AVR Compiler and Toolchain Options: GUI

To get help about AVR GNU toolchain, you can do the following:

For information about avr32-gcc usage in Atmel Studio and general parameters, consult the GCC Project Options and Configuration section
The API reference for the AVR libc implementation can be found here

The API Alphabetical index can be consulted here
For general information about GCC, visit the official GNU GCC web site
Alternatively, you can write avr32-gcc --help and see explanations on some of the parameters in the command output

This section illustrates the GUI options that are available for the AVR GNU toolchain from the Atmel Studio frontend.

Figure 1. AVR GNU Toolchain Options

AVR GNU C Compiler Options

Table 1. AVR GNU C Compiler Options
Option	Description
General options
-mcall-prologues	Use subroutines for functions prologues and epilogues
-mno-interrupts	Change stack pointer without disabling interrupts
-funsigned-char	Default char type is unsigned
-funsigned-bitfield	Default bit field is unsigned
Preprocessor options
-nostdinc	Do not search system directories
-E	Preprocess only
Symbols options
One can define (-D) or undefine (-U) a number of in-source symbols. New symbol declarations can be added, modified, or reordered, using the interface buttons below: Add a new symbol. This and all following icons are reused with the same meaning in other parts of Atmel Studio interface. Remove a symbol. Edit symbol. Move the symbol up in the parsing order. Move the symbol down in the parsing order.
Include directories
Contains all the included header and definition directories, can be modified, using the same interface as symbols.
Optimization options
Optimization level (drop-down menu): -O0, -O1, -O2, -O3, -Os	No optimization, optimize for speed (level 1 - 3), optimize for size
Other optimization flags (manual input form)	Here you should write optimization flags specific to the platform and your requirements
-ffunction-sections	Prepare functions for garbage collection, if a function is never used, its memory will be scrapped
-fpack-struct	Pack structure members together
-fshort-enums	Allocate only as many bytes needed by the enumerated types
-mshort-calls	Use rjmp/rcall limited range instructions on the >8K devices
Debug options
Debug level (drop-down menu): none, -g1, -g2, -g3	Specifies the level of tracing and debugging code and headers left or inserted in the source code
Other debug options (form field)	Architecture-specific debug options
Warning messages output options
-Wall	All warnings
-Werror	Escalate warnings to errors
-fsyntax-only	Check syntax only
-pedantic	Check conformity to GNU, raise warnings on non-standard programming practice
-pedantic-errors	Same as above, plus escalate warnings to errors
Miscellaneous options
Other flags (form field)	Input other project-specific flags
-v	Verbose
-ansi	Support ANSI programs
-save-temps	Do not delete temporary files

AVR GCC Linker Options

Table 2. AVR GCC Linker Options
Option	Description
-Wl -nostartfiles	Do not use standard files
-Wl -nodefault	Do not use default libraries
-Wl -nostdlib	No start-up or default libraries
-Wl -s	Omit all symbol information
-Wl -static	Link statically
Libraries options
Libraries -Wl, -l (form field)	You can add, prioritize, or edit library names here, using those buttons: , , , ,
Library search path -Wl,-L (form field)	You can add, prioritize, or edit path where the linker will search for dynamically linked libraries, same interface as above
Optimization options
-Wl, -gc-sections	Garbage collect unused sections
--rodata-writable	Put read-only data in writable spaces
-mrelax	Relax branches
Miscellaneous options
Other linker flags (form field)	Input other project-specific flags

Memory Settings

Displays a dialog where it is possible to configure memory segments. (Syntax for specifying segment values: <segmentname> = <address>, for example boot=0xff)

The address must be given as a hexadecimal number prefixed with 0x. It is interpreted as a word address for flash memory and a byte address for SRAM and EEPROM memory.

Figure 2. Memory Settings

Notes about the AVR port of GCC

The AVR is a Harvard architecture CPU. This means that it separates instruction memory and data memory. The GCC was originally designed to support Von Neumann architectures which define a single storage structure to hold both instructions and data. This dichotomy is solved by a series of nifty tricks in the AVR port of GCC, of which three should be noted:

The .text segment starts at 0x0
The .data segment starts at 0x800000
The .eeprom segment starts at 0x810000

These peculiarities have been abstracted away by the GUI, but users will see the truth when building projects with relocated segments.

A relocation definition for flash will be passed to the GNU linker via avr-gcc as the option:

-Wl,-section-start=bootloader=0x1fc00

Note that the address has been multiplied by 2 to get the byte address.

A relocation definition for the .data section will be passed as:

-Wl,-section-start=anewdatasegment=0x800

AVR Assembler Options

Table 3. AVR Assembler Options
Option	Description
Optimization options
Assembler flags (form field)	Miscellaneous assembler flags
Include path (form field)	You can add, prioritize, or edit path to the architecture and platform specific included files here
-v	Announce version in the assembler output
Debugging options
Debugging (drop-down menu) None, -Wa -g	Enables debugging symbol and debugging source insertion