[ntp:questions] 1s offset

folkert folkert at vanheusden.com
Wed Mar 6 19:18:13 UTC 2013


[ garmin 18x lvc & offsets ]
...
> >Now when I run either 4.2.6p5 or dev-4.2.7p359, I always get an offset
> >of ~1s.
...
> >If I use 4.2.5p158 instead, the synchronization is perfect, on both
> >systems.

> Agreed that it's unlikely to be a firmware issue, but there is an
> interesting graph here:
>   http://www.satsignal.eu/ntp/Garmin-GSP18x-LVC-firmware-issue.htm
> specifically:
>   http://www.satsignal.eu/ntp/Garmin-18x-3.7.png
> which shows that the end of the NMEA sentence may be well over 0.5 s
> after the  PPS, and hence into the next second.  Could it be that:

True.

> (a) 4.2.5p158 looks for the start of the data, not the end

I should do a bisect. No SVN/GIT repository though?

> and:
> (b) you haven't specified the appropriate time offset value (fudge
> field) for the serial data for the other two versions of NTP?

I looked at my changes of yesterday and I saw that I tried, then "time1
1.0" which should be "time2 1.0".
And after 7 minutes it is:

     remote           refid      st t when poll reach   delay   offset  jitter
==============================================================================
o127.127.20.0    .GPS.            0 l    5   16  377    0.000   -0.060   0.006
-194.109.22.18   193.67.79.202    2 u   30   64  177   19.359   -1.282   7.608
-194.109.20.18   193.67.79.202    2 u   30   64  177   19.332   -3.155   8.272
+193.67.79.202   .PPS.            1 u   28   64  177   21.772    0.081   1.864
+192.87.106.2    194.171.167.130  2 u   31   64  177   19.754    0.205   3.468
+134.221.205.12  .PPS.            1 u   27   64  177   21.460   -0.398   5.835
+192.168.64.100  .GPS.            1 u   46   64  176    0.113   -0.025   0.273
+192.168.62.129  192.168.64.100   2 u   20   64  177    0.713    0.110   0.534
 224.0.1.1       .MCST.          16 u    -   64    0    0.000    0.000   0.000
 192.168.64.255  .BCST.          16 u    -   64    0    0.000    0.000   0.000
 172.29.0.255    .BCST.          16 u    -   64    0    0.000    0.000   0.000
 172.19.255.255  .BCST.          16 u    -   64    0    0.000    0.000   0.000

This looks promising!

I'll let it run for a night and see what is happing. The other system,
which still runs 4.2.5p158, gives after half a day:

     remote           refid      st t when poll reach   delay   offset  jitter
==============================================================================
*127.127.20.1    .GPS.            0 l   14   16  377    0.000   -0.089   0.096
-192.168.64.1    .GPS.            1 u   13   64  177    0.135   -0.016   0.185
 192.168.62.129  192.168.64.100   2 u   45   64  376    0.851    0.374   1.573
x82.95.142.92    129.70.132.36    3 u   53   64  377   38.416  -93.971   4.179
 127.127.28.0    .SHM0.           2 l    -   64    0    0.000    0.000   0.000
-194.109.22.18   193.67.79.202    2 u   35   64  377   19.307   -1.104   2.741
-194.109.20.18   193.67.79.202    2 u   21   64  377   19.382   -2.231   3.765
+193.79.237.14   .PPS.            1 u   60   64  377   20.894   -0.693   4.470
+192.87.36.4     .GPS.            1 u   10   64  377   23.136   -0.976   4.772
-134.221.205.12  .PPS.            1 u   62   64  377   22.208   -1.076   3.891
-172.29.0.11     193.67.79.202    2 u   51   64  377   20.858   -0.886   7.888


Folkert van Heusden

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