Lpc2000

At 11:45 PM 12/16/04 +0000, you wrote:


>--- In lpc2000@yahoogroups.com, "itsjustimpossible" <simonjh@b...>
>wrote:
> >
> > I don't know if anyone else has seen this but its driving me nuts.
> > I have timer1 on a 40uS interval triggering an FIQ. (All the FIQ
> > does is toggle an IO pin and exit.) No other interrupts are active.
> >
> > In practice the leading edge of the pulse produced on the IO pin
> > jitters by around 230nS to 280nS around the 40uS interval.
> > I need this pulse to be as accurate as possible, a few nS jitter at
> > most. If anyone can shed some light on this I would be very
>grateful.
>
>You can't achieve such low jitter using FIQ (unless your main program
>consists entirely of 1-clock instructions).  One clock is 16.6 ns.
>
>As another poster suggested, you can use the PWM or match outputs to
>get a jitter of 0 clocks.  Using a match output is probably the
>easiest - if you want to use the PWM, be sure to read all the fine
>print about when new MRx values take effect.

I've used this technique for 1-wire support although I wasn't that 
concerned  about that level of jitter.  You can take a look at the code it 
you like (follow the one-wire link from 
http://www.aeolusdevelopment.com/Articles/download.html ).  IT's in the 
adaptation code and is quite short and simple.

Robert

" 'Freedom' has no meaning of itself.  There are always restrictions,
be they legal, genetic, or physical.  If you don't believe me, try to
chew a radio signal. "

                         Kelvin Throop, III