Re: [avr-gcc-list] Writing ASM libraries for avr-gcc

[E. Weddington]

On 10 Sep 2002 at 11:44, Larry Barello wrote:

> Sometime ago there was a file "ctoasm.inc" which detailed the
> parameter passing sequence and the registers one could clobber in
> their assembly routine.  I cannot find it anywhere (well I found an
> old pre 2.97 one) and wanted to verify that R30:31 are clobberable
> registers in the subroutine.
> 
> Currently this is my understanding:
> 
> R24:25 - P1
> R22:23 - P2 Byte, Word, Long
> R20:21 - P3 etc
> R18:19 - P4 etc
> 
> All the above registers along with  R0 and R1 (with restoring to 0)
> R26, 27, 30 and 31 are freely clobberable.  R1-R17 and (maybe) R27:28
> need to be preserved.
> 
> Thanks!
> 

This should help:
http://savannah.gnu.org/cgi-bin/viewcvs/avr-libc/avr-
libc/doc/register-usage.txt

It's from the avrlibc CVS.

Eric
avr-gcc-list at http://avr1.org