[ntp:questions] Reasons of NTP not to use GPS source
Rob
nomail at example.com
Mon Sep 16 07:31:05 UTC 2013
Igor Pavlov <pavlov.ig at gmail.com> wrote:
> Hi!
>
> I am using GPS-receiver based on Geos-1m chip (
> http://www.geostar-navigation.com/en/navigation_05.html)
>
> I connected it to serial port and configured NTP.
> It becomes unused by NTP: when do ntpq -p reuest ti puts "x" near
> "GPS_NMEA(1)" record.
>
> What reasons can be for this?
A GPS with NMEA protocol is usually a very lousy time source.
You can see this in your output: the time offset relative to
the internet sources is very large:
> remote refid st t when poll reach delay offset
> jitter
> ==============================================================================
> xGPS_NMEA(1) .GPS. 0 l 14 16 377 0.000 -303.07
> 4.292
> *stratum1.net .PPS. 1 u 62 64 377 62.800 -68.052
> 43.693
> +dl120g7.naviteh 194.190.168.1 2 u 58 64 377 30.151 -100.04
> 52.432
> +89.221.207.113 192.36.133.25 2 u - 64 377 10.006 -105.88
> 64.279
That is why ntpd declares the time as invalid and attempts to use the
3 other sources instead.
When you want to fix this, you should use PPS with the receiver,
when possible.
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