AW: [avr-gcc-list] interrupt optimization

[Haase Bjoern (PT-BEU/EMT) *]

Hi,

I'd like to suggest the following:

1.) use a seperate asm file for the part of your ISR that is excecuted
frequently.
2.) define an additional function that will safe all of the used
registers by

  void __attribute__ ((signal))
  to_be_excecuted_seldomly (void);

  void
  to_be_excecuted_seldomly (void)
  {
    sampling = 0x7F;
    callInlineFunction();
  }

3.) call "to_be_excecuted_seldomly" in your asm file.

You will be having a close to ideal situation. Namely the only
sub-optimal issue would be that you will be having one unnecessary call
and one unnecessary return instruction.

IMO, using the __naked__ attribute is very error-prone. I'd not
recommend that.

Bjoern.

> Hi,
>
> I have an interrupt which is called a lot of times but only really do
> something very rarely:
>
> ISR(...)
> {
>      if (sampling-- == 0)
>      {
>          sampling = 0x7F;
>          callInlineFunction();
>      }
> }
>
> The problem is that I end up with a lot of push/pop that just eat up
all
> my CPU cycles most of the time. Using an inline function helped
removing
> all registers that were not used by the function at all (don't know
why
> the optimization doesn't do this already) but I still get a lot of
push
> not necessary by the "if" and that I would like to move before the
> function call inside the "if".