RE: [avr-gcc-list] Avoid register saving

[Filipe Campos]

Hi.
In some application the save register can be good.
But if You write a little RTOS Kernell, the kernell shall do this, not the
compiler. It´s worst if You have a little RAM to use.

But You give a good idea, How the ISR can be writen in ASM and than compiled
by the AVR-GCC ?

Bye.
Filipe Campos



> -----Original Message-----
> From: Artur Lipowski [SMTP:address@hidden
> Sent: Thursday, April 01, 2004 7:30 AM
> To:   address@hidden
> Subject:      Re: [avr-gcc-list] Avoid register saving
> 
> Bernhard Huber wrote:
> 
> > How can I tell avr-gcc (gcc version 3.0 20010605 (prerelease)) that a
> > bunch of registers (r2 to r16) must not be saved when entering a
> > interrupt service routine.
> ...
> You should trust compiler. If it try save these regs it means that they 
> probably can be corrupted if not saved.
> 
> At least version 3.3.3 of the GCC (current stable) can reduce number of 
> saved registers in case when no other functions are called from given 
> ISR. There is no way to tell compiler that given function will use only 
> subset of regs and compiler must assume that whole calling convention 
> apply and it means that "call-used registers: r18-r27, r30-r31" must be 
> preserved by caller.
> 
> If saving a couple of regs does matter for your ISR that means that 
> response time is (probably) very important and it is good time to start 
> writing ISR in assembler.
> 
> Regards
> -- 
> Artur Lipowski
> 
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