[time-nuts] raspberry pi, adafruit gps & ntp

folkert folkert at vanheusden.com
Mon Jun 17 08:06:34 UTC 2013


> After 51 minutes of ntpd run-time this gives:
> 
>      remote           refid      st t when poll reach   delay   offset  jitter
> ==============================================================================
> *firewall.intran 192.168.64.2     3 u    7   64  377    0.560   -0.506   0.493
> -belle.intranet. 192.168.64.2     3 u   58   64  377    0.560   -0.470   0.405
> -time2.intranet. 194.109.20.18    3 u   56   64  377    1.034   -1.282   1.392
> +auth1.xs4all.nl 193.67.79.202    2 u   28   64  377   17.580   -0.160   0.490
> xSHM(0)          .NMEA.           0 l    1   16  377    0.000  -359.47  10.670
> +SHM(1)          .PPS.            0 l    1    8  377    0.000    2.964   0.061

After 12,5 hours:

     remote           refid      st t when poll reach   delay   offset  jitter
==============================================================================
*192.168.64.1    192.168.64.2     3 u  280 1024  377    0.534   -0.924   0.579
-192.168.64.100  192.168.64.2     3 u  451 1024  377    0.625   -0.920   0.560
-192.168.62.129  194.109.22.18    3 u  278 1024  377    1.661   -2.347   0.665
+194.109.22.18   193.67.79.202    2 u  295 1024  377   17.719   -0.357   0.978
x127.127.28.0    .NMEA.           0 l    5   16  377    0.000  -309.57  40.640
+127.127.28.1    .PPS.            0 l    4    8  377    0.000    2.231   0.005

Looking good!
It is probably selecting 192.168.64.1 due to an accidental "prefer"
keyword for that server in the configuration.
I'm surprised that the jitter goes down to 0.005 as I'm now measuring
the PPS from userspace. My program runs with "real time" scheduling and
maximum priority but still the kernel needs to do a context switch etc.
when it receives the pps pulse.


Folkert van Heusden

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