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Re: [avr-gcc-list] interrupt optimization

From: Joerg Wunsch
Subject: Re: [avr-gcc-list] interrupt optimization
Date: Fri, 3 Feb 2006 07:18:04 +0100 (MET)

Lars Noschinski <address@hidden> wrote:

> If the function call is the last thing you need to do, you can also
> replace the call by a jmp instruction (of course, you may not push
> something to the stack).

You'd need to enable interrupts before, otherwise you'll end up stuck
with interrupts disabled, as there won't be a final RETI.

However, unless you're very sure about what that called function is
doing, this is not going to be a bright idea.  You'd basically get
away with the same things the compiler is doing, namely saving all
call-clobbered registers as the called function is free to use them.
Also, keep in mind that ISRs need to also save __tmp_reg__ and
__zero_reg__, and need to make __zero_reg__ a 0 again (alas), so these
would need to be restored upon return (normal functions won't handle

Compared to that, the overhead of an additional call vs. jump is

cheers, J"org               .-.-.   --... ...--   -.. .  DL8DTL

http://www.sax.de/~joerg/                        NIC: JW11-RIPE
Never trust an operating system you don't have sources for. ;-)

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