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Re: [avr-gcc-list] Writing ASM libraries for avr-gcc
From: |
E. Weddington |
Subject: |
Re: [avr-gcc-list] Writing ASM libraries for avr-gcc |
Date: |
Tue, 10 Sep 2002 14:27:35 -0600 |
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