[ntp:questions] Pi 4 and Ultimate hat weirdness
jimp at gonzo.specsol.net
Mon Jan 25 02:06:12 UTC 2021
I got a Pi 4 and Adafruit ultimate gps hat to play with and decided to see
how good it was as a timekeeper.
First weird thing; xgps does not show a skyview but both xgps and cgps
show at least 10 satellites in use.
I don't care too much about this one as AFAIK xgps is broken on Pi.
Second weird thing; I started the 20 driver in mode 0. ntpq showed lots
of syntax errors on the $GPGGA message.
I changed the mode to 29 to deselect $GPGGA; no errors from ntpq. So maybe
it was a satellite thing, but whatever it was, no more errors.
Third and biggest weird thing; I had fudge 127.127.20.0 flag1 1 time1 0.001
in ntp.conf. After everything settled down, the clock was showing an
offset of -1043. OK, So I changed time1 to 1.044 even though it looked
too big. ntp wouldn't lie to me...
After everything settled down this time the offset was showing an average
of -738. For grins and giggles I set time1 to 0.738 and now the average
offset is -584.
It seems there is no way to get time1 to correct the offset.
Also the jitter times look high. At this moment ntpq shows:
xGPS_NMEA(0) .GPS. 0 l 6 16 367 0.000 -849.36 25.536
*SHM(0) .SHM. 0 l 4 16 377 0.000 -106.55 72.688
xPPS(0) .PPS. 0 l 4 16 377 0.000 18.702 18.812
For comparison, a GlobalSat BU-353-S4 USB GPS on a PC ubuntu system shows:
*SHM(0) .SHM. 0 l 3 16 377 0.000 -0.728 1.356
Anyone got any suggestions other than to trash the Ulitmate hat and get
another GlobalSat USB?
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