2011/8/2 Miguel Gonçalves <[email protected]>: > I figured I was using different versions of NTP: > > - 4.2.4p5 (FreeBSD 7.4) on the one that was not seeing the PPS: I was > only using the NMEA driver and I should have also added the PPS > driver. > > - 4.2.6p2 (FreeBSD 7.4 but compiled through ports) on the one that was > seeing the PPS: I had to use 4.2.6p2 so I could select 9600 bps. > > Through a series of mistakes I found out (with your help) that ntpq > should report 'o' instead of '*'. So the correct one was the 4.2.6p2 > one! :-)
Actually both were seeing the PPS signal from the start, or else you would not have been seeing offsets in the low microseconds on both. ntpd 4.2.4 never uses the 'o' tally code, PPS or not, you will see * for the controlling peer. With 4.2.6, you will see tally code 'o' for the controlling PPS, and you can also see '*' at the same time on another refclock that is "numbering the seconds" for the PPS, though not in your original configuration where a single NMEA driver is both numbering the seconds and providing the PPS, for that configuration you will see 'o' on NMEA once the PPS is engaged. You do not need to configure a separate PPS driver, and are probably best off to not. If you do, change the NMEA flag1 to 0 so it will not also attempt to process the PPS. Note the 'o' tally only appears when ntpd is talking directly to the PPSAPI interface. A common configuration on Linux systems puts gpsd in the middle, and provides the GPS and PPS information via a shared memory driver to ntpd. In that case, the selected refclock never will show 'o' regardless of ntpd version, because ntpd is not using PPSAPI. The gpsd approach has the upside of letting you use the GPS from other programs at the same time as ntpd, and also does not require PPSAPI support, which mainstream Linux hasn't had until very recently. The downside is the PPS is being timestamped in preemptively-scheduled gpsd code, rather than in an interrupt handler, so the PPS timestamps are noisier with gpsd compared to direct PPSAPI from ntpd. Cheers, Dave Hart _______________________________________________ questions mailing list [email protected] http://lists.ntp.org/listinfo/questions
