Re: [avr-gcc-list] Avoid register saving

[Artur Lipowski]

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Bernhard Huber wrote:

> How can I tell avr-gcc (gcc version 3.0 20010605 (prerelease)) that a
> bunch of registers (r2 to r16) must not be saved when entering a
> interrupt service routine.
...
You should trust compiler. If it try save these regs it means that they 
probably can be corrupted if not saved.

At least version 3.3.3 of the GCC (current stable) can reduce number of 
saved registers in case when no other functions are called from given 
ISR. There is no way to tell compiler that given function will use only 
subset of regs and compiler must assume that whole calling convention 
apply and it means that "call-used registers: r18-r27, r30-r31" must be 
preserved by caller.

If saving a couple of regs does matter for your ISR that means that 
response time is (probably) very important and it is good time to start 
writing ISR in assembler.

Regards
--
Artur Lipowski

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