[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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