RE: [avr-gcc-list] loop deleted using optimization

[Dave Hansen]

From: alee <address@hidden>
> Why does avr-gcc delete my empty "for" loops if I compile with optimization 
> on?
> I am able to preserve the loop if I add a NOP in the loop but that will eat 
> up one clock cycle.  Is there a way to preserve the empty loops without 
> adding any NOP clock cycles?  Is this a bug?  Below is

It's not a bug, it's a feature.  GCC realized the loops weren't doing 
anything, and so optimized them out.  To keep them, you have to give GCC a 
reason to keep them.  As you found, adding a nop to the loop body (probably 
with asm volatile) gave gcc the reason.

Rather than inserting a nop, you could simply make the loop variable 
volatile.  The volatile keyword tells the compler that it should do exactly 
what you say to the variable, no more, no less, no "as-if."

Or if you really just want a short delay, look at the functions in delay.h.

HTH,
  -=Dave

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