[ntp:questions] Atomized NMEA using second numbering from other server

Terje Mathisen "terje.mathisen at tmsw.no" at ntp.org
Sat Oct 15 12:58:43 UTC 2011


Miguel Gonçalves wrote:
> Hi Dave!
>
> 2011/10/14 Miguel Gonçalves<mail at miguelgoncalves.com>:
>> tock# /usr/local/bin/ntpq -p -c as
>>      remote           refid      st t when poll reach   delay   offset  jitter
>> ==============================================================================
>> oGPS_NMEA(0)     .GPS.            0 l    5   16  377    0.000   -0.004   0.004
>> *ntp-p1.obspm.fr .TS-3.           1 u   54   64  377   50.254   -1.269   7.885
>> +ptbtime1.ptb.de .DCFa.           1 u   59   64  377   69.087   -0.863  11.519
>> +ntp1.oma.be     .PPS.            1 u   64   64  377   60.841    1.052   8.067
>> +canon.inria.fr  .GPSi.           1 u   58   64  377   54.529   -2.730   9.511
>> -ntp1.nl.uu.net  .PPS.            1 u   54   64  377   58.920    3.072   1.294
>>
>> ind assid status  conf reach auth condition  last_event cnt
>> ===========================================================
>>   1 64946  974a   yes   yes  none  pps.peer    sys_peer  4
>>   2 64947  963a   yes   yes  none  sys.peer    sys_peer  3
>>   3 64948  9424   yes   yes  none candidate   reachable  2
>>   4 64949  9424   yes   yes  none candidate   reachable  2
>>   5 64950  9424   yes   yes  none candidate   reachable  2
>>   6 64951  9324   yes   yes  none   outlyer   reachable  2
>
> The NMEA clock is being selected as a PPS peer and it was (last_event)
> a sys_peer. At the moment an Internet server is the PPS peer.
>
> When fiddling with another machine with a GPS clock last night I found
> out this morning that the clock was being considered a false tick:
>
> tock# ntpq -p
>       remote           refid      st t when poll reach   delay   offset  jitter
> ==============================================================================
> xGPS_NMEA(0)     .GPS.            0 l    3   16  377    0.000   -0.003   0.001
>
> I decided to use NMEA for second numbering and the PPS driver for the
> PPS. I found out that the NMEA clock was showing a lot of jitter so
> NTP couldn't use NMEA for second numbering and was thus marking it as
> false ticker. So I added
>
> tos mindist 0.25
>
> to ntp.conf and it is now
>
> tock# ntpq -p
>       remote           refid      st t when poll reach   delay   offset  jitter
> ==============================================================================
> *GPS_NMEA(0)     .GPS.            0 l    9   16  377    0.000   -9.147   8.775
> oPPS(0)          .PPS.            0 l    8   16  377    0.000    0.001   0.002
>
> I did the same on the other machine (the one I reported earlier and
> that is a pool server) and I am getting the expected behaviour:
>
> tick# ntpq -p
>       remote           refid      st t when poll reach   delay   offset  jitter
> ==============================================================================
> oGPS_NMEA(0)     .GPS.            0 l    9   16  377    0.000    0.000   0.004
> +ntp-p1.obspm.fr .TS-3.           1 u    4   64  377   44.041    1.249   3.316
> +ptbtime1.ptb.de .DCFa.           1 u   11   64  377   67.837    0.566   3.670
> -ntp1.oma.be     .PPS.            1 u    9   64  377   53.601    4.567   5.302
> +canon.inria.fr  .GPSi.           1 u   11   64  377   44.790    1.415   1.406
> +ntp1.nl.uu.net  .PPS.            1 u   13   64  377   58.364    3.385 142.094
>
> By the way, why are servers that use GPSi or PPSa as the refid? I
> searched the archives and couldn't find an answer.

The refid is an arbitrary set of up to 4 ascii characters, each driver 
has a default name, but this can be easily overridden:

fudge x.x.x.x refid 'XYZ'

Terje
-- 
- <Terje.Mathisen at tmsw.no>
"almost all programming can be viewed as an exercise in caching"



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