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

Miguel Gonçalves mail at miguelgoncalves.com
Sat Oct 15 10:58:07 UTC 2011


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.

Cheers,
Miguel


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