AVR-LibC

Introduction

The latest version of this document is always available from https://avrdudes.github.io/avr-libc/

This documentation is distributed under the same licensing conditions as the entire library itself, see License below.

The AVR-LibC package provides a subset of the standard C library for Microchip (formerly 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.

Note

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 to ensure the issue won't be forgotten.

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 I/O 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.

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 to support these devices at library compile-time.

megaAVR Devices:

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, ATmega324PB, ATmega325, ATmega325A, ATmega325P, ATmega325PA, ATmega3250, ATmega3250A, ATmega3250P, ATmega3250PA, ATmega328, ATmega328P, ATmega328PB, 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

megaAVR 0-Series Devices:

ATmega808, ATmega809, ATmega1608, ATmega1609, ATmega3208, ATmega3209, ATmega4808, ATmega4809

tinyAVR Devices:

ATtiny11 [1], ATtiny12 [1], ATtiny13, ATtiny13A, ATtiny15 [1], ATtiny22, ATtiny24, ATtiny24A, ATtiny25, ATtiny26, ATtiny261, ATtiny261A, ATtiny28 [1], ATtiny2313, ATtiny2313A, ATtiny4313, ATtiny43U, ATtiny44, ATtiny44A, ATtiny441, ATtiny45, ATtiny461, ATtiny461A, ATtiny48, ATtiny828, ATtiny84, ATtiny84A, ATtiny841, ATtiny85, ATtiny861, ATtiny861A, ATtiny88, ATtiny1634

tinyAVR 0-Series Devices:

ATtiny202, ATtiny204, ATtiny402, ATtiny404, ATtiny406, ATtiny804, ATtiny806, ATtiny807, ATtiny1604, ATtiny1606, ATtiny1607

tinyAVR 1-Series Devices:

ATtiny212, ATtiny214, ATtiny412, ATtiny414, ATtiny416, ATtiny417, ATtiny814, ATtiny816, ATtiny817, ATtiny1614, ATtiny1616, ATtiny1617, ATtiny3214, ATtiny3216, ATtiny3217

tinyAVR 2-Series Devices:

ATtiny424, ATtiny426, ATtiny427, ATtiny824, ATtiny826, ATtiny827, ATtiny1624, ATtiny1626, ATtiny1627, ATtiny3224, ATtiny3226, ATtiny3227

Reduced tinyAVR Devices with only 16 GPRs:

ATtiny4, ATtiny5, ATtiny9, ATtiny10, ATtiny102, ATtiny104, ATtiny20, ATtiny40

Automotive AVR Devices:

ATtiny87, ATtiny167, ATA5505, ATA5272, ATA5702M322, ATA5782, ATA5790, ATA5790N, ATA5831, ATA5795, ATA6285, ATA6286, ATA6289, ATA6612C, ATA6613C, ATA6614Q, ATA6616C, ATA6617C, ATA664251

Automotive CAN AVR Devices:

ATmega16M1, ATmega32C1, ATmega32M1, ATmega64C1, ATmega64M1

CAN AVR Devices:

AT90CAN32, AT90CAN64, AT90CAN128

LCD AVR Devices:

ATmega169, ATmega169A, ATmega169P, ATmega169PA, ATmega329, ATmega329A, ATmega329P, ATmega329PA, ATmega3290, ATmega3290A, 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, ATmega64HVE2, ATmega406

USB AVR Devices:

AT76C711 [3], AT90USB82, AT90USB162, AT90USB646, AT90USB647, AT90USB1286, AT90USB1287, ATmega8U2, ATmega16U2, ATmega16U4, ATmega32U2, ATmega32U4, ATmega32U6, AT43USB320, AT43USB355

XMEGA Devices:

ATxmega8E5, ATxmega16A4, ATxmega16D4, ATxmega32A4, ATxmega32D3, ATxmega32D4, ATxmega32E5, ATxmega64A1, ATxmega64A3, ATxmega64D3, ATxmega64D4, ATxmega128A1, ATxmega128A3, ATxmega128D3, ATxmega128D4, ATxmega192A3, ATxmega192D3, ATxmega256A3, ATxmega256A3B, ATxmega256D3

USB XMEGA Devices:

ATxmega16A4U, ATxmega16C4, ATxmega32A4U, ATxmega32C3, ATxmega32C4, ATxmega64A1U, ATxmega64A3U, ATxmega64A4U, ATxmega64B1, ATxmega64B3, ATxmega64C3, ATxmega128A1U, ATxmega128A3U, ATxmega128A4U, ATxmega128B1, ATxmega128B3, ATxmega128C3, ATxmega192A3U, ATxmega192C3, ATxmega256A3U, ATxmega256A3BU, ATxmega256C3, ATxmega384C3, ATxmega384D3

AVR-Dx Devices:

AVR16DD14, AVR16DD20, AVR16DD28, AVR16DD32, AVR32DA28, AVR32DA32, AVR32DA48, AVR32DB28, AVR32DB32, AVR32DB48, AVR32DD14, AVR32DD20, AVR32DD28, AVR32DD32, AVR64DA28, AVR64DA32, AVR64DA48, AVR64DA64, AVR64DB28, AVR64DB32, AVR64DB48, AVR64DB64, AVR64DD14, AVR64DD20, AVR64DD28, AVR64DD32, AVR128DA28, AVR128DA32, AVR128DA48, AVR128DA64, AVR128DB28, AVR128DB32, AVR128DB48, AVR128DB64

USB AVR-Dx Devices:

AVR64DU28, AVR64DU32

AVR-Ex Devices:

AVR16EA28, AVR16EA32, AVR16EA48, AVR16EB14, AVR16EB20, AVR16EB28, AVR16EB32, AVR32EA28, AVR32EA32, AVR32EA48, AVR64EA28, AVR64EA32, AVR64EA48

Wireless AVR Devices:

ATmega644RFR2, ATmega64RFR2, ATmega128RFA1, ATmega1284RFR2, ATmega128RFR2, ATmega2564RFR2, ATmega256RFR2

Miscellaneous Devices:

AT94K [2], AT86RF401, AT90SCR100, M3000 [4]

Classic AVR Devices:

AT90S1200 [1], AT90S2313, 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.

AVR-LibC License

AVR-LibC can be freely used and redistributed, provided the following license conditions are met.

The contents of AVR-LibC are licensed with a Modified BSD License.

All of this is supposed to be Free Software, Open Source, DFSG-free,
GPL-compatible, and OK to use in both free and proprietary applications.

See the license information in the individual source files for details.

Additions and corrections to this file are welcome.

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Portions of avr-libc are Copyright (c) 1999-2024
Werner Boellmann,
Dean Camera,
Pieter Conradie,
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Michael Stumpf,
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egnite Software GmbH,
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