The gpsd turns on several additional NMEA strings (other than the $GPGGA) when run with a Garmin gps35. At 4800 baud, these additional strings have a negative impact on the linuxpps server.
The first two plots show the disturbance caused by the gpsd data
streams. The week plot shows that the gpsd turned on the extra streams
sometime Saturday.
This plot shows the offset when the gps35 has been returned to only
the $GPGGA NMEA data string configuration.
There is code-to-be for gpsd that will mitigate this via configure flag:
There is a new configure option to gpsd in SVN: --disable-reconfigure do not allow gpsd to change device settings It is for folks that set their GPS the way they want it and do not want gpsd to muck with the settings!
For reference, here are the strings to put the gps35 into $GPGGA only mode:
Turn output off $PGRMO,,2 Turn on $GPGGA $PGRMO,GPGGA,1 Turn on PPS: $PGRMC,,,,,,,,,,,,2(Note: turning on pps requires you to power cycle the gps35)