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. time1 offset 0.001 -1043 1.044 -738 0.738 -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? -- Jim Pennino _______________________________________________ questions mailing list questions@lists.ntp.org http://lists.ntp.org/listinfo/questions
