On Mon, 31 Jan 2005 23:14:01 +0100, Wouter van Ooijen <wouter@voti.nl> wrote:
> > No, I meant what I wrote.
> >
> > If the PID calculation was done in the background loop, there would be
> > a variable number of instructions between the setting of the DO_IT_NOW
> > flag and the start of the PID update.
> 
> I don't grok this. Which instructions would be inbetween? There are
> techniques to re-start a loop at fixed intervals, with zero jitter.

while (TRUE)
   {
    if (DO_IT_NOW)
      pid_calculations();
   code_a();
   code_b();
   code_c();
   code_d();
   }

since the DO_IT_NOW flag could be set at any time by
the interrupt (or the TMR1IF flag), the PID code could run
immediately, or after all the other routines, or...

Bill
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