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avr-libc Reference Manual
1.4.0
Generated by Doxygen 1.4.1
Sat Nov 19 23:00:48 2005
CONTENTS
Contents
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General information about this library
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3 avr-libc Data Structure Index
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5 avr-libc Module Documentation
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<avr/boot.h>: Bootloader Support Utilities
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<avr/eeprom.h>: EEPROM handling
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<avr/io.h>: AVR device-specific IO definitions
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<avr/pgmspace.h>: Program Space String Utilities
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CONTENTS ii
Additional notes from <avr/sfr_defs.h>
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<avr/sleep.h>: Power Management and Sleep Modes
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<avr/version.h>: avr-libc version macros
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<avr/wdt.h>: Watchdog timer handling
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5.10 <compat/deprecated.h>: Deprecated items
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5.11 <compat/ina90.h>: Compatibility with IAR EWB 3.x
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5.12 <ctype.h>: Character Operations
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5.14 <inttypes.h>: Integer Type conversions
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5.16 <setjmp.h>: Non-local goto
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CONTENTS iii
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5.17 <stdint.h>: Standard Integer Types
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5.18 <stdio.h>: Standard IO facilities
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5.19 <stdlib.h>: General utilities
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5.21 <util/crc16.h>: CRC Computations
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5.22 <util/delay.h>: Busy-wait delay loops
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5.23 <util/parity.h>: Parity bit generation
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5.24 <util/twi.h>: TWI bit mask definitions
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CONTENTS iv
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5.25 <avr/interrupt.h>: Interrupts
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5.26 <avr/sfr_defs.h>: Special function registers
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5.28.4 Examining the Object File
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5.29 Example using the two-wire interface (TWI)
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5.29.2 The TWI example project
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6 avr-libc Data Structure Documentation
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CONTENTS v
avr-libc and assembler programs
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My program doesn’t recognize a variable updated within an interrupt routine
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I get "undefined reference to..." for functions like "sin()"
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How to permanently bind a variable to a register?
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How to modify MCUCR or WDTCR early?
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What is all this _BV() stuff about?
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Shouldn’t I initialize all my variables?
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Why do some 16-bit timer registers sometimes get trashed?
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7.3.10 How do I use a #define’d constant in an asm statement?
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7.3.11 Why does the PC randomly jump around when single-stepping through my program in avr-gdb?
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7.3.12 How do I trace an assembler file in avr-gdb?
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7.3.13 How do I pass an IO port as a parameter to a function?
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7.3.14 What registers are used by the C compiler?
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7.3.15 How do I put an array of strings completely in ROM?
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7.3.16 How to use external RAM?
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7.3.18 How do I relocate code to a fixed address?
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7.3.19 My UART is generating nonsense! My ATmega128 keeps crashing! Port F is completely broken!
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7.3.20 Why do all my "foo...bar" strings eat up the SRAM?
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7.3.22 How to detect RAM memory and variable overlap problems?
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CONTENTS vi
7.3.23 Is it really impossible to program the ATtinyXX in C?
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7.3.24 What is this "clock skew detected" messsage?
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7.3.25 Why are (many) interrupt flags cleared by writing a logical 1?
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7.3.26 Why have "programmed" fuses the bit value 0?
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7.3.27 Which AVR-specific assembler operators are available?
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C Names Used in Assembler Code
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Release Numbering and Methodology
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Release Version Numbering Scheme
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Using Sections in Assembler Code
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1 AVR Libc 1
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GNU Binutils for the AVR target
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7.10.1 Options for the C compiler avr-gcc
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7.10.2 Options for the assembler avr-as
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7.10.3 Controlling the linker avr-ld
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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 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
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1.2
General information about this library 2 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
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 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 guarenteed 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 context, undefined behaviour will result.
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.
AT90S Type Devices:
• at90s1200
• at90s2313
• at90s2323
• at90s2333
• at90s2343
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1.3
Supported Devices
• at90s4414
• at90s4433
• at90s4434
• at90s8515
• at90c8534
• at90s8535
• at90can32
• at90can64
• at90can128
ATmega Type Devices:
• atmega8
• atmega103
• atmega128
• atmega1280
• atmega1281
• atmega16
• atmega161
• atmega162
• atmega163
• atmega164
• atmega165
• atmega168
• atmega169
• atmega32
• atmega323
• atmega324
• atmega325
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3
1.3
Supported Devices
• atmega3250
• atmega329
• atmega3290
• atmega48
• atmega64
• atmega640
• atmega644
• atmega645
• atmega6450
• atmega649
• atmega6490
• atmega8515
• atmega8535
• atmega88
ATtiny Type Devices:
• attiny11
• attiny12
• attiny13
• attiny15
• attiny22
• attiny25
• attiny26
• attiny28
• attiny2313
• attiny45
• attiny85
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4
2 avr-libc Module Index
Misc Devices:
• at94K
• at76c711
• at43usb320
• at43usb355
• at86rf401
• at90pwm2/at90pwm3
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
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.
2 avr-libc Module Index
2.1
avr-libc Modules
Here is a list of all modules:
<assert.h>: Diagnostics
<avr/boot.h>: Bootloader Support Utilities
<avr/eeprom.h>: EEPROM handling
<avr/io.h>: AVR device-specific IO definitions
<avr/pgmspace.h>: Program Space String Utilities
5
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2.1
avr-libc Modules
<avr/sleep.h>: Power Management and Sleep Modes
<avr/version.h>: avr-libc version macros
<avr/wdt.h>: Watchdog timer handling
<compat/deprecated.h>: Deprecated items
<compat/ina90.h>: Compatibility with IAR EWB 3.x
<ctype.h>: Character Operations
<errno.h>: System Errors
<inttypes.h>: Integer Type conversions
<math.h>: Mathematics
<setjmp.h>: Non-local goto
<stdint.h>: Standard Integer Types
<stdio.h>: Standard IO facilities
<stdlib.h>: General utilities
<string.h>: Strings
<util/crc16.h>: CRC Computations
<util/delay.h>: Busy-wait delay loops
<util/parity.h>: Parity bit generation
<util/twi.h>: TWI bit mask definitions
<avr/interrupt.h>: Interrupts
<avr/sfr_defs.h>: Special function registers
Additional notes from <avr/sfr_defs.h>
Demo projects
A simple project
Example using the two-wire interface (TWI)
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3 avr-libc Data Structure Index
3 avr-libc Data Structure Index
3.1
avr-libc Data Structures
Here are the data structures with brief descriptions:
4 avr-libc Page Index
4.1
avr-libc Related Pages
Here is a list of all related documentation pages:
Acknowledgments avr-libc and assembler programs
Frequently Asked Questions
Inline Asm
Using malloc()
Release Numbering and Methodology
Memory Sections
Installing the GNU Tool Chain
Using the avrdude program
Using the GNU tools
Todo List
Deprecated List
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5 avr-libc Module Documentation 8
5 avr-libc Module Documentation
5.1
<assert.h>: Diagnostics
5.1.1
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
will be called to halt the application.
Defines
• #define
5.1.2
Define Documentation
5.1.2.1
#define assert(expression)
Parameters: expression Expression to test for.
The
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
is called, effectively terminating the program.
If expression is true, the
macro does nothing.
The
macro may be removed at compile time by defining NDEBUG as a macro
(e.g., by using the compiler option -DNDEBUG).
5.2
<avr/boot.h>: Bootloader Support Utilities
5.2.1
Detailed Description
#include <avr/io.h>
#include <avr/boot.h>
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5.2
<avr/boot.h>: Bootloader Support Utilities 9
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.
Note:
Not all AVR processors provide bootloader support. See your processor datasheet to see if it provides bootloader support.
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); boot_spm_busy_wait();
// Store buffer in flash page.
// 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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5.2
<avr/boot.h>: Bootloader Support Utilities 10
}
// Re-enable interrupts (if they were ever enabled).
SREG = sreg;
Defines
• #define
__attribute__ ((section (".bootloader")))
• #define
() (__SPM_REG |= ( uint8_t )_BV(SPMIE))
• #define
(__SPM_REG &=
BV(SPMIE))
• #define
() (__SPM_REG & ( uint8_t )_BV(SPMIE))
• #define
() (__SPM_REG & ( uint8_t )_BV(__COMMON_ASB))
• #define
() (__SPM_REG & ( uint8_t )_BV(SPMEN))
• #define
boot_spm_busy_wait () do{}while(boot_spm_busy())
• #define
(0x0000)
• #define
(0x0001)
• #define
(0x0002)
• #define
(0x0003)
• #define
boot_lock_fuse_bits_get (address)
• #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
• #define
boot_lock_bits_set_safe (lock_bits)
5.2.2
Define Documentation
5.2.2.1
#define boot_is_spm_interrupt() (__SPM_REG &
BV(SPMIE))
Check if the SPM interrupt is enabled.
5.2.2.2
#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.
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5.2
<avr/boot.h>: Bootloader Support Utilities 11
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 (BLB12));
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.
5.2.2.3
#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
except waits for eeprom and spm operations to complete before setting the lock bits.
5.2.2.4
#define boot_lock_fuse_bits_get(address)
Value:
(__extension__({ uint8_t __result;
__asm__ __volatile__
(
"ldi r30, %3\n\t"
"ldi r31, 0\n\t"
"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),
"M" (address)
: "r0", "r30", "r31"
);
__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.
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5.2
<avr/boot.h>: Bootloader Support Utilities 12
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.
5.2.2.5
#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.
5.2.2.6
#define boot_page_erase_safe(address)
Value: do { \ boot_spm_busy_wait(); eeprom_busy_wait(); boot_page_erase (address);
} while (0)
\
\
\
Same as
except it waits for eeprom and spm operations to complete before erasing the page.
5.2.2.7
#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.
5.2.2.8
#define boot_page_fill_safe(address, data)
Value: do { \ boot_spm_busy_wait(); eeprom_busy_wait(); boot_page_fill(address, data);
} while (0)
\
\
\
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5.2
<avr/boot.h>: Bootloader Support Utilities 13
Same as
except it waits for eeprom and spm operations to complete before filling the page.
5.2.2.9
#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.
5.2.2.10
#define boot_page_write_safe(address)
Value: do { \ boot_spm_busy_wait(); eeprom_busy_wait(); boot_page_write (address);
} while (0)
\
\
\
Same as
except it waits for eeprom and spm operations to complete before writing the page.
5.2.2.11
#define boot_rww_busy() (__SPM_REG &
COMMON_ASB))
Check if the RWW section is busy.
5.2.2.12
#define boot_rww_enable() __boot_rww_enable()
Enable the Read-While-Write memory section.
5.2.2.13
#define boot_rww_enable_safe()
Value: do { \ boot_spm_busy_wait(); eeprom_busy_wait(); boot_rww_enable();
} while (0)
\
\
\
Same as
except waits for eeprom and spm operations to complete before enabling the RWW mameory.
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5.2
<avr/boot.h>: Bootloader Support Utilities 14
5.2.2.14
#define boot_spm_busy() (__SPM_REG & ( uint8_t )_BV(SPMEN))
Check if the SPM instruction is busy.
5.2.2.15
#define boot_spm_busy_wait() do{}while(boot_spm_busy())
Wait while the SPM instruction is busy.
5.2.2.16
#define boot_spm_interrupt_disable() (__SPM_REG &= ( uint8_t )∼_-
BV(SPMIE))
Disable the SPM interrupt.
5.2.2.17
#define boot_spm_interrupt_enable() (__SPM_REG |= ( uint8_t )_-
BV(SPMIE))
Enable the SPM interrupt.
5.2.2.18
#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.
5.2.2.19
#define GET_EXTENDED_FUSE_BITS (0x0002) address to read the extended fuse bits, using boot_lock_fuse_bits_get
5.2.2.20
#define GET_HIGH_FUSE_BITS (0x0003) address to read the high fuse bits, using boot_lock_fuse_bits_get
5.2.2.21
#define GET_LOCK_BITS (0x0001) address to read the lock bits, using boot_lock_fuse_bits_get
5.2.2.22
#define GET_LOW_FUSE_BITS (0x0000) address to read the low fuse bits, using boot_lock_fuse_bits_get
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5.3
<avr/eeprom.h>: EEPROM handling 15
5.3
<avr/eeprom.h>: EEPROM handling
5.3.1
Detailed Description
#include <avr/eeprom.h>
This header file declares the interface to some simple library routines suitable for handling 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.
Note:
All of the read/write functions first make sure the EEPROM is ready to be accessed. Since this may cause long delays if a write operation is still pending, timecritical applications should first poll the EEPROM e. g. using
before attempting any actual I/O.
This header file declares inline functions that call the assembler subroutines directly. This prevents that the compiler generates push/pops for the call-clobbered registers. This way also a specific calling convention could be used for the eeprom routines e.g. by passing values in __tmp_reg__, eeprom addresses in X and memory addresses in Z registers. Method is optimized for code size.
Presently supported are two locations of the EEPROM register set:
0x1F,0x20,0x21 and 0x1C,0x1D,0x1E (see
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).
avr-libc declarations
• #define
__attribute__((section(".eeprom")))
• #define
• #define
eeprom_busy_wait () do {} while (!eeprom_is_ready())
•
(const
∗addr)
•
(const
∗addr)
• void
(void ∗pointer_ram, const void ∗pointer_eeprom, size_t n)
• void
∗addr,
value)
• void
∗addr,
value)
• void
(const void ∗pointer_ram, void ∗pointer_eeprom, size_t n)
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5.3
<avr/eeprom.h>: EEPROM handling 16
IAR C compatibility defines
• #define
(addr, val) eeprom_write_byte (( uint8_t ∗)(addr), ( uint8_t )(val))
• #define
(var, addr) (var) = eeprom_read_byte (( uint8_t
∗)(addr))
Defines
• #define
1C1D1E
5.3.2
Define Documentation
5.3.2.1
#define __EEPROM_REG_LOCATIONS__ 1C1D1E
In order to be able to work without a requiring a multilib approach for dealing with controllers having the EEPROM registers at different positions in memory space, the eeprom functions evaluate __EEPROM_REG_LOCATIONS__: It is assumed to be defined by the device io header and contains 6 uppercase hex digits encoding the addresses of EECR,EEDR and EEAR. First two letters: EECR address. Second two letters: EEDR address. Last two letters: EEAR address. The default 1C1D1E corresponds to the register location that is valid for most controllers. The value of this define symbol is used for appending it to the base name of the assembler functions.
5.3.2.2
#define _EEGET(var,
addr) (var) = eeprom_read_byte (( uint8_t
∗)(addr))
Read a byte from EEPROM. Compatibility define for IAR C.
5.3.2.3
#define _EEPUT(addr, val) eeprom_write_byte (( uint8_t
∗)(addr),
Write a byte to EEPROM. Compatibility define for IAR C.
5.3.2.4
#define EEMEM __attribute__((section(".eeprom")))
Attribute expression causing a variable to be allocated within the .eeprom section.
5.3.2.5
#define eeprom_busy_wait() do {} while (!eeprom_is_ready())
Loops until the eeprom is no longer busy.
Returns:
Nothing.
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5.4
<avr/io.h>: AVR device-specific IO definitions 17
5.3.2.6
#define eeprom_is_ready()
Returns:
1 if EEPROM is ready for a new read/write operation, 0 if not.
5.3.3
Function Documentation
5.3.3.1
void eeprom_read_block (void ∗ pointer_ram, const void ∗ pointer_eeprom, size_t n)
Read a block of n bytes from EEPROM address pointer_eeprom to pointer_ram . For constant n <= 256 bytes a library function is used. For block sizes unknown at compile time or block sizes > 256 an inline loop is expanded.
5.3.3.2
eeprom_read_byte (const
∗ addr)
Read one byte from EEPROM address addr.
5.3.3.3
eeprom_read_word (const
∗ addr)
Read one 16-bit word (little endian) from EEPROM address addr.
5.3.3.4
void eeprom_write_block (const void ∗ pointer_ram, void ∗ pointer_eeprom, size_t n)
Write a block of n bytes to EEPROM address pointer_eeprom from pointer_ram .
5.3.3.5
void eeprom_write_byte ( uint8_t
∗ addr,
value)
Write a byte value to EEPROM address addr.
5.3.3.6
void eeprom_write_word ( uint16_t
∗ addr,
value)
Write a word value to EEPROM address addr.
5.4
<avr/io.h>: AVR device-specific IO definitions
#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 diverting to the appropriate file <avr/ioXXXX.h> which should never be included directly. Some
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5.5
<avr/pgmspace.h>: Program Space String Utilities 18 register names common to all AVR devices are defined directly within <avr/io.h>, but most of the details come from the respective include file.
Note that this file always includes
#include <avr/sfr_defs.h>
See
<avr/sfr_defs.h>: Special function registers
for the details.
Included are definitions of the IO register set and their respective bit values as specified in the Atmel documentation. Note that Atmel is not very consistent in its 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 documented
Finally, the following macros are defined:
• RAMEND
A constant describing the last on-chip RAM location.
• XRAMEND
A constant describing the last possible location in RAM. This is equal to RA-
MEND for devices that do not allow for external RAM.
• E2END
A constant describing the address of the last EEPROM cell.
• FLASHEND
A constant describing the last byte address in flash ROM.
• SPM_PAGESIZE
For devices with bootloader support, the flash pagesize (in bytes) to be used for the SPM instruction.
5.5
<avr/pgmspace.h>: Program Space String Utilities
5.5.1
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.
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5.5
<avr/pgmspace.h>: Program Space String Utilities 19
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 standard string functions described in
If possible, put your constant tables in the lower 64K and use
or
instead of
or
since it is more efficient that way, and you can still use the upper 64K for executable code.
Defines
• #define
__ATTR_PROGMEM__
• #define
PSTR (s) ((const PROGMEM char ∗)(s))
• #define
(address_short) __LPM(( uint16_t )(address_short))
• #define
• #define
pgm_read_dword_near (address_short)
__LPM_dword(( uint16_t )(address_short))
• #define
(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_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
const
∗
• #define
const
∗
Typedefs
• typedef void PROGMEM
• typedef char PROGMEM
• typedef unsigned char PROGMEM
• typedef
PROGMEM
• typedef
PROGMEM
• typedef
PROGMEM
• typedef
PROGMEM
• typedef
PROGMEM
• typedef
PROGMEM
• typedef
PROGMEM
• typedef
PROGMEM
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5.5
<avr/pgmspace.h>: Program Space String Utilities 20
Functions
• void ∗
(void ∗, PGM_VOID_P, size_t)
• int
(const char ∗, PGM_P) __ATTR_PURE__
• char ∗
(char ∗, PGM_P)
• int
(const char ∗, PGM_P) __ATTR_PURE__
• char ∗
(char ∗, PGM_P)
• size_t
(char ∗, PGM_P, size_t)
• size_t
(char ∗, PGM_P, size_t)
• size_t
(PGM_P) __ATTR_CONST__
• int
(const char ∗, PGM_P, size_t) __ATTR_PURE__
• char ∗
(char ∗, PGM_P, size_t)
• int
(const char ∗, PGM_P, size_t) __ATTR_PURE__
• char ∗
(char ∗, PGM_P, size_t)
• size_t
(PGM_P, size_t) __ATTR_CONST__
5.5.2
Define Documentation
5.5.2.1
#define PGM_P const
∗
Used to declare a variable that is a pointer to a string in program space.
5.5.2.2
#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.
5.5.2.3
#define
pgm_read_byte_far(address_long)
Read a byte from the program space with a 32-bit (far) address.
Note:
The address is a byte address. The address is in the program space.
5.5.2.4
#define
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.
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5.5
<avr/pgmspace.h>: Program Space String Utilities 21
5.5.2.5
#define near(address_short) pgm_read_dword(address_short) pgm_read_dword_-
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.
5.5.2.6
#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.
5.5.2.7
#define pgm_read_dword_near(address_short)
dword(( uint16_t )(address_short))
Read a double word from the program space with a 16-bit (near) address.
__LPM_-
Note:
The address is a byte address. The address is in the program space.
5.5.2.8
#define near(address_short) pgm_read_word(address_short)
Read a word from the program space with a 16-bit (near) address.
pgm_read_word_-
Note:
The address is a byte address. The address is in the program space.
5.5.2.9
#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.
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5.5
<avr/pgmspace.h>: Program Space String Utilities 22
5.5.2.10
#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.
5.5.2.11
#define PGM_VOID_P const
∗
Used to declare a generic pointer to an object in program space.
5.5.2.12
#define PROGMEM __ATTR_PROGMEM__
Attribute to use in order to declare an object being located in flash ROM.
5.5.2.13
#define PSTR(s) ((const PROGMEM char ∗)(s))
Used to declare a static pointer to a string in program space.
5.5.3
Typedef Documentation
5.5.3.1
Type of a "char" object located in flash ROM.
5.5.3.2
Type of an "int16_t" object located in flash ROM.
5.5.3.3
Type of an "int32_t" object located in flash ROM.
5.5.3.4
Type of an "int64_t" object located in flash ROM.
5.5.3.5
Type of an "int8_t" object located in flash ROM.
5.5.3.6
Type of an "unsigned char" object located in flash ROM.
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5.5
<avr/pgmspace.h>: Program Space String Utilities 23
5.5.3.7
Type of an "uint16_t" object located in flash ROM.
5.5.3.8
Type of an "uint32_t" object located in flash ROM.
5.5.3.9
Type of an "uint64_t" object located in flash ROM.
5.5.3.10
Type of an "uint8_t" object located in flash ROM.
5.5.3.11
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.
5.5.4
Function Documentation
5.5.4.1
void ∗ memcpy_P (void ∗ dest, PGM_VOID_P src, size_t n)
The
function is similar to
memcpy() , except the src string resides in pro-
gram space.
The
function returns a pointer to dest.
5.5.4.2
int strcasecmp_P (const char ∗ s1, PGM_P s2)
Compare two strings ignoring case.
The
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.
s2 A pointer to a string in the devices Flash.
The
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.
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5.5
<avr/pgmspace.h>: Program Space String Utilities 24
5.5.4.3
char ∗ strcat_P (char ∗ dest, PGM_P src)
The
function is similar to
except that the src string must be located in program space (flash).
The
function returns a pointer to the resulting string dest.
5.5.4.4
int strcmp_P (const char ∗ s1, PGM_P s2)
The
function is similar to
except that s2 is pointer to a string in program space.
The
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.
5.5.4.5
char ∗ strcpy_P (char ∗ dest, PGM_P src)
The
function is similar to
except that src is a pointer to a string in program space.
The
function returns a pointer to the destination string dest.
5.5.4.6
size_t strlcat_P (char ∗ dst, PGM_P, size_t siz)
Concatenate two strings.
The
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)).
The
function returns strlen(src) + MIN(siz, strlen(initial dst)). If retval
>= siz, truncation occurred.
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5.5
<avr/pgmspace.h>: Program Space String Utilities 25
5.5.4.7
size_t strlcpy_P (char ∗ dst, PGM_P, 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
function returns strlen(src). If retval >= siz, truncation occurred.
5.5.4.8
size_t strlen_P (PGM_P src)
The
function is similar to
strlen() , except that src is a pointer to a string in
program space.
The
function returns the number of characters in src.
5.5.4.9
int strncasecmp_P (const char ∗ s1, PGM_P s2, size_t n)
Compare two strings ignoring case.
The
function is similar to
strcasecmp_P() , except it only compares the
first n characters of s1.
Parameters: s1 A pointer to a string in the devices SRAM.
s2 A pointer to a string in the devices Flash.
n The maximum number of bytes to compare.
The
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.
5.5.4.10
char ∗ strncat_P (char ∗ dest, PGM_P src, size_t len)
Concatenate two strings.
The
function is similar to
strncat() , except that the src string must be located
in program space (flash).
The
function returns a pointer to the resulting string dest.
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5.6
Additional notes from <avr/sfr_defs.h> 26
5.5.4.11
int strncmp_P (const char ∗ s1, PGM_P s2, size_t n)
The
function is similar to
except it only compares the first (at most) n characters of s1 and s2.
The
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.
5.5.4.12
char ∗ strncpy_P (char ∗ dest, PGM_P src, size_t n)
The
function is similar to
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.
The
function returns a pointer to the destination string dest.
5.5.4.13
size_t strnlen_P (PGM_P src, size_t len)
Determine the length of a fixed-size string.
The
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.
5.6
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/iom128.h> to show how to define such macros:
#define PORTA _SFR_IO8(0x1b)
#define TCNT1 _SFR_IO16(0x2c)
#define PORTF _SFR_MEM8(0x61)
#define TCNT3 _SFR_MEM16(0x88)
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5.6
Additional notes from <avr/sfr_defs.h> 27
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 (addresses of the I/O registers). This is necessary when included in preprocessed assembler (∗.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 assembler 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 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).
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5.7
<avr/sleep.h>: Power Management and Sleep Modes 28
5.7
<avr/sleep.h>: Power Management and Sleep Modes
5.7.1
Detailed Description
#include <avr/sleep.h>
Use of the SLEEP instruction can allow your application to reduce it’s power comsumption considerably. AVR devices can be put into different sleep modes. Refer to the datasheet for the details relating to the device you are using.
Sleep Modes
Note:
Some of these modes are not available on all devices. See the datasheet for target device for the available sleep modes.
• #define
0
• #define
_BV(SM0)
• #define
_BV(SM1)
• #define
(_BV(SM0) | _BV(SM1))
• #define
(_BV(SM1) | _BV(SM2))
• #define
(_BV(SM0) | _BV(SM1) | _-
BV(SM2))
Sleep Functions
• void
mode)
• void
(void)
5.7.2
Define Documentation
5.7.2.1
#define SLEEP_MODE_ADC _BV(SM0)
ADC Noise Reduction Mode.
5.7.2.2
#define SLEEP_MODE_EXT_STANDBY (_BV(SM0) | _BV(SM1) | _-
BV(SM2))
Extended Standby Mode.
5.7.2.3
#define SLEEP_MODE_IDLE 0
Idle mode.
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5.8
<avr/version.h>: avr-libc version macros 29
5.7.2.4
#define SLEEP_MODE_PWR_DOWN _BV(SM1)
Power Down Mode.
5.7.2.5
#define SLEEP_MODE_PWR_SAVE (_BV(SM0) | _BV(SM1))
Power Save Mode.
5.7.2.6
#define SLEEP_MODE_STANDBY (_BV(SM1) | _BV(SM2))
Standby Mode.
5.7.3
Function Documentation
5.7.3.1
mode)
Select a sleep mode.
5.7.3.2
void sleep_mode (void)
Put the device in sleep mode. How the device is brought out of sleep mode depends on the specific mode selected with the
function. See the data sheet for your device for more details.
5.8
<avr/version.h>: avr-libc version macros
5.8.1
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.
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 backwardscompatible 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.
Defines
• #define
"1.4.0"
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5.8
<avr/version.h>: avr-libc version macros 30
• #define
10400UL
• #define
"20051119"
• #define
20051119UL
• #define
1
• #define
4
• #define
0
5.8.2
Define Documentation
5.8.2.1
#define __AVR_LIBC_DATE_ 20051119UL
Numerical representation of the release date.
5.8.2.2
#define __AVR_LIBC_DATE_STRING__ "20051119"
String literal representation of the release date.
5.8.2.3
#define __AVR_LIBC_MAJOR__ 1
Library major version number.
5.8.2.4
#define __AVR_LIBC_MINOR__ 4
Library minor version number.
5.8.2.5
#define __AVR_LIBC_REVISION__ 0
Library revision number.
5.8.2.6
#define __AVR_LIBC_VERSION__ 10400UL
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 monotonically increasing numerical value that can easily be used in numerical checks.
5.8.2.7
#define __AVR_LIBC_VERSION_STRING__ "1.4.0"
String literal representation of the current library version.
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5.9
<avr/wdt.h>: Watchdog timer handling 31
5.9
<avr/wdt.h>: Watchdog timer handling
5.9.1
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 configuration 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 option 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; void get_mcusr(void) \
__attribute__((naked)) \
__attribute__((section(".init3"))); void get_mcusr(void)
{ mcusr_mirror = MCUSR;
MCUSR = 0; wdt_disable();
}
Saving the value of MCUSR in mcusr_mirror is only needed if the application later wants to examine the reset source, but clearing in particular the watchdog reset flag before disabling the watchdog is required, according to the datasheet.
Defines
• #define
wdt_reset () __asm__ __volatile__ ("wdr")
• #define
• #define
wdt_enable (timeout) _wdt_write(timeout)
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5.9
<avr/wdt.h>: Watchdog timer handling 32
• #define
0
• #define
1
• #define
2
• #define
3
• #define
4
• #define
5
• #define
6
• #define
7
• #define
8
• #define
9
5.9.2
Define Documentation
5.9.2.1
#define wdt_disable()
Value:
__asm__ __volatile__ ( \
"in __tmp_reg__, __SREG__" "\n\t" \
"cli" "\n\t" \
"out %0, %1" "\n\t" \
"out %0, __zero_reg__" "\n\t" \
"out __SREG__,__tmp_reg__" "\n\t" \
: /* no outputs */ \
: "I" (_SFR_IO_ADDR(_WD_CONTROL_REG)), \
"r" ((uint8_t)(_BV(_WD_CHANGE_BIT) | _BV(WDE))) \
: "r0" \
)
Disable the watchdog timer, if possible. This attempts to turn off the Enable bit in the watchdog control register. See the datasheet for details.
5.9.2.2
#define wdt_enable(timeout) _wdt_write(timeout)
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.
5.9.2.3
#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.
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5.9
<avr/wdt.h>: Watchdog timer handling 33
5.9.2.4
#define WDTO_120MS 3
See WDT0_15MS
5.9.2.5
#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);
5.9.2.6
#define WDTO_1S 6
See WDT0_15MS
5.9.2.7
#define WDTO_250MS 4
See WDT0_15MS
5.9.2.8
#define WDTO_2S 7
See WDT0_15MS
5.9.2.9
#define WDTO_30MS 1
See WDT0_15MS
5.9.2.10
#define WDTO_4S 8
See WDT0_15MS Note: This is only available on the ATtiny2313, ATtiny25, ATtiny45, ATtiny85, ATmega48, ATmega88, ATmega164, ATmega168, ATmega324,
ATmega644, ATmega640, ATmega1280, ATmega1281, AT90PWM2, and the
AT90PWM3.
5.9.2.11
#define WDTO_500MS 5
See WDT0_15MS
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5.10
<compat/deprecated.h>: Deprecated items 34
5.9.2.12
#define WDTO_60MS 2
WDT0_15MS
5.9.2.13
#define WDTO_8S 9
See WDT0_15MS Note: This is only available on the ATtiny2313, ATtiny25, ATtiny45, ATtiny85, ATmega48, ATmega88, ATmega164, ATmega168, ATmega324,
ATmega644, ATmega640, ATmega1280, ATmega1281, AT90PWM2, and the
AT90PWM3.
5.10
<compat/deprecated.h>: Deprecated items
5.10.1
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/deprected.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.
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.
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5.10
<compat/deprecated.h>: Deprecated items 35
• #define
enable_external_int (mask) (__EICR = mask)
• #define
• static __inline__ void
(unsigned char ints)
Obsolete IO macros
Back in a time when AVR-GCC and avr-libc could not handle IO port access in the direct 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.
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
• #define
outp (port, val) (port) = (val)
• #define
sbi (port, bit) (port) |= (1 << (bit))
• #define
cbi (port, bit) (port) &= ∼(1 << (bit))
5.10.2
Define Documentation
5.10.2.1
#define cbi(port, bit) (port) &= ∼(1 << (bit))
Clear bit in IO port port.
5.10.2.2
#define enable_external_int(mask) (__EICR = mask)
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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5.10
<compat/deprecated.h>: Deprecated items
5.10.2.3
#define inp(port) (port)
Read a value from an IO port port.
5.10.2.4
#define INTERRUPT(signame)
Value: void signame (void) __attribute__ ((interrupt)); void signame (void)
\
36
Introduces an interrupt handler function that runs with global interrupts initially enabled. 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
5.10.2.5
#define outp(port, val) (port) = (val)
Write val to IO port port.
5.10.2.6
#define sbi(port, bit) (port) |= (1 << (bit))
Set bit in IO port port.
5.10.3
Function Documentation
5.10.3.1
static __inline__ void timer_enable_int (unsigned char ints)
[static]
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5.11
<compat/ina90.h>: Compatibility with IAR EWB 3.x
37
This function modifies the timsk register. The value you pass via ints is device specific.
5.11
<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% compatibility though.
Note:
For actual documentation, please see the IAR manual.
5.12
<ctype.h>: Character Operations
5.12.1
Detailed Description
These functions perform various operations on characters.
#include <ctype.h>
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.
returns true if its argument is any value ’0’ though ’9’, inclusive.)
• int
(int __c) __ATTR_CONST__
• int
(int __c) __ATTR_CONST__
• int
(int __c) __ATTR_CONST__
• int
(int __c) __ATTR_CONST__
• int
(int __c) __ATTR_CONST__
• int
(int __c) __ATTR_CONST__
• int
(int __c) __ATTR_CONST__
• int
(int __c) __ATTR_CONST__
• int
(int __c) __ATTR_CONST__
• int
(int __c) __ATTR_CONST__
• int
(int __c) __ATTR_CONST__
• int
(int __c) __ATTR_CONST__
• int
(int __c) __ATTR_CONST__
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5.12
<ctype.h>: Character Operations 38
Character convertion routines
If c is not an unsigned char value, or EOF, the behaviour of these functions is undefined.
• int
(int __c) __ATTR_CONST__
• int
(int __c) __ATTR_CONST__
• int
(int __c) __ATTR_CONST__
5.12.2
Function Documentation
5.12.2.1
int isalnum (int __c)
Checks for an alphanumeric character.
It is equivalent to (isalpha(c) || isdigit(c)) .
5.12.2.2
int isalpha (int __c)
Checks for an alphabetic character.
It is equivalent to (isupper(c) || islower(c)) .
5.12.2.3
int isascii (int __c)
Checks whether c is a 7-bit unsigned char value that fits into the ASCII character set.
5.12.2.4
int isblank (int __c)
Checks for a blank character, that is, a space or a tab.
5.12.2.5
int iscntrl (int __c)
Checks for a control character.
5.12.2.6
int isdigit (int __c)
Checks for a digit (0 through 9).
5.12.2.7
int isgraph (int __c)
Checks for any printable character except space.
5.12.2.8
int islower (int __c)
Checks for a lower-case character.
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5.13
<errno.h>: System Errors 39
5.12.2.9
int isprint (int __c)
Checks for any printable character including space.
5.12.2.10
int ispunct (int __c)
Checks for any printable character which is not a space or an alphanumeric character.
5.12.2.11
int isspace (int __c)
Checks for white-space characters. For the avr-libc library, these are: space, formfeed (’\f’), newline (’\n’), carriage return (’\r’), horizontal tab (’\t’), and vertical tab
(’\v’).
5.12.2.12
int isupper (int __c)
Checks for an uppercase letter.
5.12.2.13
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.
5.12.2.14
int toascii (int __c)
Converts c to 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.
5.12.2.15
int tolower (int __c)
Converts the letter c to lower case, if possible.
5.12.2.16
int toupper (int __c)
Converts the letter c to upper case, if possible.
5.13
<errno.h>: System Errors
5.13.1
Detailed Description
#include <errno.h>
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5.14
<inttypes.h>: Integer Type conversions 40
Some functions in the library set the global variable errno when an error occurs. The
>, provides symbolic names for various error codes.
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.
Defines
• #define
33
• #define
34
5.13.2
Define Documentation
5.13.2.1
#define EDOM 33
Domain error.
5.13.2.2
#define ERANGE 34
Range error.
5.14
<inttypes.h>: Integer Type conversions
5.14.1
Detailed Description
#include <inttypes.h>
This header file includes the exact-width integer definitions from < stdint.h
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
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
>, a macro will be supplied that portably allows formatting an object of that
type in
or
operations. Example:
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5.14
<inttypes.h>: Integer Type conversions 41
#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); macros for printf and scanf format specifiers
For C++, these are only included if __STDC_LIMIT_MACROS is defined before in-
• #define
"d"
• #define
"d"
• #define
"d"
• #define
"i"
• #define
"i"
• #define
"i"
• #define
"d"
• #define
"d"
• #define
"d"
• #define
"i"
• #define
"i"
• #define
"i"
• #define
"ld"
• #define
"ld"
• #define
"ld"
• #define
"li"
• #define
"li"
• #define
"li"
• #define
PRId16
• #define
PRIi16
• #define
"o"
• #define
"o"
• #define
"o"
• #define
"u"
• #define
"u"
• #define
"u"
• #define
"x"
• #define
"x"
• #define
"x"
• #define
"X"
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5.14
<inttypes.h>: Integer Type conversions
• #define
"X"
• #define
"X"
• #define
"o"
• #define
"o"
• #define
"o"
• #define
"u"
• #define
"u"
• #define
"u"
• #define
"x"
• #define
"x"
• #define
"x"
• #define
"X"
• #define
"X"
• #define
"X"
• #define
"lo"
• #define
"lo"
• #define
"lo"
• #define
"lu"
• #define
"lu"
• #define
"lu"
• #define
"lx"
• #define
"lx"
• #define
"lx"
• #define
"lX"
• #define
"lX"
• #define
"lX"
• #define
PRIo16
• #define
PRIu16
• #define
PRIx16
• #define
PRIX16
• #define
"d"
• #define
"d"
• #define
"d"
• #define
"i"
• #define
"i"
• #define
"i"
• #define
"ld"
• #define
"ld"
• #define
"ld"
• #define
"li"
• #define
"li"
• #define
"li"
• #define
SCNd16
Generated on Sat Nov 19 23:00:48 2005 for avr-libc by Doxygen
42
5.14
<inttypes.h>: Integer Type conversions
• #define
SCNi16
• #define
"o"
• #define
"o"
• #define
"o"
• #define
"u"
• #define
"u"
• #define
"u"
• #define
"x"
• #define
"x"
• #define
"x"
• #define
"lo"
• #define
"lo"
• #define
"lo"
• #define
"lu"
• #define
"lu"
• #define
"lu"
• #define
"lx"
• #define
"lx"
• #define
"lx"
• #define
SCNo16
• #define
SCNu16
• #define
SCNx16
Far pointers for memory access >64K
• typedef
• typedef
5.14.2
Define Documentation
5.14.2.1
#define PRId16 "d" decimal printf format for int16_t
5.14.2.2
#define PRId32 "ld" decimal printf format for int32_t
5.14.2.3
#define PRId8 "d" decimal printf format for int8_t
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43
5.14
<inttypes.h>: Integer Type conversions
5.14.2.4
#define PRIdFAST16 "d" decimal printf format for int_fast16_t
5.14.2.5
#define PRIdFAST32 "ld" decimal printf format for int_fast32_t
5.14.2.6
#define PRIdFAST8 "d" decimal printf format for int_fast8_t
5.14.2.7
#define PRIdLEAST16 "d" decimal printf format for int_least16_t
5.14.2.8
#define PRIdLEAST32 "ld" decimal printf format for int_least32_t
5.14.2.9
#define PRIdLEAST8 "d" decimal printf format for int_least8_t
5.14.2.10
#define PRIdPTR PRId16 decimal printf format for intptr_t
5.14.2.11
#define PRIi16 "i" integer printf format for int16_t
5.14.2.12
#define PRIi32 "li" integer printf format for int32_t
5.14.2.13
#define PRIi8 "i" integer printf format for int8_t
5.14.2.14
#define PRIiFAST16 "i" integer printf format for int_fast16_t
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44
5.14
<inttypes.h>: Integer Type conversions
5.14.2.15
#define PRIiFAST32 "li" integer printf format for int_fast32_t
5.14.2.16
#define PRIiFAST8 "i" integer printf format for int_fast8_t
5.14.2.17
#define PRIiLEAST16 "i" integer printf format for int_least16_t
5.14.2.18
#define PRIiLEAST32 "li" integer printf format for int_least32_t
5.14.2.19
#define PRIiLEAST8 "i" integer printf format for int_least8_t
5.14.2.20
#define PRIiPTR PRIi16 integer printf format for intptr_t
5.14.2.21
#define PRIo16 "o" octal printf format for uint16_t
5.14.2.22
#define PRIo32 "lo" octal printf format for uint32_t
5.14.2.23
#define PRIo8 "o" octal printf format for uint8_t
5.14.2.24
#define PRIoFAST16 "o" octal printf format for uint_fast16_t
5.14.2.25
#define PRIoFAST32 "lo" octal printf format for uint_fast32_t
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45
5.14
<inttypes.h>: Integer Type conversions
5.14.2.26
#define PRIoFAST8 "o" octal printf format for uint_fast8_t
5.14.2.27
#define PRIoLEAST16 "o" octal printf format for uint_least16_t
5.14.2.28
#define PRIoLEAST32 "lo" octal printf format for uint_least32_t
5.14.2.29
#define PRIoLEAST8 "o" octal printf format for uint_least8_t
5.14.2.30
#define PRIoPTR PRIo16 octal printf format for uintptr_t
5.14.2.31
#define PRIu16 "u" decimal printf format for uint16_t
5.14.2.32
#define PRIu32 "lu" decimal printf format for uint32_t
5.14.2.33
#define PRIu8 "u" decimal printf format for uint8_t
5.14.2.34
#define PRIuFAST16 "u" decimal printf format for uint_fast16_t
5.14.2.35
#define PRIuFAST32 "lu" decimal printf format for uint_fast32_t
5.14.2.36
#define PRIuFAST8 "u" decimal printf format for uint_fast8_t
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46
5.14
<inttypes.h>: Integer Type conversions
5.14.2.37
#define PRIuLEAST16 "u" decimal printf format for uint_least16_t
5.14.2.38
#define PRIuLEAST32 "lu" decimal printf format for uint_least32_t
5.14.2.39
#define PRIuLEAST8 "u" decimal printf format for uint_least8_t
5.14.2.40
#define PRIuPTR PRIu16 decimal printf format for uintptr_t
5.14.2.41
#define PRIX16 "X" uppercase hexadecimal printf format for uint16_t
5.14.2.42
#define PRIx16 "x" hexadecimal printf format for uint16_t
5.14.2.43
#define PRIX32 "lX" uppercase hexadecimal printf format for uint32_t
5.14.2.44
#define PRIx32 "lx" hexadecimal printf format for uint32_t
5.14.2.45
#define PRIX8 "X" uppercase hexadecimal printf format for uint8_t
5.14.2.46
#define PRIx8 "x" hexadecimal printf format for uint8_t
5.14.2.47
#define PRIXFAST16 "X" uppercase hexadecimal printf format for uint_fast16_t
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47
5.14
<inttypes.h>: Integer Type conversions
5.14.2.48
#define PRIxFAST16 "x" hexadecimal printf format for uint_fast16_t
5.14.2.49
#define PRIXFAST32 "lX" uppercase hexadecimal printf format for uint_fast32_t
5.14.2.50
#define PRIxFAST32 "lx" hexadecimal printf format for uint_fast32_t
5.14.2.51
#define PRIXFAST8 "X" uppercase hexadecimal printf format for uint_fast8_t
5.14.2.52
#define PRIxFAST8 "x" hexadecimal printf format for uint_fast8_t
5.14.2.53
#define PRIXLEAST16 "X" uppercase hexadecimal printf format for uint_least16_t
5.14.2.54
#define PRIxLEAST16 "x" hexadecimal printf format for uint_least16_t
5.14.2.55
#define PRIXLEAST32 "lX" uppercase hexadecimal printf format for uint_least32_t
5.14.2.56
#define PRIxLEAST32 "lx" hexadecimal printf format for uint_least32_t
5.14.2.57
#define PRIXLEAST8 "X" uppercase hexadecimal printf format for uint_least8_t
5.14.2.58
#define PRIxLEAST8 "x" hexadecimal printf format for uint_least8_t
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48
5.14
<inttypes.h>: Integer Type conversions
5.14.2.59
#define PRIXPTR PRIX16 uppercase hexadecimal printf format for uintptr_t
5.14.2.60
#define PRIxPTR PRIx16 hexadecimal printf format for uintptr_t
5.14.2.61
#define SCNd16 "d" decimal scanf format for int16_t
5.14.2.62
#define SCNd32 "ld" decimal scanf format for int32_t
5.14.2.63
#define SCNdFAST16 "d" decimal scanf format for int_fast16_t
5.14.2.64
#define SCNdFAST32 "ld" decimal scanf format for int_fast32_t
5.14.2.65
#define SCNdLEAST16 "d" decimal scanf format for int_least16_t
5.14.2.66
#define SCNdLEAST32 "ld" decimal scanf format for int_least32_t
5.14.2.67
#define SCNdPTR SCNd16 decimal scanf format for intptr_t
5.14.2.68
#define SCNi16 "i" generic-integer scanf format for int16_t
5.14.2.69
#define SCNi32 "li" generic-integer scanf format for int32_t
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49
5.14
<inttypes.h>: Integer Type conversions
5.14.2.70
#define SCNiFAST16 "i" generic-integer scanf format for int_fast16_t
5.14.2.71
#define SCNiFAST32 "li" generic-integer scanf format for int_fast32_t
5.14.2.72
#define SCNiLEAST16 "i" generic-integer scanf format for int_least16_t
5.14.2.73
#define SCNiLEAST32 "li" generic-integer scanf format for int_least32_t
5.14.2.74
#define SCNiPTR SCNi16 generic-integer scanf format for intptr_t
5.14.2.75
#define SCNo16 "o" octal scanf format for uint16_t
5.14.2.76
#define SCNo32 "lo" octal scanf format for uint32_t
5.14.2.77
#define SCNoFAST16 "o" octal scanf format for uint_fast16_t
5.14.2.78
#define SCNoFAST32 "lo" octal scanf format for uint_fast32_t
5.14.2.79
#define SCNoLEAST16 "o" octal scanf format for uint_least16_t
5.14.2.80
#define SCNoLEAST32 "lo" octal scanf format for uint_least32_t
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50
5.14
<inttypes.h>: Integer Type conversions
5.14.2.81
#define SCNoPTR SCNo16 octal scanf format for uintptr_t
5.14.2.82
#define SCNu16 "u" decimal scanf format for uint16_t
5.14.2.83
#define SCNu32 "lu" decimal scanf format for uint32_t
5.14.2.84
#define SCNuFAST16 "u" decimal scanf format for uint_fast16_t
5.14.2.85
#define SCNuFAST32 "lu" decimal scanf format for uint_fast32_t
5.14.2.86
#define SCNuLEAST16 "u" decimal scanf format for uint_least16_t
5.14.2.87
#define SCNuLEAST32 "lu" decimal scanf format for uint_least32_t
5.14.2.88
#define SCNuPTR SCNu16 decimal scanf format for uintptr_t
5.14.2.89
#define SCNx16 "x" hexadecimal scanf format for uint16_t
5.14.2.90
#define SCNx32 "lx" hexadecimal scanf format for uint32_t
5.14.2.91
#define SCNxFAST16 "x" hexadecimal scanf format for uint_fast16_t
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51
5.15
<math.h>: Mathematics 52
5.14.2.92
#define SCNxFAST32 "lx" hexadecimal scanf format for uint_fast32_t
5.14.2.93
#define SCNxLEAST16 "x" hexadecimal scanf format for uint_least16_t
5.14.2.94
#define SCNxLEAST32 "lx" hexadecimal scanf format for uint_least32_t
5.14.2.95
#define SCNxPTR SCNx16 hexadecimal scanf format for uintptr_t
5.14.3
Typedef Documentation
5.14.3.1
typedef
signed integer type that can hold a pointer > 64 KB
5.14.3.2
typedef
unsigned integer type that can hold a pointer > 64 KB
5.15
<math.h>: Mathematics
5.15.1
Detailed Description
#include <math.h>
This header file declares basic mathematics constants and functions.
Note:
In order to access the functions delcared herein, it is usually also required to additionally link against the library libm.a. See also the related
Defines
• #define
3.141592653589793238462643
• #define
1.4142135623730950488016887
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5.15
<math.h>: Mathematics 53
Functions
• double
(double __x) __ATTR_CONST__
• double
(double __x) __ATTR_CONST__
• double
(double __x, double __y) __ATTR_CONST__
• double
(double __value, double ∗__iptr)
• double
(double __x) __ATTR_CONST__
• double
(double __x) __ATTR_CONST__
• double
(double __x) __ATTR_CONST__
• double
(double __x) __ATTR_CONST__
• double
(double __x) __ATTR_CONST__
• double
(double __value, int ∗__exp)
• double
(double __x, int __exp) __ATTR_CONST__
• double
(double __x) __ATTR_CONST__
• double
(double __x) __ATTR_CONST__
• double
(double __x) __ATTR_CONST__
• double
(double __x) __ATTR_CONST__
• double
(double __x) __ATTR_CONST__
• double
(double __x) __ATTR_CONST__
• double
(double __x) __ATTR_CONST__
• double
(double __y, double __x) __ATTR_CONST__
• double
(double __x) __ATTR_CONST__
• double
(double __x) __ATTR_CONST__
• double
(double __x, double __y) __ATTR_CONST__
• int
(double __x) __ATTR_CONST__
• int
(double __x) __ATTR_CONST__
• double
(double __x) __ATTR_CONST__
5.15.2
Define Documentation
5.15.2.1
#define M_PI 3.141592653589793238462643
The constant pi.
5.15.2.2
#define M_SQRT2 1.4142135623730950488016887
The square root of 2.
5.15.3
Function Documentation
5.15.3.1
double acos (double __x)
The
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].
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5.15
<math.h>: Mathematics 54
5.15.3.2
double asin (double __x)
The
function computes the principal value of the arc sine of x. The returned value is in the range [0, pi] radians. A domain error occurs for arguments not in the range [-1, +1].
5.15.3.3
double atan (double __x)
The
function computes the principal value of the arc tangent of x. The returned value is in the range [0, pi] radians. A domain error occurs for arguments not in the range [-1, +1].
5.15.3.4
double atan2 (double __y, double __x)
The
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. If both x and y are zero, the global variable errno is set to EDOM.
5.15.3.5
double ceil (double __x)
The
function returns the smallest integral value greater than or equal to x, expressed as a floating-point number.
5.15.3.6
double cos (double __x)
The
function returns the cosine of x, measured in radians.
5.15.3.7
double cosh (double __x)
The
function returns the hyperbolic cosine of x.
5.15.3.8
double exp (double __x)
The
function returns the exponential value of x.
5.15.3.9
double fabs (double __x)
The
function computes the absolute value of a floating-point number x.
5.15.3.10
double floor (double __x)
The
function returns the largest integral value less than or equal to x, expressed as a floating-point number.
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5.15
<math.h>: Mathematics 55
5.15.3.11
double fmod (double __x, double __y)
The function
returns the floating-point remainder of x / y.
5.15.3.12
double frexp (double __value, int ∗ __exp)
The
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 exp.
The
function returns the value x, such that x is a double with magnitude in the interval [1/2, 1) or zero, and value equals x times 2 raised to the power ∗exp. If value is zero, both parts of the result are zero.
5.15.3.13
int isinf (double __x)
The function
returns 1 if the argument x is either positive or negative infinity, otherwise 0.
5.15.3.14
int isnan (double __x)
The function
returns 1 if the argument x represents a "not-a-number" (NaN) object, otherwise 0.
5.15.3.15
double ldexp (double __x, int __exp)
The
function multiplies a floating-point number by an integral power of 2.
The
function returns the value of x times 2 raised to the power exp.
If the resultant value would cause an overflow, the global variable errno is set to
ERANGE, and the value NaN is returned.
5.15.3.16
double log (double __x)
The
function returns the natural logarithm of argument x.
If the argument is less than or equal 0, a domain error will occur.
5.15.3.17
double log10 (double __x)
The
function returns the logarithm of argument x to base 10.
If the argument is less than or equal 0, a domain error will occur.
5.15.3.18
double modf (double __value, double ∗ __iptr)
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5.16
<setjmp.h>: Non-local goto 56
The
function breaks the argument value 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
function returns the signed fractional part of value.
5.15.3.19
double pow (double __x, double __y)
The function
returns the value of x to the exponent y.
5.15.3.20
double sin (double __x)
The
function returns the sine of x, measured in radians.
5.15.3.21
double sinh (double __x)
The
function returns the hyperbolic sine of x.
5.15.3.22
double sqrt (double __x)
The
function returns the non-negative square root of x.
5.15.3.23
double square (double __x)
The function
returns x ∗ x.
Note:
This function does not belong to the C standard definition.
5.15.3.24
double tan (double __x)
The
function returns the tangent of x, measured in radians.
5.15.3.25
double tanh (double __x)
The
function returns the hyperbolic tangent of x.
5.16
<setjmp.h>: Non-local goto
5.16.1
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)
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5.16
<setjmp.h>: Non-local goto 57 function, the C library provides the
and
functions.
and
are useful for dealing with errors and interrupts encountered in a low-level subroutine of a program.
and
make programs hard to understand and maintain. If possible, an alternative should be used.
can destroy changes made to global register variables (see
How to permanently 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);
}
}
Functions
• int
(jmp_buf __jmpb)
• void
(jmp_buf __jmpb, int __ret) __ATTR_NORETURN__
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5.17
<stdint.h>: Standard Integer Types 58
5.16.2
Function Documentation
5.16.2.1
void longjmp (jmp_buf __jmpb, int __ret)
Non-local jump to a saved stack context.
#include <setjmp.h>
restores the environment saved by the last call of
with the corresponding __jmpb argument. After
is completed, program execution continues as if the corresponding call of
had just returned the value __ret.
cannot cause 0 to be returned. If
is invoked with a second argument of 0, 1 will be returned instead.
Parameters:
__jmpb Information saved by a previous call to
__ret Value to return to the caller of
Returns:
This function never returns.
5.16.2.2
int setjmp (jmp_buf __jmpb)
Save stack context for non-local goto.
#include <setjmp.h>
saves the stack context/environment in __jmpb for later use by
stack context will be invalidated if the function which called
returns.
Parameters:
__jmpb Variable of type jmp_buf which holds the stack information such that the environment can be restored.
returns 0 if returning directly, and non-zero when returning from
using the saved context.
5.17
<stdint.h>: Standard Integer Types
5.17.1
Detailed Description
#include <stdint.h>
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5.17
<stdint.h>: Standard Integer Types 59
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.
Limits of specified-width integer types
C++ implementations should define these macros only when __STDC_LIMIT_-
MACROS is defined before < stdint.h
• #define
0x7f
• #define
(-INT8_MAX - 1)
• #define
(__CONCAT(INT8_MAX, U) ∗ 2U + 1U)
• #define
0x7fff
• #define
(-INT16_MAX - 1)
• #define
(__CONCAT(INT16_MAX, U) ∗ 2U + 1U)
• #define
0x7fffffffL
• #define
(-INT32_MAX - 1L)
• #define
(__CONCAT(INT32_MAX, U) ∗ 2UL + 1UL)
• #define
0x7fffffffffffffffLL
• #define
(-INT64_MAX - 1LL)
• #define
(__CONCAT(INT64_MAX, U) ∗ 2ULL + 1ULL)
Limits of minimum-width integer types
• #define
INT8_MAX
• #define
INT8_MIN
• #define
UINT8_MAX
• #define
INT16_MAX
• #define
INT16_MIN
• #define
UINT16_MAX
• #define
INT32_MAX
• #define
INT32_MIN
• #define
UINT32_MAX
• #define
INT64_MAX
• #define
INT64_MIN
• #define
UINT64_MAX
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5.17
<stdint.h>: Standard Integer Types 60
Limits of fastest minimum-width integer types
• #define
INT8_MAX
• #define
INT8_MIN
• #define
UINT8_MAX
• #define
INT16_MAX
• #define
INT16_MIN
• #define
UINT16_MAX
• #define
INT32_MAX
• #define
INT32_MIN
• #define
UINT32_MAX
• #define
INT64_MAX
• #define
INT64_MIN
• #define
UINT64_MAX
Limits of integer types capable of holding object pointers
• #define
INT16_MAX
• #define
INT16_MIN
• #define
UINT16_MAX
Limits of greatest-width integer types
• #define
INT64_MAX
• #define
INT64_MIN
• #define
UINT64_MAX
Limits of other integer types
• #define
INT16_MAX
• #define
INT16_MIN
• #define
INT8_MAX
• #define
INT8_MIN
• #define
(__CONCAT(INT16_MAX, U))
Macros for integer constants
C++ implementations should define these macros only when __STDC_CONSTANT_-
MACROS is defined before < stdint.h
These definitions are valid for integer constants without suffix and for macros defined as integer constant without suffix
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5.17
<stdint.h>: Standard Integer Types
• #define
• #define
(value) (( uint8_t ) __CONCAT(value, U))
• #define
• #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)
Exact-width integer types
Integer types having exactly the specified width
• typedef signed char
• typedef unsigned char
• typedef signed int
• typedef unsigned int
• typedef signed long int
• typedef unsigned long int
• typedef signed long long int
• typedef unsigned long long int
Integer types capable of holding object pointers
These allow you to declare variables of the same size as a pointer.
• typedef
• typedef
Minimum-width integer types
Integer types having at least the specified width
• typedef
• typedef
• typedef
• typedef
• typedef
• typedef
• typedef
• typedef
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5.17
<stdint.h>: Standard Integer Types 62
Fastest minimum-width integer types
Integer types being usually fastest having at least the specified width
• typedef
• typedef
• typedef
• typedef
• typedef
• typedef
• typedef
• typedef
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
• typedef
5.17.2
Define Documentation
5.17.2.1
#define INT16_C(value) value define a constant of type int16_t
5.17.2.2
#define INT16_MAX 0x7fff largest positive value an int16_t can hold.
5.17.2.3
#define INT16_MIN (-INT16_MAX - 1) smallest negative value an int16_t can hold.
5.17.2.4
#define INT32_C(value) __CONCAT(value, L) define a constant of type int32_t
5.17.2.5
#define INT32_MAX 0x7fffffffL largest positive value an int32_t can hold.
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5.17
<stdint.h>: Standard Integer Types
5.17.2.6
#define INT32_MIN (-INT32_MAX - 1L) smallest negative value an int32_t can hold.
5.17.2.7
#define INT64_C(value) __CONCAT(value, LL) define a constant of type int64_t
5.17.2.8
#define INT64_MAX 0x7fffffffffffffffLL largest positive value an int64_t can hold.
5.17.2.9
#define INT64_MIN (-INT64_MAX - 1LL) smallest negative value an int64_t can hold.
5.17.2.10
#define INT8_C(value) (( int8_t ) value)
define a constant of type int8_t
5.17.2.11
#define INT8_MAX 0x7f largest positive value an int8_t can hold.
5.17.2.12
#define INT8_MIN (-INT8_MAX - 1) smallest negative value an int8_t can hold.
5.17.2.13
#define INT_FAST16_MAX INT16_MAX largest positive value an int_fast16_t can hold.
5.17.2.14
#define INT_FAST16_MIN INT16_MIN smallest negative value an int_fast16_t can hold.
5.17.2.15
#define INT_FAST32_MAX INT32_MAX largest positive value an int_fast32_t can hold.
5.17.2.16
#define INT_FAST32_MIN INT32_MIN smallest negative value an int_fast32_t can hold.
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5.17
<stdint.h>: Standard Integer Types
5.17.2.17
#define INT_FAST64_MAX INT64_MAX largest positive value an int_fast64_t can hold.
5.17.2.18
#define INT_FAST64_MIN INT64_MIN smallest negative value an int_fast64_t can hold.
5.17.2.19
#define INT_FAST8_MAX INT8_MAX largest positive value an int_fast8_t can hold.
5.17.2.20
#define INT_FAST8_MIN INT8_MIN smallest negative value an int_fast8_t can hold.
5.17.2.21
#define INT_LEAST16_MAX INT16_MAX largest positive value an int_least16_t can hold.
5.17.2.22
#define INT_LEAST16_MIN INT16_MIN smallest negative value an int_least16_t can hold.
5.17.2.23
#define INT_LEAST32_MAX INT32_MAX largest positive value an int_least32_t can hold.
5.17.2.24
#define INT_LEAST32_MIN INT32_MIN smallest negative value an int_least32_t can hold.
5.17.2.25
#define INT_LEAST64_MAX INT64_MAX largest positive value an int_least64_t can hold.
5.17.2.26
#define INT_LEAST64_MIN INT64_MIN smallest negative value an int_least64_t can hold.
5.17.2.27
#define INT_LEAST8_MAX INT8_MAX largest positive value an int_least8_t can hold.
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5.17
<stdint.h>: Standard Integer Types
5.17.2.28
#define INT_LEAST8_MIN INT8_MIN smallest negative value an int_least8_t can hold.
5.17.2.29
#define INTMAX_C(value) __CONCAT(value, LL) define a constant of type intmax_t
5.17.2.30
#define INTMAX_MAX INT64_MAX largest positive value an intmax_t can hold.
5.17.2.31
#define INTMAX_MIN INT64_MIN smallest negative value an intmax_t can hold.
5.17.2.32
#define INTPTR_MAX INT16_MAX largest positive value an intptr_t can hold.
5.17.2.33
#define INTPTR_MIN INT16_MIN smallest negative value an intptr_t can hold.
5.17.2.34
#define PTRDIFF_MAX INT16_MAX largest positive value a ptrdiff_t can hold.
5.17.2.35
#define PTRDIFF_MIN INT16_MIN smallest negative value a ptrdiff_t can hold.
5.17.2.36
#define SIG_ATOMIC_MAX INT8_MAX largest positive value a sig_atomic_t can hold.
5.17.2.37
#define SIG_ATOMIC_MIN INT8_MIN smallest negative value a sig_atomic_t can hold.
5.17.2.38
#define SIZE_MAX (__CONCAT(INT16_MAX, U)) largest value a size_t can hold.
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5.17
<stdint.h>: Standard Integer Types 66
5.17.2.39
#define UINT16_C(value) __CONCAT(value, U) define a constant of type uint16_t
5.17.2.40
#define UINT16_MAX (__CONCAT(INT16_MAX, U) ∗ 2U + 1U) largest value an uint16_t can hold.
5.17.2.41
#define UINT32_C(value) __CONCAT(value, UL) define a constant of type uint32_t
5.17.2.42
#define UINT32_MAX (__CONCAT(INT32_MAX, U) ∗ 2UL + 1UL) largest value an uint32_t can hold.
5.17.2.43
#define UINT64_C(value) __CONCAT(value, ULL) define a constant of type uint64_t
5.17.2.44
#define UINT64_MAX (__CONCAT(INT64_MAX, U) ∗ 2ULL +
1ULL) largest value an uint64_t can hold.
5.17.2.45
#define UINT8_C(value) (( uint8_t ) __CONCAT(value, U))
define a constant of type uint8_t
5.17.2.46
#define UINT8_MAX (__CONCAT(INT8_MAX, U) ∗ 2U + 1U) largest value an uint8_t can hold.
5.17.2.47
#define UINT_FAST16_MAX UINT16_MAX largest value an uint_fast16_t can hold.
5.17.2.48
#define UINT_FAST32_MAX UINT32_MAX largest value an uint_fast32_t can hold.
5.17.2.49
#define UINT_FAST64_MAX UINT64_MAX largest value an uint_fast64_t can hold.
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5.17
<stdint.h>: Standard Integer Types
5.17.2.50
#define UINT_FAST8_MAX UINT8_MAX largest value an uint_fast8_t can hold.
5.17.2.51
#define UINT_LEAST16_MAX UINT16_MAX largest value an uint_least16_t can hold.
5.17.2.52
#define UINT_LEAST32_MAX UINT32_MAX largest value an uint_least32_t can hold.
5.17.2.53
#define UINT_LEAST64_MAX UINT64_MAX largest value an uint_least64_t can hold.
5.17.2.54
#define UINT_LEAST8_MAX UINT8_MAX largest value an uint_least8_t can hold.
5.17.2.55
#define UINTMAX_C(value) __CONCAT(value, ULL) define a constant of type uintmax_t
5.17.2.56
#define UINTMAX_MAX UINT64_MAX largest value an uintmax_t can hold.
5.17.2.57
#define UINTPTR_MAX UINT16_MAX largest value an uintptr_t can hold.
5.17.3
Typedef Documentation
5.17.3.1
typedef signed int
16-bit signed type.
5.17.3.2
typedef signed long int
32-bit signed type.
5.17.3.3
typedef signed long long int
64-bit signed type.
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5.17
<stdint.h>: Standard Integer Types
5.17.3.4
typedef signed char
8-bit signed type.
5.17.3.5
typedef
fastest signed int with at least 16 bits.
5.17.3.6
typedef
fastest signed int with at least 32 bits.
5.17.3.7
typedef
fastest signed int with at least 64 bits.
5.17.3.8
typedef
fastest signed int with at least 8 bits.
5.17.3.9
typedef
signed int with at least 16 bits.
5.17.3.10
typedef
signed int with at least 32 bits.
5.17.3.11
typedef
signed int with at least 64 bits.
5.17.3.12
typedef
signed int with at least 8 bits.
5.17.3.13
typedef
largest signed int available.
5.17.3.14
typedef
Signed pointer compatible type.
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5.17
<stdint.h>: Standard Integer Types
5.17.3.15
typedef unsigned int
16-bit unsigned type.
5.17.3.16
typedef unsigned long int
32-bit unsigned type.
5.17.3.17
typedef unsigned long long int
64-bit unsigned type.
5.17.3.18
typedef unsigned char
8-bit unsigned type.
5.17.3.19
typedef
fastest unsigned int with at least 16 bits.
5.17.3.20
typedef
fastest unsigned int with at least 32 bits.
5.17.3.21
typedef
fastest unsigned int with at least 64 bits.
5.17.3.22
typedef
fastest unsigned int with at least 8 bits.
5.17.3.23
typedef
unsigned int with at least 16 bits.
5.17.3.24
typedef
unsigned int with at least 32 bits.
5.17.3.25
typedef
unsigned int with at least 64 bits.
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5.18
<stdio.h>: Standard IO facilities 70
5.17.3.26
typedef
unsigned int with at least 8 bits.
5.17.3.27
typedef
largest unsigned int available.
5.17.3.28
typedef
Unsigned pointer compatible type.
5.18
<stdio.h>: Standard IO facilities
5.18.1
Detailed Description
#include <stdio.h>
Introduction to the Standard IO facilities This file declares the standard IO facilities 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 implementation 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 the format string at run-time. Whenever possible, resorting to the (sometimes nonstandard) 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
which is the heart of the printf family can be selected in different flavours using linker options. See the documentation of
for a detailed description. The same applies to
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 applicable devices, these streams are not already pre-initialized at application startup. Also,
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5.18
<stdio.h>: Standard IO facilities 71 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
function
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
As an alternative method to
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
that opens a stream for reading will cause the resulting stream to be aliased to stdin. Likewise, the first call to
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
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
end put and get functions can then extract this user data using
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
String Utilities ) becomes very handy for declaring these format strings.
Running stdio without
By default,
as well as the floating-point versions of the printf and scanf family require
malloc() . As this is often not desired in
the limited environment of a microcontroller, an alternative option is provided to run completely without
The macro
is provided to prepare a user-supplied FILE buffer for operation with stdio. If floating-point operation is desired, a user-supplied buffer can as well be passed for the internal buffering for the floating-point numbers (and processing of %[ scanf data).
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5.18
<stdio.h>: Standard IO facilities 72
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’); 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
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
should be issued for these streams. While calling
itself is harmless, it will cause an undefined reference to
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.
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
that talks to a UART interface might look like this:
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5.18
<stdio.h>: Standard IO facilities 73 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
instead of fprintf(mystream, ...) saves typing work, but since avr-gcc needs to resort 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 ability to pass one parameter less by implying stdin will also save some execution time.
Defines
• #define
struct __file
• #define
(__iob[0])
• #define
(__iob[1])
• #define
(__iob[2])
• #define
(-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
__SRD
• #define
__SWR
• #define
(__SRD|__SWR)
• #define
(-1)
• #define
(-2)
• #define
FDEV_SETUP_STREAM (put, get, rwflag)
• #define
• #define
putc (__c, __stream) fputc(__c, __stream)
• #define
putchar (__c) fputc(__c, stdout)
• #define
getc (__stream) fgetc(__stream)
• #define
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5.18
<stdio.h>: Standard IO facilities 74
Functions
• int
(FILE ∗__stream)
• int
(FILE ∗__stream, const char ∗__fmt, va_list __ap)
• int
(FILE ∗__stream, const char ∗__fmt, va_list __ap)
• int
(int __c, FILE ∗__stream)
• int
(const char ∗__fmt,...)
• int
(const char ∗__fmt,...)
• int
(const char ∗__fmt, va_list __ap)
• int
(char ∗__s, const char ∗__fmt,...)
• int
(char ∗__s, const char ∗__fmt,...)
• int
(char ∗__s, size_t __n, const char ∗__fmt,...)
• int
(char ∗__s, size_t __n, const char ∗__fmt,...)
• int
(char ∗__s, const char ∗__fmt, va_list ap)
• int
(char ∗__s, const char ∗__fmt, va_list ap)
• int
(char ∗__s, size_t __n, const char ∗__fmt, va_list ap)
• int
(char ∗__s, size_t __n, const char ∗__fmt, va_list ap)
• int
(FILE ∗__stream, const char ∗__fmt,...)
• int
(FILE ∗__stream, const char ∗__fmt,...)
• int
(const char ∗__str, FILE ∗__stream)
• int
(const char ∗__str, FILE ∗__stream)
• int
(const char ∗__str)
• int
(const char ∗__str)
• size_t
(const void ∗__ptr, size_t __size, size_t __nmemb, FILE ∗__stream)
• int
(FILE ∗__stream)
• int
(int __c, FILE ∗__stream)
• char ∗
(char ∗__str, int __size, FILE ∗__stream)
• char ∗
(char ∗__str)
• size_t
(void ∗__ptr, size_t __size, size_t __nmemb, FILE ∗__stream)
• void
(FILE ∗__stream)
• int
(FILE ∗__stream)
• int
(FILE ∗__stream)
• int
(FILE ∗__stream, const char ∗__fmt, va_list __ap)
• int
(FILE ∗__stream, const char ∗__fmt, va_list __ap)
• int
(FILE ∗__stream, const char ∗__fmt,...)
• int
(FILE ∗__stream, const char ∗__fmt,...)
• int
(const char ∗__fmt,...)
• int
(const char ∗__fmt,...)
• int
(const char ∗__fmt, va_list __ap)
• int
(const char ∗__buf, const char ∗__fmt,...)
• int
(const char ∗__buf, const char ∗__fmt,...)
• int
(FILE ∗stream)
• FILE ∗
(int(∗put)(char, FILE ∗), int(∗get)(FILE ∗))
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5.18
<stdio.h>: Standard IO facilities 75
5.18.2
Define Documentation
5.18.2.1
#define _FDEV_EOF (-2)
Return code for an end-of-file condition during device read.
To be used in the get function of
5.18.2.2
#define _FDEV_ERR (-1)
Return code for an error condition during device read.
To be used in the get function of
5.18.2.3
#define _FDEV_SETUP_READ __SRD
with read intent
5.18.2.4
#define _FDEV_SETUP_RW (__SRD|__SWR)
with read/write intent
5.18.2.5
#define _FDEV_SETUP_WRITE __SWR
with write intent
5.18.2.6
#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.
5.18.2.7
#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.)
5.18.2.8
#define fdev_get_udata(stream) ((stream) → udata)
This macro retrieves a pointer to user defined data from a FILE stream object.
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5.18
<stdio.h>: Standard IO facilities 76
5.18.2.9
#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
function.
5.18.2.10
#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
5.18.2.11
#define fdev_setup_stream(stream, put, get, rwflag)
Setup a user-supplied buffer as an stdio stream.
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
The buffer to setup must be of type FILE.
The arguments put and get are identical to those that need to be passed to
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, respectively.
Note:
No assignments to the standard streams will be performed by
If standard streams are to be used, these need to be assigned by the user. See also under
Running stdio without malloc() .
5.18.2.12
#define FILE struct __file
FILE is the opaque structure that is passed around between the various standard IO functions.
5.18.2.13
#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.
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5.18
<stdio.h>: Standard IO facilities 77
5.18.2.14
#define getchar(void) fgetc(stdin)
The macro getchar reads a character from stdin. Return values and error handling is identical to
5.18.2.15
#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.
5.18.2.16
#define putchar(__c) fputc(__c, stdout)
The macro putchar sends character c to stdout.
5.18.2.17
#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
must be explicitly assigned to it without closing the previous stderr (since this would also close stdout).
5.18.2.18
#define stdin (__iob[0])
Stream that will be used as an input stream by the simplified functions that don’t take a stream argument.
The first stream opened with read intent using
will be assigned to stdin .
5.18.2.19
#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
will be assigned to both, stdin , and stderr.
5.18.3
Function Documentation
5.18.3.1
void clearerr (FILE ∗ __stream)
Clear the error and end-of-file flags of stream.
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5.18
<stdio.h>: Standard IO facilities 78
5.18.3.2
int fclose (FILE ∗ __stream)
This function closes stream, and disallows and further IO to and from it.
When using
to setup the stream, a call to
is needed in order to free the internal resources allocated.
If the stream has been set up using
or
instead.
It currently always returns 0 (for success).
5.18.3.3
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 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.
uses
(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
will be chosen that is backwards compatible with avr-libc version 1.2 and before. This is solely intented for providing a simple migration path without the need to immediately change all source code. Do not use for new code.
5.18.3.4
int feof (FILE ∗ __stream)
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<stdio.h>: Standard IO facilities 79
Test the end-of-file flag of stream. This flag can only be cleared by a call to
5.18.3.5
int ferror (FILE ∗ __stream)
Test the error flag of stream. This flag can only be cleared by a call to
5.18.3.6
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.
5.18.3.7
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
or
must be used to distinguish between both situations.
5.18.3.8
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.
5.18.3.9
int fprintf (FILE ∗ __stream, const char ∗ __fmt, ...)
The function fprintf performs formatted output to stream. See
for details.
5.18.3.10
int fprintf_P (FILE ∗ __stream, const char ∗ __fmt, ...)
Variant of
that uses a fmt string that resides in program memory.
5.18.3.11
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.
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5.18.3.12
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.
5.18.3.13
int fputs_P (const char ∗ __str, FILE ∗ __stream)
Variant of
where str resides in program memory.
5.18.3.14
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.
and
must be used to distinguish between these two conditions.
5.18.3.15
int fscanf (FILE ∗ __stream, const char ∗ __fmt, ...)
The function fscanf performs formatted input, reading the input data from stream.
See
for details.
5.18.3.16
int fscanf_P (FILE ∗ __stream, const char ∗ __fmt, ...)
Variant of
using a fmt string in program memory.
5.18.3.17
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.
5.18.3.18
char∗ gets (char ∗ __str)
Similar to
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.
5.18.3.19
int printf (const char ∗ __fmt, ...)
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<stdio.h>: Standard IO facilities 81
The function printf performs formatted output to stream stderr.
See
for details.
5.18.3.20
int printf_P (const char ∗ __fmt, ...)
Variant of
that uses a fmt string that resides in program memory.
5.18.3.21
int puts (const char ∗ __str)
Write the string pointed to by str, and a trailing newline character, to stdout.
5.18.3.22
int puts_P (const char ∗ __str)
Variant of
where str resides in program memory.
5.18.3.23
int scanf (const char ∗ __fmt, ...)
The function scanf performs formatted input from stream stdin.
See
for details.
5.18.3.24
int scanf_P (const char ∗ __fmt, ...)
Variant of
where fmt resides in program memory.
5.18.3.25
int snprintf (char ∗ __s, size_t __n, const char ∗ __fmt, ...)
Like
sprintf() , but instead of assuming s to 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 s if there were enough space.
5.18.3.26
int snprintf_P (char ∗ __s, size_t __n, const char ∗ __fmt, ...)
Variant of
that uses a fmt string that resides in program memory.
5.18.3.27
int sprintf (char ∗ __s, const char ∗ __fmt, ...)
Variant of
that sends the formatted characters to string s.
5.18.3.28
int sprintf_P (char ∗ __s, const char ∗ __fmt, ...)
Variant of
that uses a fmt string that resides in program memory.
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5.18.3.29
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
for details.
5.18.3.30
int sscanf_P (const char ∗ __buf, const char ∗ __fmt, ...)
Variant of
using a fmt string in program memory.
5.18.3.31
int ungetc (int __c, FILE ∗ __stream)
The
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.
Currently, only a single character can be pushed back onto the stream.
The
function returns the character pushed back after the conversion, or EOF if the operation fails. If the value of the argument c character equals EOF, the operation will fail and the stream will remain unchanged.
5.18.3.32
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.
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– 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 converted value has fewer characters than the field width, it will be padded with spaces on the left (or right, if the left-adjust173 ment 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 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 s conversions.
• An optional l length modifier, that specifies that the argument for the d, i, o, u, x, or X conversion is a "long int" rather than 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.
• p The void ∗ argument is taken as an unsigned integer, and converted similarly as a #x command would do.
• c The int argument is converted to an "unsigned char", and the resulting character is written.
• s The "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.
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• A is written. No argument is converted. The complete conversion specification is "%%".
• eE The double argument is rounded and converted in the format
"[-]d.ddde177dd" where there is one digit before the decimal-point character 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 E conversion 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 f or e (or F or E for G conversions). 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 e is 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.
• S Similar to the s format, except the pointer is expected to point to a programmemory (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
can be selected using linker options. The default
implements all the mentioned functionality except floating point conversions.
A minimized version of
is available that only implements the very basic integer and string conversion facilities, but none of the additional options that 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
-Wl,-u,vfprintf -lprintf_min
If the full functionality including the floating point conversions is required, the following options should be used:
-Wl,-u,vfprintf -lprintf_flt -lm
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<stdio.h>: Standard IO facilities 85
Limitations:
• The specified width and precision can be at most 127.
• For floating-point conversions, trailing digits will be lost if a number close to
DBL_MAX is converted with a precision > 0.
5.18.3.33
int vfprintf_P (FILE ∗ __stream, const char ∗ __fmt, va_list __ap)
Variant of
that uses a fmt string that resides in program memory.
5.18.3.34
int vfscanf (FILE ∗ __stream, const char ∗ __fmt, va_list __ap)
Formatted input. This function is the heart of the scanf family of functions.
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 h indicating that the argument is a pointer to short int (rather than int),
• the character l indicating 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 127 characters which is also the default value (except for the c conversion that defaults to 1).
The following conversion flags are supported:
• Matches a literal character. This is not a conversion.
• d Matches an optionally signed decimal integer; the next pointer must be a pointer to int.
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• i Matches 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.
• o Matches an octal integer; the next pointer must be a pointer to unsigned int .
• u Matches an optionally signed decimal integer; the next pointer must be a pointer to unsigned int.
• x Matches an optionally signed hexadecimal integer; the next pointer must be a pointer to unsigned int.
• f Matches an optionally signed floating-point number; the next pointer must be a pointer to float.
• e, g, E, G Equivalent to f.
• s Matches 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.
• c Matches 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 circumflex
∧
. 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 everything 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.
• p Matches a pointer value (as printed by p in
printf() ); the next pointer must be
a pointer to void.
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<stdio.h>: Standard IO facilities 87
• n Nothing 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 d conversion. 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 %[ conversion. These conversions will be available in the extended version provided by the library libscanf_flt.a. Note that either of these conversions requires the availability of a buffer that needs to be obtained at run-time using
malloc() . If this buffer cannot be obtained, the operation is aborted, returning the
value EOF. To link a program against the extended version, use the following compiler flags in the link stage:
-Wl,-u,vfscanf -lscanf_flt -lm
A third version is available for environments that are tight on space. 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
In addition to the restrictions of the standard version, this version implements no field width specification, no conversion assignment suppression flag (∗), no n specification, and no general format character matching at all. All characters in fmt that do not comprise a conversion specification will simply be ignored, including white space (that is normally used to consume any amount of white space in the input stream). However, the usual skip of initial white space in the formats that support it is implemented.
5.18.3.35
int vfscanf_P (FILE ∗ __stream, const char ∗ __fmt, va_list __ap)
Variant of
using a fmt string in program memory.
5.18.3.36
int vprintf (const char ∗ __fmt, va_list __ap)
The function vprintf performs formatted output to stream stdout, taking a variable argument list as in
See
for details.
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<stdlib.h>: General utilities 88
5.18.3.37
int vscanf (const char ∗ __fmt, va_list __ap)
The function vscanf performs formatted input from stream stdin, taking a variable argument list as in
See
for details.
5.18.3.38
int vsnprintf (char ∗ __s, size_t __n, const char ∗ __fmt, va_list ap)
Like
vsprintf() , but instead of assuming s to 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 s if there were enough space.
5.18.3.39
int vsnprintf_P (char ∗ __s, size_t __n, const char ∗ __fmt, va_list ap)
Variant of
that uses a fmt string that resides in program memory.
5.18.3.40
int vsprintf (char ∗ __s, const char ∗ __fmt, va_list ap)
Like
but takes a variable argument list for the arguments.
5.18.3.41
int vsprintf_P (char ∗ __s, const char ∗ __fmt, va_list ap)
Variant of
that uses a fmt string that resides in program memory.
5.19
<stdlib.h>: General utilities
5.19.1
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.
Data Structures
• struct
• struct
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<stdlib.h>: General utilities 89
Non-standard (i.e. non-ISO C) functions.
• #define
0x7FFFFFFF
• char ∗
(int __val, char ∗__s, int __radix)
• char ∗
(long int __val, char ∗__s, int __radix)
• char ∗
(unsigned int __val, char ∗__s, int __radix)
• char ∗
(unsigned long int __val, char ∗__s, int __radix)
• long
(void)
• void
(unsigned long __seed)
• long
(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
0x01
• #define
0x02
• #define
0x04
• char ∗
(double __val, char ∗__s, unsigned char __prec, unsigned char
__flags)
• char ∗
(double __val, char __width, char __prec, char ∗__s)
Defines
• #define
0x7FFF
Typedefs
• typedef int(∗
)(const void ∗, const void ∗)
Functions
• __inline__ void
(void) __ATTR_NORETURN__
• int
(int __i) __ATTR_CONST__
• long
(long __i) __ATTR_CONST__
• void ∗
(const void ∗__key, const void ∗__base, size_t __nmemb, size_t
__size, int(∗__compar)(const void ∗, const void ∗))
•
(int __num, int __denom) __asm__("__divmodhi4") __ATTR_-
CONST__
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•
(long __num, long __denom) __asm__("__divmodsi4") __ATTR_-
CONST__
• void
(void ∗__base, size_t __nmemb, size_t __size,
__compar)
• long
(const char ∗__nptr, char ∗∗__endptr, int __base)
• unsigned long
(const char ∗__nptr, char ∗∗__endptr, int __base)
• __inline__ long
(const char ∗__nptr) __ATTR_PURE__
• __inline__ int
(const char ∗__nptr) __ATTR_PURE__
• void
(int __status) __ATTR_NORETURN__
• void ∗
(size_t __size) __ATTR_MALLOC__
• void
(void ∗__ptr)
• void ∗
(size_t __nele, size_t __size) __ATTR_MALLOC__
• void ∗
(void ∗__ptr, size_t __size) __ATTR_MALLOC__
• double
(const char ∗__nptr, char ∗∗__endptr)
• double
(const char ∗__nptr)
• int
(void)
• void
(unsigned int __seed)
• int
(unsigned long ∗ctx)
Variables
• size_t
• char ∗
• char ∗
5.19.2
Define Documentation
5.19.2.1
#define DTOSTR_ALWAYS_SIGN 0x01
Bit value that can be passed in flags to
5.19.2.2
#define DTOSTR_PLUS_SIGN 0x02
Bit value that can be passed in flags to
5.19.2.3
#define DTOSTR_UPPERCASE 0x04
Bit value that can be passed in flags to
5.19.2.4
#define RAND_MAX 0x7FFF
Highest number that can be generated by
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5.19.2.5
#define RANDOM_MAX 0x7FFFFFFF
Highest number that can be generated by
5.19.3
Typedef Documentation
5.19.3.1
typedef int(∗
__compar_fn_t )(const void ∗, const void ∗)
Comparision function type for
qsort() , just for convenience.
5.19.4
Function Documentation
5.19.4.1
__inline__ void abort (void)
The
function causes abnormal program termination to occur. In the limited
AVR environment, execution is effectively halted by entering an infinite loop.
5.19.4.2
int abs (int __i)
The
function computes the absolute value of the integer i.
Note:
The
and
functions are builtins of gcc.
5.19.4.3
double atof (const char ∗ __nptr)
The
function converts the initial portion of the string pointed to by nptr to double representation.
It is equivalent to calling strtod(nptr, (char **)NULL);
5.19.4.4
int atoi (const char ∗ string)
Convert a string to an integer.
The
function converts the initial portion of the string pointed to by nptr to integer representation.
It is equivalent to:
(int)strtol(nptr, (char **)NULL, 10); except that
does not detect errors.
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5.19.4.5
long int atol (const char ∗ string)
Convert a string to a long integer.
The
function converts the initial portion of the string pointed to by stringp to integer representation.
It is equivalent to: strtol(nptr, (char **)NULL, 10); except that
does not detect errors.
5.19.4.6
void∗ bsearch (const void ∗ __key, const void ∗ __base, size_t __nmemb, size_t __size, int(∗)(const void ∗, const void ∗) __compar)
The
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 comparison 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.
The
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.
5.19.4.7
void∗ calloc (size_t __nele, size_t __size)
Allocate nele elements of size each. Identical to calling
using nele
∗ size as argument, except the allocated memory will be cleared to zero.
5.19.4.8
div (int __num, int __denom)
The
function computes the value num/denom and returns the quotient and remainder in a structure named
that contains two int members named quot and rem .
5.19.4.9
char∗ dtostre (double __val, char ∗ __s, unsigned char __prec, unsigned char __flags)
The
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.
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Conversion is done in the format "[-]d.ddde177dd" 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 DTOSTRE_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 DTOSTRE_ALWAYS_SIGN bit set, a space character will be placed into the leading position for positive numbers.
If flags has the DTOSTRE_PLUS_SIGN bit set, a plus sign will be used instead of a space character in this case.
The
function returns the pointer to the converted string s.
5.19.4.10
char∗ dtostrf (double __val, char __width, char __prec, char ∗ __s)
The
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 ’.’ and the possible sign for negative values) is given in width , and prec determines the number of digits after the decimal sign.
The
function returns the pointer to the converted string s.
5.19.4.11
void exit (int __status)
The
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.
In a C++ context, global destructors will be called before halting execution.
5.19.4.12
void free (void ∗ __ptr)
The
function causes the allocated memory referenced by ptr to be made available for future allocations. If ptr is NULL, no action occurs.
5.19.4.13
char∗ itoa (int __val, char ∗ __s, int __radix)
Convert an integer to a string.
The function
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 .
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5.19
<stdlib.h>: General utilities 94
Note:
The minimal size of the buffer s depends 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
function returns the pointer passed as s.
5.19.4.14
long labs (long __i)
The
function computes the absolute value of the long integer i.
Note:
The
and
functions are builtins of gcc.
5.19.4.15
ldiv (long __num, long __denom)
The
function computes the value num/denom and returns the quotient and remainder in a structure named
that contains two long integer members named quot and rem.
5.19.4.16
char∗ ltoa (long int __val, char ∗ __s, int __radix)
Convert a long integer to a string.
The function
converts the long 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 s depends 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.
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<stdlib.h>: General utilities 95
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
function returns the pointer passed as s.
5.19.4.17
void∗ malloc (size_t __size)
The
function allocates size bytes of memory. If
fails, a NULL pointer is returned.
Note that
does not initialize the returned memory to zero bytes.
See the chapter about
for implementation details.
5.19.4.18
void qsort (void ∗ __base, size_t __nmemb, size_t __size,
__compar)
The
function is a modified partition-exchange sort, or quicksort.
The
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 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.
5.19.4.19
int rand (void)
The
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
function sets its argument seed as the seed for a new sequence of pseudorandom numbers to be returned by
rand() . These sequences are repeatable by calling
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 precision. See
for an alternate set of functions that retains full 32-bit precision.
5.19.4.20
int rand_r (unsigned long ∗ ctx)
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<stdlib.h>: General utilities 96
Variant of
that stores the context in the user-supplied variable located at ctx instead of a static library variable so the function becomes re-entrant.
5.19.4.21
long random (void)
The
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
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
with the same seed value.
If no seed value is provided, the functions are automatically seeded with a value of 1.
5.19.4.22
long random_r (unsigned long ∗ ctx)
Variant of
that stores the context in the user-supplied variable located at ctx instead of a static library variable so the function becomes re-entrant.
5.19.4.23
void∗ realloc (void ∗ __ptr, size_t __size)
The
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.
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
will behave identical to
If the new memory cannot be allocated,
returns NULL, and the region at ptr will not be changed.
5.19.4.24
void srand (unsigned int __seed)
Pseudo-random number generator seeding; see
5.19.4.25
void srandom (unsigned long __seed)
Pseudo-random number generator seeding; see
5.19.4.26
double strtod (const char ∗ __nptr, char ∗∗ __endptr)
The
function converts the initial portion of the string pointed to by nptr to double representation.
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<stdlib.h>: General utilities 97
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, optionally 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
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 HUGE_VAL is returned (according 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.
FIXME: HUGE_VAL needs to be defined somewhere. The bit pattern is 0x7fffffff, but what number would this be?
5.19.4.27
long strtol (const char ∗ __nptr, char ∗∗ __endptr, int __base)
The
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
isspace() ) 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 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,
stores the address of the first invalid character in
∗endptr. If there were no digits at all, however,
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
function returns the result of the conversion, unless the value would underflow or overflow. If no conversion could be performed, 0 is returned. If an overflow or underflow occurs, errno is set to
and the function return value is clamped to LONG_MIN or LONG_MAX, respectively.
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5.19
<stdlib.h>: General utilities 98
5.19.4.28
unsigned long strtoul (const char ∗ __nptr, char ∗∗ __endptr, int __base)
The
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
isspace() ) 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,
stores the address of the first invalid character in
∗endptr. If there were no digits at all, however,
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
function return either the result of the conversion or, if there was a leading minus sign, the negation of the result of the conversion, unless the original (nonnegated) value would overflow; in the latter case,
returns ULONG_MAX, and errno is set to
ERANGE . If no conversion could be performed, 0 is returned.
5.19.4.29
char∗ ultoa (unsigned long int __val, char ∗ __s, int __radix)
Convert an unsigned long integer to a string.
The function
converts the unsigned long 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 s depends 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’.
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<string.h>: Strings 99
The
function returns the pointer passed as s.
5.19.4.30
char∗ utoa (unsigned int __val, char ∗ __s, int __radix)
Convert an unsigned integer to a string.
The function
converts the unsigned 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 s depends 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
function returns the pointer passed as s.
5.19.5
Variable Documentation
5.19.5.1
char∗
5.19.5.2
char∗
5.19.5.3
size_t
5.20
<string.h>: Strings
5.20.1
Detailed Description
#include <string.h>
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<string.h>: Strings 100
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 String
Defines
• #define
Functions
• int
(int) __attribute__((const ))
• int
(long) __attribute__((const ))
• int
(long long) __attribute__((const ))
• void ∗
(void ∗, const void ∗, int, size_t)
• void ∗
(const void ∗, int, size_t) __ATTR_PURE__
• int
(const void ∗, const void ∗, size_t) __ATTR_PURE__
• void ∗
(void ∗, const void ∗, size_t)
• void ∗
(void ∗, const void ∗, size_t)
• void ∗
(void ∗, int, size_t)
• int
(const char ∗, const char ∗) __ATTR_PURE__
• char ∗
(char ∗, const char ∗)
• char ∗
(const char ∗, int) __ATTR_PURE__
• int
(const char ∗, const char ∗) __ATTR_PURE__
• char ∗
(char ∗, const char ∗)
• size_t
(char ∗, const char ∗, size_t)
• size_t
(char ∗, const char ∗, size_t)
• size_t
(const char ∗) __ATTR_PURE__
• char ∗
(char ∗)
• int
(const char ∗, const char ∗, size_t) __ATTR_PURE__
• char ∗
(char ∗, const char ∗, size_t)
• int
(const char ∗, const char ∗, size_t) __ATTR_PURE__
• char ∗
(char ∗, const char ∗, size_t)
• size_t
(const char ∗, size_t) __ATTR_PURE__
• char ∗
(const char ∗, int) __ATTR_PURE__
• char ∗
(char ∗)
• char ∗
(char ∗∗, const char ∗)
• char ∗
(const char ∗, const char ∗) __ATTR_PURE__
• char ∗
(char ∗, const char ∗, char ∗∗)
• char ∗
(char ∗)
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5.20
<string.h>: Strings 101
5.20.2
Define Documentation
5.20.2.1
#define _FFS(x)
This macro finds the first (least significant) bit set in the input value.
This macro is very similar to the function
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.
The
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.
5.20.3
Function Documentation
5.20.3.1
int ffs (int val) const
This function finds the first (least significant) bit set in the input value.
The
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.
Note:
For expressions that are constant at compile time, consider using the
macro instead.
5.20.3.2
int ffsl (long val) const
Same as
ffs() , for an argument of type long.
5.20.3.3
int ffsll (long long val) const
Same as
ffs() , for an argument of type long long.
5.20.3.4
void ∗ memccpy (void ∗ dest, const void ∗ src, int val, size_t len)
Copy memory area.
The
function copies no more than len bytes from memory area src to memory area dest, stopping when the character val is found.
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The
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.
5.20.3.5
void ∗ memchr (const void ∗ src, int val, size_t len)
Scan memory for a character.
The
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.
The
function returns a pointer to the matching byte or NULL if the character does not occur in the given memory area.
5.20.3.6
int memcmp (const void ∗ s1, const void ∗ s2, size_t len)
Compare memory areas.
The
function compares the first len bytes of the memory areas s1 and s2.
The comparision is performed using unsigned char operations.
The
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.
5.20.3.7
void ∗ memcpy (void ∗ dest, const void ∗ src, size_t len)
Copy a memory area.
The
function copies len bytes from memory area src to memory area dest.
The memory areas may not overlap. Use
if the memory areas do overlap.
The
function returns a pointer to dest.
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5.20.3.8
void ∗ memmove (void ∗ dest, const void ∗ src, size_t len)
Copy memory area.
The
function copies len bytes from memory area src to memory area dest.
The memory areas may overlap.
The
function returns a pointer to dest.
5.20.3.9
void ∗ memset (void ∗ dest, int val, size_t len)
Fill memory with a constant byte.
The
function fills the first len bytes of the memory area pointed to by dest with the constant byte val.
The
function returns a pointer to the memory area dest.
5.20.3.10
int strcasecmp (const char ∗ s1, const char ∗ s2)
Compare two strings ignoring case.
The
function compares the two strings s1 and s2, ignoring the case of the characters.
The
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.
5.20.3.11
char ∗ strcat (char ∗ dest, const char ∗ src)
Concatenate two strings.
The
function appends the src string to the dest string overwriting the ’\0’ character 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.
The
function returns a pointer to the resulting string dest.
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<string.h>: Strings 104
5.20.3.12
char ∗ strchr (const char ∗ src, int val)
Locate character in string.
The
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.
The
function returns a pointer to the matched character or NULL if the character is not found.
5.20.3.13
int strcmp (const char ∗ s1, const char ∗ s2)
Compare two strings.
The
function compares the two strings s1 and s2.
The
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.
5.20.3.14
char ∗ strcpy (char ∗ dest, const char ∗ src)
Copy a string.
The
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.
The
function returns a pointer to the destination string dest.
Note:
If the destination string of a
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.
5.20.3.15
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)).
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<string.h>: Strings 105
The
function returns strlen(src) + MIN(siz, strlen(initial dst)). If retval >= siz, truncation occurred.
5.20.3.16
size_t strlcpy (char ∗ dst, const char ∗ src, size_t siz)
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).
The
function returns strlen(src). If retval >= siz, truncation occurred.
5.20.3.17
size_t strlen (const char ∗ src)
Calculate the length of a string.
The
function calculates the length of the string src, not including the terminating ’\0’ character.
The
function returns the number of characters in src.
5.20.3.18
char ∗ strlwr (char ∗ string)
Convert a string to lower case.
The
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.
The
function returns a pointer to the converted string.
5.20.3.19
int strncasecmp (const char ∗ s1, const char ∗ s2, size_t len)
Compare two strings ignoring case.
The
function is similar to
strcasecmp() , except it only compares the first
n characters of s1.
The
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.
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<string.h>: Strings 106
5.20.3.20
char ∗ strncat (char ∗ dest, const char ∗ src, size_t len)
Concatenate two strings.
The
function is similar to
strcat() , except that only the first n characters of src
are appended to dest.
The
function returns a pointer to the resulting string dest.
5.20.3.21
int strncmp (const char ∗ s1, const char ∗ s2, size_t len)
Compare two strings.
The
function is similar to
strcmp() , except it only compares the first (at most)
n characters of s1 and s2.
The
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.
5.20.3.22
char ∗ strncpy (char ∗ dest, const char ∗ src, size_t len)
Copy a string.
The
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.
The
function returns a pointer to the destination string dest.
5.20.3.23
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.
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<string.h>: Strings 107
5.20.3.24
char ∗ strrchr (const char ∗ src, int val)
Locate character in string.
The
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.
The
function returns a pointer to the matched character or NULL if the character is not found.
5.20.3.25
char ∗ strrev (char ∗ string)
Reverse a string.
The
function reverses the order of the string.
The
function returns a pointer to the beginning of the reversed string.
5.20.3.26
char ∗ strsep (char ∗∗ string, const char ∗ delim)
Parse a string into tokens.
The
function locates, in the string referenced by ∗string, 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 ∗string. 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 ∗string to ’\0’.
The
function returns a pointer to the original value of ∗string. If ∗stringp is initially NULL,
returns NULL.
5.20.3.27
char ∗ strstr (const char ∗ s1, const char ∗ s2)
Locate a substring.
The
function finds the first occurrence of the substring s2 in the string s1. The terminating ’\0’ characters are not compared.
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<util/crc16.h>: CRC Computations 108
The
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.
5.20.3.28
char ∗ strtok_r (char ∗ string, const char ∗ delim, char ∗∗ last)
Parses the string s into tokens.
strtok_r parses the string s 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().
The
function returns a pointer to the next token or NULL when no more tokens are found.
5.20.3.29
char ∗ strupr (char ∗ string)
Convert a string to upper case.
The
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.
The
function returns a pointer to the converted string. The pointer is the same as that passed in since the operation is perform in place.
5.21
<util/crc16.h>: CRC Computations
5.21.1
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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5.21
<util/crc16.h>: CRC Computations 109
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
}
Functions
• static __inline__
__crc,
__data)
• static __inline__
__crc,
__data)
• static __inline__
__crc,
__data)
• static __inline__
__crc,
__data)
5.21.2
Function Documentation
5.21.2.1
static __inline__
uint16_t _crc16_update ( uint16_t
__crc,
__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.
5.21.2.2
static __inline__
uint16_t _crc_ccitt_update ( uint16_t
__crc,
__data) [static]
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5.21
<util/crc16.h>: CRC Computations 110
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));
}
5.21.2.3
static __inline__
uint8_t _crc_ibutton_update ( uint8_t
__crc,
_-
_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 crc >>= 1;
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5.22
<util/delay.h>: Busy-wait delay loops
}
} return crc;
111
5.21.2.4
static __inline__
uint16_t _crc_xmodem_update ( uint16_t
__crc,
__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;
}
5.22
<util/delay.h>: Busy-wait delay loops
5.22.1
Detailed Description
#define F_CPU 1000000UL // 1 MHz
//#define F_CPU 14.7456E6
#include <util/delay.h>
Note:
As an alternative method, it is possible to pass the F_CPU macro down to the compiler from the Makefile. Obviously, in that case, no #define statement should be used.
The functions in this header file implement simple delay loops that perform a busywaiting. They are typically used to facilitate short delays in the program execution.
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5.22
<util/delay.h>: Busy-wait delay loops 112
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.
Two wrapper functions allow the specification of microsecond, and millisecond delays directly, using the application-supplied macro F_CPU as the CPU clock frequency (in
Hertz). These functions operate on double typed arguments, however when optimization is turned on, the entire floating-point calculation will be done at compile-time.
Note:
When using
and
_delay_ms() , the expressions passed as arguments to
these functions shall be compile-time constants, otherwise the floating-point calculations to setup the loops will be done at run-time, thereby drastically increasing both the resulting code size, as well as the time required to setup the loops.
Functions
• void
__count)
• void
__count)
• void
(double __us)
• void
(double __ms)
5.22.2
Function Documentation
5.22.2.1
__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.
5.22.2.2
__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 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.
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5.23
<util/parity.h>: Parity bit generation 113
5.22.2.3
void _delay_ms (double __ms)
Perform a delay of __ms milliseconds, using
The macro F_CPU is supposed to be defined to a constant defining the CPU clock frequency (in Hertz).
The maximal possible delay is 262.14 ms / F_CPU in MHz.
5.22.2.4
void _delay_us (double __us)
Perform a delay of __us microseconds, using
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.
5.23
<util/parity.h>: Parity bit generation
5.23.1
Detailed Description
#include <util/parity.h>
This header file contains optimized assembler code to calculate the parity bit for a byte.
Defines
• #define
5.23.2
Define Documentation
5.23.2.1
#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"
\
\
\
\
\
\
\
\
\
\
\
\
\
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5.24
<util/twi.h>: TWI bit mask definitions
);
(((__t + 1) >> 1) & 1);
}))
Returns:
1 if val has an odd number of bits set.
\
\
5.24
<util/twi.h>: TWI bit mask definitions
5.24.1
Detailed Description
#include <util/twi.h>
This header file contains bit mask definitions for use with the AVR TWI interface.
TWSR values
Mnemonics:
TW_MT_xxx - master transmitter
TW_MR_xxx - master receiver
TW_ST_xxx - slave transmitter
TW_SR_xxx - slave receiver
• #define
0x08
• #define
0x10
• #define
0x18
• #define
0x20
• #define
0x28
• #define
0x30
• #define
0x38
• #define
0x38
• #define
0x40
• #define
0x48
• #define
0x50
• #define
0x58
• #define
0xA8
• #define
0xB0
• #define
0xB8
• #define
0xC0
• #define
0xC8
• #define
0x60
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114
5.24
<util/twi.h>: TWI bit mask definitions
• #define
0x68
• #define
0x70
• #define
0x78
• #define
0x80
• #define
0x88
• #define
0x90
• #define
0x98
• #define
0xA0
• #define
0xF8
• #define
0x00
• #define
• #define
(TWSR & TW_STATUS_MASK)
R/∼W bit in SLA+R/W address field.
• #define
1
• #define
0
5.24.2
Define Documentation
5.24.2.1
#define TW_BUS_ERROR 0x00 illegal start or stop condition
5.24.2.2
#define TW_MR_ARB_LOST 0x38 arbitration lost in SLA+R or NACK
5.24.2.3
#define TW_MR_DATA_ACK 0x50 data received, ACK returned
5.24.2.4
#define TW_MR_DATA_NACK 0x58 data received, NACK returned
5.24.2.5
#define TW_MR_SLA_ACK 0x40
SLA+R transmitted, ACK received
5.24.2.6
#define TW_MR_SLA_NACK 0x48
SLA+R transmitted, NACK received
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115
5.24
<util/twi.h>: TWI bit mask definitions
5.24.2.7
#define TW_MT_ARB_LOST 0x38 arbitration lost in SLA+W or data
5.24.2.8
#define TW_MT_DATA_ACK 0x28 data transmitted, ACK received
5.24.2.9
#define TW_MT_DATA_NACK 0x30 data transmitted, NACK received
5.24.2.10
#define TW_MT_SLA_ACK 0x18
SLA+W transmitted, ACK received
5.24.2.11
#define TW_MT_SLA_NACK 0x20
SLA+W transmitted, NACK received
5.24.2.12
#define TW_NO_INFO 0xF8 no state information available
5.24.2.13
#define TW_READ 1
SLA+R address
5.24.2.14
#define TW_REP_START 0x10 repeated start condition transmitted
5.24.2.15
#define TW_SR_ARB_LOST_GCALL_ACK 0x78 arbitration lost in SLA+RW, general call received, ACK returned
5.24.2.16
#define TW_SR_ARB_LOST_SLA_ACK 0x68 arbitration lost in SLA+RW, SLA+W received, ACK returned
5.24.2.17
#define TW_SR_DATA_ACK 0x80 data received, ACK returned
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116
5.24
<util/twi.h>: TWI bit mask definitions
5.24.2.18
#define TW_SR_DATA_NACK 0x88 data received, NACK returned
5.24.2.19
#define TW_SR_GCALL_ACK 0x70 general call received, ACK returned
5.24.2.20
#define TW_SR_GCALL_DATA_ACK 0x90 general call data received, ACK returned
5.24.2.21
#define TW_SR_GCALL_DATA_NACK 0x98 general call data received, NACK returned
5.24.2.22
#define TW_SR_SLA_ACK 0x60
SLA+W received, ACK returned
5.24.2.23
#define TW_SR_STOP 0xA0 stop or repeated start condition received while selected
5.24.2.24
#define TW_ST_ARB_LOST_SLA_ACK 0xB0 arbitration lost in SLA+RW, SLA+R received, ACK returned
5.24.2.25
#define TW_ST_DATA_ACK 0xB8 data transmitted, ACK received
5.24.2.26
#define TW_ST_DATA_NACK 0xC0 data transmitted, NACK received
5.24.2.27
#define TW_ST_LAST_DATA 0xC8 last data byte transmitted, ACK received
5.24.2.28
#define TW_ST_SLA_ACK 0xA8
SLA+R received, ACK returned
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117
5.25
<avr/interrupt.h>: Interrupts 118
5.24.2.29
#define TW_START 0x08 start condition transmitted
5.24.2.30
#define TW_STATUS (TWSR & TW_STATUS_MASK)
TWSR, masked by TW_STATUS_MASK
5.24.2.31
#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.
5.24.2.32
#define TW_WRITE 0
SLA+W address
5.25
<avr/interrupt.h>: Interrupts
5.25.1
Detailed Description
Note:
This discussion of interrupts was originally taken from Rich Neswold’s document.
See
Introduction to avr-libc’s interrupt handling It’s nearly impossible to find compilers 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.
In the AVR-GCC environment, the vector table is predefined to point to interrupt routines 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)) .
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5.25
<avr/interrupt.h>: Interrupts 119
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
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
for an explanation about interrupt 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 __vector_default which should be defined with
as such.
#include <avr/interrupt.h>
ISR(__vector_default)
{
// user code here
}
Nested interrupts The AVR hardware clears the global interrupt flag in SREG before 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 eventually 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 few instructions inside the compiler-generated function prologue to run with global interrupts 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: void XXX_vect(void) __attribute__((interrupt)); void XXX_vect(void) {
...
}
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5.25
<avr/interrupt.h>: Interrupts 120 where XXX_vect is the name of a valid interrupt vector for the MCU type in question, as explained below.
Chosing 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 convention.
The historical naming style might become deprecated in a future release, so it is not recommended for new projects.
Note:
The
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 suspiciously looking name of a
function (i.e. one that after macro replacement does not start with "__vector_").
Vector name
ADC_vect
ANALOG_-
COMP_0_vect
ANALOG_-
COMP_1_vect
Old name vector
SIG_ADC
Description
ADC Conversion
Complete
SIG_-
COMPARATOR0
SIG_-
COMPARATOR1
Analog parator 0
Analog parator 1
Com-
Com-
Applicable for device
AT90S2333, AT90S4433, AT90S4434,
AT90S8535, AT90PWM3, AT90PWM2,
AT90CAN128, AT90CAN32, AT90CAN64,
ATmega103, ATmega128, ATmega16,
ATmega163, ATmega165, ATmega169,
ATmega32, ATmega323, ATmega325,
ATmega3250, ATmega329, ATmega3290,
ATmega64, ATmega645, ATmega6450,
ATmega649, ATmega6490, ATmega8,
ATmega8535, ATmega168, ATmega48,
ATmega88, ATmega640, ATmega1280,
ATmega1281, ATmega324, ATmega164,
ATmega644, ATtiny13, ATtiny15, ATtiny26,
ATtiny45
AT90PWM3, AT90PWM2
AT90PWM3, AT90PWM2
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5.25
<avr/interrupt.h>: Interrupts 121
Vector name
ANALOG_-
COMP_2_vect
ANALOG_-
COMP_vect
ANA_-
COMP_vect
CANIT_vect SIG_CAN_-
INTERRUPT1
EEPROM_-
READY_vect
SIG_-
EEPROM_-
READY,
SIG_EE_-
READY
EE_RDY_vect SIG_-
EEPROM_-
READY
EE_READY_vect
Old name
SIG_vector
COMPARATOR2
SIG_-
COMPARATOR
SIG_-
COMPARATOR
Description
Analog parator 2
Analog parator
Analog parator
Com-
Com-
Com-
CAN Transfer
Complete or
Error
Applicable for device
AT90PWM3, AT90PWM2
AT90CAN128, AT90CAN32, AT90CAN64,
ATmega103, ATmega128, ATmega165, ATmega169, ATmega325, ATmega3250, ATmega329, ATmega3290, ATmega64, ATmega645, ATmega6450, ATmega649, ATmega6490, ATmega168, ATmega48, ATmega88, ATmega640, ATmega1280, ATmega1281, ATmega324, ATmega164, ATmega644
AT90S1200, AT90S2313, AT90S2333,
AT90S4414, AT90S4433, AT90S4434,
AT90S8515, AT90S8535, ATmega16,
ATmega161, ATmega162, ATmega163,
ATmega32, ATmega323, ATmega8, ATmega8515, ATmega8535, ATtiny11,
ATtiny12, ATtiny13, ATtiny15, ATtiny2313,
ATtiny26, ATtiny28, ATtiny45
AT90CAN128, AT90CAN32, AT90CAN64
SIG_-
EEPROM_-
READY
EEPROM Ready
EEPROM Ready
ATtiny2313
AT90S2333, AT90S4433, AT90S4434,
AT90S8535, ATmega16, ATmega161,
ATmega162, ATmega163, ATmega32,
ATmega323, ATmega8, ATmega8515, ATmega8535, ATtiny12, ATtiny13, ATtiny15,
ATtiny26, ATtiny45
AT90PWM3, AT90PWM2, AT90CAN128,
AT90CAN32, AT90CAN64, ATmega103,
ATmega128, ATmega165, ATmega169, ATmega325, ATmega3250, ATmega329, ATmega3290, ATmega64, ATmega645, ATmega6450, ATmega649, ATmega6490, ATmega168, ATmega48, ATmega88, ATmega640, ATmega1280, ATmega1281, ATmega324, ATmega164, ATmega644
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5.25
<avr/interrupt.h>: Interrupts 122
Vector name
INT0_vect
INT1_vect
INT2_vect
INT3_vect
INT4_vect
INT5_vect
INT6_vect
INT7_vect
Old name
SIG_vector
INTERRUPT0
SIG_-
INTERRUPT1
SIG_-
INTERRUPT2
SIG_-
INTERRUPT3
SIG_-
INTERRUPT4
SIG_-
INTERRUPT5
SIG_-
INTERRUPT6
SIG_-
INTERRUPT7
Description
External Interrupt
0
External Interrupt
Request 1
External Interrupt
Request 2
External Interrupt
Request 3
External Interrupt
Request 4
External Interrupt
Request 5
External Interrupt
Request 6
External Interrupt
Request 7
Applicable for device
AT90S1200, AT90S2313, AT90S2323,
AT90S2333, AT90S2343, AT90S4414,
AT90S4433, AT90S4434, AT90S8515,
AT90S8535, AT90PWM3, AT90PWM2,
AT90CAN128, AT90CAN32, AT90CAN64,
ATmega103, ATmega128, ATmega16,
ATmega161, ATmega162, ATmega163,
ATmega165, ATmega169, ATmega32,
ATmega323, ATmega325, ATmega3250,
ATmega329, ATmega3290, ATmega64,
ATmega645, ATmega6450, ATmega649,
ATmega6490, ATmega8, ATmega8515,
ATmega8535, ATmega168, ATmega48,
ATmega88, ATmega640, ATmega1280,
ATmega1281, ATmega324, ATmega164,
ATmega644, ATtiny11, ATtiny12, ATtiny13, ATtiny15, ATtiny22, ATtiny2313,
ATtiny26, ATtiny28, ATtiny45
AT90S2313, AT90S2333, AT90S4414,
AT90S4433, AT90S4434, AT90S8515,
AT90S8535, AT90PWM3, AT90PWM2,
AT90CAN128, AT90CAN32, AT90CAN64,
ATmega103, ATmega128, ATmega16,
ATmega161, ATmega162, ATmega163,
ATmega32, ATmega323, ATmega64,
ATmega8, ATmega8515, ATmega8535,
ATmega168, ATmega48, ATmega88, ATmega640, ATmega1280, ATmega1281,
ATmega324, ATmega164, ATmega644,
ATtiny2313, ATtiny28
AT90PWM3, AT90PWM2, AT90CAN128,
AT90CAN32, AT90CAN64, ATmega103,
ATmega128, ATmega16, ATmega161, ATmega162, ATmega32, ATmega323, ATmega64, ATmega8515, ATmega8535, ATmega640, ATmega1280, ATmega1281, ATmega324, ATmega164, ATmega644
AT90PWM3, AT90PWM2, AT90CAN128,
AT90CAN32, AT90CAN64, ATmega103,
ATmega128, ATmega64, ATmega640, ATmega1280, ATmega1281
AT90CAN128, AT90CAN32, AT90CAN64,
ATmega103, ATmega128, ATmega64, ATmega640, ATmega1280, ATmega1281
AT90CAN128, AT90CAN32, AT90CAN64,
ATmega103, ATmega128, ATmega64, ATmega640, ATmega1280, ATmega1281
AT90CAN128, AT90CAN32, AT90CAN64,
ATmega103, ATmega128, ATmega64, ATmega640, ATmega1280, ATmega1281
AT90CAN128, AT90CAN32, AT90CAN64,
ATmega103, ATmega128, ATmega64, ATmega640, ATmega1280, ATmega1281
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5.25
<avr/interrupt.h>: Interrupts 123
Vector name
IO_PINS_vect
LCD_vect
LOWLEVEL_-
IO_PINS_vect
OVRIT_vect
PCINT0_vect
Old name vector
SIG_PIN,
SIG_PIN_-
CHANGE
SIG_LCD
SIG_PIN
SIG_CAN_-
OVERFLOW1
SIG_PIN_-
CHANGE0
Description
External Interrupt
Request 0
LCD Start of
Frame
Low-level Input on Port B
CAN
Overrun
Timer
Pin Change Interrupt Request 0
PCINT1_vect
PCINT2_vect
PCINT3_vect
PCINT_vect
SIG_PIN_-
CHANGE1
SIG_PIN_-
CHANGE2
Applicable for device
ATtiny11, ATtiny12, ATtiny15, ATtiny26
ATmega169, ATmega329, ATmega3290,
ATmega649, ATmega6490
ATtiny28
AT90CAN128, AT90CAN32, AT90CAN64
Pin Change Interrupt Request 1
Pin Change Interrupt Request 2
Pin Change Interrupt Request 3
ATmega162, ATmega165, ATmega169, ATmega325, ATmega3250, ATmega329, ATmega3290, ATmega645, ATmega6450, ATmega649, ATmega6490, ATmega168, ATmega48, ATmega88, ATmega640, ATmega1280, ATmega1281, ATmega324, ATmega164, ATmega644, ATtiny13, ATtiny45
ATmega162, ATmega165, ATmega169, ATmega325, ATmega3250, ATmega329, ATmega3290, ATmega645, ATmega6450, ATmega649, ATmega6490, ATmega168, ATmega48, ATmega88, ATmega640, ATmega1280, ATmega1281, ATmega324, ATmega164, ATmega644
ATmega3250, ATmega3290, ATmega6450,
ATmega6490, ATmega168, ATmega48, ATmega88, ATmega640, ATmega1280, ATmega1281, ATmega324, ATmega164, ATmega644
ATmega3250, ATmega3290, ATmega6450,
ATmega6490, ATmega324, ATmega164,
ATmega644
ATtiny2313
PSC0_-
CAPT_vect
PSC0_EC_vect
PSC1_-
CAPT_vect
PSC1_EC_vect
PSC2_-
CAPT_vect
PSC2_EC_vect
SIG_PIN_-
CHANGE3
SIG_PIN_-
CHANGE,
SIG_PCINT
SIG_PSC0_-
CAPTURE
SIG_PSC0_-
END_CYCLE
SIG_PSC1_-
CAPTURE
SIG_PSC1_-
END_CYCLE
SIG_PSC2_-
CAPTURE
SIG_PSC2_-
END_CYCLE
PSC0
Event
PSC0 End Cycle
PSC1
Event
Capture
Capture
PSC1 End Cycle
PSC2
Event
Capture
PSC2 End Cycle
AT90PWM3, AT90PWM2
AT90PWM3, AT90PWM2
AT90PWM3, AT90PWM2
AT90PWM3, AT90PWM2
AT90PWM3, AT90PWM2
AT90PWM3, AT90PWM2
Generated on Sat Nov 19 23:00:48 2005 for avr-libc by Doxygen
5.25
<avr/interrupt.h>: Interrupts 124
Vector name
SPI_STC_vect
SPM_RDY_vect
SPM_-
READY_vect
TIM0_-
COMPA_vect
TIM0_-
COMPB_vect
TIM0_OVF_vect
TIM1_-
COMPA_vect
TIM1_-
COMPB_vect
TIM1_OVF_vect
TIMER0_-
COMPA_vect
TIMER0_-
COMPB_vect
Old name
SIG_SPI
SIG_SPM_-
READY
SIG_SPM_-
READY
SIG_vector
OUTPUT_-
COMPARE0A
SIG_-
OUTPUT_-
COMPARE0B
SIG_-
OVERFLOW0
SIG_-
OUTPUT_-
COMPARE1A
SIG_-
OUTPUT_-
COMPARE1B
SIG_-
OVERFLOW1
SIG_-
OUTPUT_-
COMPARE0A
SIG_-
OUTPUT_-
COMPARE0B,
SIG_-
OUTPUT_-
COMPARE0_-
B
Description
Serial Transfer
Complete
Store
Store
Timer Counter 0
Compare Match
B
Program
Memory Ready
Program
Memory Read
Timer/Counter
Compare Match
A
Timer/Counter
Compare Match
B
Timer/Counter0
Overflow
Timer/Counter1
Compare Match
1A
Timer/Counter1
Compare Match
B
Timer/Counter1
Overflow
TimerCounter0
Compare Match
A
Applicable for device
AT90S2333, AT90S4414, AT90S4433,
AT90S4434, AT90S8515, AT90S8535,
AT90PWM3, AT90PWM2, AT90CAN128,
AT90CAN32, AT90CAN64, ATmega103,
ATmega128, ATmega16, ATmega161,
ATmega162, ATmega163, ATmega165,
ATmega169, ATmega32, ATmega323,
ATmega325, ATmega3250, ATmega329,
ATmega3290, ATmega64, ATmega645,
ATmega6450, ATmega649, ATmega6490,
ATmega8, ATmega8515, ATmega8535,
ATmega168, ATmega48, ATmega88, ATmega640, ATmega1280, ATmega1281,
ATmega324, ATmega164, ATmega644
ATmega16, ATmega162, ATmega32, ATmega323, ATmega8, ATmega8515, ATmega8535
AT90PWM3, AT90PWM2, AT90CAN128,
AT90CAN32, AT90CAN64, ATmega128,
ATmega165, ATmega169, ATmega325, ATmega3250, ATmega329, ATmega3290, ATmega64, ATmega645, ATmega6450, ATmega649, ATmega6490, ATmega168, ATmega48, ATmega88, ATmega640, ATmega1280, ATmega1281, ATmega324, ATmega164, ATmega644
ATtiny13, ATtiny45
ATtiny13, ATtiny45
ATtiny13, ATtiny45
ATtiny45
ATtiny45
ATtiny45
ATmega168, ATmega48, ATmega88, ATmega640, ATmega1280, ATmega1281, ATmega324, ATmega164, ATmega644, ATtiny2313
AT90PWM3, AT90PWM2, ATmega168,
ATmega48, ATmega88, ATmega640, ATmega1280, ATmega1281, ATmega324, ATmega164, ATmega644, ATtiny2313
Generated on Sat Nov 19 23:00:48 2005 for avr-libc by Doxygen
5.25
<avr/interrupt.h>: Interrupts 125
Vector name
TIMER0_-
COMP_A_vect
TIMER0_-
COMP_vect
TIMER0_-
OVF0_vect
TIMER0_-
OVF_vect
TIMER1_-
CAPT1_vect
TIMER1_-
CAPT_vect
TIMER1_-
CMPA_vect
Old name
SIG_vector
OUTPUT_-
COMPARE0A,
SIG_-
OUTPUT_-
COMPARE0_-
A
SIG_-
OUTPUT_-
COMPARE0
Description
Timer/Counter0
Compare Match
A
Timer/Counter0
Compare Match
SIG_-
OVERFLOW0
SIG_-
OVERFLOW0
SIG_INPUT_-
CAPTURE1
SIG_INPUT_-
CAPTURE1
SIG_-
OUTPUT_-
COMPARE1A
Applicable for device
AT90PWM3, AT90PWM2
Timer/Counter0
Overflow
Timer/Counter0
Overflow
AT90CAN128, AT90CAN32, AT90CAN64,
ATmega103, ATmega128, ATmega16, ATmega161, ATmega162, ATmega165, ATmega169, ATmega32, ATmega323, ATmega325, ATmega3250, ATmega329, ATmega3290, ATmega64, ATmega645, ATmega6450, ATmega649, ATmega6490, ATmega8515, ATmega8535
AT90S2313, AT90S2323, AT90S2343, ATtiny22, ATtiny26
AT90S1200, AT90S2333, AT90S4414,
AT90S4433, AT90S4434, AT90S8515,
AT90S8535, AT90PWM3, AT90PWM2,
AT90CAN128, AT90CAN32, AT90CAN64,
ATmega103, ATmega128, ATmega16,
ATmega161, ATmega162, ATmega163,
ATmega165, ATmega169, ATmega32,
ATmega323, ATmega325, ATmega3250,
ATmega329, ATmega3290, ATmega64,
ATmega645, ATmega6450, ATmega649,
ATmega6490, ATmega8, ATmega8515,
ATmega8535, ATmega168, ATmega48,
ATmega88, ATmega640, ATmega1280,
ATmega1281, ATmega324, ATmega164,
ATmega644, ATtiny11, ATtiny12, ATtiny15,
ATtiny2313, ATtiny28
AT90S2313 Timer/Counter1
Capture Event
Timer/Counter
Capture Event
Timer/Counter1
Compare Match
1A
AT90S2333, AT90S4414, AT90S4433,
AT90S4434, AT90S8515, AT90S8535,
AT90PWM3, AT90PWM2, AT90CAN128,
AT90CAN32, AT90CAN64, ATmega103,
ATmega128, ATmega16, ATmega161,
ATmega162, ATmega163, ATmega165,
ATmega169, ATmega32, ATmega323,
ATmega325, ATmega3250, ATmega329,
ATmega3290, ATmega64, ATmega645,
ATmega6450, ATmega649, ATmega6490,
ATmega8, ATmega8515, ATmega8535,
ATmega168, ATmega48, ATmega88, ATmega640, ATmega1280, ATmega1281,
ATmega324, ATmega164, ATmega644,
ATtiny2313
ATtiny26
Generated on Sat Nov 19 23:00:48 2005 for avr-libc by Doxygen
5.25
<avr/interrupt.h>: Interrupts 126
Vector name
TIMER1_-
CMPB_vect
TIMER1_-
COMP1_vect
TIMER1_-
COMPA_vect
TIMER1_-
COMPB_vect
TIMER1_-
COMPC_vect
TIMER1_-
COMP_vect
TIMER1_-
OVF1_vect
Old name
SIG_vector
OUTPUT_-
COMPARE1B
SIG_-
OUTPUT_-
COMPARE1A
SIG_-
OUTPUT_-
COMPARE1A
Description
Timer/Counter1
Compare Match
1B
Timer/Counter1
Compare Match
Timer/Counter1
Compare Match
A
SIG_-
OUTPUT_-
COMPARE1B
SIG_-
OUTPUT_-
COMPARE1C
SIG_-
OUTPUT_-
COMPARE1A
SIG_-
OVERFLOW1
Applicable for device
ATtiny26
AT90S2313
Timer/Counter1
Compare MatchB
Timer/Counter1
Compare Match
C
Timer/Counter1
Compare Match
Timer/Counter1
Overflow
AT90S4414, AT90S4434, AT90S8515,
AT90S8535, AT90PWM3, AT90PWM2,
AT90CAN128, AT90CAN32, AT90CAN64,
ATmega103, ATmega128, ATmega16,
ATmega161, ATmega162, ATmega163,
ATmega165, ATmega169, ATmega32,
ATmega323, ATmega325, ATmega3250,
ATmega329, ATmega3290, ATmega64,
ATmega645, ATmega6450, ATmega649,
ATmega6490, ATmega8, ATmega8515,
ATmega8535, ATmega168, ATmega48,
ATmega88, ATmega640, ATmega1280,
ATmega1281, ATmega324, ATmega164,
ATmega644, ATtiny2313
AT90S4414, AT90S4434, AT90S8515,
AT90S8535, AT90PWM3, AT90PWM2,
AT90CAN128, AT90CAN32, AT90CAN64,
ATmega103, ATmega128, ATmega16,
ATmega161, ATmega162, ATmega163,
ATmega165, ATmega169, ATmega32,
ATmega323, ATmega325, ATmega3250,
ATmega329, ATmega3290, ATmega64,
ATmega645, ATmega6450, ATmega649,
ATmega6490, ATmega8, ATmega8515,
ATmega8535, ATmega168, ATmega48,
ATmega88, ATmega640, ATmega1280,
ATmega1281, ATmega324, ATmega164,
ATmega644, ATtiny2313
AT90CAN128, AT90CAN32, AT90CAN64,
ATmega128, ATmega64, ATmega640, ATmega1280, ATmega1281
AT90S2333, AT90S4433, ATtiny15
AT90S2313, ATtiny26
Generated on Sat Nov 19 23:00:48 2005 for avr-libc by Doxygen
5.25
<avr/interrupt.h>: Interrupts 127
Vector name
TIMER1_-
OVF_vect
TIMER2_-
COMPA_vect
TIMER2_-
COMPB_vect
TIMER2_-
COMP_vect
TIMER2_-
OVF_vect
TIMER3_-
CAPT_vect
TIMER3_-
COMPA_vect
TIMER3_-
COMPB_vect
TIMER3_-
COMPC_vect
Old name
SIG_vector
OVERFLOW1
SIG_-
OUTPUT_-
COMPARE2A
SIG_-
OUTPUT_-
COMPARE2B
SIG_-
OUTPUT_-
COMPARE2
SIG_-
OVERFLOW2
SIG_INPUT_-
CAPTURE3
SIG_-
OUTPUT_-
COMPARE3A
SIG_-
OUTPUT_-
COMPARE3B
SIG_-
OUTPUT_-
COMPARE3C
Description
Timer/Counter1
Overflow
Timer/Counter2
Compare Match
A
Timer/Counter2
Compare Match
A
Timer/Counter2
Compare Match
Timer/Counter2
Overflow
Timer/Counter3
Capture Event
Timer/Counter3
Compare Match
A
Timer/Counter3
Compare Match
B
Timer/Counter3
Compare Match
C
Applicable for device
AT90S2333, AT90S4414, AT90S4433,
AT90S4434, AT90S8515, AT90S8535,
AT90PWM3, AT90PWM2, AT90CAN128,
AT90CAN32, AT90CAN64, ATmega103,
ATmega128, ATmega16, ATmega161,
ATmega162, ATmega163, ATmega165,
ATmega169, ATmega32, ATmega323,
ATmega325, ATmega3250, ATmega329,
ATmega3290, ATmega64, ATmega645,
ATmega6450, ATmega649, ATmega6490,
ATmega8, ATmega8515, ATmega8535,
ATmega168, ATmega48, ATmega88, ATmega640, ATmega1280, ATmega1281,
ATmega324, ATmega164, ATmega644,
ATtiny15, ATtiny2313
ATmega168, ATmega48, ATmega88, ATmega640, ATmega1280, ATmega1281, ATmega324, ATmega164, ATmega644
ATmega168, ATmega48, ATmega88, ATmega640, ATmega1280, ATmega1281, ATmega324, ATmega164, ATmega644
AT90S4434, AT90S8535, AT90CAN128,
AT90CAN32, AT90CAN64, ATmega103,
ATmega128, ATmega16, ATmega161, ATmega162, ATmega163, ATmega165, ATmega169, ATmega32, ATmega323, ATmega325, ATmega3250, ATmega329, ATmega3290, ATmega64, ATmega645, ATmega6450, ATmega649, ATmega6490, ATmega8, ATmega8535
AT90S4434, AT90S8535, AT90CAN128,
AT90CAN32, AT90CAN64, ATmega103,
ATmega128, ATmega16, ATmega161, ATmega162, ATmega163, ATmega165, ATmega169, ATmega32, ATmega323, ATmega325, ATmega3250, ATmega329, ATmega3290, ATmega64, ATmega645, ATmega6450, ATmega649, ATmega6490, ATmega8, ATmega8535, ATmega168, ATmega48, ATmega88, ATmega640, ATmega1280, ATmega1281, ATmega324, ATmega164, ATmega644
AT90CAN128, AT90CAN32, AT90CAN64,
ATmega128, ATmega162, ATmega64, ATmega640, ATmega1280, ATmega1281
AT90CAN128, AT90CAN32, AT90CAN64,
ATmega128, ATmega162, ATmega64, ATmega640, ATmega1280, ATmega1281
AT90CAN128, AT90CAN32, AT90CAN64,
ATmega128, ATmega162, ATmega64, ATmega640, ATmega1280, ATmega1281
AT90CAN128, AT90CAN32, AT90CAN64,
ATmega128, ATmega64, ATmega640, ATmega1280, ATmega1281
Generated on Sat Nov 19 23:00:48 2005 for avr-libc by Doxygen
5.25
<avr/interrupt.h>: Interrupts 128
Vector name
TIMER3_-
OVF_vect
TIMER4_-
CAPT_vect
TIMER4_-
COMPA_vect
TIMER4_-
COMPB_vect
TIMER4_-
COMPC_vect
TIMER4_-
OVF_vect
TIMER5_-
CAPT_vect
TIMER5_-
COMPA_vect
TIMER5_-
COMPB_vect
TIMER5_-
COMPC_vect
TIMER5_-
OVF_vect
TWI_vect
TXDONE_vect
TXEMPTY_vect
UART0_RX_vect
UART0_TX_vect
UART0_-
UDRE_vect
UART1_RX_vect
SIG_-
TXDONE
SIG_TXBE
SIG_-
UART0_-
RECV
SIG_-
UART0_-
TRANS
SIG_-
UART0_-
DATA
SIG_-
UART1_-
RECV
Old name
SIG_vector
OVERFLOW3
SIG_INPUT_-
CAPTURE4
SIG_-
OUTPUT_-
COMPARE4A
SIG_-
OUTPUT_-
COMPARE4B
SIG_-
OUTPUT_-
COMPARE4C
SIG_-
OVERFLOW4
SIG_INPUT_-
CAPTURE5
SIG_-
OUTPUT_-
COMPARE5A
SIG_-
OUTPUT_-
COMPARE5B
SIG_-
OUTPUT_-
COMPARE5C
SIG_-
OVERFLOW5
SIG_2WIRE_-
SERIAL
Description
Timer/Counter3
Overflow
Timer/Counter4
Capture Event
Timer/Counter4
Compare Match
A
Timer/Counter4
Compare Match
B
Timer/Counter4
Compare Match
C
Timer/Counter4
Overflow
Timer/Counter5
Capture Event
Timer/Counter5
Compare Match
A
Timer/Counter5
Compare Match
B
Timer/Counter5
Compare Match
C
Timer/Counter5
Overflow
2-wire Serial Interface
Applicable for device
AT90CAN128, AT90CAN32, AT90CAN64,
ATmega128, ATmega162, ATmega64, ATmega640, ATmega1280, ATmega1281
ATmega640, ATmega1280, ATmega1281
ATmega640, ATmega1280, ATmega1281
ATmega640, ATmega1280, ATmega1281
ATmega640, ATmega1280, ATmega1281
ATmega640, ATmega1280, ATmega1281
ATmega640, ATmega1280, ATmega1281
ATmega640, ATmega1280, ATmega1281
ATmega640, ATmega1280, ATmega1281
ATmega640, ATmega1280, ATmega1281
ATmega640, ATmega1280, ATmega1281
AT90CAN128, AT90CAN32, AT90CAN64,
ATmega128, ATmega16, ATmega163, ATmega32, ATmega323, ATmega64, ATmega8, ATmega8535, ATmega168, ATmega48, ATmega88, ATmega640, ATmega1280, ATmega1281, ATmega324, ATmega164, ATmega644
AT86RF401 Transmission
Done, Bit Timer
Flag 2 Interrupt
Transmit Buffer
Empty, Bit Itmer
Flag 0 Interrupt
UART0,
Complete
Rx
AT86RF401
ATmega161
UART0,
Complete
UART0 Data
Register Empty
UART1,
Complete
Tx
Rx
ATmega161
ATmega161
ATmega161
Generated on Sat Nov 19 23:00:48 2005 for avr-libc by Doxygen
5.25
<avr/interrupt.h>: Interrupts 129
Vector name
UART1_TX_vect
UART1_-
UDRE_vect
UART_RX_vect
UART_TX_vect
UART_-
UDRE_vect
USART0_-
RXC_vect
USART0_-
RX_vect
USART0_-
TXC_vect
USART0_-
TX_vect
USART0_-
UDRE_vect
USART1_-
RXC_vect
USART1_-
RX_vect
USART1_-
TXC_vect
Old name
SIG_vector
UART1_-
TRANS
SIG_-
UART1_-
DATA
SIG_UART_-
RECV
SIG_UART_-
TRANS
SIG_UART_-
DATA
Description
UART1,
Complete
UART1
UART, Tx Complete
UART Data Register Empty
Data
Register Empty
Tx
UART, Rx Complete
Rx
Applicable for device
ATmega161
ATmega161
AT90S2313, AT90S2333, AT90S4414,
AT90S4433, AT90S4434, AT90S8515,
AT90S8535, ATmega103, ATmega163,
ATmega8515
AT90S2313, AT90S2333, AT90S4414,
AT90S4433, AT90S4434, AT90S8515,
AT90S8535, ATmega103, ATmega163,
ATmega8515
AT90S2313, AT90S2333, AT90S4414,
AT90S4433, AT90S4434, AT90S8515,
AT90S8535, ATmega103, ATmega163,
ATmega8515
ATmega162 SIG_-
USART0_-
RECV
SIG_-
UART0_-
RECV
USART0,
Complete
USART0,
Complete
Rx
Tx
AT90CAN128, AT90CAN32, AT90CAN64,
ATmega128, ATmega165, ATmega169, ATmega325, ATmega329, ATmega64, ATmega645, ATmega649, ATmega640, ATmega1280, ATmega1281, ATmega324, ATmega164, ATmega644
ATmega162 SIG_-
USART0_-
TRANS
SIG_-
UART0_-
TRANS
USART0,
Complete
USART0,
Complete
Tx
SIG_-
UART0_-
DATA
USART0 Data
Register Empty
Rx
AT90CAN128, AT90CAN32, AT90CAN64,
ATmega128, ATmega165, ATmega169, ATmega325, ATmega3250, ATmega329, ATmega3290, ATmega64, ATmega645, ATmega6450, ATmega649, ATmega6490, ATmega640, ATmega1280, ATmega1281, ATmega324, ATmega164, ATmega644
AT90CAN128, AT90CAN32, AT90CAN64,
ATmega128, ATmega162, ATmega165, ATmega169, ATmega325, ATmega329, ATmega64, ATmega645, ATmega649, ATmega640, ATmega1280, ATmega1281, ATmega324, ATmega164, ATmega644
ATmega162 SIG_-
USART1_-
RECV
SIG_-
UART1_-
RECV
SIG_-
USART1_-
TRANS
USART1,
Complete
USART1,
Complete
USART1,
Complete
Rx
Tx
AT90CAN128, AT90CAN32, AT90CAN64,
ATmega128, ATmega64, ATmega640, ATmega1280, ATmega1281, ATmega324, ATmega164, ATmega644
ATmega162
Generated on Sat Nov 19 23:00:48 2005 for avr-libc by Doxygen
5.25
<avr/interrupt.h>: Interrupts 130
Vector name
USART1_-
TX_vect
USART1_-
UDRE_vect
Old name
SIG_vector
UART1_-
TRANS
SIG_-
UART1_-
DATA
USART2_-
RX_vect
USART2_-
TX_vect
USART2_-
UDRE_vect
USART3_-
RX_vect
USART3_-
TX_vect
USART3_-
UDRE_vect
USART_-
RXC_vect
USART_RX_vect
USART_-
TXC_vect
USART_TX_vect
USART_-
UDRE_vect
USART_-
RECV, SIG_-
UART_RECV
SIG_-
USART_-
RECV, SIG_-
UART_RECV
SIG_-
USART_-
TRANS,
SIG_UART_-
TRANS
SIG_-
USART_-
TRANS,
SIG_UART_-
TRANS
SIG_-
USART_-
DATA, SIG_-
UART_DATA
SIG_-
USART2_-
RECV
SIG_-
USART2_-
TRANS
SIG_-
USART2_-
DATA
SIG_-
USART3_-
RECV
SIG_-
USART3_-
TRANS
SIG_-
USART3_-
DATA
SIG_-
USI_-
OVERFLOW_vect
SIG_USI_-
OVERFLOW
Description
USART1,
Complete
Tx
USART1, Data
Register Empty
USART2,
Complete
USART2,
Complete
USART,
Complete
USART,
Complete
USART,
Complete
Rx
Tx
USART3 Data register Empty
USART,
Complete
Rx
Rx
Tx
Tx
Applicable for device
AT90CAN128, AT90CAN32, AT90CAN64,
ATmega128, ATmega64, ATmega640, ATmega1280, ATmega1281, ATmega324, ATmega164, ATmega644
AT90CAN128, AT90CAN32, AT90CAN64,
ATmega128, ATmega162, ATmega64, ATmega640, ATmega1280, ATmega1281, ATmega324, ATmega164, ATmega644
ATmega640, ATmega1280, ATmega1281
ATmega640, ATmega1280, ATmega1281
USART2 Data register Empty
ATmega640, ATmega1280, ATmega1281
Rx ATmega640, ATmega1280, ATmega1281 USART3,
Complete
USART3,
Complete
Tx ATmega640, ATmega1280, ATmega1281
ATmega640, ATmega1280, ATmega1281
ATmega16, ATmega32, ATmega323, ATmega8
AT90PWM3, AT90PWM2, ATmega3250,
ATmega3290, ATmega6450, ATmega6490,
ATmega8535, ATmega168, ATmega48, ATmega88, ATtiny2313
ATmega16, ATmega32, ATmega323, ATmega8
AT90PWM3, AT90PWM2, ATmega8535,
ATmega168, ATmega48, ATmega88, ATtiny2313
USART Data
Register Empty
USI Overflow
AT90PWM3, AT90PWM2, ATmega16, ATmega32, ATmega323, ATmega3250, ATmega3290, ATmega6450, ATmega6490, ATmega8, ATmega8535, ATmega168, ATmega48, ATmega88, ATtiny2313
ATmega165, ATmega169, ATmega325, ATmega3250, ATmega329, ATmega3290, ATmega645, ATmega6450, ATmega649, ATmega6490, ATtiny2313
Generated on Sat Nov 19 23:00:48 2005 for avr-libc by Doxygen
5.25
<avr/interrupt.h>: Interrupts 131
Vector name
USI_OVF_vect
USI_START_vect
USI_STRT_vect
WDT_-
OVERFLOW_vect
WDT_vect
Old name vector
SIG_USI_-
OVERFLOW
SIG_USI_-
START
SIG_USI_-
START
SIG_-
WATCHDOG_-
TIMEOUT,
SIG_WDT_-
OVERFLOW
SIG_WDT,
SIG_-
WATCHDOG_-
TIMEOUT
Description
USI Overflow
USI Start Condition
USI Start
Watchdog Timer
Overflow
Watchdog Timeout Interrupt
Applicable for device
ATtiny26, ATtiny45
ATmega165, ATmega169, ATmega325, ATmega3250, ATmega329, ATmega3290, ATmega645, ATmega6450, ATmega649, ATmega6490, ATtiny2313, ATtiny45
ATtiny26
ATtiny2313
AT90PWM3, AT90PWM2, ATmega168,
ATmega48, ATmega88, ATmega640, ATmega1280, ATmega1281, ATmega324, ATmega164, ATmega644, ATtiny13, ATtiny45
Macros for writing interrupt handler functions
• #define
• #define
• #define
5.25.2
Define Documentation
5.25.2.1
#define EMPTY_INTERRUPT(vector)
Value: void vector (void) __attribute__ ((naked)); \ void vector (void) { __asm__ __volatile__ ("reti" ::); }
#include <avr/interrupt.h>
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);
5.25.2.2
#define ISR(vector)
Value:
Generated on Sat Nov 19 23:00:48 2005 for avr-libc by Doxygen
5.26
<avr/sfr_defs.h>: Special function registers 132 void vector (void) __attribute__ ((signal)); void vector (void)
#include <avr/interrupt.h>
\
Introduces an interrupt handler function (interrupt service routine) that runs with global interrupts initially disabled.
vector must be one of the interrupt vector names that are valid for the particular
MCU type.
5.25.2.3
#define SIGNAL(signame)
Value: void signame (void) __attribute__ ((signal)); void signame (void)
#include <avr/interrupt.h>
\
Introduces an interrupt handler function that runs with global interrupts initially disabled.
This is the same as the ISR macro.
Note:
Do not use anymore in new code, it will be deprecated in a future release.
5.26
<avr/sfr_defs.h>: Special function registers
5.26.1
Detailed Description
When working with microcontrollers, many of the tasks usually consist of controlling the peripherals that are connected to the device, respectively programming the subsystems that are contained in the controller (which by itself communicate with the circuitry connected to the controller).
The AVR series of microcontrollers offers two different paradigms to perform this task.
There’s a separate IO address space available (as it is known from some high-level
CISC CPUs) that can be addressed with specific IO instructions that are applicable to some or all of the IO address space (in, out, sbi etc.). The entire IO address space is also made available as memory-mapped IO, i. e. it can be accessed using all the
MCU instructions that are applicable to normal data memory. 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 either address 0x60, or 0x100 depending on the device.)
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<avr/sfr_defs.h>: Special function registers 133
AVR Libc supports both these paradigms. While by default, the implementation uses memory-mapped IO access, this is hidden from the programmer. So the programmer can access IO registers either with a special function like outb():
#include <avr/io.h> outb(PORTA, 0x33); or they can assign a value directly to the symbolic address:
PORTA = 0x33;
The compiler’s choice of which method to use when actually accessing the IO port is completely independent of the way the programmer chooses to write the code. So even if the programmer uses the memory-mapped paradigm and writes
PORTA |= 0x40; the compiler can optimize this into the use of an sbi instruction (of course, provided the target address is within the allowable range for this instruction, and the right-hand side of the expression is a constant value known at compile-time).
The advantage of using the memory-mapped paradigm in C programs is that it makes the programs more portable to other C compilers for the AVR platform. Some people might also feel that this is more readable. For example, the following two statements would be equivalent: outb(DDRD, inb(DDRD) & ~LCDBITS);
DDRD &= ~LCDBITS;
The generated code is identical for both. Without optimization, the compiler strictly generates code following the memory-mapped paradigm, while with optimization turned on, code is generated using the (faster and smaller) in/out MCU instructions.
Note that special care must be taken when accessing some of the 16-bit timer IO registers 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 sbi/cbi
As described above, access to the AVR single bit set and clear instructions are provided via the standard C bit manipulation commands. The sbi and cbi commands are no longer directly supported. sbi (sfr,bit) can be replaced by sfr |=
.
ie:
sbi(PORTB, PB1) ; is now PORTB |=
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This actually is more flexible than having sbi directly, as the optimizer will use a hardware sbi if appropriate, or a read/or/write if not. You do not need to keep track of which registers sbi/cbi will operate on.
Likewise, cbi (sfr,bit) is now sfr &= ∼( _BV(bit) );
Modules
•
Additional notes from <avr/sfr_defs.h>
Bit manipulation
• #define
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))
5.26.2
Define Documentation
5.26.2.1
#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
5.26.2.2
#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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5.26.2.3
#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.
5.26.2.4
#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.
5.26.2.5
#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.
5.27
Demo projects
5.27.1
Detailed Description
Various small demo projects are provided to illustrate several aspects of using the opensource utilities for the AVR controller series. It should be kept in mind that these demos 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
is somewhat like the "Hello world!" application for a microcontroller, 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
Example using the two-wire interface (TWI)
project explains the use of the twowire hardware interface (also known as "I2C") that is present on many AVR controllers.
Modules
•
•
Example using the two-wire interface (TWI)
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5.28
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.
5.28.1
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 (pincompatible) ATtiny2313 for the project, or perhaps the ATmega8 or one of its successors (ATmega48/88/168) which have become quite popular since the original 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 internal 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.
VCC
GND
R1
20K
GND
C2
C1
18pf
18pf
1
4
5
20
10
IC1
RESET
XTAL2
XTAL1
(SCK)PB7
(MISO)PB6
(MOSI)PB5
PB4
(OCI)PB3
PB2
(AIN1)PB1
(AIN0)PB0
VCC
GND
(ICP)PD6
(T1)PD5
(T0)PD4
(INT1)PD3
(INT0)PD2
(TXD)PD1
(RXD)PD0
AT90S2313P
6
3
2
8
7
11
9
15
14
13
12
19
18
17
16
R2
*
See note [7]
GND
Figure 1: Schematic of circuit for demo project
The source code is given in
. For the sake of this example, create a file called
containing this source code. Some of the more important parts of the code are:
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Note [1]:
The PWM is being used in 10-bit mode, so we need a 16-bit variable to remember the current value.
is a macro that marks the function as an interrupt routine. In this case, the function will get called when the timer overflows. Setting up interrupts is explained in greater detail in
<avr/interrupt.h>: Interrupts .
Note [3]:
This section determines the new value of the PWM.
Note [4]:
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
Note [5]:
This routine gets called after a reset. It initializes the PWM and enables interrupts.
Note [6]:
The main loop of the program does nothing – all the work is done by the interrupt routine! If this was a real product, we’d probably put a SLEEP instruction in this loop to conserve power.
Note [7]:
Early AVR devices saturate their outputs at rather low currents when sourcing current, 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.
5.28.2
The Source Code
/*
* ----------------------------------------------------------------------------
* "THE BEER-WARE LICENSE" (Revision 42):
* <[email protected]> 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
* ----------------------------------------------------------------------------
*
* Simple AVR demonstration.
Controls a LED that can be directly
* connected from OC1/OC1A to GND.
The brightness of the LED is
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* controlled with the PWM.
After each period of the PWM, the PWM
* value is either incremented or decremented, that’s all.
*
* $Id: demo.c,v 1.6 2005/11/04 22:55:15 joerg_wunsch Exp $
*/
#include <inttypes.h>
#include <avr/io.h>
#include <avr/interrupt.h>
#if defined(__AVR_AT90S2313__)
# define OC1 PB3
# define OCR OCR1
# define DDROC DDRB
#elif defined(__AVR_AT90S2333__) || defined(__AVR_AT90S4433__)
# define OC1 PB1
# define DDROC DDRB
# define OCR OCR1
#elif defined(__AVR_AT90S4414__) || defined(__AVR_AT90S8515__) || \ defined(__AVR_AT90S4434__) || defined(__AVR_AT90S8535__) || \ defined(__AVR_ATmega163__)
# define OC1 PD5
# define DDROC DDRD
# define OCR OCR1A
#elif defined(__AVR_ATmega8__)
# define OC1 PB1
# define DDROC DDRB
# define OCR OCR1A
# define PWM10 WGM10
# define PWM11 WGM11
#elif defined(__AVR_ATmega32__) || defined(__AVR_ATmega16__)
# define OC1 PD5
# define DDROC DDRD
# define OCR OCR1A
# define PWM10 WGM10
# define PWM11 WGM11
#elif defined(__AVR_ATmega64__) || defined(__AVR_ATmega128__)
# define OC1 PB5
# define DDROC DDRB
# define OCR OCR1A
# define PWM10 WGM10
# define PWM11 WGM11
#else
# error "Don’t know what kind of MCU you are compiling for"
#endif
#if defined(COM11)
# define XCOM11 COM11
#elif defined(COM1A1)
# define XCOM11 COM1A1
#else
# error "need either COM1A1 or COM11"
#endif enum { UP, DOWN }; volatile uint16_t pwm; /* Note [1] */
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ISR (TIMER1_OVF_vect) /* Note [2] */
{ switch (direction) /* Note [3] */
{ case UP: if (++pwm == 1023) direction = DOWN; break; case DOWN: if (--pwm == 0) direction = UP; break;
}
OCR = pwm; /* Note [4] */
} void ioinit (void) /* Note [5] */
{
/* tmr1 is 10-bit PWM */
TCCR1A = _BV (PWM10) | _BV (PWM11) | _BV (XCOM11);
/* tmr1 running on full MCU clock */
TCCR1B = _BV (CS10);
/* set PWM value to 0 */
OCR = 0;
/* enable OC1 and PB2 as output */
DDROC = _BV (OC1);
/* enable interrupts */
TIMSK = _BV (TOIE1); sei ();
} int main (void)
{ ioinit ();
/* loop forever, the interrupts are doing the rest */ for (;;) /* Note [6] */
; return (0);
}
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5.28.3
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=at90s2333 -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=at90s2333 -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.
5.28.4
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.
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 intersperses 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:
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A simple project demo.elf: file format elf32-avr
Sections:
Idx Name
0 .text
1 .data
2 .bss
Size VMA LMA File off Algn
000000e0 00000000 00000000 00000094 2**0
CONTENTS, ALLOC, LOAD, READONLY, CODE
00000000 00800060 000000e0 00000174 2**0
CONTENTS, ALLOC, LOAD, DATA
00000003 00800060 00800060 00000174 2**0
ALLOC
3 .noinit
4 .eeprom
5 .stab
00000000 00800063 00800063 00000174 2**0
CONTENTS
00000000 00810000 00810000 00000174 2**0
CONTENTS
00000768 00000000 00000000 00000174 2**2
CONTENTS, READONLY, DEBUGGING
6 .stabstr
000007da 00000000 00000000 000008dc 2**0
CONTENTS, READONLY, DEBUGGING
Disassembly of section .text:
00000000 <__vectors>:
0: 12 c0 rjmp .+36
2: 6d c0
4: 6c c0
6: 6b c0 rjmp .+218 rjmp .+216 rjmp .+214
8: 6a c0 a: 69 c0 c: 68 c0 e: 67 c0
10: 11 c0 rjmp .+212 rjmp .+210 rjmp .+208 rjmp .+206 rjmp .+34
12: 65 c0
14: 64 c0
16: 63 c0
18: 62 c0
1a: 61 c0
1c: 60 c0
1e: 5f c0
20: 5e c0
22: 5d c0
24: 5c c0 rjmp .+202 rjmp .+200 rjmp .+198 rjmp .+196 rjmp .+194 rjmp .+192 rjmp .+190 rjmp .+188 rjmp .+186 rjmp .+184
; 0x26 <__ctors_end>
; 0xde <__bad_interrupt>
; 0xde <__bad_interrupt>
; 0xde <__bad_interrupt>
; 0xde <__bad_interrupt>
; 0xde <__bad_interrupt>
; 0xde <__bad_interrupt>
; 0xde <__bad_interrupt>
; 0x34 <__vector_8>
; 0xde <__bad_interrupt>
; 0xde <__bad_interrupt>
; 0xde <__bad_interrupt>
; 0xde <__bad_interrupt>
; 0xde <__bad_interrupt>
; 0xde <__bad_interrupt>
; 0xde <__bad_interrupt>
; 0xde <__bad_interrupt>
; 0xde <__bad_interrupt>
; 0xde <__bad_interrupt>
00000026 <__ctors_end>:
26: 11 24 eor r1, r1
28: 1f be
2a: cf e5 out 0x3f, r1 ; 63 ldi r28, 0x5F ; 95
2c: d4 e0
2e: de bf
30: cd bf
32: 4f c0 ldi r29, 0x04 ; 4 out 0x3e, r29 ; 62 out 0x3d, r28 ; 61 rjmp .+158 ; 0xd2 <main>
00000034 <__vector_8>: volatile uint16_t pwm; /* Note [1] */ volatile uint8_t direction;
ISR (TIMER1_OVF_vect) /* Note [2] */
{
34: 1f 92 push r1
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36: 0f 92
38: 0f b6
3a: 0f 92
3c: 11 24
3e: 2f 93 push r0 in r0, 0x3f ; 63 push r0 eor r1, r1 push r18
40: 8f 93
42: 9f 93 push r24 push r25 switch (direction) /* Note [3] */
44: 80 91 60 00 lds r24, 0x0060
48: 99 27 eor r25, r25
4a: 00 97
4c: 19 f0
4e: 01 97
50: 31 f5
52: 14 c0 sbiw r24, 0x00 ; 0 breq .+6 ; 0x54 <__SREG__+0x15> sbiw r24, 0x01 ; 1 brne .+76 ; 0x9e <__SREG__+0x5f> rjmp .+40 ; 0x7c <__SREG__+0x3d>
{ case UP: if (++pwm == 1023)
54: 80 91 61 00 lds r24, 0x0061
58: 90 91 62 00 lds r25, 0x0062
5c: 01 96 adiw r24, 0x01 ; 1
5e: 90 93 62 00 sts 0x0062, r25
62: 80 93 61 00 sts 0x0061, r24
66: 80 91 61 00 lds r24, 0x0061
6a: 90 91 62 00 lds r25, 0x0062
6e: 8f 5f
70: 93 40
72: a9 f4
74: 81 e0 subi r24, 0xFF ; 255 sbci r25, 0x03 ; 3 brne .+42 direction = DOWN;
; 0x9e <__SREG__+0x5f> ldi r24, 0x01 ; 1
76: 80 93 60 00 sts 0x0060, r24
7a: 11 c0 rjmp .+34 ; 0x9e <__SREG__+0x5f> break; case DOWN: if (--pwm == 0)
7c: 80 91 61 00 lds r24, 0x0061
80: 90 91 62 00 lds r25, 0x0062
84: 01 97 sbiw r24, 0x01 ; 1
86: 90 93 62 00 sts 0x0062, r25
8a: 80 93 61 00 sts 0x0061, r24
8e: 80 91 61 00 lds r24, 0x0061
92: 90 91 62 00 lds r25, 0x0062
96: 89 2b or r24, r25
98: 11 f4 brne .+4 ; 0x9e <__SREG__+0x5f> direction = UP;
9a: 10 92 60 00 sts 0x0060, r1 break;
}
OCR = pwm; /* Note [4] */
9e: 80 91 61 00 lds r24, 0x0061 a2: 90 91 62 00 lds r25, 0x0062 a6: 9b bd out 0x2b, r25 ; 43 a8: 8a bd aa: 9f 91 out 0x2a, r24 ; 42 pop r25 ac: 8f 91 pop r24
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000000ba <ioinit>:
} pop r18 pop r0 out 0x3f, r0 ; 63 pop r0 pop r1 reti void ioinit (void) /* Note [5] */
{
/* tmr1 is 10-bit PWM */
TCCR1A = _BV (PWM10) | _BV (PWM11) | _BV (XCOM11); ba: 83 e8 bc: 8f bd ldi r24, 0x83 ; 131 out 0x2f, r24 ; 47
/* tmr1 running on full MCU clock */
TCCR1B = _BV (CS10); be: 81 e0 c0: 8e bd ldi r24, 0x01 ; 1 out 0x2e, r24 ; 46
/* set PWM value to 0 */
OCR = 0; c2: 1b bc c4: 1a bc out 0x2b, r1 ; 43 out 0x2a, r1 ; 42
/* enable OC1 and PB2 as output */
DDROC = _BV (OC1); c6: 82 e0 c8: 87 bb ldi r24, 0x02 ; 2 out 0x17, r24 ; 23
/* enable interrupts */
TIMSK = _BV (TOIE1); ca: 84 e0 cc: 89 bf sei (); ce: 78 94 d0: 08 95 ldi r24, 0x04 ; 4 out 0x39, r24 ; 57 sei ret
000000d2 <main>:
} int main (void)
{ d2: cf e5 d4: d4 e0 d6: de bf d8: cd bf ioinit (); da: ef df dc: ff cf ldi r28, 0x5F ; 95 ldi r29, 0x04 ; 4 out 0x3e, r29 ; 62 out 0x3d, r28 ; 61 rcall .-34 rjmp .-2
000000de <__bad_interrupt>: de: 90 cf rjmp .-224
; 0xba <ioinit>
; 0xdc <main+0xa>
; 0x0 <__heap_end>
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5.28.5
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=at90s2313 -Wl,-Map,demo.map -o demo.elf demo.o
Some points of interest in the demo.map file are:
.rela.plt
*(.rela.plt)
.text
*(.vectors)
.vectors
0x00000000
0x00000000
0x00000000
0x00000000
0x00000026
0xe0
0x26 /junk/AVR/avr-libc-1.4/avr/lib/avr4/atmega8/crtm8.o
__vectors
__vector_default
__ctors_start = .
The .text segment (where program instructions are stored) starts at location 0x0.
*(.fini2)
*(.fini1)
*(.fini0)
0x000000e0
.data
0x00800060
0x00800060
*(.data)
*(.gnu.linkonce.d*)
0x00800060
0x00800060
0x00800060
.bss
0x00800060
0x00800060
*(.bss)
*(COMMON)
COMMON
.noinit
0x00800060
0x00800060
0x00800061
0x00800063
0x000000e0
0x000000e0
0x00800063
0x00800063
_etext = .
0x0 load address 0x000000e0
PROVIDE (__data_start, .)
0x3
. = ALIGN (0x2)
_edata = .
PROVIDE (__data_end, .)
PROVIDE (__bss_start, .)
0x3 demo.o
direction pwm
PROVIDE (__bss_end, .)
__data_load_start = LOADADDR (.data)
__data_load_end = (__data_load_start + SIZEOF (.data))
0x0
PROVIDE (__noinit_start, .)
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*(.noinit*)
.eeprom
*(.eeprom*)
0x00800063
0x00800063
0x00800063
0x00810000
0x00810000
0x0
PROVIDE (__noinit_end, .)
_end = .
PROVIDE (__heap_start, .)
__eeprom_end = .
The last address in the .text segment is location 0xf2 ( denoted by _etext ), so the instructions use up 242 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 a 2313 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.
5.28.6
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:
:1000000012C06DC06CC06BC06AC069C068C067C0F8
:1000100011C065C064C063C062C061C060C05FC021
:100020005EC05DC05CC011241FBECFE5D4E0DEBF62
:10003000CDBF4FC01F920F920FB60F9211242F9376
:100040008F939F93809160009927009719F00197F3
:1000500031F514C0809161009091620001969093F7
:1000600062008093610080916100909162008F5FD7
:100070009340A9F481E08093600011C080916100F9
:10008000909162000197909362008093610080914B
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5.28
A simple project 146
:10009000610090916200892B11F4109260008091B0
:1000A0006100909162009BBD8ABD9F918F912F91BD
:1000B0000F900FBE0F901F90189583E88FBD81E0C1
:1000C0008EBD1BBC1ABC82E087BB84E089BF7894DC
:1000D0000895CFE5D4E0DEBFCDBFEFDFFFCF90CFF7
: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
The resulting demo_eeprom.hex file contains:
:00000001FF which is an empty .hex file (which is expected, since we didn’t define any EEPROM variables).
5.28.7
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
OBJ
MCU_TARGET
OPTIMIZE
= demo
= demo.o
= atmega8
= -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 override LDFLAGS
OBJCOPY
OBJDUMP
= -g -Wall $(OPTIMIZE) -mmcu=$(MCU_TARGET) $(DEFS)
= -Wl,-Map,$(PRG).map
= avr-objcopy
= avr-objdump all: $(PRG).elf lst text eeprom
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A simple project 147
$(PRG).elf: $(OBJ)
$(CC) $(CFLAGS) $(LDFLAGS) -o $@ $^ $(LIBS) 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
$(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 $< $@
%_eeprom.srec: %.elf
$(OBJCOPY) -j .eeprom --change-section-lma .eeprom=0 -O srec $< $@
%_eeprom.bin: %.elf
$(OBJCOPY) -j .eeprom --change-section-lma .eeprom=0 -O binary $< $@
# Every thing below here is used by avr-libc’s build system and can be ignored
# by the casual user.
= fig2dev
= *.hex *.bin *.srec
FIG2DEV
EXTRA_CLEAN_FILES dox: eps png pdf eps: $(PRG).eps
png: $(PRG).png
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5.29
Example using the two-wire interface (TWI) pdf: $(PRG).pdf
%.eps: %.fig
$(FIG2DEV) -L eps $< $@
%.pdf: %.fig
$(FIG2DEV) -L pdf $< $@
%.png: %.fig
$(FIG2DEV) -L png $< $@
148
5.29
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 the original Philips documentation, see http://www.semiconductors.philips.com/buses/i2c/index.html
5.29.1
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 frequency, 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.)
5.29.2
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 implementation 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
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5.29
Example using the two-wire interface (TWI) 149 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.
5.29.3
The Source Code
/*
* ----------------------------------------------------------------------------
* "THE BEER-WARE LICENSE" (Revision 42):
* <[email protected]> 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
* ----------------------------------------------------------------------------
*/
/* $Id: twitest.c,v 1.6 2005/11/05 22:32:46 joerg_wunsch Exp $ */
/*
* Simple demo program that talks to a 24Cxx IšC EEPROM using the
* builtin TWI interface of an ATmega device.
*/
#include <inttypes.h>
#include <stdio.h>
#include <stdlib.h>
#include <avr/io.h>
#include <util/twi.h>
#define DEBUG 1
/*
* System clock in Hz.
*/
#define F_CPU 14745600UL
/* Note [1] */
/* Note [2] */
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5.29
Example using the two-wire interface (TWI) 150
/*
* Compatibility defines.
This should work on ATmega8, ATmega16,
* ATmega163, ATmega323 and ATmega128 (IOW: on all devices that
* provide a builtin TWI interface).
*
* On the 128, it defaults to USART 1.
*/
#ifndef UCSRB
# ifdef UCSR1A
# define UCSRA UCSR1A
/* ATmega128 */
# define UCSRB UCSR1B
# define UBRR UBRR1L
# define UDR UDR1
# else /* ATmega8 */
# define UCSRA USR
# define UCSRB UCR
# endif
#endif
#ifndef UBRR
# define UBRR UBRRL
#endif
/*
* Note [3]
* TWI address for 24Cxx EEPROM:
*
* 1 0 1 0 E2 E1 E0 R/~W
* 1 0 1 0 E2 E1 A8 R/~W
* 1 0 1 0 E2 A9 A8 R/~W
* 1 0 1 0 A10 A9 A8 R/~W
*/
#define TWI_SLA_24CXX 0xa0
24C01/24C02
24C04
24C08
24C16
/* E2 E1 E0 = 0 0 0 */
/*
* Maximal number of iterations to wait for a device to respond for a
* selection.
Should be large enough to allow for a pending write to
* complete, but low enough to properly abort an infinite loop in case
* a slave is broken or not present at all.
With 100 kHz TWI clock,
* transfering the start condition and SLA+R/W packet takes about 10
* ¸
The longest write period is supposed to not exceed ~ 10 ms.
* Thus, normal operation should not require more than 100 iterations
* to get the device to respond to a selection.
*/
#define MAX_ITER 200
/*
* Number of bytes that can be written in a row, see comments for
* ee24xx_write_page() below.
Some vendor’s devices would accept 16,
* but 8 seems to be the lowest common denominator.
*
* Note that the page size must be a power of two, this simplifies the
* page boundary calculations below.
*/
#define PAGE_SIZE 8
/*
* Saved TWI status register, for error messages only.
We need to
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5.29
Example using the two-wire interface (TWI) 151
* save it in a variable, since the datasheet only guarantees the TWSR
* register to have valid contents while the TWINT bit in TWCR is set.
*/ uint8_t twst;
/*
* Do all the startup-time peripheral initializations: UART (for our
* debug/test output), and TWI clock.
*/ void ioinit(void)
{
#if F_CPU <= 1000000UL
/*
* Note [4]
* Slow system clock, double Baud rate to improve rate error.
*/
UCSRA = _BV(U2X);
UBRR = (F_CPU / (8 * 9600UL)) - 1; /* 9600 Bd */
#else
UBRR = (F_CPU / (16 * 9600UL)) - 1; /* 9600 Bd */
#endif
UCSRB = _BV(TXEN); /* tx enable */
/* initialize TWI clock: 100 kHz clock, TWPS = 0 => prescaler = 1 */
#if defined(TWPS0)
/* has prescaler (mega128 & newer) */
TWSR = 0;
#endif
#if F_CPU < 3600000UL
TWBR = 10; /* smallest TWBR value, see note [5] */
#else
TWBR = (F_CPU / 100000UL - 16) / 2;
#endif
}
/*
* Note [6]
* Send character c down the UART Tx, wait until tx holding register
* is empty.
*/ int uart_putchar(char c, FILE *unused)
{
} if (c == ’\n’) uart_putchar(’\r’, 0); loop_until_bit_is_set(UCSRA, UDRE);
UDR = c; return 0;
/*
* Note [7]
*
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5.29
Example using the two-wire interface (TWI) 152
* Read "len" bytes from EEPROM starting at "eeaddr" into "buf".
*
* This requires two bus cycles: during the first cycle, the device
* will be selected (master transmitter mode), and the address
* transfered.
Address bits exceeding 256 are transfered in the
* E2/E1/E0 bits (subaddress bits) of the device selector.
*
* The second bus cycle will reselect the device (repeated start
* condition, going into master receiver mode), and transfer the data
* from the device to the TWI master.
Multiple bytes can be
* transfered by ACKing the client’s transfer.
The last transfer will
* be NACKed, which the client will take as an indication to not
* initiate further transfers.
*/ int ee24xx_read_bytes(uint16_t eeaddr, int len, uint8_t *buf)
{ uint8_t sla, twcr, n = 0; int rv = 0;
/* patch high bits of EEPROM address into SLA */ sla = TWI_SLA_24CXX | (((eeaddr >> 8) & 0x07) << 1);
/*
* Note [8]
* First cycle: master transmitter mode
*/ restart: if (n++ >= MAX_ITER) return -1; begin:
TWCR = _BV(TWINT) | _BV(TWSTA) | _BV(TWEN); /* send start condition */ while ((TWCR & _BV(TWINT)) == 0) ; /* wait for transmission */ switch ((twst = TW_STATUS))
{ case TW_REP_START: case TW_START: break;
/* OK, but should not happen */ case TW_MT_ARB_LOST: goto begin; default: return -1;
/* Note [9] */
/* error: not in start condition */
/* NB: do /not/ send stop condition */
}
/* Note [10] */
/* send SLA+W */
TWDR = sla | TW_WRITE;
TWCR = _BV(TWINT) | _BV(TWEN); /* clear interrupt to start transmission */ while ((TWCR & _BV(TWINT)) == 0) ; /* wait for transmission */ switch ((twst = TW_STATUS))
{ case TW_MT_SLA_ACK: break;
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5.29
Example using the two-wire interface (TWI) 153 case TW_MT_SLA_NACK: goto restart;
/* nack during select: device busy writing */
/* Note [11] */ case TW_MT_ARB_LOST: goto begin; default: goto error;
}
/* re-arbitrate */
/* must send stop condition */
TWDR = eeaddr; /* low 8 bits of addr */
TWCR = _BV(TWINT) | _BV(TWEN); /* clear interrupt to start transmission */ while ((TWCR & _BV(TWINT)) == 0) ; /* wait for transmission */ switch ((twst = TW_STATUS))
{ case TW_MT_DATA_ACK: break; case TW_MT_DATA_NACK: goto quit; case TW_MT_ARB_LOST: goto begin; default: goto error;
}
/* must send stop condition */
/*
* Note [12]
* Next cycle(s): master receiver mode
*/
TWCR = _BV(TWINT) | _BV(TWSTA) | _BV(TWEN); /* send (rep.) start condition */ while ((TWCR & _BV(TWINT)) == 0) ; /* wait for transmission */ switch ((twst = TW_STATUS))
{ case TW_START: case TW_REP_START:
/* OK, but should not happen */ break; case TW_MT_ARB_LOST: goto begin; default: goto error;
}
/* send SLA+R */
TWDR = sla | TW_READ;
TWCR = _BV(TWINT) | _BV(TWEN); /* clear interrupt to start transmission */ while ((TWCR & _BV(TWINT)) == 0) ; /* wait for transmission */ switch ((twst = TW_STATUS))
{ case TW_MR_SLA_ACK: break;
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5.29
Example using the two-wire interface (TWI) 154 case TW_MR_SLA_NACK: goto quit; case TW_MR_ARB_LOST: goto begin; default: goto error;
} for (twcr = _BV(TWINT) | _BV(TWEN) | _BV(TWEA) /* Note [13] */; len > 0; len--)
{ if (len == 1) twcr = _BV(TWINT) | _BV(TWEN); /* send NAK this time */
TWCR = twcr; /* clear int to start transmission */ while ((TWCR & _BV(TWINT)) == 0) ; /* wait for transmission */ switch ((twst = TW_STATUS))
{ case TW_MR_DATA_NACK: len = 0;
/* FALLTHROUGH */ case TW_MR_DATA_ACK:
/* force end of loop */
*buf++ = TWDR; rv++; break; default: goto error;
}
} quit:
/* Note [14] */
TWCR = _BV(TWINT) | _BV(TWSTO) | _BV(TWEN); /* send stop condition */ return rv;
} error: rv = -1; goto quit;
/*
* Write "len" bytes into EEPROM starting at "eeaddr" from "buf".
*
* This is a bit simpler than the previous function since both, the
* address and the data bytes will be transfered in master transmitter
* mode, thus no reselection of the device is necessary.
However, the
* EEPROMs are only capable of writing one "page" simultaneously, so
* care must be taken to not cross a page boundary within one write
* cycle.
The amount of data one page consists of varies from
* manufacturer to manufacturer: some vendors only use 8-byte pages
* for the smaller devices, and 16-byte pages for the larger devices,
* while other vendors generally use 16-byte pages.
We thus use the
* smallest common denominator of 8 bytes per page, declared by the
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5.29
Example using the two-wire interface (TWI) 155
* macro PAGE_SIZE above.
*
* The function simply returns after writing one page, returning the
* actual number of data byte written.
It is up to the caller to
* re-invoke it in order to write further data.
*/ int ee24xx_write_page(uint16_t eeaddr, int len, uint8_t *buf)
{ uint8_t sla, n = 0; int rv = 0; uint16_t endaddr; if (eeaddr + len < (eeaddr | (PAGE_SIZE - 1))) endaddr = eeaddr + len; else endaddr = (eeaddr | (PAGE_SIZE - 1)) + 1; len = endaddr - eeaddr;
/* patch high bits of EEPROM address into SLA */ sla = TWI_SLA_24CXX | (((eeaddr >> 8) & 0x07) << 1); restart: if (n++ >= MAX_ITER) return -1; begin:
/* Note [15] */
TWCR = _BV(TWINT) | _BV(TWSTA) | _BV(TWEN); /* send start condition */ while ((TWCR & _BV(TWINT)) == 0) ; /* wait for transmission */ switch ((twst = TW_STATUS))
{ case TW_REP_START: /* OK, but should not happen */ case TW_START: break; case TW_MT_ARB_LOST: goto begin; default: return -1;
}
/* error: not in start condition */
/* NB: do /not/ send stop condition */
/* send SLA+W */
TWDR = sla | TW_WRITE;
TWCR = _BV(TWINT) | _BV(TWEN); /* clear interrupt to start transmission */ while ((TWCR & _BV(TWINT)) == 0) ; /* wait for transmission */ switch ((twst = TW_STATUS))
{ case TW_MT_SLA_ACK: break; case TW_MT_SLA_NACK: goto restart;
/* nack during select: device busy writing */ case TW_MT_ARB_LOST: /* re-arbitrate */
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5.29
Example using the two-wire interface (TWI) 156 goto begin; default: goto error;
}
/* must send stop condition */
TWDR = eeaddr; /* low 8 bits of addr */
TWCR = _BV(TWINT) | _BV(TWEN); /* clear interrupt to start transmission */ while ((TWCR & _BV(TWINT)) == 0) ; /* wait for transmission */ switch ((twst = TW_STATUS))
{ case TW_MT_DATA_ACK: break; case TW_MT_DATA_NACK: goto quit; case TW_MT_ARB_LOST: goto begin; default: goto error;
}
/* must send stop condition */ for (; len > 0; len--)
{
TWDR = *buf++;
TWCR = _BV(TWINT) | _BV(TWEN); /* start transmission */ while ((TWCR & _BV(TWINT)) == 0) ; /* wait for transmission */ switch ((twst = TW_STATUS))
{ case TW_MT_DATA_NACK: goto error; /* device write protected -- Note [16] */ case TW_MT_DATA_ACK: rv++; break; default: goto error;
}
} quit:
TWCR = _BV(TWINT) | _BV(TWSTO) | _BV(TWEN); /* send stop condition */ return rv;
} error: rv = -1; goto quit;
/*
* Wrapper around ee24xx_write_page() that repeats calling this
* function until either an error has been returned, or all bytes
* have been written.
*/
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5.29
Example using the two-wire interface (TWI) 157 int ee24xx_write_bytes(uint16_t eeaddr, int len, uint8_t *buf)
{ int rv, total; total = 0; do
{
#if DEBUG printf("Calling ee24xx_write_page(%d, %d, %p)", eeaddr, len, buf);
#endif rv = ee24xx_write_page(eeaddr, len, buf);
#if DEBUG printf(" => %d\n", rv);
#endif if (rv == -1) return -1; eeaddr += rv; len -= rv; buf += rv; total += rv;
} while (len > 0);
} return total; void error(void)
{
} printf("error: TWI status %#x\n", twst); exit(0);
FILE mystdout = FDEV_SETUP_STREAM(uart_putchar, NULL, _FDEV_SETUP_WRITE); void main(void)
{ uint16_t a; int rv; uint8_t b[16]; uint8_t x; ioinit(); stdout = &mystdout; for (a = 0; a < 256;)
{ printf("%#04x: ", a); rv = ee24xx_read_bytes(a, 16, b); if (rv <= 0) error(); if (rv < 16)
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5.29
Example using the two-wire interface (TWI) 158 printf("warning: short read %d\n", rv); a += rv; for (x = 0; x < rv; x++) printf("%02x ", b[x]); putchar(’\n’);
}
#define EE_WRITE(addr, str) ee24xx_write_bytes(addr, sizeof(str)-1, str) rv = EE_WRITE(55, "The quick brown fox jumps over the lazy dog."); if (rv < 0) error(); printf("Wrote %d bytes.\n", rv); for (a = 0; a < 256;)
{ printf("%#04x: ", a); rv = ee24xx_read_bytes(a, 16, b); if (rv <= 0) error(); if (rv < 16) printf("warning: short read %d\n", rv); a += rv; for (x = 0; x < rv; x++) printf("%02x ", b[x]); putchar(’\n’);
} printf("done.\n");
}
Note [1]
The header file <util/twi.h> contains some macro definitions for symbolic constants 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 subaddress 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)
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Example using the two-wire interface (TWI) 159
"steal" subaddress bits and use them for the EEPROM cell address bits 9 to 11 as required. 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 [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]
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 address 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 manually 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.
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5.29
Example using the two-wire interface (TWI)
Note [9]
160
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.
Note [10]
Next, the device slave is going to be reselected (using a so-called repeated start condition 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
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6 avr-libc Data Structure Documentation 161 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 deasserted 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.
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.
6 avr-libc Data Structure Documentation
6.1
div_t Struct Reference
6.1.1
Detailed Description
Result type for function
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6.2
ldiv_t Struct Reference
Data Fields
• int
• int
6.1.2
Field Documentation
6.1.2.1
int
The Quotient.
6.1.2.2
int
The Remainder.
The documentation for this struct was generated from the following file:
• stdlib.h
6.2
ldiv_t Struct Reference
6.2.1
Detailed Description
Result type for function
Data Fields
• long
• long
6.2.2
Field Documentation
6.2.2.1
long
The Quotient.
6.2.2.2
long
The Remainder.
The documentation for this struct was generated from the following file:
• stdlib.h
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162
7 avr-libc Page Documentation 163
7 avr-libc Page Documentation
7.1
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 [ [email protected]
] for making the AVR-specific changes to the GNU tools.
• Denis Chertykov and Marek Michalkiewicz [ [email protected]
] for developing the standard libraries and startup code for AVR-GCC.
• Uros Platise for developing the AVR programmer tool, uisp.
• Joerg Wunsch [ [email protected]
] for adding all the AVR development tools to the FreeBSD [ http://www.freebsd.org
] ports tree and for providing the basics for the
• Brian Dean [ [email protected]
] for developing avrdude (an alternative to uisp) and for contributing
which describes how to use it. Avrdude was previously called avrprog.
• Eric Weddington [ [email protected]
] for maintaining the WinAVR package and thus making the continued improvements to the Opensource 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
• 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 suggestions, 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. ;-)
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7.2
avr-libc and assembler programs 164
7.2
avr-libc and assembler programs
7.2.1
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
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.
7.2.2
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 appropriate options to locate additional libraries as well as the application start-up code
(crtXXX.o) and linker script.
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7.2
avr-libc and assembler programs 165
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 made based on the case of the filename suffix given on the command-line, not based on the actual filename from the file system.
Alternatively, the language can explicitly be specified using the -x assembler-with-cpp option.
7.2.3
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> work tmp
=
=
16
17 inttmp = intsav =
19
0
SQUARE = PD6
; Note [1]
; Note [2] tmconst= 10700000 / 200000 fuzz= 8
.section .text
.global main main:
1: rcall rjmp ioinit
1b
; Note [3]
; Note [4]:
; 100 kHz => 200000 edges/s
; # clocks in ISR until TCNT0 is set
.global TIMER0_OVF_vect
TIMER0_OVF_vect: ldi out inttmp, 256 - tmconst + fuzz
_SFR_IO_ADDR(TCNT0), inttmp
1:
2: in sbic rjmp sbi rjmp cbi intsav, _SFR_IO_ADDR(SREG)
_SFR_IO_ADDR(PORTD), SQUARE
1f
_SFR_IO_ADDR(PORTD), SQUARE
2f
_SFR_IO_ADDR(PORTD), SQUARE out _SFR_IO_ADDR(SREG), intsav
; Note [5]
; Note [6]
; Note [7]
; Note [8]
; Note [9]
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7.2
avr-libc and assembler programs 166 reti ioinit: sbi ldi out ldi out ldi out sei
_SFR_IO_ADDR(DDRD), SQUARE work, _BV(TOIE0)
_SFR_IO_ADDR(TIMSK), work work, _BV(CS00) ; tmr0: CK/1
_SFR_IO_ADDR(TCCR0), work work, 256 - tmconst
_SFR_IO_ADDR(TCNT0), work ret
.global __vector_default
__vector_default: reti
.end
; Note [10]
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]
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7.2
avr-libc and assembler programs 167
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.
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 desired 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
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_N should appear, with N being 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.)
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7.2
avr-libc and assembler programs 168
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.
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
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.)
7.2.4
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)
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7.3
Frequently Asked Questions 169
• .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)
• .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 anyway
Note that .org is available in gas as well, but is a fairly pointless pseudo-op in an assembler 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 AVRspecific 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 address. 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 .
7.3
Frequently Asked Questions
7.3.1
FAQ Index
1.
My program doesn’t recognize a variable updated within an interrupt routine
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7.3
Frequently Asked Questions 170
2.
I get "undefined reference to..." for functions like "sin()"
3.
How to permanently bind a variable to a register?
4.
How to modify MCUCR or WDTCR early?
5.
What is all this _BV() stuff about?
6.
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 program 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.
16.
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.
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" messsage?
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?
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7.3
Frequently Asked Questions 171
7.3.2
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 completely 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
7.3.3
I get "undefined reference to..." for functions like "sin()"
In order to access the mathematical functions that are declared in < math.h
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 requires knowledge of where the build system will exactly find those library files, this is deprecated for system libraries.
Back to
7.3.4
How to permanently bind a variable to a register?
This can be done with
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7.3
Frequently Asked Questions 172 register unsigned char counter asm("r3");
Typically, it should be possible to use r2 through r15 that way.
See
C Names Used in Assembler Code
for more details.
Back to
7.3.5
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 .initN sections (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 special 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
preferrably be placed into section .init3 as the code in .init2 ensures the internal register __zero_reg__ is already cleared.
Back to
7.3.6
What is all this _BV() stuff about?
When performing low-level output work, which is a very central point in microcontroller programming, it is quite common that a particular bit needs to be set or cleared
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7.3
Frequently Asked Questions 173 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
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
7.3.7
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 automatically 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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7.3
Frequently Asked Questions 174
• 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 microcontrollers, 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 invocation 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
7.3.8
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
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
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
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
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7.3
Frequently Asked Questions 175 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 nonzero.
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
7.3.9
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
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;
}
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7.3
Frequently Asked Questions 176
Back to
7.3.10
How do I use a #define’d constant in an asm statement?
So you tried this: asm volatile("sbi 0x18,0x07;");
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 transform this into a single SBI instruction, assuming the operands allow for this.
Back to
7.3.11
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 optimized 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 execution 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 optimzation 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
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7.3
Frequently Asked Questions 177 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 optimization can easily change the bug pattern. In most cases, you are better off leaving optimizations enabled while debugging.
Back to
7.3.12
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. Otherwise, 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
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7.3
Frequently Asked Questions 178
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 b for a backward reference, or f for 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 push push push push
...
eor ldi
1:
2: ldi rjmp ld
...
breq
...
inc cmp brlo
1: pop pop pop pop pop ret r16 r17 r18
YL
YH r16, r16 ; start loop
YL, lo8(sometable)
YH, hi8(sometable)
2f ; jump to loop test at end r17, Y+ ; loop continues here
1f ; return from myfunc prematurely r16 r16, r18
1b
YH
YL r18 r17 r16
; jump back to top of loop
Back to
7.3.13
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
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7.3
Frequently Asked Questions 179 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 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
10c:
10e:
88 b3
0e 94 65 00 in call r24, 0x18
0xca
; 170
; 24
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
114: 88 e3 ldi r24, 0x38
116:
118:
90 e0
0e 94 7c 00 ldi call r25, 0x00
0xf8
; 85
; 56
; 0
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;
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7.3
Frequently Asked Questions 180 fa: fc: fe:
}
100:
80 81
86 2b
80 83
08 95 ld or st ret r24, Z r24, r22
Z, r24
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 data sheet.
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
11e:
120:
80 6f
88 bb ori out r24, 0xF0
0x18, r24
; 24
; 240
; 24
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
7.3.14
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 the whole
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7.3
Frequently Asked Questions 181
128K program memory space on the ATmega devices with > 64 KB of flash
ROM). 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 responsible for saving and restoring.
• Call-saved registers (r2-r17, r28-r29):
May be allocated by gcc for local data. Calling C subroutines leaves them unchanged. 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.
• 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 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 caller
(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.
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7.3
Frequently Asked Questions 182
Back to
7.3.15
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 want 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:
#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>:
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7.3
Frequently Asked Questions 183
26:
28:
2e 00
2a 00
0000002a <bar>:
2a: 42 61 72 00
0000002e <foo>:
2e: 46 6f 6f 00
.word
.word
0x002e ; ????
0x002a ; ????
Bar.
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:
76:
78:
7a:
7c:
7e:
80:
6a 5d
7f 4f
42 e0
50 e0 ce 01
81 96
08 d0 subi sbci ldi ldi movw adiw rcall r22, 0xDA r23, 0xFF r20, 0x02 r21, 0x00 r24, r28 r24, 0x21
.+16
; 218
; 255
; 2
; 0
; 33
; 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 accomodate 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 p is computed by adding its offset within the stack frame (33) to the Y pointer register, and memcpy_P is called.
strcpy_P(buf, p);
82:
84:
86:
88:
8a:
69 a1
7a a1 ce 01
01 96
0c d0 ldd ldd movw adiw rcall r22, Y+33 r23, Y+34 r24, r28 r24, 0x01
.+24
; 0x21
; 0x22
; 1
; 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
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7.3
Frequently Asked Questions 184
7.3.16
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
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
The explanation of
contains a
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 initialization 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 external RAM is slower than internal RAM, and errata of some AVR devices even prevent this configuration from working properly at all.
Back to
7.3.17
Which -O flag to use?
There’s a common misconception that larger numbers behind the -O option might automatically cause "better" optimization. First, there’s no universal definition for "better", with optimization often being a speed vs. code size tradeoff. See the
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
using the standard library
strcmp() , test #2 used a function that sorted the strings by their size (thus had
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7.3
Frequently Asked Questions 185 two calls to
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.
Size of .text
Time for test #1 Time for test #2 Optimization flags
-O3
-O2
-Os
-Os
-mcall-prologues
6898
6666
6618
6474
903 µs
972 µs
955 µs
972 µs
19.7 ms
20.1 ms
20.1 ms
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" optimization level. Only applications that need to get the last few percent of speed benefit from using -O3.
Back to
7.3.18
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,--section-start=.bootloader=0x1E000
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
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7.3
Frequently Asked Questions 186
7.3.19
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 ATmega103 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 unavailable for regular IO.
Back to
7.3.20
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. However, 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 functions 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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7.3
Frequently Asked Questions 187
#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
macro.
Back to
7.3.21
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:
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7.3
Frequently Asked Questions 188 var &= (unsigned char)~mask;
Back to
7.3.22
How to detect RAM memory and variable overlap problems?
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 avaialable 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
dynamic memory is also located there. See
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
7.3.23
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
7.3.24
What is this "clock skew detected" messsage?
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 second when calculating the timestamp of an updated file in case the current time cannot
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7.3
Frequently Asked Questions 189 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.
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 systems, like NTP. As a workaround, synchronize the client’s clock frequently with the server’s clock.
Back to
7.3.25
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 respective 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
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7.4
Inline Asm 190 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
TIFR = _BV(TOV0);
Back to
7.3.26
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
7.3.27
Which AVR-specific assembler operators are available?
See
Back to
7.4
Inline Asm
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.
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.
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7.4
Inline Asm 191
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. Permission 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. Anyway, 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/.
7.4.1
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))
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7.4
Inline Asm 192
4. Clobbered registers, left empty in our example.
You can write assembler instructions in much the same way as you would write assembler 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.
0 refers to the first 1 to the second operand and so forth. From the above example:
0 refers to "=r" (value) and
1 refers 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 included code was not generated by the compilation of C statements, but by inline assembler 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)));
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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7.4
Inline Asm 193
7.4.2
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 compiler 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
__SREG__
__SP_H__
__SP_L__
__tmp_reg__
__zero_reg__
Register
Status register at address 0x3F
Stack pointer high byte at address 0x3E
Stack pointer low byte at address 0x3D
Register r0, used for temporary storage
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.
7.4.3
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 x register is r27:r26, the y register is r29:r28, and the z register is r31:r30
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7.4
Inline Asm 194
Constraint a b
J
M
N
O
P q
K l
L t r w d e
G
I
Used for
Simple upper registers
Base pointer registers pairs
Upper register
Pointer register pairs
Floating point constant
6-bit positive integer constant
6-bit negative integer constant
Integer constant
Integer constant
Lower registers
8-bit integer constant
Integer constant
Integer constant
Integer constant
Stack pointer register
Any register
Temporary register
Special upper register pairs
Pointer register pair X
Pointer register pair Y
Pointer register pair Z
Range r16 to r23 y, z r16 to r31 x, y, z
0.0
0 to 63
-63 to 0
2
0 r0 to r15
0 to 255
-1
8, 16, 24
1
SPH:SPL r0 to r31 r0 r24, r26, r28, r30 x y z x (r27:r26) y (r29:r28) z (r31:r30)
These definitions seem not to fit properly to the AVR instruction set. The author’s assumption is, that this part of the compiler has never been really finished in this version, but that assumption may be wrong. 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 assembler 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
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7.4
Inline Asm 195 constants to the range 0 to 7 for bit set and bit clear operations.
lsr movw neg ori pop rol sbc sbi sbiw sbrc ser std sub swap com cpc cpse elpm in ld ldi lpm
Mnemonic adc adiw andi bclr brbc bset cbi
Constraints r,r w,I d,M
I
I,label
I
I,I r r,r r,r t,z r,I r,e d,M t,z r r,r r d,M r r r,r
I,I w,I r,I d b,r r,r r
Mnemonic add and asr bld brbs bst cbr cp cpi dec eor inc ldd lds lsl mov mul or out push ror sbci sbic sbr sbrs st sts subi
Constraint characters may be prepended by a single constraint modifier. Contraints without a modifier specify read-only operands. Modifiers are: r,r r,r r,r
I,r r r d,M
I,I d,M r,I e,r label,r d,M r,r d,M r r,r r r,b r,label r
Constraints r,r r,r r r,I
I,label r,I d,I
Modifier
=
+
Specifies
Write-only operand, usually used for all output operands.
Read-write operand (not supported by inline assembler)
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.
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7.4
Inline Asm 196
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));
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 output, 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
section. You can use this register without saving its contents. Completely new are those letters A and B in %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"
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7.4
Inline Asm 197
"mov %B0, %C0" "\n\t"
"mov %C0, __tmp_reg__" "\n\t"
: "=r" (value)
: "0" (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 a following the percent sign, then the compiler will create the proper assembler line.
7.4.4
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.
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7.4
Inline Asm 198 asm volatile(
"cli"
"ld r24, %a0"
"inc r24"
"st %a0, r24"
"sei"
:
: "e" (ptr)
: "r24"
);
"\n\t"
"\n\t"
"\n\t"
"\n\t"
"\n\t"
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 temporary register __tmp_reg__ defined by the compiler.
asm volatile(
"cli"
"ld __tmp_reg__, %a0"
"inc __tmp_reg__"
"st %a0, __tmp_reg__"
"sei"
:
: "e" (ptr)
);
"\n\t"
"\n\t"
"\n\t"
"\n\t"
"\n\t"
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__"
"cli"
"ld __tmp_reg__, %a1"
"inc __tmp_reg__"
"st %a1, __tmp_reg__"
"out __SREG__, %0"
: "=&r" (s)
: "e" (ptr)
);
}
"\n\t"
"\n\t"
"\n\t"
"\n\t"
"\n\t"
"\n\t"
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7.4
Inline Asm 199
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:
{ uint8_t s; asm volatile(
"in %0, __SREG__"
"cli"
"ld __tmp_reg__, %a1"
"inc __tmp_reg__"
"st %a1, __tmp_reg__"
"out __SREG__, %0"
: "=&r" (s)
: "e" (ptr)
: "memory"
);
}
"\n\t"
"\n\t"
"\n\t"
"\n\t"
"\n\t"
"\n\t"
The special clobber "memory" informs the compiler that the assembler code may modify 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.
7.4.5
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.
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7.4
Inline Asm 200
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) \
)
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) \
)
7.4.6
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)
);
}
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7.4
Inline Asm 201
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
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))
); return result;
}
Note: inw() is supplied by avr-libc.
7.4.7
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 variable will not be referenced any longer, the register may be re-used. But the compiler
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7.5
Using malloc() 202 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 .
7.4.8
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/
7.5
Using malloc()
7.5.1
Introduction
On a simple device like a microcontroller, implementing dynamic memory allocation is quite a challenge.
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
.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.
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7.5
Using malloc() 203
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.
on−board RAM
.data
variables
.bss
variables heap
!
stack external RAM
SP RAMEND brkval (<= *SP − __malloc_margin)
__bss_end
__malloc_heap_start == __heap_start
__data_end == __bss_start
__data_start
Figure 2: RAM map of a device with internal RAM
Finally, there’s a challenge to make the memory allocator 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 since microcontrollers aren’t only often low on space, but 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 constraints, and offers some tuning options that can be used if there are more resources available than in the default configuration.
7.5.2
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 external 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.
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7.5
Using malloc() 204
7.5.3
Tunables for malloc()
There are a number of variables that can be tuned to adapt the behavior of
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
sequence.
The variables __malloc_heap_start and __malloc_heap_end can be used to restrict the
function to a certain memory region. These variables are statically 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
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,-Tdata=0x801100,--defsym=__heap_end=0x80ffff ...
Note:
See
for offset 0x800000. See the chapter about
for the -Wl options.
on−board RAM external RAM stack
.data
variables
.bss
variables heap
SP
RAMEND
__malloc_heap_end == __heap_end brkval
__malloc_heap_start == __heap_start
__bss_end
__data_end == __bss_start
__data_start
Figure 3: 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
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7.5
Using malloc() 205 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 ...
external RAM on−board RAM
.data
variables
.bss
variables stack heap
SP
RAMEND
__bss_end
__data_end == __bss_start
__data_start
__malloc_heap_end == __heap_end brkval
__malloc_heap_start == __heap_start
Figure 4: 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.
7.5.4
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
returned address points just beyond that header. Thus, if the application accidentally writes before the returned memory region, the internal consistency of the memory allocator 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.
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7.5
Using malloc() 206
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.
A call to
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
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
will simply do nothing, and return the original region.
When growing the region, it is first checked whether the existing allocation can be extended 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.
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,
will be called with the new request size, the existing data will be copied over, and
will be called on the old region.
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7.6
Release Numbering and Methodology 207
7.6
Release Numbering and Methodology
7.6.1
Release Version Numbering Scheme
7.6.1.1
Stable Versions A stable release will always have a minor number that is an even number. This implies that you should be able to upgrade to a new version of the library with the same major and minor numbers without fear that any of the APIs have changed. The only changes that should be made to a stable branch are bug fixes and under some circumstances, additional functionality (e.g. adding support for a new device).
If major version number has changed, this implies that the required versions of gcc and binutils have changed. Consult the README file in the toplevel directory of the AVR
Libc source for which versions are required.
7.6.1.2
Development Versions The major version number of a development series is always the same as the last stable release.
The minor version number of a development series is always an odd number and is 1 more than the last stable release.
The patch version number of a development series is always 0 until a new branch is cut at which point the patch number is changed to 90 to denote the branch is approaching a release and the date appended to the version to denote that it is still in development.
All versions in development in cvs will also always have the date appended as a fourth version number. The format of the date will be YYYYMMDD.
So, the development version number will look like this:
1.1.0.20030825
While a pre-release version number on a branch (destined to become either 1.2 or 2.0) will look like this:
1.1.90.20030828
7.6.2
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 cvs 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.
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7.6
Release Numbering and Methodology 208
7.6.2.1
Creating a cvs branch The following steps should be taken to cut a branch in cvs:
1. Check out a fresh source tree from cvs HEAD.
2. Update the NEWS file with pending release number and commit to cvs HEAD:
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):
’cvs tag avr-libc-<major>_<minor>-branchpoint’
4. Create the branch:
’cvs tag -b avr-libc-<major>_<minor>-branch’
5. Update the package version in configure.ac and commit configure.ac to cvs
HEAD:
Change minor number to next odd value.
6. Update the NEWS file and commit to cvs HEAD:
Add ”Changes since avr-libc-<this_release>:”
7. Check out a new tree for the branch:
’cvs co -r avr-libc-<major>_<minor>-branch’
8. Update the package version in configure.ac and commit configure.ac to cvs 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. Announce the branch and the branch tag to the avr-libc-dev list so other developers can checkout the branch.
Note:
CVS tags do not allow the use of periods (’.’).
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7.6
Release Numbering and Methodology 209
7.6.2.2
Making a release A stable release will only be done on a branch, not from the cvs HEAD.
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:
’cvs update -r avr-libc-<major>_<minor>-branch’
2. Update the package version in configure.in and commit it to cvs.
3. Update the gnu tool chain version requirements in the README and commit to cvs.
4. Update the ChangeLog file to note the release and commit to cvs on the branch:
Add ”Released avr-libc-<this_release>.”
5. Update the NEWS file with pending release number and commit to cvs:
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:
’cvs tag avr-libc-<major>_<minor>_<patch>-release’
9. Upload the tarball to savannah.
10. Update the NEWS file, and commit to cvs:
Add ”Changes since avr-libc-<major>_<minor>_<patch>:”
11. Generate the latest documentation and upload to savannah.
12. Announce the release.
The following hypothetical diagram should help clarify version and branch relationships.
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7.7
Memory Sections 210
HEAD 1.0 Branch cvs tag avr−libc−1_0−branchpoint set version to 1.1.0.<date> cvs tag −b avr−libc−1_0−branch set version to 0.90.90.<date>
1.2 Branch set version to 1.0
cvs tag avr−libc−1_0−release set version to 1.0.0.<date> set version to 1.0.1
cvs tag avr−libc−1_0_1−release cvs tag avr−libc−1_2−branchpoint set version to 1.3.0.<date> cvs tag −b avr−libc−1_2−branch set version to 1.1.90.<date> set version to 1.2
cvs tag avr−libc−1_2−release cvs tag avr−libc−2.0−branchpoint set version to 2.1.0.<date>
Figure 5: Release tree
7.7
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.
7.7.1
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.
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7.7
Memory Sections 211
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.
7.7.2
The .data Section
This section contains static data which was defined in your code. Things like the following 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
Note:
When using
in the application (which could even happen inside library calls),
are required.
7.7.3
The .bss Section
Uninitialized global or static variables end up in the .bss section.
7.7.4
The .eeprom Section
This is where eeprom variables are stored.
7.7.5
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")));
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7.7
Memory Sections 212 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. Otherwise, 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.]
7.7.6
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
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
and
can 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 immediately after a reset.
.init1:
Unused. User definable.
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7.7
Memory Sections 213
.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.
.init8:
Unused. User definable.
.init9:
Jumps into main().
7.7.7
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
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.
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7.7
Memory Sections 214
.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).
7.7.8
Using Sections in Assembler Code
Example:
#include <avr/io.h>
.section .init1,"ax",@progbits ldi r0, 0xff out out
_SFR_IO_ADDR(PORTB), r0
_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 on the .section directive, see the gas user manual.
7.7.9
Using Sections in C Code
Example:
#include <avr/io.h> void my_init_portb (void) __attribute__ ((naked)) \
__attribute__ ((section (".init3"))); void my_init_portb (void)
{
PORTB = 0xff;
DDRB = 0xff;
}
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7.8
Installing the GNU Tool Chain 215
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.
7.8
Installing the GNU Tool Chain
Note:
This discussion was taken directly from Rich Neswold’s document. (See
This discussion is Unix specific. [FIXME: troth/2002-08-13: we need a volunteer to add windows specific notes to these instructions.]
This chapter shows how to build and install a complete development environment for the AVR processors using the GNU toolset.
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 example, 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 directory 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:
$ 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.
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7.8
Installing the GNU Tool Chain 216
Note:
It is usually the best to use the latest released version of each of the tools.
7.8.1
Required Tools
• GNU Binutils http://sources.redhat.com/binutils/
• GCC http://gcc.gnu.org/
• AVR Libc http://savannah.gnu.org/projects/avr-libc/
7.8.2
Optional Tools
You can develop programs for AVR devices without the following tools. They may or may not be of use for you.
• uisp http://savannah.gnu.org/projects/uisp/
• avrdude http://savannah.nongnu.org/projects/avrdude/
• GDB http://sources.redhat.com/gdb/
• Simulavr http://savannah.gnu.org/projects/simulavr/
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7.8
Installing the GNU Tool Chain 217
• AVaRice http://avarice.sourceforge.net/
7.8.3
GNU Binutils for the AVR target
The binutils package provides all the low-level utilities needed in building and manipulating object files. Once installed, your environment will have an AVR assembler
(avr-as), linker (avr-ld), and librarian (avr-ar and avr-ranlib). In addition, you get tools which extract data from object files (avr-objcopy), dissassemble 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 with the version of the package you downloaded.
Note:
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 changing 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
Makefile s that are custom tailored to your platform. At this point, you can build the project.
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7.8
Installing the GNU Tool Chain 218
$ 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.
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
environment variable before going to build avr-gcc.
7.8.4
GCC for the AVR target
Warning:
You must install
and make sure your
properly before installing avr-gcc.
The steps to build avr-gcc are essentially same as for
$ 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 --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.
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.
7.8.5
AVR Libc
Warning:
You must install
and make sure your
properly before installing avr-libc.
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7.8
Installing the GNU Tool Chain 219
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:
$ gunzip -c avr-libc-<version>.tar.gz | tar xf -
$ cd avr-libc-<version>
$ ./configure --build=‘./config.guess‘ --host=avr
$ make
$ make install
Note:
Other configure options might follow, notably –prefix in order to change the directory prefix for the installed files from its default /usr/local.
7.8.6
UISP
Uisp also uses the configure system, so to build and install:
$ gunzip -c uisp-<version>.tar.gz | tar xf -
$ cd uisp-<version>
$ mkdir obj-avr
$ cd obj-avr
$ ../configure --prefix=$PREFIX
$ make
$ make install
7.8.7
Avrdude
Note:
It has been ported to windows (via cygwin) and linux. 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:
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7.8
Installing the GNU Tool Chain 220
$ gunzip -c avrdude-<version>.tar.gz | tar xf -
$ cd avrdude-<version>
$ mkdir obj-avr
$ cd obj-avr
$ ../configure --prefix=$PREFIX
$ make
$ make install
7.8.8
GDB for the AVR target
Gdb also uses the configure system, so to build and install:
$ 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
or
since avr-gdb needs one of these to run as a a remote target backend.
7.8.9
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
and
if you want to have the test programs built in the simulavr source.
7.8.10
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.
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7.9
Using the avrdude program 221
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
<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
7.9
Using the avrdude program
Note:
This section was contributed by Brian Dean [ [email protected]
].
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 programming 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
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7.9
Using the avrdude program 222 avrdude: AVR device initialized and ready to accept instructions 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 read
: dump memory : dump <memtype> <addr> <N-Bytes>
: alias for dump write : write memory : write <memtype> <addr> <b1> <b2> ... <bN> erase : perform a chip erase sig : display device signature bytes part send help
: display the current part information
: send a raw command : send <b1> <b2> <b3> <b4>
: help
?
: help
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7.10
Using the GNU tools 223 quit : quit
Use the ’part’ command to display valid memory types for use with the
’dump’ and ’write’ commands.
avrdude>
7.10
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.
7.10.1
Options for the C compiler avr-gcc
7.10.1.1
Machine-specific options for the AVR The following machine-specific options are recognized by the C compiler frontend.
• -mmcu=architecture
Compile code for architecture. Currently known architectures are avr1 avr2 avr3 avr4 avr5
Simple CPU core, only assembler support
"Classic" CPU core, up to 8 KB of
ROM
"Classic" CPU core, more than 8 KB of
ROM
"Enhanced" CPU core, up to 8 KB of
ROM
"Enhanced" CPU core, more than 8 KB of ROM
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.
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7.10
Using the GNU tools avr4 avr4 avr4 avr5 avr5 avr5 avr5 avr5 avr5 avr5 avr5 avr3 avr3 avr3 avr3 avr3 avr4 avr4 avr4 avr4 avr2 avr2 avr2 avr2 avr2 avr2 avr2 avr2 avr2 avr2 avr2 avr2 avr2 avr2 avr2 avr2 avr2
Architecture MCU name Macro avr1 avr1 at90s1200 attiny11
__AVR_AT90S1200__
__AVR_ATtiny11__ avr1 avr1 avr1 avr2 attiny12 attiny15 attiny28 at90s2313
__AVR_ATtiny12__
__AVR_ATtiny15__
__AVR_ATtiny28__
__AVR_AT90S2313__ at90s2323 at90s2333 at90s2343 attiny22 attiny25 attiny26 attiny45 attiny85 at90s4414
__AVR_AT90S2323__
__AVR_AT90S2333__
__AVR_AT90S2343__
__AVR_ATtiny22__
__AVR_ATtiny25__
__AVR_ATtiny26__
__AVR_ATtiny45__
__AVR_ATtiny85__
__AVR_AT90S4414__ at90s4433 at90s4434 at90s8515 at90c8534 at90s8535 at86rf401 attiny13 attiny2313 atmega103 atmega603 at43usb320 at43usb355 at76c711 atmega48 atmega8 atmega8515 atmega8535
__AVR_AT90S4433__
__AVR_AT90S4434__
__AVR_AT90S8515__
__AVR_AT90C8534__
__AVR_AT90S8535__
__AVR_AT86RF401__
__AVR_ATtiny13__
__AVR_ATtiny2313__
__AVR_ATmega103__
__AVR_ATmega603__
__AVR_AT43USB320__
__AVR_AT43USB355__
__AVR_AT76C711__
__AVR_ATmega48__
__AVR_ATmega8__
__AVR_ATmega8515__
__AVR_ATmega8535__ atmega88 at90pwm2 at90pwm3 at90can32
__AVR_ATmega88__
__AVR_AT90PWM2__
__AVR_AT90PWM3__
__AVR_AT90CAN32__ at90can64 __AVR_AT90CAN64__ at90can128 __AVR_AT90CAN128__ atmega128 __AVR_ATmega128__ atmega1280 __AVR_ATmega1280__ atmega1281 __AVR_ATmega1281__ atmega16 __AVR_ATmega16__ atmega161 __AVR_ATmega161__
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224
7.10
Using the GNU tools 225 avr5 avr5 avr5 avr5 avr5 avr5 avr5 avr5 avr5 avr5 avr5 avr5 avr5 avr5 avr5 avr5
Architecture MCU name Macro avr5 atmega162 __AVR_ATmega162__ avr5 atmega163 __AVR_ATmega163__ avr5 avr5 avr5 atmega164 atmega165 atmega168
__AVR_ATmega164__
__AVR_ATmega165__
__AVR_ATmega168__ atmega169 atmega32 atmega323 atmega324 atmega325 atmega3250 atmega329 atmega3290
__AVR_ATmega169__
__AVR_ATmega32__
__AVR_ATmega323__
__AVR_ATmega324__
__AVR_ATmega325__
__AVR_ATmega3250__
__AVR_ATmega329__
__AVR_ATmega3290__ atmega64 atmega640 atmega644 atmega645
__AVR_ATmega64__
__AVR_ATmega640__
__AVR_ATmega644__
__AVR_ATmega645__ atmega6450 __AVR_ATmega6450__ atmega649 __AVR_ATmega649__ atmega6490 __AVR_ATmega6490__ at94k __AVR_AT94K__
• -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 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
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7.10
Using the GNU tools 226
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.
• -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.
• -minit-stack=nnnn
Set the initial stack pointer to nnnn. By default, the stack pointer is initialized to the symbol __stack, which is set to RAMEND by the run-time initialization code.
• -mtiny-stack
Change only the low 8 bits of the stack pointer.
• -mno-tablejump
Do not generate tablejump instructions. By default, jump tables can be used to optimize 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.
• -mshort-calls
Use rjmp/rcall (limited range) on >8K devices. On avr2 and avr4 architectures (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
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7.10
Using the GNU tools 227
Dump the address, size, and relative cost of each statement into comments in the generated assembler code. Used for debugging avr-gcc.
• -mdeb
Generate lots of debugging information to stderr.
7.10.1.2
Selected general compiler options The following general gcc options might be of some interest to AVR users.
• -On
Optimization level n. Increasing n is 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
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()
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7.10
Using the GNU tools 228 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
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
at run-time.
• -funsigned-char
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.
7.10.2
Options for the assembler avr-as
7.10.2.1
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.
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7.10
Using the GNU tools 229
• -mno-skip-bug
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 devices 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:
• c omit false conditionals
• d omit debugging directives
• h include high-level source
• l include assembly
• m include macro expansions
• n omit forms processing
• s include 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.
Generated on Sat Nov 19 23:00:48 2005 for avr-libc by Doxygen
7.10
Using the GNU tools 230
7.10.2.2
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 assembler generate line number debugging information for it, the following command can be used:
$ 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).
7.10.3
Controlling the linker avr-ld
7.10.3.1
Selected linker options While there are no machine-specific options for avr-ld, a number of the standard options 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 consists 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.
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7.10
Using the GNU tools 231
• -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.
• -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.
Default 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
will be linked together.
7.10.3.2
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). avrlibc 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
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
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7.11
Todo List 232 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:
$ avr-gcc -mmcu=atmega128 -o foo.out -Wl,-Tdata,0x802000
See the explanation of the
for why 0x800000 needs to be added to the actual value. Note that unless a -minit-stack option has been given when compiling the C source file that contains the function main(), 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
will still be placed after all the variables in the data section, so in this situation, no stack/heap collision can occur.
7.11
Todo List
Group
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.
7.12
Deprecated List
Global
Generated on Sat Nov 19 23:00:48 2005 for avr-libc by Doxygen
7.12
Deprecated List
Global
Global
timer_enable_int (unsigned char ints)
Global
Global
Global
Global
233
Generated on Sat Nov 19 23:00:48 2005 for avr-libc by Doxygen
Index
$PATH,
$PREFIX,
–prefix,
<assert.h>: Diagnostics,
<avr/boot.h>: Bootloader Support Utilities,
<avr/eeprom.h>: EEPROM handling,
<avr/interrupt.h>: Interrupts,
<avr/io.h>: AVR device-specific IO definitions,
<avr/pgmspace.h>: Program
String Utilities,
Space
<avr/sfr_defs.h>: Special function registers,
<avr/sleep.h>: Power Management and
Sleep Modes,
<avr/version.h>: macros,
avr-libc version
<avr/wdt.h>: Watchdog timer handling,
<compat/deprecated.h>: items,
Deprecated
<compat/ina90.h>: Compatibility with
IAR EWB 3.x,
<ctype.h>: Character Operations,
<errno.h>: System Errors,
<inttypes.h>: Integer Type conversions,
<math.h>: Mathematics,
<setjmp.h>: Non-local goto,
<stdint.h>: Standard Integer Types,
<stdio.h>: Standard IO facilities,
<stdlib.h>: General utilities,
<string.h>: Strings,
<util/crc16.h>: CRC Computations,
<util/delay.h>: Busy-wait delay loops,
<util/parity.h>: Parity bit generation,
<util/twi.h>: TWI bit mask definitions,
_BV avr_sfr,
_EEGET avr_eeprom,
_EEPUT avr_eeprom,
_FDEV_EOF avr_stdio,
_FDEV_ERR avr_stdio,
_FDEV_SETUP_READ avr_stdio,
_FDEV_SETUP_RW avr_stdio,
_FDEV_SETUP_WRITE avr_stdio,
_FFS avr_string,
__AVR_LIBC_DATE_ avr_version,
__AVR_LIBC_DATE_STRING__ avr_version,
__AVR_LIBC_MAJOR__ avr_version,
__AVR_LIBC_MINOR__ avr_version,
__AVR_LIBC_REVISION__ avr_version,
__AVR_LIBC_VERSION_STRING__ avr_version,
__AVR_LIBC_VERSION__ avr_version,
__EEPROM_REG_LOCATIONS__ avr_eeprom,
__compar_fn_t avr_stdlib,
__malloc_heap_end avr_stdlib,
__malloc_heap_start avr_stdlib,
__malloc_margin avr_stdlib,
_crc16_update util_crc,
INDEX 235
_crc_ccitt_update util_crc, util_crc, util_crc,
_delay_ms
_delay_us
_crc_ibutton_update
_crc_xmodem_update
_delay_loop_1 util_delay,
_delay_loop_2 util_delay, util_delay, util_delay,
A simple project,
abort avr_stdlib,
abs avr_stdlib,
acos avr_math,
Additional notes from <avr/sfr_defs.h>,
asin assert avr_math,
avr_assert,
atan atan2 avr_math,
avr_math,
atof avr_stdlib,
atoi avr_stdlib,
atol avr_stdlib,
avr_assert assert,
avr_boot boot_is_spm_interrupt,
boot_lock_bits_set,
boot_lock_bits_set_safe,
boot_lock_fuse_bits_get,
boot_page_erase,
boot_page_erase_safe,
boot_page_fill,
boot_page_fill_safe,
boot_page_write,
boot_page_write_safe,
boot_rww_busy,
boot_rww_enable,
boot_rww_enable_safe,
boot_spm_busy,
boot_spm_busy_wait,
boot_spm_interrupt_disable,
boot_spm_interrupt_enable,
BOOTLOADER_SECTION,
GET_EXTENDED_FUSE_BITS,
GET_HIGH_FUSE_BITS,
GET_LOCK_BITS,
GET_LOW_FUSE_BITS,
avr_eeprom
_EEGET,
_EEPUT,
__EEPROM_REG_LOCATIONS_-
_,
EEMEM,
eeprom_busy_wait,
eeprom_is_ready,
eeprom_read_block,
eeprom_read_byte,
eeprom_read_word,
eeprom_write_block,
eeprom_write_byte,
eeprom_write_word,
avr_errno
EDOM,
ERANGE,
avr_interrupts
EMPTY_INTERRUPT,
ISR,
SIGNAL,
avr_inttypes int_farptr_t,
PRId16,
PRId32,
PRId8,
PRIdFAST16,
PRIdFAST32,
Generated on Sat Nov 19 23:00:48 2005 for avr-libc by Doxygen
INDEX
PRIoPTR,
PRIu16,
PRIu32,
PRIu8,
PRIuFAST16,
PRIuFAST32,
PRIuFAST8,
PRIuLEAST16,
PRIuLEAST32,
PRIuLEAST8,
PRIuPTR,
PRIX16,
PRIx16,
PRIX32,
PRIx32,
PRIX8,
PRIx8,
PRIXFAST16,
PRIxFAST16,
PRIXFAST32,
PRIxFAST32,
PRIXFAST8,
PRIdFAST8,
PRIdLEAST16,
PRIdLEAST32,
PRIdLEAST8,
PRIdPTR,
PRIi16,
PRIi32,
PRIi8,
PRIiFAST16,
PRIiFAST32,
PRIiFAST8,
PRIiLEAST16,
PRIiLEAST32,
PRIiLEAST8,
PRIiPTR,
PRIo16,
PRIo32,
PRIo8,
PRIoFAST16,
PRIoFAST32,
PRIoFAST8,
PRIoLEAST16,
PRIoLEAST32,
PRIoLEAST8,
Generated on Sat Nov 19 23:00:48 2005 for avr-libc by Doxygen
PRIxFAST8,
PRIXLEAST16,
PRIxLEAST16,
PRIXLEAST32,
PRIxLEAST32,
PRIXLEAST8,
PRIxLEAST8,
PRIXPTR,
PRIxPTR,
SCNd16,
SCNd32,
SCNdFAST16,
SCNdFAST32,
SCNdLEAST16,
SCNdLEAST32,
SCNdPTR,
SCNi16,
SCNi32,
SCNiFAST16,
SCNiFAST32,
SCNiLEAST16,
SCNiLEAST32,
SCNiPTR,
SCNo16,
SCNo32,
SCNoFAST16,
SCNoFAST32,
SCNoLEAST16,
SCNoLEAST32,
SCNoPTR,
SCNu16,
SCNu32,
SCNuFAST16,
SCNuFAST32,
SCNuLEAST16,
SCNuLEAST32,
SCNuPTR,
SCNx16,
SCNx32,
SCNxFAST16,
SCNxFAST32,
SCNxLEAST16,
SCNxLEAST32,
SCNxPTR,
uint_farptr_t,
avr_math
236
INDEX 237 acos,
asin,
atan,
atan2,
ceil,
cos,
cosh,
exp,
fabs,
floor,
fmod,
frexp,
isinf,
isnan,
ldexp,
log,
log10,
M_PI,
M_SQRT2,
modf,
pow,
sin,
sinh,
sqrt,
square,
tan,
tanh,
avr_pgmspace memcpy_P,
PGM_P,
pgm_read_byte,
pgm_read_byte_far,
pgm_read_byte_near,
pgm_read_dword,
pgm_read_dword_far,
pgm_read_dword_near,
pgm_read_word,
pgm_read_word_far,
pgm_read_word_near,
PGM_VOID_P,
prog_char,
prog_int16_t,
prog_int32_t,
prog_int64_t,
prog_int8_t,
prog_uchar,
Generated on Sat Nov 19 23:00:48 2005 for avr-libc by Doxygen prog_uint16_t,
prog_uint32_t,
prog_uint64_t,
prog_uint8_t,
prog_void,
PROGMEM,
PSTR,
strcasecmp_P,
strcat_P,
strcmp_P,
strcpy_P,
strlcat_P,
strlcpy_P,
strlen_P,
strncasecmp_P,
strncat_P,
strncmp_P,
strncpy_P,
strnlen_P,
avr_sfr
_BV,
bit_is_clear,
bit_is_set,
loop_until_bit_is_clear,
loop_until_bit_is_set,
avr_sleep set_sleep_mode,
sleep_mode,
SLEEP_MODE_ADC,
SLEEP_MODE_EXT_STANDBY,
SLEEP_MODE_IDLE,
SLEEP_MODE_PWR_DOWN,
SLEEP_MODE_PWR_SAVE,
SLEEP_MODE_STANDBY,
avr_stdint
INT16_C,
INT16_MAX,
INT16_MIN,
int16_t,
INT32_C,
INT32_MAX,
INT32_MIN,
int32_t,
INT64_C,
INT64_MAX,
INDEX
INT64_MIN,
int64_t,
INT8_C,
INT8_MAX,
INT8_MIN,
int8_t,
INT_FAST16_MAX,
INT_FAST16_MIN,
int_fast16_t,
INT_FAST32_MAX,
INT_FAST32_MIN,
int_fast32_t,
INT_FAST64_MAX,
INT_FAST64_MIN,
int_fast64_t,
INT_FAST8_MAX,
INT_FAST8_MIN,
int_fast8_t,
INT_LEAST16_MAX,
INT_LEAST16_MIN,
int_least16_t,
INT_LEAST32_MAX,
INT_LEAST32_MIN,
int_least32_t,
INT_LEAST64_MAX,
INT_LEAST64_MIN,
int_least64_t,
INT_LEAST8_MAX,
INT_LEAST8_MIN,
int_least8_t,
INTMAX_C,
INTMAX_MAX,
INTMAX_MIN,
intmax_t,
INTPTR_MAX,
INTPTR_MIN,
intptr_t,
PTRDIFF_MAX,
PTRDIFF_MIN,
SIG_ATOMIC_MAX,
SIG_ATOMIC_MIN,
SIZE_MAX,
UINT16_C,
UINT16_MAX,
uint16_t,
UINT32_C,
Generated on Sat Nov 19 23:00:48 2005 for avr-libc by Doxygen
UINT32_MAX,
uint32_t,
UINT64_C,
UINT64_MAX,
uint64_t,
UINT8_C,
UINT8_MAX,
uint8_t,
UINT_FAST16_MAX,
uint_fast16_t,
UINT_FAST32_MAX,
uint_fast32_t,
UINT_FAST64_MAX,
uint_fast64_t,
UINT_FAST8_MAX,
uint_fast8_t,
UINT_LEAST16_MAX,
uint_least16_t,
UINT_LEAST32_MAX,
uint_least32_t,
UINT_LEAST64_MAX,
uint_least64_t,
UINT_LEAST8_MAX,
uint_least8_t,
UINTMAX_C,
UINTMAX_MAX,
uintmax_t,
UINTPTR_MAX,
uintptr_t,
avr_stdio
_FDEV_EOF,
_FDEV_ERR,
_FDEV_SETUP_READ,
_FDEV_SETUP_RW,
_FDEV_SETUP_WRITE,
clearerr,
EOF,
fclose,
fdev_close,
fdev_get_udata,
fdev_set_udata,
FDEV_SETUP_STREAM,
fdev_setup_stream,
fdevopen,
feof,
ferror,
238
INDEX snprintf,
snprintf_P,
sprintf,
sprintf_P,
sscanf,
sscanf_P,
stderr,
stdin,
stdout,
ungetc,
vfprintf,
vfprintf_P,
vfscanf,
vfscanf_P,
vprintf,
vscanf,
vsnprintf,
vsnprintf_P,
vsprintf,
vsprintf_P,
avr_stdlib
__compar_fn_t,
fflush,
fgetc,
fgets,
FILE,
fprintf,
fprintf_P,
fputc,
fputs,
fputs_P,
fread,
fscanf,
fscanf_P,
fwrite,
getc,
getchar,
gets,
printf,
printf_P,
putc,
putchar,
puts,
puts_P,
scanf,
scanf_P,
Generated on Sat Nov 19 23:00:48 2005 for avr-libc by Doxygen
__malloc_heap_end,
__malloc_heap_start,
__malloc_margin,
abort,
abs,
atof,
atoi,
atol,
bsearch,
calloc,
div,
DTOSTR_ALWAYS_SIGN,
DTOSTR_PLUS_SIGN,
DTOSTR_UPPERCASE,
dtostre,
dtostrf,
exit,
free,
itoa,
labs,
ldiv,
ltoa,
malloc,
qsort,
rand,
RAND_MAX,
rand_r,
random,
RANDOM_MAX,
random_r,
realloc,
srand,
srandom,
strtod,
strtol,
strtoul,
ultoa,
utoa,
avr_string
_FFS,
ffs,
ffsl,
ffsll,
memccpy,
memchr,
memcmp,
239
INDEX memcpy,
memmove,
memset,
strcasecmp,
strcat,
strchr,
strcmp,
strcpy,
strlcat,
strlcpy,
strlen,
strlwr,
strncasecmp,
strncat,
strncmp,
strncpy,
strnlen,
strrchr,
strrev,
strsep,
strstr,
strtok_r,
strupr,
avr_version
__AVR_LIBC_DATE_,
__AVR_LIBC_DATE_STRING__,
__AVR_LIBC_MAJOR__,
__AVR_LIBC_MINOR__,
__AVR_LIBC_REVISION__,
__AVR_LIBC_VERSION_-
STRING__,
__AVR_LIBC_VERSION__,
avr_watchdog wdt_disable,
wdt_enable,
wdt_reset,
WDTO_120MS,
WDTO_15MS,
WDTO_1S,
WDTO_250MS,
WDTO_2S,
WDTO_30MS,
WDTO_4S,
WDTO_500MS,
WDTO_60MS,
WDTO_8S,
avrdude, usage,
avrprog, usage,
bit_is_clear avr_sfr,
bit_is_set avr_sfr,
boot_is_spm_interrupt avr_boot,
boot_lock_bits_set avr_boot,
boot_lock_bits_set_safe avr_boot,
boot_lock_fuse_bits_get avr_boot,
boot_page_erase avr_boot,
boot_page_erase_safe avr_boot,
boot_page_fill avr_boot,
boot_page_fill_safe avr_boot,
boot_page_write avr_boot,
boot_page_write_safe avr_boot,
boot_rww_busy avr_boot,
boot_rww_enable avr_boot,
boot_rww_enable_safe avr_boot,
boot_spm_busy avr_boot,
boot_spm_busy_wait avr_boot,
boot_spm_interrupt_disable avr_boot,
boot_spm_interrupt_enable avr_boot,
BOOTLOADER_SECTION avr_boot,
bsearch avr_stdlib,
Generated on Sat Nov 19 23:00:48 2005 for avr-libc by Doxygen
240
INDEX 241 calloc avr_stdlib,
cbi deprecated_items,
ceil avr_math,
clearerr avr_stdio,
cos avr_math,
cosh ctype avr_math,
isalnum,
isalpha,
isascii,
isblank,
iscntrl,
isdigit,
isgraph,
islower,
isprint,
ispunct,
isspace,
isupper,
isxdigit,
toascii,
tolower,
toupper,
Demo projects,
deprecated_items cbi,
enable_external_int,
inp,
INTERRUPT,
outp,
sbi,
timer_enable_int,
disassembling,
div avr_stdlib,
div_t,
quot,
rem,
DTOSTR_ALWAYS_SIGN
Generated on Sat Nov 19 23:00:48 2005 for avr-libc by Doxygen avr_stdlib,
DTOSTR_PLUS_SIGN avr_stdlib,
DTOSTR_UPPERCASE avr_stdlib,
dtostre avr_stdlib,
dtostrf avr_stdlib,
EDOM avr_errno,
EEMEM avr_eeprom,
eeprom_busy_wait avr_eeprom,
eeprom_is_ready avr_eeprom,
eeprom_read_block avr_eeprom,
eeprom_read_byte avr_eeprom,
eeprom_read_word avr_eeprom,
eeprom_write_block avr_eeprom,
eeprom_write_byte avr_eeprom,
eeprom_write_word avr_eeprom,
EMPTY_INTERRUPT avr_interrupts,
enable_external_int deprecated_items,
EOF avr_stdio,
ERANGE avr_errno,
Example using the two-wire interface
(TWI),
exit avr_stdlib,
exp avr_math,
fabs
INDEX avr_math,
FAQ,
fclose avr_stdio,
fdev_close avr_stdio,
fdev_get_udata avr_stdio,
fdev_set_udata avr_stdio,
FDEV_SETUP_STREAM avr_stdio,
fdev_setup_stream avr_stdio,
fdevopen avr_stdio,
feof ferror avr_stdio,
fflush avr_stdio,
avr_stdio,
ffs avr_string,
ffsl avr_string,
ffsll fgetc avr_string,
avr_stdio,
fgets
FILE avr_stdio,
avr_stdio,
floor fmod avr_math,
avr_math,
fprintf avr_stdio,
fprintf_P fputc avr_stdio,
fputs avr_stdio,
avr_stdio,
Generated on Sat Nov 19 23:00:48 2005 for avr-libc by Doxygen fputs_P avr_stdio,
fread avr_stdio,
free frexp avr_stdlib,
avr_math,
fscanf avr_stdio,
fscanf_P avr_stdio,
fwrite avr_stdio,
GET_EXTENDED_FUSE_BITS avr_boot,
GET_HIGH_FUSE_BITS avr_boot,
GET_LOCK_BITS avr_boot,
GET_LOW_FUSE_BITS avr_boot,
getc avr_stdio,
getchar avr_stdio,
gets avr_stdio,
inp deprecated_items,
installation,
installation, avarice,
installation, avr-libc,
installation, avrdude,
installation, avrprog,
installation, binutils,
installation, gcc,
Installation, gdb,
installation, simulavr,
installation, uisp,
INT16_C avr_stdint,
INT16_MAX avr_stdint,
242
INDEX
INT16_MIN avr_stdint,
int16_t avr_stdint,
INT32_C avr_stdint,
INT32_MAX avr_stdint,
INT32_MIN avr_stdint,
int32_t avr_stdint,
INT64_C avr_stdint,
INT64_MAX avr_stdint,
INT64_MIN avr_stdint,
int64_t avr_stdint,
INT8_C avr_stdint,
INT8_MAX avr_stdint,
INT8_MIN avr_stdint,
int8_t avr_stdint,
int_farptr_t avr_inttypes,
INT_FAST16_MAX avr_stdint,
INT_FAST16_MIN avr_stdint,
int_fast16_t avr_stdint,
INT_FAST32_MAX avr_stdint,
INT_FAST32_MIN avr_stdint,
int_fast32_t avr_stdint,
INT_FAST64_MAX avr_stdint,
INT_FAST64_MIN avr_stdint,
Generated on Sat Nov 19 23:00:48 2005 for avr-libc by Doxygen int_fast64_t avr_stdint,
INT_FAST8_MAX avr_stdint,
INT_FAST8_MIN avr_stdint,
int_fast8_t avr_stdint,
INT_LEAST16_MAX avr_stdint,
INT_LEAST16_MIN avr_stdint,
int_least16_t avr_stdint,
INT_LEAST32_MAX avr_stdint,
INT_LEAST32_MIN avr_stdint,
int_least32_t avr_stdint,
INT_LEAST64_MAX avr_stdint,
INT_LEAST64_MIN avr_stdint,
int_least64_t avr_stdint,
INT_LEAST8_MAX avr_stdint,
INT_LEAST8_MIN avr_stdint,
int_least8_t avr_stdint,
INTERRUPT deprecated_items,
INTMAX_C avr_stdint,
INTMAX_MAX avr_stdint,
INTMAX_MIN avr_stdint,
intmax_t avr_stdint,
INTPTR_MAX avr_stdint,
INTPTR_MIN avr_stdint,
243
INDEX intptr_t avr_stdint,
isalnum ctype,
isalpha ctype,
isascii ctype,
isblank ctype,
iscntrl ctype,
isdigit ctype,
isgraph ctype,
isinf avr_math,
islower isnan ctype,
avr_math,
isprint ctype,
ispunct ctype,
ISR avr_interrupts,
isspace ctype,
isupper ctype,
isxdigit ctype,
itoa avr_stdlib,
labs ldexp avr_stdlib,
avr_math,
ldiv avr_stdlib,
ldiv_t,
quot,
rem,
Generated on Sat Nov 19 23:00:48 2005 for avr-libc by Doxygen log log10 avr_math,
avr_math,
longjmp setjmp,
loop_until_bit_is_clear avr_sfr,
loop_until_bit_is_set avr_sfr,
ltoa avr_stdlib,
M_PI avr_math,
M_SQRT2 avr_math,
malloc avr_stdlib,
memccpy avr_string,
memchr avr_string,
memcmp avr_string,
memcpy avr_string,
memcpy_P avr_pgmspace,
memmove avr_string,
memset modf avr_string,
avr_math,
outp deprecated_items,
parity_even_bit util_parity,
PGM_P avr_pgmspace,
pgm_read_byte avr_pgmspace,
pgm_read_byte_far
244
INDEX avr_pgmspace,
pgm_read_byte_near avr_pgmspace,
pgm_read_dword avr_pgmspace,
pgm_read_dword_far avr_pgmspace,
pgm_read_dword_near avr_pgmspace,
pgm_read_word avr_pgmspace,
pgm_read_word_far avr_pgmspace,
pgm_read_word_near avr_pgmspace,
PGM_VOID_P avr_pgmspace,
pow avr_math,
PRId16 avr_inttypes,
PRId32 avr_inttypes,
PRId8 avr_inttypes,
PRIdFAST16 avr_inttypes,
PRIdFAST32 avr_inttypes,
PRIdFAST8 avr_inttypes,
PRIdLEAST16 avr_inttypes,
PRIdLEAST32 avr_inttypes,
PRIdLEAST8 avr_inttypes,
PRIdPTR avr_inttypes,
PRIi16 avr_inttypes,
PRIi32 avr_inttypes,
PRIi8 avr_inttypes,
PRIiFAST16
Generated on Sat Nov 19 23:00:48 2005 for avr-libc by Doxygen avr_inttypes,
PRIiFAST32 avr_inttypes,
PRIiFAST8 avr_inttypes,
PRIiLEAST16 avr_inttypes,
PRIiLEAST32 avr_inttypes,
PRIiLEAST8 avr_inttypes,
PRIiPTR avr_inttypes,
printf avr_stdio,
printf_P avr_stdio,
PRIo16 avr_inttypes,
PRIo32 avr_inttypes,
PRIo8 avr_inttypes,
PRIoFAST16 avr_inttypes,
PRIoFAST32 avr_inttypes,
PRIoFAST8 avr_inttypes,
PRIoLEAST16 avr_inttypes,
PRIoLEAST32 avr_inttypes,
PRIoLEAST8 avr_inttypes,
PRIoPTR avr_inttypes,
PRIu16 avr_inttypes,
PRIu32 avr_inttypes,
PRIu8 avr_inttypes,
PRIuFAST16 avr_inttypes,
PRIuFAST32
245
INDEX avr_inttypes,
PRIuFAST8 avr_inttypes,
PRIuLEAST16 avr_inttypes,
PRIuLEAST32 avr_inttypes,
PRIuLEAST8 avr_inttypes,
PRIuPTR avr_inttypes,
PRIX16 avr_inttypes,
PRIx16 avr_inttypes,
PRIX32 avr_inttypes,
PRIx32 avr_inttypes,
PRIX8 avr_inttypes,
PRIx8 avr_inttypes,
PRIXFAST16 avr_inttypes,
PRIxFAST16 avr_inttypes,
PRIXFAST32 avr_inttypes,
PRIxFAST32 avr_inttypes,
PRIXFAST8 avr_inttypes,
PRIxFAST8 avr_inttypes,
PRIXLEAST16 avr_inttypes,
PRIxLEAST16 avr_inttypes,
PRIXLEAST32 avr_inttypes,
PRIxLEAST32 avr_inttypes,
PRIXLEAST8 avr_inttypes,
PRIxLEAST8
Generated on Sat Nov 19 23:00:48 2005 for avr-libc by Doxygen avr_inttypes,
PRIXPTR avr_inttypes,
PRIxPTR avr_inttypes,
prog_char avr_pgmspace,
prog_int16_t avr_pgmspace,
prog_int32_t avr_pgmspace,
prog_int64_t avr_pgmspace,
prog_int8_t avr_pgmspace,
prog_uchar avr_pgmspace,
prog_uint16_t avr_pgmspace,
prog_uint32_t avr_pgmspace,
prog_uint64_t avr_pgmspace,
prog_uint8_t avr_pgmspace,
prog_void avr_pgmspace,
PROGMEM avr_pgmspace,
PSTR avr_pgmspace,
PTRDIFF_MAX avr_stdint,
PTRDIFF_MIN avr_stdint,
putc avr_stdio,
putchar avr_stdio,
puts avr_stdio,
puts_P avr_stdio,
qsort avr_stdlib,
246
INDEX quot div_t,
ldiv_t,
rand avr_stdlib,
RAND_MAX avr_stdlib,
rand_r avr_stdlib,
random avr_stdlib,
RANDOM_MAX avr_stdlib,
random_r avr_stdlib,
realloc avr_stdlib,
rem div_t,
ldiv_t,
sbi scanf deprecated_items,
avr_stdio,
scanf_P avr_stdio,
SCNd16 avr_inttypes,
SCNd32 avr_inttypes,
SCNdFAST16 avr_inttypes,
SCNdFAST32 avr_inttypes,
SCNdLEAST16 avr_inttypes,
SCNdLEAST32 avr_inttypes,
SCNdPTR avr_inttypes,
SCNi16 avr_inttypes,
SCNi32 avr_inttypes,
SCNiFAST16 avr_inttypes,
SCNiFAST32 avr_inttypes,
SCNiLEAST16 avr_inttypes,
SCNiLEAST32 avr_inttypes,
SCNiPTR avr_inttypes,
SCNo16 avr_inttypes,
SCNo32 avr_inttypes,
SCNoFAST16 avr_inttypes,
SCNoFAST32 avr_inttypes,
SCNoLEAST16 avr_inttypes,
SCNoLEAST32 avr_inttypes,
SCNoPTR avr_inttypes,
SCNu16 avr_inttypes,
SCNu32 avr_inttypes,
SCNuFAST16 avr_inttypes,
SCNuFAST32 avr_inttypes,
SCNuLEAST16 avr_inttypes,
SCNuLEAST32 avr_inttypes,
SCNuPTR avr_inttypes,
SCNx16 avr_inttypes,
SCNx32 avr_inttypes,
SCNxFAST16 avr_inttypes,
SCNxFAST32 avr_inttypes,
Generated on Sat Nov 19 23:00:48 2005 for avr-libc by Doxygen
247
INDEX
SCNxLEAST16 avr_inttypes,
SCNxLEAST32 avr_inttypes,
SCNxPTR avr_inttypes,
set_sleep_mode avr_sleep,
setjmp longjmp,
setjmp,
SIG_ATOMIC_MAX avr_stdint,
SIG_ATOMIC_MIN avr_stdint,
SIGNAL avr_interrupts,
sin avr_math,
sinh avr_math,
SIZE_MAX avr_stdint,
sleep_mode avr_sleep,
SLEEP_MODE_ADC avr_sleep,
SLEEP_MODE_EXT_STANDBY avr_sleep,
SLEEP_MODE_IDLE avr_sleep,
SLEEP_MODE_PWR_DOWN avr_sleep,
SLEEP_MODE_PWR_SAVE avr_sleep,
SLEEP_MODE_STANDBY avr_sleep,
snprintf avr_stdio,
snprintf_P avr_stdio,
sprintf avr_stdio,
sprintf_P avr_stdio,
sqrt
Generated on Sat Nov 19 23:00:48 2005 for avr-libc by Doxygen avr_math,
square srand avr_math,
avr_stdlib,
srandom avr_stdlib,
sscanf avr_stdio,
sscanf_P avr_stdio,
stderr avr_stdio,
stdin avr_stdio,
stdout avr_stdio,
strcasecmp avr_string,
strcasecmp_P strcat avr_pgmspace,
avr_string,
strcat_P strchr avr_pgmspace,
avr_string,
strcmp avr_string,
strcmp_P avr_pgmspace,
strcpy avr_string,
strcpy_P avr_pgmspace,
strlcat avr_string,
strlcat_P avr_pgmspace,
strlcpy avr_string,
strlcpy_P avr_pgmspace,
strlen avr_string,
strlen_P
248
INDEX avr_pgmspace,
strlwr avr_string,
strncasecmp avr_string,
strncasecmp_P avr_pgmspace,
strncat avr_string,
strncat_P avr_pgmspace,
strncmp avr_string,
strncmp_P avr_pgmspace,
strncpy avr_string,
strncpy_P avr_pgmspace,
strnlen avr_string,
strnlen_P avr_pgmspace,
strrchr strrev avr_string,
avr_string,
strsep strstr avr_string,
strtod avr_string,
avr_stdlib,
strtok_r strtol avr_string,
avr_stdlib,
strtoul avr_stdlib,
strupr avr_string,
supported devices,
tan tanh avr_math,
avr_math,
timer_enable_int deprecated_items,
toascii ctype,
tolower ctype,
tools, optional,
tools, required,
toupper ctype,
TW_BUS_ERROR util_twi,
TW_MR_ARB_LOST util_twi,
TW_MR_DATA_ACK util_twi,
TW_MR_DATA_NACK util_twi,
TW_MR_SLA_ACK util_twi,
TW_MR_SLA_NACK util_twi,
TW_MT_ARB_LOST util_twi,
TW_MT_DATA_ACK util_twi,
TW_MT_DATA_NACK util_twi,
TW_MT_SLA_ACK util_twi,
TW_MT_SLA_NACK util_twi,
TW_NO_INFO util_twi,
TW_READ util_twi,
TW_REP_START util_twi,
TW_SR_ARB_LOST_GCALL_ACK util_twi,
TW_SR_ARB_LOST_SLA_ACK util_twi,
TW_SR_DATA_ACK util_twi,
TW_SR_DATA_NACK
Generated on Sat Nov 19 23:00:48 2005 for avr-libc by Doxygen
249
INDEX util_twi,
TW_SR_GCALL_ACK util_twi,
TW_SR_GCALL_DATA_ACK util_twi,
TW_SR_GCALL_DATA_NACK util_twi,
TW_SR_SLA_ACK util_twi,
TW_SR_STOP util_twi,
TW_ST_ARB_LOST_SLA_ACK util_twi,
TW_ST_DATA_ACK util_twi,
TW_ST_DATA_NACK util_twi,
TW_ST_LAST_DATA util_twi,
TW_ST_SLA_ACK util_twi,
TW_START util_twi,
TW_STATUS util_twi,
TW_STATUS_MASK util_twi,
TW_WRITE util_twi,
UINT16_C avr_stdint,
UINT16_MAX avr_stdint,
uint16_t avr_stdint,
UINT32_C avr_stdint,
UINT32_MAX avr_stdint,
uint32_t avr_stdint,
UINT64_C avr_stdint,
UINT64_MAX avr_stdint,
uint64_t avr_stdint,
UINT8_C avr_stdint,
UINT8_MAX avr_stdint,
uint8_t avr_stdint,
uint_farptr_t avr_inttypes,
UINT_FAST16_MAX avr_stdint,
uint_fast16_t avr_stdint,
UINT_FAST32_MAX avr_stdint,
uint_fast32_t avr_stdint,
UINT_FAST64_MAX avr_stdint,
uint_fast64_t avr_stdint,
UINT_FAST8_MAX avr_stdint,
uint_fast8_t avr_stdint,
UINT_LEAST16_MAX avr_stdint,
uint_least16_t avr_stdint,
UINT_LEAST32_MAX avr_stdint,
uint_least32_t avr_stdint,
UINT_LEAST64_MAX avr_stdint,
uint_least64_t avr_stdint,
UINT_LEAST8_MAX avr_stdint,
uint_least8_t avr_stdint,
UINTMAX_C avr_stdint,
UINTMAX_MAX avr_stdint,
Generated on Sat Nov 19 23:00:48 2005 for avr-libc by Doxygen
250
INDEX 251 uintmax_t avr_stdint,
UINTPTR_MAX avr_stdint,
uintptr_t avr_stdint,
ultoa avr_stdlib,
ungetc avr_stdio,
util_crc
_crc16_update,
_crc_ccitt_update,
_crc_ibutton_update,
_crc_xmodem_update,
util_delay
_delay_loop_1,
_delay_loop_2,
_delay_ms,
_delay_us,
util_parity parity_even_bit,
util_twi
TW_BUS_ERROR,
TW_MR_ARB_LOST,
TW_MR_DATA_ACK,
TW_MR_DATA_NACK,
TW_MR_SLA_ACK,
TW_MR_SLA_NACK,
TW_MT_ARB_LOST,
TW_MT_DATA_ACK,
TW_MT_DATA_NACK,
TW_MT_SLA_ACK,
TW_MT_SLA_NACK,
TW_NO_INFO,
TW_READ,
TW_REP_START,
TW_SR_ARB_LOST_GCALL_-
ACK,
TW_SR_ARB_LOST_SLA_ACK,
TW_SR_DATA_ACK,
TW_SR_DATA_NACK,
TW_SR_GCALL_ACK,
TW_SR_GCALL_DATA_ACK,
utoa
TW_SR_GCALL_DATA_NACK,
TW_SR_SLA_ACK,
TW_SR_STOP,
TW_ST_ARB_LOST_SLA_ACK,
TW_ST_DATA_ACK,
TW_ST_DATA_NACK,
TW_ST_LAST_DATA,
TW_ST_SLA_ACK,
TW_START,
TW_STATUS,
TW_STATUS_MASK,
TW_WRITE, avr_stdlib,
vfprintf avr_stdio,
vfprintf_P avr_stdio,
vfscanf avr_stdio,
vfscanf_P avr_stdio,
vprintf avr_stdio,
vscanf avr_stdio,
vsnprintf avr_stdio,
vsnprintf_P avr_stdio,
vsprintf avr_stdio,
vsprintf_P avr_stdio,
wdt_disable avr_watchdog,
wdt_enable avr_watchdog,
wdt_reset avr_watchdog,
WDTO_120MS avr_watchdog,
Generated on Sat Nov 19 23:00:48 2005 for avr-libc by Doxygen
INDEX
WDTO_15MS avr_watchdog,
WDTO_1S avr_watchdog,
WDTO_250MS avr_watchdog,
WDTO_2S avr_watchdog,
WDTO_30MS avr_watchdog,
WDTO_4S avr_watchdog,
WDTO_500MS avr_watchdog,
WDTO_60MS avr_watchdog,
WDTO_8S avr_watchdog,
252
Generated on Sat Nov 19 23:00:48 2005 for avr-libc by Doxygen
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