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

Mark C. Stephens marks at non-stop.com.au
Mon Sep 16 10:44:59 UTC 2013


Igor, please post the contents of 
1. /etc/ntp.conf
2. /etc/issue



-----Original Message-----
From: questions-bounces+marks=non-stop.com.au at lists.ntp.org [mailto:questions-bounces+marks=non-stop.com.au at lists.ntp.org] On Behalf Of Igor Pavlov
Sent: Monday, 16 September 2013 5:56 PM
To: Rob
Cc: questions
Subject: Re: [ntp:questions] Reasons of NTP not to use GPS source

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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>> questions at lists.ntp.org
>> http://lists.ntp.org/listinfo/questions
>>
>
>
>
> --
> Игорь Павлов
>



--
Игорь Павлов
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