How do you have your wiring done up? I found that when I just twisted the wire together and wrapped them in electrical tape for testing, I had very bad serial port behaviour. Doing a "cat /dev/gps1" I saw a lot of garbarge in stream and I was sometimes only seeing every third or fourth NMEA sentence. Soldering everything together snapped everything together.
Erik. > Date: Thu, 24 Jan 2008 10:23:18 -0500 > From: [EMAIL PROTECTED] > To: [email protected] > Subject: [ntp:questions] First attempt GPSD/PPS ->NTP time server > > All, > > This is my first attempt to build an 'accurate' GPS-based time server. > There is no Internet connectivity, so the GPS (and it's PPS) are the > only sources of timing data. > > I'm using a San Jose Navigation FV-M8 [1]. As a GPS, it works great. I > piped the PPS signal to the CTS line (gpsd-2.36 supports this) and with > a minor tweak to gpsd (until I can find the sentence to change the pulse > length), gpsd finds the pulse and hands everything off to ntpd as per > the gpsd man page [2]. > > Watching ntpd from 'ntpq -p' appears to work as expected. When the > offset (SHM(0), average gps) is less than 1 second, gpsd sends the > appropriate info to SHM(1) (gps pps), which ntpd uses ('ntpq -p' SHM(1) > reach changes from 0 to positive values). > > Basically, I think I have the hardware set up right. However, I left it > running over night because I kept seeing the following: > > # watch -n3 ntpq -p > remote refid st t when poll reach delay offset > jitter > ============================================================================== > *SHM(0) .GPS. 0 l - 16 377 0.000 1831.01 > 771.100 > SHM(1) .GPS1. 0 l 86 16 40 0.000 0.000 > 0.004 > > Sorry if it's line wrapped. The offset of SHM(0) will wander from less > than a second (< 1000.00) to around 8 seconds. Each time it gets close > (< 1000.00) the numbers for SHM(1) start changing, which tells me it's > trying to use the PPS to pull it in tight. But, then SHM(0) will wander > off again. > > What is normal? How long should it take a stand alone GPS time server > to lock in? What should I tweak to fix this? Any insight would be > appreciated. > > /etc/ntp.conf appended. > > Note: I tried deleting the drift file, and changing the time1 value, to > no avail. (I'm shooting in the dark with that one ;-) ) > > thx, > > Jason. > > > [1] - http://www.sanav.com/gps_engine_board/FV-M8.htm > [2] - http://gpsd.berlios.de/gpsd.html > Section: "Use with NTP" > > > ######## /etc/ntp.conf ############################################### > [snipped commented out stuff] > > # Added 20080122 to sync to GPS > server 127.127.28.0 minpoll 4 maxpoll 4 > #fudge 127.127.28.0 time1 0.420 refid GPS > fudge 127.127.28.0 time1 0.320 refid GPS > > server 127.127.28.1 minpoll 4 maxpoll 4 prefer > fudge 127.127.28.1 refid GPS1 > > [snipped out more comments] > > # you should not need to modify the following paths > driftfile /var/lib/ntp/ntp.drift > > [snip] > > # To deny other machines from changing the > # configuration but allow localhost: > restrict default nomodify nopeer > restrict 127.0.0.1 > > ###################################################################### > _______________________________________________ > questions mailing list > [email protected] > https://lists.ntp.org/mailman/listinfo/questions _________________________________________________________________ _______________________________________________ questions mailing list [email protected] https://lists.ntp.org/mailman/listinfo/questions
