Code size is smaller. Set the size in bits of the double or long double type, respectively. Possible values for bits are 32 and Assume int to be 8-bit integer. This affects the sizes of all types: a char is 1 byte, an int is 1 byte, a long is 2 bytes, and long long is 4 bytes.
Please note that this option does not conform to the C standards, but it results in smaller code size. Do not save registers in main. It is activated per default if optimization is on. Try to replace CALL resp. RJMP instruction if applicable. Jump relaxing is performed by the linker because jump offsets are not known before code is located. Therefore, the assembler code generated by the compiler is the same, but the instructions in the executable may differ from instructions in the assembler code.
Relaxing must be turned on if linker stubs are needed, see the section on EIND and linker stubs below. In general, it has been the goal to stick as best as possible to established standards while implementing this library.
Unless otherwise noted, functions of this library are not guaranteed to be reentrant. In particular, any functions that store local state are known to be non-reentrant, as well as functions that manipulate IO registers like the EEPROM access routines.
If these functions are used within both standard and interrupt contexts undefined behaviour will result. 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.
On avr2 and avr4 architectures less than 8 KB or flash memory , this is always the case. Dump the internal compilation result called "RTL" into comments in the generated assembler code.
Used for debugging avr-gcc. Dump the address, size, and relative cost of each statement into comments in the generated assembler code. 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. Note also that turning off all optimizations will prevent some warnings from being issued since the generation of those warnings depends on code analysis steps that are only performed when optimizing unreachable code, unused variables.
See also the appropriate FAQ entry for issues regarding debugging optimized code. Pass the listed options to the assembler, or linker, respectively.
Assume a "freestanding" environment as per the C standard. It also makes the compiler not complain when main is declared with a void return type which makes some sense in a microcontroller environment where the application cannot meaningfully provide a return value to its environment in most cases, main won't even return anyway.
However, this also turns off all optimizations normally done by the compiler which assume that functions known by a certain name behave as described by the standard. Make any unqualfied char type an unsigned char. Without this option, they default to a signed char.
Allocate to an enum type only as many bytes as it needs for the declared range of possible values. Thank you very much for your reply. Posted by dl8dtl : Tue. Posts: 11 View posts. Level: Moderator. Location: using avr-gcc in Finchingfield, Essex, England. Posted by clawson : Sun. Posted by joeymorin : Sun. Experience comes from bad judgement. Pick two. Nov 12, - PM Reply to 6. Nov 12, - PM Reply to 7.
Ah Joey! Now lets see what documents it link
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