[ntp:questions] 1000s offset between GPS module and NTP servers

Lloyd Dizon thecarrionkind at gmail.com
Mon Jan 23 14:29:38 UTC 2017


On Mon, Jan 23, 2017 at 1:03 PM, Harlan Stenn <stenn at ntp.org> wrote:

> Lloyd Dizon writes:
> > Hi.
> > I've installed a GPS module on a Raspberry Pi and I'm getting 1000ms
> > offsets between the GPS readings and network NTPs.
> >
> > lloyd at jadzia:~ $ ntpq -p
> >      remote           refid      st t when poll reach   delay   offset
> > jitter
> > ============================================================
> =================
> > =
> >  LOCAL(0)        .LOCL.          10 l  447   64  100    0.000    0.000
> > 0.001
>
> Why are you using the LOCAL refclock?
>

I shouldn't. I removed it now.


> xGPS_NMEA(0)     .GPS.            0 l    -   16  377    0.000    6.229
> > 142.320
>
> Is your NMEA source identifying the wrong second?
>
> > *ntp0.as34288.ne 85.158.25.74     2 u   24   64    3    9.810  1004.83
> > 1.687
> > +246.11.25.212.f 162.23.41.10     2 u   19   64    3   10.636  1004.22
> > 1.376
> > +ch-ntp01.10g.ch 81.94.123.17     3 u   21   64    3   10.493  1001.79
> > 3.299
> > -khyber.madduck. 192.33.96.102    2 u   20   64    3    8.703  1001.72
> > 4.474
>
> Your NMEA source is sending ntpd samples every 16 seconds.  It's filling
> the sample buffer, and the the other sources (are you using iburst on
> these?  You should be...) are taking a while to provide enough samples
> to detect that your NMEA source is "off" by a second.
>

I changed the min and maxpoll to 6 to be consistent with the network
servers.
I'm still getting a 1000ms offset though.


> Anybody has a clue what is going on?
>
> I think your NMEA signal is identifying the wrong second.
>

So my NMEA device is broken then. Is there a way to compensate manually if
the device is systematically adding (or subtracting) 1000ms. Is is correct
to compensate manually.
I looked at the time1 argument to fudge but I only had 300ms removed from
the offset.

Before using "time1 1":

Every 1.0s: ntpq
-pn
Mon Jan 23 15:27:46 2017

     remote           refid      st t when poll reach   delay   offset
jitter
==============================================================================
x127.127.20.0    .GPS.            0 l   48   64   17    0.000   10.095
6.428
*178.209.53.202  166.171.80.13    3 u   31   64   37   11.298  1015.56
9.837
+81.94.123.16    85.158.25.74     2 u   30   64   37    9.788  1013.30
9.577
+212.51.144.44   .PPS.            1 u   28   64   37    9.864  1013.35
9.723
+82.197.188.130  195.186.1.100    3 u   32   64   37    9.832  1013.75
9.664


After using time1 1:
Every 1.0s: ntpq
-pn
Mon Jan 23 15:28:27 2017

     remote           refid      st t when poll reach   delay   offset
jitter
==============================================================================
 127.127.20.0    .GPS.            0 l   16   64    0    0.000    0.000
0.001
*192.33.96.102   .PPS.            1 u    4   64    1   13.617  721.727
0.112
+5.148.175.134   131.188.3.222    2 u    4   64    1    9.377  720.615
0.436
+81.94.123.17    85.158.25.74     2 u    3   64    1    9.659  720.234
0.552
-46.22.26.12     162.23.41.56     2 u    2   64    1   15.923  722.333
0.171


More information about the questions mailing list