[time-nuts] PPS offset between GPS receivers
azelio.boriani at screen.it
Sat Dec 8 12:55:09 UTC 2012
Yes, this is a good test: to evaluate how your preferred uP can perform as
a time interval counter, you can hook two GPDSOs' PPS to it and see the
result. The best would be to have at hand also a real TIC (HP53132A,
PM6681, SR620 or similar) and compare.
On Sat, Dec 8, 2012 at 4:28 AM, Bob Camp <lists at rtty.us> wrote:
> A lot depends on exactly what the interrupt structure is. It may also
> depend on the phase of the cpu clock relative to the pps signal. What's
> reasonably sure is that there is indeed some offset between the two where
> the answer is indeed "ft's" random. Another thing to check - how wide is
> the random region?
> On Dec 7, 2012, at 9:19 PM, Chris Albertson <albertson.chris at gmail.com>
> > One more test to try. Connect one PPS signal to both GPIO ports and see
> > how close to zero offset you get. It would likely be random which gets
> > read first.
> > On Wed, Dec 5, 2012 at 5:37 AM, Gabs Ricalde <gsricalde at gmail.com>
> >> Hi everyone,
> >> As Tom suggested, I redid the test with less than 1 ft. of wire from the
> >> PPS output to the GPIO without any logic gates or line receivers. Same
> >> result,
> >> the SKG25A1 was 2 microseconds ahead of the 58534A. Without any other
> >> of
> >> testing, I would probably trust the output of the timing receiver more
> >> than the SkyNav module. Anyway the SkyNav board is an inexpensive unit
> >> I wouldn't mind setting an offset in ntpd.
> >> I don't have a scope yet, and a low jitter PPS GPIO is the closest
> thing I
> >> have
> >> to a TIC.
> >> _______________________________________________
> >> time-nuts mailing list -- time-nuts at febo.com
> >> To unsubscribe, go to
> >> https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
> >> and follow the instructions there.
> > --
> > Chris Albertson
> > Redondo Beach, California
> > _______________________________________________
> > time-nuts mailing list -- time-nuts at febo.com
> > To unsubscribe, go to
> > and follow the instructions there.
> time-nuts mailing list -- time-nuts at febo.com
> To unsubscribe, go to
> and follow the instructions there.
More information about the time-nuts