define INTPTR_MIN INT16_MIN
smallest negative value an intptr_t can hold.
23.8.2.34 #define PTRDIFF_MAX INT16_MAX
largest positive value a ptrdiff_t can hold.
23.8.2.35 #define PTRDIFF_MIN INT16_MIN
smallest negative value a ptrdiff_t can hold.
23.8.2.36 #define SIG_ATOMIC_MAX INT8_MAX
largest positive value a sig_atomic_t can hold.
23.8.2.37 #define SIG_ATOMIC_MIN INT8_MIN
smallest negative value a sig_atomic_t can hold.
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23.8 <stdint.h>: Standard Integer Types 169
23.8.2.38 #define SIZE_MAX UINT16_MAX
largest value a size_t can hold.
23.8.2.39 #define UINT16_C(value) __CONCAT(value, U)
define a constant of type uint16_t
23.8.2.40 #define UINT16_MAX (__CONCAT(INT16_MAX, U) ∗2U + 1U)
largest value an uint16_t can hold.
23.8.2.41 #define UINT32_C(value) __CONCAT(value, UL)
define a constant of type uint32_t
23.8.2.42 #define UINT32_MAX (__CONCAT(INT32_MAX, U) ∗2UL + 1UL)
largest value an uint32_t can hold.
23.8.2.43 #define UINT64_C(value) __CONCAT(value, ULL)
define a constant of type uint64_t
23.8.2.44 #define UINT64_MAX (__CONCAT(INT64_MAX, U) ∗2ULL +
1ULL)
largest value an uint64_t can hold.
23.8.2.45 #define UINT8_C(value) ((uint8_t) __CONCAT(value, U))
define a constant of type uint8_t
23.8.2.46 #define UINT8_MAX (INT8_MAX ∗2 + 1)
largest value an uint8_t can hold.
23.8.2.47 #define UINT_FAST16_MAX UINT16_MAX
largest value an uint_fast16_t can hold.
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23.8 <stdint.h>: Standard Integer Types 170
23.8.2.48 #define UINT_FAST32_MAX UINT32_MAX
largest value an uint_fast32_t can hold.
23.8.2.49 #define UINT_FAST64_MAX UINT64_MAX
largest value an uint_fast64_t can hold.
23.8.2.50 #define UINT_FAST8_MAX UINT8_MAX
largest value an uint_fast8_t can hold.
23.8.2.51 #define UINT_LEAST16_MAX UINT16_MAX
largest value an uint_least16_t can hold.
23.8.2.52 #define UINT_LEAST32_MAX UINT32_MAX
largest value an uint_least32_t can hold.
23.8.2.53 #define UINT_LEAST64_MAX UINT64_MAX
largest value an uint_least64_t can hold.
23.8.2.54 #define UINT_LEAST8_MAX UINT8_MAX
largest value an uint_least8_t can hold.
23.8.2.55 #define UINTMAX_C(value) __CONCAT(value, ULL)
define a constant of type uintmax_t
23.8.2.56 #define UINTMAX_MAX UINT64_MAX
largest value an uintmax_t can hold.
23.8.2.57 #define UINTPTR_MAX UINT16_MAX
largest value an uintptr_t can hold.
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23.8 <stdint.h>: Standard Integer Types 171
23.8.3 Typedef Documentation
23.8.3.1 typedef signed int int16_t
16-bit signed type.
23.8.3.2 typedef signed long int int32_t
32-bit signed type.
23.8.3.3 typedef signed long long int int64_t
64-bit signed type.
Note
This type is not available when the compiler option -mint8 is in effect.
23.8.3.4 typedef signed char int8_t
8-bit signed type.
23.8.3.5 typedef int16_t int_fast16_t
fastest signed int with at least 16 bits.
23.8.3.6 typedef int32_t int_fast32_t
fastest signed int with at least 32 bits.
23.8.3.7 typedef int64_t int_fast64_t
fastest signed int with at least 64 bits.
Note
This type is not available when the compiler option -mint8 is in effect.
23.8.3.8 typedef int8_t int_fast8_t
fastest signed int with at least 8 bits.
23.8.3.9 typedef int16_t int_least16_t
signed int with at least 16 bits.
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23.8 <stdint.h>: Standard Integer Types 172
23.8.3.10 typedef int32_t int_least32_t
signed int with at least 32 bits.
23.8.3.11 typedef int64_t int_least64_t
signed int with at least 64 bits.
Note
This type is not available when the compiler option -mint8 is in effect.
23.8.3.12 typedef int8_t int_least8_t
signed int with at least 8 bits.
23.8.3.13 typedef int64_t intmax_t
largest signed int available.
23.8.3.14 typedef int16_t intptr_t
Signed pointer compatible type.
23.8.3.15 typedef unsigned int uint16_t
16-bit unsigned type.
23.8.3.16 typedef unsigned long int uint32_t
32-bit unsigned type.
23.8.3.17 typedef unsigned long long int uint64_t
64-bit unsigned type.
Note
This type is not available when the compiler option -mint8 is in effect.
23.8.3.18 typedef unsigned char uint8_t
8-bit unsigned type.
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23.8 <stdint.h>: Standard Integer Types 173
23.8.3.19 typedef uint16_t uint_fast16_t
fastest unsigned int with at least 16 bits.
23.8.3.20 typedef uint32_t uint_fast32_t
fastest unsigned int with at least 32 bits.
23.8.3.21 typedef uint64_t uint_fast64_t
fastest unsigned int with at least 64 bits.
Note
This type is not available when the compiler option -mint8 is in effect.
23.8.3.22 typedef uint8_t uint_fast8_t
fastest unsigned int with at least 8 bits.
23.8.3.23 typedef uint16_t uint_least16_t
unsigned int with at least 16 bits.
23.8.3.24 typedef uint32_t uint_least32_t
unsigned int with at least 32 bits.
23.8.3.25 typedef uint64_t uint_least64_t
unsigned int with at least 64 bits.
Note
This type is not available when the compiler option -mint8 is in effect.
23.8.3.26 typedef uint8_t uint_least8_t
unsigned int with at least 8 bits.
23.8.3.27 typedef uint64_t uintmax_t
largest unsigned int available.
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23.9 <stdio.h>: Standard IO facilities 174
23.8.3.28 typedef uint16_t uintptr_t
Unsigned pointer compatible type.
23.9 <stdio.h>: Standard IO facilities
Defines
• #define stdin (__iob[0])
• #define stdout (__iob[1])
• #define stderr (__iob[2])
• #define EOF (-1)
• #define fdev_set_udata(stream, u) do { (stream)->udata = u; } while(0)
• #define fdev_get_udata(stream) ((stream)->udata)
• #define fdev_setup_stream(stream, put, get, rwflag)
• #define _FDEV_SETUP_READ __SRD
• #define _FDEV_SETUP_WRITE __SWR
• #define _FDEV_SETUP_RW (__SRD|__SWR)
• #define _FDEV_ERR (-1)
• #define _FDEV_EOF (-2)
• #define FDEV_SETUP_STREAM(put, get, rwflag)
• #define fdev_close()
• #define putc(__c, __stream) fputc(__c, __stream)
• #define putchar(__c) fputc(__c, stdout)
• #define getc(__stream) fgetc(__stream)
• #define getchar() fgetc(stdin)
Typedefs
• typedef struct __file FILE
Functions
• int fclose (FILE ∗__stream)
• int vfprintf (FILE ∗__stream, const char ∗__fmt, va_list __ap)
• int vfprintf_P (FILE ∗__stream, const char ∗__fmt, va_list __ap)
• int fputc (int __c, FILE ∗__stream)
• int printf (const char ∗__fmt,...)
• int printf_P (const char ∗__fmt,...)
• int vprintf (const char ∗__fmt, va_list __ap)
• int sprintf (char ∗__s, const char ∗__fmt,...)
• int sprintf_P (char ∗__s, const char ∗__fmt,...)
• int snprintf (char ∗__s, size_t __n, const char ∗__fmt,...)
• int snprintf_P (char ∗__s, size_t __n, const char ∗__fmt,...)
• int vsprintf (char ∗__s, const char ∗__fmt, va_list ap)
• int vsprintf_P (char ∗__s, const char ∗__fmt, va_list ap)
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23.9 <stdio.h>: Standard IO facilities 175
• int vsnprintf (char ∗__s, size_t __n, const char ∗__fmt, va_list ap)
• int vsnprintf_P (char ∗__s, size_t __n, const char ∗__fmt, va_list ap)
• int fprintf (FILE ∗__stream, const char ∗__fmt,...)
• int fprintf_P (FILE ∗__stream, const char ∗__fmt,...)
• int fputs (const char ∗__str, FILE ∗__stream)
• int fputs_P (const char ∗__str, FILE ∗__stream)
• int puts (const char ∗__str)
• int puts_P (const char ∗__str)
• size_t fwrite (const void ∗__ptr, size_t __size, size_t __nmemb, FILE ∗__-
stream)
• int fgetc (FILE ∗__stream)
• int ungetc (int __c, FILE ∗__stream)
• char ∗fgets (char ∗__str, int __size, FILE ∗__stream)
• char ∗gets (char ∗__str)
• size_t fread (void ∗__ptr, size_t __size, size_t __nmemb, FILE ∗__stream)
• void clearerr (FILE ∗__stream)
• int feof (FILE ∗__stream)
• int ferror (FILE ∗__stream)
• int vfscanf (FILE ∗__stream, const char ∗__fmt, va_list __ap)
• int vfscanf_P (FILE ∗__stream, const char ∗__fmt, va_list __ap)
• int fscanf (FILE ∗__stream, const char ∗__fmt,...)
• int fscanf_P (FILE ∗__stream, const char ∗__fmt,...)
• int scanf (const char ∗__fmt,...)
• int scanf_P (const char ∗__fmt,...)
• int vscanf (const char ∗__fmt, va_list __ap)
• int sscanf (const char ∗__buf, const char ∗__fmt,...)
• int sscanf_P (const char ∗__buf, const char ∗__fmt,...)
• int fflush (FILE ∗stream)
•FILE ∗fdevopen (int(∗put)(char, FILE ∗), int(∗get)(FILE ∗))
23.9.1 Detailed Description
#include <stdio.h>
Introduction to the Standard IO facilities This file declares the standard IO facili-
ties that are implemented in avr-libc. Due to the nature of the underlying hardware,
only a limited subset of standard IO is implemented. There is no actual file implementa-
tion available, so only device IO can be performed. Since there’s no operating system,
the application needs to provide enough details about their devices in order to make
them usable by the standard IO facilities.
Due to space constraints, some functionality has not been implemented at all (like some
of the printf conversions that have been left out). Nevertheless, potential users of
this implementation should be warned: the printf and scanf families of functions,
although usually associated with presumably simple things like the famous "Hello,
world!" program, are actually fairly complex which causes their inclusion to eat up
a fair amount of code space. Also, they are not fast due to the nature of interpreting
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23.9 <stdio.h>: Standard IO facilities 176
the format string at run-time. Whenever possible, resorting to the (sometimes non-
standard) predetermined conversion facilities that are offered by avr-libc will usually
cost much less in terms of speed and code size.
Tunable options for code size vs. feature set In order to allow programmers a code
size vs. functionality tradeoff, the function vfprintf() which is the heart of the printf
family can be selected in different flavours using linker options. See the documentation
of vfprintf() for a detailed description. The same applies to vfscanf() and the scanf
family of functions.
Outline of the chosen API The standard streams stdin,stdout, and stderr are
provided, but contrary to the C standard, since avr-libc has no knowledge about appli-
cable devices, these streams are not already pre-initialized at application startup. Also,
since there is no notion of "file" whatsoever to avr-libc, there is no function fopen()
that could be used to associate a stream to some device. (See note 1.) Instead, the
function fdevopen() is provided to associate a stream to a device, where the device
needs to provide a function to send a character, to receive a character, or both. There
is no differentiation between "text" and "binary" streams inside avr-libc. Character \n
is sent literally down to the device’s put() function. If the device requires a carriage
return (\r) character to be sent before the linefeed, its put() routine must implement
this (see note 2).
As an alternative method to fdevopen(), the macro fdev_setup_stream() might be used
to setup a user-supplied FILE structure.
It should be noted that the automatic conversion of a newline character into a carriage
return - newline sequence breaks binary transfers. If binary transfers are desired, no
automatic conversion should be performed, but instead any string that aims to issue a
CR-LF sequence must use "\r\n" explicitly.
For convenience, the first call to fdevopen() that opens a stream for reading
will cause the resulting stream to be aliased to stdin. Likewise, the first call to
fdevopen() that opens a stream for writing will cause the resulting stream to be
aliased to both, stdout, and stderr. Thus, if the open was done with both, read
and write intent, all three standard streams will be identical. Note that these aliases are
indistinguishable from each other, thus calling fclose() on such a stream will also
effectively close all of its aliases (note 3).
It is possible to tie additional user data to a stream, using fdev_set_udata(). The back-
end put and get functions can then extract this user data using fdev_get_udata(), and act
appropriately. For example, a single put function could be used to talk to two different
UARTs that way, or the put and get functions could keep internal state between calls
there.
Format strings in flash ROM All the printf and scanf family functions come
in two flavours: the standard name, where the format string is expected to be in SRAM,
as well as a version with the suffix "_P" where the format string is expected to reside
in the flash ROM. The macro PSTR (explained in <avr/pgmspace.h>: Program Space
Utilities) becomes very handy for declaring these format strings.
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23.9 <stdio.h>: Standard IO facilities 177
Running stdio without malloc() By default, fdevopen() requires malloc(). As this is
often not desired in the limited environment of a microcontroller, an alternative option
is provided to run completely without malloc().
The macro fdev_setup_stream() is provided to prepare a user-supplied FILE buffer for
operation with stdio.
Example
#include <stdio.h>
static int uart_putchar(char c, FILE *stream);
static FILE mystdout = FDEV_SETUP_STREAM(uart_putchar, NULL,
_FDEV_SETUP_WRITE);
static int
uart_putchar(char c, FILE *stream)
{
if (c == ’\n’)
uart_putchar(’\r’, stream);
loop_until_bit_is_set(UCSRA, UDRE);
UDR = c;
return 0;
}
int
main(void)
{
init_uart();
stdout = &mystdout;
printf("Hello, world!\n");
return 0;
}
This example uses the initializer form FDEV_SETUP_STREAM() rather than the
function-like fdev_setup_stream(), so all data initialization happens during C start-up.
If streams initialized that way are no longer needed, they can be destroyed by first
calling the macro fdev_close(), and then destroying the object itself. No call to fclose()
should be issued for these streams. While calling fclose() itself is harmless, it will cause
an undefined reference to free() and thus cause the linker to link the malloc module into
the application.
Notes
Note 1:
It might have been possible to implement a device abstraction that is compatible
with fopen() but since this would have required to parse a string, and to take all
the information needed either out of this string, or out of an additional table that
would need to be provided by the application, this approach was not taken.
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23.9 <stdio.h>: Standard IO facilities 178
Note 2:
This basically follows the Unix approach: if a device such as a terminal needs
special handling, it is in the domain of the terminal device driver to provide this
functionality. Thus, a simple function suitable as put() for fdevopen() that
talks to a UART interface might look like this:
int
uart_putchar(char c, FILE *stream)
{
if (c == ’\n’)
uart_putchar(’\r’);
loop_until_bit_is_set(UCSRA, UDRE);
UDR = c;
return 0;
}
Note 3:
This implementation has been chosen because the cost of maintaining an alias
is considerably smaller than the cost of maintaining full copies of each stream.
Yet, providing an implementation that offers the complete set of standard
streams was deemed to be useful. Not only that writing printf() instead of
fprintf(mystream, ...) saves typing work, but since avr-gcc needs to re-
sort to pass all arguments of variadic functions on the stack (as opposed to passing
them in registers for functions that take a fixed number of parameters), the abil-
ity to pass one parameter less by implying stdin or stdout will also save some
execution time.
23.9.2 Define Documentation
23.9.2.1 #define _FDEV_EOF (-2)
Return code for an end-of-file condition during device read.
To be used in the get function of fdevopen().
23.9.2.2 #define _FDEV_ERR (-1)
Return code for an error condition during device read.
To be used in the get function of fdevopen().
23.9.2.3 #define _FDEV_SETUP_READ __SRD
fdev_setup_stream() with read intent
23.9.2.4 #define _FDEV_SETUP_RW (__SRD|__SWR)
fdev_setup_stream() with read/write intent
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23.9 <stdio.h>: Standard IO facilities 179
23.9.2.5 #define _FDEV_SETUP_WRITE __SWR
fdev_setup_stream() with write intent
23.9.2.6 #define EOF (-1)
EOF declares the value that is returned by various standard IO functions in
case of an error. Since the AVR platform (currently) doesn’t contain an abstraction for
actual files, its origin as "end of file" is somewhat meaningless here.
23.9.2.7 #define fdev_close()
This macro frees up any library resources that might
be associated with stream. It should be called if stream is no longer needed, right
before the application is going to destroy the stream object itself.
(Currently, this macro evaluates to nothing, but this might change in future versions of
the library.)
23.9.2.8 #define fdev_get_udata(stream) ((stream)->udata)
This macro retrieves a pointer to user defined data from a FILE stream object.
23.9.2.9 #define fdev_set_udata(stream, u) do { (stream)->udata = u; } while(0)
This macro inserts a pointer to user defined data into a FILE stream object.
The user data can be useful for tracking state in the put and get functions supplied to
the fdevopen() function.
23.9.2.10 #define FDEV_SETUP_STREAM(put, get, rwflag)
Initializer for a user-supplied stdio stream.
This macro acts similar to fdev_setup_stream(), but it is to be used as the initializer of
a variable of type FILE.
The remaining arguments are to be used as explained in fdev_setup_stream().
23.9.2.11 #define fdev_setup_stream(stream, put, get, rwflag)
Setup a user-supplied buffer as an stdio stream.
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23.9 <stdio.h>: Standard IO facilities 180
This macro takes a user-supplied buffer stream, and sets it up as a stream that is valid
for stdio operations, similar to one that has been obtained dynamically from fdevopen().
The buffer to setup must be of type FILE.
The arguments put and get are identical to those that need to be passed to fdevopen().
The rwflag argument can take one of the values _FDEV_SETUP_READ, _FDEV_-
SETUP_WRITE, or _FDEV_SETUP_RW, for read, write, or read/write intent, respec-
tively.
Note
No assignments to the standard streams will be performed by fdev_setup_stream().
If standard streams are to be used, these need to be assigned by the user. See also
under Running stdio without malloc().
23.9.2.12 #define getc(__stream) fgetc(__stream)
The macro getc used to be a "fast" macro implementation with a functionality
identical to fgetc(). For space constraints, in avr-libc, it is just an alias for fgetc.
23.9.2.13 #define getchar(void) fgetc(stdin)
The macro getchar reads a character from stdin. Return values and error
handling is identical to fgetc().
23.9.2.14 #define putc(__c, __stream) fputc(__c, __stream)
The macro putc used to be a "fast" macro implementation with a functionality
identical to fputc(). For space constraints, in avr-libc, it is just an alias for fputc.
23.9.2.15 #define putchar(__c) fputc(__c, stdout)
The macro putchar sends character cto stdout.
23.9.2.16 #define stderr (__iob[2])
Stream destined for error output. Unless specifically assigned, identical to stdout.
If stderr should point to another stream, the result of another fdevopen() must
be explicitly assigned to it without closing the previous stderr (since this would also
close stdout).
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23.9 <stdio.h>: Standard IO facilities 181
23.9.2.17 #define stdin (__iob[0])
Stream that will be used as an input stream by the simplified functions that don’t take
astream argument.
The first stream opened with read intent using fdevopen() will be assigned to
stdin.
23.9.2.18 #define stdout (__iob[1])
Stream that will be used as an output stream by the simplified functions that don’t
take a stream argument.
The first stream opened with write intent using fdevopen() will be assigned to both,
stdin, and stderr.
23.9.3 Typedef Documentation
23.9.3.1 typedef struct __file FILE
FILE is the opaque structure that is passed around between the various standard IO
functions.
23.9.4 Function Documentation
23.9.4.1 void clearerr (FILE ∗__stream)
Clear the error and end-of-file flags of stream.
23.9.4.2 int fclose (FILE ∗__stream)
This function closes stream, and disallows and further IO to and from it.
When using fdevopen() to setup the stream, a call to fclose() is needed in order to free
the internal resources allocated.
If the stream has been set up using fdev_setup_stream() or FDEV_SETUP_-
STREAM(), use fdev_close() instead.
It currently always returns 0 (for success).
23.9.4.3 FILE∗fdevopen (int(∗)(char, FILE ∗)put, int(∗)(FILE ∗)get)
This function is a replacement for fopen().
It opens a stream for a device where the actual device implementation needs to be
provided by the application. If successful, a pointer to the structure for the opened
stream is returned. Reasons for a possible failure currently include that neither the
put nor the get argument have been provided, thus attempting to open a stream with
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23.9 <stdio.h>: Standard IO facilities 182
no IO intent at all, or that insufficient dynamic memory is available to establish a new
stream.
If the put function pointer is provided, the stream is opened with write intent. The
function passed as put shall take two arguments, the first a character to write to the
device, and the second a pointer to FILE, and shall return 0 if the output was successful,
and a nonzero value if the character could not be sent to the device.
If the get function pointer is provided, the stream is opened with read intent. The
function passed as get shall take a pointer to FILE as its single argument, and return
one character from the device, passed as an int type. If an error occurs when trying
to read from the device, it shall return _FDEV_ERR. If an end-of-file condition was
reached while reading from the device, _FDEV_EOF shall be returned.
If both functions are provided, the stream is opened with read and write intent.
The first stream opened with read intent is assigned to stdin, and the first one opened
with write intent is assigned to both, stdout and stderr.
fdevopen() uses calloc() (und thus malloc()) in order to allocate the storage for the new
stream.
Note
If the macro __STDIO_FDEVOPEN_COMPAT_12 is declared before including
<stdio.h>, a function prototype for fdevopen() will be chosen that is backwards
compatible with avr-libc version 1.2 and before. This is solely intented for pro-
viding a simple migration path without the need to immediately change all source
code. Do not use for new code.
23.9.4.4 int feof (FILE ∗__stream)
Test the end-of-file flag of stream. This flag can only be cleared by a call to
clearerr().
23.9.4.5 int ferror (FILE ∗__stream)
Test the error flag of stream. This flag can only be cleared by a call to clearerr().
23.9.4.6 int fflush (FILE ∗stream)
Flush stream.
This is a null operation provided for source-code compatibility only, as the standard IO
implementation currently does not perform any buffering.
23.9.4.7 int fgetc (FILE ∗__stream)
The function fgetc reads a character from stream. It
returns the character, or EOF in case end-of-file was encountered or an error occurred.
The routines feof() or ferror() must be used to distinguish between both situations.
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23.9 <stdio.h>: Standard IO facilities 183
23.9.4.8 char∗fgets (char ∗__str, int __size, FILE ∗__stream)
Read at most
size - 1 bytes from stream, until a newline character was encountered, and store
the characters in the buffer pointed to by str. Unless an error was encountered while
reading, the string will then be terminated with a NUL character.
If an error was encountered, the function returns NULL and sets the error flag of
stream, which can be tested using ferror(). Otherwise, a pointer to the string will
be returned.
23.9.4.9 int fprintf (FILE ∗__stream, const char ∗__fmt,...)
The function fprintf performs formatted output to stream. See vfprintf()
for details.
23.9.4.10 int fprintf_P (FILE ∗__stream, const char ∗__fmt,...)
Variant of fprintf() that uses a fmt string that resides in program memory.
23.9.4.11 int fputc (int __c, FILE ∗__stream)
The function fputc sends the character c(though given as type int) to stream. It
returns the character, or EOF in case an error occurred.
23.9.4.12 int fputs (const char ∗__str, FILE ∗__stream)
Write the string pointed to by str to stream stream.
Returns 0 on success and EOF on error.
23.9.4.13 int fputs_P (const char ∗__str, FILE ∗__stream)
Variant of fputs() where str resides in program memory.
23.9.4.14 size_t fread (void ∗__ptr, size_t __size, size_t __nmemb, FILE ∗
__stream)
Read nmemb objects, size bytes each, from stream, to the buffer pointed to by
ptr.
Returns the number of objects successfully read, i. e. nmemb unless an input error
occured or end-of-file was encountered. feof() and ferror() must be used to distinguish
between these two conditions.
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23.9 <stdio.h>: Standard IO facilities 184
23.9.4.15 int fscanf (FILE ∗__stream, const char ∗__fmt,...)
The function fscanf performs formatted input, reading the input data from
stream.
See vfscanf() for details.
23.9.4.16 int fscanf_P (FILE ∗__stream, const char ∗__fmt,...)
Variant of fscanf() using a fmt string in program memory.
23.9.4.17 size_t fwrite (const void ∗__ptr, size_t __size, size_t __nmemb, FILE
∗__stream)
Write nmemb objects, size bytes each, to stream. The first byte of the first object
is referenced by ptr.
Returns the number of objects successfully written, i. e. nmemb unless an output error
occured.
23.9.4.18 char∗gets (char ∗__str)
Similar to fgets() except that it will operate on stream stdin, and the
trailing newline (if any) will not be stored in the string. It is the caller’s responsibility
to provide enough storage to hold the characters read.
23.9.4.19 int printf (const char ∗__fmt,...)
The function printf performs formatted output to stream stdout. See
vfprintf() for details.
23.9.4.20 int printf_P (const char ∗__fmt,...)
Variant of printf() that uses a fmt string that resides in program memory.
23.9.4.21 int puts (const char ∗__str)
Write the string pointed to by str, and a trailing newline character, to stdout.
23.9.4.22 int puts_P (const char ∗__str)
Variant of puts() where str resides in program memory.
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23.9 <stdio.h>: Standard IO facilities 185
23.9.4.23 int scanf (const char ∗__fmt,...)
The function scanf performs formatted input from stream stdin.
See vfscanf() for details.
23.9.4.24 int scanf_P (const char ∗__fmt,...)
Variant of scanf() where fmt resides in program memory.
23.9.4.25 int snprintf (char ∗__s, size_t __n, const char ∗__fmt,...)
Like sprintf(), but instead of assuming sto be of infinite size, no more than n
characters (including the trailing NUL character) will be converted to s.
Returns the number of characters that would have been written to sif there were
enough space.
23.9.4.26 int snprintf_P (char ∗__s, size_t __n, const char ∗__fmt,...)
Variant of snprintf() that uses a fmt string that resides in program memory.
23.9.4.27 int sprintf (char ∗__s, const char ∗__fmt,...)
Variant of printf() that sends the formatted characters to string s.
23.9.4.28 int sprintf_P (char ∗__s, const char ∗__fmt,...)
Variant of sprintf() that uses a fmt string that resides in program memory.
23.9.4.29 int sscanf (const char ∗__buf, const char ∗__fmt,...)
The function sscanf performs formatted input, reading the input data from the
buffer pointed to by buf.
See vfscanf() for details.
23.9.4.30 int sscanf_P (const char ∗__buf, const char ∗__fmt,...)
Variant of sscanf() using a fmt string in program memory.
23.9.4.31 int ungetc (int __c, FILE ∗__stream)
The ungetc() function pushes the character c(converted to an unsigned char)
back onto the input stream pointed to by stream. The pushed-back character will be
returned by a subsequent read on the stream.
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23.9 <stdio.h>: Standard IO facilities 186
Currently, only a single character can be pushed back onto the stream.
The ungetc() function returns the character pushed back after the conversion, or EOF if
the operation fails. If the value of the argument ccharacter equals EOF, the operation
will fail and the stream will remain unchanged.
23.9.4.32 int vfprintf (FILE ∗__stream, const char ∗__fmt, va_list __ap)
vfprintf is the central facility of the printf family of functions. It
outputs values to stream under control of a format string passed in fmt. The actual
values to print are passed as a variable argument list ap.
vfprintf returns the number of characters written to stream, or EOF in case of
an error. Currently, this will only happen if stream has not been opened with write
intent.
The format string is composed of zero or more directives: ordinary characters (not
%), which are copied unchanged to the output stream; and conversion specifications,
each of which results in fetching zero or more subsequent arguments. Each conversion
specification is introduced by the %character. The arguments must properly correspond
(after type promotion) with the conversion specifier. After the %, the following appear
in sequence:
• Zero or more of the following flags:
–#The value should be converted to an "alternate form". For c, d, i, s, and
u conversions, this option has no effect. For o conversions, the precision of
the number is increased to force the first character of the output string to
a zero (except if a zero value is printed with an explicit precision of zero).
For x and X conversions, a non-zero result has the string ‘0x’ (or ‘0X’ for
X conversions) prepended to it.
–0(zero) Zero padding. For all conversions, the converted value is padded
on the left with zeros rather than blanks. If a precision is given with a
numeric conversion (d, i, o, u, i, x, and X), the 0 flag is ignored.
–-A negative field width flag; the converted value is to be left adjusted on
the field boundary. The converted value is padded on the right with blanks,
rather than on the left with blanks or zeros. A - overrides a 0 if both are
given.
–’ ’ (space) A blank should be left before a positive number produced by a
signed conversion (d, or i).
–+A sign must always be placed before a number produced by a signed
conversion. A + overrides a space if both are used.
• An optional decimal digit string specifying a minimum field width. If the con-
verted value has fewer characters than the field width, it will be padded with
spaces on the left (or right, if the left-adjustment flag has been given) to fill out
the field width.
• An optional precision, in the form of a period . followed by an optional digit
string. If the digit string is omitted, the precision is taken as zero. This gives the
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23.9 <stdio.h>: Standard IO facilities 187
minimum number of digits to appear for d, i, o, u, x, and X conversions, or the
maximum number of characters to be printed from a string for sconversions.
• An optional lor hlength modifier, that specifies that the argument for the d, i,
o, u, x, or X conversion is a "long int" rather than int. The his ignored,
as "short int" is equivalent to int.
• A character that specifies the type of conversion to be applied.
The conversion specifiers and their meanings are:
•diouxX The int (or appropriate variant) argument is converted to signed decimal
(d and i), unsigned octal (o), unsigned decimal (u), or unsigned hexadecimal
(x and X) notation. The letters "abcdef" are used for x conversions; the letters
"ABCDEF" are used for X conversions. The precision, if any, gives the minimum
number of digits that must appear; if the converted value requires fewer digits, it
is padded on the left with zeros.
•pThe void ∗argument is taken as an unsigned integer, and converted similarly
as a %#x command would do.
•cThe int argument is converted to an "unsigned char", and the resulting
character is written.
•sThe "char ∗"argument is expected to be a pointer to an array of character
type (pointer to a string). Characters from the array are written up to (but not
including) a terminating NUL character; if a precision is specified, no more than
the number specified are written. If a precision is given, no null character need
be present; if the precision is not specified, or is greater than the size of the array,
the array must contain a terminating NUL character.
•%A%is written. No argument is converted. The complete conversion specifica-
tion is "%%".
•eE The double argument is rounded and converted in the format
"[-]d.ddde±dd" where there is one digit before the decimal-point charac-
ter and the number of digits after it is equal to the precision; if the precision
is missing, it is taken as 6; if the precision is zero, no decimal-point character
appears. An Econversion uses the letter ’E’ (rather than ’e’) to introduce
the exponent. The exponent always contains two digits; if the value is zero, the
exponent is 00.
•fF The double argument is rounded and converted to decimal notation in the
format "[-]ddd.ddd", where the number of digits after the decimal-point
character is equal to the precision specification. If the precision is missing, it is
taken as 6; if the precision is explicitly zero, no decimal-point character appears.
If a decimal point appears, at least one digit appears before it.
•gG The double argument is converted in style for e(or For Efor Gconver-
sions). The precision specifies the number of significant digits. If the precision
is missing, 6 digits are given; if the precision is zero, it is treated as 1. Style eis
used if the exponent from its conversion is less than -4 or greater than or equal to
the precision. Trailing zeros are removed from the fractional part of the result; a
decimal point appears only if it is followed by at least one digit.
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23.9 <stdio.h>: Standard IO facilities 188
•SSimilar to the sformat, except the pointer is expected to point to a program-
memory (ROM) string instead of a RAM string.
In no case does a non-existent or small field width cause truncation of a numeric field;
if the result of a conversion is wider than the field width, the field is expanded to contain
the conversion result.
Since the full implementation of all the mentioned features becomes fairly large, three
different flavours of vfprintf() can be selected using linker options. The default vf-
printf() implements all the mentioned functionality except floating point conversions.
A minimized version of vfprintf() is available that only implements the very basic in-
teger and string conversion facilities, but only the #additional option can be specified
using conversion flags (these flags are parsed correctly from the format specification,
but then simply ignored). This version can be requested using the following compiler
options:
-Wl,-u,vfprintf -lprintf_min
If the full functionality including the floating point conversions is required, the follow-
ing options should be used:
-Wl,-u,vfprintf -lprintf_flt -lm
Limitations:
• The specified width and precision can be at most 255.
Notes:
• For floating-point conversions, if you link default or minimized version of
vfprintf(), the symbol ? will be output and double argument will be skiped.
So you output below will not be crashed. For default version the width field
and the "pad to left" ( symbol minus ) option will work in this case.
• The hh length modifier is ignored (char argument is promouted to int).
More exactly, this realization does not check the number of hsymbols.
• But the ll length modifier will to abort the output, as this realization does
not operate long long arguments.
• The variable width or precision field (an asterisk ∗symbol) is not realized
and will to abort the output.
23.9.4.33 int vfprintf_P (FILE ∗__stream, const char ∗__fmt, va_list __ap)
Variant of vfprintf() that uses a fmt string that resides in program memory.
23.9.4.34 int vfscanf (FILE ∗stream, const char ∗fmt, va_list ap)
Formatted input. This function is the heart of the scanf family of functions.
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23.9 <stdio.h>: Standard IO facilities 189
Characters are read from stream and processed in a way described by fmt. Conversion
results will be assigned to the parameters passed via ap.
The format string fmt is scanned for conversion specifications. Anything that doesn’t
comprise a conversion specification is taken as text that is matched literally against
the input. White space in the format string will match any white space in the data
(including none), all other characters match only itself. Processing is aborted as soon as
the data and format string no longer match, or there is an error or end-of-file condition
on stream.
Most conversions skip leading white space before starting the actual conversion.
Conversions are introduced with the character %. Possible options can follow the %:
• a ∗indicating that the conversion should be performed but the conversion result
is to be discarded; no parameters will be processed from ap,
• the character hindicating that the argument is a pointer to short int (rather
than int),
• the 2 characters hh indicating that the argument is a pointer to char (rather than
int).
• the character lindicating that the argument is a pointer to long int (rather
than int, for integer type conversions), or a pointer to double (for floating
point conversions),
In addition, a maximal field width may be specified as a nonzero positive decimal
integer, which will restrict the conversion to at most this many characters from the
input stream. This field width is limited to at most 255 characters which is also the
default value (except for the cconversion that defaults to 1).
The following conversion flags are supported:
•%Matches a literal %character. This is not a conversion.
•dMatches an optionally signed decimal integer; the next pointer must be a
pointer to int.
•iMatches an optionally signed integer; the next pointer must be a pointer to
int. The integer is read in base 16 if it begins with 0x or 0X, in base 8 if it
begins with 0, and in base 10 otherwise. Only characters that correspond to the
base are used.
•oMatches an octal integer; the next pointer must be a pointer to unsigned
int.
•uMatches an optionally signed decimal integer; the next pointer must be a
pointer to unsigned int.
•xMatches an optionally signed hexadecimal integer; the next pointer must be a
pointer to unsigned int.
•fMatches an optionally signed floating-point number; the next pointer must be
a pointer to float.
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23.9 <stdio.h>: Standard IO facilities 190
•e, g, F, E, G Equivalent to f.
•sMatches a sequence of non-white-space characters; the next pointer must be a
pointer to char, and the array must be large enough to accept all the sequence
and the terminating NUL character. The input string stops at white space or at the
maximum field width, whichever occurs first.
•cMatches a sequence of width count characters (default 1); the next pointer must
be a pointer to char, and there must be enough room for all the characters (no
terminating NUL is added). The usual skip of leading white space is suppressed.
To skip white space first, use an explicit space in the format.
• [ Matches a nonempty sequence of characters from the specified set of accepted
characters; the next pointer must be a pointer to char, and there must be enough
room for all the characters in the string, plus a terminating NUL character. The
usual skip of leading white space is suppressed. The string is to be made up
of characters in (or not in) a particular set; the set is defined by the characters
between the open bracket [ character and a close bracket ] character. The set
excludes those characters if the first character after the open bracket is a circum-
flex ∧. To include a close bracket in the set, make it the first character after the
open bracket or the circumflex; any other position will end the set. The hyphen
character -is also special; when placed between two other characters, it adds all
intervening characters to the set. To include a hyphen, make it the last character
before the final close bracket. For instance, [∧]0-9-] means the set of every-
thing except close bracket, zero through nine, and hyphen. The string ends with
the appearance of a character not in the (or, with a circumflex, in) set or when
the field width runs out. Note that usage of this conversion enlarges the stack
expense.
•pMatches a pointer value (as printed by pin printf()); the next pointer must be
a pointer to void.
•nNothing is expected; instead, the number of characters consumed thus far from
the input is stored through the next pointer, which must be a pointer to int. This
is not a conversion, although it can be suppressed with the ∗flag.
These functions return the number of input items assigned, which can be fewer than
provided for, or even zero, in the event of a matching failure. Zero indicates that, while
there was input available, no conversions were assigned; typically this is due to an
invalid input character, such as an alphabetic character for a dconversion. The value
EOF is returned if an input failure occurs before any conversion such as an end-of-file
occurs. If an error or end-of-file occurs after conversion has begun, the number of
conversions which were successfully completed is returned.
By default, all the conversions described above are available except the floating-point
conversions and the width is limited to 255 characters. The float-point conversion will
be available in the extended version provided by the library libscanf_flt.a. Also
in this case the width is not limited (exactly, it is limited to 65535 characters). To link
a program against the extended version, use the following compiler flags in the link
stage:
-Wl,-u,vfscanf -lscanf_flt -lm
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23.9 <stdio.h>: Standard IO facilities 191
A third version is available for environments that are tight on space. In addition to
the restrictions of the standard one, this version implements no %[ specification. This
version is provided in the library libscanf_min.a, and can be requested using the
following options in the link stage:
-Wl,-u,vfscanf -lscanf_min -lm
23.9.4.35 int vfscanf_P (FILE ∗__stream, const char ∗__fmt, va_list __ap)
Variant of vfscanf() using a fmt string in program memory.
23.9.4.36 int vprintf (const char ∗__fmt, va_list __ap)
The function vprintf performs formatted output to stream stdout, taking a
variable argument list as in vfprintf().
See vfprintf() for details.
23.9.4.37 int vscanf (const char ∗__fmt, va_list __ap)
The function vscanf performs formatted input from stream stdin, taking a
variable argument list as in vfscanf().
See vfscanf() for details.
23.9.4.38 int vsnprintf (char ∗__s, size_t __n, const char ∗__fmt, va_list ap)
Like vsprintf(), but instead of assuming sto be of infinite size, no more than n
characters (including the trailing NUL character) will be converted to s.
Returns the number of characters that would have been written to sif there were
enough space.
23.9.4.39 int vsnprintf_P (char ∗__s, size_t __n, const char ∗__fmt, va_list ap)
Variant of vsnprintf() that uses a fmt string that resides in program memory.
23.9.4.40 int vsprintf (char ∗__s, const char ∗__fmt, va_list ap)
Like sprintf() but takes a variable argument list for the arguments.
23.9.4.41 int vsprintf_P (char ∗__s, const char ∗__fmt, va_list ap)
Variant of vsprintf() that uses a fmt string that resides in program memory.
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23.10 <stdlib.h>: General utilities 192
23.10 <stdlib.h>: General utilities
Data Structures
• struct div_t
• struct ldiv_t
Defines
• #define RAND_MAX 0x7FFF
Typedefs
• typedef int(∗__compar_fn_t )(const void ∗, const void ∗)
Functions
• void abort (void) __ATTR_NORETURN__
• int abs (int __i)
• long labs (long __i)
• void ∗bsearch (const void ∗__key, const void ∗__base, size_t __nmemb, size_t
__size, int(∗__compar)(const void ∗, const void ∗))
•div_t div (int __num, int __denom) __asm__("__divmodhi4")
•ldiv_t ldiv (long __num, long __denom) __asm__("__divmodsi4")
• void qsort (void ∗__base, size_t __nmemb, size_t __size, __compar_fn_t __-
compar)
• long strtol (const char ∗__nptr, char ∗∗__endptr, int __base)
• unsigned long strtoul (const char ∗__nptr, char ∗∗__endptr, int __base)
• long atol (const char ∗__s) __ATTR_PURE__
• int atoi (const char ∗__s) __ATTR_PURE__
• void exit (int __status) __ATTR_NORETURN__
• void ∗malloc (size_t __size) __ATTR_MALLOC__
• void free (void ∗__ptr)
• void ∗calloc (size_t __nele, size_t __size) __ATTR_MALLOC__
• void ∗realloc (void ∗__ptr, size_t __size) __ATTR_MALLOC__
• double strtod (const char ∗__nptr, char ∗∗__endptr)
• double atof (const char ∗__nptr)
• int rand (void)
• void srand (unsigned int __seed)
• int rand_r (unsigned long ∗__ctx)
Variables
• size_t __malloc_margin
• char ∗__malloc_heap_start
• char ∗__malloc_heap_end
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23.10 <stdlib.h>: General utilities 193
Non-standard (i.e. non-ISO C) functions.
• char ∗ltoa (long val, char ∗s, int radix)
• char ∗utoa (unsigned int val, char ∗s, int radix)
• char ∗ultoa (unsigned long val, char ∗s, int radix)
• long random (void)
• void srandom (unsigned long __seed)
• long random_r (unsigned long ∗__ctx)
• char ∗itoa (int val, char ∗s, int radix)
• #define RANDOM_MAX 0x7FFFFFFF
Conversion functions for double arguments.
Note that these functions are not located in the default library, libc.a, but in the
mathematical library, libm.a. So when linking the application, the -lm option needs
to be specified.
• char ∗dtostre (double __val, char ∗__s, unsigned char __prec, unsigned char
__flags)
• char ∗dtostrf (double __val, signed char __width, unsigned char __prec, char
∗__s)
• #define DTOSTR_ALWAYS_SIGN 0x01
• #define DTOSTR_PLUS_SIGN 0x02
• #define DTOSTR_UPPERCASE 0x04
• #define EXIT_SUCCESS 0
• #define EXIT_FAILURE 1
23.10.1 Detailed Description
#include <stdlib.h>
This file declares some basic C macros and functions as defined by the ISO standard,
plus some AVR-specific extensions.
23.10.2 Define Documentation
23.10.2.1 #define DTOSTR_ALWAYS_SIGN 0x01
Bit value that can be passed in flags to dtostre().
23.10.2.2 #define DTOSTR_PLUS_SIGN 0x02
Bit value that can be passed in flags to dtostre().
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23.10 <stdlib.h>: General utilities 194
23.10.2.3 #define DTOSTR_UPPERCASE 0x04
Bit value that can be passed in flags to dtostre().
23.10.2.4 #define EXIT_FAILURE 1
Unsuccessful termination for exit(); evaluates to a non-zero value.
23.10.2.5 #define EXIT_SUCCESS 0
Successful termination for exit(); evaluates to 0.
23.10.2.6 #define RAND_MAX 0x7FFF
Highest number that can be generated by rand().
23.10.2.7 #define RANDOM_MAX 0x7FFFFFFF
Highest number that can be generated by random().
23.10.3 Typedef Documentation
23.10.3.1 typedef int(∗__compar_fn_t)(const void ∗, const void ∗)
Comparision function type for qsort(), just for convenience.
23.10.4 Function Documentation
23.10.4.1 void abort (void)
The abort() function causes abnormal program termination to
occur. This realization disables interrupts and jumps to _exit() function with argument
equal to 1. In the limited AVR environment, execution is effectively halted by entering
an infinite loop.
23.10.4.2 int abs (int __i)
The abs() function computes the absolute value of the integer i.
Note
The abs() and labs() functions are builtins of gcc.
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23.10 <stdlib.h>: General utilities 195
23.10.4.3 double atof (const char ∗nptr)
The atof() function converts the initial portion of the string pointed to by nptr to
double representation.
It is equivalent to calling
strtod(nptr, (char **)0);
23.10.4.4 int atoi (const char ∗s)
Convert a string to an integer.
The atoi() function converts the initial portion of the string pointed to by sto integer
representation. In contrast to
(int)strtol(s, (char **)NULL, 10);
this function does not detect overflow (errno is not changed and the result value is
not predictable), uses smaller memory (flash and stack) and works more quickly.
23.10.4.5 long atol (const char ∗s)
Convert a string to a long integer.
The atol() function converts the initial portion of the string pointed to by sto long
integer representation. In contrast to
strtol(s, (char **)NULL, 10);
this function does not detect overflow (errno is not changed and the result value is
not predictable), uses smaller memory (flash and stack) and works more quickly.
23.10.4.6 void∗bsearch (const void ∗__key, const void ∗__base, size_t
__nmemb, size_t __size, int(∗)(const void ∗, const void ∗)__compar)
The bsearch() function searches an array of nmemb objects, the initial member of
which is pointed to by base, for a member that matches the object pointed to by key.
The size of each member of the array is specified by size.
The contents of the array should be in ascending sorted order according to the compar-
ison function referenced by compar. The compar routine is expected to have two
arguments which point to the key object and to an array member, in that order, and
should return an integer less than, equal to, or greater than zero if the key object is
found, respectively, to be less than, to match, or be greater than the array member.
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23.10 <stdlib.h>: General utilities 196
The bsearch() function returns a pointer to a matching member of the array, or a null
pointer if no match is found. If two members compare as equal, which member is
matched is unspecified.
23.10.4.7 void∗calloc (size_t __nele, size_t __size)
Allocate nele elements of size each. Identical to calling malloc() using nele
∗size as argument, except the allocated memory will be cleared to zero.
23.10.4.8 div_t div (int __num, int __denom)
The div() function computes the value num/denom
and returns the quotient and remainder in a structure named div_t that contains two
int members named quot and rem.
23.10.4.9 char∗dtostre (double __val, char ∗__s, unsigned char __prec,
unsigned char __flags)
The dtostre() function converts
the double value passed in val into an ASCII representation that will be stored under
s. The caller is responsible for providing sufficient storage in s.
Conversion is done in the format "[-]d.ddde±dd" where there is one digit before
the decimal-point character and the number of digits after it is equal to the precision
prec; if the precision is zero, no decimal-point character appears. If flags has
the DTOSTR_UPPERCASE bit set, the letter ’E’ (rather than ’e’ ) will be used to
introduce the exponent. The exponent always contains two digits; if the value is zero,
the exponent is "00".
If flags has the DTOSTR_ALWAYS_SIGN bit set, a space character will be placed
into the leading position for positive numbers.
If flags has the DTOSTR_PLUS_SIGN bit set, a plus sign will be used instead of a
space character in this case.
The dtostre() function returns the pointer to the converted string s.
23.10.4.10 char∗dtostrf (double __val, signed char __width, unsigned char
__prec, char ∗__s)
The dtostrf() function converts the double value passed in
val into an ASCII representationthat will be stored under s. The caller is responsible
for providing sufficient storage in s.
Conversion is done in the format "[-]d.ddd". The minimum field width of the
output string (including the possible ’.’ and the possible sign for negative values) is
given in width, and prec determines the number of digits after the decimal sign.
width is signed value, negative for left adjustment.
The dtostrf() function returns the pointer to the converted string s.
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23.10 <stdlib.h>: General utilities 197
23.10.4.11 void exit (int __status)
The exit() function terminates the application. Since there
is no environment to return to, status is ignored, and code execution will eventually
reach an infinite loop, thereby effectively halting all code processing. Before entering
the infinite loop, interrupts are globally disabled.
In a C++ context, global destructors will be called before halting execution.
23.10.4.12 void free (void ∗__ptr)
The free() function causes the allocated memory referenced by ptr to be made
available for future allocations. If ptr is NULL, no action occurs.
23.10.4.13 char∗itoa (int val, char ∗s, int radix)
Convert an integer to a string.
The function itoa() converts the integer value from val into an ASCII representation
that will be stored under s. The caller is responsible for providing sufficient storage in
s.
Note
The minimal size of the buffer sdepends on the choice of radix. For example, if
the radix is 2 (binary), you need to supply a buffer with a minimal length of 8 ∗
sizeof (int) + 1 characters, i.e. one character for each bit plus one for the string
terminator. Using a larger radix will require a smaller minimal buffer size.
Warning
If the buffer is too small, you risk a buffer overflow.
Conversion is done using the radix as base, which may be a number between 2
(binary conversion) and up to 36. If radix is greater than 10, the next digit after
’9’ will be the letter ’a’.
If radix is 10 and val is negative, a minus sign will be prepended.
The itoa() function returns the pointer passed as s.
23.10.4.14 long labs (long __i)
The labs() function computes the absolute value of the long integer i.
Note
The abs() and labs() functions are builtins of gcc.
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23.10 <stdlib.h>: General utilities 198
23.10.4.15 ldiv_t ldiv (long __num, long __denom)
The ldiv() function
computes the value num/denom and returns the quotient and remainder in a structure
named ldiv_t that contains two long integer members named quot and rem.
23.10.4.16 char∗ltoa (long val, char ∗s, int radix)
Convert a long integer to a string.
The function ltoa() converts the long integer value from val into an ASCII represen-
tation that will be stored under s. The caller is responsible for providing sufficient
storage in s.
Note
The minimal size of the buffer sdepends on the choice of radix. For example,
if the radix is 2 (binary), you need to supply a buffer with a minimal length of 8
∗sizeof (long int) + 1 characters, i.e. one character for each bit plus one for the
string terminator. Using a larger radix will require a smaller minimal buffer size.
Warning
If the buffer is too small, you risk a buffer overflow.
Conversion is done using the radix as base, which may be a number between 2
(binary conversion) and up to 36. If radix is greater than 10, the next digit after
’9’ will be the letter ’a’.
If radix is 10 and val is negative, a minus sign will be prepended.
The ltoa() function returns the pointer passed as s.
23.10.4.17 void∗malloc (size_t __size)
The malloc() function allocates size bytes of memory. If malloc() fails, a NULL
pointer is returned.
Note that malloc() does not initialize the returned memory to zero bytes.
See the chapter about malloc() usage for implementation details.
23.10.4.18 void qsort (void ∗__base, size_t __nmemb, size_t __size,
__compar_fn_t __compar)
The qsort() function is a modified partition-exchange sort, or quicksort.
The qsort() function sorts an array of nmemb objects, the initial member of which is
pointed to by base. The size of each object is specified by size. The contents of the
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array base are sorted in ascending order according to a comparison function pointed to
by compar, which requires two arguments pointing to the objects being compared.
The comparison function must return an integer less than, equal to, or greater than zero
if the first argument is considered to be respectively less than, equal to, or greater than
the second.
23.10.4.19 int rand (void)
The rand() function computes a sequence of pseudo-random integers in the range of 0
to RAND_MAX (as defined by the header file <stdlib.h>).
The srand() function sets its argument seed as the seed for a new sequence of pseudo-
random numbers to be returned by rand(). These sequences are repeatable by calling
srand() with the same seed value.
If no seed value is provided, the functions are automatically seeded with a value of 1.
In compliance with the C standard, these functions operate on int arguments. Since
the underlying algorithm already uses 32-bit calculations, this causes a loss of preci-
sion. See random() for an alternate set of functions that retains full 32-bit precision.
23.10.4.20 int rand_r (unsigned long ∗__ctx)
Variant of rand() that stores the context in the user-supplied variable located at ctx
instead of a static library variable so the function becomes re-entrant.
23.10.4.21 long random (void)
The random() function computes a sequence of pseudo-random integers in the range
of 0 to RANDOM_MAX (as defined by the header file <stdlib.h>).
The srandom() function sets its argument seed as the seed for a new sequence of
pseudo-random numbers to be returned by rand(). These sequences are repeatable by
calling srandom() with the same seed value.
If no seed value is provided, the functions are automatically seeded with a value of 1.
23.10.4.22 long random_r (unsigned long ∗__ctx)
Variant of random() that stores the context in the user-supplied variable located at
ctx instead of a static library variable so the function becomes re-entrant.
23.10.4.23 void∗realloc (void ∗__ptr, size_t __size)
The realloc() function tries to change the size of the region allocated at ptr to the
new size value. It returns a pointer to the new region. The returned pointer might be
the same as the old pointer, or a pointer to a completely different region.
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23.10 <stdlib.h>: General utilities 200
The contents of the returned region up to either the old or the new size value (whatever
is less) will be identical to the contents of the old region, even in case a new region had
to be allocated.
It is acceptable to pass ptr as NULL, in which case realloc() will behave identical to
malloc().
If the new memory cannot be allocated, realloc() returns NULL, and the region at ptr
will not be changed.
23.10.4.24 void srand (unsigned int __seed)
Pseudo-random number generator seeding; see rand().
23.10.4.25 void srandom (unsigned long __seed)
Pseudo-random number generator seeding; see random().
23.10.4.26 double strtod (const char ∗nptr, char ∗∗ endptr)
The strtod() function converts the initial portion of the string pointed to by nptr to
double representation.
The expected form of the string is an optional plus ( ’+’ ) or minus sign ( ’-’ )
followed by a sequence of digits optionally containing a decimal-point character, op-
tionally followed by an exponent. An exponent consists of an ’E’ or ’e’, followed
by an optional plus or minus sign, followed by a sequence of digits.
Leading white-space characters in the string are skipped.
The strtod() function returns the converted value, if any.
If endptr is not NULL, a pointer to the character after the last character used in the
conversion is stored in the location referenced by endptr.
If no conversion is performed, zero is returned and the value of nptr is stored in the
location referenced by endptr.
If the correct value would cause overflow, plus or minus INFINITY is returned (ac-
cording to the sign of the value), and ERANGE is stored in errno. If the correct value
would cause underflow, zero is returned and ERANGE is stored in errno.
23.10.4.27 long strtol (const char ∗__nptr, char ∗∗ __endptr, int __base)
The strtol() function converts the string in nptr to a long value. The conversion is
done according to the given base, which must be between 2 and 36 inclusive, or be the
special value 0.
The string may begin with an arbitrary amount of white space (as determined by iss-
pace()) followed by a single optional ’+’ or ’-’ sign. If base is zero or 16, the string
may then include a "0x" prefix, and the number will be read in base 16; otherwise, a
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23.10 <stdlib.h>: General utilities 201
zero base is taken as 10 (decimal) unless the next character is ’0’, in which case it is
taken as 8 (octal).
The remainder of the string is converted to a long value in the obvious manner, stopping
at the first character which is not a valid digit in the given base. (In bases above 10, the
letter ’A’ in either upper or lower case represents 10, ’B’ represents 11, and so forth,
with ’Z’ representing 35.)
If endptr is not NULL, strtol() stores the address of the first invalid character in
∗endptr. If there were no digits at all, however, strtol() stores the original value of
nptr in endptr. (Thus, if ∗nptr is not ’\0’ but ∗∗endptr is ’\0’ on return, the
entire string was valid.)
The strtol() function returns the result of the conversion, unless the value would under-
flow or overflow. If no conversion could be performed, 0 is returned. If an overflow or
underflow occurs, errno is set to ERANGE and the function return value is clamped
to LONG_MIN or LONG_MAX, respectively.
23.10.4.28 unsigned long strtoul (const char ∗__nptr, char ∗∗ __endptr, int
__base)
The strtoul() function converts the string in nptr to an
unsigned long value. The conversion is done according to the given base, which must
be between 2 and 36 inclusive, or be the special value 0.
The string may begin with an arbitrary amount of white space (as determined by iss-
pace()) followed by a single optional ’+’ or ’-’ sign. If base is zero or 16, the string
may then include a "0x" prefix, and the number will be read in base 16; otherwise, a
zero base is taken as 10 (decimal) unless the next character is ’0’, in which case it is
taken as 8 (octal).
The remainder of the string is converted to an unsigned long value in the obvious
manner, stopping at the first character which is not a valid digit in the given base.
(In bases above 10, the letter ’A’ in either upper or lower case represents 10, ’B’
represents 11, and so forth, with ’Z’ representing 35.)
If endptr is not NULL, strtoul() stores the address of the first invalid character in
∗endptr. If there were no digits at all, however, strtoul() stores the original value of
nptr in endptr. (Thus, if ∗nptr is not ’\0’ but ∗∗endptr is ’\0’ on return, the
entire string was valid.)
The strtoul() function return either the result of the conversion or, if there was a lead-
ing minus sign, the negation of the result of the conversion, unless the original (non-
negated) value would overflow; in the latter case, strtoul() returns ULONG_MAX, and
errno is set to ERANGE. If no conversion could be performed, 0 is returned.
23.10.4.29 char∗ultoa (unsigned long val, char ∗s, int radix)
Convert an unsigned long integer to a string.
The function ultoa() converts the unsigned long integer value from val into an ASCII
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23.10 <stdlib.h>: General utilities 202
representation that will be stored under s. The caller is responsible for providing suf-
ficient storage in s.
Note
The minimal size of the buffer sdepends on the choice of radix. For example, if
the radix is 2 (binary), you need to supply a buffer with a minimal length of 8 ∗
sizeof (unsigned long int) + 1 characters, i.e. one character for each bit plus one
for the string terminator. Using a larger radix will require a smaller minimal buffer
size.
Warning
If the buffer is too small, you risk a buffer overflow.
Conversion is done using the radix as base, which may be a number between 2
(binary conversion) and up to 36. If radix is greater than 10, the next digit after
’9’ will be the letter ’a’.
The ultoa() function returns the pointer passed as s.
23.10.4.30 char∗utoa (unsigned int val, char ∗s, int radix)
Convert an unsigned integer to a string.
The function utoa() converts the unsigned integer value from val into an ASCII repre-
sentation that will be stored under s. The caller is responsible for providing sufficient
storage in s.
Note
The minimal size of the buffer sdepends on the choice of radix. For example, if
the radix is 2 (binary), you need to supply a buffer with a minimal length of 8 ∗
sizeof (unsigned int) + 1 characters, i.e. one character for each bit plus one for the
string terminator. Using a larger radix will require a smaller minimal buffer size.
Warning
If the buffer is too small, you risk a buffer overflow.
Conversion is done using the radix as base, which may be a number between 2
(binary conversion) and up to 36. If radix is greater than 10, the next digit after
’9’ will be the letter ’a’.
The utoa() function returns the pointer passed as s.
23.10.5 Variable Documentation
23.10.5.1 char∗__malloc_heap_end
malloc() tunable.
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23.10.5.2 char∗__malloc_heap_start
malloc() tunable.
23.10.5.3 size_t __malloc_margin
malloc() tunable.
23.11 <string.h>: Strings
Defines
• #define _FFS(x)
Functions
• int ffs (int __val)
• int ffsl (long __val)
• __extension__ int ffsll (long long __val)
• void ∗memccpy (void ∗, const void ∗, int, size_t)
• void ∗memchr (const void ∗, int, size_t) __ATTR_PURE__
• int memcmp (const void ∗, const void ∗, size_t) __ATTR_PURE__
• void ∗memcpy (void ∗, const void ∗, size_t)
• void ∗memmem (const void ∗, size_t, const void ∗, size_t) __ATTR_PURE__
• void ∗memmove (void ∗, const void ∗, size_t)
• void ∗memrchr (const void ∗, int, size_t) __ATTR_PURE__
• void ∗memset (void ∗, int, size_t)
• char ∗strcat (char ∗, const char ∗)
• char ∗strchr (const char ∗, int) __ATTR_PURE__
• char ∗strchrnul (const char ∗, int) __ATTR_PURE__
• int strcmp (const char ∗, const char ∗) __ATTR_PURE__
• char ∗strcpy (char ∗, const char ∗)
• int strcasecmp (const char ∗, const char ∗) __ATTR_PURE__
• char ∗strcasestr (const char ∗, const char ∗) __ATTR_PURE__
• size_t strcspn (const char ∗__s, const char ∗__reject) __ATTR_PURE__
• char ∗strdup (const char ∗s1)
• size_t strlcat (char ∗, const char ∗, size_t)
• size_t strlcpy (char ∗, const char ∗, size_t)
• size_t strlen (const char ∗) __ATTR_PURE__
• char ∗strlwr (char ∗)
• char ∗strncat (char ∗, const char ∗, size_t)
• int strncmp (const char ∗, const char ∗, size_t) __ATTR_PURE__
• char ∗strncpy (char ∗, const char ∗, size_t)
• int strncasecmp (const char ∗, const char ∗, size_t) __ATTR_PURE__
• size_t strnlen (const char ∗, size_t) __ATTR_PURE__
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• char ∗strpbrk (const char ∗__s, const char ∗__accept) __ATTR_PURE__
• char ∗strrchr (const char ∗, int) __ATTR_PURE__
• char ∗strrev (char ∗)
• char ∗strsep (char ∗∗, const char ∗)
• size_t strspn (const char ∗__s, const char ∗__accept) __ATTR_PURE__
• char ∗strstr (const char ∗, const char ∗) __ATTR_PURE__
• char ∗strtok (char ∗, const char ∗)
• char ∗strtok_r (char ∗, const char ∗, char ∗∗)
• char ∗strupr (char ∗)
23.11.1 Detailed Description
#include <string.h>
The string functions perform string operations on NULL terminated strings.
Note
If the strings you are working on resident in program space (flash), you will need to
use the string functions described in <avr/pgmspace.h>: Program Space Utilities.
23.11.2 Define Documentation
23.11.2.1 #define _FFS(x)
This macro finds the first (least significant) bit set in the input value.
This macro is very similar to the function ffs() except that it evaluates its argument at
compile-time, so it should only be applied to compile-time constant expressions where
it will reduce to a constant itself. Application of this macro to expressions that are not
constant at compile-time is not recommended, and might result in a huge amount of
code generated.
Returns
The _FFS() macro returns the position of the first (least significant) bit set in the
word val, or 0 if no bits are set. The least significant bit is position 1. Only 16 bits
of argument are evaluted.
23.11.3 Function Documentation
23.11.3.1 int ffs (int val)
This function finds the first (least significant) bit set in the input value.
Returns
The ffs() function returns the position of the first (least significant) bit set in the
word val, or 0 if no bits are set. The least significant bit is position 1.
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Note
For expressions that are constant at compile time, consider using the _FFS macro
instead.
23.11.3.2 int ffsl (long __val)
Same as ffs(), for an argument of type long.
23.11.3.3 int ffsll (long long __val)
Same as ffs(), for an argument of type long long.
23.11.3.4 void ∗memccpy (void ∗dest, const void ∗src, int val, size_t len)
Copy memory area.
The memccpy() function copies no more than len bytes from memory area src to
memory area dest, stopping when the character val is found.
Returns
The memccpy() function returns a pointer to the next character in dest after val,
or NULL if val was not found in the first len characters of src.
23.11.3.5 void ∗memchr (const void ∗src, int val, size_t len)
Scan memory for a character.
The memchr() function scans the first len bytes of the memory area pointed to by src
for the character val. The first byte to match val (interpreted as an unsigned character)
stops the operation.
Returns
The memchr() function returns a pointer to the matching byte or NULL if the
character does not occur in the given memory area.
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23.11.3.6 int memcmp (const void ∗s1, const void ∗s2, size_t len)
Compare memory areas.
The memcmp() function compares the first len bytes of the memory areas s1 and s2.
The comparision is performed using unsigned char operations.
Returns
The memcmp() function returns an integer less than, equal to, or greater than zero
if the first len bytes of s1 is found, respectively, to be less than, to match, or be
greater than the first len bytes of s2.
Note
Be sure to store the result in a 16 bit variable since you may get incorrect results if
you use an unsigned char or char due to truncation.
Warning
This function is not -mint8 compatible, although if you only care about testing for
equality, this function should be safe to use.
23.11.3.7 void ∗memcpy (void ∗dest, const void ∗src, size_t len)
Copy a memory area.
The memcpy() function copies len bytes from memory area src to memory area dest.
The memory areas may not overlap. Use memmove() if the memory areas do overlap.
Returns
The memcpy() function returns a pointer to dest.
23.11.3.8 void ∗memmem (const void ∗s1, size_t len1, const void ∗s2, size_t
len2)
The memmem() function finds the start of the first occurrence of the substring s2 of
length len2 in the memory area s1 of length len1.
Returns
The memmem() function returns a pointer to the beginning of the substring, or
NULL if the substring is not found. If len2 is zero, the function returns s1.
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23.11.3.9 void ∗memmove (void ∗dest, const void ∗src, size_t len)
Copy memory area.
The memmove() function copies len bytes from memory area src to memory area dest.
The memory areas may overlap.
Returns
The memmove() function returns a pointer to dest.
23.11.3.10 void ∗memrchr (const void ∗src, int val, size_t len)
The memrchr() function is like the memchr() function, except that it searches
backwards from the end of the len bytes pointed to by src instead of forwards from
the front. (Glibc, GNU extension.)
Returns
The memrchr() function returns a pointer to the matching byte or NULL if the
character does not occur in the given memory area.
23.11.3.11 void ∗memset (void ∗dest, int val, size_t len)
Fill memory with a constant byte.
The memset() function fills the first len bytes of the memory area pointed to by dest
with the constant byte val.
Returns
The memset() function returns a pointer to the memory area dest.
23.11.3.12 int strcasecmp (const char ∗s1, const char ∗s2)
Compare two strings ignoring case.
The strcasecmp() function compares the two strings s1 and s2, ignoring the case of
the characters.
Returns
The strcasecmp() function returns an integer less than, equal to, or greater than
zero if s1 is found, respectively, to be less than, to match, or be greater than
s2. A consequence of the ordering used by strcasecmp() is that if s1 is an initial
substring of s2, then s1 is considered to be "less than" s2.
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23.11.3.13 char ∗strcasestr (const char ∗s1, const char ∗s2)
The strcasestr() function finds the first occurrence of the substring s2 in the string
s1. This is like strstr(), except that it ignores case of alphabetic symbols in searching
for the substring. (Glibc, GNU extension.)
Returns
The strcasestr() function returns a pointer to the beginning of the substring, or
NULL if the substring is not found. If s2 points to a string of zero length, the
function returns s1.
23.11.3.14 char ∗strcat (char ∗dest, const char ∗src)
Concatenate two strings.
The strcat() function appends the src string to the dest string overwriting the ’\0’ char-
acter at the end of dest, and then adds a terminating ’\0’ character. The strings may not
overlap, and the dest string must have enough space for the result.
Returns
The strcat() function returns a pointer to the resulting string dest.
23.11.3.15 char ∗strchr (const char ∗src, int val)
Locate character in string.
The strchr() function returns a pointer to the first occurrence of the character val in
the string src.
Here "character" means "byte" - these functions do not work with wide or multi-byte
characters.
Returns
The strchr() function returns a pointer to the matched character or NULL if the
character is not found.
23.11.3.16 char ∗strchrnul (const char ∗s, int c)
The strchrnul() function is like strchr() except that if cis not found
in s, then it returns a pointer to the null byte at the end of s, rather than NULL. (Glibc,
GNU extension.)
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Returns
The strchrnul() function returns a pointer to the matched character, or a pointer to
the null byte at the end of s(i.e., s+strlen(s)) if the character is not found.
23.11.3.17 int strcmp (const char ∗s1, const char ∗s2)
Compare two strings.
The strcmp() function compares the two strings s1 and s2.
Returns
The strcmp() function returns an integer less than, equal to, or greater than zero
if s1 is found, respectively, to be less than, to match, or be greater than s2. A
consequence of the ordering used by strcmp() is that if s1 is an initial substring of
s2, then s1 is considered to be "less than" s2.
23.11.3.18 char ∗strcpy (char ∗dest, const char ∗src)
Copy a string.
The strcpy() function copies the string pointed to by src (including the terminating
’\0’ character) to the array pointed to by dest. The strings may not overlap, and the
destination string dest must be large enough to receive the copy.
Returns
The strcpy() function returns a pointer to the destination string dest.
Note
If the destination string of a strcpy() is not large enough (that is, if the programmer
was stupid/lazy, and failed to check the size before copying) then anything might
happen. Overflowing fixed length strings is a favourite cracker technique.
23.11.3.19 size_t strcspn (const char ∗s, const char ∗reject)
The strcspn() function calculates the length of the initial segment of swhich consists
entirely of characters not in reject.
Returns
The strcspn() function returns the number of characters in the initial segment of s
which are not in the string reject. The terminating zero is not considered as a
part of string.
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23.11.3.20 char ∗strdup (const char ∗s1)
Duplicate a string.
The strdup() function allocates memory and copies into it the string addressed by s1,
including the terminating null character.
Warning
The strdup() function calls malloc() to allocate the memory for the duplicated
string! The user is responsible for freeing the memory by calling free().
Returns
The strdup() function returns a pointer to the resulting string dest. If malloc()
cannot allocate enough storage for the string, strdup() will return NULL.
Warning
Be sure to check the return value of the strdup() function to make sure that the
function has succeeded in allocating the memory!
23.11.3.21 size_t strlcat (char ∗dst, const char ∗src, size_t siz)
Concatenate two strings.
Appends src to string dst of size siz (unlike strncat(),siz is the full size of dst,
not space left). At most siz-1 characters will be copied. Always NULL terminates
(unless siz <=strlen(dst)).
Returns
The strlcat() function returns strlen(src) + MIN(siz, strlen(initial dst)). If retval >=
siz, truncation occurred.
Appends src to string dst of size siz (unlike strncat(), siz is the full size of dst, not space
left). At most siz-1 characters will be copied. Always NULL terminates (unless siz <=
strlen(dst)).
Returns
The strlcat() function returns strlen(src) + MIN(siz, strlen(initial dst)). If retval >=
siz, truncation occurred.
23.11.3.22 size_t strlcpy (char ∗dst, const char ∗src, size_t siz)
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Copy a string.
Copy src to string dst of size siz. At most siz-1 characters will be copied.
Always NULL terminates (unless siz == 0).
Returns
The strlcpy() function returns strlen(src). If retval >= siz, truncation occurred.
Copy src to string dst of size siz. At most siz-1 characters will be copied. Always
NULL terminates (unless siz == 0).
Returns
The strlcpy() function returns strlen(src). If retval >= siz, truncation occurred.
23.11.3.23 size_t strlen (const char ∗src)
Calculate the length of a string.
The strlen() function calculates the length of the string src, not including the terminat-
ing ’\0’ character.
Returns
The strlen() function returns the number of characters in src.
23.11.3.24 char ∗strlwr (char ∗s)
Convert a string to lower case.
The strlwr() function will convert a string to lower case. Only the upper case alphabetic
characters [A .. Z] are converted. Non-alphabetic characters will not be changed.
Returns
The strlwr() function returns a pointer to the converted string.
23.11.3.25 int strncasecmp (const char ∗s1, const char ∗s2, size_t len)
Compare two strings ignoring case.
The strncasecmp() function is similar to strcasecmp(), except it only compares the first
len characters of s1.
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Returns
The strncasecmp() function returns an integer less than, equal to, or greater than
zero if s1 (or the first len bytes thereof) is found, respectively, to be less than, to
match, or be greater than s2. A consequence of the ordering used by strncasecmp()
is that if s1 is an initial substring of s2, then s1 is considered to be "less than"
s2.
23.11.3.26 char ∗strncat (char ∗dest, const char ∗src, size_t len)
Concatenate two strings.
The strncat() function is similar to strcat(), except that only the first n characters of src
are appended to dest.
Returns
The strncat() function returns a pointer to the resulting string dest.
23.11.3.27 int strncmp (const char ∗s1, const char ∗s2, size_t len)
Compare two strings.
The strncmp() function is similar to strcmp(), except it only compares the first (at most)
n characters of s1 and s2.
Returns
The strncmp() function returns an integer less than, equal to, or greater than zero
if s1 (or the first n bytes thereof) is found, respectively, to be less than, to match,
or be greater than s2.
23.11.3.28 char ∗strncpy (char ∗dest, const char ∗src, size_t len)
Copy a string.
The strncpy() function is similar to strcpy(), except that not more than n bytes of src
are copied. Thus, if there is no null byte among the first n bytes of src, the result will
not be null-terminated.
In the case where the length of src is less than that of n, the remainder of dest will be
padded with nulls.
Returns
The strncpy() function returns a pointer to the destination string dest.
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23.11 <string.h>: Strings 213
23.11.3.29 size_t strnlen (const char ∗src, size_t len)
Determine the length of a fixed-size string.
The strnlen function returns the number of characters in the string pointed to by src, not
including the terminating ’\0’ character, but at most len. In doing this, strnlen looks
only at the first len characters at src and never beyond src+len.
Returns
The strnlen function returns strlen(src), if that is less than len, or len if there is no
’\0’ character among the first len characters pointed to by src.
23.11.3.30 char ∗strpbrk (const char ∗s, const char ∗accept)
The strpbrk() function locates the first occurrence in the string sof any of the
characters in the string accept.
Returns
The strpbrk() function returns a pointer to the character in sthat matches one of
the characters in accept, or NULL if no such character is found. The terminating
zero is not considered as a part of string: if one or both args are empty, the result
will be NULL.
23.11.3.31 char ∗strrchr (const char ∗src, int val)
Locate character in string.
The strrchr() function returns a pointer to the last occurrence of the character val in the
string src.
Here "character" means "byte" - these functions do not work with wide or multi-byte
characters.
Returns
The strrchr() function returns a pointer to the matched character or NULL if the
character is not found.
23.11.3.32 char ∗strrev (char ∗s)
Reverse a string.
The strrev() function reverses the order of the string.
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23.11 <string.h>: Strings 214
Returns
The strrev() function returns a pointer to the beginning of the reversed string.
23.11.3.33 char ∗strsep (char ∗∗ sp, const char ∗delim)
Parse a string into tokens.
The strsep() function locates, in the string referenced by ∗sp, the first occurrence of
any character in the string delim (or the terminating ’\0’ character) and replaces it
with a ’\0’. The location of the next character after the delimiter character (or NULL,
if the end of the string was reached) is stored in ∗sp. An “empty” field, i.e. one
caused by two adjacent delimiter characters, can be detected by comparing the location
referenced by the pointer returned in ∗sp to ’\0’.
Returns
The strsep() function returns a pointer to the original value of ∗sp. If ∗sp is
initially NULL,strsep() returns NULL.
23.11.3.34 size_t strspn (const char ∗s, const char ∗accept)
The strspn() function calculates the length of the initial segment of swhich consists
entirely of characters in accept.
Returns
The strspn() function returns the number of characters in the initial segment of
swhich consist only of characters from accept. The terminating zero is not
considered as a part of string.
23.11.3.35 char ∗strstr (const char ∗s1, const char ∗s2)
Locate a substring.
The strstr() function finds the first occurrence of the substring s2 in the string s1. The
terminating ’\0’ characters are not compared.
Returns
The strstr() function returns a pointer to the beginning of the substring, or NULL
if the substring is not found. If s2 points to a string of zero length, the function
returns s1.
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23.11 <string.h>: Strings 215
23.11.3.36 char ∗strtok (char ∗s, const char ∗delim)
Parses the string s into tokens.
strtok parses the string s into tokens. The first call to strtok should have s as its first
argument. Subsequent calls should have the first argument set to NULL. If a token
ends with a delimiter, this delimiting character is overwritten with a ’\0’ and a pointer
to the next character is saved for the next call to strtok. The delimiter string delim may
be different for each call.
Returns
The strtok() function returns a pointer to the next token or NULL when no more
tokens are found.
Note
strtok() is NOT reentrant. For a reentrant version of this function see strtok_-
r().
23.11.3.37 char ∗strtok_r (char ∗string, const char ∗delim, char ∗∗ last)
Parses string into tokens.
strtok_r parses string into tokens. The first call to strtok_r should have string as its
first argument. Subsequent calls should have the first argument set to NULL. If a token
ends with a delimiter, this delimiting character is overwritten with a ’\0’ and a pointer
to the next character is saved for the next call to strtok_r. The delimiter string delim
may be different for each call. last is a user allocated char∗pointer. It must be the
same while parsing the same string. strtok_r is a reentrant version of strtok().
Returns
The strtok_r() function returns a pointer to the next token or NULL when no more
tokens are found.
23.11.3.38 char ∗strupr (char ∗s)
Convert a string to upper case.
The strupr() function will convert a string to upper case. Only the lower case alphabetic
characters [a .. z] are converted. Non-alphabetic characters will not be changed.
Returns
The strupr() function returns a pointer to the converted string. The pointer is the
same as that passed in since the operation is perform in place.
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23.12 <time.h>: Time 216
23.12 <time.h>: Time
Data Structures
• struct tm
• struct week_date
Defines
• #define ONE_HOUR 3600
• #define ONE_DEGREE 3600
• #define ONE_DAY 86400
• #define UNIX_OFFSET 946684800
• #define NTP_OFFSET 3155673600
Typedefs
• typedef uint32_t time_t
Enumerations
• enum _WEEK_DAYS_ {
SUNDAY,MONDAY,TUESDAY,WEDNESDAY,
THURSDAY,FRIDAY,SATURDAY }
• enum _MONTHS_ {
JANUARY,FEBRUARY,MARCH,APRIL,
MAY,JUNE,JULY,AUGUST,
SEPTEMBER,OCTOBER,NOVEMBER,DECEMBER }
Functions
•time_t time (time_t ∗timer)
•int32_t difftime (time_t time1, time_t time0)
•time_t mktime (struct tm ∗timeptr)
•time_t mk_gmtime (const struct tm ∗timeptr)
• struct tm ∗gmtime (const time_t ∗timer)
• void gmtime_r (const time_t ∗timer, struct tm ∗timeptr)
• struct tm ∗localtime (const time_t ∗timer)
• void localtime_r (const time_t ∗timer, struct tm ∗timeptr)
• char ∗asctime (const struct tm ∗timeptr)
• void asctime_r (const struct tm ∗timeptr, char ∗buf)
• char ∗ctime (const time_t ∗timer)
• void ctime_r (const time_t ∗timer, char ∗buf)
• char ∗isotime (const struct tm ∗tmptr)
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23.12 <time.h>: Time 217
• void isotime_r (const struct tm ∗, char ∗)
• size_t strftime (char ∗s, size_t maxsize, const char ∗format, const struct tm
∗timeptr)
• void set_dst (int(∗)(const time_t ∗,int32_t ∗))
• void set_zone (int32_t)
• void set_system_time (time_t timestamp)
• void system_tick (void)
•uint8_t is_leap_year (int16_t year)
•uint8_t month_length (int16_t year, uint8_t month)
•uint8_t week_of_year (const struct tm ∗timeptr, uint8_t start)
•uint8_t week_of_month (const struct tm ∗timeptr, uint8_t start)
• struct week_date ∗iso_week_date (int year, int yday)
• void iso_week_date_r (int year, int yday, struct week_date ∗)
•uint32_t fatfs_time (const struct tm ∗timeptr)
• void set_position (int32_t latitude, int32_t longitude)
•int16_t equation_of_time (const time_t ∗timer)
•int32_t daylight_seconds (const time_t ∗timer)
•time_t solar_noon (const time_t ∗timer)
•time_t sun_rise (const time_t ∗timer)
•time_t sun_set (const time_t ∗timer)
• double solar_declination (const time_t ∗timer)
•int8_t moon_phase (const time_t ∗timer)
• unsigned long gm_sidereal (const time_t ∗timer)
• unsigned long lm_sidereal (const time_t ∗timer)
23.12.1 Detailed Description
#include <time.h>
Introduction to the Time functions This file declares the time functions imple-
mented in avr-libc.
The implementation aspires to conform with ISO/IEC 9899 (C90). However, due to
limitations of the target processor and the nature of its development environment, a
practical implementation must of necessity deviate from the standard.
Section 7.23.2.1 clock() The type clock_t, the macro CLOCKS_PER_SEC, and the
function clock() are not implemented. We consider these items belong to operating
system code, or to application code when no operating system is present.
Section 7.23.2.3 mktime() The standard specifies that mktime() should return (time_t)
-1, if the time cannot be represented. This implementation always returns a ’best effort’
representation.
Section 7.23.2.4 time() The standard specifies that time() should return (time_t) -1, if
the time is not available. Since the application must initialize the time system, this
functionality is not implemented.
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23.12 <time.h>: Time 218
Section 7.23.2.2, difftime() Due to the lack of a 64 bit double, the function difftime()
returns a long integer. In most cases this change will be invisible to the user, handled
automatically by the compiler.
Section 7.23.1.4 struct tm Per the standard, struct tm->tm_isdst is greater than zero
when Daylight Saving time is in effect. This implementation further specifies that,
when positive, the value of tm_isdst represents the amount time is advanced during
Daylight Saving time.
Section 7.23.3.5 strftime() Only the ’C’ locale is supported, therefore the modifiers ’E’
and ’O’ are ignored. The ’Z’ conversion is also ignored, due to the lack of time zone
name.
In addition to the above departures from the standard, there are some behaviors which
are different from what is often expected, though allowed under the standard.
There is no ’platform standard’ method to obtain the current time, time zone, or day-
light savings ’rules’ in the AVR environment. Therefore the application must initialize
the time system with this information. The functions set_zone(),set_dst(), and set_-
system_time() are provided for initialization. Once initialized, system time is main-
tained by calling the function system_tick() at one second intervals.
Though not specified in the standard, it is often expected that time_t is a signed integer
representing an offset in seconds from Midnight Jan 1 1970... i.e. ’Unix time’. This
implementation uses an unsigned 32 bit integer offset from Midnight Jan 1 2000. The
use of this ’epoch’ helps to simplify the conversion functions, while the 32 bit value
allows time to be properly represented until Tue Feb 7 06:28:15 2136 UTC. The macros
UNIX_OFFSET and NTP_OFFSET are defined to assist in converting to and from
Unix and NTP time stamps.
Unlike desktop counterparts, it is impractical to implement or maintain the ’zoneinfo’
database. Therefore no attempt is made to account for time zone, daylight saving,
or leap seconds in past dates. All calculations are made according to the currently
configured time zone and daylight saving ’rule’.
In addition to C standard functions, re-entrant versions of ctime(),asctime(),gmtime()
and localtime() are provided which, in addition to being re-entrant, have the property
of claiming less permanent storage in RAM. An additional time conversion, isotime()
and its re-entrant version, uses far less storage than either ctime() or asctime().
Along with the usual smattering of utility functions, such as is_leap_year(), this library
includes a set of functions related the sun and moon, as well as sidereal time functions.
23.12.2 Define Documentation
23.12.2.1 #define NTP_OFFSET 3155673600
Difference between the Y2K and the NTP epochs, in seconds. To convert a Y2K
timestamp to NTP...
unsigned long ntp;
time_t y2k;
y2k = time(NULL);
ntp = y2k + NTP_OFFSET;
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23.12 <time.h>: Time 219
23.12.2.2 #define ONE_DAY 86400
One day, expressed in seconds
23.12.2.3 #define ONE_DEGREE 3600
Angular degree, expressed in arc seconds
23.12.2.4 #define ONE_HOUR 3600
One hour, expressed in seconds
23.12.2.5 #define UNIX_OFFSET 946684800
Difference between the Y2K and the UNIX epochs, in seconds. To convert a Y2K
timestamp to UNIX...
long unix;
time_t y2k;
y2k = time(NULL);
unix = y2k + UNIX_OFFSET;
23.12.3 Typedef Documentation
23.12.3.1 typedef uint32_t time_t
time_t represents seconds elapsed from Midnight, Jan 1 2000 UTC (the
Y2K ’epoch’). Its range allows this implementation to represent time up to Tue Feb 7
06:28:15 2136 UTC.
23.12.4 Enumeration Type Documentation
23.12.4.1 enum _MONTHS_
Enumerated labels for the months.
23.12.4.2 enum _WEEK_DAYS_
Enumerated labels for the days of the week.
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23.12 <time.h>: Time 220
23.12.5 Function Documentation
23.12.5.1 char∗asctime (const struct tm ∗timeptr)
The asctime function converts the broken-down time of timeptr, into an ascii string in
the form
Sun Mar 23 01:03:52 2013
23.12.5.2 void asctime_r (const struct tm ∗timeptr, char ∗buf)
Re entrant version of asctime().
23.12.5.3 char∗ctime (const time_t ∗timer)
The ctime function is equivalent to asctime(localtime(timer))
23.12.5.4 void ctime_r (const time_t ∗timer, char ∗buf)
Re entrant version of ctime().
23.12.5.5 int32_t daylight_seconds (const time_t ∗timer)
Computes the amount of time the sun is above the horizon, at the location of the
observer.
NOTE: At observer locations inside a polar circle, this value can be zero during the
winter, and can exceed ONE_DAY during the summer.
The returned value is in seconds.
23.12.5.6 int32_t difftime (time_t time1, time_t time0)
The difftime function returns the difference between two binary time stamps, time1 -
time0.
23.12.5.7 int16_t equation_of_time (const time_t ∗timer)
Computes the difference between apparent solar time and mean solar time. The
returned value is in seconds.
23.12.5.8 uint32_t fatfs_time (const struct tm ∗timeptr)
Convert a Y2K time stamp into a FAT file system time stamp.
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23.12 <time.h>: Time 221
23.12.5.9 unsigned long gm_sidereal (const time_t ∗timer)
Returns Greenwich Mean Sidereal Time, as seconds into the sidereal day. The
returned value will range from 0 through 86399 seconds.
23.12.5.10 struct tm∗gmtime (const time_t ∗timer)[read]
The gmtime function converts the time stamp pointed to by timer into broken-down
time, expressed as UTC.
23.12.5.11 void gmtime_r (const time_t ∗timer, struct tm ∗timeptr)
Re entrant version of gmtime().
23.12.5.12 uint8_t is_leap_year (int16_t year)
Return 1 if year is a leap year, zero if it is not.
23.12.5.13 struct week_date∗iso_week_date (int year, int yday)[read]
Return a week_date
structure with the ISO_8601 week based date corresponding to the given year and day
of year. See http://en.wikipedia.org/wiki/ISO_week_date for more
information.
23.12.5.14 void iso_week_date_r (int year, int yday, struct week_date ∗)
Re-entrant version of iso-week_date.
23.12.5.15 char∗isotime (const struct tm ∗tmptr)
The isotime function constructs an ascii string in the form
2013-03-23 01:03:52
23.12.5.16 void isotime_r (const struct tm ∗, char ∗)
Re entrant version of isotime()
23.12.5.17 unsigned long lm_sidereal (const time_t ∗timer)
Returns Local Mean Sidereal Time, as seconds into the sidereal day. The returned
value will range from 0 through 86399 seconds.
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23.12 <time.h>: Time 222
23.12.5.18 struct tm∗localtime (const time_t ∗timer)[read]
The localtime function converts the time stamp pointed to by timer into broken-down
time, expressed as Local time.
23.12.5.19 void localtime_r (const time_t ∗timer, struct tm ∗timeptr)
Re entrant version of localtime().
23.12.5.20 time_t mk_gmtime (const struct tm ∗timeptr)
This function ’compiles’ the elements of a broken-down time structure, returning a
binary time stamp. The elements of timeptr are interpreted as representing UTC.
The original values of the tm_wday and tm_yday elements of the structure are ignored,
and the original values of the other elements are not restricted to the ranges stated for
struct tm.
Unlike mktime(), this function DOES NOT modify the elements of timeptr.
23.12.5.21 time_t mktime (struct tm ∗timeptr)
This function ’compiles’ the elements of a broken-down time structure,
returning a binary time stamp. The elements of timeptr are interpreted as representing
Local Time.
The original values of the tm_wday and tm_yday elements of the structure are ignored,
and the original values of the other elements are not restricted to the ranges stated for
struct tm.
On successful completion, the values of all elements of timeptr are set to the appropri-
ate range.
23.12.5.22 uint8_t month_length (int16_t year, uint8_t month)
Return the length of month, given the year and month, where month is in the range 1
to 12.
23.12.5.23 int8_t moon_phase (const time_t ∗timer)
Returns an approximation to the phase of the moon. The sign of the returned value
indicates a waning or waxing phase. The magnitude of the returned value indicates the
percentage illumination.
23.12.5.24 void set_dst (int(∗)(const time_t ∗, int32_t ∗))
Specify the Daylight Saving function.
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23.12 <time.h>: Time 223
The Daylight Saving function should examine its parameters to determine whether
Daylight Saving is in effect, and return a value appropriate for tm_isdst.
Working examples for the USA and the EU are available..
#include <util/eu_dst.h>
for the European Union, and
#include <util/usa_dst.h>
for the United States
If a Daylight Saving function is not specified, the system will ignore Daylight Saving.
23.12.5.25 void set_position (int32_t latitude, int32_t longitude)
Set the geographic coordinates of the ’observer’, for use with several of the
following functions. Parameters are passed as seconds of North Latitude, and seconds
of East Longitude.
For New York City...
set_position( 40.7142 *ONE_DEGREE, -74.0064 *ONE_DEGREE);
23.12.5.26 void set_system_time (time_t timestamp)
Initialize the system time. Examples are...
From a Clock / Calendar type RTC:
struct tm rtc_time;
read_rtc(&rtc_time);
rtc_time.tm_isdst = 0;
set_system_time( mktime(&rtc_time) );
From a Network Time Protocol time stamp:
set_system_time(ntp_timestamp - NTP_OFFSET);
From a UNIX time stamp:
set_system_time(unix_timestamp - UNIX_OFFSET);
23.12.5.27 void set_zone (int32_t)
Set the ’time zone’. The parameter is given in seconds East of the Prime Meridian.
Example for New York City:
set_zone(-5 *ONE_HOUR);
If the time zone is not set, the time system will operate in UTC only.
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23.12 <time.h>: Time 224
23.12.5.28 double solar_declination (const time_t ∗timer)
Returns the declination of the sun in radians.
23.12.5.29 time_t solar_noon (const time_t ∗timer)
Computes the time of solar noon, at the location of the observer.
23.12.5.30 size_t strftime (char ∗s, size_t maxsize, const char ∗format, const
struct tm ∗timeptr)
A complete description of strftime() is beyond the pale of this document. Refer to
ISO/IEC document 9899 for details.
All conversions are made using the ’C Locale’, ignoring the E or O modifiers. Due to
the lack of a time zone ’name’, the ’Z’ conversion is also ignored.
23.12.5.31 time_t sun_rise (const time_t ∗timer)
Return the time of sunrise, at the location of the observer. See the note about
daylight_seconds().
23.12.5.32 time_t sun_set (const time_t ∗timer)
Return the time of sunset, at the location of the observer. See the note about
daylight_seconds().
23.12.5.33 void system_tick (void)
Maintain the system time by calling this function at a rate of 1 Hertz.
It is anticipated that this function will typically be called from within an Interrupt Ser-
vice Routine, (though that is not required). It therefore includes code which makes it
simple to use from within a ’Naked’ ISR, avoiding the cost of saving and restoring all
the cpu registers.
Such an ISR may resemble the following example...
ISR(RTC_OVF_vect, ISR_NAKED)
{
system_tick();
reti();
}
23.12.5.34 time_t time (time_t ∗timer)
The time function returns the systems current time stamp. If timer is not a null
pointer, the return value is also assigned to the object it points to.
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23.13 <avr/boot.h>: Bootloader Support Utilities 225
23.12.5.35 uint8_t week_of_month (const struct tm ∗timeptr, uint8_t start)
Return the calendar week of month, where the first week is considered to begin on the
day of week specified by ’start’. The returned value may range from zero to 5.
23.12.5.36 uint8_t week_of_year (const struct tm ∗timeptr, uint8_t start)
Return the calendar week of year, where week 1 is considered to begin on the day of
week specified by ’start’. The returned value may range from zero to 52.
23.13 <avr/boot.h>: Bootloader Support Utilities
Defines
• #define BOOTLOADER_SECTION __attribute__ ((section (".bootloader")))
• #define boot_spm_interrupt_enable() (__SPM_REG |= (uint8_t)_BV(SPMIE))
• #define boot_spm_interrupt_disable() (__SPM_REG &= (uint8_t)∼_-
BV(SPMIE))
• #define boot_is_spm_interrupt() (__SPM_REG & (uint8_t)_BV(SPMIE))
• #define boot_rww_busy() (__SPM_REG & (uint8_t)_BV(__COMMON_ASB))
• #define boot_spm_busy() (__SPM_REG & (uint8_t)_BV(__SPM_ENABLE))
• #define boot_spm_busy_wait() do{}while(boot_spm_busy())
• #define GET_LOW_FUSE_BITS (0x0000)
• #define GET_LOCK_BITS (0x0001)
• #define GET_EXTENDED_FUSE_BITS (0x0002)
• #define GET_HIGH_FUSE_BITS (0x0003)
• #define boot_lock_fuse_bits_get(address)
• #define boot_signature_byte_get(addr)
• #define boot_page_fill(address, data) __boot_page_fill_normal(address, data)
• #define boot_page_erase(address) __boot_page_erase_normal(address)
• #define boot_page_write(address) __boot_page_write_normal(address)
• #define boot_rww_enable() __boot_rww_enable()
• #define boot_lock_bits_set(lock_bits) __boot_lock_bits_set(lock_bits)
• #define boot_page_fill_safe(address, data)
• #define boot_page_erase_safe(address)
• #define boot_page_write_safe(address)
• #define boot_rww_enable_safe()
• #define boot_lock_bits_set_safe(lock_bits)
23.13.1 Detailed Description
#include <avr/io.h>
#include <avr/boot.h>
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23.13 <avr/boot.h>: Bootloader Support Utilities 226
The macros in this module provide a C language interface to the bootloader support
functionality of certain AVR processors. These macros are designed to work with all
sizes of flash memory.
Global interrupts are not automatically disabled for these macros. It is left up to the
programmer to do this. See the code example below. Also see the processor datasheet
for caveats on having global interrupts enabled during writing of the Flash.
Note
Not all AVR processors provide bootloader support. See your processor datasheet
to see if it provides bootloader support.
Todo
From email with Marek: On smaller devices (all except ATmega64/128), __SPM_-
REG is in the I/O space, accessible with the shorter "in" and "out" instructions -
since the boot loader has a limited size, this could be an important optimization.
API Usage Example
The following code shows typical usage of the boot API.
#include <inttypes.h>
#include <avr/interrupt.h>
#include <avr/pgmspace.h>
void boot_program_page (uint32_t page, uint8_t *buf)
{
uint16_t i;
uint8_t sreg;
// Disable interrupts.
sreg = SREG;
cli();
eeprom_busy_wait ();
boot_page_erase (page);
boot_spm_busy_wait (); // Wait until the memory is erased.
for (i=0; i<SPM_PAGESIZE; i+=2)
{
// Set up little-endian word.
uint16_t w = *buf++;
w += (*buf++) << 8;
boot_page_fill (page + i, w);
}
boot_page_write (page); // Store buffer in flash page.
boot_spm_busy_wait(); // Wait until the memory is written.
// Reenable RWW-section again. We need this if we want to jump back
// to the application after bootloading.
boot_rww_enable ();
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23.13 <avr/boot.h>: Bootloader Support Utilities 227
// Re-enable interrupts (if they were ever enabled).
SREG = sreg;
}
23.13.2 Define Documentation
23.13.2.1 #define boot_is_spm_interrupt() (__SPM_REG &
(uint8_t)_BV(SPMIE))
Check if the SPM interrupt is enabled.
23.13.2.2 #define boot_lock_bits_set(lock_bits) __boot_lock_bits_set(lock_bits)
Set the bootloader lock bits.
Parameters
lock_bits A mask of which Boot Loader Lock Bits to set.
Note
In this context, a ’set bit’ will be written to a zero value. Note also that only BLBxx
bits can be programmed by this command.
For example, to disallow the SPM instruction from writing to the Boot Loader memory
section of flash, you would use this macro as such:
boot_lock_bits_set (_BV (BLB11));
Note
Like any lock bits, the Boot Loader Lock Bits, once set, cannot be cleared again
except by a chip erase which will in turn also erase the boot loader itself.
23.13.2.3 #define boot_lock_bits_set_safe(lock_bits)
Value:
do { \
boot_spm_busy_wait(); \
eeprom_busy_wait(); \
boot_lock_bits_set (lock_bits); \
} while (0)
Same as boot_lock_bits_set() except waits for eeprom and spm operations to complete
before setting the lock bits.
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23.13 <avr/boot.h>: Bootloader Support Utilities 228
23.13.2.4 #define boot_lock_fuse_bits_get(address)
Value:
(__extension__({ \
uint8_t __result; \
__asm__ __volatile__ \
( \
"sts %1, %2\n\t" \
"lpm %0, Z\n\t" \
: "=r" (__result) \
: "i" (_SFR_MEM_ADDR(__SPM_REG)), \
"r" ((uint8_t)(__BOOT_LOCK_BITS_SET)), \
"z" ((uint16_t)(address)) \
); \
__result; \
}))
Read the lock or fuse bits at address.
Parameter address can be any of GET_LOW_FUSE_BITS, GET_LOCK_BITS,
GET_EXTENDED_FUSE_BITS, or GET_HIGH_FUSE_BITS.
Note
The lock and fuse bits returned are the physical values, i.e. a bit returned as 0
means the corresponding fuse or lock bit is programmed.
23.13.2.5 #define boot_page_erase(address) __boot_page_erase_-
normal(address)
Erase the flash page that contains address.
Note
address is a byte address in flash, not a word address.
23.13.2.6 #define boot_page_erase_safe(address)
Value:
do { \
boot_spm_busy_wait(); \
eeprom_busy_wait(); \
boot_page_erase (address); \
} while (0)
Same as boot_page_erase() except it waits for eeprom and spm operations to complete
before erasing the page.
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23.13 <avr/boot.h>: Bootloader Support Utilities 229
23.13.2.7 #define boot_page_fill(address, data) __boot_page_fill_-
normal(address, data)
Fill the bootloader temporary page buffer for flash address with data word.
Note
The address is a byte address. The data is a word. The AVR writes data to the
buffer a word at a time, but addresses the buffer per byte! So, increment your
address by 2 between calls, and send 2 data bytes in a word format! The LSB of
the data is written to the lower address; the MSB of the data is written to the higher
address.
23.13.2.8 #define boot_page_fill_safe(address, data)
Value:
do { \
boot_spm_busy_wait(); \
eeprom_busy_wait(); \
boot_page_fill(address, data); \
} while (0)
Same as boot_page_fill() except it waits for eeprom and spm operations to complete
before filling the page.
23.13.2.9 #define boot_page_write(address) __boot_page_write_-
normal(address)
Write the bootloader temporary page buffer to flash page that contains address.
Note
address is a byte address in flash, not a word address.
23.13.2.10 #define boot_page_write_safe(address)
Value:
do { \
boot_spm_busy_wait(); \
eeprom_busy_wait(); \
boot_page_write (address); \
} while (0)
Same as boot_page_write() except it waits for eeprom and spm operations to complete
before writing the page.
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23.13 <avr/boot.h>: Bootloader Support Utilities 230
23.13.2.11 #define boot_rww_busy() (__SPM_REG &
(uint8_t)_BV(__COMMON_ASB))
Check if the RWW section is busy.
23.13.2.12 #define boot_rww_enable() __boot_rww_enable()
Enable the Read-While-Write memory section.
23.13.2.13 #define boot_rww_enable_safe()
Value:
do { \
boot_spm_busy_wait(); \
eeprom_busy_wait(); \
boot_rww_enable(); \
} while (0)
Same as boot_rww_enable() except waits for eeprom and spm operations to complete
before enabling the RWW mameory.
23.13.2.14 #define boot_signature_byte_get(addr)
Value:
(__extension__({ \
uint8_t __result; \
__asm__ __volatile__ \
( \
"sts %1, %2\n\t" \
"lpm %0, Z" "\n\t" \
: "=r" (__result) \
: "i" (_SFR_MEM_ADDR(__SPM_REG)), \
"r" ((uint8_t)(__BOOT_SIGROW_READ)), \
"z" ((uint16_t)(addr)) \
); \
__result; \
}))
Read the Signature Row byte at address. For some MCU types, this function can
also retrieve the factory-stored oscillator calibration bytes.
Parameter address can be 0-0x1f as documented by the datasheet.
Note
The values are MCU type dependent.
23.13.2.15 #define boot_spm_busy() (__SPM_REG &
(uint8_t)_BV(__SPM_ENABLE))
Check if the SPM instruction is busy.
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23.14 <avr/cpufunc.h>: Special AVR CPU functions 231
23.13.2.16 #define boot_spm_busy_wait() do{}while(boot_spm_busy())
Wait while the SPM instruction is busy.
23.13.2.17 #define boot_spm_interrupt_disable() (__SPM_REG &=
(uint8_t)∼_BV(SPMIE))
Disable the SPM interrupt.
23.13.2.18 #define boot_spm_interrupt_enable() (__SPM_REG |=
(uint8_t)_BV(SPMIE))
Enable the SPM interrupt.
23.13.2.19 #define BOOTLOADER_SECTION __attribute__ ((section
(".bootloader")))
Used to declare a function or variable to be placed into a new section called
.bootloader. This section and its contents can then be relocated to any address (such as
the bootloader NRWW area) at link-time.
23.13.2.20 #define GET_EXTENDED_FUSE_BITS (0x0002)
address to read the extended fuse bits, using boot_lock_fuse_bits_get
23.13.2.21 #define GET_HIGH_FUSE_BITS (0x0003)
address to read the high fuse bits, using boot_lock_fuse_bits_get
23.13.2.22 #define GET_LOCK_BITS (0x0001)
address to read the lock bits, using boot_lock_fuse_bits_get
23.13.2.23 #define GET_LOW_FUSE_BITS (0x0000)
address to read the low fuse bits, using boot_lock_fuse_bits_get
23.14 <avr/cpufunc.h>: Special AVR CPU functions
Defines
• #define _NOP()
• #define _MemoryBarrier()
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23.15 <avr/eeprom.h>: EEPROM handling 232
Functions
• void ccp_write_io (uint8_t ∗__ioaddr, uint8_t __value)
23.14.1 Detailed Description
#include <avr/cpufunc.h>
This header file contains macros that access special functions of the AVR CPU which
do not fit into any of the other header files.
23.14.2 Define Documentation
23.14.2.1 #define _MemoryBarrier()
Implement a read/write memory barrier. A memory barrier
instructs the compiler to not cache any memory data in registers beyond the barrier.
This can sometimes be more effective than blocking certain optimizations by declaring
some object with a volatile qualifier.
See Problems with reordering code for things to be taken into account with respect to
compiler optimizations.
23.14.2.2 #define _NOP()
Execute a no operation (NOP)
CPU instruction. This should not be used to implement delays, better use the functions
from <util/delay_basic.h>or <util/delay.h>for this. For debugging purposes, a NOP
can be useful to have an instruction that is guaranteed to be not optimized away by the
compiler, so it can always become a breakpoint in the debugger.
23.14.3 Function Documentation
23.14.3.1 void ccp_write_io (uint8_t ∗__ioaddr, uint8_t __value)
Write __value to Configuration Change Protected (CCP) IO register at __ioaddr.
23.15 <avr/eeprom.h>: EEPROM handling
Defines
• #define EEMEM __attribute__((section(".eeprom")))
• #define eeprom_is_ready()
• #define eeprom_busy_wait() do {} while (!eeprom_is_ready())
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23.15 <avr/eeprom.h>: EEPROM handling 233
Functions
•uint8_t eeprom_read_byte (const uint8_t ∗__p) __ATTR_PURE__
•uint16_t eeprom_read_word (const uint16_t ∗__p) __ATTR_PURE__
•uint32_t eeprom_read_dword (const uint32_t ∗__p) __ATTR_PURE__
• float eeprom_read_float (const float ∗__p) __ATTR_PURE__
• void eeprom_read_block (void ∗__dst, const void ∗__src, size_t __n)
• void eeprom_write_byte (uint8_t ∗__p, uint8_t __value)
• void eeprom_write_word (uint16_t ∗__p, uint16_t __value)
• void eeprom_write_dword (uint32_t ∗__p, uint32_t __value)
• void eeprom_write_float (float ∗__p, float __value)
• void eeprom_write_block (const void ∗__src, void ∗__dst, size_t __n)
• void eeprom_update_byte (uint8_t ∗__p, uint8_t __value)
• void eeprom_update_word (uint16_t ∗__p, uint16_t __value)
• void eeprom_update_dword (uint32_t ∗__p, uint32_t __value)
• void eeprom_update_float (float ∗__p, float __value)
• void eeprom_update_block (const void ∗__src, void ∗__dst, size_t __n)
IAR C compatibility defines
• #define _EEPUT(addr, val) eeprom_write_byte ((uint8_t ∗)(addr), (uint8_-
t)(val))
• #define __EEPUT(addr, val) eeprom_write_byte ((uint8_t ∗)(addr), (uint8_-
t)(val))
• #define _EEGET(var, addr) (var) = eeprom_read_byte ((const uint8_t ∗)(addr))
• #define __EEGET(var, addr) (var) = eeprom_read_byte ((const uint8_t ∗)(addr))
23.15.1 Detailed Description
#include <avr/eeprom.h>
This header file declares the interface to some simple library routines suitable for han-
dling the data EEPROM contained in the AVR microcontrollers. The implementation
uses a simple polled mode interface. Applications that require interrupt-controlled
EEPROM access to ensure that no time will be wasted in spinloops will have to deploy
their own implementation.
Notes:
• In addition to the write functions there is a set of update ones. This functions read
each byte first and skip the burning if the old value is the same with new. The
scaning direction is from high address to low, to obtain quick return in common
cases.
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23.15 <avr/eeprom.h>: EEPROM handling 234
• All of the read/write functions first make sure the EEPROM is ready to be ac-
cessed. Since this may cause long delays if a write operation is still pending,
time-critical applications should first poll the EEPROM e. g. using eeprom_-
is_ready() before attempting any actual I/O. But this functions are not wait until
SELFPRGEN in SPMCSR becomes zero. Do this manually, if your softwate
contains the Flash burning.
• As these functions modify IO registers, they are known to be non-reentrant. If
any of these functions are used from both, standard and interrupt context, the
applications must ensure proper protection (e.g. by disabling interrupts before
accessing them).
• All write functions force erase_and_write programming mode.
• For Xmega the EEPROM start address is 0, like other architectures. The reading
functions add the 0x2000 value to use EEPROM mapping into data space.
23.15.2 Define Documentation
23.15.2.1 #define __EEGET(var, addr) (var) = eeprom_read_byte ((const
uint8_t ∗)(addr))
Read a byte from EEPROM. Compatibility define for IAR C.
23.15.2.2 #define __EEPUT(addr, val) eeprom_write_byte ((uint8_t ∗)(addr),
(uint8_t)(val))
Write a byte to EEPROM. Compatibility define for IAR C.
23.15.2.3 #define _EEGET(var, addr) (var) = eeprom_read_byte ((const
uint8_t ∗)(addr))
Read a byte from EEPROM. Compatibility define for IAR C.
23.15.2.4 #define _EEPUT(addr, val) eeprom_write_byte ((uint8_t ∗)(addr),
(uint8_t)(val))
Write a byte to EEPROM. Compatibility define for IAR C.
23.15.2.5 #define EEMEM __attribute__((section(".eeprom")))
Attribute expression causing a variable to be allocated within the .eeprom section.
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23.15 <avr/eeprom.h>: EEPROM handling 235
23.15.2.6 #define eeprom_busy_wait() do {} while (!eeprom_is_ready())
Loops until the eeprom is no longer busy.
Returns
Nothing.
23.15.2.7 #define eeprom_is_ready()
Returns
1 if EEPROM is ready for a new read/write operation, 0 if not.
23.15.3 Function Documentation
23.15.3.1 void eeprom_read_block (void ∗__dst, const void ∗__src, size_t __n)
Read a block of __n bytes from EEPROM address __src to SRAM __dst.
23.15.3.2 uint8_t eeprom_read_byte (const uint8_t ∗__p)
Read one byte from EEPROM address __p.
23.15.3.3 uint32_t eeprom_read_dword (const uint32_t ∗__p)
Read one 32-bit double word (little endian) from EEPROM address __p.
23.15.3.4 float eeprom_read_float (const float ∗__p)
Read one float value (little endian) from EEPROM address __p.
23.15.3.5 uint16_t eeprom_read_word (const uint16_t ∗__p)
Read one 16-bit word (little endian) from EEPROM address __p.
23.15.3.6 void eeprom_update_block (const void ∗__src, void ∗__dst, size_t
__n)
Update a block of __n bytes to EEPROM address __dst from __src.
Note
The argument order is mismatch with common functions like strcpy().
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23.15 <avr/eeprom.h>: EEPROM handling 236
23.15.3.7 void eeprom_update_byte (uint8_t ∗__p, uint8_t __value)
Update a byte __value to EEPROM address __p.
23.15.3.8 void eeprom_update_dword (uint32_t ∗__p, uint32_t __value)
Update a 32-bit double word __value to EEPROM address __p.
23.15.3.9 void eeprom_update_float (float ∗__p, float __value)
Update a float __value to EEPROM address __p.
23.15.3.10 void eeprom_update_word (uint16_t ∗__p, uint16_t __value)
Update a word __value to EEPROM address __p.
23.15.3.11 void eeprom_write_block (const void ∗__src, void ∗__dst, size_t
__n)
Write a block of __n bytes to EEPROM address __dst from __src.
Note
The argument order is mismatch with common functions like strcpy().
23.15.3.12 void eeprom_write_byte (uint8_t ∗__p, uint8_t __value)
Write a byte __value to EEPROM address __p.
23.15.3.13 void eeprom_write_dword (uint32_t ∗__p, uint32_t __value)
Write a 32-bit double word __value to EEPROM address __p.
23.15.3.14 void eeprom_write_float (float ∗__p, float __value)
Write a float __value to EEPROM address __p.
23.15.3.15 void eeprom_write_word (uint16_t ∗__p, uint16_t __value)
Write a word __value to EEPROM address __p.
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23.16 <avr/fuse.h>: Fuse Support 237
23.16 <avr/fuse.h>: Fuse Support
Introduction
The Fuse API allows a user to specify the fuse settings for the specific AVR device they
are compiling for. These fuse settings will be placed in a special section in the ELF
output file, after linking.
Programming tools can take advantage of the fuse information embedded in the ELF
file, by extracting this information and determining if the fuses need to be programmed
before programming the Flash and EEPROM memories. This also allows a single ELF
file to contain all the information needed to program an AVR.
To use the Fuse API, include the <avr/io.h>header file, which in turn automatically
includes the individual I/O header file and the <avr/fuse.h>file. These other two files
provides everything necessary to set the AVR fuses.
Fuse API
Each I/O header file must define the FUSE_MEMORY_SIZE macro which is defined
to the number of fuse bytes that exist in the AVR device.
A new type, __fuse_t, is defined as a structure. The number of fields in this structure
are determined by the number of fuse bytes in the FUSE_MEMORY_SIZE macro.
If FUSE_MEMORY_SIZE == 1, there is only a single field: byte, of type unsigned
char.
If FUSE_MEMORY_SIZE == 2, there are two fields: low, and high, of type unsigned
char.
If FUSE_MEMORY_SIZE == 3, there are three fields: low, high, and extended, of
type unsigned char.
If FUSE_MEMORY_SIZE >3, there is a single field: byte, which is an array of
unsigned char with the size of the array being FUSE_MEMORY_SIZE.
A convenience macro, FUSEMEM, is defined as a GCC attribute for a custom-named
section of ".fuse".
A convenience macro, FUSES, is defined that declares a variable, __fuse, of type __-
fuse_t with the attribute defined by FUSEMEM. This variable allows the end user to
easily set the fuse data.
Note
If a device-specific I/O header file has previously defined FUSEMEM, then FUSE-
MEM is not redefined. If a device-specific I/O header file has previously defined
FUSES, then FUSES is not redefined.
Each AVR device I/O header file has a set of defined macros which specify the actual
fuse bits available on that device. The AVR fuses have inverted values, logical 1 for
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23.16 <avr/fuse.h>: Fuse Support 238
an unprogrammed (disabled) bit and logical 0 for a programmed (enabled) bit. The
defined macros for each individual fuse bit represent this in their definition by a bit-
wise inversion of a mask. For example, the FUSE_EESAVE fuse in the ATmega128 is
defined as:
#define FUSE_EESAVE ~_BV(3)
Note
The _BV macro creates a bit mask from a bit number. It is then inverted to repre-
sent logical values for a fuse memory byte.
To combine the fuse bits macros together to represent a whole fuse byte, use the bitwise
AND operator, like so:
(FUSE_BOOTSZ0 & FUSE_BOOTSZ1 & FUSE_EESAVE & FUSE_SPIEN & FUSE_JTAGEN)
Each device I/O header file also defines macros that provide default values for each fuse
byte that is available. LFUSE_DEFAULT is defined for a Low Fuse byte. HFUSE_-
DEFAULT is defined for a High Fuse byte. EFUSE_DEFAULT is defined for an Ex-
tended Fuse byte.
If FUSE_MEMORY_SIZE >3, then the I/O header file defines macros that pro-
vide default values for each fuse byte like so: FUSE0_DEFAULT FUSE1_DEFAULT
FUSE2_DEFAULT FUSE3_DEFAULT FUSE4_DEFAULT ....
API Usage Example
Putting all of this together is easy. Using C99’s designated initializers:
#include <avr/io.h>
FUSES =
{
.low = LFUSE_DEFAULT,
.high = (FUSE_BOOTSZ0 & FUSE_BOOTSZ1 & FUSE_EESAVE & FUSE_SPIEN & FUSE_JT
AGEN),
.extended = EFUSE_DEFAULT,
};
int main(void)
{
return 0;
}
Or, using the variable directly instead of the FUSES macro,
#include <avr/io.h>
__fuse_t __fuse __attribute__((section (".fuse"))) =
{
.low = LFUSE_DEFAULT,
.high = (FUSE_BOOTSZ0 & FUSE_BOOTSZ1 & FUSE_EESAVE & FUSE_SPIEN & FUSE_JT
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23.16 <avr/fuse.h>: Fuse Support 239
AGEN),
.extended = EFUSE_DEFAULT,
};
int main(void)
{
return 0;
}
If you are compiling in C++, you cannot use the designated intializers so you must do:
#include <avr/io.h>
FUSES =
{
LFUSE_DEFAULT, // .low
(FUSE_BOOTSZ0 & FUSE_BOOTSZ1 & FUSE_EESAVE & FUSE_SPIEN & FUSE_JTAGEN), /
/ .high
EFUSE_DEFAULT, // .extended
};
int main(void)
{
return 0;
}
However there are a number of caveats that you need to be aware of to use this API
properly.
Be sure to include <avr/io.h>to get all of the definitions for the API. The FUSES
macro defines a global variable to store the fuse data. This variable is assigned to its
own linker section. Assign the desired fuse values immediately in the variable initial-
ization.
The .fuse section in the ELF file will get its values from the initial variable assignment
ONLY. This means that you can NOT assign values to this variable in functions and the
new values will not be put into the ELF .fuse section.
The global variable is declared in the FUSES macro has two leading underscores,
which means that it is reserved for the "implementation", meaning the library, so it
will not conflict with a user-named variable.
You must initialize ALL fields in the __fuse_t structure. This is because the fuse bits
in all bytes default to a logical 1, meaning unprogrammed. Normal uninitialized data
defaults to all locgial zeros. So it is vital that all fuse bytes are initialized, even with
default data. If they are not, then the fuse bits may not programmed to the desired
settings.
Be sure to have the -mmcu=device flag in your compile command line and your linker
command line to have the correct device selected and to have the correct I/O header
file included when you include <avr/io.h>.
You can print out the contents of the .fuse section in the ELF file by using this command
line:
avr-objdump -s -j .fuse <ELF file>
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23.17 <avr/interrupt.h>: Interrupts 240
The section contents shows the address on the left, then the data going from lower
address to a higher address, left to right.
23.17 <avr/interrupt.h>: Interrupts
Global manipulation of the interrupt flag
The global interrupt flag is maintained in the I bit of the status register (SREG).
Handling interrupts frequently requires attention regarding atomic access to objects
that could be altered by code running within an interrupt context, see <util/atomic.h>.
Frequently, interrupts are being disabled for periods of time in order to perform certain
operations without being disturbed; see Problems with reordering code for things to be
taken into account with respect to compiler optimizations.
• #define sei()
• #define cli()
Macros for writing interrupt handler functions
• #define ISR(vector, attributes)
• #define SIGNAL(vector)
• #define EMPTY_INTERRUPT(vector)
• #define ISR_ALIAS(vector, target_vector)
• #define reti()
• #define BADISR_vect
ISR attributes
• #define ISR_BLOCK
• #define ISR_NOBLOCK
• #define ISR_NAKED
• #define ISR_ALIASOF(target_vector)
23.17.1 Detailed Description
Note
This discussion of interrupts was originally taken from Rich Neswold’s document.
See Acknowledgments.
Introduction to avr-libc’s interrupt handling It’s nearly impossible to find compil-
ers that agree on how to handle interrupt code. Since the C language tries to stay away
from machine dependent details, each compiler writer is forced to design their method
of support.
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23.17 <avr/interrupt.h>: Interrupts 241
In the AVR-GCC environment, the vector table is predefined to point to interrupt rou-
tines with predetermined names. By using the appropriate name, your routine will be
called when the corresponding interrupt occurs. The device library provides a set of
default interrupt routines, which will get used if you don’t define your own.
Patching into the vector table is only one part of the problem. The compiler uses, by
convention, a set of registers when it’s normally executing compiler-generated code.
It’s important that these registers, as well as the status register, get saved and restored.
The extra code needed to do this is enabled by tagging the interrupt function with __-
attribute__((signal)).
These details seem to make interrupt routines a little messy, but all these details are
handled by the Interrupt API. An interrupt routine is defined with ISR(). This macro
register and mark the routine as an interrupt handler for the specified peripheral. The
following is an example definition of a handler for the ADC interrupt.
#include <avr/interrupt.h>
ISR(ADC_vect)
{
// user code here
}
Refer to the chapter explaining assembler programming for an explanation about inter-
rupt routines written solely in assembler language.
Catch-all interrupt vector If an unexpected interrupt occurs (interrupt is enabled
and no handler is installed, which usually indicates a bug), then the default action is
to reset the device by jumping to the reset vector. You can override this by supplying
a function named BADISR_vect which should be defined with ISR() as such. (The
name BADISR_vect is actually an alias for __vector_default. The latter must be used
inside assembly code in case <avr/interrupt.h>is not included.)
#include <avr/interrupt.h>
ISR(BADISR_vect)
{
// user code here
}
Nested interrupts The AVR hardware clears the global interrupt flag in SREG be-
fore entering an interrupt vector. Thus, normally interrupts will remain disabled inside
the handler until the handler exits, where the RETI instruction (that is emitted by the
compiler as part of the normal function epilogue for an interrupt handler) will even-
tually re-enable further interrupts. For that reason, interrupt handlers normally do not
nest. For most interrupt handlers, this is the desired behaviour, for some it is even
required in order to prevent infinitely recursive interrupts (like UART interrupts, or
level-triggered external interrupts). In rare circumstances though it might be desired to
re-enable the global interrupt flag as early as possible in the interrupt handler, in order
to not defer any other interrupt more than absolutely needed. This could be done using
an sei() instruction right at the beginning of the interrupt handler, but this still leaves
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23.17 <avr/interrupt.h>: Interrupts 242
few instructions inside the compiler-generated function prologue to run with global in-
terrupts disabled. The compiler can be instructed to insert an SEI instruction right at
the beginning of an interrupt handler by declaring the handler the following way:
ISR(XXX_vect, ISR_NOBLOCK)
{
...
}
where XXX_vect is the name of a valid interrupt vector for the MCU type in question,
as explained below.
Two vectors sharing the same code In some circumstances, the actions to be taken
upon two different interrupts might be completely identical so a single implementa-
tion for the ISR would suffice. For example, pin-change interrupts arriving from two
different ports could logically signal an event that is independent from the actual port
(and thus interrupt vector) where it happened. Sharing interrupt vector code can be
accomplished using the ISR_ALIASOF() attribute to the ISR macro:
ISR(PCINT0_vect)
{
...
// Code to handle the event.
}
ISR(PCINT1_vect, ISR_ALIASOF(PCINT0_vect));
Note
There is no body to the aliased ISR.
Note that the ISR_ALIASOF() feature requires GCC 4.2 or above (or a patched version
of GCC 4.1.x). See the documentation of the ISR_ALIAS() macro for an implementa-
tion which is less elegant but could be applied to all compiler versions.
Empty interrupt service routines In rare circumstances, in interrupt vector does not
need any code to be implemented at all. The vector must be declared anyway, so when
the interrupt triggers it won’t execute the BADISR_vect code (which by default restarts
the application).
This could for example be the case for interrupts that are solely enabled for the purpose
of getting the controller out of sleep_mode().
A handler for such an interrupt vector can be declared using the EMPTY_-
INTERRUPT() macro:
EMPTY_INTERRUPT(ADC_vect);
Note
There is no body to this macro.
Generated on Wed Jul 25 09:38:10 2018 for avr-libc by Doxygen
23.17 <avr/interrupt.h>: Interrupts 243
Manually defined ISRs In some circumstances, the compiler-generated prologue
and epilogue of the ISR might not be optimal for the job, and a manually defined ISR
could be considered particularly to speedup the interrupt handling.
One solution to this could be to implement the entire ISR as manual assembly code in
a separate (assembly) file. See Combining C and assembly source files for an example
of how to implement it that way.
Another solution is to still implement the ISR in C language but take over the com-
piler’s job of generating the prologue and epilogue. This can be done using the ISR_-
NAKED attribute to the ISR() macro. Note that the compiler does not generate any-
thing as prologue or epilogue, so the final reti() must be provided by the actual im-
plementation. SREG must be manually saved if the ISR code modifies it, and the
compiler-implied assumption of __zero_reg__ always being 0 could be wrong (e.
g. when interrupting right after of a MUL instruction).
ISR(TIMER1_OVF_vect, ISR_NAKED)
{
PORTB |= _BV(0); // results in SBI which does not affect SREG
reti();
}
Choosing the vector: Interrupt vector names The interrupt is chosen by supplying
one of the symbols in following table.
There are currently two different styles present for naming the vectors. One form uses
names starting with SIG_, followed by a relatively verbose but arbitrarily chosen name
describing the interrupt vector. This has been the only available style in avr-libc up to
version 1.2.x.
Starting with avr-libc version 1.4.0, a second style of interrupt vector names has been
added, where a short phrase for the vector description is followed by _vect. The
short phrase matches the vector name as described in the datasheet of the respective
device (and in Atmel’s XML files), with spaces replaced by an underscore and other
non-alphanumeric characters dropped. Using the suffix _vect is intented to improve
portability to other C compilers available for the AVR that use a similar naming con-
vention.
The historical naming style might become deprecated in a future release, so it is not
recommended for new projects.
Note
The ISR() macro cannot really spell-check the argument passed to them. Thus, by
misspelling one of the names below in a call to ISR(), a function will be created
that, while possibly being usable as an interrupt function, is not actually wired into
the interrupt vector table. The compiler will generate a warning if it detects a sus-
piciously looking name of a ISR() function (i.e. one that after macro replacement
does not start with "__vector_").
Vector name Old vector
name
Description Applicable for device
Generated on Wed Jul 25 09:38:10 2018 for avr-libc by Doxygen
23.17 <avr/interrupt.h>: Interrupts 244
ADC_vect SIG_ADC ADC Conversion
Complete
AT90S2333, AT90S4433, AT90S4434,
AT90S8535, AT90PWM216,
AT90PWM2B, AT90PWM316,
AT90PWM3B, AT90PWM3, AT90PWM2,
AT90PWM1, AT90CAN128, AT90CAN32,
AT90CAN64, ATmega103, ATmega128,
ATmega1284P, ATmega16, ATmega163,
ATmega165, ATmega165P, ATmega168P,
ATmega169, ATmega169P, ATmega32,
ATmega323, ATmega325, ATmega3250,
ATmega3250P, ATmega328P, ATmega329,
ATmega3290, ATmega3290P, ATmega48P,
ATmega64, ATmega645, ATmega6450,
ATmega649, ATmega6490, ATmega8,
ATmega8535, ATmega88P, ATmega168,
ATmega48, ATmega88, ATmega640, AT-
mega1280, ATmega1281, ATmega2560,
ATmega2561, ATmega324P, ATmega164P,
ATmega644P, ATmega644, ATtiny13, AT-
tiny15, ATtiny26, ATtiny43U, ATtiny48,
ATtiny24, ATtiny44, ATtiny84, ATtiny45,
ATtiny25, ATtiny85, ATtiny261, ATtiny461,
ATtiny861, AT90USB1287, AT90USB1286,
AT90USB647, AT90USB646
ANALOG_-
COMP_0_vect
SIG_-
COMPARATOR0
Analog Com-
parator 0
AT90PWM3, AT90PWM2, AT90PWM1
ANALOG_-
COMP_1_vect
SIG_-
COMPARATOR1
Analog Com-
parator 1
AT90PWM3, AT90PWM2, AT90PWM1
ANALOG_-
COMP_2_vect
SIG_-
COMPARATOR2
Analog Com-
parator 2
AT90PWM3, AT90PWM2, AT90PWM1
ANALOG_-
COMP_vect
SIG_-
COMPARATOR
Analog Com-
parator
AT90CAN128, AT90CAN32, AT90CAN64,
ATmega103, ATmega128, ATmega1284P,
ATmega165, ATmega165P, ATmega168P,
ATmega169, ATmega169P, ATmega325,
ATmega3250, ATmega3250P, ATmega328P,
ATmega329, ATmega3290, ATmega3290P,
ATmega48P, ATmega64, ATmega645,
ATmega6450, ATmega649, ATmega6490,
ATmega88P, ATmega168, ATmega48,
ATmega88, ATmega640, ATmega1280,
ATmega1281, ATmega2560, ATmega2561,
ATmega324P, ATmega164P, ATmega644P,
ATmega644, AT90USB162, AT90USB82,
AT90USB1287, AT90USB1286,
AT90USB647, AT90USB646
ANA_-
COMP_vect
SIG_-
COMPARATOR
Analog Com-
parator
AT90S1200, AT90S2313, AT90S2333,
AT90S4414, AT90S4433, AT90S4434,
AT90S8515, AT90S8535, ATmega16,
ATmega161, ATmega162, ATmega163,
ATmega32, ATmega323, ATmega8, AT-
mega8515, ATmega8535, ATtiny11,
ATtiny12, ATtiny13, ATtiny15, ATtiny2313,
ATtiny26, ATtiny28, ATtiny43U, ATtiny48,
ATtiny24, ATtiny44, ATtiny84, ATtiny45,
ATtiny25, ATtiny85, ATtiny261, ATtiny461,
ATtiny861
CANIT_vect SIG_CAN_-
INTERRUPT1
CAN Transfer
Complete or
Error
AT90CAN128, AT90CAN32, AT90CAN64
Generated on Wed Jul 25 09:38:10 2018 for avr-libc by Doxygen
23.17 <avr/interrupt.h>: Interrupts 245
EEPROM_-
READY_vect
SIG_-
EEPROM_-
READY,
SIG_EE_-
READY
ATtiny2313
EE_RDY_vect SIG_-
EEPROM_-
READY
EEPROM Ready AT90S2333, AT90S4433, AT90S4434,
AT90S8535, ATmega16, ATmega161,
ATmega162, ATmega163, ATmega32,
ATmega323, ATmega8, ATmega8515,
ATmega8535, ATtiny12, ATtiny13, AT-
tiny15, ATtiny26, ATtiny43U, ATtiny48,
ATtiny24, ATtiny44, ATtiny84, ATtiny45,
ATtiny25, ATtiny85, ATtiny261, ATtiny461,
ATtiny861
EE_READY_-
vect
SIG_-
EEPROM_-
READY
EEPROM Ready AT90PWM3, AT90PWM2, AT90PWM1,
AT90CAN128, AT90CAN32, AT90CAN64,
ATmega103, ATmega128, ATmega1284P,
ATmega165, ATmega165P, ATmega168P,
ATmega169, ATmega169P, ATmega325,
ATmega3250, ATmega3250P, ATmega328P,
ATmega329, ATmega3290, ATmega3290P,
ATmega32HVB, ATmega406, ATmega48P,
ATmega64, ATmega645, ATmega6450,
ATmega649, ATmega6490, ATmega88P,
ATmega168, ATmega48, ATmega88, AT-
mega640, ATmega1280, ATmega1281, AT-
mega2560, ATmega2561, ATmega324P, AT-
mega164P, ATmega644P, ATmega644, AT-
mega16HVA, AT90USB162, AT90USB82,
AT90USB1287, AT90USB1286,
AT90USB647, AT90USB646
EXT_INT0_-
vect
SIG_-
INTERRUPT0
External Interrupt
Request 0
ATtiny24, ATtiny44, ATtiny84
INT0_vect SIG_-
INTERRUPT0
External Interrupt
0
AT90S1200, AT90S2313, AT90S2323,
AT90S2333, AT90S2343, AT90S4414,
AT90S4433, AT90S4434, AT90S8515,
AT90S8535, AT90PWM216,
AT90PWM2B, AT90PWM316,
AT90PWM3B, AT90PWM3, AT90PWM2,
AT90PWM1, AT90CAN128, AT90CAN32,
AT90CAN64, ATmega103, ATmega128,
ATmega1284P, ATmega16, ATmega161,
ATmega162, ATmega163, ATmega165,
ATmega165P, ATmega168P, ATmega169,
ATmega169P, ATmega32, ATmega323,
ATmega325, ATmega3250, ATmega3250P,
ATmega328P, ATmega329, ATmega3290,
ATmega3290P, ATmega32HVB, AT-
mega406, ATmega48P, ATmega64, AT-
mega645, ATmega6450, ATmega649,
ATmega6490, ATmega8, ATmega8515,
ATmega8535, ATmega88P, ATmega168,
ATmega48, ATmega88, ATmega640, AT-
mega1280, ATmega1281, ATmega2560,
ATmega2561, ATmega324P, ATmega164P,
ATmega644P, ATmega644, ATmega16HVA,
ATtiny11, ATtiny12, ATtiny13, ATtiny15,
ATtiny22, ATtiny2313, ATtiny26, ATtiny28,
ATtiny43U, ATtiny48, ATtiny45, ATtiny25,
ATtiny85, ATtiny261, ATtiny461, AT-
tiny861, AT90USB162, AT90USB82,
AT90USB1287, AT90USB1286,
AT90USB647, AT90USB646
Generated on Wed Jul 25 09:38:10 2018 for avr-libc by Doxygen
23.17 <avr/interrupt.h>: Interrupts 246
INT1_vect SIG_-
INTERRUPT1
External Interrupt
Request 1
AT90S2313, AT90S2333, AT90S4414,
AT90S4433, AT90S4434, AT90S8515,
AT90S8535, AT90PWM216,
AT90PWM2B, AT90PWM316,
AT90PWM3B, AT90PWM3, AT90PWM2,
AT90PWM1, AT90CAN128, AT90CAN32,
AT90CAN64, ATmega103, ATmega128,
ATmega1284P, ATmega16, ATmega161,
ATmega162, ATmega163, ATmega168P,
ATmega32, ATmega323, ATmega328P,
ATmega32HVB, ATmega406, AT-
mega48P, ATmega64, ATmega8, AT-
mega8515, ATmega8535, ATmega88P,
ATmega168, ATmega48, ATmega88, AT-
mega640, ATmega1280, ATmega1281,
ATmega2560, ATmega2561, ATmega324P,
ATmega164P, ATmega644P, ATmega644,
ATmega16HVA, ATtiny2313, ATtiny28,
ATtiny48, ATtiny261, ATtiny461, AT-
tiny861, AT90USB162, AT90USB82,
AT90USB1287, AT90USB1286,
AT90USB647, AT90USB646
INT2_vect SIG_-
INTERRUPT2
External Interrupt
Request 2
AT90PWM3, AT90PWM2, AT90PWM1,
AT90CAN128, AT90CAN32, AT90CAN64,
ATmega103, ATmega128, ATmega1284P,
ATmega16, ATmega161, ATmega162,
ATmega32, ATmega323, ATmega32HVB,
ATmega406, ATmega64, ATmega8515, AT-
mega8535, ATmega640, ATmega1280,
ATmega1281, ATmega2560, AT-
mega2561, ATmega324P, ATmega164P,
ATmega644P, ATmega644, AT-
mega16HVA, AT90USB162, AT90USB82,
AT90USB1287, AT90USB1286,
AT90USB647, AT90USB646
INT3_vect SIG_-
INTERRUPT3
External Interrupt
Request 3
AT90PWM3, AT90PWM2, AT90PWM1,
AT90CAN128, AT90CAN32, AT90CAN64,
ATmega103, ATmega128, ATmega32HVB,
ATmega406, ATmega64, ATmega640,
ATmega1280, ATmega1281, ATmega2560,
ATmega2561, AT90USB162, AT90USB82,
AT90USB1287, AT90USB1286,
AT90USB647, AT90USB646
INT4_vect SIG_-
INTERRUPT4
External Interrupt
Request 4
AT90CAN128, AT90CAN32, AT90CAN64,
ATmega103, ATmega128, AT-
mega64, ATmega640, ATmega1280,
ATmega1281, ATmega2560, AT-
mega2561, AT90USB162, AT90USB82,
AT90USB1287, AT90USB1286,
AT90USB647, AT90USB646
INT5_vect SIG_-
INTERRUPT5
External Interrupt
Request 5
AT90CAN128, AT90CAN32, AT90CAN64,
ATmega103, ATmega128, AT-
mega64, ATmega640, ATmega1280,
ATmega1281, ATmega2560, AT-
mega2561, AT90USB162, AT90USB82,
AT90USB1287, AT90USB1286,
AT90USB647, AT90USB646
Generated on Wed Jul 25 09:38:10 2018 for avr-libc by Doxygen
23.17 <avr/interrupt.h>: Interrupts 247
INT6_vect SIG_-
INTERRUPT6
External Interrupt
Request 6
AT90CAN128, AT90CAN32, AT90CAN64,
ATmega103, ATmega128, AT-
mega64, ATmega640, ATmega1280,
ATmega1281, ATmega2560, AT-
mega2561, AT90USB162, AT90USB82,
AT90USB1287, AT90USB1286,
AT90USB647, AT90USB646
INT7_vect SIG_-
INTERRUPT7
External Interrupt
Request 7
AT90CAN128, AT90CAN32, AT90CAN64,
ATmega103, ATmega128, AT-
mega64, ATmega640, ATmega1280,
ATmega1281, ATmega2560, AT-
mega2561, AT90USB162, AT90USB82,
AT90USB1287, AT90USB1286,
AT90USB647, AT90USB646
IO_PINS_vect SIG_PIN,
SIG_PIN_-
CHANGE
External Interrupt
Request 0
ATtiny11, ATtiny12, ATtiny15, ATtiny26
LCD_vect SIG_LCD LCD Start of
Frame
ATmega169, ATmega169P, ATmega329,
ATmega3290, ATmega3290P, ATmega649,
ATmega6490
LOWLEVEL_-
IO_PINS_vect
SIG_PIN Low-level Input
on Port B
ATtiny28
OVRIT_vect SIG_CAN_-
OVERFLOW1
CAN Timer
Overrun
AT90CAN128, AT90CAN32, AT90CAN64
PCINT0_vect SIG_PIN_-
CHANGE0
Pin Change Inter-
rupt Request 0
ATmega162, ATmega165, ATmega165P,
ATmega168P, ATmega169, ATmega169P,
ATmega325, ATmega3250, ATmega3250P,
ATmega328P, ATmega329, ATmega3290,
ATmega3290P, ATmega32HVB, AT-
mega406, ATmega48P, ATmega645,
ATmega6450, ATmega649, ATmega6490,
ATmega88P, ATmega168, ATmega48,
ATmega88, ATmega640, ATmega1280,
ATmega1281, ATmega2560, AT-
mega2561, ATmega324P, ATmega164P,
ATmega644P, ATmega644, ATtiny13,
ATtiny43U, ATtiny48, ATtiny24, AT-
tiny44, ATtiny84, ATtiny45, ATtiny25,
ATtiny85, AT90USB162, AT90USB82,
AT90USB1287, AT90USB1286,
AT90USB647, AT90USB646
PCINT1_vect SIG_PIN_-
CHANGE1
Pin Change Inter-
rupt Request 1
ATmega162, ATmega165, ATmega165P,
ATmega168P, ATmega169, ATmega169P,
ATmega325, ATmega3250, ATmega3250P,
ATmega328P, ATmega329, ATmega3290,
ATmega3290P, ATmega32HVB, AT-
mega406, ATmega48P, ATmega645,
ATmega6450, ATmega649, ATmega6490,
ATmega88P, ATmega168, ATmega48,
ATmega88, ATmega640, ATmega1280,
ATmega1281, ATmega2560, ATmega2561,
ATmega324P, ATmega164P, ATmega644P,
ATmega644, ATtiny43U, ATtiny48, AT-
tiny24, ATtiny44, ATtiny84, AT90USB162,
AT90USB82
PCINT2_vect SIG_PIN_-
CHANGE2
Pin Change Inter-
rupt Request 2
ATmega3250, ATmega3250P, ATmega328P,
ATmega3290, ATmega3290P, ATmega48P,
ATmega6450, ATmega6490, ATmega88P,
ATmega168, ATmega48, ATmega88, AT-
mega640, ATmega1280, ATmega1281, AT-
mega2560, ATmega2561, ATmega324P, AT-
mega164P, ATmega644P, ATmega644, AT-
tiny48
Generated on Wed Jul 25 09:38:10 2018 for avr-libc by Doxygen
23.17 <avr/interrupt.h>: Interrupts 248
PCINT3_vect SIG_PIN_-
CHANGE3
Pin Change Inter-
rupt Request 3
ATmega3250, ATmega3250P, ATmega3290,
ATmega3290P, ATmega6450, ATmega6490,
ATmega324P, ATmega164P, ATmega644P,
ATmega644, ATtiny48
PCINT_vect SIG_PIN_-
CHANGE,
SIG_PCINT
ATtiny2313, ATtiny261, ATtiny461, AT-
tiny861
PSC0_-
CAPT_vect
SIG_PSC0_-
CAPTURE
PSC0 Capture
Event
AT90PWM3, AT90PWM2, AT90PWM1
PSC0_EC_-
vect
SIG_PSC0_-
END_CYCLE
PSC0 End Cycle AT90PWM3, AT90PWM2, AT90PWM1
PSC1_-
CAPT_vect
SIG_PSC1_-
CAPTURE
PSC1 Capture
Event
AT90PWM3, AT90PWM2, AT90PWM1
PSC1_EC_-
vect
SIG_PSC1_-
END_CYCLE
PSC1 End Cycle AT90PWM3, AT90PWM2, AT90PWM1
PSC2_-
CAPT_vect
SIG_PSC2_-
CAPTURE
PSC2 Capture
Event
AT90PWM3, AT90PWM2, AT90PWM1
PSC2_EC_-
vect
SIG_PSC2_-
END_CYCLE
PSC2 End Cycle AT90PWM3, AT90PWM2, AT90PWM1
SPI_STC_vect SIG_SPI Serial Transfer
Complete
AT90S2333, AT90S4414, AT90S4433,
AT90S4434, AT90S8515, AT90S8535,
AT90PWM216, AT90PWM2B,
AT90PWM316, AT90PWM3B,
AT90PWM3, AT90PWM2, AT90PWM1,
AT90CAN128, AT90CAN32, AT90CAN64,
ATmega103, ATmega128, ATmega1284P,
ATmega16, ATmega161, ATmega162,
ATmega163, ATmega165, ATmega165P,
ATmega168P, ATmega169, ATmega169P,
ATmega32, ATmega323, ATmega325,
ATmega3250, ATmega3250P, ATmega328P,
ATmega329, ATmega3290, ATmega3290P,
ATmega32HVB, ATmega48P, ATmega64,
ATmega645, ATmega6450, ATmega649,
ATmega6490, ATmega8, ATmega8515,
ATmega8535, ATmega88P, ATmega168,
ATmega48, ATmega88, ATmega640, AT-
mega1280, ATmega1281, ATmega2560,
ATmega2561, ATmega324P, ATmega164P,
ATmega644P, ATmega644, ATmega16HVA,
ATtiny48, AT90USB162, AT90USB82,
AT90USB1287, AT90USB1286,
AT90USB647, AT90USB646
SPM_RDY_-
vect
SIG_SPM_-
READY
Store Program
Memory Ready
ATmega16, ATmega162, ATmega32, AT-
mega323, ATmega8, ATmega8515, AT-
mega8535
SPM_-
READY_vect
SIG_SPM_-
READY
Store Program
Memory Read
AT90PWM3, AT90PWM2, AT90PWM1,
AT90CAN128, AT90CAN32, AT90CAN64,
ATmega128, ATmega1284P, ATmega165,
ATmega165P, ATmega168P, ATmega169,
ATmega169P, ATmega325, ATmega3250,
ATmega3250P, ATmega328P, ATmega329,
ATmega3290, ATmega3290P, ATmega406,
ATmega48P, ATmega64, ATmega645,
ATmega6450, ATmega649, ATmega6490,
ATmega88P, ATmega168, ATmega48,
ATmega88, ATmega640, ATmega1280,
ATmega1281, ATmega2560, ATmega2561,
ATmega324P, ATmega164P, ATmega644P,
ATmega644, AT90USB162, AT90USB82,
AT90USB1287, AT90USB1286,
AT90USB647, AT90USB646
Generated on Wed Jul 25 09:38:10 2018 for avr-libc by Doxygen
23.17 <avr/interrupt.h>: Interrupts 249
TIM0_-
COMPA_vect
SIG_-
OUTPUT_-
COMPARE0A
Timer/Counter
Compare Match
A
ATtiny13, ATtiny43U, ATtiny24, ATtiny44,
ATtiny84, ATtiny45, ATtiny25, ATtiny85
TIM0_-
COMPB_vect
SIG_-
OUTPUT_-
COMPARE0B
Timer/Counter
Compare Match
B
ATtiny13, ATtiny43U, ATtiny24, ATtiny44,
ATtiny84, ATtiny45, ATtiny25, ATtiny85
TIM0_OVF_-
vect
SIG_-
OVERFLOW0
Timer/Counter0
Overflow
ATtiny13, ATtiny43U, ATtiny24, ATtiny44,
ATtiny84, ATtiny45, ATtiny25, ATtiny85
TIM1_-
CAPT_vect
SIG_INPUT_-
CAPTURE1
Timer/Counter1
Capture Event
ATtiny24, ATtiny44, ATtiny84
TIM1_-
COMPA_vect
SIG_-
OUTPUT_-
COMPARE1A
Timer/Counter1
Compare Match
A
ATtiny24, ATtiny44, ATtiny84, ATtiny45,
ATtiny25, ATtiny85
TIM1_-
COMPB_vect
SIG_-
OUTPUT_-
COMPARE1B
Timer/Counter1
Compare Match
B
ATtiny24, ATtiny44, ATtiny84, ATtiny45,
ATtiny25, ATtiny85
TIM1_OVF_-
vect
SIG_-
OVERFLOW1
Timer/Counter1
Overflow
ATtiny24, ATtiny44, ATtiny84, ATtiny45,
ATtiny25, ATtiny85
TIMER0_-
CAPT_vect
SIG_INPUT_-
CAPTURE0
ADC Conversion
Complete
ATtiny261, ATtiny461, ATtiny861
TIMER0_-
COMPA_vect
SIG_-
OUTPUT_-
COMPARE0A
TimerCounter0
Compare Match
A
ATmega168, ATmega48, ATmega88, AT-
mega640, ATmega1280, ATmega1281,
ATmega2560, ATmega2561, AT-
mega324P, ATmega164P, ATmega644P,
ATmega644, ATmega16HVA, ATtiny2313,
ATtiny48, ATtiny261, ATtiny461, AT-
tiny861, AT90USB162, AT90USB82,
AT90USB1287, AT90USB1286,
AT90USB647, AT90USB646
TIMER0_-
COMPB_vect
SIG_-
OUTPUT_-
COMPARE0B,
SIG_-
OUTPUT_-
COMPARE0_-
B
Timer Counter 0
Compare Match
B
AT90PWM3, AT90PWM2, AT90PWM1,
ATmega1284P, ATmega168P, ATmega328P,
ATmega32HVB, ATmega48P, AT-
mega88P, ATmega168, ATmega48, AT-
mega88, ATmega640, ATmega1280,
ATmega1281, ATmega2560, ATmega2561,
ATmega324P, ATmega164P, ATmega644P,
ATmega644, ATmega16HVA, ATtiny2313,
ATtiny48, ATtiny261, ATtiny461, AT-
tiny861, AT90USB162, AT90USB82,
AT90USB1287, AT90USB1286,
AT90USB647, AT90USB646
TIMER0_-
COMP_A_-
vect
SIG_-
OUTPUT_-
COMPARE0A,
SIG_-
OUTPUT_-
COMPARE0_-
A
Timer/Counter0
Compare Match
A
AT90PWM3, AT90PWM2, AT90PWM1
TIMER0_-
COMP_vect
SIG_-
OUTPUT_-
COMPARE0
Timer/Counter0
Compare Match
AT90CAN128, AT90CAN32, AT90CAN64,
ATmega103, ATmega128, ATmega16, AT-
mega161, ATmega162, ATmega165, AT-
mega165P, ATmega169, ATmega169P, AT-
mega32, ATmega323, ATmega325, AT-
mega3250, ATmega3250P, ATmega329, AT-
mega3290, ATmega3290P, ATmega64, AT-
mega645, ATmega6450, ATmega649, AT-
mega6490, ATmega8515, ATmega8535
TIMER0_-
OVF0_vect
SIG_-
OVERFLOW0
Timer/Counter0
Overflow
AT90S2313, AT90S2323, AT90S2343, AT-
tiny22, ATtiny26
Generated on Wed Jul 25 09:38:10 2018 for avr-libc by Doxygen
23.17 <avr/interrupt.h>: Interrupts 250
TIMER0_-
OVF_vect
SIG_-
OVERFLOW0
Timer/Counter0
Overflow
AT90S1200, AT90S2333, AT90S4414,
AT90S4433, AT90S4434, AT90S8515,
AT90S8535, AT90PWM216,
AT90PWM2B, AT90PWM316,
AT90PWM3B, AT90PWM3, AT90PWM2,
AT90PWM1, AT90CAN128, AT90CAN32,
AT90CAN64, ATmega103, ATmega128,
ATmega1284P, ATmega16, ATmega161,
ATmega162, ATmega163, ATmega165,
ATmega165P, ATmega168P, ATmega169,
ATmega169P, ATmega32, ATmega323,
ATmega325, ATmega3250, ATmega3250P,
ATmega328P, ATmega329, ATmega3290,
ATmega3290P, ATmega32HVB, AT-
mega48P, ATmega64, ATmega645, AT-
mega6450, ATmega649, ATmega6490,
ATmega8, ATmega8515, ATmega8535,
ATmega88P, ATmega168, ATmega48,
ATmega88, ATmega640, ATmega1280,
ATmega1281, ATmega2560, ATmega2561,
ATmega324P, ATmega164P, ATmega644P,
ATmega644, ATmega16HVA, ATtiny11,
ATtiny12, ATtiny15, ATtiny2313, ATtiny28,
ATtiny48, ATtiny261, ATtiny461, AT-
tiny861, AT90USB162, AT90USB82,
AT90USB1287, AT90USB1286,
AT90USB647, AT90USB646
TIMER1_-
CAPT1_vect
SIG_INPUT_-
CAPTURE1
Timer/Counter1
Capture Event
AT90S2313
TIMER1_-
CAPT_vect
SIG_INPUT_-
CAPTURE1
Timer/Counter
Capture Event
AT90S2333, AT90S4414, AT90S4433,
AT90S4434, AT90S8515, AT90S8535,
AT90PWM216, AT90PWM2B,
AT90PWM316, AT90PWM3B,
AT90PWM3, AT90PWM2, AT90PWM1,
AT90CAN128, AT90CAN32, AT90CAN64,
ATmega103, ATmega128, ATmega1284P,
ATmega16, ATmega161, ATmega162,
ATmega163, ATmega165, ATmega165P,
ATmega168P, ATmega169, ATmega169P,
ATmega32, ATmega323, ATmega325,
ATmega3250, ATmega3250P, AT-
mega328P, ATmega329, ATmega3290,
ATmega3290P, ATmega48P, ATmega64,
ATmega645, ATmega6450, ATmega649,
ATmega6490, ATmega8, ATmega8515,
ATmega8535, ATmega88P, ATmega168,
ATmega48, ATmega88, ATmega640, AT-
mega1280, ATmega1281, ATmega2560,
ATmega2561, ATmega324P, ATmega164P,
ATmega644P, ATmega644, ATtiny2313,
ATtiny48, AT90USB162, AT90USB82,
AT90USB1287, AT90USB1286,
AT90USB647, AT90USB646
TIMER1_-
CMPA_vect
SIG_-
OUTPUT_-
COMPARE1A
Timer/Counter1
Compare Match
1A
ATtiny26
TIMER1_-
CMPB_vect
SIG_-
OUTPUT_-
COMPARE1B
Timer/Counter1
Compare Match
1B
ATtiny26
TIMER1_-
COMP1_vect
SIG_-
OUTPUT_-
COMPARE1A
Timer/Counter1
Compare Match
AT90S2313
Generated on Wed Jul 25 09:38:10 2018 for avr-libc by Doxygen
23.17 <avr/interrupt.h>: Interrupts 251
TIMER1_-
COMPA_vect
SIG_-
OUTPUT_-
COMPARE1A
Timer/Counter1
Compare Match
A
AT90S4414, AT90S4434, AT90S8515,
AT90S8535, AT90PWM216,
AT90PWM2B, AT90PWM316,
AT90PWM3B, AT90PWM3, AT90PWM2,
AT90PWM1, AT90CAN128, AT90CAN32,
AT90CAN64, ATmega103, ATmega128,
ATmega1284P, ATmega16, ATmega161,
ATmega162, ATmega163, ATmega165,
ATmega165P, ATmega168P, ATmega169,
ATmega169P, ATmega32, ATmega323,
ATmega325, ATmega3250, ATmega3250P,
ATmega328P, ATmega329, ATmega3290,
ATmega3290P, ATmega32HVB, AT-
mega48P, ATmega64, ATmega645, AT-
mega6450, ATmega649, ATmega6490,
ATmega8, ATmega8515, ATmega8535,
ATmega88P, ATmega168, ATmega48,
ATmega88, ATmega640, ATmega1280,
ATmega1281, ATmega2560, ATmega2561,
ATmega324P, ATmega164P, ATmega644P,
ATmega644, ATmega16HVA, ATtiny2313,
ATtiny48, ATtiny261, ATtiny461, AT-
tiny861, AT90USB162, AT90USB82,
AT90USB1287, AT90USB1286,
AT90USB647, AT90USB646
TIMER1_-
COMPB_vect
SIG_-
OUTPUT_-
COMPARE1B
Timer/Counter1
Compare MatchB
AT90S4414, AT90S4434, AT90S8515,
AT90S8535, AT90PWM216,
AT90PWM2B, AT90PWM316,
AT90PWM3B, AT90PWM3, AT90PWM2,
AT90PWM1, AT90CAN128, AT90CAN32,
AT90CAN64, ATmega103, ATmega128,
ATmega1284P, ATmega16, ATmega161,
ATmega162, ATmega163, ATmega165,
ATmega165P, ATmega168P, ATmega169,
ATmega169P, ATmega32, ATmega323,
ATmega325, ATmega3250, ATmega3250P,
ATmega328P, ATmega329, ATmega3290,
ATmega3290P, ATmega32HVB, AT-
mega48P, ATmega64, ATmega645, AT-
mega6450, ATmega649, ATmega6490,
ATmega8, ATmega8515, ATmega8535,
ATmega88P, ATmega168, ATmega48,
ATmega88, ATmega640, ATmega1280,
ATmega1281, ATmega2560, ATmega2561,
ATmega324P, ATmega164P, ATmega644P,
ATmega644, ATmega16HVA, ATtiny2313,
ATtiny48, ATtiny261, ATtiny461, AT-
tiny861, AT90USB162, AT90USB82,
AT90USB1287, AT90USB1286,
AT90USB647, AT90USB646
TIMER1_-
COMPC_vect
SIG_-
OUTPUT_-
COMPARE1C
Timer/Counter1
Compare Match
C
AT90CAN128, AT90CAN32, AT90CAN64,
ATmega128, ATmega64, ATmega640,
ATmega1280, ATmega1281, ATmega2560,
ATmega2561, AT90USB162, AT90USB82,
AT90USB1287, AT90USB1286,
AT90USB647, AT90USB646
TIMER1_-
COMPD_vect
SIG_-
OUTPUT_-
COMPARE0D
Timer/Counter1
Compare Match
D
ATtiny261, ATtiny461, ATtiny861
TIMER1_-
COMP_vect
SIG_-
OUTPUT_-
COMPARE1A
Timer/Counter1
Compare Match
AT90S2333, AT90S4433, ATtiny15
Generated on Wed Jul 25 09:38:10 2018 for avr-libc by Doxygen
23.17 <avr/interrupt.h>: Interrupts 252
TIMER1_-
OVF1_vect
SIG_-
OVERFLOW1
Timer/Counter1
Overflow
AT90S2313, ATtiny26
TIMER1_-
OVF_vect
SIG_-
OVERFLOW1
Timer/Counter1
Overflow
AT90S2333, AT90S4414, AT90S4433,
AT90S4434, AT90S8515, AT90S8535,
AT90PWM216, AT90PWM2B,
AT90PWM316, AT90PWM3B,
AT90PWM3, AT90PWM2, AT90PWM1,
AT90CAN128, AT90CAN32, AT90CAN64,
ATmega103, ATmega128, ATmega1284P,
ATmega16, ATmega161, ATmega162,
ATmega163, ATmega165, ATmega165P,
ATmega168P, ATmega169, ATmega169P,
ATmega32, ATmega323, ATmega325,
ATmega3250, ATmega3250P, ATmega328P,
ATmega329, ATmega3290, ATmega3290P,
ATmega32HVB, ATmega48P, AT-
mega64, ATmega645, ATmega6450,
ATmega649, ATmega6490, ATmega8,
ATmega8515, ATmega8535, ATmega88P,
ATmega168, ATmega48, ATmega88, AT-
mega640, ATmega1280, ATmega1281,
ATmega2560, ATmega2561, ATmega324P,
ATmega164P, ATmega644P, ATmega644,
ATmega16HVA, ATtiny15, ATtiny2313,
ATtiny48, ATtiny261, ATtiny461, AT-
tiny861, AT90USB162, AT90USB82,
AT90USB1287, AT90USB1286,
AT90USB647, AT90USB646
TIMER2_-
COMPA_vect
SIG_-
OUTPUT_-
COMPARE2A
Timer/Counter2
Compare Match
A
ATmega168, ATmega48, ATmega88, AT-
mega640, ATmega1280, ATmega1281,
ATmega2560, ATmega2561, AT-
mega324P, ATmega164P, ATmega644P, AT-
mega644, AT90USB1287, AT90USB1286,
AT90USB647, AT90USB646
TIMER2_-
COMPB_vect
SIG_-
OUTPUT_-
COMPARE2B
Timer/Counter2
Compare Match
A
ATmega168, ATmega48, ATmega88, AT-
mega640, ATmega1280, ATmega1281,
ATmega2560, ATmega2561, AT-
mega324P, ATmega164P, ATmega644P, AT-
mega644, AT90USB1287, AT90USB1286,
AT90USB647, AT90USB646
TIMER2_-
COMP_vect
SIG_-
OUTPUT_-
COMPARE2
Timer/Counter2
Compare Match
AT90S4434, AT90S8535, AT90CAN128,
AT90CAN32, AT90CAN64, ATmega103,
ATmega128, ATmega16, ATmega161, AT-
mega162, ATmega163, ATmega165, AT-
mega165P, ATmega169, ATmega169P, AT-
mega32, ATmega323, ATmega325, AT-
mega3250, ATmega3250P, ATmega329, AT-
mega3290, ATmega3290P, ATmega64, AT-
mega645, ATmega6450, ATmega649, AT-
mega6490, ATmega8, ATmega8535
Generated on Wed Jul 25 09:38:10 2018 for avr-libc by Doxygen
23.17 <avr/interrupt.h>: Interrupts 253
TIMER2_-
OVF_vect
SIG_-
OVERFLOW2
Timer/Counter2
Overflow
AT90S4434, AT90S8535, AT90CAN128,
AT90CAN32, AT90CAN64, ATmega103,
ATmega128, ATmega1284P, ATmega16,
ATmega161, ATmega162, ATmega163,
ATmega165, ATmega165P, ATmega168P,
ATmega169, ATmega169P, ATmega32, AT-
mega323, ATmega325, ATmega3250,
ATmega3250P, ATmega328P, AT-
mega329, ATmega3290, ATmega3290P,
ATmega48P, ATmega64, ATmega645,
ATmega6450, ATmega649, ATmega6490,
ATmega8, ATmega8535, ATmega88P,
ATmega168, ATmega48, ATmega88, AT-
mega640, ATmega1280, ATmega1281,
ATmega2560, ATmega2561, AT-
mega324P, ATmega164P, ATmega644P, AT-
mega644, AT90USB1287, AT90USB1286,
AT90USB647, AT90USB646
TIMER3_-
CAPT_vect
SIG_INPUT_-
CAPTURE3
Timer/Counter3
Capture Event
AT90CAN128, AT90CAN32, AT90CAN64,
ATmega128, ATmega1284P, ATmega162,
ATmega64, ATmega640, ATmega1280,
ATmega1281, ATmega2560, AT-
mega2561, AT90USB1287, AT90USB1286,
AT90USB647, AT90USB646
TIMER3_-
COMPA_vect
SIG_-
OUTPUT_-
COMPARE3A
Timer/Counter3
Compare Match
A
AT90CAN128, AT90CAN32, AT90CAN64,
ATmega128, ATmega1284P, ATmega162,
ATmega64, ATmega640, ATmega1280,
ATmega1281, ATmega2560, AT-
mega2561, AT90USB1287, AT90USB1286,
AT90USB647, AT90USB646
TIMER3_-
COMPB_vect
SIG_-
OUTPUT_-
COMPARE3B
Timer/Counter3
Compare Match
B
AT90CAN128, AT90CAN32, AT90CAN64,
ATmega128, ATmega1284P, ATmega162,
ATmega64, ATmega640, ATmega1280,
ATmega1281, ATmega2560, AT-
mega2561, AT90USB1287, AT90USB1286,
AT90USB647, AT90USB646
TIMER3_-
COMPC_vect
SIG_-
OUTPUT_-
COMPARE3C
Timer/Counter3
Compare Match
C
AT90CAN128, AT90CAN32, AT90CAN64,
ATmega128, ATmega64, ATmega640, AT-
mega1280, ATmega1281, ATmega2560, AT-
mega2561, AT90USB1287, AT90USB1286,
AT90USB647, AT90USB646
TIMER3_-
OVF_vect
SIG_-
OVERFLOW3
Timer/Counter3
Overflow
AT90CAN128, AT90CAN32, AT90CAN64,
ATmega128, ATmega1284P, ATmega162,
ATmega64, ATmega640, ATmega1280,
ATmega1281, ATmega2560, AT-
mega2561, AT90USB1287, AT90USB1286,
AT90USB647, AT90USB646
TIMER4_-
CAPT_vect
SIG_INPUT_-
CAPTURE4
Timer/Counter4
Capture Event
ATmega640, ATmega1280, ATmega1281,
ATmega2560, ATmega2561
TIMER4_-
COMPA_vect
SIG_-
OUTPUT_-
COMPARE4A
Timer/Counter4
Compare Match
A
ATmega640, ATmega1280, ATmega1281,
ATmega2560, ATmega2561
TIMER4_-
COMPB_vect
SIG_-
OUTPUT_-
COMPARE4B
Timer/Counter4
Compare Match
B
ATmega640, ATmega1280, ATmega1281,
ATmega2560, ATmega2561
TIMER4_-
COMPC_vect
SIG_-
OUTPUT_-
COMPARE4C
Timer/Counter4
Compare Match
C
ATmega640, ATmega1280, ATmega1281,
ATmega2560, ATmega2561
TIMER4_-
OVF_vect
SIG_-
OVERFLOW4
Timer/Counter4
Overflow
ATmega640, ATmega1280, ATmega1281,
ATmega2560, ATmega2561
TIMER5_-
CAPT_vect
SIG_INPUT_-
CAPTURE5
Timer/Counter5
Capture Event
ATmega640, ATmega1280, ATmega1281,
ATmega2560, ATmega2561
Generated on Wed Jul 25 09:38:10 2018 for avr-libc by Doxygen
23.17 <avr/interrupt.h>: Interrupts 254
TIMER5_-
COMPA_vect
SIG_-
OUTPUT_-
COMPARE5A
Timer/Counter5
Compare Match
A
ATmega640, ATmega1280, ATmega1281,
ATmega2560, ATmega2561
TIMER5_-
COMPB_vect
SIG_-
OUTPUT_-
COMPARE5B
Timer/Counter5
Compare Match
B
ATmega640, ATmega1280, ATmega1281,
ATmega2560, ATmega2561
TIMER5_-
COMPC_vect
SIG_-
OUTPUT_-
COMPARE5C
Timer/Counter5
Compare Match
C
ATmega640, ATmega1280, ATmega1281,
ATmega2560, ATmega2561
TIMER5_-
OVF_vect
SIG_-
OVERFLOW5
Timer/Counter5
Overflow
ATmega640, ATmega1280, ATmega1281,
ATmega2560, ATmega2561
TWI_vect SIG_2WIRE_-
SERIAL
2-wire Serial In-
terface
AT90CAN128, AT90CAN32, AT90CAN64,
ATmega128, ATmega1284P, ATmega16,
ATmega163, ATmega168P, ATmega32, AT-
mega323, ATmega328P, ATmega32HVB,
ATmega406, ATmega48P, ATmega64,
ATmega8, ATmega8535, ATmega88P,
ATmega168, ATmega48, ATmega88, AT-
mega640, ATmega1280, ATmega1281,
ATmega2560, ATmega2561, ATmega324P,
ATmega164P, ATmega644P, ATmega644,
ATtiny48, AT90USB1287, AT90USB1286,
AT90USB647, AT90USB646
TXDONE_-
vect
SIG_-
TXDONE
Transmission
Done, Bit Timer
Flag 2 Interrupt
AT86RF401
TXEMPTY_-
vect
SIG_TXBE Transmit Buffer
Empty, Bit Itmer
Flag 0 Interrupt
AT86RF401
UART0_RX_-
vect
SIG_-
UART0_-
RECV
UART0, Rx
Complete
ATmega161
UART0_TX_-
vect
SIG_-
UART0_-
TRANS
UART0, Tx
Complete
ATmega161
UART0_-
UDRE_vect
SIG_-
UART0_-
DATA
UART0 Data
Register Empty
ATmega161
UART1_RX_-
vect
SIG_-
UART1_-
RECV
UART1, Rx
Complete
ATmega161
UART1_TX_-
vect
SIG_-
UART1_-
TRANS
UART1, Tx
Complete
ATmega161
UART1_-
UDRE_vect
SIG_-
UART1_-
DATA
UART1 Data
Register Empty
ATmega161
UART_RX_-
vect
SIG_UART_-
RECV
UART, Rx Com-
plete
AT90S2313, AT90S2333, AT90S4414,
AT90S4433, AT90S4434, AT90S8515,
AT90S8535, ATmega103, ATmega163,
ATmega8515
UART_TX_-
vect
SIG_UART_-
TRANS
UART, Tx Com-
plete
AT90S2313, AT90S2333, AT90S4414,
AT90S4433, AT90S4434, AT90S8515,
AT90S8535, ATmega103, ATmega163,
ATmega8515
UART_-
UDRE_vect
SIG_UART_-
DATA
UART Data Reg-
ister Empty
AT90S2313, AT90S2333, AT90S4414,
AT90S4433, AT90S4434, AT90S8515,
AT90S8535, ATmega103, ATmega163,
ATmega8515
USART0_-
RXC_vect
SIG_-
USART0_-
RECV
USART0, Rx
Complete
ATmega162
Generated on Wed Jul 25 09:38:10 2018 for avr-libc by Doxygen
23.17 <avr/interrupt.h>: Interrupts 255
USART0_-
RX_vect
SIG_-
UART0_-
RECV
USART0, Rx
Complete
AT90CAN128, AT90CAN32, AT90CAN64,
ATmega128, ATmega1284P, ATmega165,
ATmega165P, ATmega169, ATmega169P,
ATmega325, ATmega329, ATmega64, AT-
mega645, ATmega649, ATmega640, AT-
mega1280, ATmega1281, ATmega2560, AT-
mega2561, ATmega324P, ATmega164P, AT-
mega644P, ATmega644
USART0_-
TXC_vect
SIG_-
USART0_-
TRANS
USART0, Tx
Complete
ATmega162
USART0_-
TX_vect
SIG_-
UART0_-
TRANS
USART0, Tx
Complete
AT90CAN128, AT90CAN32, AT90CAN64,
ATmega128, ATmega1284P, ATmega165,
ATmega165P, ATmega169, ATmega169P,
ATmega325, ATmega3250, ATmega3250P,
ATmega329, ATmega3290, ATmega3290P,
ATmega64, ATmega645, ATmega6450, AT-
mega649, ATmega6490, ATmega640, AT-
mega1280, ATmega1281, ATmega2560, AT-
mega2561, ATmega324P, ATmega164P, AT-
mega644P, ATmega644
USART0_-
UDRE_vect
SIG_-
UART0_-
DATA
USART0 Data
Register Empty
AT90CAN128, AT90CAN32, AT90CAN64,
ATmega128, ATmega1284P, ATmega162,
ATmega165, ATmega165P, ATmega169,
ATmega169P, ATmega325, ATmega329,
ATmega64, ATmega645, ATmega649,
ATmega640, ATmega1280, ATmega1281,
ATmega2560, ATmega2561, ATmega324P,
ATmega164P, ATmega644P, ATmega644
USART1_-
RXC_vect
SIG_-
USART1_-
RECV
USART1, Rx
Complete
ATmega162
USART1_-
RX_vect
SIG_-
UART1_-
RECV
USART1, Rx
Complete
AT90CAN128, AT90CAN32, AT90CAN64,
ATmega128, ATmega1284P, ATmega64,
ATmega640, ATmega1280, ATmega1281,
ATmega2560, ATmega2561, AT-
mega324P, ATmega164P, ATmega644P,
ATmega644, AT90USB162, AT90USB82,
AT90USB1287, AT90USB1286,
AT90USB647, AT90USB646
USART1_-
TXC_vect
SIG_-
USART1_-
TRANS
USART1, Tx
Complete
ATmega162
USART1_-
TX_vect
SIG_-
UART1_-
TRANS
USART1, Tx
Complete
AT90CAN128, AT90CAN32, AT90CAN64,
ATmega128, ATmega1284P, ATmega64,
ATmega640, ATmega1280, ATmega1281,
ATmega2560, ATmega2561, AT-
mega324P, ATmega164P, ATmega644P,
ATmega644, AT90USB162, AT90USB82,
AT90USB1287, AT90USB1286,
AT90USB647, AT90USB646
USART1_-
UDRE_vect
SIG_-
UART1_-
DATA
USART1, Data
Register Empty
AT90CAN128, AT90CAN32, AT90CAN64,
ATmega128, ATmega1284P, ATmega162,
ATmega64, ATmega640, ATmega1280,
ATmega1281, ATmega2560, ATmega2561,
ATmega324P, ATmega164P, ATmega644P,
ATmega644, AT90USB162, AT90USB82,
AT90USB1287, AT90USB1286,
AT90USB647, AT90USB646
USART2_-
RX_vect
SIG_-
USART2_-
RECV
USART2, Rx
Complete
ATmega640, ATmega1280, ATmega1281,
ATmega2560, ATmega2561
Generated on Wed Jul 25 09:38:10 2018 for avr-libc by Doxygen
23.17 <avr/interrupt.h>: Interrupts 256
USART2_-
TX_vect
SIG_-
USART2_-
TRANS
USART2, Tx
Complete
ATmega640, ATmega1280, ATmega1281,
ATmega2560, ATmega2561
USART2_-
UDRE_vect
SIG_-
USART2_-
DATA
USART2 Data
register Empty
ATmega640, ATmega1280, ATmega1281,
ATmega2560, ATmega2561
USART3_-
RX_vect
SIG_-
USART3_-
RECV
USART3, Rx
Complete
ATmega640, ATmega1280, ATmega1281,
ATmega2560, ATmega2561
USART3_-
TX_vect
SIG_-
USART3_-
TRANS
USART3, Tx
Complete
ATmega640, ATmega1280, ATmega1281,
ATmega2560, ATmega2561
USART3_-
UDRE_vect
SIG_-
USART3_-
DATA
USART3 Data
register Empty
ATmega640, ATmega1280, ATmega1281,
ATmega2560, ATmega2561
USART_-
RXC_vect
SIG_-
USART_-
RECV, SIG_-
UART_RECV
USART, Rx
Complete
ATmega16, ATmega32, ATmega323, AT-
mega8
USART_RX_-
vect
SIG_-
USART_-
RECV, SIG_-
UART_RECV
USART, Rx
Complete
AT90PWM3, AT90PWM2, AT90PWM1,
ATmega168P, ATmega3250, ATmega3250P,
ATmega328P, ATmega3290, ATmega3290P,
ATmega48P, ATmega6450, ATmega6490,
ATmega8535, ATmega88P, ATmega168,
ATmega48, ATmega88, ATtiny2313
USART_-
TXC_vect
SIG_-
USART_-
TRANS,
SIG_UART_-
TRANS
USART, Tx
Complete
ATmega16, ATmega32, ATmega323, AT-
mega8
USART_TX_-
vect
SIG_-
USART_-
TRANS,
SIG_UART_-
TRANS
USART, Tx
Complete
AT90PWM3, AT90PWM2, AT90PWM1,
ATmega168P, ATmega328P, ATmega48P,
ATmega8535, ATmega88P, ATmega168,
ATmega48, ATmega88, ATtiny2313
USART_-
UDRE_vect
SIG_-
USART_-
DATA, SIG_-
UART_DATA
USART Data
Register Empty
AT90PWM3, AT90PWM2, AT90PWM1,
ATmega16, ATmega168P, ATmega32, AT-
mega323, ATmega3250, ATmega3250P, AT-
mega328P, ATmega3290, ATmega3290P,
ATmega48P, ATmega6450, ATmega6490,
ATmega8, ATmega8535, ATmega88P, AT-
mega168, ATmega48, ATmega88, AT-
tiny2313
USI_-
OVERFLOW_-
vect
SIG_USI_-
OVERFLOW
USI Overflow ATmega165, ATmega165P, ATmega169,
ATmega169P, ATmega325, ATmega3250,
ATmega3250P, ATmega329, ATmega3290,
ATmega3290P, ATmega645, ATmega6450,
ATmega649, ATmega6490, ATtiny2313
USI_OVF_-
vect
SIG_USI_-
OVERFLOW
USI Overflow ATtiny26, ATtiny43U, ATtiny24, ATtiny44,
ATtiny84, ATtiny45, ATtiny25, ATtiny85,
ATtiny261, ATtiny461, ATtiny861
USI_START_-
vect
SIG_USI_-
START
USI Start Condi-
tion
ATmega165, ATmega165P, ATmega169,
ATmega169P, ATmega325, ATmega3250,
ATmega3250P, ATmega329, ATmega3290,
ATmega3290P, ATmega645, ATmega6450,
ATmega649, ATmega6490, ATtiny2313,
ATtiny43U, ATtiny45, ATtiny25, ATtiny85,
ATtiny261, ATtiny461, ATtiny861
USI_STRT_-
vect
SIG_USI_-
START
USI Start ATtiny26
USI_STR_-
vect
SIG_USI_-
START
USI START ATtiny24, ATtiny44, ATtiny84
Generated on Wed Jul 25 09:38:10 2018 for avr-libc by Doxygen
23.17 <avr/interrupt.h>: Interrupts 257
WATCHDOG_-
vect
SIG_-
WATCHDOG_-
TIMEOUT
Watchdog Time-
out
ATtiny24, ATtiny44, ATtiny84
WDT_-
OVERFLOW_-
vect
SIG_-
WATCHDOG_-
TIMEOUT,
SIG_WDT_-
OVERFLOW
Watchdog Timer
Overflow
ATtiny2313
WDT_vect SIG_WDT,
SIG_-
WATCHDOG_-
TIMEOUT
Watchdog Time-
out Interrupt
AT90PWM3, AT90PWM2, AT90PWM1,
ATmega1284P, ATmega168P, ATmega328P,
ATmega32HVB, ATmega406, ATmega48P,
ATmega88P, ATmega168, ATmega48,
ATmega88, ATmega640, ATmega1280,
ATmega1281, ATmega2560, ATmega2561,
ATmega324P, ATmega164P, ATmega644P,
ATmega644, ATmega16HVA, ATtiny13,
ATtiny43U, ATtiny48, ATtiny45, ATtiny25,
ATtiny85, ATtiny261, ATtiny461, AT-
tiny861, AT90USB162, AT90USB82,
AT90USB1287, AT90USB1286,
AT90USB647, AT90USB646
23.17.2 Define Documentation
23.17.2.1 #define BADISR_vect
#include <avr/interrupt.h>
This is a vector which is aliased to __vector_default, the vector executed when an ISR
fires with no accompanying ISR handler. This may be used along with the ISR() macro
to create a catch-all for undefined but used ISRs for debugging purposes.
23.17.2.2 #define cli()
Disables all
interrupts by clearing the global interrupt mask. This function actually compiles into a
single line of assembly, so there is no function call overhead. However, the macro also
implies a memory barrier which can cause additional loss of optimization.
In order to implement atomic access to multi-byte objects, consider using the macros
from <util/atomic.h>, rather than implementing them manually with cli() and sei().
23.17.2.3 #define EMPTY_INTERRUPT(vector)
Defines an empty interrupt handler function. This will not generate any prolog
or epilog code and will only return from the ISR. Do not define a function body as this
will define it for you. Example:
EMPTY_INTERRUPT(ADC_vect);
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23.17 <avr/interrupt.h>: Interrupts 258
23.17.2.4 #define ISR(vector, attributes)
Introduces an interrupt handler function (interrupt service routine) that runs with
global interrupts initially disabled by default with no attributes specified.
The attributes are optional and alter the behaviour and resultant generated code of the
interrupt routine. Multiple attributes may be used for a single function, with a space
seperating each attribute.
Valid attributes are ISR_BLOCK, ISR_NOBLOCK, ISR_NAKED and ISR_-
ALIASOF(vect).
vector must be one of the interrupt vector names that are valid for the particular
MCU type.
23.17.2.5 #define ISR_ALIAS(vector, target_vector)
Aliases a given vector to another one in the same manner as the ISR_ALIASOF
attribute for the ISR() macro. Unlike the ISR_ALIASOF attribute macro however, this
is compatible for all versions of GCC rather than just GCC version 4.2 onwards.
Note
This macro creates a trampoline function for the aliased macro. This will result in
a two cycle penalty for the aliased vector compared to the ISR the vector is aliased
to, due to the JMP/RJMP opcode used.
Deprecated
For new code, the use of ISR(..., ISR_ALIASOF(...)) is recommended.
Example:
ISR(INT0_vect)
{
PORTB = 42;
}
ISR_ALIAS(INT1_vect, INT0_vect);
23.17.2.6 #define ISR_ALIASOF(target_vector)
The ISR is linked to another ISR, specified by the vect parameter. This is compatible
with GCC 4.2 and greater only.
Use this attribute in the attributes parameter of the ISR macro.
23.17.2.7 #define ISR_BLOCK
Identical to an ISR with no attributes
specified. Global interrupts are initially disabled by the AVR hardware when entering
the ISR, without the compiler modifying this state.
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23.17 <avr/interrupt.h>: Interrupts 259
Use this attribute in the attributes parameter of the ISR macro.
23.17.2.8 #define ISR_NAKED
ISR is created with no prologue or epilogue code. The user code is responsible
for preservation of the machine state including the SREG register, as well as placing a
reti() at the end of the interrupt routine.
Use this attribute in the attributes parameter of the ISR macro.
23.17.2.9 #define ISR_NOBLOCK
ISR runs with global interrupts initially enabled. The interrupt enable
flag is activated by the compiler as early as possible within the ISR to ensure minimal
processing delay for nested interrupts.
This may be used to create nested ISRs, however care should be taken to avoid stack
overflows, or to avoid infinitely entering the ISR for those cases where the AVR hard-
ware does not clear the respective interrupt flag before entering the ISR.
Use this attribute in the attributes parameter of the ISR macro.
23.17.2.10 #define reti()
Returns from an interrupt routine, enabling global interrupts. This should be the last
command executed before leaving an ISR defined with the ISR_NAKED attribute.
This macro actually compiles into a single line of assembly, so there is no function call
overhead.
23.17.2.11 #define sei()
Enables interrupts by setting the global interrupt mask. This function
actually compiles into a single line of assembly, so there is no function call overhead.
However, the macro also implies a memory barrier which can cause additional loss of
optimization.
In order to implement atomic access to multi-byte objects, consider using the macros
from <util/atomic.h>, rather than implementing them manually with cli() and sei().
23.17.2.12 #define SIGNAL(vector)
Introduces an interrupt handler function that runs with global interrupts initially
disabled.
This is the same as the ISR macro without optional attributes.
Deprecated
Do not use SIGNAL() in new code. Use ISR() instead.
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23.18 <avr/io.h>: AVR device-specific IO definitions 260
23.18 <avr/io.h>: AVR device-specific IO definitions
Defines
• #define _PROTECTED_WRITE(reg, value)
• #define _PROTECTED_WRITE_SPM(reg, value)
23.18.1 Detailed Description
#include <avr/io.h>
This header file includes the apropriate IO definitions for the device that has been
specified by the -mmcu= compiler command-line switch. This is done by divert-
ing to the appropriate file <avr/ioXXXX.h>which should never be included di-
rectly. Some register names common to all AVR devices are defined directly within
<avr/common.h>, which is included in <avr/io.h>, but most of the details
come from the respective include file.
Note that this file always includes the following files:
#include <avr/sfr_defs.h>
#include <avr/portpins.h>
#include <avr/common.h>
#include <avr/version.h>
See <avr/sfr_defs.h>: Special function registers for more details about that header file.
Included are definitions of the IO register set and their respective bit values as specified
in the Atmel documentation. Note that inconsistencies in naming conventions, so even
identical functions sometimes get different names on different devices.
Also included are the specific names useable for interrupt function definitions as docu-
mented here.
Finally, the following macros are defined:
•RAMEND
The last on-chip RAM address.
•XRAMEND
The last possible RAM location that is addressable. This is equal to RAMEND
for devices that do not allow for external RAM. For devices that allow external
RAM, this will be larger than RAMEND.
•E2END
The last EEPROM address.
•FLASHEND
The last byte address in the Flash program space.
•SPM_PAGESIZE
For devices with bootloader support, the flash pagesize (in bytes) to be used for
the SPM instruction.
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23.19 <avr/lock.h>: Lockbit Support 261
•E2PAGESIZE
The size of the EEPROM page.
23.18.2 Define Documentation
23.18.2.1 #define _PROTECTED_WRITE(reg, value)
Write value value to IO register reg that is
protected through the Xmega configuration change protection (CCP) mechanism. This
implements the timed sequence that is required for CCP.
Example to modify the CPU clock:
#include <avr/io.h>
_PROTECTED_WRITE(CLK_PSCTRL, CLK_PSADIV0_bm);
_PROTECTED_WRITE(CLK_CTRL, CLK_SCLKSEL0_bm);
23.18.2.2 #define _PROTECTED_WRITE_SPM(reg, value)
Write value value to register reg that is protected through the
Xmega configuration change protection (CCP) key for self programming (SPM). This
implements the timed sequence that is required for CCP.
Example to modify the CPU clock:
#include <avr/io.h>
_PROTECTED_WRITE_SPM(NVMCTRL_CTRLA, NVMCTRL_CMD_PAGEERASEWRITE_gc);
23.19 <avr/lock.h>: Lockbit Support
Introduction
The Lockbit API allows a user to specify the lockbit settings for the specific AVR
device they are compiling for. These lockbit settings will be placed in a special section
in the ELF output file, after linking.
Programming tools can take advantage of the lockbit information embedded in the
ELF file, by extracting this information and determining if the lockbits need to be
programmed after programming the Flash and EEPROM memories. This also allows a
single ELF file to contain all the information needed to program an AVR.
To use the Lockbit API, include the <avr/io.h>header file, which in turn automatically
includes the individual I/O header file and the <avr/lock.h>file. These other two files
provides everything necessary to set the AVR lockbits.
Lockbit API
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23.19 <avr/lock.h>: Lockbit Support 262
Each I/O header file may define up to 3 macros that controls what kinds of lockbits are
available to the user.
If __LOCK_BITS_EXIST is defined, then two lock bits are available to the user and 3
mode settings are defined for these two bits.
If __BOOT_LOCK_BITS_0_EXIST is defined, then the two BLB0 lock bits are avail-
able to the user and 4 mode settings are defined for these two bits.
If __BOOT_LOCK_BITS_1_EXIST is defined, then the two BLB1 lock bits are avail-
able to the user and 4 mode settings are defined for these two bits.
If __BOOT_LOCK_APPLICATION_TABLE_BITS_EXIST is defined then two lock
bits are available to set the locking mode for the Application Table Section (which is
used in the XMEGA family).
If __BOOT_LOCK_APPLICATION_BITS_EXIST is defined then two lock bits are
available to set the locking mode for the Application Section (which is used in the
XMEGA family).
If __BOOT_LOCK_BOOT_BITS_EXIST is defined then two lock bits are available
to set the locking mode for the Boot Loader Section (which is used in the XMEGA
family).
The AVR lockbit modes have inverted values, logical 1 for an unprogrammed (dis-
abled) bit and logical 0 for a programmed (enabled) bit. The defined macros for each
individual lock bit represent this in their definition by a bit-wise inversion of a mask.
For example, the LB_MODE_3 macro is defined as:
#define LB_MODE_3 (0xFC)
‘
To combine the lockbit mode macros together to represent a whole byte, use the bitwise
AND operator, like so:
(LB_MODE_3 & BLB0_MODE_2)
<avr/lock.h>also defines a macro that provides a default lockbit value: LOCKBITS_-
DEFAULT which is defined to be 0xFF.
See the AVR device specific datasheet for more details about these lock bits and the
available mode settings.
A convenience macro, LOCKMEM, is defined as a GCC attribute for a custom-named
section of ".lock".
A convenience macro, LOCKBITS, is defined that declares a variable, __lock, of type
unsigned char with the attribute defined by LOCKMEM. This variable allows the end
user to easily set the lockbit data.
Note
If a device-specific I/O header file has previously defined LOCKMEM, then
LOCKMEM is not redefined. If a device-specific I/O header file has previously
defined LOCKBITS, then LOCKBITS is not redefined. LOCKBITS is currently
known to be defined in the I/O header files for the XMEGA devices.
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23.19 <avr/lock.h>: Lockbit Support 263
API Usage Example
Putting all of this together is easy:
#include <avr/io.h>
LOCKBITS = (LB_MODE_1 & BLB0_MODE_3 & BLB1_MODE_4);
int main(void)
{
return 0;
}
Or:
#include <avr/io.h>
unsigned char __lock __attribute__((section (".lock"))) =
(LB_MODE_1 & BLB0_MODE_3 & BLB1_MODE_4);
int main(void)
{
return 0;
}
However there are a number of caveats that you need to be aware of to use this API
properly.
Be sure to include <avr/io.h>to get all of the definitions for the API. The LOCKBITS
macro defines a global variable to store the lockbit data. This variable is assigned to
its own linker section. Assign the desired lockbit values immediately in the variable
initialization.
The .lock section in the ELF file will get its values from the initial variable assignment
ONLY. This means that you can NOT assign values to this variable in functions and the
new values will not be put into the ELF .lock section.
The global variable is declared in the LOCKBITS macro has two leading underscores,
which means that it is reserved for the "implementation", meaning the library, so it will
not conflict with a user-named variable.
You must initialize the lockbit variable to some meaningful value, even if it is the de-
fault value. This is because the lockbits default to a logical 1, meaning unprogrammed.
Normal uninitialized data defaults to all locgial zeros. So it is vital that all lockbits
are initialized, even with default data. If they are not, then the lockbits may not pro-
grammed to the desired settings and can possibly put your device into an unrecoverable
state.
Be sure to have the -mmcu=device flag in your compile command line and your linker
command line to have the correct device selected and to have the correct I/O header
file included when you include <avr/io.h>.
You can print out the contents of the .lock section in the ELF file by using this command
line:
avr-objdump -s -j .lock <ELF file>
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23.20 <avr/pgmspace.h>: Program Space Utilities 264
23.20 <avr/pgmspace.h>: Program Space Utilities
Defines
• #define PROGMEM __ATTR_PROGMEM__
• #define PGM_P const char ∗
• #define PGM_VOID_P const void ∗
• #define PSTR(s) ((const PROGMEM char ∗)(s))
• #define pgm_read_byte_near(address_short) __LPM((uint16_t)(address_short))
• #define pgm_read_word_near(address_short) __LPM_word((uint16_-
t)(address_short))
• #define pgm_read_dword_near(address_short) __LPM_dword((uint16_-
t)(address_short))
• #define pgm_read_float_near(address_short) __LPM_float((uint16_t)(address_-
short))
• #define pgm_read_ptr_near(address_short) (void∗)__LPM_word((uint16_-
t)(address_short))
• #define pgm_read_byte_far(address_long) __ELPM((uint32_t)(address_long))
• #define pgm_read_word_far(address_long) __ELPM_word((uint32_-
t)(address_long))
• #define pgm_read_dword_far(address_long) __ELPM_dword((uint32_-
t)(address_long))
• #define pgm_read_float_far(address_long) __ELPM_float((uint32_t)(address_-
long))
• #define pgm_read_ptr_far(address_long) (void∗)__ELPM_word((uint32_-
t)(address_long))
• #define pgm_read_byte(address_short) pgm_read_byte_near(address_short)
• #define pgm_read_word(address_short) pgm_read_word_near(address_short)
• #define pgm_read_dword(address_short) pgm_read_dword_near(address_short)
• #define pgm_read_float(address_short) pgm_read_float_near(address_short)
• #define pgm_read_ptr(address_short) pgm_read_ptr_near(address_short)
• #define pgm_get_far_address(var)
Typedefs
• typedef void PROGMEM prog_void
• typedef char PROGMEM prog_char
• typedef unsigned char PROGMEM prog_uchar
• typedef int8_t PROGMEM prog_int8_t
• typedef uint8_t PROGMEM prog_uint8_t
• typedef int16_t PROGMEM prog_int16_t
• typedef uint16_t PROGMEM prog_uint16_t
• typedef int32_t PROGMEM prog_int32_t
• typedef uint32_t PROGMEM prog_uint32_t
• typedef int64_t PROGMEM prog_int64_t
• typedef uint64_t PROGMEM prog_uint64_t
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23.20 <avr/pgmspace.h>: Program Space Utilities 265
Functions
• const void ∗memchr_P (const void ∗, int __val, size_t __len)
• int memcmp_P (const void ∗, const void ∗, size_t) __ATTR_PURE__
• void ∗memccpy_P (void ∗, const void ∗, int __val, size_t)
• void ∗memcpy_P (void ∗, const void ∗, size_t)
• void ∗memmem_P (const void ∗, size_t, const void ∗, size_t) __ATTR_PURE_-
_
• const void ∗memrchr_P (const void ∗, int __val, size_t __len)
• char ∗strcat_P (char ∗, const char ∗)
• const char ∗strchr_P (const char ∗, int __val)
• const char ∗strchrnul_P (const char ∗, int __val)
• int strcmp_P (const char ∗, const char ∗) __ATTR_PURE__
• char ∗strcpy_P (char ∗, const char ∗)
• int strcasecmp_P (const char ∗, const char ∗) __ATTR_PURE__
• char ∗strcasestr_P (const char ∗, const char ∗) __ATTR_PURE__
• size_t strcspn_P (const char ∗__s, const char ∗__reject) __ATTR_PURE__
• size_t strlcat_P (char ∗, const char ∗, size_t)
• size_t strlcpy_P (char ∗, const char ∗, size_t)
• size_t strnlen_P (const char ∗, size_t)
• int strncmp_P (const char ∗, const char ∗, size_t) __ATTR_PURE__
• int strncasecmp_P (const char ∗, const char ∗, size_t) __ATTR_PURE__
• char ∗strncat_P (char ∗, const char ∗, size_t)
• char ∗strncpy_P (char ∗, const char ∗, size_t)
• char ∗strpbrk_P (const char ∗__s, const char ∗__accept) __ATTR_PURE__
• const char ∗strrchr_P (const char ∗, int __val)
• char ∗strsep_P (char ∗∗__sp, const char ∗__delim)
• size_t strspn_P (const char ∗__s, const char ∗__accept) __ATTR_PURE__
• char ∗strstr_P (const char ∗, const char ∗) __ATTR_PURE__
• char ∗strtok_P (char ∗__s, const char ∗__delim)
• char ∗strtok_rP (char ∗__s, const char ∗__delim, char ∗∗__last)
• size_t strlen_PF (uint_farptr_t src)
• size_t strnlen_PF (uint_farptr_t src, size_t len)
• void ∗memcpy_PF (void ∗dest, uint_farptr_t src, size_t len)
• char ∗strcpy_PF (char ∗dest, uint_farptr_t src)
• char ∗strncpy_PF (char ∗dest, uint_farptr_t src, size_t len)
• char ∗strcat_PF (char ∗dest, uint_farptr_t src)
• size_t strlcat_PF (char ∗dst, uint_farptr_t src, size_t siz)
• char ∗strncat_PF (char ∗dest, uint_farptr_t src, size_t len)
• int strcmp_PF (const char ∗s1, uint_farptr_t s2) __ATTR_PURE__
• int strncmp_PF (const char ∗s1, uint_farptr_t s2, size_t n) __ATTR_PURE__
• int strcasecmp_PF (const char ∗s1, uint_farptr_t s2) __ATTR_PURE__
• int strncasecmp_PF (const char ∗s1, uint_farptr_t s2, size_t n) __ATTR_PURE_-
_
• char ∗strstr_PF (const char ∗s1, uint_farptr_t s2)
• size_t strlcpy_PF (char ∗dst, uint_farptr_t src, size_t siz)
• int memcmp_PF (const void ∗,uint_farptr_t, size_t) __ATTR_PURE__
• static size_t strlen_P (const char ∗s)
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23.20 <avr/pgmspace.h>: Program Space Utilities 266
23.20.1 Detailed Description
#include <avr/io.h>
#include <avr/pgmspace.h>
The functions in this module provide interfaces for a program to access data stored in
program space (flash memory) of the device. In order to use these functions, the target
device must support either the LPM or ELPM instructions.
Note
These functions are an attempt to provide some compatibility with header files
that come with IAR C, to make porting applications between different compilers
easier. This is not 100% compatibility though (GCC does not have full support for
multiple address spaces yet).
If you are working with strings which are completely based in ram, use the stan-
dard string functions described in <string.h>: Strings.
If possible, put your constant tables in the lower 64 KB and use pgm_read_byte_-
near() or pgm_read_word_near() instead of pgm_read_byte_far() or pgm_read_-
word_far() since it is more efficient that way, and you can still use the upper 64K
for executable code. All functions that are suffixed with a _P require their ar-
guments to be in the lower 64 KB of the flash ROM, as they do not use ELPM
instructions. This is normally not a big concern as the linker setup arranges any
program space constants declared using the macros from this header file so they
are placed right after the interrupt vectors, and in front of any executable code.
However, it can become a problem if there are too many of these constants, or for
bootloaders on devices with more than 64 KB of ROM. All these functions will not
work in that situation.
For Xmega devices, make sure the NVM controller command register (NVM.CMD
or NVM_CMD) is set to 0x00 (NOP) before using any of these functions.
23.20.2 Define Documentation
23.20.2.1 #define pgm_get_far_address(var)
Value:
({ \
uint_farptr_t tmp; \
\
__asm__ __volatile__( \
\
"ldi %A0, lo8(%1)" "\n\t" \
"ldi %B0, hi8(%1)" "\n\t" \
"ldi %C0, hh8(%1)" "\n\t" \
"clr %D0" "\n\t" \
: \
"=d" (tmp) \
: \
"p" (&(var)) \
); \
tmp; \
})
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23.20 <avr/pgmspace.h>: Program Space Utilities 267
This macro facilitates the obtention of a 32 bit "far" pointer (only 24 bits used) to data
even passed the 64KB limit for the 16 bit ordinary pointer. It is similar to the ’&’
operator, with some limitations.
Comments:
• The overhead is minimal and it’s mainly due to the 32 bit size operation.
• 24 bit sizes guarantees the code compatibility for use in future devices.
• hh8() is an undocumented feature but seems to give the third significant byte of
a 32 bit data and accepts symbols, complementing the functionality of hi8() and
lo8(). There is not an equivalent assembler function to get the high significant
byte.
• ’var’ has to be resolved at linking time as an existing symbol, i.e, a simple type
variable name, an array name (not an indexed element of the array, if the index
is a constant the compiler does not complain but fails to get the address if opti-
mization is enabled), a struct name or a struct field name, a function identifier, a
linker defined identifier,...
• The returned value is the identifier’s VMA (virtual memory address) determined
by the linker and falls in the corresponding memory region. The AVR Harvard
architecture requires non overlapping VMA areas for the multiple address spaces
in the processor: Flash ROM, RAM, and EEPROM. Typical offset for this are
0x00000000, 0x00800xx0, and 0x00810000 respectively, derived from the linker
script used and linker options. The value returned can be seen then as a universal
pointer.
23.20.2.2 #define PGM_P const char ∗
Used to declare a variable that is a pointer to a string in program space.
23.20.2.3 #define pgm_read_byte(address_short) pgm_read_byte_-
near(address_short)
Read a byte from the program space with a 16-bit (near) address.
Note
The address is a byte address. The address is in the program space.
23.20.2.4 #define pgm_read_byte_far(address_long) __ELPM((uint32_-
t)(address_long))
Read a byte from the program space with a 32-bit (far) address.
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23.20 <avr/pgmspace.h>: Program Space Utilities 268
Note
The address is a byte address. The address is in the program space.
23.20.2.5 #define pgm_read_byte_near(address_short) __LPM((uint16_-
t)(address_short))
Read a byte from the program space with a 16-bit (near) address.
Note
The address is a byte address. The address is in the program space.
23.20.2.6 #define pgm_read_dword(address_short) pgm_read_dword_-
near(address_short)
Read a double word from the program space with a 16-bit (near) address.
Note
The address is a byte address. The address is in the program space.
23.20.2.7 #define pgm_read_dword_far(address_long) __ELPM_-
dword((uint32_t)(address_long))
Read a double word from the program space with a 32-bit (far) address.
Note
The address is a byte address. The address is in the program space.
23.20.2.8 #define pgm_read_dword_near(address_short) __LPM_-
dword((uint16_t)(address_short))
Read a double word from the program space with a 16-bit (near) address.
Note
The address is a byte address. The address is in the program space.
23.20.2.9 #define pgm_read_float(address_short) pgm_read_float_-
near(address_short)
Read a float from the program space with a 16-bit (near) address.
Note
The address is a byte address. The address is in the program space.
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23.20 <avr/pgmspace.h>: Program Space Utilities 269
23.20.2.10 #define pgm_read_float_far(address_long) __ELPM_float((uint32_-
t)(address_long))
Read a float from the program space with a 32-bit (far) address.
Note
The address is a byte address. The address is in the program space.
23.20.2.11 #define pgm_read_float_near(address_short) __LPM_float((uint16_-
t)(address_short))
Read a float from the program space with a 16-bit (near) address.
Note
The address is a byte address. The address is in the program space.
23.20.2.12 #define pgm_read_ptr(address_short) pgm_read_ptr_-
near(address_short)
Read a pointer from the program space with a 16-bit (near) address.
Note
The address is a byte address. The address is in the program space.
23.20.2.13 #define pgm_read_ptr_far(address_long) (void∗)__ELPM_-
word((uint32_t)(address_long))
Read a pointer from the program space with a 32-bit (far) address.
Note
The address is a byte address. The address is in the program space.
23.20.2.14 #define pgm_read_ptr_near(address_short) (void∗)__LPM_-
word((uint16_t)(address_short))
Read a pointer from the program space with a 16-bit (near) address.
Note
The address is a byte address. The address is in the program space.
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23.20 <avr/pgmspace.h>: Program Space Utilities 270
23.20.2.15 #define pgm_read_word(address_short) pgm_read_word_-
near(address_short)
Read a word from the program space with a 16-bit (near) address.
Note
The address is a byte address. The address is in the program space.
23.20.2.16 #define pgm_read_word_far(address_long) __ELPM_-
word((uint32_t)(address_long))
Read a word from the program space with a 32-bit (far) address.
Note
The address is a byte address. The address is in the program space.
23.20.2.17 #define pgm_read_word_near(address_short) __LPM_-
word((uint16_t)(address_short))
Read a word from the program space with a 16-bit (near) address.
Note
The address is a byte address. The address is in the program space.
23.20.2.18 #define PGM_VOID_P const void ∗
Used to declare a generic pointer to an object in program space.
23.20.2.19 #define PROGMEM __ATTR_PROGMEM__
Attribute to use in order to declare an object being located in flash ROM.
23.20.2.20 #define PSTR(s) ((const PROGMEM char ∗)(s))
Used to declare a static pointer to a string in program space.
23.20.3 Typedef Documentation
23.20.3.1 prog_char
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23.20 <avr/pgmspace.h>: Program Space Utilities 271
Note
DEPRECATED
This typedef is now deprecated because the usage of the __progmem__ attribute on a
type is not supported in GCC. However, the use of the __progmem__ attribute on a
variable declaration is supported, and this is now the recommended usage.
The typedef is only visible if the macro __PROG_TYPES_COMPAT__ has been de-
fined before including <avr/pgmspace.h>(either by a #define directive, or by a -D
compiler option.)
Type of a "char" object located in flash ROM.
23.20.3.2 prog_int16_t
Note
DEPRECATED
This typedef is now deprecated because the usage of the __progmem__ attribute on a
type is not supported in GCC. However, the use of the __progmem__ attribute on a
variable declaration is supported, and this is now the recommended usage.
The typedef is only visible if the macro __PROG_TYPES_COMPAT__ has been de-
fined before including <avr/pgmspace.h>(either by a #define directive, or by a -D
compiler option.)
Type of an "int16_t" object located in flash ROM.
23.20.3.3 prog_int32_t
Note
DEPRECATED
This typedef is now deprecated because the usage of the __progmem__ attribute on a
type is not supported in GCC. However, the use of the __progmem__ attribute on a
variable declaration is supported, and this is now the recommended usage.
The typedef is only visible if the macro __PROG_TYPES_COMPAT__ has been de-
fined before including <avr/pgmspace.h>(either by a #define directive, or by a -D
compiler option.)
Type of an "int32_t" object located in flash ROM.
23.20.3.4 prog_int64_t
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23.20 <avr/pgmspace.h>: Program Space Utilities 272
Note
DEPRECATED
This typedef is now deprecated because the usage of the __progmem__ attribute on a
type is not supported in GCC. However, the use of the __progmem__ attribute on a
variable declaration is supported, and this is now the recommended usage.
The typedef is only visible if the macro __PROG_TYPES_COMPAT__ has been de-
fined before including <avr/pgmspace.h>(either by a #define directive, or by a -D
compiler option.)
Type of an "int64_t" object located in flash ROM.
Note
This type is not available when the compiler option -mint8 is in effect.
23.20.3.5 prog_int8_t
Note
DEPRECATED
This typedef is now deprecated because the usage of the __progmem__ attribute on a
type is not supported in GCC. However, the use of the __progmem__ attribute on a
variable declaration is supported, and this is now the recommended usage.
The typedef is only visible if the macro __PROG_TYPES_COMPAT__ has been de-
fined before including <avr/pgmspace.h>(either by a #define directive, or by a -D
compiler option.)
Type of an "int8_t" object located in flash ROM.
23.20.3.6 prog_uchar
Note
DEPRECATED
This typedef is now deprecated because the usage of the __progmem__ attribute on a
type is not supported in GCC. However, the use of the __progmem__ attribute on a
variable declaration is supported, and this is now the recommended usage.
The typedef is only visible if the macro __PROG_TYPES_COMPAT__ has been de-
fined before including <avr/pgmspace.h>(either by a #define directive, or by a -D
compiler option.)
Type of an "unsigned char" object located in flash ROM.
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23.20.3.7 prog_uint16_t
Note
DEPRECATED
This typedef is now deprecated because the usage of the __progmem__ attribute on a
type is not supported in GCC. However, the use of the __progmem__ attribute on a
variable declaration is supported, and this is now the recommended usage.
The typedef is only visible if the macro __PROG_TYPES_COMPAT__ has been de-
fined before including <avr/pgmspace.h>(either by a #define directive, or by a -D
compiler option.)
Type of an "uint16_t" object located in flash ROM.
23.20.3.8 prog_uint32_t
Note
DEPRECATED
This typedef is now deprecated because the usage of the __progmem__ attribute on a
type is not supported in GCC. However, the use of the __progmem__ attribute on a
variable declaration is supported, and this is now the recommended usage.
The typedef is only visible if the macro __PROG_TYPES_COMPAT__ has been de-
fined before including <avr/pgmspace.h>(either by a #define directive, or by a -D
compiler option.)
Type of an "uint32_t" object located in flash ROM.
23.20.3.9 prog_uint64_t
Note
DEPRECATED
This typedef is now deprecated because the usage of the __progmem__ attribute on a
type is not supported in GCC. However, the use of the __progmem__ attribute on a
variable declaration is supported, and this is now the recommended usage.
The typedef is only visible if the macro __PROG_TYPES_COMPAT__ has been de-
fined before including <avr/pgmspace.h>(either by a #define directive, or by a -D
compiler option.)
Type of an "uint64_t" object located in flash ROM.
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23.20 <avr/pgmspace.h>: Program Space Utilities 274
Note
This type is not available when the compiler option -mint8 is in effect.
23.20.3.10 prog_uint8_t
Note
DEPRECATED
This typedef is now deprecated because the usage of the __progmem__ attribute on a
type is not supported in GCC. However, the use of the __progmem__ attribute on a
variable declaration is supported, and this is now the recommended usage.
The typedef is only visible if the macro __PROG_TYPES_COMPAT__ has been de-
fined before including <avr/pgmspace.h>(either by a #define directive, or by a -D
compiler option.)
Type of an "uint8_t" object located in flash ROM.
23.20.3.11 prog_void
Note
DEPRECATED
This typedef is now deprecated because the usage of the __progmem__ attribute on a
type is not supported in GCC. However, the use of the __progmem__ attribute on a
variable declaration is supported, and this is now the recommended usage.
The typedef is only visible if the macro __PROG_TYPES_COMPAT__ has been de-
fined before including <avr/pgmspace.h>(either by a #define directive, or by a -D
compiler option.)
Type of a "void" object located in flash ROM. Does not make much sense by itself, but
can be used to declare a "void ∗" object in flash ROM.
23.20.4 Function Documentation
23.20.4.1 void ∗memccpy_P (void ∗dest, const void ∗src, int val, size_t len)
This function is similar to memccpy() except that src is pointer to a string in
program space.
23.20.4.2 const void ∗memchr_P (const void ∗s, int val, size_t len)
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23.20 <avr/pgmspace.h>: Program Space Utilities 275
Scan flash memory for a character.
The memchr_P() function scans the first len bytes of the flash memory area pointed
to by sfor the character val. The first byte to match val (interpreted as an unsigned
character) stops the operation.
Returns
The memchr_P() function returns a pointer to the matching byte or NULL if the
character does not occur in the given memory area.
23.20.4.3 int memcmp_P (const void ∗s1, const void ∗s2, size_t len)
Compare memory areas.
The memcmp_P() function compares the first len bytes of the memory areas s1 and
flash s2. The comparision is performed using unsigned char operations.
Returns
The memcmp_P() function returns an integer less than, equal to, or greater than
zero if the first len bytes of s1 is found, respectively, to be less than, to match, or
be greater than the first len bytes of s2.
23.20.4.4 int memcmp_PF (const void ∗s1, uint_farptr_t s2, size_t len)
Compare memory areas.
The memcmp_PF() function compares the first len bytes of the memory areas s1
and flash s2. The comparision is performed using unsigned char operations. It is an
equivalent of memcmp_P() function, except that it is capable working on all FLASH
including the exteded area above 64kB.
Returns
The memcmp_PF() function returns an integer less than, equal to, or greater than
zero if the first len bytes of s1 is found, respectively, to be less than, to match, or
be greater than the first len bytes of s2.
23.20.4.5 void ∗memcpy_P (void ∗dest, const void ∗src, size_t n)
The memcpy_P() function is similar to memcpy(), except the src string resides in
program space.
Returns
The memcpy_P() function returns a pointer to dest.
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23.20.4.6 void ∗memcpy_PF (void ∗dest, uint_farptr_t src, size_t n)
Copy a memory block from flash to SRAM.
The memcpy_PF() function is similar to memcpy(), except the data is copied from the
program space and is addressed using a far pointer.
Parameters
dest A pointer to the destination buffer
src A far pointer to the origin of data in flash memory
nThe number of bytes to be copied
Returns
The memcpy_PF() function returns a pointer to dst. The contents of RAMPZ SFR
are undefined when the function returns.
23.20.4.7 void ∗memmem_P (const void ∗s1, size_t len1, const void ∗s2,
size_t len2)
The memmem_P() function is similar to memmem() except that s2 is pointer to a
string in program space.
23.20.4.8 const void memrchr_P (const void ∗src, int val, size_t len)
The memrchr_P() function is like the memchr_P() function, except that it searches
backwards from the end of the len bytes pointed to by src instead of forwards from
the front. (Glibc, GNU extension.)
Returns
The memrchr_P() function returns a pointer to the matching byte or NULL if the
character does not occur in the given memory area.
23.20.4.9 int strcasecmp_P (const char ∗s1, const char ∗s2)
Compare two strings ignoring case.
The strcasecmp_P() function compares the two strings s1 and s2, ignoring the case of
the characters.
Parameters
s1 A pointer to a string in the devices SRAM.
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23.20 <avr/pgmspace.h>: Program Space Utilities 277
s2 A pointer to a string in the devices Flash.
Returns
The strcasecmp_P() function returns an integer less than, equal to, or greater than
zero if s1 is found, respectively, to be less than, to match, or be greater than s2.
A consequence of the ordering used by strcasecmp_P() is that if s1 is an initial
substring of s2, then s1 is considered to be "less than" s2.
23.20.4.10 int strcasecmp_PF (const char ∗s1, uint_farptr_t s2)
Compare two strings ignoring case.
The strcasecmp_PF() function compares the two strings s1 and s2, ignoring the case of
the characters.
Parameters
s1 A pointer to the first string in SRAM
s2 A far pointer to the second string in Flash
Returns
The strcasecmp_PF() function returns an integer less than, equal to, or greater than
zero if s1 is found, respectively, to be less than, to match, or be greater than s2.
The contents of RAMPZ SFR are undefined when the function returns.
23.20.4.11 char ∗strcasestr_P (const char ∗s1, const char ∗s2)
This funtion is similar to strcasestr() except that s2 is pointer to a string in program
space.
23.20.4.12 char ∗strcat_P (char ∗dest, const char ∗src)
The strcat_P() function is similar to strcat() except that the src string must be located
in program space (flash).
Returns
The strcat() function returns a pointer to the resulting string dest.
23.20.4.13 char ∗strcat_PF (char ∗dst, uint_farptr_t src)
Concatenates two strings.
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23.20 <avr/pgmspace.h>: Program Space Utilities 278
The strcat_PF() function is similar to strcat() except that the src string must be located
in program space (flash) and is addressed using a far pointer
Parameters
dst A pointer to the destination string in SRAM
src A far pointer to the string to be appended in Flash
Returns
The strcat_PF() function returns a pointer to the resulting string dst. The contents
of RAMPZ SFR are undefined when the function returns
23.20.4.14 const char ∗strchr_P (const char ∗s, int val)
Locate character in program space string.
The strchr_P() function locates the first occurrence of val (converted to a char) in the
string pointed to by sin program space. The terminating null character is considered
to be part of the string.
The strchr_P() function is similar to strchr() except that sis pointer to a string in
program space.
Returns
The strchr_P() function returns a pointer to the matched character or NULL if the
character is not found.
23.20.4.15 const char ∗strchrnul_P (const char ∗s, int c)
The strchrnul_P() function is like strchr_P() except that if cis not found
in s, then it returns a pointer to the null byte at the end of s, rather than NULL. (Glibc,
GNU extension.)
Returns
The strchrnul_P() function returns a pointer to the matched character, or a pointer
to the null byte at the end of s(i.e., s+strlen(s)) if the character is not found.
23.20.4.16 int strcmp_P (const char ∗s1, const char ∗s2)
The strcmp_P() function is similar to strcmp() except that s2 is pointer to a string in
program space.
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23.20 <avr/pgmspace.h>: Program Space Utilities 279
Returns
The strcmp_P() function returns an integer less than, equal to, or greater than zero
if s1 is found, respectively, to be less than, to match, or be greater than s2. A
consequence of the ordering used by strcmp_P() is that if s1 is an initial substring
of s2, then s1 is considered to be "less than" s2.
23.20.4.17 int strcmp_PF (const char ∗s1, uint_farptr_t s2)
Compares two strings.
The strcmp_PF() function is similar to strcmp() except that s2 is a far pointer to a string
in program space.
Parameters
s1 A pointer to the first string in SRAM
s2 A far pointer to the second string in Flash
Returns
The strcmp_PF() function returns an integer less than, equal to, or greater than
zero if s1 is found, respectively, to be less than, to match, or be greater than s2.
The contents of RAMPZ SFR are undefined when the function returns.
23.20.4.18 char ∗strcpy_P (char ∗dest, const char ∗src)
The strcpy_P() function is similar to strcpy() except that src is a pointer to a string in
program space.
Returns
The strcpy_P() function returns a pointer to the destination string dest.
23.20.4.19 char ∗strcpy_PF (char ∗dst, uint_farptr_t src)
Duplicate a string.
The strcpy_PF() function is similar to strcpy() except that src is a far pointer to a string
in program space.
Parameters
dst A pointer to the destination string in SRAM
src A far pointer to the source string in Flash
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23.20 <avr/pgmspace.h>: Program Space Utilities 280
Returns
The strcpy_PF() function returns a pointer to the destination string dst. The con-
tents of RAMPZ SFR are undefined when the funcion returns.
23.20.4.20 size_t strcspn_P (const char ∗s, const char ∗reject)
The strcspn_P() function calculates the length of the initial segment
of swhich consists entirely of characters not in reject. This function is similar to
strcspn() except that reject is a pointer to a string in program space.
Returns
The strcspn_P() function returns the number of characters in the initial segment of
swhich are not in the string reject. The terminating zero is not considered as a
part of string.
23.20.4.21 size_t strlcat_P (char ∗dst, const char ∗src, size_t siz)
Concatenate two strings.
The strlcat_P() function is similar to strlcat(), except that the src string must be located
in program space (flash).
Appends src to string dst of size siz (unlike strncat(),siz is the full size of dst,
not space left). At most siz-1 characters will be copied. Always NULL terminates
(unless siz <=strlen(dst)).
Returns
The strlcat_P() function returns strlen(src) + MIN(siz, strlen(initial dst)). If retval
>= siz, truncation occurred.
23.20.4.22 size_t strlcat_PF (char ∗dst, uint_farptr_t src, size_t n)
Concatenate two strings.
The strlcat_PF() function is similar to strlcat(), except that the src string must be located
in program space (flash) and is addressed using a far pointer.
Appends src to string dst of size n(unlike strncat(),nis the full size of dst, not space
left). At most n-1 characters will be copied. Always NULL terminates (unless n<=
strlen(dst)).
Parameters
dst A pointer to the destination string in SRAM
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23.20 <avr/pgmspace.h>: Program Space Utilities 281
src A far pointer to the source string in Flash
nThe total number of bytes allocated to the destination string
Returns
The strlcat_PF() function returns strlen(src) + MIN(n, strlen(initial dst)). If retval
>=n, truncation occurred. The contents of RAMPZ SFR are undefined when the
funcion returns.
23.20.4.23 size_t strlcpy_P (char ∗dst, const char ∗src, size_t siz)
Copy a string from progmem to RAM.
Copy src to string dst of size siz. At most siz-1 characters will be copied.
Always NULL terminates (unless siz == 0). The strlcpy_P() function is similar to
strlcpy() except that the src is pointer to a string in memory space.
Returns
The strlcpy_P() function returns strlen(src). If retval >= siz, truncation occurred.
23.20.4.24 size_t strlcpy_PF (char ∗dst, uint_farptr_t src, size_t siz)
Copy a string from progmem to RAM.
Copy src to string dst of size siz. At most siz-1 characters will be copied. Always
NULL terminates (unless siz == 0).
Returns
The strlcpy_PF() function returns strlen(src). If retval >= siz, truncation occurred.
The contents of RAMPZ SFR are undefined when the function returns.
23.20.4.25 size_t strlen_P (const char ∗src)[static]
The strlen_P() function is similar to strlen(), except that src is a pointer to a string in
program space.
Returns
The strlen_P() function returns the number of characters in src.
Note
strlen_P() is implemented as an inline function in the avr/pgmspace.h header file,
which will check if the length of the string is a constant and known at compile
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23.20 <avr/pgmspace.h>: Program Space Utilities 282
time. If it is not known at compile time, the macro will issue a call to __strlen_P()
which will then calculate the length of the string as normal.
23.20.4.26 size_t strlen_PF (uint_farptr_t s)
Obtain the length of a string.
The strlen_PF() function is similar to strlen(), except that sis a far pointer to a string in
program space.
Parameters
sA far pointer to the string in flash
Returns
The strlen_PF() function returns the number of characters in s. The contents of
RAMPZ SFR are undefined when the function returns.
23.20.4.27 int strncasecmp_P (const char ∗s1, const char ∗s2, size_t n)
Compare two strings ignoring case.
The strncasecmp_P() function is similar to strcasecmp_P(), except it only compares the
first ncharacters of s1.
Parameters
s1 A pointer to a string in the devices SRAM.
s2 A pointer to a string in the devices Flash.
nThe maximum number of bytes to compare.
Returns
The strncasecmp_P() function returns an integer less than, equal to, or greater
than zero if s1 (or the first nbytes thereof) is found, respectively, to be less
than, to match, or be greater than s2. A consequence of the ordering used by
strncasecmp_P() is that if s1 is an initial substring of s2, then s1 is considered to
be "less than" s2.
23.20.4.28 int strncasecmp_PF (const char ∗s1, uint_farptr_t s2, size_t n)
Compare two strings ignoring case.
The strncasecmp_PF() function is similar to strcasecmp_PF(), except it only compares
the first ncharacters of s1 and the string in flash is addressed using a far pointer.
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Parameters
s1 A pointer to a string in SRAM
s2 A far pointer to a string in Flash
nThe maximum number of bytes to compare
Returns
The strncasecmp_PF() function returns an integer less than, equal to, or greater
than zero if s1 (or the first nbytes thereof) is found, respectively, to be less than,
to match, or be greater than s2. The contents of RAMPZ SFR are undefined when
the function returns.
23.20.4.29 char ∗strncat_P (char ∗dest, const char ∗src, size_t len)
Concatenate two strings.
The strncat_P() function is similar to strncat(), except that the src string must be located
in program space (flash).
Returns
The strncat_P() function returns a pointer to the resulting string dest.
23.20.4.30 char ∗strncat_PF (char ∗dst, uint_farptr_t src, size_t n)
Concatenate two strings.
The strncat_PF() function is similar to strncat(), except that the src string must be
located in program space (flash) and is addressed using a far pointer.
Parameters
dst A pointer to the destination string in SRAM
src A far pointer to the source string in Flash
nThe maximum number of bytes to append
Returns
The strncat_PF() function returns a pointer to the resulting string dst. The contents
of RAMPZ SFR are undefined when the function returns.
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23.20.4.31 int strncmp_P (const char ∗s1, const char ∗s2, size_t n)
The strncmp_P() function is similar to strcmp_P() except it only compares the first (at
most) n characters of s1 and s2.
Returns
The strncmp_P() function returns an integer less than, equal to, or greater than zero
if s1 (or the first n bytes thereof) is found, respectively, to be less than, to match,
or be greater than s2.
23.20.4.32 int strncmp_PF (const char ∗s1, uint_farptr_t s2, size_t n)
Compare two strings with limited length.
The strncmp_PF() function is similar to strcmp_PF() except it only compares the first
(at most) ncharacters of s1 and s2.
Parameters
s1 A pointer to the first string in SRAM
s2 A far pointer to the second string in Flash
nThe maximum number of bytes to compare
Returns
The strncmp_PF() function returns an integer less than, equal to, or greater than
zero if s1 (or the first nbytes thereof) is found, respectively, to be less than, to
match, or be greater than s2. The contents of RAMPZ SFR are undefined when
the function returns.
23.20.4.33 char ∗strncpy_P (char ∗dest, const char ∗src, size_t n)
The strncpy_P() function is similar to strcpy_P() except that not more than n bytes
of src are copied. Thus, if there is no null byte among the first n bytes of src, the result
will not be null-terminated.
In the case where the length of src is less than that of n, the remainder of dest will be
padded with nulls.
Returns
The strncpy_P() function returns a pointer to the destination string dest.
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23.20.4.34 char ∗strncpy_PF (char ∗dst, uint_farptr_t src, size_t n)
Duplicate a string until a limited length.
The strncpy_PF() function is similar to strcpy_PF() except that not more than nbytes
of src are copied. Thus, if there is no null byte among the first nbytes of src, the result
will not be null-terminated.
In the case where the length of src is less than that of n, the remainder of dst will be
padded with nulls.
Parameters
dst A pointer to the destination string in SRAM
src A far pointer to the source string in Flash
nThe maximum number of bytes to copy
Returns
The strncpy_PF() function returns a pointer to the destination string dst. The con-
tents of RAMPZ SFR are undefined when the function returns.
23.20.4.35 size_t strnlen_P (const char ∗src, size_t len)
Determine the length of a fixed-size string.
The strnlen_P() function is similar to strnlen(), except that src is a pointer to a string
in program space.
Returns
The strnlen_P function returns strlen_P(src), if that is less than len, or len if
there is no ’\0’ character among the first len characters pointed to by src.
23.20.4.36 size_t strnlen_PF (uint_farptr_t s, size_t len)
Determine the length of a fixed-size string.
The strnlen_PF() function is similar to strnlen(), except that sis a far pointer to a string
in program space.
Parameters
sA far pointer to the string in Flash
len The maximum number of length to return
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Returns
The strnlen_PF function returns strlen_P(s), if that is less than len, or len if there
is no ’\0’ character among the first len characters pointed to by s. The contents of
RAMPZ SFR are undefined when the function returns.
23.20.4.37 char ∗strpbrk_P (const char ∗s, const char ∗accept)
The strpbrk_P() function locates the first occurrence in the string sof any of the
characters in the flash string accept. This function is similar to strpbrk() except that
accept is a pointer to a string in program space.
Returns
The strpbrk_P() function returns a pointer to the character in sthat matches one of
the characters in accept, or NULL if no such character is found. The terminating
zero is not considered as a part of string: if one or both args are empty, the result
will NULL.
23.20.4.38 const char ∗strrchr_P (const char ∗s, int val)
Locate character in string.
The strrchr_P() function returns a pointer to the last occurrence of the character val
in the flash string s.
Returns
The strrchr_P() function returns a pointer to the matched character or NULL if the
character is not found.
23.20.4.39 char ∗strsep_P (char ∗∗ sp, const char ∗delim)
Parse a string into tokens.
The strsep_P() function locates, in the string referenced by ∗sp, the first occurrence of
any character in the string delim (or the terminating ’\0’ character) and replaces it
with a ’\0’. The location of the next character after the delimiter character (or NULL,
if the end of the string was reached) is stored in ∗sp. An “empty” field, i.e. one
caused by two adjacent delimiter characters, can be detected by comparing the location
referenced by the pointer returned in ∗sp to ’\0’. This function is similar to strsep()
except that delim is a pointer to a string in program space.
Returns
The strsep_P() function returns a pointer to the original value of ∗sp. If ∗sp is
initially NULL,strsep_P() returns NULL.
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23.20 <avr/pgmspace.h>: Program Space Utilities 287
23.20.4.40 size_t strspn_P (const char ∗s, const char ∗accept)
The strspn_P() function calculates the length of the initial segment of
swhich consists entirely of characters in accept. This function is similar to strspn()
except that accept is a pointer to a string in program space.
Returns
The strspn_P() function returns the number of characters in the initial segment of
swhich consist only of characters from accept. The terminating zero is not
considered as a part of string.
23.20.4.41 char ∗strstr_P (const char ∗s1, const char ∗s2)
Locate a substring.
The strstr_P() function finds the first occurrence of the substring s2 in the string s1.
The terminating ’\0’ characters are not compared. The strstr_P() function is similar to
strstr() except that s2 is pointer to a string in program space.
Returns
The strstr_P() function returns a pointer to the beginning of the substring, or NULL
if the substring is not found. If s2 points to a string of zero length, the function
returns s1.
23.20.4.42 char ∗strstr_PF (const char ∗s1, uint_farptr_t s2)
Locate a substring.
The strstr_PF() function finds the first occurrence of the substring s2 in the string s1.
The terminating ’\0’ characters are not compared. The strstr_PF() function is similar
to strstr() except that s2 is a far pointer to a string in program space.
Returns
The strstr_PF() function returns a pointer to the beginning of the substring, or
NULL if the substring is not found. If s2 points to a string of zero length, the
function returns s1. The contents of RAMPZ SFR are undefined when the func-
tion returns.
23.20.4.43 char ∗strtok_P (char ∗s, const char ∗delim)
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23.21 <avr/power.h>: Power Reduction Management 288
Parses the string into tokens.
strtok_P() parses the string sinto tokens. The first call to strtok_P() should have sas
its first argument. Subsequent calls should have the first argument set to NULL. If a
token ends with a delimiter, this delimiting character is overwritten with a ’\0’ and a
pointer to the next character is saved for the next call to strtok_P(). The delimiter string
delim may be different for each call.
The strtok_P() function is similar to strtok() except that delim is pointer to a string in
program space.
Returns
The strtok_P() function returns a pointer to the next token or NULL when no more
tokens are found.
Note
strtok_P() is NOT reentrant. For a reentrant version of this function see strtok_rP().
23.20.4.44 char ∗strtok_rP (char ∗string, const char ∗delim, char ∗∗ last)
Parses string into tokens.
The strtok_rP() function parses string into tokens. The first call to strtok_rP() should
have string as its first argument. Subsequent calls should have the first argument set to
NULL. If a token ends with a delimiter, this delimiting character is overwritten with
a ’\0’ and a pointer to the next character is saved for the next call to strtok_rP(). The
delimiter string delim may be different for each call. last is a user allocated char∗
pointer. It must be the same while parsing the same string. strtok_rP() is a reentrant
version of strtok_P().
The strtok_rP() function is similar to strtok_r() except that delim is pointer to a string
in program space.
Returns
The strtok_rP() function returns a pointer to the next token or NULL when no more
tokens are found.
23.21 <avr/power.h>: Power Reduction Management
Functions
• void clock_prescale_set (clock_div_t __x)
23.21.1 Detailed Description
#include <avr/power.h>
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23.21 <avr/power.h>: Power Reduction Management 289
Many AVRs contain a Power Reduction Register (PRR) or Registers (PRRx) that allow
you to reduce power consumption by disabling or enabling various on-board peripher-
als as needed. Some devices have the XTAL Divide Control Register (XDIV) which
offer similar functionality as System Clock Prescale Register (CLKPR).
There are many macros in this header file that provide an easy interface to enable or
disable on-board peripherals to reduce power. See the table below.
Note
Not all AVR devices have a Power Reduction Register (for example the ATmega8).
On those devices without a Power Reduction Register, the power reduction macros
are not available..
Not all AVR devices contain the same peripherals (for example, the LCD inter-
face), or they will be named differently (for example, USART and USART0).
Please consult your device’s datasheet, or the header file, to find out which macros
are applicable to your device.
For device using the XTAL Divide Control Register (XDIV), when prescaler is
used, Timer/Counter0 can only be used in asynchronous mode. Keep in mind that
Timer/Counter0 source shall be less than ¼th of peripheral clock. Therefore, when
using a typical 32.768 kHz crystal, one shall not scale the clock below 131.072
kHz.
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23.21 <avr/power.h>: Power Reduction Management 290
Power Macro Description
power_aca_disable() Disable the Analog Comparator on PortA.
power_aca_enable() Enable the Analog Comparator on PortA.
power_adc_enable() Enable the Analog to Digital Converter module.
power_adc_disable() Disable the Analog to Digital Converter module.
power_adca_disable() Disable the Analog to Digital Converter module
on PortA
power_adca_enable() Enable the Analog to Digital Converter module
on PortA
power_evsys_disable() Disable the EVSYS module
power_evsys_enable() Enable the EVSYS module
power_hiresc_disable() Disable the HIRES module on PortC
power_hiresc_enable() Enable the HIRES module on PortC
power_lcd_enable() Enable the LCD module.
power_lcd_disable(). Disable the LCD module.
power_pga_enable() Enable the Programmable Gain Amplifier
module.
power_pga_disable() Disable the Programmable Gain Amplifier
module.
power_pscr_enable() Enable the Reduced Power Stage Controller
module.
power_pscr_disable() Disable the Reduced Power Stage Controller
module.
power_psc0_enable() Enable the Power Stage Controller 0 module.
power_psc0_disable() Disable the Power Stage Controller 0 module.
power_psc1_enable() Enable the Power Stage Controller 1 module.
power_psc1_disable() Disable the Power Stage Controller 1 module.
power_psc2_enable() Enable the Power Stage Controller 2 module.
power_psc2_disable() Disable the Power Stage Controller 2 module.
power_ram0_enable() Enable the SRAM block 0 .
power_ram0_disable() Disable the SRAM block 0.
power_ram1_enable() Enable the SRAM block 1 .
power_ram1_disable() Disable the SRAM block 1.
power_ram2_enable() Enable the SRAM block 2 .
power_ram2_disable() Disable the SRAM block 2.
power_ram3_enable() Enable the SRAM block 3 .
power_ram3_disable() Disable the SRAM block 3.
power_rtc_disable() Disable the RTC module
power_rtc_enable() Enable the RTC module
power_spi_enable() Enable the Serial Peripheral Interface module.
power_spi_disable() Disable the Serial Peripheral Interface module.
power_spic_disable() Disable the SPI module on PortC
power_spic_enable() Enable the SPI module on PortC
power_spid_disable() Disable the SPI module on PortD
power_spid_enable() Enable the SPI module on PortD
power_tc0c_disable() Disable the TC0 module on PortC
power_tc0c_enable() Enable the TC0 module on PortC
power_tc0d_disable() Disable the TC0 module on PortD
power_tc0d_enable() Enable the TC0 module on PortD
power_tc0e_disable() Disable the TC0 module on PortE
power_tc0e_enable() Enable the TC0 module on PortE
power_tc0f_disable() Disable the TC0 module on PortF
power_tc0f_enable() Enable the TC0 module on PortF
power_tc1c_disable() Disable the TC1 module on PortC
power_tc1c_enable() Enable the TC1 module on PortC
power_twic_disable() Disable the Two Wire Interface module on PortC
power_twic_enable() Enable the Two Wire Interface module on PortC
power_twie_disable() Disable the Two Wire Interface module on PortE
power_twie_enable() Enable the Two Wire Interface module on PortE
power_timer0_enable() Enable the Timer 0 module.
power_timer0_disable() Disable the Timer 0 module.
power_timer1_enable() Enable the Timer 1 module.
power_timer1_disable() Disable the Timer 1 module.
power_timer2_enable() Enable the Timer 2 module.
power_timer2_disable() Disable the Timer 2 module.
power_timer3_enable() Enable the Timer 3 module.
power_timer3_disable() Disable the Timer 3 module.
power_timer4_enable() Enable the Timer 4 module.
power_timer4_disable() Disable the Timer 4 module.
power_timer5_enable() Enable the Timer 5 module.
power_timer5_disable() Disable the Timer 5 module.
power_twi_enable() Enable the Two Wire Interface module.
power_twi_disable() Disable the Two Wire Interface module.
power_usart_enable() Enable the USART module.
power_usart_disable() Disable the USART module.
power_usart0_enable() Enable the USART 0 module.
power_usart0_disable() Disable the USART 0 module.
power_usart1_enable() Enable the USART 1 module.
power_usart1_disable() Disable the USART 1 module.
power_usart2_enable() Enable the USART 2 module.
power_usart2_disable() Disable the USART 2 module.
power_usart3_enable() Enable the USART 3 module.
power_usart3_disable() Disable the USART 3 module.
power_usartc0_disable() Disable the USART0 module on PortC
power_usartc0_enable() Enable the USART0 module on PortC
power_usartd0_disable() Disable the USART0 module on PortD
power_usartd0_enable() Enable the USART0 module on PortD
power_usarte0_disable() Disable the USART0 module on PortE
power_usarte0_enable() Enable the USART0 module on PortE
power_usartf0_disable() Disable the USART0 module on PortF
power_usartf0_enable() Enable the USART0 module on PortF
power_usb_enable() Enable the USB module.
power_usb_disable() Disable the USB module.
power_usi_enable() Enable the Universal Serial Interface module.
power_usi_disable() Disable the Universal Serial Interface module.
power_vadc_enable() Enable the Voltage ADC module.
power_vadc_disable() Disable the Voltage ADC module.
power_all_enable() Enable all modules.
power_all_disable() Disable all modules.
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23.21 <avr/power.h>: Power Reduction Management 291
Some of the newer AVRs contain a System Clock Prescale Register (CLKPR) that
allows you to decrease the system clock frequency and the power consumption when
the need for processing power is low. On some earlier AVRs (ATmega103, ATmega64,
ATmega128), similar functionality can be achieved through the XTAL Divide Control
Register. Below are two macros and an enumerated type that can be used to interface
to the Clock Prescale Register or XTAL Divide Control Register.
Note
Not all AVR devices have a clock prescaler. On those devices without a Clock
Prescale Register or XTAL Divide Control Register, these macros are not available.
typedef enum
{
clock_div_1 = 0,
clock_div_2 = 1,
clock_div_4 = 2,
clock_div_8 = 3,
clock_div_16 = 4,
clock_div_32 = 5,
clock_div_64 = 6,
clock_div_128 = 7,
clock_div_256 = 8,
clock_div_1_rc = 15, // ATmega128RFA1 only
} clock_div_t;
Clock prescaler setting enumerations for device using System Clock Prescale Register.
typedef enum
{
clock_div_1 = 1,
clock_div_2 = 2,
clock_div_4 = 4,
clock_div_8 = 8,
clock_div_16 = 16,
clock_div_32 = 32,
clock_div_64 = 64,
clock_div_128 = 128
} clock_div_t;
Clock prescaler setting enumerations for device using XTAL Divide Control Register.
23.21.2 Function Documentation
23.21.2.1 clock_prescale_set (clock_div_t x)
Set the clock prescaler register select bits, selecting a system clock division setting.
This function is inlined, even if compiler optimizations are disabled.
The type of xis clock_div_t.
Note
For device with XTAL Divide Control Register (XDIV), xcan actually range from
1 to 129. Thus, one does not need to use clock_div_t type as argument.
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23.22 Additional notes from <avr/sfr_defs.h>292
23.22 Additional notes from <avr/sfr_defs.h>
The <avr/sfr_defs.h>file is included by all of the <avr/ioXXXX.h>files,
which use macros defined here to make the special function register definitions look
like C variables or simple constants, depending on the _SFR_ASM_COMPAT define.
Some examples from <avr/iocanxx.h>to show how to define such macros:
#define PORTA _SFR_IO8(0x02)
#define EEAR _SFR_IO16(0x21)
#define UDR0 _SFR_MEM8(0xC6)
#define TCNT3 _SFR_MEM16(0x94)
#define CANIDT _SFR_MEM32(0xF0)
If _SFR_ASM_COMPAT is not defined, C programs can use names like PORTA directly
in C expressions (also on the left side of assignment operators) and GCC will do the
right thing (use short I/O instructions if possible). The __SFR_OFFSET definition is
not used in any way in this case.
Define _SFR_ASM_COMPAT as 1 to make these names work as simple constants (ad-
dresses of the I/O registers). This is necessary when included in preprocessed assem-
bler (∗.S) source files, so it is done automatically if __ASSEMBLER__ is defined. By
default, all addresses are defined as if they were memory addresses (used in lds/sts
instructions). To use these addresses in in/out instructions, you must subtract 0x20
from them.
For more backwards compatibility, insert the following at the start of your old assem-
bler source file:
#define __SFR_OFFSET 0
This automatically subtracts 0x20 from I/O space addresses, but it’s a hack, so it is
recommended to change your source: wrap such addresses in macros defined here, as
shown below. After this is done, the __SFR_OFFSET definition is no longer necessary
and can be removed.
Real example - this code could be used in a boot loader that is portable between devices
with SPMCR at different addresses.
<avr/iom163.h>: #define SPMCR _SFR_IO8(0x37)
<avr/iom128.h>: #define SPMCR _SFR_MEM8(0x68)
#if _SFR_IO_REG_P(SPMCR)
out _SFR_IO_ADDR(SPMCR), r24
#else
sts _SFR_MEM_ADDR(SPMCR), r24
#endif
You can use the in/out/cbi/sbi/sbic/sbis instructions, without the _SFR_-
IO_REG_P test, if you know that the register is in the I/O space (as with SREG, for
example). If it isn’t, the assembler will complain (I/O address out of range 0...0x3f),
so this should be fairly safe.
If you do not define __SFR_OFFSET (so it will be 0x20 by default), all special register
addresses are defined as memory addresses (so SREG is 0x5f), and (if code size and
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23.23 <avr/sfr_defs.h>: Special function registers 293
speed are not important, and you don’t like the ugly #if above) you can always use
lds/sts to access them. But, this will not work if __SFR_OFFSET != 0x20, so use a
different macro (defined only if __SFR_OFFSET == 0x20) for safety:
sts _SFR_ADDR(SPMCR), r24
In C programs, all 3 combinations of _SFR_ASM_COMPAT and __SFR_OFFSET are
supported - the _SFR_ADDR(SPMCR) macro can be used to get the address of the
SPMCR register (0x57 or 0x68 depending on device).
23.23 <avr/sfr_defs.h>: Special function registers
Modules
•Additional notes from <avr/sfr_defs.h>
Bit manipulation
• #define _BV(bit) (1 << (bit))
IO register bit manipulation
• #define bit_is_set(sfr, bit) (_SFR_BYTE(sfr) & _BV(bit))
• #define bit_is_clear(sfr, bit) (!(_SFR_BYTE(sfr) & _BV(bit)))
• #define loop_until_bit_is_set(sfr, bit) do { } while (bit_is_clear(sfr, bit))
• #define loop_until_bit_is_clear(sfr, bit) do { } while (bit_is_set(sfr, bit))
23.23.1 Detailed Description
When working with microcontrollers, many tasks usually consist of controlling internal
peripherals, or external peripherals that are connected to the device. The entire IO
address space is made available as memory-mapped IO, i.e. it can be accessed using
all the MCU instructions that are applicable to normal data memory. For most AVR
devices, the IO register space is mapped into the data memory address space with an
offset of 0x20 since the bottom of this space is reserved for direct access to the MCU
registers. (Actual SRAM is available only behind the IO register area, starting at some
specific address depending on the device.)
For example the user can access memory-mapped IO registers as if they were globally
defined variables like this:
PORTA = 0x33;
unsigned char foo = PINA;
The compiler will choose the correct instruction sequence to generate based on the
address of the register being accessed.
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23.23 <avr/sfr_defs.h>: Special function registers 294
The advantage of using the memory-mapped registers in C programs is that it makes
the programs more portable to other C compilers for the AVR platform.
Note that special care must be taken when accessing some of the 16-bit timer IO reg-
isters where access from both the main program and within an interrupt context can
happen. See Why do some 16-bit timer registers sometimes get trashed?.
Porting programs that use the deprecated sbi/cbi macros
Access to the AVR single bit set and clear instructions are provided via the standard C
bit manipulation commands. The sbi and cbi macros are no longer directly supported.
sbi (sfr,bit) can be replaced by sfr |=_BV(bit) .
i.e.: sbi(PORTB, PB1); is now PORTB |=_BV(PB1);
This actually is more flexible than having sbi directly, as the optimizer will use a hard-
ware sbi if appropriate, or a read/or/write operation if not appropriate. You do not need
to keep track of which registers sbi/cbi will operate on.
Likewise, cbi (sfr,bit) is now sfr &= ∼(_BV(bit));
23.23.2 Define Documentation
23.23.2.1 #define _BV(bit) (1 << (bit))
#include <avr/io.h>
Converts a bit number into a byte value.
Note
The bit shift is performed by the compiler which then inserts the result into the
code. Thus, there is no run-time overhead when using _BV().
23.23.2.2 #define bit_is_clear(sfr, bit) (!(_SFR_BYTE(sfr) & _BV(bit)))
#include <avr/io.h>
Test whether bit bit in IO register sfr is clear. This will return non-zero if the bit is
clear, and a 0 if the bit is set.
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23.24 <avr/signature.h>: Signature Support 295
23.23.2.3 #define bit_is_set(sfr, bit) (_SFR_BYTE(sfr) & _BV(bit))
#include <avr/io.h>
Test whether bit bit in IO register sfr is set. This will return a 0 if the bit is clear,
and non-zero if the bit is set.
23.23.2.4 #define loop_until_bit_is_clear(sfr, bit) do { } while (bit_is_set(sfr,
bit))
#include <avr/io.h>
Wait until bit bit in IO register sfr is clear.
23.23.2.5 #define loop_until_bit_is_set(sfr, bit) do { } while (bit_is_clear(sfr,
bit))
#include <avr/io.h>
Wait until bit bit in IO register sfr is set.
23.24 <avr/signature.h>: Signature Support
Introduction
The <avr/signature.h>header file allows the user to automatically and easily include
the device’s signature data in a special section of the final linked ELF file.
This value can then be used by programming software to compare the on-device signa-
ture with the signature recorded in the ELF file to look for a match before programming
the device.
API Usage Example
Usage is very simple; just include the header file:
#include <avr/signature.h>
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23.25 <avr/sleep.h>: Power Management and Sleep Modes 296
This will declare a constant unsigned char array and it is initialized with the three
signature bytes, MSB first, that are defined in the device I/O header file. This array is
then placed in the .signature section in the resulting linked ELF file.
The three signature bytes that are used to initialize the array are these defined macros
in the device I/O header file, from MSB to LSB: SIGNATURE_2, SIGNATURE_1,
SIGNATURE_0.
This header file should only be included once in an application.
23.25 <avr/sleep.h>: Power Management and Sleep Modes
Functions
• void sleep_enable (void)
• void sleep_disable (void)
• void sleep_cpu (void)
• void sleep_mode (void)
• void sleep_bod_disable (void)
23.25.1 Detailed Description
#include <avr/sleep.h>
Use of the SLEEP instruction can allow an application to reduce its power comsump-
tion considerably. AVR devices can be put into different sleep modes. Refer to the
datasheet for the details relating to the device you are using.
There are several macros provided in this header file to actually put the device into
sleep mode. The simplest way is to optionally set the desired sleep mode using set_-
sleep_mode() (it usually defaults to idle mode where the CPU is put on sleep but
all peripheral clocks are still running), and then call sleep_mode(). This macro
automatically sets the sleep enable bit, goes to sleep, and clears the sleep enable bit.
Example:
#include <avr/sleep.h>
...
set_sleep_mode(<mode>);
sleep_mode();
Note that unless your purpose is to completely lock the CPU (until a hardware reset),
interrupts need to be enabled before going to sleep.
As the sleep_mode() macro might cause race conditions in some situations,
the individual steps of manipulating the sleep enable (SE) bit, and actually issuing
the SLEEP instruction, are provided in the macros sleep_enable(),sleep_-
disable(), and sleep_cpu(). This also allows for test-and-sleep scenarios that
take care of not missing the interrupt that will awake the device from sleep.
Example:
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23.25 <avr/sleep.h>: Power Management and Sleep Modes 297
#include <avr/interrupt.h>
#include <avr/sleep.h>
...
set_sleep_mode(<mode>);
cli();
if (some_condition)
{
sleep_enable();
sei();
sleep_cpu();
sleep_disable();
}
sei();
This sequence ensures an atomic test of some_condition with interrupts being dis-
abled. If the condition is met, sleep mode will be prepared, and the SLEEP instruction
will be scheduled immediately after an SEI instruction. As the intruction right after
the SEI is guaranteed to be executed before an interrupt could trigger, it is sure the
device will really be put to sleep.
Some devices have the ability to disable the Brown Out Detector (BOD) before going
to sleep. This will also reduce power while sleeping. If the specific AVR device has this
ability then an additional macro is defined: sleep_bod_disable(). This macro
generates inlined assembly code that will correctly implement the timed sequence for
disabling the BOD before sleeping. However, there is a limited number of cycles af-
ter the BOD has been disabled that the device can be put into sleep mode, otherwise
the BOD will not truly be disabled. Recommended practice is to disable the BOD
(sleep_bod_disable()), set the interrupts (sei()), and then put the device to
sleep (sleep_cpu()), like so:
#include <avr/interrupt.h>
#include <avr/sleep.h>
...
set_sleep_mode(<mode>);
cli();
if (some_condition)
{
sleep_enable();
sleep_bod_disable();
sei();
sleep_cpu();
sleep_disable();
}
sei();
23.25.2 Function Documentation
23.25.2.1 void sleep_bod_disable (void)
Disable BOD before going to sleep. Not available on all devices.
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23.26 <avr/version.h>: avr-libc version macros 298
23.25.2.2 void sleep_cpu (void)
Put the device into sleep mode. The SE bit must be set beforehand, and it is
recommended to clear it afterwards.
23.25.2.3 void sleep_disable (void)
Clear the SE (sleep enable) bit.
23.25.2.4 void sleep_enable (void)
Put the device in sleep mode. How the device is brought out of sleep
mode depends on the specific mode selected with the set_sleep_mode() function. See
the data sheet for your device for more details.
Set the SE (sleep enable) bit.
23.25.2.5 void sleep_mode (void)
Put the device into sleep mode, taking care of setting the SE bit before, and clearing it
afterwards.
23.26 <avr/version.h>: avr-libc version macros
Defines
• #define __AVR_LIBC_VERSION_STRING__ "2.0.0"
• #define __AVR_LIBC_VERSION__ 20000UL
• #define __AVR_LIBC_DATE_STRING__ "20150208"
• #define __AVR_LIBC_DATE_ 20150208UL
• #define __AVR_LIBC_MAJOR__ 2
• #define __AVR_LIBC_MINOR__ 0
• #define __AVR_LIBC_REVISION__ 0
23.26.1 Detailed Description
#include <avr/version.h>
This header file defines macros that contain version numbers and strings describing the
current version of avr-libc.
The version number itself basically consists of three pieces that are separated by a
dot: the major number, the minor number, and the revision number. For development
versions (which use an odd minor number), the string representation additionally gets
the date code (YYYYMMDD) appended.
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23.27 <avr/wdt.h>: Watchdog timer handling 299
This file will also be included by <avr/io.h>. That way, portable tests can be
implemented using <avr/io.h>that can be used in code that wants to remain
backwards-compatible to library versions prior to the date when the library version
API had been added, as referenced but undefined C preprocessor macros automatically
evaluate to 0.
23.26.2 Define Documentation
23.26.2.1 #define __AVR_LIBC_DATE_ 20150208UL
Numerical representation of the release date.
23.26.2.2 #define __AVR_LIBC_DATE_STRING__ "20150208"
String literal representation of the release date.
23.26.2.3 #define __AVR_LIBC_MAJOR__ 2
Library major version number.
23.26.2.4 #define __AVR_LIBC_MINOR__ 0
Library minor version number.
23.26.2.5 #define __AVR_LIBC_REVISION__ 0
Library revision number.
23.26.2.6 #define __AVR_LIBC_VERSION__ 20000UL
Numerical representation of the current library version.
In the numerical representation, the major number is multiplied by 10000, the minor
number by 100, and all three parts are then added. It is intented to provide a monoton-
ically increasing numerical value that can easily be used in numerical checks.
23.26.2.7 #define __AVR_LIBC_VERSION_STRING__ "2.0.0"
String literal representation of the current library version.
23.27 <avr/wdt.h>: Watchdog timer handling
Defines
• #define wdt_reset() __asm__ __volatile__ ("wdr")
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23.27 <avr/wdt.h>: Watchdog timer handling 300
• #define WDTO_15MS 0
• #define WDTO_30MS 1
• #define WDTO_60MS 2
• #define WDTO_120MS 3
• #define WDTO_250MS 4
• #define WDTO_500MS 5
• #define WDTO_1S 6
• #define WDTO_2S 7
• #define WDTO_4S 8
• #define WDTO_8S 9
Functions
• static __inline__ __attribute__ ((__always_inline__)) void wdt_enable(const
uint8_t value)
23.27.1 Detailed Description
#include <avr/wdt.h>
This header file declares the interface to some inline macros handling the watchdog
timer present in many AVR devices. In order to prevent the watchdog timer configura-
tion from being accidentally altered by a crashing application, a special timed sequence
is required in order to change it. The macros within this header file handle the required
sequence automatically before changing any value. Interrupts will be disabled during
the manipulation.
Note
Depending on the fuse configuration of the particular device, further restrictions
might apply, in particular it might be disallowed to turn off the watchdog timer.
Note that for newer devices (ATmega88 and newer, effectively any AVR that has the op-
tion to also generate interrupts), the watchdog timer remains active even after a system
reset (except a power-on condition), using the fastest prescaler value (approximately
15 ms). It is therefore required to turn off the watchdog early during program startup,
the datasheet recommends a sequence like the following:
#include <stdint.h>
#include <avr/wdt.h>
uint8_t mcusr_mirror __attribute__ ((section (".noinit")));
void get_mcusr(void) \
__attribute__((naked)) \
__attribute__((section(".init3")));
void get_mcusr(void)
{
mcusr_mirror = MCUSR;
MCUSR = 0;
wdt_disable();
}
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23.27 <avr/wdt.h>: Watchdog timer handling 301
Saving the value of MCUSR in mcusr_mirror is only needed if the application
later wants to examine the reset source, but in particular, clearing the watchdog reset
flag before disabling the watchdog is required, according to the datasheet.
23.27.2 Define Documentation
23.27.2.1 #define wdt_reset() __asm__ __volatile__ ("wdr")
Reset the watchdog
timer. When the watchdog timer is enabled, a call to this instruction is required before
the timer expires, otherwise a watchdog-initiated device reset will occur.
23.27.2.2 #define WDTO_120MS 3
See WDTO_15MS
23.27.2.3 #define WDTO_15MS 0
Symbolic constants for the watchdog timeout. Since the watchdog timer
is based on a free-running RC oscillator, the times are approximate only and apply to
a supply voltage of 5 V. At lower supply voltages, the times will increase. For older
devices, the times will be as large as three times when operating at Vcc = 3 V, while
the newer devices (e. g. ATmega128, ATmega8) only experience a negligible change.
Possible timeout values are: 15 ms, 30 ms, 60 ms, 120 ms, 250 ms, 500 ms, 1 s, 2 s.
(Some devices also allow for 4 s and 8 s.) Symbolic constants are formed by the prefix
WDTO_, followed by the time.
Example that would select a watchdog timer expiry of approximately 500 ms:
wdt_enable(WDTO_500MS);
23.27.2.4 #define WDTO_1S 6
See WDTO_15MS
23.27.2.5 #define WDTO_250MS 4
See WDTO_15MS
23.27.2.6 #define WDTO_2S 7
See WDTO_15MS
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23.27 <avr/wdt.h>: Watchdog timer handling 302
23.27.2.7 #define WDTO_30MS 1
See WDTO_15MS
23.27.2.8 #define WDTO_4S 8
See WDTO_15MS Note: This is only available
on the ATtiny2313, ATtiny24, ATtiny44, ATtiny84, ATtiny84A, ATtiny25, ATtiny45,
ATtiny85, ATtiny261, ATtiny461, ATtiny861, ATmega48, ATmega88, ATmega168,
ATmega48P, ATmega88P, ATmega168P, ATmega328P, ATmega164P, ATmega324P,
ATmega644P, ATmega644, ATmega640, ATmega1280, ATmega1281, ATmega2560,
ATmega2561, ATmega8HVA, ATmega16HVA, ATmega32HVB, ATmega406, AT-
mega1284P, AT90PWM1, AT90PWM2, AT90PWM2B, AT90PWM3, AT90PWM3B,
AT90PWM216, AT90PWM316, AT90PWM81, AT90PWM161, AT90USB82,
AT90USB162, AT90USB646, AT90USB647, AT90USB1286, AT90USB1287, AT-
tiny48, ATtiny88.
Note: This value does not match the bit pattern of the respective control register. It is
solely meant to be used together with wdt_enable().
23.27.2.9 #define WDTO_500MS 5
See WDTO_15MS
23.27.2.10 #define WDTO_60MS 2
See WDTO_15MS
23.27.2.11 #define WDTO_8S 9
See WDTO_15MS Note: This is only available on the ATtiny2313,
ATtiny24, ATtiny44, ATtiny84, ATtiny84A, ATtiny25, ATtiny45, ATtiny85, AT-
tiny261, ATtiny461, ATtiny861, ATmega48, ATmega48A, ATmega48PA, ATmega88,
ATmega168, ATmega48P, ATmega88P, ATmega168P, ATmega328P, ATmega164P,
ATmega324P, ATmega644P, ATmega644, ATmega640, ATmega1280, ATmega1281,
ATmega2560, ATmega2561, ATmega8HVA, ATmega16HVA, ATmega32HVB, AT-
mega406, ATmega1284P, ATmega2564RFR2, ATmega256RFR2, ATmega1284RFR2,
ATmega128RFR2, ATmega644RFR2, ATmega64RFR2 AT90PWM1, AT90PWM2,
AT90PWM2B, AT90PWM3, AT90PWM3B, AT90PWM216, AT90PWM316,
AT90PWM81, AT90PWM161, AT90USB82, AT90USB162, AT90USB646,
AT90USB647, AT90USB1286, AT90USB1287, ATtiny48, ATtiny88, ATxmega16a4u,
ATxmega32a4u, ATxmega16c4, ATxmega32c4, ATxmega128c3, ATxmega192c3,
ATxmega256c3.
Note: This value does not match the bit pattern of the respective control register. It is
solely meant to be used together with wdt_enable().
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23.28 <util/atomic.h>Atomically and Non-Atomically Executed Code Blocks303
23.27.3 Function Documentation
23.27.3.1 static __inline__ __attribute__ ((__always_inline__)) const
[static]
Enable the watchdog timer, configuring it
for expiry after timeout (which is a combination of the WDP0 through WDP2 bits to
write into the WDTCR register; For those devices that have a WDTCSR register, it uses
the combination of the WDP0 through WDP3 bits).
See also the symbolic constants WDTO_15MS et al.
23.28 <util/atomic.h>Atomically and Non-Atomically Executed
Code Blocks
Defines
• #define ATOMIC_BLOCK(type)
• #define NONATOMIC_BLOCK(type)
• #define ATOMIC_RESTORESTATE
• #define ATOMIC_FORCEON
• #define NONATOMIC_RESTORESTATE
• #define NONATOMIC_FORCEOFF
23.28.1 Detailed Description
#include <util/atomic.h>
Note
The macros in this header file require the ISO/IEC 9899:1999 ("ISO C99") feature
of for loop variables that are declared inside the for loop itself. For that reason, this
header file can only be used if the standard level of the compiler (option --std=) is
set to either c99 or gnu99.
The macros in this header file deal with code blocks that are guaranteed to be excuted
Atomically or Non-Atmomically. The term "Atomic" in this context refers to the un-
ability of the respective code to be interrupted.
These macros operate via automatic manipulation of the Global Interrupt Status (I) bit
of the SREG register. Exit paths from both block types are all managed automatically
without the need for special considerations, i. e. the interrupt status will be restored to
the same value it has been when entering the respective block.
A typical example that requires atomic access is a 16 (or more) bit variable that is
shared between the main execution path and an ISR. While declaring such a variable
as volatile ensures that the compiler will not optimize accesses to it away, it does not
guarantee atomic access to it. Assuming the following example:
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23.28 <util/atomic.h>Atomically and Non-Atomically Executed Code Blocks304
#include <inttypes.h>
#include <avr/interrupt.h>
#include <avr/io.h>
volatile uint16_t ctr;
ISR(TIMER1_OVF_vect)
{
ctr--;
}
...
int
main(void)
{
...
ctr = 0x200;
start_timer();
while (ctr != 0)
// wait
;
...
}
There is a chance where the main context will exit its wait loop when the variable ctr
just reached the value 0xFF. This happens because the compiler cannot natively access
a 16-bit variable atomically in an 8-bit CPU. So the variable is for example at 0x100,
the compiler then tests the low byte for 0, which succeeds. It then proceeds to test the
high byte, but that moment the ISR triggers, and the main context is interrupted. The
ISR will decrement the variable from 0x100 to 0xFF, and the main context proceeds.
It now tests the high byte of the variable which is (now) also 0, so it concludes the
variable has reached 0, and terminates the loop.
Using the macros from this header file, the above code can be rewritten like:
#include <inttypes.h>
#include <avr/interrupt.h>
#include <avr/io.h>
#include <util/atomic.h>
volatile uint16_t ctr;
ISR(TIMER1_OVF_vect)
{
ctr--;
}
...
int
main(void)
{
...
ctr = 0x200;
start_timer();
sei();
uint16_t ctr_copy;
do
{
ATOMIC_BLOCK(ATOMIC_FORCEON)
{
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23.28 <util/atomic.h>Atomically and Non-Atomically Executed Code Blocks305
ctr_copy = ctr;
}
}
while (ctr_copy != 0);
...
}
This will install the appropriate interrupt protection before accessing variable ctr,
so it is guaranteed to be consistently tested. If the global interrupt state were uncer-
tain before entering the ATOMIC_BLOCK, it should be executed with the parameter
ATOMIC_RESTORESTATE rather than ATOMIC_FORCEON.
See Problems with reordering code for things to be taken into account with respect to
compiler optimizations.
23.28.2 Define Documentation
23.28.2.1 #define ATOMIC_BLOCK(type)
Creates a block of code that is guaranteed to be executed atomically. Upon
entering the block the Global Interrupt Status flag in SREG is disabled, and re-enabled
upon exiting the block from any exit path.
Two possible macro parameters are permitted, ATOMIC_RESTORESTATE and
ATOMIC_FORCEON.
23.28.2.2 #define ATOMIC_FORCEON
This is a possible parameter for ATOMIC_BLOCK. When used, it will
cause the ATOMIC_BLOCK to force the state of the SREG register on exit, enabling
the Global Interrupt Status flag bit. This saves on flash space as the previous value of
the SREG register does not need to be saved at the start of the block.
Care should be taken that ATOMIC_FORCEON is only used when it is known that
interrupts are enabled before the block’s execution or when the side effects of enabling
global interrupts at the block’s completion are known and understood.
23.28.2.3 #define ATOMIC_RESTORESTATE
This is a possible parameter for ATOMIC_BLOCK. When used,
it will cause the ATOMIC_BLOCK to restore the previous state of the SREG register,
saved before the Global Interrupt Status flag bit was disabled. The net effect of this
is to make the ATOMIC_BLOCK’s contents guaranteed atomic, without changing the
state of the Global Interrupt Status flag when execution of the block completes.
23.28.2.4 #define NONATOMIC_BLOCK(type)
Creates a block of code that is executed
non-atomically. Upon entering the block the Global Interrupt Status flag in SREG is
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23.29 <util/crc16.h>: CRC Computations 306
enabled, and disabled upon exiting the block from any exit path. This is useful when
nested inside ATOMIC_BLOCK sections, allowing for non-atomic execution of small
blocks of code while maintaining the atomic access of the other sections of the parent
ATOMIC_BLOCK.
Two possible macro parameters are permitted, NONATOMIC_RESTORESTATE and
NONATOMIC_FORCEOFF.
23.28.2.5 #define NONATOMIC_FORCEOFF
This is a possible parameter for NONATOMIC_BLOCK. When used, it
will cause the NONATOMIC_BLOCK to force the state of the SREG register on exit,
disabling the Global Interrupt Status flag bit. This saves on flash space as the previous
value of the SREG register does not need to be saved at the start of the block.
Care should be taken that NONATOMIC_FORCEOFF is only used when it is known
that interrupts are disabled before the block’s execution or when the side effects of
disabling global interrupts at the block’s completion are known and understood.
23.28.2.6 #define NONATOMIC_RESTORESTATE
This is a possible parameter for NONATOMIC_BLOCK. When used, it will cause
the NONATOMIC_BLOCK to restore the previous state of the SREG register, saved
before the Global Interrupt Status flag bit was enabled. The net effect of this is to make
the NONATOMIC_BLOCK’s contents guaranteed non-atomic, without changing the
state of the Global Interrupt Status flag when execution of the block completes.
23.29 <util/crc16.h>: CRC Computations
Functions
• static __inline__ uint16_t _crc16_update (uint16_t __crc, uint8_t __data)
• static __inline__ uint16_t _crc_xmodem_update (uint16_t __crc, uint8_t __data)
• static __inline__ uint16_t _crc_ccitt_update (uint16_t __crc, uint8_t __data)
• static __inline__ uint8_t _crc_ibutton_update (uint8_t __crc, uint8_t __data)
• static __inline__ uint8_t _crc8_ccitt_update (uint8_t __crc, uint8_t __data)
23.29.1 Detailed Description
#include <util/crc16.h>
This header file provides a optimized inline functions for calculating cyclic redundancy
checks (CRC) using common polynomials.
References:
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23.29 <util/crc16.h>: CRC Computations 307
See the Dallas Semiconductor app note 27 for 8051 assembler example and general
CRC optimization suggestions. The table on the last page of the app note is the key to
understanding these implementations.
Jack Crenshaw’s "Implementing CRCs" article in the January 1992 isue of Embedded
Systems Programming. This may be difficult to find, but it explains CRC’s in very clear
and concise terms. Well worth the effort to obtain a copy.
A typical application would look like:
// Dallas iButton test vector.
uint8_t serno[] = { 0x02, 0x1c, 0xb8, 0x01, 0, 0, 0, 0xa2 };
int
checkcrc(void)
{
uint8_t crc = 0, i;
for (i = 0; i < sizeof serno / sizeof serno[0]; i++)
crc = _crc_ibutton_update(crc, serno[i]);
return crc; // must be 0
}
23.29.2 Function Documentation
23.29.2.1 static __inline__ uint16_t _crc16_update (uint16_t __crc, uint8_t
__data)[static]
Optimized CRC-16 calculation.
Polynomial: x∧16 + x∧15 + x∧2 + 1 (0xa001)
Initial value: 0xffff
This CRC is normally used in disk-drive controllers.
The following is the equivalent functionality written in C.
uint16_t
crc16_update(uint16_t crc, uint8_t a)
{
int i;
crc ^= a;
for (i = 0; i < 8; ++i)
{
if (crc & 1)
crc = (crc >> 1) ^ 0xA001;
else
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23.29 <util/crc16.h>: CRC Computations 308
crc = (crc >> 1);
}
return crc;
}
23.29.2.2 static __inline__ uint8_t _crc8_ccitt_update (uint8_t __crc, uint8_t
__data)[static]
Optimized CRC-8-CCITT calculation.
Polynomial: x∧8+x∧2 + x + 1 (0xE0)
For use with simple CRC-8
Initial value: 0x0
For use with CRC-8-ROHC
Initial value: 0xff
Reference: http://tools.ietf.org/html/rfc3095#section-5.9.1
For use with CRC-8-ATM/ITU
Initial value: 0xff
Final XOR value: 0x55
Reference: http://www.itu.int/rec/T-REC-I.432.1-199902-I/en
The C equivalent has been originally written by Dave Hylands. Assembly code is based
on _crc_ibutton_update optimization.
The following is the equivalent functionality written in C.
uint8_t
_crc8_ccitt_update (uint8_t inCrc, uint8_t inData)
{
uint8_t i;
uint8_t data;
data = inCrc ^ inData;
for(i=0;i<8;i++)
{
if (( data & 0x80 ) != 0 )
{
data <<= 1;
data ^= 0x07;
}
else
{
data <<= 1;
}
}
return data;
}
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23.29 <util/crc16.h>: CRC Computations 309
23.29.2.3 static __inline__ uint16_t _crc_ccitt_update (uint16_t __crc, uint8_t
__data)[static]
Optimized CRC-CCITT calculation.
Polynomial: x∧16 + x∧12 + x∧5 + 1 (0x8408)
Initial value: 0xffff
This is the CRC used by PPP and IrDA.
See RFC1171 (PPP protocol) and IrDA IrLAP 1.1
Note
Although the CCITT polynomial is the same as that used by the Xmodem protocol,
they are quite different. The difference is in how the bits are shifted through the
alorgithm. Xmodem shifts the MSB of the CRC and the input first, while CCITT
shifts the LSB of the CRC and the input first.
The following is the equivalent functionality written in C.
uint16_t
crc_ccitt_update (uint16_t crc, uint8_t data)
{
data ^= lo8 (crc);
data ^= data << 4;
return ((((uint16_t)data << 8) | hi8 (crc)) ^ (uint8_t)(data >> 4)
^ ((uint16_t)data << 3));
}
23.29.2.4 static __inline__ uint8_t _crc_ibutton_update (uint8_t __crc, uint8_t
__data)[static]
Optimized Dallas (now Maxim) iButton 8-bit CRC calculation.
Polynomial: x∧8+x∧5+x∧4 + 1 (0x8C)
Initial value: 0x0
See http://www.maxim-ic.com/appnotes.cfm/appnote_number/27
The following is the equivalent functionality written in C.
uint8_t
_crc_ibutton_update(uint8_t crc, uint8_t data)
{
uint8_t i;
crc = crc ^ data;
for (i = 0; i < 8; i++)
{
if (crc & 0x01)
crc = (crc >> 1) ^ 0x8C;
else
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23.30 <util/delay.h>: Convenience functions for busy-wait delay loops 310
crc >>= 1;
}
return crc;
}
23.29.2.5 static __inline__ uint16_t _crc_xmodem_update (uint16_t __crc,
uint8_t __data)[static]
Optimized CRC-XMODEM calculation.
Polynomial: x∧16 + x∧12 + x∧5 + 1 (0x1021)
Initial value: 0x0
This is the CRC used by the Xmodem-CRC protocol.
The following is the equivalent functionality written in C.
uint16_t
crc_xmodem_update (uint16_t crc, uint8_t data)
{
int i;
crc = crc ^ ((uint16_t)data << 8);
for (i=0; i<8; i++)
{
if (crc & 0x8000)
crc = (crc << 1) ^ 0x1021;
else
crc <<= 1;
}
return crc;
}
23.30 <util/delay.h>: Convenience functions for busy-wait delay
loops
Defines
• #define F_CPU 1000000UL
Functions
• void _delay_ms (double __ms)
• void _delay_us (double __us)
23.30.1 Detailed Description
#define F_CPU 1000000UL // 1 MHz
//#define F_CPU 14.7456E6
#include <util/delay.h>
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23.30 <util/delay.h>: Convenience functions for busy-wait delay loops 311
Note
As an alternative method, it is possible to pass the F_CPU macro down to the com-
piler from the Makefile. Obviously, in that case, no #define statement should
be used.
The functions in this header file are wrappers around the basic busy-wait functions from
<util/delay_basic.h>. They are meant as convenience functions where actual time
values can be specified rather than a number of cycles to wait for. The idea behind is
that compile-time constant expressions will be eliminated by compiler optimization so
floating-point expressions can be used to calculate the number of delay cycles needed
based on the CPU frequency passed by the macro F_CPU.
Note
In order for these functions to work as intended, compiler optimizations must be
enabled, and the delay time must be an expression that is a known constant at
compile-time. If these requirements are not met, the resulting delay will be much
longer (and basically unpredictable), and applications that otherwise do not use
floating-point calculations will experience severe code bloat by the floating-point
library routines linked into the application.
The functions available allow the specification of microsecond, and millisecond delays
directly, using the application-supplied macro F_CPU as the CPU clock frequency (in
Hertz).
23.30.2 Define Documentation
23.30.2.1 #define F_CPU 1000000UL
CPU frequency in Hz.
The macro F_CPU specifies the CPU frequency to be considered by the delay macros.
This macro is normally supplied by the environment (e.g. from within a project header,
or the project’s Makefile). The value 1 MHz here is only provided as a "vanilla" fall-
back if no such user-provided definition could be found.
In terms of the delay functions, the CPU frequency can be given as a floating-point
constant (e.g. 3.6864E6 for 3.6864 MHz). However, the macros in <util/setbaud.h>
require it to be an integer value.
23.30.3 Function Documentation
23.30.3.1 void _delay_ms (double __ms)
Perform a delay of __ms milliseconds, using _delay_loop_2().
The macro F_CPU is supposed to be defined to a constant defining the CPU clock
frequency (in Hertz).
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23.30 <util/delay.h>: Convenience functions for busy-wait delay loops 312
The maximal possible delay is 262.14 ms / F_CPU in MHz.
When the user request delay which exceed the maximum possible one, _delay_ms()
provides a decreased resolution functionality. In this mode _delay_ms() will work with
a resolution of 1/10 ms, providing delays up to 6.5535 seconds (independent from CPU
frequency). The user will not be informed about decreased resolution.
If the avr-gcc toolchain has __builtin_avr_delay_cycles() support, maximal possible
delay is 4294967.295 ms/ F_CPU in MHz. For values greater than the maximal possi-
ble delay, overflows results in no delay i.e., 0ms.
Conversion of __ms into clock cycles may not always result in integer. By default, the
clock cycles rounded up to next integer. This ensures that the user gets at least __ms
microseconds of delay.
Alternatively, by defining the macro __DELAY_ROUND_DOWN__, or __DELAY_-
ROUND_CLOSEST__, before including this header file, the algorithm can be made to
round down, or round to closest integer, respectively.
Note
The implementation of _delay_ms() based on __builtin_avr_delay_cycles() is not
backward compatible with older implementations. In order to get functionality
backward compatible with previous versions, the macro "__DELAY_BACKWARD_-
COMPATIBLE__" must be defined before including this header file. Also, the back-
ward compatible algorithm will be chosen if the code is compiled in a freestanding
environment (GCC option -ffreestanding), as the math functions required for
rounding are not available to the compiler then.
23.30.3.2 void _delay_us (double __us)
Perform a delay of __us microseconds, using _delay_loop_1().
The macro F_CPU is supposed to be defined to a constant defining the CPU clock
frequency (in Hertz).
The maximal possible delay is 768 us / F_CPU in MHz.
If the user requests a delay greater than the maximal possible one, _delay_us() will
automatically call _delay_ms() instead. The user will not be informed about this case.
If the avr-gcc toolchain has __builtin_avr_delay_cycles() support, maximal possible
delay is 4294967.295 us/ F_CPU in MHz. For values greater than the maximal possible
delay, overflow results in no delay i.e., 0us.
Conversion of __us into clock cycles may not always result in integer. By default, the
clock cycles rounded up to next integer. This ensures that the user gets at least __us
microseconds of delay.
Alternatively, by defining the macro __DELAY_ROUND_DOWN__, or __DELAY_-
ROUND_CLOSEST__, before including this header file, the algorithm can be made to
round down, or round to closest integer, respectively.
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23.31 <util/delay_basic.h>: Basic busy-wait delay loops 313
Note
The implementation of _delay_ms() based on __builtin_avr_delay_cycles() is not
backward compatible with older implementations. In order to get functionality
backward compatible with previous versions, the macro __DELAY_BACKWARD_-
COMPATIBLE__ must be defined before including this header file. Also, the back-
ward compatible algorithm will be chosen if the code is compiled in a freestanding
environment (GCC option -ffreestanding), as the math functions required for
rounding are not available to the compiler then.
23.31 <util/delay_basic.h>: Basic busy-wait delay loops
Functions
• void _delay_loop_1 (uint8_t __count)
• void _delay_loop_2 (uint16_t __count)
23.31.1 Detailed Description
#include <util/delay_basic.h>
The functions in this header file implement simple delay loops that perform a busy-
waiting. They are typically used to facilitate short delays in the program execution.
They are implemented as count-down loops with a well-known CPU cycle count per
loop iteration. As such, no other processing can occur simultaneously. It should be
kept in mind that the functions described here do not disable interrupts.
In general, for long delays, the use of hardware timers is much preferrable, as they
free the CPU, and allow for concurrent processing of other events while the timer is
running. However, in particular for very short delays, the overhead of setting up a
hardware timer is too much compared to the overall delay time.
Two inline functions are provided for the actual delay algorithms.
23.31.2 Function Documentation
23.31.2.1 void _delay_loop_1 (uint8_t __count)
Delay loop using an 8-bit counter __count, so up to 256 iterations are possible.
(The value 256 would have to be passed as 0.) The loop executes three CPU cycles per
iteration, not including the overhead the compiler needs to setup the counter register.
Thus, at a CPU speed of 1 MHz, delays of up to 768 microseconds can be achieved.
23.31.2.2 void _delay_loop_2 (uint16_t __count)
Delay loop using a 16-bit counter __count, so up to 65536 iterations
are possible. (The value 65536 would have to be passed as 0.) The loop executes four
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23.32 <util/parity.h>: Parity bit generation 314
CPU cycles per iteration, not including the overhead the compiler requires to setup the
counter register pair.
Thus, at a CPU speed of 1 MHz, delays of up to about 262.1 milliseconds can be
achieved.
23.32 <util/parity.h>: Parity bit generation
Defines
• #define parity_even_bit(val)
23.32.1 Detailed Description
#include <util/parity.h>
This header file contains optimized assembler code to calculate the parity bit for a byte.
23.32.2 Define Documentation
23.32.2.1 #define parity_even_bit(val)
Value:
(__extension__({ \
unsigned char __t; \
__asm__ ( \
"mov __tmp_reg__,%0" "\n\t" \
"swap %0" "\n\t" \
"eor %0,__tmp_reg__" "\n\t" \
"mov __tmp_reg__,%0" "\n\t" \
"lsr %0" "\n\t" \
"lsr %0" "\n\t" \
"eor %0,__tmp_reg__" \
: "=r" (__t) \
: "0" ((unsigned char)(val)) \
: "r0" \
); \
(((__t + 1) >> 1) & 1); \
}))
Returns
1 if val has an odd number of bits set.
23.33 <util/setbaud.h>: Helper macros for baud rate calculations
Defines
• #define BAUD_TOL 2
• #define UBRR_VALUE
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23.33 <util/setbaud.h>: Helper macros for baud rate calculations 315
• #define UBRRL_VALUE
• #define UBRRH_VALUE
• #define USE_2X 0
23.33.1 Detailed Description
#define F_CPU 11059200
#define BAUD 38400
#include <util/setbaud.h>
This header file requires that on entry values are already defined for F_CPU and BAUD.
In addition, the macro BAUD_TOL will define the baud rate tolerance (in percent) that
is acceptable during the calculations. The value of BAUD_TOL will default to 2 %.
This header file defines macros suitable to setup the UART baud rate prescaler registers
of an AVR. All calculations are done using the C preprocessor. Including this header
file causes no other side effects so it is possible to include this file more than once
(supposedly, with different values for the BAUD parameter), possibly even within the
same function.
Assuming that the requested BAUD is valid for the given F_CPU then the macro
UBRR_VALUE is set to the required prescaler value. Two additional macros are pro-
vided for the low and high bytes of the prescaler, respectively: UBRRL_VALUE is set
to the lower byte of the UBRR_VALUE and UBRRH_VALUE is set to the upper byte.
An additional macro USE_2X will be defined. Its value is set to 1 if the desired BAUD
rate within the given tolerance could only be achieved by setting the U2X bit in the
UART configuration. It will be defined to 0 if U2X is not needed.
Example usage:
#include <avr/io.h>
#define F_CPU 4000000
static void
uart_9600(void)
{
#define BAUD 9600
#include <util/setbaud.h>
UBRRH = UBRRH_VALUE;
UBRRL = UBRRL_VALUE;
#if USE_2X
UCSRA |= (1 << U2X);
#else
UCSRA &= ~(1 << U2X);
#endif
}
static void
uart_38400(void)
{
#undef BAUD // avoid compiler warning
#define BAUD 38400
#include <util/setbaud.h>
UBRRH = UBRRH_VALUE;
UBRRL = UBRRL_VALUE;
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23.33 <util/setbaud.h>: Helper macros for baud rate calculations 316
#if USE_2X
UCSRA |= (1 << U2X);
#else
UCSRA &= ~(1 << U2X);
#endif
}
In this example, two functions are defined to setup the UART to run at 9600 Bd, and
38400 Bd, respectively. Using a CPU clock of 4 MHz, 9600 Bd can be achieved with
an acceptable tolerance without setting U2X (prescaler 25), while 38400 Bd require
U2X to be set (prescaler 12).
23.33.2 Define Documentation
23.33.2.1 #define BAUD_TOL 2
Input and output macro for <util/setbaud.h>
Define the acceptable baud rate tolerance in percent. If not set on entry, it will be set to
its default value of 2.
23.33.2.2 #define UBRR_VALUE
Output macro from <util/setbaud.h>
Contains the calculated baud rate prescaler value for the UBRR register.
23.33.2.3 #define UBRRH_VALUE
Output macro from <util/setbaud.h>
Contains the upper byte of the calculated prescaler value (UBRR_VALUE).
23.33.2.4 #define UBRRL_VALUE
Output macro from <util/setbaud.h>
Contains the lower byte of the calculated prescaler value (UBRR_VALUE).
23.33.2.5 #define USE_2X 0
Output macro from <util/setbaud.h>
Contains the value 1 if the desired baud rate tolerance could only be achieved by setting
the U2X bit in the UART configuration. Contains 0 otherwise.
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23.34 <util/twi.h>: TWI bit mask definitions 317
23.34 <util/twi.h>: TWI bit mask definitions
TWSR values
Mnemonics:
TW_MT_xxx - master transmitter
TW_MR_xxx - master receiver
TW_ST_xxx - slave transmitter
TW_SR_xxx - slave receiver
• #define TW_START 0x08
• #define TW_REP_START 0x10
• #define TW_MT_SLA_ACK 0x18
• #define TW_MT_SLA_NACK 0x20
• #define TW_MT_DATA_ACK 0x28
• #define TW_MT_DATA_NACK 0x30
• #define TW_MT_ARB_LOST 0x38
• #define TW_MR_ARB_LOST 0x38
• #define TW_MR_SLA_ACK 0x40
• #define TW_MR_SLA_NACK 0x48
• #define TW_MR_DATA_ACK 0x50
• #define TW_MR_DATA_NACK 0x58
• #define TW_ST_SLA_ACK 0xA8
• #define TW_ST_ARB_LOST_SLA_ACK 0xB0
• #define TW_ST_DATA_ACK 0xB8
• #define TW_ST_DATA_NACK 0xC0
• #define TW_ST_LAST_DATA 0xC8
• #define TW_SR_SLA_ACK 0x60
• #define TW_SR_ARB_LOST_SLA_ACK 0x68
• #define TW_SR_GCALL_ACK 0x70
• #define TW_SR_ARB_LOST_GCALL_ACK 0x78
• #define TW_SR_DATA_ACK 0x80
• #define TW_SR_DATA_NACK 0x88
• #define TW_SR_GCALL_DATA_ACK 0x90
• #define TW_SR_GCALL_DATA_NACK 0x98
• #define TW_SR_STOP 0xA0
• #define TW_NO_INFO 0xF8
• #define TW_BUS_ERROR 0x00
• #define TW_STATUS_MASK
• #define TW_STATUS (TWSR & TW_STATUS_MASK)
R/∼W bit in SLA+R/W address field.
• #define TW_READ 1
• #define TW_WRITE 0
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23.34 <util/twi.h>: TWI bit mask definitions 318
23.34.1 Detailed Description
#include <util/twi.h>
This header file contains bit mask definitions for use with the AVR TWI interface.
23.34.2 Define Documentation
23.34.2.1 #define TW_BUS_ERROR 0x00
illegal start or stop condition
23.34.2.2 #define TW_MR_ARB_LOST 0x38
arbitration lost in SLA+R or NACK
23.34.2.3 #define TW_MR_DATA_ACK 0x50
data received, ACK returned
23.34.2.4 #define TW_MR_DATA_NACK 0x58
data received, NACK returned
23.34.2.5 #define TW_MR_SLA_ACK 0x40
SLA+R transmitted, ACK received
23.34.2.6 #define TW_MR_SLA_NACK 0x48
SLA+R transmitted, NACK received
23.34.2.7 #define TW_MT_ARB_LOST 0x38
arbitration lost in SLA+W or data
23.34.2.8 #define TW_MT_DATA_ACK 0x28
data transmitted, ACK received
23.34.2.9 #define TW_MT_DATA_NACK 0x30
data transmitted, NACK received
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23.34 <util/twi.h>: TWI bit mask definitions 319
23.34.2.10 #define TW_MT_SLA_ACK 0x18
SLA+W transmitted, ACK received
23.34.2.11 #define TW_MT_SLA_NACK 0x20
SLA+W transmitted, NACK received
23.34.2.12 #define TW_NO_INFO 0xF8
no state information available
23.34.2.13 #define TW_READ 1
SLA+R address
23.34.2.14 #define TW_REP_START 0x10
repeated start condition transmitted
23.34.2.15 #define TW_SR_ARB_LOST_GCALL_ACK 0x78
arbitration lost in SLA+RW, general call received, ACK returned
23.34.2.16 #define TW_SR_ARB_LOST_SLA_ACK 0x68
arbitration lost in SLA+RW, SLA+W received, ACK returned
23.34.2.17 #define TW_SR_DATA_ACK 0x80
data received, ACK returned
23.34.2.18 #define TW_SR_DATA_NACK 0x88
data received, NACK returned
23.34.2.19 #define TW_SR_GCALL_ACK 0x70
general call received, ACK returned
23.34.2.20 #define TW_SR_GCALL_DATA_ACK 0x90
general call data received, ACK returned
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23.34 <util/twi.h>: TWI bit mask definitions 320
23.34.2.21 #define TW_SR_GCALL_DATA_NACK 0x98
general call data received, NACK returned
23.34.2.22 #define TW_SR_SLA_ACK 0x60
SLA+W received, ACK returned
23.34.2.23 #define TW_SR_STOP 0xA0
stop or repeated start condition received while selected
23.34.2.24 #define TW_ST_ARB_LOST_SLA_ACK 0xB0
arbitration lost in SLA+RW, SLA+R received, ACK returned
23.34.2.25 #define TW_ST_DATA_ACK 0xB8
data transmitted, ACK received
23.34.2.26 #define TW_ST_DATA_NACK 0xC0
data transmitted, NACK received
23.34.2.27 #define TW_ST_LAST_DATA 0xC8
last data byte transmitted, ACK received
23.34.2.28 #define TW_ST_SLA_ACK 0xA8
SLA+R received, ACK returned
23.34.2.29 #define TW_START 0x08
start condition transmitted
23.34.2.30 #define TW_STATUS (TWSR & TW_STATUS_MASK)
TWSR, masked by TW_STATUS_MASK
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23.35 <compat/deprecated.h>: Deprecated items 321
23.34.2.31 #define TW_STATUS_MASK
Value:
(_BV(TWS7)|_BV(TWS6)|_BV(TWS5)|_BV(TWS4)|\
_BV(TWS3))
The lower 3 bits of TWSR are reserved on the ATmega163. The 2 LSB carry the
prescaler bits on the newer ATmegas.
23.34.2.32 #define TW_WRITE 0
SLA+W address
23.35 <compat/deprecated.h>: Deprecated items
Allowing specific system-wide interrupts
In addition to globally enabling interrupts, each device’s particular interrupt needs to
be enabled separately if interrupts for this device are desired. While some devices
maintain their interrupt enable bit inside the device’s register set, external and timer
interrupts have system-wide configuration registers.
Example:
// Enable timer 1 overflow interrupts.
timer_enable_int(_BV(TOIE1));
// Do some work...
// Disable all timer interrupts.
timer_enable_int(0);
Note
Be careful when you use these functions. If you already have a different interrupt
enabled, you could inadvertantly disable it by enabling another intterupt.
• static __inline__ void timer_enable_int (unsigned char ints)
• #define enable_external_int(mask) (__EICR = mask)
• #define INTERRUPT(signame)
• #define __INTR_ATTRS used
Obsolete IO macros
Back in a time when AVR-GCC and avr-libc could not handle IO port access in the di-
rect assignment form as they are handled now, all IO port access had to be done through
specific macros that eventually resulted in inline assembly instructions performing the
desired action.
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23.35 <compat/deprecated.h>: Deprecated items 322
These macros became obsolete, as reading and writing IO ports can be done by simply
using the IO port name in an expression, and all bit manipulation (including those on
IO ports) can be done using generic C bit manipulation operators.
The macros in this group simulate the historical behaviour. While they are supposed to
be applied to IO ports, the emulation actually uses standard C methods, so they could
be applied to arbitrary memory locations as well.
• #define inp(port) (port)
• #define outp(val, port) (port) = (val)
• #define inb(port) (port)
• #define outb(port, val) (port) = (val)
• #define sbi(port, bit) (port) |= (1 << (bit))
• #define cbi(port, bit) (port) &= ∼(1 << (bit))
23.35.1 Detailed Description
This header file contains several items that used to be available in previous versions of
this library, but have eventually been deprecated over time.
#include <compat/deprecated.h>
These items are supplied within that header file for backward compatibility reasons
only, so old source code that has been written for previous library versions could easily
be maintained until its end-of-life. Use of any of these items in new code is strongly
discouraged.
23.35.2 Define Documentation
23.35.2.1 #define cbi(port, bit) (port) &= ∼(1 << (bit))
Deprecated
Clear bit in IO port port.
23.35.2.2 #define enable_external_int(mask) (__EICR = mask)
Deprecated
This macro gives access to the GIMSK register (or EIMSK register if using an AVR
Mega device or GICR register for others). Although this macro is essentially the same
as assigning to the register, it does adapt slightly to the type of device being used. This
macro is unavailable if none of the registers listed above are defined.
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23.35 <compat/deprecated.h>: Deprecated items 323
23.35.2.3 #define inb(port) (port)
Deprecated
Read a value from an IO port port.
23.35.2.4 #define inp(port) (port)
Deprecated
Read a value from an IO port port.
23.35.2.5 #define INTERRUPT(signame)
Value:
void signame (void) __attribute__ ((interrupt,__INTR_ATTRS)); \
void signame (void)
Deprecated
Introduces an interrupt handler function that runs with global interrupts initially en-
abled. This allows interrupt handlers to be interrupted.
As this macro has been used by too many unsuspecting people in the past, it has been
deprecated, and will be removed in a future version of the library. Users who want to
legitimately re-enable interrupts in their interrupt handlers as quickly as possible are
encouraged to explicitly declare their handlers as described above.
23.35.2.6 #define outb(port, val) (port) = (val)
Deprecated
Write val to IO port port.
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23.36 <compat/ina90.h>: Compatibility with IAR EWB 3.x 324
23.35.2.7 #define outp(val, port) (port) = (val)
Deprecated
Write val to IO port port.
23.35.2.8 #define sbi(port, bit) (port) |= (1 << (bit))
Deprecated
Set bit in IO port port.
23.35.3 Function Documentation
23.35.3.1 static __inline__ void timer_enable_int (unsigned char ints)
[static]
Deprecated
This function modifies the timsk register. The value you pass via ints is device
specific.
23.36 <compat/ina90.h>: Compatibility with IAR EWB 3.x
#include <compat/ina90.h>
This is an attempt to provide some compatibility with header files that come with IAR
C, to make porting applications between different compilers easier. No 100% compat-
ibility though.
Note
For actual documentation, please see the IAR manual.
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23.37 Demo projects 325
23.37 Demo projects
Modules
•Combining C and assembly source files
•A simple project
•A more sophisticated project
•Using the standard IO facilities
•Example using the two-wire interface (TWI)
23.37.1 Detailed Description
Various small demo projects are provided to illustrate several aspects of using the open-
source utilities for the AVR controller series. It should be kept in mind that these de-
mos serve mainly educational purposes, and are normally not directly suitable for use
in any production environment. Usually, they have been kept as simple as sufficient to
demonstrate one particular feature.
The simple project is somewhat like the "Hello world!" application for a microcon-
troller, about the most simple project that can be done. It is explained in good detail,
to allow the reader to understand the basic concepts behind using the tools on an AVR
microcontroller.
The more sophisticated demo project builds on top of that simple project, and adds
some controls to it. It touches a number of avr-libc’s basic concepts on its way.
Acomprehensive example on using the standard IO facilities intends to explain that
complex topic, using a practical microcontroller peripheral setup with one RS-232 con-
nection, and an HD44780-compatible industry-standard LCD display.
The Example using the two-wire interface (TWI) project explains the use of the two-
wire hardware interface (also known as "I2C") that is present on many AVR controllers.
Finally, the Combining C and assembly source files demo shows how C and assem-
bly language source files can collaborate within one project. While the overall project
is managed by a C program part for easy maintenance, time-critical parts are written
directly in manually optimized assembly language for shortest execution times possi-
ble. Naturally, this kind of project is very closely tied to the hardware design, thus it is
custom-tailored to a particular controller type and peripheral setup. As an alternative to
the assembly-language solution, this project also offers a C-only implementation (de-
ploying the exact same peripheral setup) based on a more sophisticated (and thus more
expensive) but pin-compatible controller.
While the simple demo is meant to run on about any AVR setup possible where a
LED could be connected to the OCR1[A] output, the large and stdio demos are mainly
targeted to the Atmel STK500 starter kit, and the TWI example requires a controller
where some 24Cxx two-wire EEPPROM can be connected to. For the STK500 demos,
the default CPU (either an AT90S8515 or an ATmega8515) should be removed from
its socket, and the ATmega16 that ships with the kit should be inserted into socket
SCKT3100A3. The ATmega16 offers an on-board ADC that is used in the large demo,
and all AVRs with an ADC feature a different pinout than the industry-standard com-
patible devices.
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23.38 Combining C and assembly source files 326
In order to fully utilize the large demo, a female 10-pin header with cable, connecting
to a 10 kOhm potentiometer will be useful.
For the stdio demo, an industry-standard HD44780-compatible LCD display of at least
16x1 characters will be needed. Among other things, the LCD4Linux project page
describes many things around these displays, including common pinouts.
23.38 Combining C and assembly source files
For time- or space-critical applications, it can often be desirable to combine C code
(for easy maintenance) and assembly code (for maximal speed or minimal code size)
together. This demo provides an example of how to do that.
The objective of the demo is to decode radio-controlled model PWM signals, and con-
trol an output PWM based on the current input signal’s value. The incoming PWM
pulses follow a standard encoding scheme where a pulse width of 920 microseconds
denotes one end of the scale (represented as 0 % pulse width on output), and 2120
microseconds mark the other end (100 % output PWM). Normally, multiple channels
would be encoded that way in subsequent pulses, followed by a larger gap, so the en-
tire frame will repeat each 14 through 20 ms, but this is ignored for the purpose of the
demo, so only a single input PWM channel is assumed.
The basic challenge is to use the cheapest controller available for the task, an ATtiny13
that has only a single timer channel. As this timer channel is required to run the out-
going PWM signal generation, the incoming PWM decoding had to be adjusted to the
constraints set by the outgoing PWM.
As PWM generation toggles the counting direction of timer 0 between up and down
after each 256 timer cycles, the current time cannot be deduced by reading TCNT0
only, but the current counting direction of the timer needs to be considered as well.
This requires servicing interrupts whenever the timer hits TOP (255) and BOTTOM (0)
to learn about each change of the counting direction. For PWM generation, it is usually
desired to run it at the highest possible speed so filtering the PWM frequency from the
modulated output signal is made easy. Thus, the PWM timer runs at full CPU speed.
This causes the overflow and compare match interrupts to be triggered each 256 CPU
clocks, so they must run with the minimal number of processor cycles possible in order
to not impose a too high CPU load by these interrupt service routines. This is the main
reason to implement the entire interrupt handling in fine-tuned assembly code rather
than in C.
In order to verify parts of the algorithm, and the underlying hardware, the demo has
been set up in a way so the pin-compatible but more expensive ATtiny45 (or its siblings
ATtiny25 and ATtiny85) could be used as well. In that case, no separate assembly code
is required, as two timer channels are avaible.
23.38.1 Hardware setup
The incoming PWM pulse train is fed into PB4. It will generate a pin change interrupt
there on eache edge of the incoming signal.
The outgoing PWM is generated through OC0B of timer channel 0 (PB1). For demon-
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23.38 Combining C and assembly source files 327
stration purposes, a LED should be connected to that pin (like, one of the LEDs of an
STK500).
The controllers run on their internal calibrated RC oscillators, 1.2 MHz on the AT-
tiny13, and 1.0 MHz on the ATtiny45.
23.38.2 A code walkthrough
23.38.2.1 asmdemo.c
After the usual include files, two variables are defined. The first one, pwm_incoming
is used to communicate the most recent pulse width detected by the incoming PWM
decoder up to the main loop.
The second variable actually only constitutes of a single bit, intbits.pwm_-
received. This bit will be set whenever the incoming PWM decoder has updated
pwm_incoming.
Both variables are marked volatile to ensure their readers will always pick up an up-
dated value, as both variables will be set by interrupt service routines.
The function ioinit() initializes the microcontroller peripheral devices. In partic-
ular, it starts timer 0 to generate the outgoing PWM signal on OC0B. Setting OCR0A
to 255 (which is the TOP value of timer 0) is used to generate a timer 0 overflow A
interrupt on the ATtiny13. This interrupt is used to inform the incoming PWM decoder
that the counting direction of channel 0 is just changing from up to down. Likewise, an
overflow interrupt will be generated whenever the countdown reached BOTTOM (value
0), where the counter will again alter its counting direction to upwards. This informa-
tion is needed in order to know whether the current counter value of TCNT0 is to be
evaluated from bottom or top.
Further, ioinit() activates the pin-change interrupt PCINT0 on any edge of PB4.
Finally, PB1 (OC0B) will be activated as an output pin, and global interrupts are being
enabled.
In the ATtiny45 setup, the C code contains an ISR for PCINT0. At each pin-change
interrupt, it will first be analyzed whether the interrupt was caused by a rising or a
falling edge. In case of the rising edge, timer 1 will be started with a prescaler of 16
after clearing the current timer value. Then, at the falling edge, the current timer value
will be recorded (and timer 1 stopped), the pin-change interrupt will be suspended, and
the upper layer will be notified that the incoming PWM measurement data is available.
Function main() first initializes the hardware by calling ioinit(), and then waits
until some incoming PWM value is available. If it is, the output PWM will be adjusted
by computing the relative value of the incoming PWM. Finally, the pin-change interrupt
is re-enabled, and the CPU is put to sleep.
23.38.2.2 project.h
In order for the interrupt service routines to be as fast as possible, some of the CPU
registers are set aside completely for use by these routines, so the compiler would not
use them for C code. This is arranged for in project.h.
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23.38 Combining C and assembly source files 328
The file is divided into one section that will be used by the assembly source code, and
another one to be used by C code. The assembly part is distinguished by the prepro-
cessing macro __ASSEMBLER__ (which will be automatically set by the compiler
front-end when preprocessing an assembly-language file), and it contains just macros
that give symbolic names to a number of CPU registers. The preprocessor will then
replace the symbolic names by their right-hand side definitions before calling the as-
sembler.
In C code, the compiler needs to see variable declarations for these objects. This is
done by using declarations that bind a variable permanently to a CPU register (see
How to permanently bind a variable to a register?). Even in case the C code never
has a need to access these variables, declaring the register binding that way causes the
compiler to not use these registers in C code at all.
The flags variable needs to be in the range of r16 through r31 as it is the target of a
load immediate (or SER) instruction that is not applicable to the entire register file.
23.38.2.3 isrs.S
This file is a preprocessed assembly source file. The C preprocessor will be run by
the compiler front-end first, resolving all #include,#define etc. directives. The
resulting program text will then be passed on to the assembler.
As the C preprocessor strips all C-style comments, preprocessed assembly source files
can have both, C-style (/∗... ∗/,// ...) as well as assembly-style (; ...)
comments.
At the top, the IO register definition file avr/io.h and the project declaration file
project.h are included. The remainder of the file is conditionally assembled only if
the target MCU type is an ATtiny13, so it will be completely ignored for the ATtiny45
option.
Next are the two interrupt service routines for timer 0 compare A match (timer 0 hits
TOP, as OCR0A is set to 255) and timer 0 overflow (timer 0 hits BOTTOM). As dis-
cussed above, these are kept as short as possible. They only save SREG (as the flags
will be modified by the INC instruction), increment the counter_hi variable which
forms the high part of the current time counter (the low part is formed by querying
TCNT0 directly), and clear or set the variable flags, respectively, in order to note
the current counting direction. The RETI instruction terminates these interrupt service
routines. Total cycle count is 8 CPU cycles, so together with the 4 CPU cycles needed
for interrupt setup, and the 2 cycles for the RJMP from the interrupt vector to the han-
dler, these routines will require 14 out of each 256 CPU cycles, or about 5 % of the
overall CPU time.
The pin-change interrupt PCINT0 will be handled in the final part of this file. The
basic algorithm is to quickly evaluate the current system time by fetching the current
timer value of TCNT0, and combining it with the overflow part in counter_hi. If
the counter is currently counting down rather than up, the value fetched from TCNT0
must be negated. Finally, if this pin-change interrupt was triggered by a rising edge,
the time computed will be recorded as the start time only. Then, at the falling edge,
this start time will be subracted from the current time to compute the actual pulse width
seen (left in pwm_incoming), and the upper layers are informed of the new value by
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23.39 A simple project 329
setting bit 0 in the intbits flags. At the same time, this pin-change interrupt will be
disabled so no new measurement can be performed until the upper layer had a chance
to process the current value.
23.38.3 The source code
The source code is installed under
$prefix/share/doc/avr-libc/examples/asmdemo/,
where $prefix is a configuration option. For Unix systems, it is usually set to either
/usr or /usr/local.
23.39 A simple project
At this point, you should have the GNU tools configured, built, and installed on your
system. In this chapter, we present a simple example of using the GNU tools in an AVR
project. After reading this chapter, you should have a better feel as to how the tools are
used and how a Makefile can be configured.
23.39.1 The Project
This project will use the pulse-width modulator (PWM) to ramp an LED on and off every
two seconds. An AT90S2313 processor will be used as the controller. The circuit for
this demonstration is shown in the schematic diagram. If you have a development kit,
you should be able to use it, rather than build the circuit, for this project.
Note
Meanwhile, the AT90S2313 became obsolete. Either use its successor, the (pin-
compatible) ATtiny2313 for the project, or perhaps the ATmega8 or one of its
successors (ATmega48/88/168) which have become quite popular since the origi-
nal demo project had been established. For all these more modern devices, it is no
longer necessary to use an external crystal for clocking as they ship with the inter-
nal 1 MHz oscillator enabled, so C1, C2, and Q1 can be omitted. Normally, for
this experiment, the external circuitry on /RESET (R1, C3) can be omitted as well,
leaving only the AVR, the LED, the bypass capacitor C4, and perhaps R2. For the
ATmega8/48/88/168, use PB1 (pin 15 at the DIP-28 package) to connect the LED
to. Additionally, this demo has been ported to many different other AVRs. The lo-
cation of the respective OC pin varies between different AVRs, and it is mandated
by the AVR hardware.
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23.39 A simple project 330
IC1
1
10
20
5
4
19
18
17
16
15
14
13
12
11
9
8
7
6
3
2
AT90S2313P
(RXD)PD0
(TXD)PD1
(INT0)PD2
(INT1)PD3
(T0)PD4
(T1)PD5
(ICP)PD6
(AIN0)PB0
(AIN1)PB1
PB2
(OCI)PB3
PB4
(MISO)PB6
(SCK)PB7
RESET
XTAL2
XTAL1
VCC
GND
(MOSI)PB5
Q1
4mhz
GND
GND
.1uf
C4
VCC
R1
20K
.01uf
C3
18pf
C2
18pf
C1 *
See note [8]
R2 LED5MM
D1
GND
Figure 5: Schematic of circuit for demo project
The source code is given in demo.c. For the sake of this example, create a file called
demo.c containing this source code. Some of the more important parts of the code
are:
Note [1]:
As the AVR microcontroller series has been developed during the past years, new
features have been added over time. Even though the basic concepts of the timer/-
counter1 are still the same as they used to be back in early 2001 when this sim-
ple demo was written initially, the names of registers and bits have been changed
slightly to reflect the new features. Also, the port and pin mapping of the output
compare match 1A (or 1 for older devices) pin which is used to control the LED
varies between different AVRs. The file iocompat.h tries to abstract between
all this differences using some preprocessor #ifdef statements, so the actual pro-
gram itself can operate on a common set of symbolic names. The macros defined
by that file are:
•OCR the name of the OCR register used to control the PWM (usually either
OCR1 or OCR1A)
•DDROC the name of the DDR (data direction register) for the OC output
•OC1 the pin number of the OC1[A] output within its port
•TIMER1_TOP the TOP value of the timer used for the PWM (1023 for 10-bit
PWMs, 255 for devices that can only handle an 8-bit PWM)
•TIMER1_PWM_INIT the initialization bits to be set into control register 1A in
order to setup 10-bit (or 8-bit) phase and frequency correct PWM mode
•TIMER1_CLOCKSOURCE the clock bits to set in the respective control regis-
ter to start the PWM timer; usually the timer runs at full CPU clock for 10-bit
PWMs, while it runs on a prescaled clock for 8-bit PWMs
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23.39 A simple project 331
Note [2]:
ISR() is a macro that marks the function as an interrupt routine. In this case, the
function will get called when timer 1 overflows. Setting up interrupts is explained
in greater detail in <avr/interrupt.h>: Interrupts.
Note [3]:
The PWM is being used in 10-bit mode, so we need a 16-bit variable to remember
the current value.
Note [4]:
This section determines the new value of the PWM.
Note [5]:
Here’s where the newly computed value is loaded into the PWM register. Since
we are in an interrupt routine, it is safe to use a 16-bit assignment to the register.
Outside of an interrupt, the assignment should only be performed with interrupts
disabled if there’s a chance that an interrupt routine could also access this register
(or another register that uses TEMP), see the appropriate FAQ entry.
Note [6]:
This routine gets called after a reset. It initializes the PWM and enables interrupts.
Note [7]:
The main loop of the program does nothing -- all the work is done by the interrupt
routine! The sleep_mode() puts the processor on sleep until the next interrupt,
to conserve power. Of course, that probably won’t be noticable as we are still
driving a LED, it is merely mentioned here to demonstrate the basic principle.
Note [8]:
Early AVR devices saturate their outputs at rather low currents when sourcing cur-
rent, so the LED can be connected directly, the resulting current through the LED
will be about 15 mA. For modern parts (at least for the ATmega 128), however
Atmel has drastically increased the IO source capability, so when operating at 5
V Vcc, R2 is needed. Its value should be about 150 Ohms. When operating the
circuit at 3 V, it can still be omitted though.
23.39.2 The Source Code
/*
*----------------------------------------------------------------------------
*"THE BEER-WARE LICENSE" (Revision 42):
*<joerg@FreeBSD.ORG> wrote this file. As long as you retain this notice you
*can do whatever you want with this stuff. If we meet some day, and you think
*this stuff is worth it, you can buy me a beer in return. Joerg Wunsch
*----------------------------------------------------------------------------
*
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23.39 A simple project 332
*Simple AVR demonstration. Controls a LED that can be directly
*connected from OC1/OC1A to GND. The brightness of the LED is
*controlled with the PWM. After each period of the PWM, the PWM
*value is either incremented or decremented, that’s all.
*
*$Id$
*/
#include <inttypes.h>
#include <avr/io.h>
#include <avr/interrupt.h>
#include <avr/sleep.h>
#include "iocompat.h" /*Note [1] */
enum { UP, DOWN };
ISR (TIMER1_OVF_vect) /*Note [2] */
{
static uint16_t pwm; /*Note [3] */
static uint8_t direction;
switch (direction) /*Note [4] */
{
case UP:
if (++pwm == TIMER1_TOP)
direction = DOWN;
break;
case DOWN:
if (--pwm == 0)
direction = UP;
break;
}
OCR = pwm; /*Note [5] */
}
void
ioinit (void) /*Note [6] */
{
/*Timer 1 is 10-bit PWM (8-bit PWM on some ATtinys). */
TCCR1A = TIMER1_PWM_INIT;
/*
*Start timer 1.
*
*NB: TCCR1A and TCCR1B could actually be the same register, so
*take care to not clobber it.
*/
TCCR1B |= TIMER1_CLOCKSOURCE;
/*
*Run any device-dependent timer 1 setup hook if present.
*/
#if defined(TIMER1_SETUP_HOOK)
TIMER1_SETUP_HOOK();
#endif
/*Set PWM value to 0. */
OCR = 0;
/*Enable OC1 as output. */
DDROC = _BV (OC1);
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23.39 A simple project 333
/*Enable timer 1 overflow interrupt. */
TIMSK = _BV (TOIE1);
sei ();
}
int
main (void)
{
ioinit ();
/*loop forever, the interrupts are doing the rest */
for (;;) /*Note [7] */
sleep_mode();
return (0);
}
23.39.3 Compiling and Linking
This first thing that needs to be done is compile the source. When compiling, the
compiler needs to know the processor type so the -mmcu option is specified. The
-Os option will tell the compiler to optimize the code for efficient space usage (at the
possible expense of code execution speed). The -g is used to embed debug info. The
debug info is useful for disassemblies and doesn’t end up in the .hex files, so I usually
specify it. Finally, the -c tells the compiler to compile and stop -- don’t link. This
demo is small enough that we could compile and link in one step. However, real-world
projects will have several modules and will typically need to break up the building of
the project into several compiles and one link.
$ avr-gcc -g -Os -mmcu=atmega8 -c demo.c
The compilation will create a demo.o file. Next we link it into a binary called
demo.elf.
$ avr-gcc -g -mmcu=atmega8 -o demo.elf demo.o
It is important to specify the MCU type when linking. The compiler uses the -mmcu
option to choose start-up files and run-time libraries that get linked together. If this
option isn’t specified, the compiler defaults to the 8515 processor environment, which
is most certainly what you didn’t want.
23.39.4 Examining the Object File
Now we have a binary file. Can we do anything useful with it (besides put it into the
processor?) The GNU Binutils suite is made up of many useful tools for manipulating
object files that get generated. One tool is avr-objdump, which takes information
from the object file and displays it in many useful ways. Typing the command by itself
will cause it to list out its options.
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23.39 A simple project 334
For instance, to get a feel of the application’s size, the -h option can be used. The
output of this option shows how much space is used in each of the sections (the .stab
and .stabstr sections hold the debugging information and won’t make it into the ROM
file).
An even more useful option is -S. This option disassembles the binary file and inter-
sperses the source code in the output! This method is much better, in my opinion, than
using the -S with the compiler because this listing includes routines from the libraries
and the vector table contents. Also, all the "fix-ups" have been satisfied. In other words,
the listing generated by this option reflects the actual code that the processor will run.
$ avr-objdump -h -S demo.elf > demo.lst
Here’s the output as saved in the demo.lst file:
demo.elf: file format elf32-avr
Sections:
Idx Name Size VMA LMA File off Algn
0 .text 000000d0 00000000 00000000 00000094 2**1
CONTENTS, ALLOC, LOAD, READONLY, CODE
1 .data 00000000 00800060 000000d0 00000164 2**0
CONTENTS, ALLOC, LOAD, DATA
2 .bss 00000003 00800060 00800060 00000164 2**0
ALLOC
3 .comment 0000002c 00000000 00000000 00000164 2**0
CONTENTS, READONLY
4 .debug_aranges 00000068 00000000 00000000 00000190 2**3
CONTENTS, READONLY, DEBUGGING
5 .debug_info 000002ce 00000000 00000000 000001f8 2**0
CONTENTS, READONLY, DEBUGGING
6 .debug_abbrev 00000107 00000000 00000000 000004c6 2**0
CONTENTS, READONLY, DEBUGGING
7 .debug_line 0000024a 00000000 00000000 000005cd 2**0
CONTENTS, READONLY, DEBUGGING
8 .debug_frame 00000060 00000000 00000000 00000818 2**2
CONTENTS, READONLY, DEBUGGING
9 .debug_str 000000f8 00000000 00000000 00000878 2**0
CONTENTS, READONLY, DEBUGGING
10 .debug_loc 00000056 00000000 00000000 00000970 2**0
CONTENTS, READONLY, DEBUGGING
11 .debug_ranges 00000018 00000000 00000000 000009c6 2**0
CONTENTS, READONLY, DEBUGGING
Disassembly of section .text:
00000000 <__ctors_end>:
/*__do_clear_bss is only necessary if there is anything in .bss section. */
#ifdef L_clear_bss
.section .init4,"ax",@progbits
DEFUN __do_clear_bss
ldi r18, hi8(__bss_end)
0: 20 e0 ldi r18, 0x00 ; 0
ldi r26, lo8(__bss_start)
2: a0 e6 ldi r26, 0x60 ; 96
ldi r27, hi8(__bss_start)
4: b0 e0 ldi r27, 0x00 ; 0
rjmp .do_clear_bss_start
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23.39 A simple project 335
6: 01 c0 rjmp .+2 ; 0xa <.do_clear_bss_start>
00000008 <.do_clear_bss_loop>:
.do_clear_bss_loop:
st X+, __zero_reg__
8: 1d 92 st X+, r1
0000000a <.do_clear_bss_start>:
.do_clear_bss_start:
cpi r26, lo8(__bss_end)
a: a3 36 cpi r26, 0x63 ; 99
cpc r27, r18
c: b2 07 cpc r27, r18
brne .do_clear_bss_loop
e: e1 f7 brne .-8 ; 0x8 <.do_clear_bss_loop>
00000010 <__vector_8>:
#include "iocompat.h" /*Note [1] */
enum { UP, DOWN };
ISR (TIMER1_OVF_vect) /*Note [2] */
{
10: 1f 92 push r1
12: 0f 92 push r0
14: 0f b6 in r0, 0x3f ; 63
16: 0f 92 push r0
18: 11 24 eor r1, r1
1a: 2f 93 push r18
1c: 8f 93 push r24
1e: 9f 93 push r25
static uint16_t pwm; /*Note [3] */
static uint8_t direction;
switch (direction) /*Note [4] */
20: 80 91 62 00 lds r24, 0x0062 ; 0x800062 <direction.1609>
24: 88 23 and r24, r24
26: f1 f0 breq .+60 ; 0x64 <__SREG__+0x25>
28: 81 30 cpi r24, 0x01 ; 1
2a: 71 f4 brne .+28 ; 0x48 <__SREG__+0x9>
if (++pwm == TIMER1_TOP)
direction = DOWN;
break;
case DOWN:
if (--pwm == 0)
2c: 80 91 60 00 lds r24, 0x0060 ; 0x800060 <_edata>
30: 90 91 61 00 lds r25, 0x0061 ; 0x800061 <_edata+0x1>
34: 01 97 sbiw r24, 0x01 ; 1
36: 90 93 61 00 sts 0x0061, r25 ; 0x800061 <_edata+0x1>
3a: 80 93 60 00 sts 0x0060, r24 ; 0x800060 <_edata>
3e: 00 97 sbiw r24, 0x00 ; 0
40: 39 f4 brne .+14 ; 0x50 <__SREG__+0x11>
direction = UP;
42: 10 92 62 00 sts 0x0062, r1 ; 0x800062 <direction.1609>
46: 04 c0 rjmp .+8 ; 0x50 <__SREG__+0x11>
48: 80 91 60 00 lds r24, 0x0060 ; 0x800060 <_edata>
4c: 90 91 61 00 lds r25, 0x0061 ; 0x800061 <_edata+0x1>
break;
}
OCR = pwm; /*Note [5] */
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23.39 A simple project 336
50: 9b bd out 0x2b, r25 ; 43
52: 8a bd out 0x2a, r24 ; 42
}
54: 9f 91 pop r25
56: 8f 91 pop r24
58: 2f 91 pop r18
5a: 0f 90 pop r0
5c: 0f be out 0x3f, r0 ; 63
5e: 0f 90 pop r0
60: 1f 90 pop r1
62: 18 95 reti
static uint8_t direction;
switch (direction) /*Note [4] */
{
case UP:
if (++pwm == TIMER1_TOP)
64: 80 91 60 00 lds r24, 0x0060 ; 0x800060 <_edata>
68: 90 91 61 00 lds r25, 0x0061 ; 0x800061 <_edata+0x1>
6c: 01 96 adiw r24, 0x01 ; 1
6e: 90 93 61 00 sts 0x0061, r25 ; 0x800061 <_edata+0x1>
72: 80 93 60 00 sts 0x0060, r24 ; 0x800060 <_edata>
76: 8f 3f cpi r24, 0xFF ; 255
78: 23 e0 ldi r18, 0x03 ; 3
7a: 92 07 cpc r25, r18
7c: 49 f7 brne .-46 ; 0x50 <__SREG__+0x11>
direction = DOWN;
7e: 21 e0 ldi r18, 0x01 ; 1
80: 20 93 62 00 sts 0x0062, r18 ; 0x800062 <direction.1609>
84: e5 cf rjmp .-54 ; 0x50 <__SREG__+0x11>
00000086 <ioinit>:
void
ioinit (void) /*Note [6] */
{
/*Timer 1 is 10-bit PWM (8-bit PWM on some ATtinys). */
TCCR1A = TIMER1_PWM_INIT;
86: 83 e8 ldi r24, 0x83 ; 131
88: 8f bd out 0x2f, r24 ; 47
*Start timer 1.
*
*NB: TCCR1A and TCCR1B could actually be the same register, so
*take care to not clobber it.
*/
TCCR1B |= TIMER1_CLOCKSOURCE;
8a: 8e b5 in r24, 0x2e ; 46
8c: 81 60 ori r24, 0x01 ; 1
8e: 8e bd out 0x2e, r24 ; 46
#if defined(TIMER1_SETUP_HOOK)
TIMER1_SETUP_HOOK();
#endif
/*Set PWM value to 0. */
OCR = 0;
90: 1b bc out 0x2b, r1 ; 43
92: 1a bc out 0x2a, r1 ; 42
/*Enable OC1 as output. */
DDROC = _BV (OC1);
94: 82 e0 ldi r24, 0x02 ; 2
96: 87 bb out 0x17, r24 ; 23
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23.39 A simple project 337
/*Enable timer 1 overflow interrupt. */
TIMSK = _BV (TOIE1);
98: 84 e0 ldi r24, 0x04 ; 4
9a: 89 bf out 0x39, r24 ; 57
sei ();
9c: 78 94 sei
9e: 08 95 ret
000000a0 <main>:
void
ioinit (void) /*Note [6] */
{
/*Timer 1 is 10-bit PWM (8-bit PWM on some ATtinys). */
TCCR1A = TIMER1_PWM_INIT;
a0: 83 e8 ldi r24, 0x83 ; 131
a2: 8f bd out 0x2f, r24 ; 47
*Start timer 1.
*
*NB: TCCR1A and TCCR1B could actually be the same register, so
*take care to not clobber it.
*/
TCCR1B |= TIMER1_CLOCKSOURCE;
a4: 8e b5 in r24, 0x2e ; 46
a6: 81 60 ori r24, 0x01 ; 1
a8: 8e bd out 0x2e, r24 ; 46
#if defined(TIMER1_SETUP_HOOK)
TIMER1_SETUP_HOOK();
#endif
/*Set PWM value to 0. */
OCR = 0;
aa: 1b bc out 0x2b, r1 ; 43
ac: 1a bc out 0x2a, r1 ; 42
/*Enable OC1 as output. */
DDROC = _BV (OC1);
ae: 82 e0 ldi r24, 0x02 ; 2
b0: 87 bb out 0x17, r24 ; 23
/*Enable timer 1 overflow interrupt. */
TIMSK = _BV (TOIE1);
b2: 84 e0 ldi r24, 0x04 ; 4
b4: 89 bf out 0x39, r24 ; 57
sei ();
b6: 78 94 sei
ioinit ();
/*loop forever, the interrupts are doing the rest */
for (;;) /*Note [7] */
sleep_mode();
b8: 85 b7 in r24, 0x35 ; 53
ba: 80 68 ori r24, 0x80 ; 128
bc: 85 bf out 0x35, r24 ; 53
be: 88 95 sleep
c0: 85 b7 in r24, 0x35 ; 53
c2: 8f 77 andi r24, 0x7F ; 127
c4: 85 bf out 0x35, r24 ; 53
c6: f8 cf rjmp .-16 ; 0xb8 <main+0x18>
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23.39 A simple project 338
000000c8 <exit>:
c8: f8 94 cli
ca: 00 c0 rjmp .+0 ; 0xcc <_exit>
000000cc <_exit>:
ENDF _exit
/*Code from .fini8 ... .fini1 sections inserted by ld script. */
.section .fini0,"ax",@progbits
cli
cc: f8 94 cli
000000ce <__stop_program>:
__stop_program:
rjmp __stop_program
ce: ff cf rjmp .-2 ; 0xce <__stop_program>
23.39.5 Linker Map Files
avr-objdump is very useful, but sometimes it’s necessary to see information about
the link that can only be generated by the linker. A map file contains this information.
A map file is useful for monitoring the sizes of your code and data. It also shows where
modules are loaded and which modules were loaded from libraries. It is yet another
view of your application. To get a map file, I usually add -Wl,-Map,demo.map to
my link command. Relink the application using the following command to generate
demo.map (a portion of which is shown below).
$ avr-gcc -g -mmcu=atmega8 -Wl,-Map,demo.map -o demo.elf demo.o
Some points of interest in the demo.map file are:
.rela.plt
*(.rela.plt)
.text 0x0000000000000000 0xd0
*(.vectors)
*(.vectors)
*(.progmem.gcc*)
0x0000000000000000 . = ALIGN (0x2)
0x0000000000000000 __trampolines_start = .
*(.trampolines)
.trampolines 0x0000000000000000 0x0 linker stubs
*(.trampolines*)
0x0000000000000000 __trampolines_end = .
*libprintf_flt.a:*(.progmem.data)
*libc.a:*(.progmem.data)
*(.progmem*)
0x0000000000000000 . = ALIGN (0x2)
*(.jumptables)
*(.jumptables*)
*(.lowtext)
*(.lowtext*)
0x0000000000000000 __ctors_start = .
The .text segment (where program instructions are stored) starts at location 0x0.
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23.39 A simple project 339
*(.fini2)
*(.fini2)
*(.fini1)
*(.fini1)
*(.fini0)
.fini0 0x00000000000000cc 0x4 /home/toolsbuild/workspace/avr8-gnu
-toolchain/avr8-gnu-toolchain-linux_x86_64/lib/gcc/avr/5.4.0/avr4/libgcc.a(_exit.
o)
*(.fini0)
0x00000000000000d0 _etext = .
.data 0x0000000000800060 0x0 load address 0x00000000000000d0
[!provide] PROVIDE (__data_start, .)
*(.data)
.data 0x0000000000800060 0x0 demo.o
.data 0x0000000000800060 0x0 /home/toolsbuild/workspace/avr8-gnu
-toolchain/src/avr-libc/avr/lib/avr4/exit.o
.data 0x0000000000800060 0x0 /home/toolsbuild/workspace/avr8-gnu
-toolchain/avr8-gnu-toolchain-linux_x86_64/lib/gcc/avr/5.4.0/avr4/libgcc.a(_exit.
o)
.data 0x0000000000800060 0x0 /home/toolsbuild/workspace/avr8-gnu
-toolchain/avr8-gnu-toolchain-linux_x86_64/lib/gcc/avr/5.4.0/avr4/libgcc.a(_clear
_bss.o)
*(.data*)
*(.gnu.linkonce.d*)
*(.rodata)
*(.rodata*)
*(.gnu.linkonce.r*)
0x0000000000800060 . = ALIGN (0x2)
0x0000000000800060 _edata = .
[!provide] PROVIDE (__data_end, .)
.bss 0x0000000000800060 0x3
0x0000000000800060 PROVIDE (__bss_start, .)
*(.bss)
.bss 0x0000000000800060 0x3 demo.o
.bss 0x0000000000800063 0x0 /home/toolsbuild/workspace/avr8-gnu
-toolchain/src/avr-libc/avr/lib/avr4/exit.o
.bss 0x0000000000800063 0x0 /home/toolsbuild/workspace/avr8-gnu
-toolchain/avr8-gnu-toolchain-linux_x86_64/lib/gcc/avr/5.4.0/avr4/libgcc.a(_exit.
o)
.bss 0x0000000000800063 0x0 /home/toolsbuild/workspace/avr8-gnu
-toolchain/avr8-gnu-toolchain-linux_x86_64/lib/gcc/avr/5.4.0/avr4/libgcc.a(_clear
_bss.o)
*(.bss*)
*(COMMON)
0x0000000000800063 PROVIDE (__bss_end, .)
0x00000000000000d0 __data_load_start = LOADADDR (.
data)
0x00000000000000d0 __data_load_end = (__data_load_
start + SIZEOF (.data))
.noinit 0x0000000000800063 0x0
[!provide] PROVIDE (__noinit_start, .)
*(.noinit*)
[!provide] PROVIDE (__noinit_end, .)
0x0000000000800063 _end = .
[!provide] PROVIDE (__heap_start, .)
.eeprom 0x0000000000810000 0x0
*(.eeprom*)
0x0000000000810000 __eeprom_end = .
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23.39 A simple project 340
The last address in the .text segment is location 0x114 ( denoted by _etext ), so the
instructions use up 276 bytes of FLASH.
The .data segment (where initialized static variables are stored) starts at location 0x60,
which is the first address after the register bank on an ATmega8 processor.
The next available address in the .data segment is also location 0x60, so the application
has no initialized data.
The .bss segment (where uninitialized data is stored) starts at location 0x60.
The next available address in the .bss segment is location 0x63, so the application uses
3 bytes of uninitialized data.
The .eeprom segment (where EEPROM variables are stored) starts at location 0x0.
The next available address in the .eeprom segment is also location 0x0, so there aren’t
any EEPROM variables.
23.39.6 Generating Intel Hex Files
We have a binary of the application, but how do we get it into the processor? Most (if
not all) programmers will not accept a GNU executable as an input file, so we need to
do a little more processing. The next step is to extract portions of the binary and save
the information into .hex files. The GNU utility that does this is called avr-objcopy.
The ROM contents can be pulled from our project’s binary and put into the file
demo.hex using the following command:
$ avr-objcopy -j .text -j .data -O ihex demo.elf demo.hex
The resulting demo.hex file contains:
:1000000020E0A0E6B0E001C01D92A336B207E1F700
:100010001F920F920FB60F9211242F938F939F93DD
:10002000809162008823F1F0813071F4809160004A
:100030009091610001979093610080936000009718
:1000400039F41092620004C08091600090916100C8
:100050009BBD8ABD9F918F912F910F900FBE0F90E6
:100060001F90189580916000909161000196909387
:100070006100809360008F3F23E0920749F721E001
:1000800020936200E5CF83E88FBD8EB581608EBD81
:100090001BBC1ABC82E087BB84E089BF78940895BA
:1000A00083E88FBD8EB581608EBD1BBC1ABC82E01B
:1000B00087BB84E089BF789485B7806885BF8895C1
:1000C00085B78F7785BFF8CFF89400C0F894FFCF3D
:00000001FF
The -j option indicates that we want the information from the .text and .data segment
extracted. If we specify the EEPROM segment, we can generate a .hex file that can be
used to program the EEPROM:
$ avr-objcopy -j .eeprom --change-section-lma .eeprom=0 -O ihex demo.elf demo_eeprom.hex
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23.39 A simple project 341
There is no demo_eeprom.hex file written, as that file would be empty.
Starting with version 2.17 of the GNU binutils, the avr-objcopy command that used
to generate the empty EEPROM files now aborts because of the empty input section
.eeprom, so these empty files are not generated. It also signals an error to the Makefile
which will be caught there, and makes it print a message about the empty file not being
generated.
23.39.7 Letting Make Build the Project
Rather than type these commands over and over, they can all be placed in a make file.
To build the demo project using make, save the following in a file called Makefile.
Note
This Makefile can only be used as input for the GNU version of make.
PRG = demo
OBJ = demo.o
#MCU_TARGET = at90s2313
#MCU_TARGET = at90s2333
#MCU_TARGET = at90s4414
#MCU_TARGET = at90s4433
#MCU_TARGET = at90s4434
#MCU_TARGET = at90s8515
#MCU_TARGET = at90s8535
#MCU_TARGET = atmega128
#MCU_TARGET = atmega1280
#MCU_TARGET = atmega1281
#MCU_TARGET = atmega1284p
#MCU_TARGET = atmega16
#MCU_TARGET = atmega163
#MCU_TARGET = atmega164p
#MCU_TARGET = atmega165
#MCU_TARGET = atmega165p
#MCU_TARGET = atmega168
#MCU_TARGET = atmega169
#MCU_TARGET = atmega169p
#MCU_TARGET = atmega2560
#MCU_TARGET = atmega2561
#MCU_TARGET = atmega32
#MCU_TARGET = atmega324p
#MCU_TARGET = atmega325
#MCU_TARGET = atmega3250
#MCU_TARGET = atmega329
#MCU_TARGET = atmega3290
#MCU_TARGET = atmega32u4
#MCU_TARGET = atmega48
#MCU_TARGET = atmega64
#MCU_TARGET = atmega640
#MCU_TARGET = atmega644
#MCU_TARGET = atmega644p
#MCU_TARGET = atmega645
#MCU_TARGET = atmega6450
#MCU_TARGET = atmega649
#MCU_TARGET = atmega6490
MCU_TARGET = atmega8
#MCU_TARGET = atmega8515
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23.39 A simple project 342
#MCU_TARGET = atmega8535
#MCU_TARGET = atmega88
#MCU_TARGET = attiny2313
#MCU_TARGET = attiny24
#MCU_TARGET = attiny25
#MCU_TARGET = attiny26
#MCU_TARGET = attiny261
#MCU_TARGET = attiny44
#MCU_TARGET = attiny45
#MCU_TARGET = attiny461
#MCU_TARGET = attiny84
#MCU_TARGET = attiny85
#MCU_TARGET = attiny861
OPTIMIZE = -O2
DEFS =
LIBS =
# You should not have to change anything below here.
CC = avr-gcc
# Override is only needed by avr-lib build system.
override CFLAGS = -g -Wall $(OPTIMIZE) -mmcu=$(MCU_TARGET) $(DEFS)
override LDFLAGS = -Wl,-Map,$(PRG).map
OBJCOPY = avr-objcopy
OBJDUMP = avr-objdump
all: $(PRG).elf lst text eeprom
$(PRG).elf: $(OBJ)
$(CC) $(CFLAGS) $(LDFLAGS) -o $@ $^ $(LIBS)
# dependency:
demo.o: demo.c iocompat.h
clean:
rm -rf *.o $(PRG).elf *.eps *.png *.pdf *.bak
rm -rf *.lst *.map $(EXTRA_CLEAN_FILES)
lst: $(PRG).lst
%.lst: %.elf
$(OBJDUMP) -h -S $< > $@
# Rules for building the .text rom images
text: hex bin srec
hex: $(PRG).hex
bin: $(PRG).bin
srec: $(PRG).srec
%.hex: %.elf
$(OBJCOPY) -j .text -j .data -O ihex $< $@
%.srec: %.elf
$(OBJCOPY) -j .text -j .data -O srec $< $@
%.bin: %.elf
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23.40 A more sophisticated project 343
$(OBJCOPY) -j .text -j .data -O binary $< $@
# Rules for building the .eeprom rom images
eeprom: ehex ebin esrec
ehex: $(PRG)_eeprom.hex
ebin: $(PRG)_eeprom.bin
esrec: $(PRG)_eeprom.srec
%_eeprom.hex: %.elf
$(OBJCOPY) -j .eeprom --change-section-lma .eeprom=0 -O ihex $< $@ \
|| { echo empty $@ not generated; exit 0; }
%_eeprom.srec: %.elf
$(OBJCOPY) -j .eeprom --change-section-lma .eeprom=0 -O srec $< $@ \
|| { echo empty $@ not generated; exit 0; }
%_eeprom.bin: %.elf
$(OBJCOPY) -j .eeprom --change-section-lma .eeprom=0 -O binary $< $@ \
|| { echo empty $@ not generated; exit 0; }
# Every thing below here is used by avr-libc’s build system and can be ignored
# by the casual user.
FIG2DEV = fig2dev
EXTRA_CLEAN_FILES = *.hex *.bin *.srec
dox: eps png pdf
eps: $(PRG).eps
png: $(PRG).png
pdf: $(PRG).pdf
%.eps: %.fig
$(FIG2DEV) -L eps $< $@
%.pdf: %.fig
$(FIG2DEV) -L pdf $< $@
%.png: %.fig
$(FIG2DEV) -L png $< $@
23.39.8 Reference to the source code
The source code is installed under
$prefix/share/doc/avr-libc/examples/demo/,
where $prefix is a configuration option. For Unix systems, it is usually set to either
/usr or /usr/local.
23.40 A more sophisticated project
This project extends the basic idea of the simple project to control a LED with a PWM
output, but adds methods to adjust the LED brightness. It employs a lot of the basic
concepts of avr-libc to achieve that goal.
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23.40 A more sophisticated project 344
Understanding this project assumes the simple project has been understood in full, as
well as being acquainted with the basic hardware concepts of an AVR microcontroller.
23.40.1 Hardware setup
The demo is set up in a way so it can be run on the ATmega16 that ships with the
STK500 development kit. The only external part needed is a potentiometer attached to
the ADC. It is connected to a 10-pin ribbon cable for port A, both ends of the poten-
tiometer to pins 9 (GND) and 10 (VCC), and the wiper to pin 1 (port A0). A bypass
capacitor from pin 1 to pin 9 (like 47 nF) is recommendable.
Figure 6: Setup of the STK500
The coloured patch cables are used to provide various interconnections. As there are
only four of them in the STK500, there are two options to connect them for this demo.
The second option for the yellow-green cable is shown in parenthesis in the table.
Alternatively, the "squid" cable from the JTAG ICE kit can be used if available.
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23.40 A more sophisticated project 345
Port Header Color Function Connect to
D0 1 brown RxD RXD of the
RS-232
header
D1 2 grey TxD TXD of the
RS-232
header
D2 3 black button
"down"
SW0 (pin 1
switches
header)
D3 4 red button "up" SW1 (pin 2
switches
header)
D4 5 green button
"ADC"
SW2 (pin 3
switches
header)
D5 6 blue LED LED0 (pin 1
LEDs header)
D6 7 (green) clock out LED1 (pin 2
LEDs header)
D7 8 white 1-second
flash
LED2 (pin 3
LEDs header)
GND 9 unused
VCC 10 unused
Figure 7: Wiring of the STK500
The following picture shows the alternate wiring where LED1 is connected but SW2 is
not:
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23.40 A more sophisticated project 346
Figure 8: Wiring option #2 of the STK500
As an alternative, this demo can also be run on the popular ATmega8 controller, or its
successor ATmega88 as well as the ATmega48 and ATmega168 variants of the latter.
These controllers do not have a port named "A", so their ADC inputs are located on
port C instead, thus the potentiometer needs to be attached to port C. Likewise, the
OC1A output is not on port D pin 5 but on port B pin 1 (PB1). Thus, the above
cabling scheme needs to be changed so that PB1 connects to the LED0 pin. (PD6
remains unconnected.) When using the STK500, use one of the jumper cables for this
connection. All other port D pins should be connected the same way as described for
the ATmega16 above.
When not using an STK500 starter kit, attach the LEDs through some resistor to Vcc
(low-active LEDs), and attach pushbuttons from the respective input pins to GND. The
internal pull-up resistors are enabled for the pushbutton pins, so no external resistors
are needed.
Finally, the demo has been ported to the ATtiny2313 as well. As this AVR does not
offer an ADC, everything related to handling the ADC is disabled in the code for that
MCU type. Also, port D of this controller type only features 6 pins, so the 1-second
flash LED had to be moved from PD6 to PD4. (PD4 is used as the ADC control button
on the other MCU types, but that is not needed here.) OC1A is located at PB3 on this
device.
The MCU_TARGET macro in the Makefile needs to be adjusted appropriately for the
alternative controller types.
The flash ROM and RAM consumption of this demo are way below the resources
of even an ATmega48, and still well within the capabilities of an ATtiny2313. The
major advantage of experimenting with the ATmega16 (in addition that it ships together
with an STK500 anyway) is that it can be debugged online via JTAG. Likewise, the
ATmega48/88/168 and ATtiny2313 devices can be debugged through debugWire, using
the Atmel JTAG ICE mkII or the low-cost AVR Dragon.
Note that in the explanation below, all port/pin names are applicable to the ATmega16
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23.40 A more sophisticated project 347
setup.
23.40.2 Functional overview
PD6 will be toggled with each internal clock tick (approx. 10 ms). PD7 will flash once
per second.
PD0 and PD1 are configured as UART IO, and can be used to connect the demo kit to
a PC (9600 Bd, 8N1 frame format). The demo application talks to the serial port, and
it can be controlled from the serial port.
PD2 through PD4 are configured as inputs, and control the application unless control
has been taken over by the serial port. Shorting PD2 to GND will decrease the current
PWM value, shorting PD3 to GND will increase it.
While PD4 is shorted to GND, one ADC conversion for channel 0 (ADC input is on
PA0) will be triggered each internal clock tick, and the resulting value will be used as
the PWM value. So the brightness of the LED follows the analog input value on PC0.
VAREF on the STK500 should be set to the same value as VCC.
When running in serial control mode, the function of the watchdog timer can be demon-
strated by typing an ‘r’. This will make the demo application run in a tight loop without
retriggering the watchdog so after some seconds, the watchdog will reset the MCU.
This situation can be figured out on startup by reading the MCUCSR register.
The current value of the PWM is backed up in an EEPROM cell after about 3 seconds
of idle time after the last change. If that EEPROM cell contains a reasonable (i. e.
non-erased) value at startup, it is taken as the initial value for the PWM. This virtually
preserves the last value across power cycles. By not updating the EEPROM immme-
diately but only after a timeout, EEPROM wear is reduced considerably compared to
immediately writing the value at each change.
23.40.3 A code walkthrough
This section explains the ideas behind individual parts of the code. The source code
has been divided into numbered parts, and the following subsections explain each of
these parts.
23.40.3.1 Part 1: Macro definitions
A number of preprocessor macros are defined to improve readability and/or portability
of the application.
The first macros describe the IO pins our LEDs and pushbuttons are connected to. This
provides some kind of mini-HAL (hardware abstraction layer) so should some of the
connections be changed, they don’t need to be changed inside the code but only on
top. Note that the location of the PWM output itself is mandated by the hardware, so it
cannot be easily changed. As the ATmega48/88/168 controllers belong to a more recent
generation of AVRs, a number of register and bit names have been changed there, so
they are mapped back to their ATmega8/16 equivalents to keep the actual program code
portable.
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23.40 A more sophisticated project 348
The name F_CPU is the conventional name to describe the CPU clock frequency of
the controller. This demo project just uses the internal calibrated 1 MHz RC oscillator
that is enabled by default. Note that when using the <util/delay.h>functions,
F_CPU needs to be defined before including that file.
The remaining macros have their own comments in the source code. The macro
TMR1_SCALE shows how to use the preprocessor and the compiler’s constant expres-
sion computation to calculate the value of timer 1’s post-scaler in a way so it only
depends on F_CPU and the desired software clock frequency. While the formula looks
a bit complicated, using a macro offers the advantage that the application will auto-
matically scale to new target softclock or master CPU frequencies without having to
manually re-calculate hardcoded constants.
23.40.3.2 Part 2: Variable definitions
The intflags structure demonstrates a way to allocate bit variables in memory. Each
of the interrupt service routines just sets one bit within that structure, and the applica-
tion’s main loop then monitors the bits in order to act appropriately.
Like all variables that are used to communicate values between an interrupt service
routine and the main application, it is declared volatile.
The variable ee_pwm is not a variable in the classical C sense that could be used as an
lvalue or within an expression to obtain its value. Instead, the
__attribute__((section(".eeprom")))
marks it as belonging to the EEPROM section. This section is merely used as a place-
holder so the compiler can arrange for each individual variable’s location in EEPROM.
The compiler will also keep track of initial values assigned, and usually the Makefile
is arranged to extract these initial values into a separate load file (largedemo_-
eeprom.∗in this case) that can be used to initialize the EEPROM.
The actual EEPROM IO must be performed manually.
Similarly, the variable mcucsr is kept in the .noinit section in order to prevent it from
being cleared upon application startup.
23.40.3.3 Part 3: Interrupt service routines
The ISR to handle timer 1’s overflow interrupt arranges for the software clock. While
timer 1 runs the PWM, it calls its overflow handler rather frequently, so the TMR1_-
SCALE value is used as a postscaler to reduce the internal software clock frequency
further. If the software clock triggers, it sets the tmr_int bitfield, and defers all
further tasks to the main loop.
The ADC ISR just fetches the value from the ADC conversion, disables the ADC
interrupt again, and announces the presence of the new value in the adc_int bitfield.
The interrupt is kept disabled while not needed, because the ADC will also be triggered
by executing the SLEEP instruction in idle mode (which is the default sleep mode).
Another option would be to turn off the ADC completely here, but that increases the
ADC’s startup time (not that it would matter much for this application).
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23.40 A more sophisticated project 349
23.40.3.4 Part 4: Auxiliary functions
The function handle_mcucsr() uses two __attribute__ declarators to
achieve specific goals. First, it will instruct the compiler to place the generated code
into the .init3 section of the output. Thus, it will become part of the application ini-
tialization sequence. This is done in order to fetch (and clear) the reason of the last
hardware reset from MCUCSR as early as possible. There is a short period of time
where the next reset could already trigger before the current reason has been evaluated.
This also explains why the variable mcucsr that mirrors the register’s value needs to
be placed into the .noinit section, because otherwise the default initialization (which
happens after .init3) would blank the value again.
As the initialization code is not called using CALL/RET instructions but rather con-
catenated together, the compiler needs to be instructed to omit the entire function pro-
logue and epilogue. This is performed by the naked attribute. So while syntactically,
handle_mcucsr() is a function to the compiler, the compiler will just emit the in-
structions for it without setting up any stack frame, and not even a RET instruction at
the end.
Function ioinit() centralizes all hardware setup. The very last part of that function
demonstrates the use of the EEPROM variable ee_pwm to obtain an EEPROM address
that can in turn be applied as an argument to eeprom_read_word().
The following functions handle UART character and string output. (UART input
is handled by an ISR.) There are two string output functions, printstr() and
printstr_p(). The latter function fetches the string from program memory. Both
functions translate a newline character into a carriage return/newline sequence, so a
simple \ncan be used in the source code.
The function set_pwm() propagates the new PWM value to the PWM, performing
range checking. When the value has been changed, the new percentage will be an-
nounced on the serial link. The current value is mirrored in the variable pwm so others
can use it in calculations. In order to allow for a simple calculation of a percentage
value without requiring floating-point mathematics, the maximal value of the PWM is
restricted to 1000 rather than 1023, so a simple division by 10 can be used. Due to the
nature of the human eye, the difference in LED brightness between 1000 and 1023 is
not noticable anyway.
23.40.3.5 Part 5: main()
At the start of main(), a variable mode is declared to keep the current mode of
operation. An enumeration is used to improve the readability. By default, the compiler
would allocate a variable of type int for an enumeration. The packed attribute declarator
instructs the compiler to use the smallest possible integer type (which would be an 8-bit
type here).
After some initialization actions, the application’s main loop follows. In an embedded
application, this is normally an infinite loop as there is nothing an application could
"exit" into anyway.
At the beginning of the loop, the watchdog timer will be retriggered. If that timer is
not triggered for about 2 seconds, it will issue a hardware reset. Care needs to be taken
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23.41 Using the standard IO facilities 350
that no code path blocks longer than this, or it needs to frequently perform watchdog
resets of its own. An example of such a code path would be the string IO functions: for
an overly large string to print (about 2000 characters at 9600 Bd), they might block for
too long.
The loop itself then acts on the interrupt indication bitfields as appropriate, and will
eventually put the CPU on sleep at its end to conserve power.
The first interrupt bit that is handled is the (software) timer, at a frequency of approx-
imately 100 Hz. The CLOCKOUT pin will be toggled here, so e. g. an oscilloscope
can be used on that pin to measure the accuracy of our software clock. Then, the LED
flasher for LED2 ("We are alive"-LED) is built. It will flash that LED for about 50
ms, and pause it for another 950 ms. Various actions depending on the operation mode
follow. Finally, the 3-second backup timer is implemented that will write the PWM
value back to EEPROM once it is not changing anymore.
The ADC interrupt will just adjust the PWM value only.
Finally, the UART Rx interrupt will dispatch on the last character received from the
UART.
All the string literals that are used as informational messages within main() are
placed in program memory so no SRAM needs to be allocated for them. This is done
by using the PSTR macro, and passing the string to printstr_p().
23.40.4 The source code
The source code is installed under
$prefix/share/doc/avr-libc/examples/largedemo/largedemo.c,
where $prefix is a configuration option. For Unix systems, it is usually set to either
/usr or /usr/local.
23.41 Using the standard IO facilities
This project illustrates how to use the standard IO facilities (stdio) provided by this
library. It assumes a basic knowledge of how the stdio subsystem is used in standard C
applications, and concentrates on the differences in this library’s implementation that
mainly result from the differences of the microcontroller environment, compared to a
hosted environment of a standard computer.
This demo is meant to supplement the documentation, not to replace it.
23.41.1 Hardware setup
The demo is set up in a way so it can be run on the ATmega16 that ships with the
STK500 development kit. The UART port needs to be connected to the RS-232 "spare"
port by a jumper cable that connects PD0 to RxD and PD1 to TxD. The RS-232 channel
is set up as standard input (stdin) and standard output (stdout), respectively.
In order to have a different device available for a standard error channel (stderr), an
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23.41 Using the standard IO facilities 351
industry-standard LCD display with an HD44780-compatible LCD controller has been
chosen. This display needs to be connected to port A of the STK500 in the following
way:
Port Header Function
A0 1 LCD D4
A1 2 LCD D5
A2 3 LCD D6
A3 4 LCD D7
A4 5 LCD R/∼W
A5 6 LCD E
A6 7 LCD RS
A7 8 unused
GND 9 GND
VCC 10 Vcc
Figure 9: Wiring of the STK500
The LCD controller is used in 4-bit mode, including polling the "busy" flag so the
R/∼W line from the LCD controller needs to be connected. Note that the LCD con-
troller has yet another supply pin that is used to adjust the LCD’s contrast (V5). Typ-
ically, that pin connects to a potentiometer between Vcc and GND. Often, it might
work to just connect that pin to GND, while leaving it unconnected usually yields an
unreadable display.
Port A has been chosen as 7 pins are needed to connect the LCD, yet all other ports are
already partially in use: port B has the pins for in-system programming (ISP), port C
has the ports for JTAG (can be used for debugging), and port D is used for the UART
connection.
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23.41 Using the standard IO facilities 352
23.41.2 Functional overview
The project consists of the following files:
•stdiodemo.c This is the main example file.
•defines.h Contains some global defines, like the LCD wiring
•hd44780.c Implementation of an HD44780 LCD display driver
•hd44780.h Interface declarations for the HD44780 driver
•lcd.c Implementation of LCD character IO on top of the HD44780 driver
•lcd.h Interface declarations for the LCD driver
•uart.c Implementation of a character IO driver for the internal UART
•uart.h Interface declarations for the UART driver
23.41.3 A code walkthrough
23.41.3.1 stdiodemo.c
As usual, include files go first. While conventionally, system header files (those in
angular brackets <... >) go before application-specific header files (in double quotes),
defines.h comes as the first header file here. The main reason is that this file defines
the value of F_CPU which needs to be known before including <utils/delay.h>.
The function ioinit() summarizes all hardware initialization tasks. As this function
is declared to be module-internal only (static), the compiler will notice its simplic-
ity, and with a reasonable optimization level in effect, it will inline that function. That
needs to be kept in mind when debugging, because the inlining might cause the debug-
ger to "jump around wildly" at a first glance when single-stepping.
The definitions of uart_str and lcd_str set up two stdio streams. The initial-
ization is done using the FDEV_SETUP_STREAM() initializer template macro, so a
static object can be constructed that can be used for IO purposes. This initializer macro
takes three arguments, two function macros to connect the corresponding output and
input functions, respectively, the third one describes the intent of the stream (read,
write, or both). Those functions that are not required by the specified intent (like the
input function for lcd_str which is specified to only perform output operations) can
be given as NULL.
The stream uart_str corresponds to input and output operations performed over the
RS-232 connection to a terminal (e.g. from/to a PC running a terminal program), while
the lcd_str stream provides a method to display character data on the LCD text
display.
The function delay_1s() suspends program execution for approximately one sec-
ond. This is done using the _delay_ms() function from <util/delay.h>
which in turn needs the F_CPU macro in order to adjust the cycle counts. As the
_delay_ms() function has a limited range of allowable argument values (depending
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23.41 Using the standard IO facilities 353
on F_CPU), a value of 10 ms has been chosen as the base delay which would be safe
for CPU frequencies of up to about 26 MHz. This function is then called 100 times to
accomodate for the actual one-second delay.
In a practical application, long delays like this one were better be handled by a hardware
timer, so the main CPU would be free for other tasks while waiting, or could be put on
sleep.
At the beginning of main(), after initializing the peripheral devices, the default stdio
streams stdin,stdout, and stderr are set up by using the existing static FILE
stream objects. While this is not mandatory, the availability of stdin and stdout
allows to use the shorthand functions (e.g. printf() instead of fprintf()), and
stderr can mnemonically be referred to when sending out diagnostic messages.
Just for demonstration purposes, stdin and stdout are connected to a stream that
will perform UART IO, while stderr is arranged to output its data to the LCD text
display.
Finally, a main loop follows that accepts simple "commands" entered via the RS-232
connection, and performs a few simple actions based on the commands.
First, a prompt is sent out using printf_P() (which takes a program space string).
The string is read into an internal buffer as one line of input, using fgets(). While it
would be also possible to use gets() (which implicitly reads from stdin), gets()
has no control that the user’s input does not overflow the input buffer provided so it
should never be used at all.
If fgets() fails to read anything, the main loop is left. Of course, normally the main
loop of a microcontroller application is supposed to never finish, but again, for demon-
strational purposes, this explains the error handling of stdio. fgets() will return
NULL in case of an input error or end-of-file condition on input. Both these condi-
tions are in the domain of the function that is used to establish the stream, uart_-
putchar() in this case. In short, this function returns EOF in case of a serial line
"break" condition (extended start condition) has been recognized on the serial line.
Common PC terminal programs allow to assert this condition as some kind of out-of-
band signalling on an RS-232 connection.
When leaving the main loop, a goodbye message is sent to standard error output (i.e. to
the LCD), followed by three dots in one-second spacing, followed by a sequence that
will clear the LCD. Finally, main() will be terminated, and the library will add an
infinite loop, so only a CPU reset will be able to restart the application.
There are three "commands" recognized, each determined by the first letter of the line
entered (converted to lower case):
• The ’q’ (quit) command has the same effect of leaving the main loop.
• The ’l’ (LCD) command takes its second argument, and sends it to the LCD.
• The ’u’ (UART) command takes its second argument, and sends it back to the
UART connection.
Command recognition is done using sscanf() where the first format in the format
string just skips over the command itself (as the assignment suppression modifier ∗is
given).
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23.41 Using the standard IO facilities 354
23.41.3.2 defines.h
This file just contains a few peripheral definitions.
The F_CPU macro defines the CPU clock frequency, to be used in delay loops, as well
as in the UART baud rate calculation.
The macro UART_BAUD defines the RS-232 baud rate. Depending on the actual CPU
frequency, only a limited range of baud rates can be supported.
The remaining macros customize the IO port and pins used for the HD44780 LCD
driver. Each definition consists of a letter naming the port this pin is attached to, and a
respective bit number. For accessing the data lines, only the first data line gets its own
macro (line D4 on the HD44780, lines D0 through D3 are not used in 4-bit mode), all
other data lines are expected to be in ascending order next to D4.
23.41.3.3 hd44780.h
This file describes the public interface of the low-level LCD driver that interfaces to
the HD44780 LCD controller. Public functions are available to initialize the controller
into 4-bit mode, to wait for the controller’s busy bit to be clear, and to read or write one
byte from or to the controller.
As there are two different forms of controller IO, one to send a command or receive
the controller status (RS signal clear), and one to send or receive data to/from the
controller’s SRAM (RS asserted), macros are provided that build on the mentioned
function primitives.
Finally, macros are provided for all the controller commands to allow them to be used
symbolically. The HD44780 datasheet explains these basic functions of the controller
in more detail.
23.41.3.4 hd44780.c
This is the implementation of the low-level HD44780 LCD controller driver.
On top, a few preprocessor glueing tricks are used to establish symbolic access to
the hardware port pins the LCD controller is attached to, based on the application’s
definitions made in defines.h.
The hd44780_pulse_e() function asserts a short pulse to the controller’s E (en-
able) pin. Since reading back the data asserted by the LCD controller needs to be
performed while E is active, this function reads and returns the input data if the param-
eter readback is true. When called with a compile-time constant parameter that is
false, the compiler will completely eliminate the unused readback operation, as well as
the return value as part of its optimizations.
As the controller is used in 4-bit interface mode, all byte IO to/from the controller
needs to be handled as two nibble IOs. The functions hd44780_outnibble() and
hd44780_innibble() implement this. They do not belong to the public interface,
so they are declared static.
Building upon these, the public functions hd44780_outbyte() and hd44780_-
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23.41 Using the standard IO facilities 355
inbyte() transfer one byte to/from the controller.
The function hd44780_wait_ready() waits for the controller to become ready,
by continuously polling the controller’s status (which is read by performing a byte read
with the RS signal cleard), and examining the BUSY flag within the status byte. This
function needs to be called before performing any controller IO.
Finally, hd44780_init() initializes the LCD controller into 4-bit mode, based on
the initialization sequence mandated by the datasheet. As the BUSY flag cannot be
examined yet at this point, this is the only part of this code where timed delays are
used. While the controller can perform a power-on reset when certain constraints on
the power supply rise time are met, always calling the software initialization routine
at startup ensures the controller will be in a known state. This function also puts the
interface into 4-bit mode (which would not be done automatically after a power-on
reset).
23.41.3.5 lcd.h
This function declares the public interface of the higher-level (character IO) LCD
driver.
23.41.3.6 lcd.c
The implementation of the higher-level LCD driver. This driver builds on top of the
HD44780 low-level LCD controller driver, and offers a character IO interface suitable
for direct use by the standard IO facilities. Where the low-level HD44780 driver deals
with setting up controller SRAM addresses, writing data to the controller’s SRAM,
and controlling display functions like clearing the display, or moving the cursor, this
high-level driver allows to just write a character to the LCD, in the assumption this will
somehow show up on the display.
Control characters can be handled at this level, and used to perform specific actions
on the LCD. Currently, there is only one control character that is being dealt with: a
newline character (\n) is taken as an indication to clear the display and set the cursor
into its initial position upon reception of the next character, so a "new line" of text
can be displayed. Therefore, a received newline character is remembered until more
characters have been sent by the application, and will only then cause the display to be
cleared before continuing. This provides a convenient abstraction where full lines of
text can be sent to the driver, and will remain visible at the LCD until the next line is
to be displayed.
Further control characters could be implemented, e. g. using a set of escape sequences.
That way, it would be possible to implement self-scrolling display lines etc.
The public function lcd_init() first calls the initialization entry point of the lower-
level HD44780 driver, and then sets up the LCD in a way we’d like to (display cleared,
non-blinking cursor enabled, SRAM addresses are increasing so characters will be
written left to right).
The public function lcd_putchar() takes arguments that make it suitable for be-
ing passed as a put() function pointer to the stdio stream initialization functions and
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23.41 Using the standard IO facilities 356
macros (fdevopen(),FDEV_SETUP_STREAM() etc.). Thus, it takes two argu-
ments, the character to display itself, and a reference to the underlying stream object,
and it is expected to return 0 upon success.
This function remembers the last unprocessed newline character seen in the function-
local static variable nl_seen. If a newline character is encountered, it will simply set
this variable to a true value, and return to the caller. As soon as the first non-newline
character is to be displayed with nl_seen still true, the LCD controller is told to clear
the display, put the cursor home, and restart at SRAM address 0. All other characters
are sent to the display.
The single static function-internal variable nl_seen works for this purpose. If mul-
tiple LCDs should be controlled using the same set of driver functions, that would not
work anymore, as a way is needed to distinguish between the various displays. This is
where the second parameter can be used, the reference to the stream itself: instead of
keeping the state inside a private variable of the function, it can be kept inside a private
object that is attached to the stream itself. A reference to that private object can be at-
tached to the stream (e.g. inside the function lcd_init() that then also needs to be
passed a reference to the stream) using fdev_set_udata(), and can be accessed
inside lcd_putchar() using fdev_get_udata().
23.41.3.7 uart.h
Public interface definition for the RS-232 UART driver, much like in lcd.h except there
is now also a character input function available.
As the RS-232 input is line-buffered in this example, the macro RX_BUFSIZE deter-
mines the size of that buffer.
23.41.3.8 uart.c
This implements an stdio-compatible RS-232 driver using an AVR’s standard UART
(or USART in asynchronous operation mode). Both, character output as well as char-
acter input operations are implemented. Character output takes care of converting the
internal newline \ninto its external representation carriage return/line feed (\r\n).
Character input is organized as a line-buffered operation that allows to minimally edit
the current line until it is "sent" to the application when either a carriage return (\r)
or newline (\n) character is received from the terminal. The line editing functions
implemented are:
•\b(back space) or \177 (delete) deletes the previous character
•∧u (control-U, ASCII NAK) deletes the entire input buffer
•∧w (control-W, ASCII ETB) deletes the previous input word, delimited by white
space
•∧r (control-R, ASCII DC2) sends a \r, then reprints the buffer (refresh)
•\t(tabulator) will be replaced by a single space
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23.42 Example using the two-wire interface (TWI) 357
The function uart_init() takes care of all hardware initialization that is required to
put the UART into a mode with 8 data bits, no parity, one stop bit (commonly referred
to as 8N1) at the baud rate configured in defines.h. At low CPU clock frequencies, the
U2X bit in the UART is set, reducing the oversampling from 16x to 8x, which allows
for a 9600 Bd rate to be achieved with tolerable error using the default 1 MHz RC
oscillator.
The public function uart_putchar() again has suitable arguments for direct use
by the stdio stream interface. It performs the \ninto \r\ntranslation by recursively
calling itself when it sees a \ncharacter. Just for demonstration purposes, the \a
(audible bell, ASCII BEL) character is implemented by sending a string to stderr,
so it will be displayed on the LCD.
The public function uart_getchar() implements the line editor. If there are char-
acters available in the line buffer (variable rxp is not NULL), the next character will
be returned from the buffer without any UART interaction.
If there are no characters inside the line buffer, the input loop will be entered. Charac-
ters will be read from the UART, and processed accordingly. If the UART signalled a
framing error (FE bit set), typically caused by the terminal sending a line break con-
dition (start condition held much longer than one character period), the function will
return an end-of-file condition using _FDEV_EOF. If there was a data overrun condi-
tion on input (DOR bit set), an error condition will be returned as _FDEV_ERR.
Line editing characters are handled inside the loop, potentially modifying the buffer
status. If characters are attempted to be entered beyond the size of the line buffer, their
reception is refused, and a \acharacter is sent to the terminal. If a \ror \ncharacter is
seen, the variable rxp (receive pointer) is set to the beginning of the buffer, the loop is
left, and the first character of the buffer will be returned to the application. (If no other
characters have been entered, this will just be the newline character, and the buffer is
marked as being exhausted immediately again.)
23.41.4 The source code
The source code is installed under
$prefix/share/doc/avr-libc/examples/stdiodemo/,
where $prefix is a configuration option. For Unix systems, it is usually set to either
/usr or /usr/local.
23.42 Example using the two-wire interface (TWI)
Some newer devices of the ATmega series contain builtin support for interfacing the
microcontroller to a two-wire bus, called TWI. This is essentially the same called I2C
by Philips, but that term is avoided in Atmel’s documentation due to patenting issues.
For further documentation, see:
http://www.nxp.com/documents/user_manual/UM10204.pdf
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23.42 Example using the two-wire interface (TWI) 358
23.42.1 Introduction into TWI
The two-wire interface consists of two signal lines named SDA (serial data) and SCL
(serial clock) (plus a ground line, of course). All devices participating in the bus are
connected together, using open-drain driver circuitry, so the wires must be terminated
using appropriate pullup resistors. The pullups must be small enough to recharge
the line capacity in short enough time compared to the desired maximal clock fre-
quency, yet large enough so all drivers will not be overloaded. There are formulas in
the datasheet that help selecting the pullups.
Devices can either act as a master to the bus (i. e., they initiate a transfer), or as a
slave (they only act when being called by a master). The bus is multi-master capable,
and a particular device implementation can act as either master or slave at different
times. Devices are addressed using a 7-bit address (coordinated by Philips) transfered
as the first byte after the so-called start condition. The LSB of that byte is R/∼W, i. e.
it determines whether the request to the slave is to read or write data during the next
cycles. (There is also an option to have devices using 10-bit addresses but that is not
covered by this example.)
23.42.2 The TWI example project
The ATmega TWI hardware supports both, master and slave operation. This example
will only demonstrate how to use an AVR microcontroller as TWI master. The imple-
mentation is kept simple in order to concentrate on the steps that are required to talk to
a TWI slave, so all processing is done in polled-mode, waiting for the TWI interface to
indicate that the next processing step is due (by setting the TWINT interrupt bit). If it
is desired to have the entire TWI communication happen in "background", all this can
be implemented in an interrupt-controlled way, where only the start condition needs to
be triggered from outside the interrupt routine.
There is a variety of slave devices available that can be connected to a TWI bus. For the
purpose of this example, an EEPROM device out of the industry-standard 24Cxx series
has been chosen (where xx can be one of 01,02,04,08, or 16) which are available from
various vendors. The choice was almost arbitrary, mainly triggered by the fact that an
EEPROM device is being talked to in both directions, reading and writing the slave
device, so the example will demonstrate the details of both.
Usually, there is probably not much need to add more EEPROM to an ATmega system
that way: the smallest possible AVR device that offers hardware TWI support is the
ATmega8 which comes with 512 bytes of EEPROM, which is equivalent to an 24C04
device. The ATmega128 already comes with twice as much EEPROM as the 24C16
would offer. One exception might be to use an externally connected EEPROM device
that is removable; e. g. SDRAM PC memory comes with an integrated TWI EEPROM
that carries the RAM configuration information.
23.42.3 The Source Code
The source code is installed under
$prefix/share/doc/avr-libc/examples/twitest/twitest.c,
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23.42 Example using the two-wire interface (TWI) 359
where $prefix is a configuration option. For Unix systems, it is usually set to either
/usr or /usr/local.
Note [1]
The header file <util/twi.h>contains some macro definitions for symbolic con-
stants used in the TWI status register. These definitions match the names used in the
Atmel datasheet except that all names have been prefixed with TW_.
Note [2]
The clock is used in timer calculations done by the compiler, for the UART baud rate
and the TWI clock rate.
Note [3]
The address assigned for the 24Cxx EEPROM consists of 1010 in the upper four bits.
The following three bits are normally available as slave sub-addresses, allowing to
operate more than one device of the same type on a single bus, where the actual sub-
address used for each device is configured by hardware strapping. However, since the
next data packet following the device selection only allows for 8 bits that are used as
an EEPROM address, devices that require more than 8 address bits (24C04 and above)
"steal" subaddress bits and use them for the EEPROM cell address bits 9 to 11 as re-
quired. This example simply assumes all subaddress bits are 0 for the smaller devices,
so the E0, E1, and E2 inputs of the 24Cxx must be grounded.
Note [3a]
EEPROMs of type 24C32 and above cannot be addressed anymore even with the sub-
address bit trick. Thus, they require the upper address bits being sent separately on the
bus. When activating the WORD_ADDRESS_16BIT define, the algorithm implements
that auxiliary address byte transmission.
Note [4]
For slow clocks, enable the 2 x U[S]ART clock multiplier, to improve the baud rate
error. This will allow a 9600 Bd communication using the standard 1 MHz calibrated
RC oscillator. See also the Baud rate tables in the datasheets.
Note [5]
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23.42 Example using the two-wire interface (TWI) 360
The datasheet explains why a minimum TWBR value of 10 should be maintained when
running in master mode. Thus, for system clocks below 3.6 MHz, we cannot run the
bus at the intented clock rate of 100 kHz but have to slow down accordingly.
Note [6]
This function is used by the standard output facilities that are utilized in this example
for debugging and demonstration purposes.
Note [7]
In order to shorten the data to be sent over the TWI bus, the 24Cxx EEPROMs support
multiple data bytes transfered within a single request, maintaining an internal address
counter that is updated after each data byte transfered successfully. When reading
data, one request can read the entire device memory if desired (the counter would wrap
around and start back from 0 when reaching the end of the device).
Note [8]
When reading the EEPROM, a first device selection must be made with write intent
(R/∼W bit set to 0 indicating a write operation) in order to transfer the EEPROM ad-
dress to start reading from. This is called master transmitter mode. Each completion
of a particular step in TWI communication is indicated by an asserted TWINT bit in
TWCR. (An interrupt would be generated if allowed.) After performing any actions
that are needed for the next communication step, the interrupt condition must be man-
ually cleared by setting the TWINT bit. Unlike with many other interrupt sources, this
would even be required when using a true interrupt routine, since as soon as TWINT is
re-asserted, the next bus transaction will start.
Note [9]
Since the TWI bus is multi-master capable, there is potential for a bus contention when
one master starts to access the bus. Normally, the TWI bus interface unit will detect this
situation, and will not initiate a start condition while the bus is busy. However, in case
two masters were starting at exactly the same time, the way bus arbitration works, there
is always a chance that one master could lose arbitration of the bus during any transmit
operation. A master that has lost arbitration is required by the protocol to immediately
cease talking on the bus; in particular it must not initiate a stop condition in order to not
corrupt the ongoing transfer from the active master. In this example, upon detecting a
lost arbitration condition, the entire transfer is going to be restarted. This will cause a
new start condition to be initiated, which will normally be delayed until the currently
active master has released the bus.
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23.42 Example using the two-wire interface (TWI) 361
Note [10]
Next, the device slave is going to be reselected (using a so-called repeated start con-
dition which is meant to guarantee that the bus arbitration will remain at the current
master) using the same slave address (SLA), but this time with read intent (R/∼W bit
set to 1) in order to request the device slave to start transfering data from the slave to
the master in the next packet.
Note [11]
If the EEPROM device is still busy writing one or more cells after a previous write
request, it will simply leave its bus interface drivers at high impedance, and does not
respond to a selection in any way at all. The master selecting the device will see the
high level at SDA after transfering the SLA+R/W packet as a NACK to its selection
request. Thus, the select process is simply started over (effectively causing a repeated
start condition), until the device will eventually respond. This polling procedure is
recommended in the 24Cxx datasheet in order to minimize the busy wait time when
writing. Note that in case a device is broken and never responds to a selection (e. g.
since it is no longer present at all), this will cause an infinite loop. Thus the maximal
number of iterations made until the device is declared to be not responding at all, and
an error is returned, will be limited to MAX_ITER.
Note [12]
This is called master receiver mode: the bus master still supplies the SCL clock, but the
device slave drives the SDA line with the appropriate data. After 8 data bits, the master
responds with an ACK bit (SDA driven low) in order to request another data transfer
from the slave, or it can leave the SDA line high (NACK), indicating to the slave that
it is going to stop the transfer now. Assertion of ACK is handled by setting the TWEA
bit in TWCR when starting the current transfer.
Note [13]
The control word sent out in order to initiate the transfer of the next data packet is
initially set up to assert the TWEA bit. During the last loop iteration, TWEA is de-
asserted so the client will get informed that no further transfer is desired.
Note [14]
Except in the case of lost arbitration, all bus transactions must properly be terminated
by the master initiating a stop condition.
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24 Data Structure Documentation 362
Note [15]
Writing to the EEPROM device is simpler than reading, since only a master transmitter
mode transfer is needed. Note that the first packet after the SLA+W selection is always
considered to be the EEPROM address for the next operation. (This packet is exactly
the same as the one above sent before starting to read the device.) In case a master
transmitter mode transfer is going to send more than one data packet, all following
packets will be considered data bytes to write at the indicated address. The internal
address pointer will be incremented after each write operation.
Note [16]
24Cxx devices can become write-protected by strapping their ∼WC pin to logic high.
(Leaving it unconnected is explicitly allowed, and constitutes logic low level, i. e. no
write protection.) In case of a write protected device, all data transfer attempts will be
NACKed by the device. Note that some devices might not implement this.
24 Data Structure Documentation
24.1 div_t Struct Reference
Data Fields
• int quot
• int rem
24.1.1 Detailed Description
Result type for function div().
24.1.2 Field Documentation
24.1.2.1 int div_t::quot
The Quotient.
24.1.2.2 int div_t::rem
The Remainder.
The documentation for this struct was generated from the following file:
•stdlib.h
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24.2 ldiv_t Struct Reference 363
24.2 ldiv_t Struct Reference
Data Fields
• long quot
• long rem
24.2.1 Detailed Description
Result type for function ldiv().
24.2.2 Field Documentation
24.2.2.1 long ldiv_t::quot
The Quotient.
24.2.2.2 long ldiv_t::rem
The Remainder.
The documentation for this struct was generated from the following file:
•stdlib.h
24.3 tm Struct Reference
Data Fields
•int8_t tm_sec
•int8_t tm_min
•int8_t tm_hour
•int8_t tm_mday
•int8_t tm_wday
•int8_t tm_mon
•int16_t tm_year
•int16_t tm_yday
•int16_t tm_isdst
24.3.1 Detailed Description
The tm structure contains a representation of time ’broken down’ into components of
the Gregorian calendar.
The value of tm_isdst is zero if Daylight Saving Time is not in effect, and is negative
if the information is not available.
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24.3 tm Struct Reference 364
When Daylight Saving Time is in effect, the value represents the number of seconds
the clock is advanced.
See the set_dst() function for more information about Daylight Saving.
24.3.2 Field Documentation
24.3.2.1 int8_t tm::tm_hour
hours since midnight - [ 0 to 23 ]
24.3.2.2 int16_t tm::tm_isdst
Daylight Saving Time flag
24.3.2.3 int8_t tm::tm_mday
day of the month - [ 1 to 31 ]
24.3.2.4 int8_t tm::tm_min
minutes after the hour - [ 0 to 59 ]
24.3.2.5 int8_t tm::tm_mon
months since January - [ 0 to 11 ]
24.3.2.6 int8_t tm::tm_sec
seconds after the minute - [ 0 to 59 ]
24.3.2.7 int8_t tm::tm_wday
days since Sunday - [ 0 to 6 ]
24.3.2.8 int16_t tm::tm_yday
days since January 1 - [ 0 to 365 ]
24.3.2.9 int16_t tm::tm_year
years since 1900
The documentation for this struct was generated from the following file:
Generated on Wed Jul 25 09:38:10 2018 for avr-libc by Doxygen
24.4 week_date Struct Reference 365
•time.h
24.4 week_date Struct Reference
Data Fields
• int year
• int week
• int day
24.4.1 Detailed Description
Structure which represents a date as a year, week number of that year, and day of week.
See http://en.wikipedia.org/wiki/ISO_week_date for more informa-
tion.
24.4.2 Field Documentation
24.4.2.1 int week_date::day
day within week
24.4.2.2 int week_date::week
week number (#1 is where first Thursday is in)
24.4.2.3 int week_date::year
year number (Gregorian calendar)
The documentation for this struct was generated from the following file:
•time.h
25 File Documentation
25.1 assert.h File Reference
Defines
• #define assert(expression)
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25.2 atoi.S File Reference 366
25.1.1 Detailed Description
25.2 atoi.S File Reference
25.2.1 Detailed Description
25.3 atol.S File Reference
25.3.1 Detailed Description
25.4 atomic.h File Reference
Defines
• #define ATOMIC_BLOCK(type)
• #define NONATOMIC_BLOCK(type)
• #define ATOMIC_RESTORESTATE
• #define ATOMIC_FORCEON
• #define NONATOMIC_RESTORESTATE
• #define NONATOMIC_FORCEOFF
25.4.1 Detailed Description
25.5 boot.h File Reference
Defines
• #define BOOTLOADER_SECTION __attribute__ ((section (".bootloader")))
• #define boot_spm_interrupt_enable() (__SPM_REG |= (uint8_t)_BV(SPMIE))
• #define boot_spm_interrupt_disable() (__SPM_REG &= (uint8_t)∼_-
BV(SPMIE))
• #define boot_is_spm_interrupt() (__SPM_REG & (uint8_t)_BV(SPMIE))
• #define boot_rww_busy() (__SPM_REG & (uint8_t)_BV(__COMMON_ASB))
• #define boot_spm_busy() (__SPM_REG & (uint8_t)_BV(__SPM_ENABLE))
• #define boot_spm_busy_wait() do{}while(boot_spm_busy())
• #define GET_LOW_FUSE_BITS (0x0000)
• #define GET_LOCK_BITS (0x0001)
• #define GET_EXTENDED_FUSE_BITS (0x0002)
• #define GET_HIGH_FUSE_BITS (0x0003)
• #define boot_lock_fuse_bits_get(address)
• #define boot_signature_byte_get(addr)
• #define boot_page_fill(address, data) __boot_page_fill_normal(address, data)
• #define boot_page_erase(address) __boot_page_erase_normal(address)
• #define boot_page_write(address) __boot_page_write_normal(address)
• #define boot_rww_enable() __boot_rww_enable()
• #define boot_lock_bits_set(lock_bits) __boot_lock_bits_set(lock_bits)
• #define boot_page_fill_safe(address, data)
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25.6 cpufunc.h File Reference 367
• #define boot_page_erase_safe(address)
• #define boot_page_write_safe(address)
• #define boot_rww_enable_safe()
• #define boot_lock_bits_set_safe(lock_bits)
25.5.1 Detailed Description
25.6 cpufunc.h File Reference
Defines
• #define _NOP()
• #define _MemoryBarrier()
Functions
• void ccp_write_io (uint8_t ∗__ioaddr, uint8_t __value)
25.6.1 Detailed Description
25.7 crc16.h File Reference
Functions
• static __inline__ uint16_t _crc16_update (uint16_t __crc, uint8_t __data)
• static __inline__ uint16_t _crc_xmodem_update (uint16_t __crc, uint8_t __data)
• static __inline__ uint16_t _crc_ccitt_update (uint16_t __crc, uint8_t __data)
• static __inline__ uint8_t _crc_ibutton_update (uint8_t __crc, uint8_t __data)
• static __inline__ uint8_t _crc8_ccitt_update (uint8_t __crc, uint8_t __data)
25.7.1 Detailed Description
25.8 ctype.h File Reference
Functions
Character classification routines
These functions perform character classification. They return true or false status
depending whether the character passed to the function falls into the function’s
classification (i.e. isdigit() returns true if its argument is any value ’0’ though ’9’,
inclusive). If the input is not an unsigned char value, all of this function return
false.
• int isalnum (int __c)
• int isalpha (int __c)
• int isascii (int __c)
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25.9 delay.h File Reference 368
• int isblank (int __c)
• int iscntrl (int __c)
• int isdigit (int __c)
• int isgraph (int __c)
• int islower (int __c)
• int isprint (int __c)
• int ispunct (int __c)
• int isspace (int __c)
• int isupper (int __c)
• int isxdigit (int __c)
Character convertion routines
This realization permits all possible values of integer argument. The toascii() func-
tion clears all highest bits. The tolower() and toupper() functions return an input
argument as is, if it is not an unsigned char value.
• int toascii (int __c)
• int tolower (int __c)
• int toupper (int __c)
25.8.1 Detailed Description
25.9 delay.h File Reference
Defines
• #define F_CPU 1000000UL
Functions
• void _delay_ms (double __ms)
• void _delay_us (double __us)
25.9.1 Detailed Description
25.10 delay_basic.h File Reference
Functions
• void _delay_loop_1 (uint8_t __count)
• void _delay_loop_2 (uint16_t __count)
25.10.1 Detailed Description
25.11 errno.h File Reference
Defines
• #define EDOM 33
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25.12 fdevopen.c File Reference 369
• #define ERANGE 34
Variables
• int errno
25.11.1 Detailed Description
25.12 fdevopen.c File Reference
Functions
•FILE ∗fdevopen (int(∗put)(char, FILE ∗), int(∗get)(FILE ∗))
25.12.1 Detailed Description
25.13 fuse.h File Reference
25.13.1 Detailed Description
25.14 interrupt.h File Reference
Defines
Global manipulation of the interrupt flag
The global interrupt flag is maintained in the I bit of the status register (SREG).
Handling interrupts frequently requires attention regarding atomic access to ob-
jects that could be altered by code running within an interrupt context, see
<util/atomic.h>.
Frequently, interrupts are being disabled for periods of time in order to perform
certain operations without being disturbed; see Problems with reordering code for
things to be taken into account with respect to compiler optimizations.
• #define sei()
• #define cli()
Macros for writing interrupt handler functions
• #define ISR(vector, attributes)
• #define SIGNAL(vector)
• #define EMPTY_INTERRUPT(vector)
• #define ISR_ALIAS(vector, target_vector)
• #define reti()
• #define BADISR_vect
ISR attributes
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25.15 inttypes.h File Reference 370
• #define ISR_BLOCK
• #define ISR_NOBLOCK
• #define ISR_NAKED
• #define ISR_ALIASOF(target_vector)
25.14.1 Detailed Description
@{
25.15 inttypes.h File Reference
Defines
macros for printf and scanf format specifiers
For C++, these are only included if __STDC_LIMIT_MACROS is defined before
including <inttypes.h>.
• #define PRId8 "d"
• #define PRIdLEAST8 "d"
• #define PRIdFAST8 "d"
• #define PRIi8 "i"
• #define PRIiLEAST8 "i"
• #define PRIiFAST8 "i"
• #define PRId16 "d"
• #define PRIdLEAST16 "d"
• #define PRIdFAST16 "d"
• #define PRIi16 "i"
• #define PRIiLEAST16 "i"
• #define PRIiFAST16 "i"
• #define PRId32 "ld"
• #define PRIdLEAST32 "ld"
• #define PRIdFAST32 "ld"
• #define PRIi32 "li"
• #define PRIiLEAST32 "li"
• #define PRIiFAST32 "li"
• #define PRIdPTR PRId16
• #define PRIiPTR PRIi16
• #define PRIo8 "o"
• #define PRIoLEAST8 "o"
• #define PRIoFAST8 "o"
• #define PRIu8 "u"
• #define PRIuLEAST8 "u"
• #define PRIuFAST8 "u"
• #define PRIx8 "x"
• #define PRIxLEAST8 "x"
• #define PRIxFAST8 "x"
• #define PRIX8 "X"
• #define PRIXLEAST8 "X"
• #define PRIXFAST8 "X"
• #define PRIo16 "o"
• #define PRIoLEAST16 "o"
• #define PRIoFAST16 "o"
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25.15 inttypes.h File Reference 371
• #define PRIu16 "u"
• #define PRIuLEAST16 "u"
• #define PRIuFAST16 "u"
• #define PRIx16 "x"
• #define PRIxLEAST16 "x"
• #define PRIxFAST16 "x"
• #define PRIX16 "X"
• #define PRIXLEAST16 "X"
• #define PRIXFAST16 "X"
• #define PRIo32 "lo"
• #define PRIoLEAST32 "lo"
• #define PRIoFAST32 "lo"
• #define PRIu32 "lu"
• #define PRIuLEAST32 "lu"
• #define PRIuFAST32 "lu"
• #define PRIx32 "lx"
• #define PRIxLEAST32 "lx"
• #define PRIxFAST32 "lx"
• #define PRIX32 "lX"
• #define PRIXLEAST32 "lX"
• #define PRIXFAST32 "lX"
• #define PRIoPTR PRIo16
• #define PRIuPTR PRIu16
• #define PRIxPTR PRIx16
• #define PRIXPTR PRIX16
• #define SCNd8 "hhd"
• #define SCNdLEAST8 "hhd"
• #define SCNdFAST8 "hhd"
• #define SCNi8 "hhi"
• #define SCNiLEAST8 "hhi"
• #define SCNiFAST8 "hhi"
• #define SCNd16 "d"
• #define SCNdLEAST16 "d"
• #define SCNdFAST16 "d"
• #define SCNi16 "i"
• #define SCNiLEAST16 "i"
• #define SCNiFAST16 "i"
• #define SCNd32 "ld"
• #define SCNdLEAST32 "ld"
• #define SCNdFAST32 "ld"
• #define SCNi32 "li"
• #define SCNiLEAST32 "li"
• #define SCNiFAST32 "li"
• #define SCNdPTR SCNd16
• #define SCNiPTR SCNi16
• #define SCNo8 "hho"
• #define SCNoLEAST8 "hho"
• #define SCNoFAST8 "hho"
• #define SCNu8 "hhu"
• #define SCNuLEAST8 "hhu"
• #define SCNuFAST8 "hhu"
• #define SCNx8 "hhx"
• #define SCNxLEAST8 "hhx"
• #define SCNxFAST8 "hhx"
• #define SCNo16 "o"
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25.16 io.h File Reference 372
• #define SCNoLEAST16 "o"
• #define SCNoFAST16 "o"
• #define SCNu16 "u"
• #define SCNuLEAST16 "u"
• #define SCNuFAST16 "u"
• #define SCNx16 "x"
• #define SCNxLEAST16 "x"
• #define SCNxFAST16 "x"
• #define SCNo32 "lo"
• #define SCNoLEAST32 "lo"
• #define SCNoFAST32 "lo"
• #define SCNu32 "lu"
• #define SCNuLEAST32 "lu"
• #define SCNuFAST32 "lu"
• #define SCNx32 "lx"
• #define SCNxLEAST32 "lx"
• #define SCNxFAST32 "lx"
• #define SCNoPTR SCNo16
• #define SCNuPTR SCNu16
• #define SCNxPTR SCNx16
Typedefs
Far pointers for memory access >64K
• typedef int32_t int_farptr_t
• typedef uint32_t uint_farptr_t
25.15.1 Detailed Description
25.16 io.h File Reference
25.16.1 Detailed Description
25.17 lock.h File Reference
25.17.1 Detailed Description
25.18 math.h File Reference
Defines
• #define M_E 2.7182818284590452354
• #define M_LOG2E 1.4426950408889634074
• #define M_LOG10E 0.43429448190325182765
• #define M_LN2 0.69314718055994530942
• #define M_LN10 2.30258509299404568402
• #define M_PI 3.14159265358979323846
• #define M_PI_2 1.57079632679489661923
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25.18 math.h File Reference 373
• #define M_PI_4 0.78539816339744830962
• #define M_1_PI 0.31830988618379067154
• #define M_2_PI 0.63661977236758134308
• #define M_2_SQRTPI 1.12837916709551257390
• #define M_SQRT2 1.41421356237309504880
• #define M_SQRT1_2 0.70710678118654752440
• #define NAN __builtin_nan("")
• #define INFINITY __builtin_inf()
• #define cosf cos
• #define sinf sin
• #define tanf tan
• #define fabsf fabs
• #define fmodf fmod
• #define cbrtf cbrt
• #define hypotf hypot
• #define squaref square
• #define floorf floor
• #define ceilf ceil
• #define frexpf frexp
• #define ldexpf ldexp
• #define expf exp
• #define coshf cosh
• #define sinhf sinh
• #define tanhf tanh
• #define acosf acos
• #define asinf asin
• #define atanf atan
• #define atan2f atan2
• #define logf log
• #define log10f log10
• #define powf pow
• #define isnanf isnan
• #define isinff isinf
• #define isfinitef isfinite
• #define copysignf copysign
• #define signbitf signbit
• #define fdimf fdim
• #define fmaf fma
• #define fmaxf fmax
• #define fminf fmin
• #define truncf trunc
• #define roundf round
• #define lroundf lround
• #define lrintf lrint
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25.18 math.h File Reference 374
Functions
• double cos (double __x)
• double sin (double __x)
• double tan (double __x)
• double fabs (double __x)
• double fmod (double __x, double __y)
• double modf (double __x, double ∗__iptr)
• float modff (float __x, float ∗__iptr)
• double sqrt (double __x)
• float sqrtf (float)
• double cbrt (double __x)
• double hypot (double __x, double __y)
• double square (double __x)
• double floor (double __x)
• double ceil (double __x)
• double frexp (double __x, int ∗__pexp)
• double ldexp (double __x, int __exp)
• double exp (double __x)
• double cosh (double __x)
• double sinh (double __x)
• double tanh (double __x)
• double acos (double __x)
• double asin (double __x)
• double atan (double __x)
• double atan2 (double __y, double __x)
• double log (double __x)
• double log10 (double __x)
• double pow (double __x, double __y)
• int isnan (double __x)
• int isinf (double __x)
• static int isfinite (double __x)
• static double copysign (double __x, double __y)
• int signbit (double __x)
• double fdim (double __x, double __y)
• double fma (double __x, double __y, double __z)
• double fmax (double __x, double __y)
• double fmin (double __x, double __y)
• double trunc (double __x)
• double round (double __x)
• long lround (double __x)
• long lrint (double __x)
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25.19 parity.h File Reference 375
25.18.1 Detailed Description
25.19 parity.h File Reference
Defines
• #define parity_even_bit(val)
25.19.1 Detailed Description
25.20 pgmspace.h File Reference
Defines
• #define PROGMEM __ATTR_PROGMEM__
• #define PGM_P const char ∗
• #define PGM_VOID_P const void ∗
• #define PSTR(s) ((const PROGMEM char ∗)(s))
• #define pgm_read_byte_near(address_short) __LPM((uint16_t)(address_short))
• #define pgm_read_word_near(address_short) __LPM_word((uint16_-
t)(address_short))
• #define pgm_read_dword_near(address_short) __LPM_dword((uint16_-
t)(address_short))
• #define pgm_read_float_near(address_short) __LPM_float((uint16_t)(address_-
short))
• #define pgm_read_ptr_near(address_short) (void∗)__LPM_word((uint16_-
t)(address_short))
• #define pgm_read_byte_far(address_long) __ELPM((uint32_t)(address_long))
• #define pgm_read_word_far(address_long) __ELPM_word((uint32_-
t)(address_long))
• #define pgm_read_dword_far(address_long) __ELPM_dword((uint32_-
t)(address_long))
• #define pgm_read_float_far(address_long) __ELPM_float((uint32_t)(address_-
long))
• #define pgm_read_ptr_far(address_long) (void∗)__ELPM_word((uint32_-
t)(address_long))
• #define pgm_read_byte(address_short) pgm_read_byte_near(address_short)
• #define pgm_read_word(address_short) pgm_read_word_near(address_short)
• #define pgm_read_dword(address_short) pgm_read_dword_near(address_short)
• #define pgm_read_float(address_short) pgm_read_float_near(address_short)
• #define pgm_read_ptr(address_short) pgm_read_ptr_near(address_short)
• #define pgm_get_far_address(var)
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25.20 pgmspace.h File Reference 376
Typedefs
• typedef void PROGMEM prog_void
• typedef char PROGMEM prog_char
• typedef unsigned char PROGMEM prog_uchar
• typedef int8_t PROGMEM prog_int8_t
• typedef uint8_t PROGMEM prog_uint8_t
• typedef int16_t PROGMEM prog_int16_t
• typedef uint16_t PROGMEM prog_uint16_t
• typedef int32_t PROGMEM prog_int32_t
• typedef uint32_t PROGMEM prog_uint32_t
• typedef int64_t PROGMEM prog_int64_t
• typedef uint64_t PROGMEM prog_uint64_t
Functions
• const void ∗memchr_P (const void ∗, int __val, size_t __len)
• int memcmp_P (const void ∗, const void ∗, size_t) __ATTR_PURE__
• void ∗memccpy_P (void ∗, const void ∗, int __val, size_t)
• void ∗memcpy_P (void ∗, const void ∗, size_t)
• void ∗memmem_P (const void ∗, size_t, const void ∗, size_t) __ATTR_PURE_-
_
• const void ∗memrchr_P (const void ∗, int __val, size_t __len)
• char ∗strcat_P (char ∗, const char ∗)
• const char ∗strchr_P (const char ∗, int __val)
• const char ∗strchrnul_P (const char ∗, int __val)
• int strcmp_P (const char ∗, const char ∗) __ATTR_PURE__
• char ∗strcpy_P (char ∗, const char ∗)
• int strcasecmp_P (const char ∗, const char ∗) __ATTR_PURE__
• char ∗strcasestr_P (const char ∗, const char ∗) __ATTR_PURE__
• size_t strcspn_P (const char ∗__s, const char ∗__reject) __ATTR_PURE__
• size_t strlcat_P (char ∗, const char ∗, size_t)
• size_t strlcpy_P (char ∗, const char ∗, size_t)
• size_t strnlen_P (const char ∗, size_t)
• int strncmp_P (const char ∗, const char ∗, size_t) __ATTR_PURE__
• int strncasecmp_P (const char ∗, const char ∗, size_t) __ATTR_PURE__
• char ∗strncat_P (char ∗, const char ∗, size_t)
• char ∗strncpy_P (char ∗, const char ∗, size_t)
• char ∗strpbrk_P (const char ∗__s, const char ∗__accept) __ATTR_PURE__
• const char ∗strrchr_P (const char ∗, int __val)
• char ∗strsep_P (char ∗∗__sp, const char ∗__delim)
• size_t strspn_P (const char ∗__s, const char ∗__accept) __ATTR_PURE__
• char ∗strstr_P (const char ∗, const char ∗) __ATTR_PURE__
• char ∗strtok_P (char ∗__s, const char ∗__delim)
• char ∗strtok_rP (char ∗__s, const char ∗__delim, char ∗∗__last)
• size_t strlen_PF (uint_farptr_t src)
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25.21 power.h File Reference 377
• size_t strnlen_PF (uint_farptr_t src, size_t len)
• void ∗memcpy_PF (void ∗dest, uint_farptr_t src, size_t len)
• char ∗strcpy_PF (char ∗dest, uint_farptr_t src)
• char ∗strncpy_PF (char ∗dest, uint_farptr_t src, size_t len)
• char ∗strcat_PF (char ∗dest, uint_farptr_t src)
• size_t strlcat_PF (char ∗dst, uint_farptr_t src, size_t siz)
• char ∗strncat_PF (char ∗dest, uint_farptr_t src, size_t len)
• int strcmp_PF (const char ∗s1, uint_farptr_t s2) __ATTR_PURE__
• int strncmp_PF (const char ∗s1, uint_farptr_t s2, size_t n) __ATTR_PURE__
• int strcasecmp_PF (const char ∗s1, uint_farptr_t s2) __ATTR_PURE__
• int strncasecmp_PF (const char ∗s1, uint_farptr_t s2, size_t n) __ATTR_PURE_-
_
• char ∗strstr_PF (const char ∗s1, uint_farptr_t s2)
• size_t strlcpy_PF (char ∗dst, uint_farptr_t src, size_t siz)
• int memcmp_PF (const void ∗,uint_farptr_t, size_t) __ATTR_PURE__
• static size_t strlen_P (const char ∗s)
25.20.1 Detailed Description
25.21 power.h File Reference
Defines
• #define clock_prescale_get() (clock_div_t)(CLKPR & (uint8_-
t)((1<<CLKPS0)|(1<<CLKPS1)|(1<<CLKPS2)|(1<<CLKPS3)))
Functions
• static __inline void __attribute__ ((__always_inline__)) __power_all_enable()
• void clock_prescale_set (clock_div_t __x)
25.21.1 Detailed Description
25.21.2 Define Documentation
25.21.2.1 #define clock_prescale_get() (clock_div_t)(CLKPR & (uint8_-
t)((1<<CLKPS0)|(1<<CLKPS1)|(1<<CLKPS2)|(1<<CLKPS3)))
Gets and returns the clock prescaler register setting. The return type is
clock_div_t.
Note
For device with XTAL Divide Control Register (XDIV), return can actually range
from 1 to 129. Care should be taken has the return value could differ from the
typedef enum clock_div_t. This should only happen if clock_prescale_set was
previously called with a value other than those defined by clock_div_t.
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25.22 setbaud.h File Reference 378
25.22 setbaud.h File Reference
Defines
• #define BAUD_TOL 2
• #define UBRR_VALUE
• #define UBRRL_VALUE
• #define UBRRH_VALUE
• #define USE_2X 0
25.22.1 Detailed Description
25.23 setjmp.h File Reference
Functions
• int setjmp (jmp_buf __jmpb)
• void longjmp (jmp_buf __jmpb, int __ret) __ATTR_NORETURN__
25.23.1 Detailed Description
25.24 signature.h File Reference
25.24.1 Detailed Description
25.25 sleep.h File Reference
Functions
• void sleep_enable (void)
• void sleep_disable (void)
• void sleep_cpu (void)
• void sleep_mode (void)
• void sleep_bod_disable (void)
25.25.1 Detailed Description
25.26 stdint.h File Reference
Defines
Limits of specified-width integer types
C++ implementations should define these macros only when __STDC_LIMIT_-
MACROS is defined before <stdint.h>is included
• #define INT8_MAX 0x7f
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25.26 stdint.h File Reference 379
• #define INT8_MIN (-INT8_MAX - 1)
• #define UINT8_MAX (INT8_MAX ∗2 + 1)
• #define INT16_MAX 0x7fff
• #define INT16_MIN (-INT16_MAX - 1)
• #define UINT16_MAX (__CONCAT(INT16_MAX, U) ∗2U + 1U)
• #define INT32_MAX 0x7fffffffL
• #define INT32_MIN (-INT32_MAX - 1L)
• #define UINT32_MAX (__CONCAT(INT32_MAX, U) ∗2UL + 1UL)
• #define INT64_MAX 0x7fffffffffffffffLL
• #define INT64_MIN (-INT64_MAX - 1LL)
• #define UINT64_MAX (__CONCAT(INT64_MAX, U) ∗2ULL + 1ULL)
Limits of minimum-width integer types
• #define INT_LEAST8_MAX INT8_MAX
• #define INT_LEAST8_MIN INT8_MIN
• #define UINT_LEAST8_MAX UINT8_MAX
• #define INT_LEAST16_MAX INT16_MAX
• #define INT_LEAST16_MIN INT16_MIN
• #define UINT_LEAST16_MAX UINT16_MAX
• #define INT_LEAST32_MAX INT32_MAX
• #define INT_LEAST32_MIN INT32_MIN
• #define UINT_LEAST32_MAX UINT32_MAX
• #define INT_LEAST64_MAX INT64_MAX
• #define INT_LEAST64_MIN INT64_MIN
• #define UINT_LEAST64_MAX UINT64_MAX
Limits of fastest minimum-width integer types
• #define INT_FAST8_MAX INT8_MAX
• #define INT_FAST8_MIN INT8_MIN
• #define UINT_FAST8_MAX UINT8_MAX
• #define INT_FAST16_MAX INT16_MAX
• #define INT_FAST16_MIN INT16_MIN
• #define UINT_FAST16_MAX UINT16_MAX
• #define INT_FAST32_MAX INT32_MAX
• #define INT_FAST32_MIN INT32_MIN
• #define UINT_FAST32_MAX UINT32_MAX
• #define INT_FAST64_MAX INT64_MAX
• #define INT_FAST64_MIN INT64_MIN
• #define UINT_FAST64_MAX UINT64_MAX
Limits of integer types capable of holding object pointers
• #define INTPTR_MAX INT16_MAX
• #define INTPTR_MIN INT16_MIN
• #define UINTPTR_MAX UINT16_MAX
Limits of greatest-width integer types
• #define INTMAX_MAX INT64_MAX
• #define INTMAX_MIN INT64_MIN
• #define UINTMAX_MAX UINT64_MAX
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25.26 stdint.h File Reference 380
Limits of other integer types
C++ implementations should define these macros only when __STDC_LIMIT_-
MACROS is defined before <stdint.h>is included
• #define PTRDIFF_MAX INT16_MAX
• #define PTRDIFF_MIN INT16_MIN
• #define SIG_ATOMIC_MAX INT8_MAX
• #define SIG_ATOMIC_MIN INT8_MIN
• #define SIZE_MAX UINT16_MAX
• #define WCHAR_MAX __WCHAR_MAX__
• #define WCHAR_MIN __WCHAR_MIN__
• #define WINT_MAX __WINT_MAX__
• #define WINT_MIN __WINT_MIN__
Macros for integer constants
C++ implementations should define these macros only when __STDC_-
CONSTANT_MACROS is defined before <stdint.h>is included.
These definitions are valid for integer constants without suffix and for macros de-
fined as integer constant without suffix
• #define INT8_C(value) ((int8_t) value)
• #define UINT8_C(value) ((uint8_t) __CONCAT(value, U))
• #define INT16_C(value) value
• #define UINT16_C(value) __CONCAT(value, U)
• #define INT32_C(value) __CONCAT(value, L)
• #define UINT32_C(value) __CONCAT(value, UL)
• #define INT64_C(value) __CONCAT(value, LL)
• #define UINT64_C(value) __CONCAT(value, ULL)
• #define INTMAX_C(value) __CONCAT(value, LL)
• #define UINTMAX_C(value) __CONCAT(value, ULL)
Typedefs
Exact-width integer types
Integer types having exactly the specified width
• typedef signed char int8_t
• typedef unsigned char uint8_t
• typedef signed int int16_t
• typedef unsigned int uint16_t
• typedef signed long int int32_t
• typedef unsigned long int uint32_t
• typedef signed long long int int64_t
• typedef unsigned long long int uint64_t
Integer types capable of holding object pointers
These allow you to declare variables of the same size as a pointer.
• typedef int16_t intptr_t
• typedef uint16_t uintptr_t
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25.27 stdio.h File Reference 381
Minimum-width integer types
Integer types having at least the specified width
• typedef int8_t int_least8_t
• typedef uint8_t uint_least8_t
• typedef int16_t int_least16_t
• typedef uint16_t uint_least16_t
• typedef int32_t int_least32_t
• typedef uint32_t uint_least32_t
• typedef int64_t int_least64_t
• typedef uint64_t uint_least64_t
Fastest minimum-width integer types
Integer types being usually fastest having at least the specified width
• typedef int8_t int_fast8_t
• typedef uint8_t uint_fast8_t
• typedef int16_t int_fast16_t
• typedef uint16_t uint_fast16_t
• typedef int32_t int_fast32_t
• typedef uint32_t uint_fast32_t
• typedef int64_t int_fast64_t
• typedef uint64_t uint_fast64_t
Greatest-width integer types
Types designating integer data capable of representing any value of any integer
type in the corresponding signed or unsigned category
• typedef int64_t intmax_t
• typedef uint64_t uintmax_t
25.26.1 Detailed Description
25.27 stdio.h File Reference
Defines
• #define stdin (__iob[0])
• #define stdout (__iob[1])
• #define stderr (__iob[2])
• #define EOF (-1)
• #define fdev_set_udata(stream, u) do { (stream)->udata = u; } while(0)
• #define fdev_get_udata(stream) ((stream)->udata)
• #define fdev_setup_stream(stream, put, get, rwflag)
• #define _FDEV_SETUP_READ __SRD
• #define _FDEV_SETUP_WRITE __SWR
• #define _FDEV_SETUP_RW (__SRD|__SWR)
• #define _FDEV_ERR (-1)
• #define _FDEV_EOF (-2)
Generated on Wed Jul 25 09:38:10 2018 for avr-libc by Doxygen
25.27 stdio.h File Reference 382
• #define FDEV_SETUP_STREAM(put, get, rwflag)
• #define fdev_close()
• #define putc(__c, __stream) fputc(__c, __stream)
• #define putchar(__c) fputc(__c, stdout)
• #define getc(__stream) fgetc(__stream)
• #define getchar() fgetc(stdin)
Typedefs
• typedef struct __file FILE
Functions
• int fclose (FILE ∗__stream)
• int vfprintf (FILE ∗__stream, const char ∗__fmt, va_list __ap)
• int vfprintf_P (FILE ∗__stream, const char ∗__fmt, va_list __ap)
• int fputc (int __c, FILE ∗__stream)
• int printf (const char ∗__fmt,...)
• int printf_P (const char ∗__fmt,...)
• int vprintf (const char ∗__fmt, va_list __ap)
• int sprintf (char ∗__s, const char ∗__fmt,...)
• int sprintf_P (char ∗__s, const char ∗__fmt,...)
• int snprintf (char ∗__s, size_t __n, const char ∗__fmt,...)
• int snprintf_P (char ∗__s, size_t __n, const char ∗__fmt,...)
• int vsprintf (char ∗__s, const char ∗__fmt, va_list ap)
• int vsprintf_P (char ∗__s, const char ∗__fmt, va_list ap)
• int vsnprintf (char ∗__s, size_t __n, const char ∗__fmt, va_list ap)
• int vsnprintf_P (char ∗__s, size_t __n, const char ∗__fmt, va_list ap)
• int fprintf (FILE ∗__stream, const char ∗__fmt,...)
• int fprintf_P (FILE ∗__stream, const char ∗__fmt,...)
• int fputs (const char ∗__str, FILE ∗__stream)
• int fputs_P (const char ∗__str, FILE ∗__stream)
• int puts (const char ∗__str)
• int puts_P (const char ∗__str)
• size_t fwrite (const void ∗__ptr, size_t __size, size_t __nmemb, FILE ∗__-
stream)
• int fgetc (FILE ∗__stream)
• int ungetc (int __c, FILE ∗__stream)
• char ∗fgets (char ∗__str, int __size, FILE ∗__stream)
• char ∗gets (char ∗__str)
• size_t fread (void ∗__ptr, size_t __size, size_t __nmemb, FILE ∗__stream)
• void clearerr (FILE ∗__stream)
• int feof (FILE ∗__stream)
• int ferror (FILE ∗__stream)
• int vfscanf (FILE ∗__stream, const char ∗__fmt, va_list __ap)
• int vfscanf_P (FILE ∗__stream, const char ∗__fmt, va_list __ap)
Generated on Wed Jul 25 09:38:10 2018 for avr-libc by Doxygen
25.28 stdlib.h File Reference 383
• int fscanf (FILE ∗__stream, const char ∗__fmt,...)
• int fscanf_P (FILE ∗__stream, const char ∗__fmt,...)
• int scanf (const char ∗__fmt,...)
• int scanf_P (const char ∗__fmt,...)
• int vscanf (const char ∗__fmt, va_list __ap)
• int sscanf (const char ∗__buf, const char ∗__fmt,...)
• int sscanf_P (const char ∗__buf, const char ∗__fmt,...)
• int fflush (FILE ∗stream)
25.27.1 Detailed Description
25.28 stdlib.h File Reference
Data Structures
• struct div_t
• struct ldiv_t
Defines
• #define RAND_MAX 0x7FFF
Typedefs
• typedef int(∗__compar_fn_t )(const void ∗, const void ∗)
Functions
• void abort (void) __ATTR_NORETURN__
• int abs (int __i)
• long labs (long __i)
• void ∗bsearch (const void ∗__key, const void ∗__base, size_t __nmemb, size_t
__size, int(∗__compar)(const void ∗, const void ∗))
•div_t div (int __num, int __denom) __asm__("__divmodhi4")
•ldiv_t ldiv (long __num, long __denom) __asm__("__divmodsi4")
• void qsort (void ∗__base, size_t __nmemb, size_t __size, __compar_fn_t __-
compar)
• long strtol (const char ∗__nptr, char ∗∗__endptr, int __base)
• unsigned long strtoul (const char ∗__nptr, char ∗∗__endptr, int __base)
• long atol (const char ∗__s) __ATTR_PURE__
• int atoi (const char ∗__s) __ATTR_PURE__
• void exit (int __status) __ATTR_NORETURN__
• void ∗malloc (size_t __size) __ATTR_MALLOC__
• void free (void ∗__ptr)
• void ∗calloc (size_t __nele, size_t __size) __ATTR_MALLOC__
Generated on Wed Jul 25 09:38:10 2018 for avr-libc by Doxygen
25.29 string.h File Reference 384
• void ∗realloc (void ∗__ptr, size_t __size) __ATTR_MALLOC__
• double strtod (const char ∗__nptr, char ∗∗__endptr)
• double atof (const char ∗__nptr)
• int rand (void)
• void srand (unsigned int __seed)
• int rand_r (unsigned long ∗__ctx)
Variables
• size_t __malloc_margin
• char ∗__malloc_heap_start
• char ∗__malloc_heap_end
Non-standard (i.e. non-ISO C) functions.
• #define RANDOM_MAX 0x7FFFFFFF
• char ∗itoa (int val, char ∗s, int radix)
• char ∗ltoa (long val, char ∗s, int radix)
• char ∗utoa (unsigned int val, char ∗s, int radix)
• char ∗ultoa (unsigned long val, char ∗s, int radix)
• long random (void)
• void srandom (unsigned long __seed)
• long random_r (unsigned long ∗__ctx)
Conversion functions for double arguments.
Note that these functions are not located in the default library, libc.a, but in the
mathematical library, libm.a. So when linking the application, the -lm option needs
to be specified.
• #define DTOSTR_ALWAYS_SIGN 0x01
• #define DTOSTR_PLUS_SIGN 0x02
• #define DTOSTR_UPPERCASE 0x04
• #define EXIT_SUCCESS 0
• #define EXIT_FAILURE 1
• char ∗dtostre (double __val, char ∗__s, unsigned char __prec, unsigned char
__flags)
• char ∗dtostrf (double __val, signed char __width, unsigned char __prec, char
∗__s)
25.28.1 Detailed Description
25.29 string.h File Reference
Defines
• #define _FFS(x)
Generated on Wed Jul 25 09:38:10 2018 for avr-libc by Doxygen
25.30 time.h File Reference 385
Functions
• int ffs (int __val)
• int ffsl (long __val)
• __extension__ int ffsll (long long __val)
• void ∗memccpy (void ∗, const void ∗, int, size_t)
• void ∗memchr (const void ∗, int, size_t) __ATTR_PURE__
• int memcmp (const void ∗, const void ∗, size_t) __ATTR_PURE__
• void ∗memcpy (void ∗, const void ∗, size_t)
• void ∗memmem (const void ∗, size_t, const void ∗, size_t) __ATTR_PURE__
• void ∗memmove (void ∗, const void ∗, size_t)
• void ∗memrchr (const void ∗, int, size_t) __ATTR_PURE__
• void ∗memset (void ∗, int, size_t)
• char ∗strcat (char ∗, const char ∗)
• char ∗strchr (const char ∗, int) __ATTR_PURE__
• char ∗strchrnul (const char ∗, int) __ATTR_PURE__
• int strcmp (const char ∗, const char ∗) __ATTR_PURE__
• char ∗strcpy (char ∗, const char ∗)
• int strcasecmp (const char ∗, const char ∗) __ATTR_PURE__
• char ∗strcasestr (const char ∗, const char ∗) __ATTR_PURE__
• size_t strcspn (const char ∗__s, const char ∗__reject) __ATTR_PURE__
• char ∗strdup (const char ∗s1)
• size_t strlcat (char ∗, const char ∗, size_t)
• size_t strlcpy (char ∗, const char ∗, size_t)
• size_t strlen (const char ∗) __ATTR_PURE__
• char ∗strlwr (char ∗)
• char ∗strncat (char ∗, const char ∗, size_t)
• int strncmp (const char ∗, const char ∗, size_t) __ATTR_PURE__
• char ∗strncpy (char ∗, const char ∗, size_t)
• int strncasecmp (const char ∗, const char ∗, size_t) __ATTR_PURE__
• size_t strnlen (const char ∗, size_t) __ATTR_PURE__
• char ∗strpbrk (const char ∗__s, const char ∗__accept) __ATTR_PURE__
• char ∗strrchr (const char ∗, int) __ATTR_PURE__
• char ∗strrev (char ∗)
• char ∗strsep (char ∗∗, const char ∗)
• size_t strspn (const char ∗__s, const char ∗__accept) __ATTR_PURE__
• char ∗strstr (const char ∗, const char ∗) __ATTR_PURE__
• char ∗strtok (char ∗, const char ∗)
• char ∗strtok_r (char ∗, const char ∗, char ∗∗)
• char ∗strupr (char ∗)
25.29.1 Detailed Description
25.30 time.h File Reference
Data Structures
• struct tm
• struct week_date
Generated on Wed Jul 25 09:38:10 2018 for avr-libc by Doxygen
25.30 time.h File Reference 386
Defines
• #define ONE_HOUR 3600
• #define ONE_DEGREE 3600
• #define ONE_DAY 86400
• #define UNIX_OFFSET 946684800
• #define NTP_OFFSET 3155673600
Typedefs
• typedef uint32_t time_t
Enumerations
• enum _WEEK_DAYS_ {
SUNDAY,MONDAY,TUESDAY,WEDNESDAY,
THURSDAY,FRIDAY,SATURDAY }
• enum _MONTHS_ {
JANUARY,FEBRUARY,MARCH,APRIL,
MAY,JUNE,JULY,AUGUST,
SEPTEMBER,OCTOBER,NOVEMBER,DECEMBER }
Functions
•time_t time (time_t ∗timer)
•int32_t difftime (time_t time1, time_t time0)
•time_t mktime (struct tm ∗timeptr)
•time_t mk_gmtime (const struct tm ∗timeptr)
• struct tm ∗gmtime (const time_t ∗timer)
• void gmtime_r (const time_t ∗timer, struct tm ∗timeptr)
• struct tm ∗localtime (const time_t ∗timer)
• void localtime_r (const time_t ∗timer, struct tm ∗timeptr)
• char ∗asctime (const struct tm ∗timeptr)
• void asctime_r (const struct tm ∗timeptr, char ∗buf)
• char ∗ctime (const time_t ∗timer)
• void ctime_r (const time_t ∗timer, char ∗buf)
• char ∗isotime (const struct tm ∗tmptr)
• void isotime_r (const struct tm ∗, char ∗)
• size_t strftime (char ∗s, size_t maxsize, const char ∗format, const struct tm
∗timeptr)
• void set_dst (int(∗)(const time_t ∗,int32_t ∗))
• void set_zone (int32_t)
• void set_system_time (time_t timestamp)
• void system_tick (void)
•uint8_t is_leap_year (int16_t year)
Generated on Wed Jul 25 09:38:10 2018 for avr-libc by Doxygen
25.31 twi.h File Reference 387
•uint8_t month_length (int16_t year, uint8_t month)
•uint8_t week_of_year (const struct tm ∗timeptr, uint8_t start)
•uint8_t week_of_month (const struct tm ∗timeptr, uint8_t start)
• struct week_date ∗iso_week_date (int year, int yday)
• void iso_week_date_r (int year, int yday, struct week_date ∗)
•uint32_t fatfs_time (const struct tm ∗timeptr)
• void set_position (int32_t latitude, int32_t longitude)
•int16_t equation_of_time (const time_t ∗timer)
•int32_t daylight_seconds (const time_t ∗timer)
•time_t solar_noon (const time_t ∗timer)
•time_t sun_rise (const time_t ∗timer)
•time_t sun_set (const time_t ∗timer)
• double solar_declination (const time_t ∗timer)
•int8_t moon_phase (const time_t ∗timer)
• unsigned long gm_sidereal (const time_t ∗timer)
• unsigned long lm_sidereal (const time_t ∗timer)
25.30.1 Detailed Description
25.31 twi.h File Reference
Defines
TWSR values
Mnemonics:
TW_MT_xxx - master transmitter
TW_MR_xxx - master receiver
TW_ST_xxx - slave transmitter
TW_SR_xxx - slave receiver
• #define TW_START 0x08
• #define TW_REP_START 0x10
• #define TW_MT_SLA_ACK 0x18
• #define TW_MT_SLA_NACK 0x20
• #define TW_MT_DATA_ACK 0x28
• #define TW_MT_DATA_NACK 0x30
• #define TW_MT_ARB_LOST 0x38
• #define TW_MR_ARB_LOST 0x38
• #define TW_MR_SLA_ACK 0x40
• #define TW_MR_SLA_NACK 0x48
• #define TW_MR_DATA_ACK 0x50
• #define TW_MR_DATA_NACK 0x58
• #define TW_ST_SLA_ACK 0xA8
• #define TW_ST_ARB_LOST_SLA_ACK 0xB0
• #define TW_ST_DATA_ACK 0xB8
• #define TW_ST_DATA_NACK 0xC0
• #define TW_ST_LAST_DATA 0xC8
• #define TW_SR_SLA_ACK 0x60
Generated on Wed Jul 25 09:38:10 2018 for avr-libc by Doxygen
25.32 wdt.h File Reference 388
• #define TW_SR_ARB_LOST_SLA_ACK 0x68
• #define TW_SR_GCALL_ACK 0x70
• #define TW_SR_ARB_LOST_GCALL_ACK 0x78
• #define TW_SR_DATA_ACK 0x80
• #define TW_SR_DATA_NACK 0x88
• #define TW_SR_GCALL_DATA_ACK 0x90
• #define TW_SR_GCALL_DATA_NACK 0x98
• #define TW_SR_STOP 0xA0
• #define TW_NO_INFO 0xF8
• #define TW_BUS_ERROR 0x00
• #define TW_STATUS_MASK
• #define TW_STATUS (TWSR & TW_STATUS_MASK)
R/∼W bit in SLA+R/W address field.
• #define TW_READ 1
• #define TW_WRITE 0
25.31.1 Detailed Description
25.32 wdt.h File Reference
Defines
• #define wdt_reset() __asm__ __volatile__ ("wdr")
• #define WDTO_15MS 0
• #define WDTO_30MS 1
• #define WDTO_60MS 2
• #define WDTO_120MS 3
• #define WDTO_250MS 4
• #define WDTO_500MS 5
• #define WDTO_1S 6
• #define WDTO_2S 7
• #define WDTO_4S 8
• #define WDTO_8S 9
Functions
• static __inline__ __attribute__ ((__always_inline__)) void wdt_enable(const
uint8_t value)
25.32.1 Detailed Description
Generated on Wed Jul 25 09:38:10 2018 for avr-libc by Doxygen
Index
<alloca.h>: Allocate space in the stack,
128
<assert.h>: Diagnostics, 129
<avr/boot.h>: Bootloader Support Utili-
ties, 225
<avr/cpufunc.h>: Special AVR CPU
functions, 231
<avr/eeprom.h>: EEPROM handling,
232
<avr/fuse.h>: Fuse Support, 237
<avr/interrupt.h>: Interrupts, 240
<avr/io.h>: AVR device-specific IO defi-
nitions, 260
<avr/lock.h>: Lockbit Support, 261
<avr/pgmspace.h>: Program Space Util-
ities, 264
<avr/power.h>: Power Reduction Man-
agement, 288
<avr/sfr_defs.h>: Special function regis-
ters, 293
<avr/signature.h>: Signature Support,
295
<avr/sleep.h>: Power Management and
Sleep Modes, 296
<avr/version.h>: avr-libc version
macros, 298
<avr/wdt.h>: Watchdog timer handling,
299
<compat/deprecated.h>: Deprecated
items, 321
<compat/ina90.h>: Compatibility with
IAR EWB 3.x, 324
<ctype.h>: Character Operations, 130
<errno.h>: System Errors, 132
<inttypes.h>: Integer Type conversions,
133
<math.h>: Mathematics, 147
<setjmp.h>: Non-local goto, 160
<stdint.h>: Standard Integer Types, 162
<stdio.h>: Standard IO facilities, 174
<stdlib.h>: General utilities, 192
<string.h>: Strings, 203
<time.h>: Time, 216
<util/atomic.h>Atomically and Non-
Atomically Executed Code
Blocks, 303
<util/crc16.h>: CRC Computations, 306
<util/delay.h>: Convenience functions
for busy-wait delay loops, 310
<util/delay_basic.h>: Basic busy-wait
delay loops, 313
<util/parity.h>: Parity bit generation, 314
<util/setbaud.h>: Helper macros for
baud rate calculations, 314
<util/twi.h>: TWI bit mask definitions,
317
$PATH, 87
$PREFIX, 87
--prefix, 87
_BV
avr_sfr, 294
_EEGET
avr_eeprom, 234
_EEPUT
avr_eeprom, 234
_FDEV_EOF
avr_stdio, 178
_FDEV_ERR
avr_stdio, 178
_FDEV_SETUP_READ
avr_stdio, 178
_FDEV_SETUP_RW
avr_stdio, 178
_FDEV_SETUP_WRITE
avr_stdio, 178
_FFS
avr_string, 204
_MONTHS_
avr_time, 219
_MemoryBarrier
avr_cpufunc, 232
_NOP
avr_cpufunc, 232
_PROTECTED_WRITE
avr_io, 261
_PROTECTED_WRITE_SPM
avr_io, 261
_WEEK_DAYS_
avr_time, 219
__AVR_LIBC_DATE_
avr_version, 299
__AVR_LIBC_DATE_STRING__
INDEX 390
avr_version, 299
__AVR_LIBC_MAJOR__
avr_version, 299
__AVR_LIBC_MINOR__
avr_version, 299
__AVR_LIBC_REVISION__
avr_version, 299
__AVR_LIBC_VERSION_STRING__
avr_version, 299
__AVR_LIBC_VERSION__
avr_version, 299
__EEGET
avr_eeprom, 234
__EEPUT
avr_eeprom, 234
__attribute__
avr_watchdog, 303
__compar_fn_t
avr_stdlib, 194
__malloc_heap_end
avr_stdlib, 202
__malloc_heap_start
avr_stdlib, 202
__malloc_margin
avr_stdlib, 203
_crc16_update
util_crc, 307
_crc8_ccitt_update
util_crc, 308
_crc_ccitt_update
util_crc, 308
_crc_ibutton_update
util_crc, 309
_crc_xmodem_update
util_crc, 310
_delay_loop_1
util_delay_basic, 313
_delay_loop_2
util_delay_basic, 313
_delay_ms
util_delay, 311
_delay_us
util_delay, 312
A more sophisticated project, 343
A simple project, 329
abort
avr_stdlib, 194
abs
avr_stdlib, 194
acos
avr_math, 154
acosf
avr_math, 149
Additional notes from <avr/sfr_defs.h>,
292
alloca
alloca, 128
asctime
avr_time, 220
asctime_r
avr_time, 220
asin
avr_math, 154
asinf
avr_math, 149
assert
avr_assert, 129
assert.h, 365
atan
avr_math, 154
atan2
avr_math, 154
atan2f
avr_math, 149
atanf
avr_math, 150
atof
avr_stdlib, 194
atoi
avr_stdlib, 195
atoi.S, 366
atol
avr_stdlib, 195
atol.S, 366
atomic.h, 366
ATOMIC_BLOCK
util_atomic, 305
ATOMIC_FORCEON
util_atomic, 305
ATOMIC_RESTORESTATE
util_atomic, 305
avr_assert
assert, 129
avr_boot
boot_is_spm_interrupt, 227
boot_lock_bits_set, 227
boot_lock_bits_set_safe, 227
boot_lock_fuse_bits_get, 227
boot_page_erase, 228
Generated on Wed Jul 25 09:38:10 2018 for avr-libc by Doxygen
INDEX 391
boot_page_erase_safe, 228
boot_page_fill, 228
boot_page_fill_safe, 229
boot_page_write, 229
boot_page_write_safe, 229
boot_rww_busy, 229
boot_rww_enable, 230
boot_rww_enable_safe, 230
boot_signature_byte_get, 230
boot_spm_busy, 230
boot_spm_busy_wait, 230
boot_spm_interrupt_disable, 231
boot_spm_interrupt_enable, 231
BOOTLOADER_SECTION, 231
GET_EXTENDED_FUSE_BITS,
231
GET_HIGH_FUSE_BITS, 231
GET_LOCK_BITS, 231
GET_LOW_FUSE_BITS, 231
avr_cpufunc
_MemoryBarrier, 232
_NOP, 232
ccp_write_io, 232
avr_eeprom
_EEGET, 234
_EEPUT, 234
__EEGET, 234
__EEPUT, 234
EEMEM, 234
eeprom_busy_wait, 234
eeprom_is_ready, 235
eeprom_read_block, 235
eeprom_read_byte, 235
eeprom_read_dword, 235
eeprom_read_float, 235
eeprom_read_word, 235
eeprom_update_block, 235
eeprom_update_byte, 235
eeprom_update_dword, 236
eeprom_update_float, 236
eeprom_update_word, 236
eeprom_write_block, 236
eeprom_write_byte, 236
eeprom_write_dword, 236
eeprom_write_float, 236
eeprom_write_word, 236
avr_errno
EDOM, 133
ERANGE, 133
errno, 133
avr_interrupts
BADISR_vect, 257
cli, 257
EMPTY_INTERRUPT, 257
ISR, 257
ISR_ALIAS, 258
ISR_ALIASOF, 258
ISR_BLOCK, 258
ISR_NAKED, 259
ISR_NOBLOCK, 259
reti, 259
sei, 259
SIGNAL, 259
avr_inttypes
int_farptr_t, 147
PRId16, 137
PRId32, 137
PRId8, 137
PRIdFAST16, 137
PRIdFAST32, 137
PRIdFAST8, 137
PRIdLEAST16, 137
PRIdLEAST32, 137
PRIdLEAST8, 137
PRIdPTR, 137
PRIi16, 137
PRIi32, 138
PRIi8, 138
PRIiFAST16, 138
PRIiFAST32, 138
PRIiFAST8, 138
PRIiLEAST16, 138
PRIiLEAST32, 138
PRIiLEAST8, 138
PRIiPTR, 138
PRIo16, 138
PRIo32, 138
PRIo8, 139
PRIoFAST16, 139
PRIoFAST32, 139
PRIoFAST8, 139
PRIoLEAST16, 139
PRIoLEAST32, 139
PRIoLEAST8, 139
PRIoPTR, 139
PRIu16, 139
PRIu32, 139
PRIu8, 139
PRIuFAST16, 140
PRIuFAST32, 140
Generated on Wed Jul 25 09:38:10 2018 for avr-libc by Doxygen
INDEX 392
PRIuFAST8, 140
PRIuLEAST16, 140
PRIuLEAST32, 140
PRIuLEAST8, 140
PRIuPTR, 140
PRIX16, 140
PRIx16, 140
PRIX32, 140
PRIx32, 140
PRIX8, 141
PRIx8, 141
PRIXFAST16, 141
PRIxFAST16, 141
PRIXFAST32, 141
PRIxFAST32, 141
PRIXFAST8, 141
PRIxFAST8, 141
PRIXLEAST16, 141
PRIxLEAST16, 141
PRIXLEAST32, 141
PRIxLEAST32, 142
PRIXLEAST8, 142
PRIxLEAST8, 142
PRIXPTR, 142
PRIxPTR, 142
SCNd16, 142
SCNd32, 142
SCNd8, 142
SCNdFAST16, 142
SCNdFAST32, 142
SCNdFAST8, 142
SCNdLEAST16, 143
SCNdLEAST32, 143
SCNdLEAST8, 143
SCNdPTR, 143
SCNi16, 143
SCNi32, 143
SCNi8, 143
SCNiFAST16, 143
SCNiFAST32, 143
SCNiFAST8, 143
SCNiLEAST16, 143
SCNiLEAST32, 144
SCNiLEAST8, 144
SCNiPTR, 144
SCNo16, 144
SCNo32, 144
SCNo8, 144
SCNoFAST16, 144
SCNoFAST32, 144
SCNoFAST8, 144
SCNoLEAST16, 144
SCNoLEAST32, 144
SCNoLEAST8, 145
SCNoPTR, 145
SCNu16, 145
SCNu32, 145
SCNu8, 145
SCNuFAST16, 145
SCNuFAST32, 145
SCNuFAST8, 145
SCNuLEAST16, 145
SCNuLEAST32, 145
SCNuLEAST8, 145
SCNuPTR, 146
SCNx16, 146
SCNx32, 146
SCNx8, 146
SCNxFAST16, 146
SCNxFAST32, 146
SCNxFAST8, 146
SCNxLEAST16, 146
SCNxLEAST32, 146
SCNxLEAST8, 146
SCNxPTR, 146
uint_farptr_t, 147
avr_io
_PROTECTED_WRITE, 261
_PROTECTED_WRITE_SPM, 261
avr_math
acos, 154
acosf, 149
asin, 154
asinf, 149
atan, 154
atan2, 154
atan2f, 149
atanf, 150
cbrt, 154
cbrtf, 150
ceil, 155
ceilf, 150
copysign, 155
copysignf, 150
cos, 155
cosf, 150
cosh, 155
coshf, 150
exp, 155
expf, 150
Generated on Wed Jul 25 09:38:10 2018 for avr-libc by Doxygen
INDEX 393
fabs, 155
fabsf, 150
fdim, 155
fdimf, 150
floor, 155
floorf, 150
fma, 155
fmaf, 150
fmax, 156
fmaxf, 151
fmin, 156
fminf, 151
fmod, 156
fmodf, 151
frexp, 156
frexpf, 151
hypot, 156
hypotf, 151
INFINITY, 151
isfinite, 156
isfinitef, 151
isinf, 157
isinff, 151
isnan, 157
isnanf, 151
ldexp, 157
ldexpf, 151
log, 157
log10, 157
log10f, 151
logf, 152
lrint, 157
lrintf, 152
lround, 157
lroundf, 152
M_1_PI, 152
M_2_PI, 152
M_2_SQRTPI, 152
M_E, 152
M_LN10, 152
M_LN2, 152
M_LOG10E, 152
M_LOG2E, 152
M_PI, 153
M_PI_2, 153
M_PI_4, 153
M_SQRT1_2, 153
M_SQRT2, 153
modf, 158
modff, 158
NAN, 153
pow, 158
powf, 153
round, 158
roundf, 153
signbit, 158
signbitf, 153
sin, 159
sinf, 153
sinh, 159
sinhf, 153
sqrt, 159
sqrtf, 159
square, 159
squaref, 154
tan, 159
tanf, 154
tanh, 159
tanhf, 154
trunc, 159
truncf, 154
avr_pgmspace
memccpy_P, 274
memchr_P, 274
memcmp_P, 275
memcmp_PF, 275
memcpy_P, 275
memcpy_PF, 275
memmem_P, 276
memrchr_P, 276
pgm_get_far_address, 266
PGM_P, 267
pgm_read_byte, 267
pgm_read_byte_far, 267
pgm_read_byte_near, 268
pgm_read_dword, 268
pgm_read_dword_far, 268
pgm_read_dword_near, 268
pgm_read_float, 268
pgm_read_float_far, 268
pgm_read_float_near, 269
pgm_read_ptr, 269
pgm_read_ptr_far, 269
pgm_read_ptr_near, 269
pgm_read_word, 269
pgm_read_word_far, 270
pgm_read_word_near, 270
PGM_VOID_P, 270
prog_char, 270
prog_int16_t, 271
Generated on Wed Jul 25 09:38:10 2018 for avr-libc by Doxygen
INDEX 394
prog_int32_t, 271
prog_int64_t, 271
prog_int8_t, 272
prog_uchar, 272
prog_uint16_t, 272
prog_uint32_t, 273
prog_uint64_t, 273
prog_uint8_t, 274
prog_void, 274
PROGMEM, 270
PSTR, 270
strcasecmp_P, 276
strcasecmp_PF, 277
strcasestr_P, 277
strcat_P, 277
strcat_PF, 277
strchr_P, 278
strchrnul_P, 278
strcmp_P, 278
strcmp_PF, 279
strcpy_P, 279
strcpy_PF, 279
strcspn_P, 280
strlcat_P, 280
strlcat_PF, 280
strlcpy_P, 281
strlcpy_PF, 281
strlen_P, 281
strlen_PF, 282
strncasecmp_P, 282
strncasecmp_PF, 282
strncat_P, 283
strncat_PF, 283
strncmp_P, 283
strncmp_PF, 284
strncpy_P, 284
strncpy_PF, 284
strnlen_P, 285
strnlen_PF, 285
strpbrk_P, 286
strrchr_P, 286
strsep_P, 286
strspn_P, 286
strstr_P, 287
strstr_PF, 287
strtok_P, 287
strtok_rP, 288
avr_power
clock_prescale_set, 291
avr_sfr
_BV, 294
bit_is_clear, 294
bit_is_set, 294
loop_until_bit_is_clear, 295
loop_until_bit_is_set, 295
avr_sleep
sleep_bod_disable, 297
sleep_cpu, 297
sleep_disable, 298
sleep_enable, 298
sleep_mode, 298
avr_stdint
INT16_C, 165
INT16_MAX, 165
INT16_MIN, 165
int16_t, 171
INT32_C, 165
INT32_MAX, 165
INT32_MIN, 166
int32_t, 171
INT64_C, 166
INT64_MAX, 166
INT64_MIN, 166
int64_t, 171
INT8_C, 166
INT8_MAX, 166
INT8_MIN, 166
int8_t, 171
INT_FAST16_MAX, 166
INT_FAST16_MIN, 166
int_fast16_t, 171
INT_FAST32_MAX, 166
INT_FAST32_MIN, 166
int_fast32_t, 171
INT_FAST64_MAX, 167
INT_FAST64_MIN, 167
int_fast64_t, 171
INT_FAST8_MAX, 167
INT_FAST8_MIN, 167
int_fast8_t, 171
INT_LEAST16_MAX, 167
INT_LEAST16_MIN, 167
int_least16_t, 171
INT_LEAST32_MAX, 167
INT_LEAST32_MIN, 167
int_least32_t, 171
INT_LEAST64_MAX, 167
INT_LEAST64_MIN, 167
int_least64_t, 172
INT_LEAST8_MAX, 167
Generated on Wed Jul 25 09:38:10 2018 for avr-libc by Doxygen
INDEX 395
INT_LEAST8_MIN, 168
int_least8_t, 172
INTMAX_C, 168
INTMAX_MAX, 168
INTMAX_MIN, 168
intmax_t, 172
INTPTR_MAX, 168
INTPTR_MIN, 168
intptr_t, 172
PTRDIFF_MAX, 168
PTRDIFF_MIN, 168
SIG_ATOMIC_MAX, 168
SIG_ATOMIC_MIN, 168
SIZE_MAX, 168
UINT16_C, 169
UINT16_MAX, 169
uint16_t, 172
UINT32_C, 169
UINT32_MAX, 169
uint32_t, 172
UINT64_C, 169
UINT64_MAX, 169
uint64_t, 172
UINT8_C, 169
UINT8_MAX, 169
uint8_t, 172
UINT_FAST16_MAX, 169
uint_fast16_t, 172
UINT_FAST32_MAX, 169
uint_fast32_t, 173
UINT_FAST64_MAX, 170
uint_fast64_t, 173
UINT_FAST8_MAX, 170
uint_fast8_t, 173
UINT_LEAST16_MAX, 170
uint_least16_t, 173
UINT_LEAST32_MAX, 170
uint_least32_t, 173
UINT_LEAST64_MAX, 170
uint_least64_t, 173
UINT_LEAST8_MAX, 170
uint_least8_t, 173
UINTMAX_C, 170
UINTMAX_MAX, 170
uintmax_t, 173
UINTPTR_MAX, 170
uintptr_t, 173
avr_stdio
_FDEV_EOF, 178
_FDEV_ERR, 178
_FDEV_SETUP_READ, 178
_FDEV_SETUP_RW, 178
_FDEV_SETUP_WRITE, 178
clearerr, 181
EOF, 179
fclose, 181
fdev_close, 179
fdev_get_udata, 179
fdev_set_udata, 179
FDEV_SETUP_STREAM, 179
fdev_setup_stream, 179
fdevopen, 181
feof, 182
ferror, 182
fflush, 182
fgetc, 182
fgets, 182
FILE, 181
fprintf, 183
fprintf_P, 183
fputc, 183
fputs, 183
fputs_P, 183
fread, 183
fscanf, 183
fscanf_P, 184
fwrite, 184
getc, 180
getchar, 180
gets, 184
printf, 184
printf_P, 184
putc, 180
putchar, 180
puts, 184
puts_P, 184
scanf, 184
scanf_P, 185
snprintf, 185
snprintf_P, 185
sprintf, 185
sprintf_P, 185
sscanf, 185
sscanf_P, 185
stderr, 180
stdin, 180
stdout, 181
ungetc, 185
vfprintf, 186
vfprintf_P, 188
Generated on Wed Jul 25 09:38:10 2018 for avr-libc by Doxygen
INDEX 396
vfscanf, 188
vfscanf_P, 191
vprintf, 191
vscanf, 191
vsnprintf, 191
vsnprintf_P, 191
vsprintf, 191
vsprintf_P, 191
avr_stdlib
__compar_fn_t, 194
__malloc_heap_end, 202
__malloc_heap_start, 202
__malloc_margin, 203
abort, 194
abs, 194
atof, 194
atoi, 195
atol, 195
bsearch, 195
calloc, 196
div, 196
DTOSTR_ALWAYS_SIGN, 193
DTOSTR_PLUS_SIGN, 193
DTOSTR_UPPERCASE, 193
dtostre, 196
dtostrf, 196
exit, 196
EXIT_FAILURE, 194
EXIT_SUCCESS, 194
free, 197
itoa, 197
labs, 197
ldiv, 197
ltoa, 198
malloc, 198
qsort, 198
rand, 199
RAND_MAX, 194
rand_r, 199
random, 199
RANDOM_MAX, 194
random_r, 199
realloc, 199
srand, 200
srandom, 200
strtod, 200
strtol, 200
strtoul, 201
ultoa, 201
utoa, 202
avr_string
_FFS, 204
ffs, 204
ffsl, 205
ffsll, 205
memccpy, 205
memchr, 205
memcmp, 205
memcpy, 206
memmem, 206
memmove, 206
memrchr, 207
memset, 207
strcasecmp, 207
strcasestr, 207
strcat, 208
strchr, 208
strchrnul, 208
strcmp, 209
strcpy, 209
strcspn, 209
strdup, 209
strlcat, 210
strlcpy, 210
strlen, 211
strlwr, 211
strncasecmp, 211
strncat, 212
strncmp, 212
strncpy, 212
strnlen, 212
strpbrk, 213
strrchr, 213
strrev, 213
strsep, 214
strspn, 214
strstr, 214
strtok, 214
strtok_r, 215
strupr, 215
avr_time
_MONTHS_, 219
_WEEK_DAYS_, 219
asctime, 220
asctime_r, 220
ctime, 220
ctime_r, 220
daylight_seconds, 220
difftime, 220
equation_of_time, 220
Generated on Wed Jul 25 09:38:10 2018 for avr-libc by Doxygen
INDEX 397
fatfs_time, 220
gm_sidereal, 220
gmtime, 221
gmtime_r, 221
is_leap_year, 221
iso_week_date, 221
iso_week_date_r, 221
isotime, 221
isotime_r, 221
lm_sidereal, 221
localtime, 221
localtime_r, 222
mk_gmtime, 222
mktime, 222
month_length, 222
moon_phase, 222
NTP_OFFSET, 218
ONE_DAY, 219
ONE_DEGREE, 219
ONE_HOUR, 219
set_dst, 222
set_position, 223
set_system_time, 223
set_zone, 223
solar_declination, 223
solar_noon, 224
strftime, 224
sun_rise, 224
sun_set, 224
system_tick, 224
time, 224
time_t, 219
UNIX_OFFSET, 219
week_of_month, 224
week_of_year, 225
avr_version
__AVR_LIBC_DATE_, 299
__AVR_LIBC_DATE_STRING__,
299
__AVR_LIBC_MAJOR__, 299
__AVR_LIBC_MINOR__, 299
__AVR_LIBC_REVISION__, 299
__AVR_LIBC_VERSION_-
STRING__, 299
__AVR_LIBC_VERSION__, 299
avr_watchdog
__attribute__, 303
wdt_reset, 301
WDTO_120MS, 301
WDTO_15MS, 301
WDTO_1S, 301
WDTO_250MS, 301
WDTO_2S, 301
WDTO_30MS, 301
WDTO_4S, 302
WDTO_500MS, 302
WDTO_60MS, 302
WDTO_8S, 302
avrdude, usage, 117
avrprog, usage, 117
BADISR_vect
avr_interrupts, 257
BAUD_TOL
util_setbaud, 316
bit_is_clear
avr_sfr, 294
bit_is_set
avr_sfr, 294
boot.h, 366
boot_is_spm_interrupt
avr_boot, 227
boot_lock_bits_set
avr_boot, 227
boot_lock_bits_set_safe
avr_boot, 227
boot_lock_fuse_bits_get
avr_boot, 227
boot_page_erase
avr_boot, 228
boot_page_erase_safe
avr_boot, 228
boot_page_fill
avr_boot, 228
boot_page_fill_safe
avr_boot, 229
boot_page_write
avr_boot, 229
boot_page_write_safe
avr_boot, 229
boot_rww_busy
avr_boot, 229
boot_rww_enable
avr_boot, 230
boot_rww_enable_safe
avr_boot, 230
boot_signature_byte_get
avr_boot, 230
boot_spm_busy
avr_boot, 230
Generated on Wed Jul 25 09:38:10 2018 for avr-libc by Doxygen
INDEX 398
boot_spm_busy_wait
avr_boot, 230
boot_spm_interrupt_disable
avr_boot, 231
boot_spm_interrupt_enable
avr_boot, 231
BOOTLOADER_SECTION
avr_boot, 231
bsearch
avr_stdlib, 195
calloc
avr_stdlib, 196
cbi
deprecated_items, 322
cbrt
avr_math, 154
cbrtf
avr_math, 150
ccp_write_io
avr_cpufunc, 232
ceil
avr_math, 155
ceilf
avr_math, 150
clearerr
avr_stdio, 181
cli
avr_interrupts, 257
clock_prescale_get
power.h, 377
clock_prescale_set
avr_power, 291
Combining C and assembly source files,
326
copysign
avr_math, 155
copysignf
avr_math, 150
cos
avr_math, 155
cosf
avr_math, 150
cosh
avr_math, 155
coshf
avr_math, 150
cpufunc.h, 367
crc16.h, 367
ctime
avr_time, 220
ctime_r
avr_time, 220
ctype
isalnum, 131
isalpha, 131
isascii, 131
isblank, 131
iscntrl, 131
isdigit, 131
isgraph, 131
islower, 131
isprint, 131
ispunct, 131
isspace, 132
isupper, 132
isxdigit, 132
toascii, 132
tolower, 132
toupper, 132
ctype.h, 367
day
week_date, 365
daylight_seconds
avr_time, 220
delay.h, 368
delay_basic.h, 368
Demo projects, 325
deprecated_items
cbi, 322
enable_external_int, 322
inb, 322
inp, 323
INTERRUPT, 323
outb, 323
outp, 323
sbi, 324
timer_enable_int, 324
difftime
avr_time, 220
disassembling, 333
div
avr_stdlib, 196
div_t, 362
quot, 362
rem, 362
DTOSTR_ALWAYS_SIGN
avr_stdlib, 193
DTOSTR_PLUS_SIGN
Generated on Wed Jul 25 09:38:10 2018 for avr-libc by Doxygen
INDEX 399
avr_stdlib, 193
DTOSTR_UPPERCASE
avr_stdlib, 193
dtostre
avr_stdlib, 196
dtostrf
avr_stdlib, 196
EDOM
avr_errno, 133
EEMEM
avr_eeprom, 234
eeprom_busy_wait
avr_eeprom, 234
eeprom_is_ready
avr_eeprom, 235
eeprom_read_block
avr_eeprom, 235
eeprom_read_byte
avr_eeprom, 235
eeprom_read_dword
avr_eeprom, 235
eeprom_read_float
avr_eeprom, 235
eeprom_read_word
avr_eeprom, 235
eeprom_update_block
avr_eeprom, 235
eeprom_update_byte
avr_eeprom, 235
eeprom_update_dword
avr_eeprom, 236
eeprom_update_float
avr_eeprom, 236
eeprom_update_word
avr_eeprom, 236
eeprom_write_block
avr_eeprom, 236
eeprom_write_byte
avr_eeprom, 236
eeprom_write_dword
avr_eeprom, 236
eeprom_write_float
avr_eeprom, 236
eeprom_write_word
avr_eeprom, 236
EMPTY_INTERRUPT
avr_interrupts, 257
enable_external_int
deprecated_items, 322
EOF
avr_stdio, 179
equation_of_time
avr_time, 220
ERANGE
avr_errno, 133
errno
avr_errno, 133
errno.h, 368
Example using the two-wire interface
(TWI), 357
exit
avr_stdlib, 196
EXIT_FAILURE
avr_stdlib, 194
EXIT_SUCCESS
avr_stdlib, 194
exp
avr_math, 155
expf
avr_math, 150
F_CPU
util_delay, 311
fabs
avr_math, 155
fabsf
avr_math, 150
FAQ, 59
fatfs_time
avr_time, 220
fclose
avr_stdio, 181
fdev_close
avr_stdio, 179
fdev_get_udata
avr_stdio, 179
fdev_set_udata
avr_stdio, 179
FDEV_SETUP_STREAM
avr_stdio, 179
fdev_setup_stream
avr_stdio, 179
fdevopen
avr_stdio, 181
fdevopen.c, 369
fdim
avr_math, 155
fdimf
avr_math, 150
Generated on Wed Jul 25 09:38:10 2018 for avr-libc by Doxygen
INDEX 400
feof
avr_stdio, 182
ferror
avr_stdio, 182
fflush
avr_stdio, 182
ffs
avr_string, 204
ffsl
avr_string, 205
ffsll
avr_string, 205
fgetc
avr_stdio, 182
fgets
avr_stdio, 182
FILE
avr_stdio, 181
floor
avr_math, 155
floorf
avr_math, 150
fma
avr_math, 155
fmaf
avr_math, 150
fmax
avr_math, 156
fmaxf
avr_math, 151
fmin
avr_math, 156
fminf
avr_math, 151
fmod
avr_math, 156
fmodf
avr_math, 151
fprintf
avr_stdio, 183
fprintf_P
avr_stdio, 183
fputc
avr_stdio, 183
fputs
avr_stdio, 183
fputs_P
avr_stdio, 183
fread
avr_stdio, 183
free
avr_stdlib, 197
frexp
avr_math, 156
frexpf
avr_math, 151
fscanf
avr_stdio, 183
fscanf_P
avr_stdio, 184
fuse.h, 369
fwrite
avr_stdio, 184
GET_EXTENDED_FUSE_BITS
avr_boot, 231
GET_HIGH_FUSE_BITS
avr_boot, 231
GET_LOCK_BITS
avr_boot, 231
GET_LOW_FUSE_BITS
avr_boot, 231
getc
avr_stdio, 180
getchar
avr_stdio, 180
gets
avr_stdio, 184
gm_sidereal
avr_time, 220
gmtime
avr_time, 221
gmtime_r
avr_time, 221
hypot
avr_math, 156
hypotf
avr_math, 151
inb
deprecated_items, 322
INFINITY
avr_math, 151
inp
deprecated_items, 323
installation, 87
installation, avarice, 92
installation, avr-libc, 90
installation, avrdude, 91
Generated on Wed Jul 25 09:38:10 2018 for avr-libc by Doxygen
INDEX 401
installation, avrprog, 91
installation, binutils, 89
installation, gcc, 90
Installation, gdb, 91
installation, simulavr, 92
INT16_C
avr_stdint, 165
INT16_MAX
avr_stdint, 165
INT16_MIN
avr_stdint, 165
int16_t
avr_stdint, 171
INT32_C
avr_stdint, 165
INT32_MAX
avr_stdint, 165
INT32_MIN
avr_stdint, 166
int32_t
avr_stdint, 171
INT64_C
avr_stdint, 166
INT64_MAX
avr_stdint, 166
INT64_MIN
avr_stdint, 166
int64_t
avr_stdint, 171
INT8_C
avr_stdint, 166
INT8_MAX
avr_stdint, 166
INT8_MIN
avr_stdint, 166
int8_t
avr_stdint, 171
int_farptr_t
avr_inttypes, 147
INT_FAST16_MAX
avr_stdint, 166
INT_FAST16_MIN
avr_stdint, 166
int_fast16_t
avr_stdint, 171
INT_FAST32_MAX
avr_stdint, 166
INT_FAST32_MIN
avr_stdint, 166
int_fast32_t
avr_stdint, 171
INT_FAST64_MAX
avr_stdint, 167
INT_FAST64_MIN
avr_stdint, 167
int_fast64_t
avr_stdint, 171
INT_FAST8_MAX
avr_stdint, 167
INT_FAST8_MIN
avr_stdint, 167
int_fast8_t
avr_stdint, 171
INT_LEAST16_MAX
avr_stdint, 167
INT_LEAST16_MIN
avr_stdint, 167
int_least16_t
avr_stdint, 171
INT_LEAST32_MAX
avr_stdint, 167
INT_LEAST32_MIN
avr_stdint, 167
int_least32_t
avr_stdint, 171
INT_LEAST64_MAX
avr_stdint, 167
INT_LEAST64_MIN
avr_stdint, 167
int_least64_t
avr_stdint, 172
INT_LEAST8_MAX
avr_stdint, 167
INT_LEAST8_MIN
avr_stdint, 168
int_least8_t
avr_stdint, 172
INTERRUPT
deprecated_items, 323
interrupt.h, 369
INTMAX_C
avr_stdint, 168
INTMAX_MAX
avr_stdint, 168
INTMAX_MIN
avr_stdint, 168
intmax_t
avr_stdint, 172
INTPTR_MAX
avr_stdint, 168
Generated on Wed Jul 25 09:38:10 2018 for avr-libc by Doxygen
INDEX 402
INTPTR_MIN
avr_stdint, 168
intptr_t
avr_stdint, 172
inttypes.h, 370
io.h, 372
is_leap_year
avr_time, 221
isalnum
ctype, 131
isalpha
ctype, 131
isascii
ctype, 131
isblank
ctype, 131
iscntrl
ctype, 131
isdigit
ctype, 131
isfinite
avr_math, 156
isfinitef
avr_math, 151
isgraph
ctype, 131
isinf
avr_math, 157
isinff
avr_math, 151
islower
ctype, 131
isnan
avr_math, 157
isnanf
avr_math, 151
iso_week_date
avr_time, 221
iso_week_date_r
avr_time, 221
isotime
avr_time, 221
isotime_r
avr_time, 221
isprint
ctype, 131
ispunct
ctype, 131
ISR
avr_interrupts, 257
ISR_ALIAS
avr_interrupts, 258
ISR_ALIASOF
avr_interrupts, 258
ISR_BLOCK
avr_interrupts, 258
ISR_NAKED
avr_interrupts, 259
ISR_NOBLOCK
avr_interrupts, 259
isspace
ctype, 132
isupper
ctype, 132
isxdigit
ctype, 132
itoa
avr_stdlib, 197
labs
avr_stdlib, 197
ldexp
avr_math, 157
ldexpf
avr_math, 151
ldiv
avr_stdlib, 197
ldiv_t, 363
quot, 363
rem, 363
lm_sidereal
avr_time, 221
localtime
avr_time, 221
localtime_r
avr_time, 222
lock.h, 372
log
avr_math, 157
log10
avr_math, 157
log10f
avr_math, 151
logf
avr_math, 152
longjmp
setjmp, 161
loop_until_bit_is_clear
avr_sfr, 295
loop_until_bit_is_set
Generated on Wed Jul 25 09:38:10 2018 for avr-libc by Doxygen
INDEX 403
avr_sfr, 295
lrint
avr_math, 157
lrintf
avr_math, 152
lround
avr_math, 157
lroundf
avr_math, 152
ltoa
avr_stdlib, 198
M_1_PI
avr_math, 152
M_2_PI
avr_math, 152
M_2_SQRTPI
avr_math, 152
M_E
avr_math, 152
M_LN10
avr_math, 152
M_LN2
avr_math, 152
M_LOG10E
avr_math, 152
M_LOG2E
avr_math, 152
M_PI
avr_math, 153
M_PI_2
avr_math, 153
M_PI_4
avr_math, 153
M_SQRT1_2
avr_math, 153
M_SQRT2
avr_math, 153
malloc
avr_stdlib, 198
math.h, 372
memccpy
avr_string, 205
memccpy_P
avr_pgmspace, 274
memchr
avr_string, 205
memchr_P
avr_pgmspace, 274
memcmp
avr_string, 205
memcmp_P
avr_pgmspace, 275
memcmp_PF
avr_pgmspace, 275
memcpy
avr_string, 206
memcpy_P
avr_pgmspace, 275
memcpy_PF
avr_pgmspace, 275
memmem
avr_string, 206
memmem_P
avr_pgmspace, 276
memmove
avr_string, 206
memrchr
avr_string, 207
memrchr_P
avr_pgmspace, 276
memset
avr_string, 207
mk_gmtime
avr_time, 222
mktime
avr_time, 222
modf
avr_math, 158
modff
avr_math, 158
month_length
avr_time, 222
moon_phase
avr_time, 222
NAN
avr_math, 153
NONATOMIC_BLOCK
util_atomic, 305
NONATOMIC_FORCEOFF
util_atomic, 306
NONATOMIC_RESTORESTATE
util_atomic, 306
NTP_OFFSET
avr_time, 218
ONE_DAY
avr_time, 219
ONE_DEGREE
Generated on Wed Jul 25 09:38:10 2018 for avr-libc by Doxygen
INDEX 404
avr_time, 219
ONE_HOUR
avr_time, 219
outb
deprecated_items, 323
outp
deprecated_items, 323
parity.h, 375
parity_even_bit
util_parity, 314
pgm_get_far_address
avr_pgmspace, 266
PGM_P
avr_pgmspace, 267
pgm_read_byte
avr_pgmspace, 267
pgm_read_byte_far
avr_pgmspace, 267
pgm_read_byte_near
avr_pgmspace, 268
pgm_read_dword
avr_pgmspace, 268
pgm_read_dword_far
avr_pgmspace, 268
pgm_read_dword_near
avr_pgmspace, 268
pgm_read_float
avr_pgmspace, 268
pgm_read_float_far
avr_pgmspace, 268
pgm_read_float_near
avr_pgmspace, 269
pgm_read_ptr
avr_pgmspace, 269
pgm_read_ptr_far
avr_pgmspace, 269
pgm_read_ptr_near
avr_pgmspace, 269
pgm_read_word
avr_pgmspace, 269
pgm_read_word_far
avr_pgmspace, 270
pgm_read_word_near
avr_pgmspace, 270
PGM_VOID_P
avr_pgmspace, 270
pgmspace.h, 375
pow
avr_math, 158
power.h, 377
clock_prescale_get, 377
powf
avr_math, 153
PRId16
avr_inttypes, 137
PRId32
avr_inttypes, 137
PRId8
avr_inttypes, 137
PRIdFAST16
avr_inttypes, 137
PRIdFAST32
avr_inttypes, 137
PRIdFAST8
avr_inttypes, 137
PRIdLEAST16
avr_inttypes, 137
PRIdLEAST32
avr_inttypes, 137
PRIdLEAST8
avr_inttypes, 137
PRIdPTR
avr_inttypes, 137
PRIi16
avr_inttypes, 137
PRIi32
avr_inttypes, 138
PRIi8
avr_inttypes, 138
PRIiFAST16
avr_inttypes, 138
PRIiFAST32
avr_inttypes, 138
PRIiFAST8
avr_inttypes, 138
PRIiLEAST16
avr_inttypes, 138
PRIiLEAST32
avr_inttypes, 138
PRIiLEAST8
avr_inttypes, 138
PRIiPTR
avr_inttypes, 138
printf
avr_stdio, 184
printf_P
avr_stdio, 184
PRIo16
avr_inttypes, 138
Generated on Wed Jul 25 09:38:10 2018 for avr-libc by Doxygen
INDEX 405
PRIo32
avr_inttypes, 138
PRIo8
avr_inttypes, 139
PRIoFAST16
avr_inttypes, 139
PRIoFAST32
avr_inttypes, 139
PRIoFAST8
avr_inttypes, 139
PRIoLEAST16
avr_inttypes, 139
PRIoLEAST32
avr_inttypes, 139
PRIoLEAST8
avr_inttypes, 139
PRIoPTR
avr_inttypes, 139
PRIu16
avr_inttypes, 139
PRIu32
avr_inttypes, 139
PRIu8
avr_inttypes, 139
PRIuFAST16
avr_inttypes, 140
PRIuFAST32
avr_inttypes, 140
PRIuFAST8
avr_inttypes, 140
PRIuLEAST16
avr_inttypes, 140
PRIuLEAST32
avr_inttypes, 140
PRIuLEAST8
avr_inttypes, 140
PRIuPTR
avr_inttypes, 140
PRIX16
avr_inttypes, 140
PRIx16
avr_inttypes, 140
PRIX32
avr_inttypes, 140
PRIx32
avr_inttypes, 140
PRIX8
avr_inttypes, 141
PRIx8
avr_inttypes, 141
PRIXFAST16
avr_inttypes, 141
PRIxFAST16
avr_inttypes, 141
PRIXFAST32
avr_inttypes, 141
PRIxFAST32
avr_inttypes, 141
PRIXFAST8
avr_inttypes, 141
PRIxFAST8
avr_inttypes, 141
PRIXLEAST16
avr_inttypes, 141
PRIxLEAST16
avr_inttypes, 141
PRIXLEAST32
avr_inttypes, 141
PRIxLEAST32
avr_inttypes, 142
PRIXLEAST8
avr_inttypes, 142
PRIxLEAST8
avr_inttypes, 142
PRIXPTR
avr_inttypes, 142
PRIxPTR
avr_inttypes, 142
prog_char
avr_pgmspace, 270
prog_int16_t
avr_pgmspace, 271
prog_int32_t
avr_pgmspace, 271
prog_int64_t
avr_pgmspace, 271
prog_int8_t
avr_pgmspace, 272
prog_uchar
avr_pgmspace, 272
prog_uint16_t
avr_pgmspace, 272
prog_uint32_t
avr_pgmspace, 273
prog_uint64_t
avr_pgmspace, 273
prog_uint8_t
avr_pgmspace, 274
prog_void
avr_pgmspace, 274
Generated on Wed Jul 25 09:38:10 2018 for avr-libc by Doxygen
INDEX 406
PROGMEM
avr_pgmspace, 270
PSTR
avr_pgmspace, 270
PTRDIFF_MAX
avr_stdint, 168
PTRDIFF_MIN
avr_stdint, 168
putc
avr_stdio, 180
putchar
avr_stdio, 180
puts
avr_stdio, 184
puts_P
avr_stdio, 184
qsort
avr_stdlib, 198
quot
div_t, 362
ldiv_t, 363
rand
avr_stdlib, 199
RAND_MAX
avr_stdlib, 194
rand_r
avr_stdlib, 199
random
avr_stdlib, 199
RANDOM_MAX
avr_stdlib, 194
random_r
avr_stdlib, 199
realloc
avr_stdlib, 199
rem
div_t, 362
ldiv_t, 363
reti
avr_interrupts, 259
round
avr_math, 158
roundf
avr_math, 153
sbi
deprecated_items, 324
scanf
avr_stdio, 184
scanf_P
avr_stdio, 185
SCNd16
avr_inttypes, 142
SCNd32
avr_inttypes, 142
SCNd8
avr_inttypes, 142
SCNdFAST16
avr_inttypes, 142
SCNdFAST32
avr_inttypes, 142
SCNdFAST8
avr_inttypes, 142
SCNdLEAST16
avr_inttypes, 143
SCNdLEAST32
avr_inttypes, 143
SCNdLEAST8
avr_inttypes, 143
SCNdPTR
avr_inttypes, 143
SCNi16
avr_inttypes, 143
SCNi32
avr_inttypes, 143
SCNi8
avr_inttypes, 143
SCNiFAST16
avr_inttypes, 143
SCNiFAST32
avr_inttypes, 143
SCNiFAST8
avr_inttypes, 143
SCNiLEAST16
avr_inttypes, 143
SCNiLEAST32
avr_inttypes, 144
SCNiLEAST8
avr_inttypes, 144
SCNiPTR
avr_inttypes, 144
SCNo16
avr_inttypes, 144
SCNo32
avr_inttypes, 144
SCNo8
avr_inttypes, 144
SCNoFAST16
Generated on Wed Jul 25 09:38:10 2018 for avr-libc by Doxygen
INDEX 407
avr_inttypes, 144
SCNoFAST32
avr_inttypes, 144
SCNoFAST8
avr_inttypes, 144
SCNoLEAST16
avr_inttypes, 144
SCNoLEAST32
avr_inttypes, 144
SCNoLEAST8
avr_inttypes, 145
SCNoPTR
avr_inttypes, 145
SCNu16
avr_inttypes, 145
SCNu32
avr_inttypes, 145
SCNu8
avr_inttypes, 145
SCNuFAST16
avr_inttypes, 145
SCNuFAST32
avr_inttypes, 145
SCNuFAST8
avr_inttypes, 145
SCNuLEAST16
avr_inttypes, 145
SCNuLEAST32
avr_inttypes, 145
SCNuLEAST8
avr_inttypes, 145
SCNuPTR
avr_inttypes, 146
SCNx16
avr_inttypes, 146
SCNx32
avr_inttypes, 146
SCNx8
avr_inttypes, 146
SCNxFAST16
avr_inttypes, 146
SCNxFAST32
avr_inttypes, 146
SCNxFAST8
avr_inttypes, 146
SCNxLEAST16
avr_inttypes, 146
SCNxLEAST32
avr_inttypes, 146
SCNxLEAST8
avr_inttypes, 146
SCNxPTR
avr_inttypes, 146
sei
avr_interrupts, 259
set_dst
avr_time, 222
set_position
avr_time, 223
set_system_time
avr_time, 223
set_zone
avr_time, 223
setbaud.h, 378
setjmp
longjmp, 161
setjmp, 161
setjmp.h, 378
SIG_ATOMIC_MAX
avr_stdint, 168
SIG_ATOMIC_MIN
avr_stdint, 168
SIGNAL
avr_interrupts, 259
signature.h, 378
signbit
avr_math, 158
signbitf
avr_math, 153
sin
avr_math, 159
sinf
avr_math, 153
sinh
avr_math, 159
sinhf
avr_math, 153
SIZE_MAX
avr_stdint, 168
sleep.h, 378
sleep_bod_disable
avr_sleep, 297
sleep_cpu
avr_sleep, 297
sleep_disable
avr_sleep, 298
sleep_enable
avr_sleep, 298
sleep_mode
avr_sleep, 298
Generated on Wed Jul 25 09:38:10 2018 for avr-libc by Doxygen
INDEX 408
snprintf
avr_stdio, 185
snprintf_P
avr_stdio, 185
solar_declination
avr_time, 223
solar_noon
avr_time, 224
sprintf
avr_stdio, 185
sprintf_P
avr_stdio, 185
sqrt
avr_math, 159
sqrtf
avr_math, 159
square
avr_math, 159
squaref
avr_math, 154
srand
avr_stdlib, 200
srandom
avr_stdlib, 200
sscanf
avr_stdio, 185
sscanf_P
avr_stdio, 185
stderr
avr_stdio, 180
stdin
avr_stdio, 180
stdint.h, 378
stdio.h, 381
stdlib.h, 383
stdout
avr_stdio, 181
strcasecmp
avr_string, 207
strcasecmp_P
avr_pgmspace, 276
strcasecmp_PF
avr_pgmspace, 277
strcasestr
avr_string, 207
strcasestr_P
avr_pgmspace, 277
strcat
avr_string, 208
strcat_P
avr_pgmspace, 277
strcat_PF
avr_pgmspace, 277
strchr
avr_string, 208
strchr_P
avr_pgmspace, 278
strchrnul
avr_string, 208
strchrnul_P
avr_pgmspace, 278
strcmp
avr_string, 209
strcmp_P
avr_pgmspace, 278
strcmp_PF
avr_pgmspace, 279
strcpy
avr_string, 209
strcpy_P
avr_pgmspace, 279
strcpy_PF
avr_pgmspace, 279
strcspn
avr_string, 209
strcspn_P
avr_pgmspace, 280
strdup
avr_string, 209
strftime
avr_time, 224
string.h, 384
strlcat
avr_string, 210
strlcat_P
avr_pgmspace, 280
strlcat_PF
avr_pgmspace, 280
strlcpy
avr_string, 210
strlcpy_P
avr_pgmspace, 281
strlcpy_PF
avr_pgmspace, 281
strlen
avr_string, 211
strlen_P
avr_pgmspace, 281
strlen_PF
avr_pgmspace, 282
Generated on Wed Jul 25 09:38:10 2018 for avr-libc by Doxygen
INDEX 409
strlwr
avr_string, 211
strncasecmp
avr_string, 211
strncasecmp_P
avr_pgmspace, 282
strncasecmp_PF
avr_pgmspace, 282
strncat
avr_string, 212
strncat_P
avr_pgmspace, 283
strncat_PF
avr_pgmspace, 283
strncmp
avr_string, 212
strncmp_P
avr_pgmspace, 283
strncmp_PF
avr_pgmspace, 284
strncpy
avr_string, 212
strncpy_P
avr_pgmspace, 284
strncpy_PF
avr_pgmspace, 284
strnlen
avr_string, 212
strnlen_P
avr_pgmspace, 285
strnlen_PF
avr_pgmspace, 285
strpbrk
avr_string, 213
strpbrk_P
avr_pgmspace, 286
strrchr
avr_string, 213
strrchr_P
avr_pgmspace, 286
strrev
avr_string, 213
strsep
avr_string, 214
strsep_P
avr_pgmspace, 286
strspn
avr_string, 214
strspn_P
avr_pgmspace, 286
strstr
avr_string, 214
strstr_P
avr_pgmspace, 287
strstr_PF
avr_pgmspace, 287
strtod
avr_stdlib, 200
strtok
avr_string, 214
strtok_P
avr_pgmspace, 287
strtok_r
avr_string, 215
strtok_rP
avr_pgmspace, 288
strtol
avr_stdlib, 200
strtoul
avr_stdlib, 201
strupr
avr_string, 215
sun_rise
avr_time, 224
sun_set
avr_time, 224
supported devices, 2
system_tick
avr_time, 224
tan
avr_math, 159
tanf
avr_math, 154
tanh
avr_math, 159
tanhf
avr_math, 154
time
avr_time, 224
time.h, 385
time_t
avr_time, 219
timer_enable_int
deprecated_items, 324
tm, 363
tm_hour, 364
tm_isdst, 364
tm_mday, 364
tm_min, 364
Generated on Wed Jul 25 09:38:10 2018 for avr-libc by Doxygen
INDEX 410
tm_mon, 364
tm_sec, 364
tm_wday, 364
tm_yday, 364
tm_year, 364
tm_hour
tm, 364
tm_isdst
tm, 364
tm_mday
tm, 364
tm_min
tm, 364
tm_mon
tm, 364
tm_sec
tm, 364
tm_wday
tm, 364
tm_yday
tm, 364
tm_year
tm, 364
toascii
ctype, 132
tolower
ctype, 132
tools, optional, 88
tools, required, 88
toupper
ctype, 132
trunc
avr_math, 159
truncf
avr_math, 154
TW_BUS_ERROR
util_twi, 318
TW_MR_ARB_LOST
util_twi, 318
TW_MR_DATA_ACK
util_twi, 318
TW_MR_DATA_NACK
util_twi, 318
TW_MR_SLA_ACK
util_twi, 318
TW_MR_SLA_NACK
util_twi, 318
TW_MT_ARB_LOST
util_twi, 318
TW_MT_DATA_ACK
util_twi, 318
TW_MT_DATA_NACK
util_twi, 318
TW_MT_SLA_ACK
util_twi, 318
TW_MT_SLA_NACK
util_twi, 319
TW_NO_INFO
util_twi, 319
TW_READ
util_twi, 319
TW_REP_START
util_twi, 319
TW_SR_ARB_LOST_GCALL_ACK
util_twi, 319
TW_SR_ARB_LOST_SLA_ACK
util_twi, 319
TW_SR_DATA_ACK
util_twi, 319
TW_SR_DATA_NACK
util_twi, 319
TW_SR_GCALL_ACK
util_twi, 319
TW_SR_GCALL_DATA_ACK
util_twi, 319
TW_SR_GCALL_DATA_NACK
util_twi, 319
TW_SR_SLA_ACK
util_twi, 320
TW_SR_STOP
util_twi, 320
TW_ST_ARB_LOST_SLA_ACK
util_twi, 320
TW_ST_DATA_ACK
util_twi, 320
TW_ST_DATA_NACK
util_twi, 320
TW_ST_LAST_DATA
util_twi, 320
TW_ST_SLA_ACK
util_twi, 320
TW_START
util_twi, 320
TW_STATUS
util_twi, 320
TW_STATUS_MASK
util_twi, 320
TW_WRITE
util_twi, 321
twi.h, 387
Generated on Wed Jul 25 09:38:10 2018 for avr-libc by Doxygen
INDEX 411
UBRR_VALUE
util_setbaud, 316
UBRRH_VALUE
util_setbaud, 316
UBRRL_VALUE
util_setbaud, 316
UINT16_C
avr_stdint, 169
UINT16_MAX
avr_stdint, 169
uint16_t
avr_stdint, 172
UINT32_C
avr_stdint, 169
UINT32_MAX
avr_stdint, 169
uint32_t
avr_stdint, 172
UINT64_C
avr_stdint, 169
UINT64_MAX
avr_stdint, 169
uint64_t
avr_stdint, 172
UINT8_C
avr_stdint, 169
UINT8_MAX
avr_stdint, 169
uint8_t
avr_stdint, 172
uint_farptr_t
avr_inttypes, 147
UINT_FAST16_MAX
avr_stdint, 169
uint_fast16_t
avr_stdint, 172
UINT_FAST32_MAX
avr_stdint, 169
uint_fast32_t
avr_stdint, 173
UINT_FAST64_MAX
avr_stdint, 170
uint_fast64_t
avr_stdint, 173
UINT_FAST8_MAX
avr_stdint, 170
uint_fast8_t
avr_stdint, 173
UINT_LEAST16_MAX
avr_stdint, 170
uint_least16_t
avr_stdint, 173
UINT_LEAST32_MAX
avr_stdint, 170
uint_least32_t
avr_stdint, 173
UINT_LEAST64_MAX
avr_stdint, 170
uint_least64_t
avr_stdint, 173
UINT_LEAST8_MAX
avr_stdint, 170
uint_least8_t
avr_stdint, 173
UINTMAX_C
avr_stdint, 170
UINTMAX_MAX
avr_stdint, 170
uintmax_t
avr_stdint, 173
UINTPTR_MAX
avr_stdint, 170
uintptr_t
avr_stdint, 173
ultoa
avr_stdlib, 201
ungetc
avr_stdio, 185
UNIX_OFFSET
avr_time, 219
USE_2X
util_setbaud, 316
Using the standard IO facilities, 350
util_atomic
ATOMIC_BLOCK, 305
ATOMIC_FORCEON, 305
ATOMIC_RESTORESTATE, 305
NONATOMIC_BLOCK, 305
NONATOMIC_FORCEOFF, 306
NONATOMIC_RESTORESTATE,
306
util_crc
_crc16_update, 307
_crc8_ccitt_update, 308
_crc_ccitt_update, 308
_crc_ibutton_update, 309
_crc_xmodem_update, 310
util_delay
_delay_ms, 311
_delay_us, 312
Generated on Wed Jul 25 09:38:10 2018 for avr-libc by Doxygen
INDEX 412
F_CPU, 311
util_delay_basic
_delay_loop_1, 313
_delay_loop_2, 313
util_parity
parity_even_bit, 314
util_setbaud
BAUD_TOL, 316
UBRR_VALUE, 316
UBRRH_VALUE, 316
UBRRL_VALUE, 316
USE_2X, 316
util_twi
TW_BUS_ERROR, 318
TW_MR_ARB_LOST, 318
TW_MR_DATA_ACK, 318
TW_MR_DATA_NACK, 318
TW_MR_SLA_ACK, 318
TW_MR_SLA_NACK, 318
TW_MT_ARB_LOST, 318
TW_MT_DATA_ACK, 318
TW_MT_DATA_NACK, 318
TW_MT_SLA_ACK, 318
TW_MT_SLA_NACK, 319
TW_NO_INFO, 319
TW_READ, 319
TW_REP_START, 319
TW_SR_ARB_LOST_GCALL_-
ACK, 319
TW_SR_ARB_LOST_SLA_ACK,
319
TW_SR_DATA_ACK, 319
TW_SR_DATA_NACK, 319
TW_SR_GCALL_ACK, 319
TW_SR_GCALL_DATA_ACK, 319
TW_SR_GCALL_DATA_NACK,
319
TW_SR_SLA_ACK, 320
TW_SR_STOP, 320
TW_ST_ARB_LOST_SLA_ACK,
320
TW_ST_DATA_ACK, 320
TW_ST_DATA_NACK, 320
TW_ST_LAST_DATA, 320
TW_ST_SLA_ACK, 320
TW_START, 320
TW_STATUS, 320
TW_STATUS_MASK, 320
TW_WRITE, 321
utoa
avr_stdlib, 202
vfprintf
avr_stdio, 186
vfprintf_P
avr_stdio, 188
vfscanf
avr_stdio, 188
vfscanf_P
avr_stdio, 191
vprintf
avr_stdio, 191
vscanf
avr_stdio, 191
vsnprintf
avr_stdio, 191
vsnprintf_P
avr_stdio, 191
vsprintf
avr_stdio, 191
vsprintf_P
avr_stdio, 191
wdt.h, 388
wdt_reset
avr_watchdog, 301
WDTO_120MS
avr_watchdog, 301
WDTO_15MS
avr_watchdog, 301
WDTO_1S
avr_watchdog, 301
WDTO_250MS
avr_watchdog, 301
WDTO_2S
avr_watchdog, 301
WDTO_30MS
avr_watchdog, 301
WDTO_4S
avr_watchdog, 302
WDTO_500MS
avr_watchdog, 302
WDTO_60MS
avr_watchdog, 302
WDTO_8S
avr_watchdog, 302
week
week_date, 365
week_date, 365
day, 365
Generated on Wed Jul 25 09:38:10 2018 for avr-libc by Doxygen
INDEX 413
week, 365
year, 365
week_of_month
avr_time, 224
week_of_year
avr_time, 225
year
week_date, 365
Generated on Wed Jul 25 09:38:10 2018 for avr-libc by Doxygen

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