On 08/27/2014 08:46 PM, David Lord wrote: > Mike S wrote: >> On 8/27/2014 5:48 AM, [email protected] wrote: >>> I not sure, how should I write the ntp.conf file to achieve the >>> maximum accuracy using pps. >>> i don't know if the ntpd use the pps or not in my case! >>> Sometimes it is recognized as a "falseticker" (x) and sometimes it >>> is OK(o) !!! >> >> Try adding "tos mindist 0.02" to your config. >> >> NMEA tends to wander around - the default mindist of 0.001 can result >> in what you see. You might try setting it even higher, and work your >> way down to a reliable minimum. > > Hi > > For several years I've used: > tos minsane 3 > tos orphan 10 > tos mindist 0.4 > > currently with PPS, NMEA, 2 x local pcs, 4 x local pool.ntp.org > servers and one remote source. > > ntp-dev-4.2.7p444 on NetBSD-6/i386 > > > David > The basic problem is that using a PPS clock and a GPS(NMEA) clock separates what belongs together: the time message and the PPS pulse. Using the PPS-support flag at the NMEA driver and *not* using a separate PPS clock avoids the problem.
As already mentioned, some receivers (e.g. my Garmin GPS18xLVC) have a serial timing that leaves something to be desired... I decided to use the NMEA-internal PPS support and had no problems whith that since years. Pearly >> >> From the docs: >> mindist mindistance >> Specify the minimum distance used by the selection and anticlockhop >> algorithm. Larger values increase the tolerance for outliers; smaller >> values increase the selectivity. The default is .001 s. In some >> cases, such as reference clocks with high jitter and a PPS signal, it >> is useful to increase the value to insure the intersection interval >> is always nonempty. >> >>> >>> I tested different ntp.conf and here are some results (ntp.conf and >>> ntpq-p): >>> >>> #TEST:1 >>> >>> ----- ntp.conf------- >>> server 127.127.22.1 minpoll 4 #PPS >>> server 127.127.20.1 prefer minpoll 4 mode 16 #GPS >>> fudge 127.127.20.1 flag1 1 flag3 1 >>> ----- >>> GPS on COM port (PPS connected to DCD pin) >>> remote refid st t when poll reach delay offset >>> jitter >>> ============================================================================== >>> >>> xPPS(1) .PPS. 0 l 3 16 377 0.000 >>> 30.681 29.011 >>> oGPS_NMEA(1) .GPS. 0 l 2 16 377 0.000 >>> 29.964 29.404 > > _______________________________________________ > questions mailing list > [email protected] > http://lists.ntp.org/listinfo/questions > _______________________________________________ questions mailing list [email protected] http://lists.ntp.org/listinfo/questions
