>  I'd like to specify that, and not have to worry about how many 
> instructions I spent doing those other things. And I want to be able 
> to specify that in loops too.

We have something trivial like:

#define TIMER_START(timer, ms) (timer = msclock() + ms)
#define TIMER_RUNNING(timer) (msclock() < timer)

where msclock() returns some automatically-incremented counter
(interrupt driven here, but it could be a cycle counter if you
have one, or a bare timer register.)

Then you can do

	TIMER_START(my_timer, 10);  /* Wait for at least 10 ms */
	do_some_work();
     do_some_more_work();
	   :
     work_almost_done();
     while (TIMER_RUNNING(my_timer))
	    ;		/* Wait for rest of 10mS to pass */

Beware counter wraparound and sign changes...

BillW

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