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

Igor Pavlov pavlov.ig at gmail.com
Mon Sep 16 07:55:41 UTC 2013


Sorry, didn't see the first part of your answer.
I thought that offset - it's offset of current system time from NMEA-based
info.
But if system time would be set to this NMEA-based time, than offset would
not be so great. Isn't it?
But NTP prefer to sync to other sources - Why?


2013/9/16 Igor Pavlov <pavlov.ig at gmail.com>

> 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
>



-- 
Игорь Павлов


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