Yo Martin! On Fri, 3 Nov 2017 14:27:52 +0100 Martin Burnicki <martin.burni...@meinberg.de> wrote:
> >> Anyway, gpsd seems to accept the raw GPS time as UTC time, feeds > >> it to ntpd, and ntpd sets the Linux system time off by a number of > >> seconds. > > > > Which is why gpsd should rarely be the only input into your ntp > > daemon. > > Hm. According to my own observations, if you get most accurate time > from your GPS receiver operating normally, as single time source, and > then add some upstream NTP sources beside the GPS refclock the > resulting accuracy of the system time becomes worse. That can happen, but there are mitigation strategies. First I use the prefer keyword on my PPS time. I'm not seeing that here: remote refid st t when poll reach delay offset jitter *SHM(1) .PPS. 0 l 1 2 377 0ns 722ns 968ns +spidey.rellim.c .PPS. 1 u 25 32 377 254.35µs 57.594µs 63.995µs -pi.rellim.com .PPS. 1 u 22 32 377 416.27µs -654.8µs 154.28µs pi2.rellim.com .PPS. 1 u 9d 32 0 581.89µs 28.000µs 0ns pi4.rellim.com .STEP. 16 u - 32 0 0ns 0ns 954ns -catbert.rellim. .PPS. 1 u 30 32 377 376.48µs 455.34µs 49.887µs -kong.rellim.com 204.17.205.8 2 u 59 32 266 347.37µs 196.00µs 30.736µs -backup.rellim.c 204.17.205.8 2 u 22 32 377 412.37µs 158.38µs 48.486µs +SHM(0) .GPS. 0 l 13 16 377 0ns 507.16µs 672.13µs Note the 722 ns offset and 960ns jitter on mmy PPS. > So it's not generally better to use other time sources beside a GPS > receiver. Until your GPS goes wacky... > You can simply try this if you look at the smoothness of the loopstats > generated with a GPS receiver only vs. the loopstats generated with a > GPS receiver plus some NTP servers on the network. I've got a dozen chimers up now with PPS, not seeing it. > ntpd doesn't anyway accept the time from a source that indicates that > its time is not synchronized. So it wouldn't accept the time from the > GPS receiver (directly or via gpsd/SHM) if a "not synchronized" status > was available from the receiver and passed to ntpd. Which is NOT what the OP was complaining about. His GPS was saying synced, but was off by the UTC/GPS offset which had not been downloaded yet. RGDS GARY --------------------------------------------------------------------------- Gary E. Miller Rellim 109 NW Wilmington Ave., Suite E, Bend, OR 97703 g...@rellim.com 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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