-----BEGIN PGP SIGNED MESSAGE----- Hash: RIPEMD160 David J Taylor wrote: > David J Taylor wrote: >> Folks, I'm thinking of adding my new Garmin GPS 18 LVC just to see how >> well it might function with serial input alone, so I have some >> questions. >> With the NMEA refclock driver (type 20): >> >> - is it possible to select the baud rate without re-compiling or must >> it be 4800? I would have thought that having the higher baud rate >> might perhaps improve jitter. >> >> - is a PPS signal actually required, or will the driver function with >> just the serial input (I realise that accuracy will be much worse >> without the PPS, but his is just for testing). >> >> - is it possible to use NTP just to observe a refclock, without >> actually syncing time with it? >> >> Thanks, >> David > > OK, I did some testing! I'd still like to know if you can select the COM > port and baud rate without recompiling.
Nope it's a hard define in refclock_nmea.c #define SPEED232 B4800 /* uart speed (4800 bps) */ > > - yes, it works without the PPS input, although the jitter seems as high > as 5 msec Sounds about right - 1 byte = ~2ms @ 4800 - be sure to use a "real" serial port as a USB one will add lots of jitter. If you use the Garmin utils to turn off all the NMEA messages apart from the one you want it will be a bit better (mine was ~1ms on FreeBSD) - compared to around ~8us with PPS. > > - set stratum to 10 to stop it syncing and just observe - would that work? Sounds like a good strategy - I don't know if "noselect" works for refclocks (never tried it) but if it does that will give you what you are looking for. > > David > > John -----BEGIN PGP SIGNATURE----- Version: GnuPG v1.4.1 (MingW32) iD8DBQFD288WaVyA7PElsKkRAyUEAKDXOcrdPyhLIszXd/18aMcFzRQHMQCfYQH7 6mdlrMPE633KVpQnymvzRdo= =h+ez -----END PGP SIGNATURE----- _______________________________________________ questions mailing list [email protected] https://lists.ntp.isc.org/mailman/listinfo/questions
