John Pettitt wrote: > David J Taylor wrote: >> I just spent an interesting few hours setting up a FreeBSD 5.4 >> system from scratch, and interfacing it to a Garmin GPS 18 LVC. >> Well, there was a lot of help in the Web, and it must be 10 or more >> years since I messed with UNIX. >> >> I'm getting what seem to be sensible results, but the jitter from >> the GPS seems to be higher than some of the Internet servers (3ms >> versus 1ms), so I'm wondering if the PPS signal on the DCD line is >> being used at all. I've set flag3 = 1 in the fudge command. >> >> Any suggestions? I'm really new to FreeBSD so I might have missed >> the glaringly obvious! >> >> Thanks, >> David >> >> > > I have the same setup. > > Jitter from a GPS18LVC should be on the order of 3-5 microseconds so > I think your PPS is not working. > > Things to check > > 1) PPS is wired to DCD > 2) you are on a real serial port not a USB one > 3) you made the sym link from /dev/pps0 to /dev/ttyd? > 4) you have pps enabled in the GPS18 (download the garmin utils and > turn off all the NMEA stuff you don't need and make sure PPS is on) > 5) you have "options PPS_SYNC" in your kernel config > > John
John, Many thanks for that. 1 is OK - I can see the pulse with a 'scope on pin 1 of the DB9 connector 2 - OK 3 - I'm using COM1 for the GPS, and the sym link I found elsewhere was: ln -s cuaa0 gps1 (my ntp.conf includes server 127.127.20.1) So should I be linking cuaa0 or ttyd0, and should it be to pps0 or pps1? I have tried "ln -s ttyd0 pps1". Ntpdc -c kern shows: pixie# ntpdc -c kern pll offset: -0.0408704 s pll frequency: 100.840 ppm maximum error: 0.126969 s estimated error: 0.007626 s status: 2001 pll nano pll time constant: 6 precision: 1e-09 s frequency tolerance: 496 ppm 4 - is OK, I can see the pulse and just the GPRMC messages. 5 - I have not done that explicity. How could I check that, and change it if required? It's been 10+ years since I ran UNIX. Thanks, David _______________________________________________ questions mailing list [email protected] https://lists.ntp.isc.org/mailman/listinfo/questions
