[ntp:questions] Reasons of NTP not to use GPS source

Igor Pavlov pavlov.ig at gmail.com
Mon Sep 16 07:51:08 UTC 2013


I already tryed to use PPS from my GPS receiver connected to DCD-pin of the
same RS-232.
But I had PPS also marked as "x", that is why I tryed first to fix problems
with NMEA-based GPS data separate from PPS.
I will try to connect PPS again.

But I can't understand why it is marked "x"? What is wrong with it?


2013/9/16 Rob <nomail at example.com>

> 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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>



-- 
Игорь Павлов


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