[time-nuts] looking for low-power system for gps ntp timekeeping NANOSG20
folkert
folkert at vanheusden.com
Wed Jul 3 16:14:59 EDT 2013
> folkert at vanheusden.com said:
> remote refid st t when poll reach delay offset jitter
> ==============================================================================
> x127.127.28.0 .NMEA. 0 l 3 16 377 0.000 -994.05 7.857
> x127.127.28.1 .PPS. 0 l 7 16 377 0.000 -250.13 572.812
> +192.168.64.18 .PPS. 1 u 66 128 377 0.553 -0.055 0.033
> *192.168.64.2 .PPS. 1 u 99 128 377 0.237 -0.062 0.039
> +192.168.64.168 .PPS. 1 u 44 128 377 0.646 -0.013 0.321
>
> Something is broken. What NMEA device are you using? Why are you using gpsd
It is a garmin 18x lvc.
> rather than ntpd's NMEA driver?
Oh for convenience. I need to patch ntpd to use linux pps (afaik) and on
other systems I successfully run gpsd with ntpd (read: low jitter).
> It looks like the NMEA side it is off by a second. Some devices do that.
> You can fix that with some fudging.
Yes, I'm not so worried about the nmea part, I might even decide to
remove it from the configuration. What I mean is: if I set the clock to
the current time, than it is only a matter of keeping it at that with
the pps.
> The PPS stuff is off by 250 ms. Are you using the wrong edge? (Got a scope
> handy?)
Well, the offset is not constant. If you look at
http://keetweej.vanheusden.com/~folkert/nanosg20.png you see it is
between 0 and -1ms. I now notice that it is not random-ish but consists
of a few specific values:
folkert at belle:~$ cat peerstats | grep 127.127.28.1 | awk '{ print $5; }' | cut -c 1-6 | sort | uniq -c | sort -rn
503 -0.874
497 -0.875
486 -0.999
467 -1.000
365 -0.249
332 -0.250
201 -0.857
188 -0.125
184 -0.142
140 -0.124
131 -0.000
113 0.0000
108 -0.166
24 -0.833
5 -0.200
2 -0.856
2 -0.799
2 -0.199
1 -0.167
1 -0.143
1 0.0002
1 0.0001
This is with 3754 lines.
If I clean it a little:
1000x -0.8745
953x -0.9995
697x -0.2495
328x -0.1245
and so on.
Folkert van Heusden
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