[ntp:questions] Pi 4 and Ultimate hat weirdness
jimp at gonzo.specsol.net
Tue Jan 26 15:45:45 UTC 2021
On Tue, Jan 26, 2021 at 11:06:41AM +0000, David Taylor wrote:
> 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
The ultimate hat is a GPS board that has a connector that sits on
top of the Raspberry Pi 4 GPIO connector. The "cable length" is
about 1/4 of an inch.
I'm don't know what you mean by "over 12 hours" ntpq report?".
> I would suggest a much higher baud rate, and disabling sentences other
> than $GPRMC. You don't then need any lower bits set.
If you mean disabling sentences from the GPS board, I can find no
documentation on how to control anything on the GPS.
> 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.
Well, they seem to be co-existing, but as I said before, I started with
just the type 20 driver with NO gpsd and there does not seem to be any
difference either way. All the message types show up in peerstats.
Running both the type 20 and type 28 drivers at the same time was an
act of desperation.
sudo cat /dev/ttyAMA0 with gpsd running shows data.
> 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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