Hal Murray wrote: >> I'm not sure whether the NMEA driver attempts to send anything /to/ the >> GPS device. If not, three lines might to (ground, TX from GPS, PPS), >> otherwise four lines are required. If you want to take USB power from the >> server (as I now do), it's five lines minimum. > > The driver expects the data to arrive without any help. That > works with all the NMEA devices I've worked with. You set them > up ahead of time by sending them a sequence of commands which > differ from device to device. > > The driver does send "$PMOTG,RMC,0000*1D\r\n" every poll interval, > with a comment about some Motorola device needing it. (That's one > per poll interval rather than one per second. I don't expect it > to work very well.)
I used input to disable non required NMEA sentences but I'm not sure if any apparent improvement is due to that, temperature or system load or other effects. This system doesn't have network connection or mrtg. Ntp offsets taken at 30 minute intervals with/without PPS and with default NMEA sentences vs RMC only. Garmin gps18x-lvc nmea_std.dat * +/-offset Num Tot % * (ms) * 0.12 5 25 56 * 0.16 2 40 89 * 0.17 5 45 100 pps_std.dat * +/-offset Num Tot % * (ms) * 0.004 25 79 52 * 0.010 7 148 97 * 0.014 2 153 100 nmea_rmc.dat * +/-offset Num Tot % * (ms) * 0.07 5 27 51 * 0.16 3 49 92 * 0.20 1 53 100 pps_rmc.dat * +/-offset Num Tot % * (ms) * 0.002 49 76 54 * 0.005 7 140 99 * 0.006 1 141 100 David _______________________________________________ questions mailing list [email protected] https://lists.ntp.org/mailman/listinfo/questions
