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 startup code needed by most applications.
There is a wealth of information in this document which goes beyond simply describing 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 Questions chapter of this document.
If you think you've found a bug, or have a suggestion for an improvement, either 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.
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.
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.
atmega103
atmega128
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
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
atmega88
atmega88a
atmega88p
atmega88pa
atmega88pb
atmega8515
atmega8535
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
attiny43u
attiny44
attiny44a
attiny441
attiny45
attiny461
attiny461a
attiny48
attiny828
attiny84
attiny84a
attiny841
attiny85
attiny861
attiny861a
attiny87
attiny88
attiny1634
atmega16m1
atmega32c1
atmega32m1
atmega64c1
atmega64m1
attiny167
ata5505
ata5272
ata5702m322
ata5782
ata5790
ata5790n
ata5791
ata5795
ata5831
ata6612c
ata6613c
ata6614q
ata6616c
ata6617c
ata664251
ata8210
ata8510
at90can32
at90can64
at90can128
atmega169
atmega169a
atmega169p
atmega169pa
atmega329
atmega329a
atmega329p
atmega329pa
atmega3290
atmega3290a
atmega3290p
atmega3290pa
atmega649
atmega649a
atmega6490
atmega6490a
atmega6490p
atmega649p
at90pwm1
at90pwm2
at90pwm2b
at90pwm216
at90pwm3
at90pwm3b
at90pwm316
at90pwm161
at90pwm81
atmega8hva
atmega16hva
atmega16hva2
atmega16hvb
atmega16hvbrevb
atmega32hvb
atmega32hvbrevb
atmega64hve
atmega64hve2
atmega406
at90usb82
at90usb162
at90usb646
at90usb647
at90usb1286
at90usb1287
atmega8u2
atmega16u2
atmega16u4
atmega32u2
atmega32u4
atmega32u6
atxmega8e5
atxmega16a4
atxmega16a4u
atxmega16c4
atxmega16d4
atxmega16e5
atxmega32a4
atxmega32a4u
atxmega32c3
atxmega32c4
atxmega32d3
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
atxmega256c3
atxmega256d3
atxmega384c3
atxmega384d3
atmega644rfr2
atmega64rfr2
atmega128rfa1
atmega1284rfr2
atmega128rfr2
atmega2564rfr2
atmega256rfr2
at90s1200 [1]
at90s2313
at90s2323
at90s2333
at90s2343
at90s4414
at90s4433
at90s4434
at90s8515
at90c8534
at90s8535
[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.
[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.]
[3] The at76c711 is a USB to fast serial interface bridge chip using an AVR core.
[4] The m3000 is a motor controller AVR ASIC from Intelligent Motion Systems (IMS) / Schneider Electric.
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, 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.