[ntp:questions] custom NMEA messages
leonmccalla at hotmail.com
Mon Dec 28 15:16:56 UTC 2015
>Normally, the GPRMC gets sent every second even when the puck doesn't have
>fix. There is a field that says OK vs no-fix. ntpd checks that field.
10 satelite fix indoors. GPS is operating.
> Normal timing setup is to have the device send only one NMEA GPRMC message
> at 1s interval, and tweak driver fudge time1 until offset measured against
> other sources averages around zero.
the GPS sends 3 GPRMC messages in a 3 second window but NOT 1 per second.
>Beware. The SiRF chips are well known not co cooperate with that approach,
>depending upon what you expect. They have lots of wander that you can't
>filter out. If you tweak the fudge so that it is working correctly, it
This is my problem. I bought a GPS based on an inferior chipset.
>My GPS18xLVC+PPS averages within 1us and peaks about 50us jitter on
Garmin is a real GPS. please don’t mock me...
it is because of these instability that I analyzed that messages in detail
and noticed GPGBS being sent every 3 seconds with under 10 ms jitter. This
is the reason I am asking how difficult will it be for me to modify the NMEA
driver to accept GPGBS messages with mode 16? Should this question be on
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