Rockbox mail archive
Subject: Re: busy loop
2010/6/15 Edgar Toernig <froese_at_gmx.de>
> pouly amaury wrote:
> > for (x = (unsigned)(FREQ>>22); x; x--)
> > asm volatile("":::"memory");
> > Clobbering memory is likely to prevent gcc from optimizing the loop away.
> But it will break with loop-unrolling (i.e. -O3). x times nothing
> is nothing ;-) You *have* to use a nop-instruction.
> And the cast is bogus - only silences the compiler without fixing
> the problem.
> Ciao, ET.
Tell me if I'm wrong but the compiler can hardly unroll a loop with a
non-constant size. As FREQ is a define for cpu_frequency which has external
linkage. The cast was there before, I didn't modify it.
But anyway, rewriting it in assembly is cleary the safe way :)
Received on 2010-06-15
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