[ntp:questions] GPX18x LVC 3.50 firmware - high serial delay problem workround
David J Taylor
david-taylor at blueyonder.co.uk.invalid
Fri Jan 14 08:40:25 UTC 2011
Folks,
You may recall that I had a problem with a Garmin GPS18x LVC after
firmware upgrades, where the offset between the leading edge of the PPS
signal and the end of the NMEA serial data exceeded one second. With some
help from Hal Murray who knows more of NTP than I do, we have worked round
the problem as described here:
http://www.satsignal.eu/ntp/FreeBSD-GPS-PPS.htm#gps-18x
The basic steps were:
- make the GPX18x LVC "noselect" so that NTP would not use it
- enable the peerstats to measure where NTP thought the 18x end of message
occurred
- analyse the peerstats file to determine the apparent offset (which
was -1.000 seconds, as it happened)
- add that offset (as +1.000 seconds) to the fudge time2 value for the 18x
in the ntp.conf
- restart NTP
I hope that helps someone.
Cheers,
David
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