r3 - 2006-05-18 - 18:48:17 - SteveKosteckeYou are here: NTP >  Support Web > HelpWanted > HowToParseTSIPTrimbleLassenSQ
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Using the Parse refclock with a modern Trimble GPS in TSIP mode

I'm trying to get NTP working with a Trimble 'Lassen SQ' GPS module. I have used NTP for a few years, but previously only with peers & internet servers, this is my first attempt at a 'real' local refclock.

The machine is running Centos 4.3 on x86_64 architecture (Athlon 64 CPU). I have built NTP 4.2.0a with Parse & TSIP configured. (I have not figured out how to get it to run from /usr/sbin but that's another question..)

As far as I can see from the info I can find, the Lassen SQ appears to use exactly the same TSIP commands as the SV6 the parse refclock is supposed to support, but it does not give any sign of seeing data from the 'generic' server. ntpq -c peers shows all zeros except a '-' in the 'when' column.

I have enabled debugging in the parse module and initially I was seeing errors relating to invalid time data. The strings being dumped looked reasonable except occasional 0xff bytes, which I guessed were due to parity settings. The default parity for the module was Odd, I've changed this to None and the data errors have stopped.

I'm still getting an occasional error along the lines of 'data not received within poll interval'.

Notes:

  1. I have built the kernel with pps support. It's 2.6.16.9 with the latest ppskit-lite patch (for 2.6.15 with rejects added by hand).
  2. I have not yet included any reference to pps in ntp.conf, I believe the basic parse clock should work regardless?
(I've got to do a mod on the GPS module to extend it's PPS pulse & not got around to this yet).

I also have three other servers (one local & two internet) to ensure ntpd can get it's initial sync.

Does anyone have any ideas on getting this setup working? Or, is there another refclock that supports standard TSIP GPSs rather than just the dedicated time receivers?

-- RobertJenkins - 24 Apr 2006

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