[ntp:questions] Pi 4 and Ultimate hat weirdness
davidtaylor at writeme.com
Tue Jan 26 11:06:41 UTC 2021
On 25/01/2021 16:33, Jim Pennino wrote:
> But the PPS has a lot of jitter. Note the xPPS(0) in the ntpq line.
> The default for NTP is 4800 baud, but I am running at 9600 and there is
> no loss of data.
> It doesn't make any difference if I run the 20 driver in mode 1 (lower
> bits) or 13, it still has the uncorrectable offset problem.
> Right now, having been running for a little over 12 hours, ntpq shows:
> x127.127.20.0 .GPS. 0 l 14 16 335 0.000 -761.21 307.138
> *127.127.28.0 .SHM. 0 l 12 16 377 0.000 -30.575 35.029
> o127.127.22.0 .PPS. 0 l 3 16 377 0.000 -0.378 0.034
> I'm going to let it run for several days without disturbing anything.
> I doubt it will keep the 28 clock selected with that high jitter.
If the PPS has a lot of jitter I would try to check it with an
oscilloscope. Possibly there is a poor connection, or if you are using
a very long cable (unlikely) there could be capacitive coupling between
signals. How did you correct the problem for your "over 12 hours" ntpq
I would suggest a much higher baud rate, and disabling sentences other
than $GPRMC. You don't then need any lower bits set.
Are you sure that the type 20 and type 28 driver can co-exist? I note
that minicom can't access ttyAMA0 when gpsd is using it.
From data I'm recording from another GPS I see offsets between -100 and
+100 milliseconds from a nominal, with an older Skylab SKG16B device
running at 9600 baud.
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Email: david-taylor at blueyonder.co.uk
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