Chuck wrote: > hmm... this is what i have so far from messing around. this keeps the offset > for the gps clock in reasonable range or else it is skewed off by 230ms or so > and there is always an X by it. i suppose it doesnt matter since the pulse > (gps1) is always * and is usually within 100 us at worst, 5us at best. > > there seems to be a considerable change from poll to poll. it never settles > down into a nice small range hardly varying as i expected it to do. > > server 127.127.28.0 minpoll 4 maxpoll 4 > fudge 127.127.28.0 time1 -0.200 refid GPS > > server 127.127.28.1 minpoll 4 maxpoll 4 prefer > fudge 127.127.28.1 refid GPS1 > > >> -- >> Simon Arlott
I had a similar discussion on the list recently about the GPS 18 LVC. Here is what Rob Janssen had to say about gpsd: Rob wrote: > The message-based time (SHM(0)) is very inaccurate because of deficiencies > in most GPS receivers and their comms protocols. It is completely unclear > what time the timestamp in the message refers to, and usually it jitters > wildly. > The PPS output pulse is accurate, and the message-based time is only > required to bring the local clock well within one second, at which time > the PPS should take over. > Indeed, the whole operation is much more reliable when you have a couple > of references for NTP to choose from. I have a GPS 18 LVC on Linux, and use the PPS output only, via the shmpps driver from http://time.qnan.org/#driver-shm . When I tried gpsd, it introduced a few more us in the jitter and noise variables, and the offset was less consistent than with shmpps. With shmpps, I routinely show 1us noise and jitter, and +-4us offset. Not that it really matters anyway, as serving time over Ethernet degrades accuracy to the low millisecond range. Also, since I was going to have a few internet servers in my ntp.conf for sanity checks anyway, it really defeated the purpose of getting time from a local refclock. Might as well get the time from the internet servers and get rid of the ugly GPS time. -- Dennis Hilberg, Jr. [EMAIL PROTECTED] NTP Server Information: http://saturn.dennishilberg.com/ntp.php _______________________________________________ timekeepers mailing list [email protected] https://fortytwo.ch/mailman/cgi-bin/listinfo/timekeepers
