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Re: [avr-gcc-list] FW: optimalisation level setting from within C-source

From: Joerg Wunsch
Subject: Re: [avr-gcc-list] FW: optimalisation level setting from within C-source code....
Date: Tue, 16 Oct 2007 20:46:36 +0200 (MET DST)

"=?iso-8859-2?Q?Ing.Ji=F8=ED_Petr=E1k_-_PERYS?=" <address@hidden> wrote:

> first of all - I am first time writing to avr-gcc list members, and
> - I am only true hobbist of AVR programming..

Please subscribe to the list, you might miss some answers otherwise,
and I had to manually approve your posting.

> Is it possible to set the optimalisation level for some functions
> (or part of source-code) to different level than optimalisation used
> for this project as default?

The only option would be at the file level, i.e. you compile one source
file with -O0, other files with -Os.

However, I would not really recommend you that.  Instead, write your
code in an optimization-independent manner, as much as possible.  For
exact timing delays, please have a look at the functions in
<avr/delay_basic.h> and their convenience wrappers in <avr/delay.h>.
Note that the latter use floating-point calculations that are meant to
be optimized away at compile time, so they are required to be compiled
with optimization enabled.  The functions from <avr/delay_basic.h> are
truely optimzation independent but you have to manually pre-calculate
the cycle counts then.

Mnoho uspechov!
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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