On 2017-01-24 13:19, Lloyd Dizon wrote: > Hi all. > I'm using this GPS module with a MTK3339 chipset. Bought from here: > https://www.adafruit.com/product/790 > And I'm using ntpd with have PPS support compiled-in.
Should have bought the HAT: https://www.adafruit.com/products/2324 which has instructions: https://learn.adafruit.com/adafruit-ultimate-gps-hat-for-raspberry-pi which you should follow anyway, as it uses the same chip, delta any differences between your chip connection and the HAT GPIO 14/TXD, 15/RXD, 4/PPS, your RPi model, Debian release, and Linux kernel. See also: http://www.satsignal.eu/ntp/Raspberry-Pi-NTP.html http://www.satsignal.eu/ntp/Raspberry_Time%20-%20Broadband%20Ham%20Net.pdf https://forums.adafruit.com/viewtopic.php?f=50&t=70133&start=60#p359668 and elsewhere from searching "RPi NTP stratum 1". > Juergen, thanks for pointing out the documentation. I've understood > more about NMEA receivers now. > I've tried Brian's and Juergen's server and fudge configuration, > using time2 to align with the NMEA data-stream and now getting better > results. > I don't have a scope, so how do you suggest I determine the correct > values to use for time2? If you follow the above instructions for setting up PPS, and ensure that the chip only generates $GPRMC messages, you won't need to, as the PPS timestamp replaces the NMEA timestamp if the message is received within about .4s of time2 fudge of PPS, and the tally code will change to "o", indicating it is synced to kernel PPS. > server 127.127.20.0 mode 17 prefer minpoll 4 maxpoll 4 > fudge 127.127.20.0 flag1 1 flag3 1 time2 0.500 # pps kernel msg offset .5s > remote refid st t when poll reach delay offset jitter > ============================================================================== > *GPS_NMEA(0) .GPS. 0 l 15 16 377 0.000 -49.176 25.007 > +time.sunrise.ne 195.141.230.78 2 u 22 64 377 8.357 114.864 17.534 > +192.33.214.47 129.194.21.195 2 u 23 64 377 13.382 115.777 18.286 > +ntp0.as34288.ne 85.158.25.74 2 u 32 64 377 6.914 113.929 17.013 > +eudyptula.init7 217.147.223.78 3 u 26 64 377 9.683 115.067 17.673 With a bit more tweaking, you'll do better by three or four orders of magnitude. My logarithmic human rating scale for servers by offset MSD goes (units ms as from ntpq; ntpd resets by stepping time if offset > 128ms): 128 100 10 1 .1 .01 .001 ms unsynced available poor fair good great best time-nut [time-nuts are a group interested in time measurement from us down to fs]. -- Take care. Thanks, Brian Inglis, Calgary, Alberta, Canada _______________________________________________ questions mailing list questions@lists.ntp.org http://lists.ntp.org/listinfo/questions
