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Re: [avr-gcc-list] optimizer removes volatile pin access code. why?

From: Joerg Wunsch
Subject: Re: [avr-gcc-list] optimizer removes volatile pin access code. why?
Date: Tue, 27 Oct 2009 20:17:46 +0100 (MET)

Joerg Desch <address@hidden> wrote:

> With -Os enables, the setup of the port pin is removed! Without
> optimization the pin toggles as expected.

How did you verify it?

I don't believe the compiler removed the code.  (If you really think
it does, please supply a compilable code example.)  However, the
optimized code will just toggle the pin for a single CPU cycles only,
while the pin will stay a little longer at high in the non-optimized
example.  So if your oscilloscope is too slow, you might not notice
the pin actually becoming high for one clock period.

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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