Yo Mathew! On Sun, 8 Jan 2017 20:04:25 -0500 Mathew Crane <[email protected]> wrote:
> Hit send too early. It was my understanding that PPS was the > canonical time source, and GPS was just a reference. Taken from here: > http://www.catb.org/gpsd/gpsd-time-service-howto.html#_performance_tuning We need to define our terms better. The PPS comes from the GPS! By GPS I was actually referring to the NMEA time from the GPS that is used to match the closest second to the PPS to form the SHM(0) which is a combinaaaaation of the NMEA and PPS from the GPS. > "The asterisk in this example indicates that ntpd has correctly > preferred .PPS. over .GPS., as it should. If for some reason it locks > on to GPS time as a preferred source, you can add an overlarge fudge > to the NMEA time to discourage it. Or add the suffix noselect so GPS > time is never used, just monitored" Yup, I wrote that. You can do that, or use noselect if you have other sources of coarse time. > My versions and configs: > > gpsd: 3.17~dev (revision release-3.16-535-ga5bbf14) > ntpd ntpsec-0.9.6+149 2017-01-07T12:44:49-0800 Very good. > /etc/ntp.conf: > > # GPS Serial data reference (NTP0) > *refclock shm unit 0 time1 0.120 refid GPS* You want that LAST in the file. On startup ntpd prefers reflocks at the top of the file, and you do not want to prefer SHM(0) it is your worst source. And make the time1 a lot bigger, or add noselect. 0.120 is way too small for the reasons noted above. > # GPS PPS reference (NTP1) > refclock shm unit 1 refid PPS prefer Should be at the top of the file so it gets tried first. For the RasPi you also want: minpoll 2 maxpoll 2 > server 10.3.123.1 minpoll 5 > pool us.pool.ntp.org iburst prefer I'm not a fan of the pool for fixed locations. Find some good public servers near you and hard code them. > # Drift file etc. > driftfile /var/lib/ntp/ntp.drift Good. RGDS GARY --------------------------------------------------------------------------- Gary E. Miller Rellim 109 NW Wilmington Ave., Suite E, Bend, OR 97703 [email protected] Tel:+1 541 382 8588 Veritas liberabit vos. -- Quid est veritas? "If you can’t measure it, you can’t improve it." - Lord Kelvin
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