[ntp:questions] Problem with Trimble Placer 450 - gpsd - ntpd

Rob nomail at example.com
Thu Dec 30 08:14:38 UTC 2010

Bruce Dale <bdale at stny.rr.com> wrote:
> Hello,
> I'm new to this list, if this subject belongs in a different list, 
> please let me know.
> I have a Trimble Placer 450 GPS receiver generating a PPS signal and 
> NMEA sentences to gpsd (2.95), which passes that information to ntpd 
> (4.2.6p2) over the shared memory interface (reference clock driver type 28).

Does this receiver not support the Trimble binary protocol?
gpsd should switch it to binary protocol and maybe there are
no problems with that.

> When the Placer 450 has a consistent 3D fix on several satellites, 
> ntpd selects SHM(1), the PPS signal, as the syspeer. No problem.
> The problems occur when the Placer 450 loses satellite fix. In my 
> environment, this happens multiple times a day.
> Problem #1:
> The Placer 450 does not report loss of satellite fix as expected in 
> the NMEA sentences. I have been working with the gpsd folks to work 
> around this problem and they are happy to do so.

How about reporting this bug to Trimble?
I thought they were a respectable manufacturer of reliable GPS receivers,
not some careless company that ships products with bugs like that and
does nothing to fix them.

> Problem #2:
> The time server is a system consisting of the Trimble GPS receiver, 
> gpsd and ntpd. The gpsd folks are happy to implement a fix to the 
> problems with the Placer 450, but how are problems between gpsd and 
> ntpd resolved? Specifically, how should a GPS receiver report a loss 
> of satellite fix to ntpd over the shared memory interface? Should 
> ntpd ignore the PPS during the interval of no fix? And what is the 
> correct behavior of ntpd when this happens?

This works OK in gpsd.  When the receiver indicates there is no fix,
the PPS routine in gpsd stops providing time information and gpsd will
select a different source.
Of course it can only work when you DO have a different source.

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