Re: push r1, pop r0

Hi Matthijs,

I believe you are right, that makes sense.

(I should have realized that, but it was a quite a while ago I read/wrote
AVR asm... well you learn something new every day;)

Thank you.

It was compiled with  -O1.
Compiling with -Os does not seem to make a difference.

Best regards,
Szikra Istvan

On Tue, Nov 7, 2017 at 9:48 PM, Matthijs Kooijman <[email protected]> wrote:

> Hi Szikra,
>
> I believe these pushes and pops are just meant to allocate 2 bytes on
> the stack.
>
> >  222: cd b7        in r28, 0x3d ; 61
> >  224: de b7        in r29, 0x3e ; 62
> This loads Y with SP, so the location of the 2 pushed bytes
>
> >  226: 2e b7        in r18, 0x3e ; 62
> >  228: 8d b7        in r24, 0x3d ; 61
> >  22a: 90 e0        ldi r25, 0x00 ; 0
> >  22c: 92 2b        or r25, r18
> This is the load SP from your code variable
>
> >  22e: 89 83        std Y+1, r24 ; 0x01
> >  230: 9a 83        std Y+2, r25 ; 0x02
> This stores SP to your sp variable on the stack
>
> >  232: 89 81        ldd r24, Y+1 ; 0x01
> >  234: 9a 81        ldd r25, Y+2 ; 0x02
> This loads your sp variable into the return value
>
> I wonder why this even forces the value onto the stack, since that's
> really not needed at all. Perhaps the "volatile" on your "sp" variable
> causes this, or perhaps you're compiling without optimization?
>
> Gr.
>
> Matthijs
>

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