Xref: news2.mv.net comp.os.msdos.djgpp:5038
From: Shawn Hargreaves <slh100 AT york DOT ac DOT uk>
Newsgroups: comp.os.msdos.djgpp
Subject: Re: How to tell djgpp NOT to optimate a line of code
Date: Thu, 13 Jun 1996 17:44:34 +0100
Organization: The University of York, UK
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On Thu, 13 Jun 1996, Lennart Steinke wrote:

> I wrote a ISR which hook into the timer interrupt and updates
> a global variable.
> 
> b=g;
> while (b==g);
> 
> this loop is always optimazed to 
> while(1);
> 
> ist there a possibilty to tell gcc not to touch the code
> (similar to the __volatile__ keyword)?

Yes, the volatile keyword :-) That's what it means...

The global variable that you alter in your IRQ handler should be declared 
as 'volatile int', to tell the optimiser that it may be changed by things 
outside the current block of code (eg. your interrupt).


/*
 *	Shawn Hargreaves.        Why is 'phonetic' spelt with a ph?
 *	Check out Allegro and FED on http://www.york.ac.uk/~slh100/
 */