[ntp:questions] GPS_NEMA, but high offset and jitter?
David J Taylor
david-taylor at blueyonder.co.not-this-part.nor-this.uk
Wed Feb 24 20:07:43 UTC 2010
"Kelsey Cummings" <kgc at sonic.net> wrote in message
news:4b8580e5$0$1616$742ec2ed at news.sonic.net...
> I'm not sure why it lost sync but I went ahead and upgraded to 4.2.7p5
> from the ntp-dev port.
> I'm still seeing high offset and variable jitter.
> xGPS_NMEA(1) .GPS. 0 l 45 64 377 0.000 -311.36 75.859
> -time.sr 207.200.81.. 2 u 348 512 377 0.643 0.977 2.984
> *clock.sjc.he .CDMA. 1 u 362 512 377 6.348 -2.584 0.289
> Or: http://kgc.users.sonic.net/ntp_127_127_20_1-day.png
> The initial spike was the last restart.
> # Garmin GPS 18 LVC
> server 127.127.20.1 mode 0 prefer
> fudge 127.127.20.1 flag1 1
> Does the GPS_NEMA driver actually make use of the PPS signal (currently
> wired to DCD on serial port) at all or does it just use the GPS
> I'm wired up following http://www.satsignal.eu/ntp/GPS-interface-2.png
> except that I used a NPN transistor to drive the PPS led so it wouldn't
> load the PPS signal.
Kelsey, at least you now have a reach of 377 for the GPS!
The offset of -300ms suggests to me that you could be syncing on the wrong
edge of the PPS signal.
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