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Re: [avr-gcc-list] saving __zero_reg__ in interrupt

From: Marek Michalkiewicz
Subject: Re: [avr-gcc-list] saving __zero_reg__ in interrupt
Date: Tue Jan 30 05:13:04 2001

> both gcc 2.97 and 2.95 save, clear and restore the __zero_reg__
> in interrupt routines. (-->6 Bytes for each interrupt).
> Saving/restoring seems redundant as this register 
> should hold (holds) zero anyway.

It is not - some code (generated by avr-gcc, or hand-optimized assembler)
uses this register as a second temporary register (it's OK as long as you
zero it after use).  Interrupt comes in at the right moment (when r1 is
nonzero) and you lose.

> Is there a way to switch off this behaviour?

Don't ;)


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