[ntp:questions] ntp use, was Re: Garmin GPS 18 firmware update -> 200ms offset

rtxo gnu at wraith.sf.ca.us
Tue Nov 29 20:54:27 UTC 2005


Patrick Klos wrote:

> I'm sure you can't rely on the NMEA strings coming out with any specific
> relationship to the pulse.  We've seen Garmin GPS's get very busy inside
> and skew the NMEA strings all over the place, including after the NEXT PPS.

I'd suggest turning off all output of the GPS, except for the
$GPGGA or $GPRMC strings, and turning on the PPS. This should
provide good operation with the Dave Mills NTP software.
I've run a Garmin GPS35 this way and have had consistent
1 microsecond PPS performance with NTP.

Look around at www.wraith.sf.ca.us/ntp for more info if
you're using j-random gps with a PC running GNU/linux or freebsd.

../Steven




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