Re: Rising/falling edge detection

On Thu, Sep 07, 2023 at 05:15:10PM +0700, James Clark wrote:
> Note that it reduces the maximum allowed error of the time source which
> > completes the PPS
> > samples. If the duty cycle is configurable, 50% should be preferred in
> > order to maximise the allowed error.
> 
> 
> I don't understand this. I would have thought 50% was the worst possible
> configuration because it prevents the use of the time between pulses being
> used to identify which is the rising edge.

The explanation is that the code doesn't care about the interval
between edges. In only checks how well each pulse aligns with the
last sample from the locked refclock. An advantage of this approach is
that it works even when only one edge is reported, so existing
configuration won't break if the hw/driver suddently starts filtering
the unexpected edges, and I think it's also more resilienty to
spurious pulses.

Maybe an alternative filtering could be implemented for the extreme
widths.

-- 
Miroslav Lichvar


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