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Re: [avr-gcc-list] Compiler error creating ISR prologue?

From: Johannes Bauer
Subject: Re: [avr-gcc-list] Compiler error creating ISR prologue?
Date: Thu, 12 Aug 2010 19:45:02 +0200
User-agent: Mozilla/5.0 (X11; U; Linux x86_64; en-US; rv: Gecko/20100713 Thunderbird/3.0.6


On 12.08.2010 19:13, István wrote:

if I am not deluded by my memory, r1 permanently holds 0. Actually clr
r1 is redundant.

Not in an ISR. http://www.nongnu.org/avr-libc/user-manual/FAQ.html says under "What registers are used by the C compiler?"

r1 - assumed to be always zero in any C code, may be used to remember something for a while within one piece of assembler code, but must then be cleared after use (clr r1). This includes any use of the [f]mul[s[u]] instructions, which return their result in r1:r0. Interrupt handlers save and clear r1 on entry, and restore r1 on exit (in case it was non-zero).


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