[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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