[ntp:questions] fudge time1 for gps-18x-LVC?

David Lord snews at lordynet.org
Sat Feb 6 00:12:01 UTC 2010

unruh wrote:
> On 2010-02-05, David Lord <snews at lordynet.org> wrote:


> What sentences is the nmea sending out?
> Why not use something like gpsd and the shm driver to combine the nmea
> and the PPS into one very accurate time stamp?


I tried gpsd with shm but without pps in attempt to improve
performance of my Globalsat BR-304. Results were worse than when
using nmea driver which gave 50% level at offset 9.5ms and
jitter 2.6ms, 95% level at 52.4ms and 28.2ms.

I didn't even tabulate results as that useless. The BR-304 isn't
anywhere near as sensitive as the gps-18x-LVC and in November
when weather was bad I could see reach rarely staying at 377
and gpsd was often only showing single sat. Couple of weeks ago
even the Garmin was struggling with reach dropping to 0 (layer
of ice on window - inside and outside?). At the moment other
than when ntpd restarted reach has stayed at 377.

I've put checking with gpsd + shm + pps (serial and parallel)
with the Garmin on todo list, maybe sometime next week.



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