[time-nuts] GPSDO and holdover

David McQuate mcquate at sonic.net
Fri Apr 25 19:34:08 UTC 2014

Some timing GPS units (eg Oncore UT) can be set to omit 1PPS pulses if 
no satellites are being tracked, or if the RAIM alarm limit is exceeded.


On 4/25/2014 10:20 AM, Paul wrote:
> On Tue, Apr 22, 2014 at 9:57 PM, Tom Van Baak<tvb at leapsecond.com>  wrote:
>> I have noticed skipped 1PPS on the Adafruit GPS also.
> I've always assumed this could happen but as a result of RF signal loss not
> a glitch in the gps.  So I've started recording event timestamp deltas
> using the Linux kernel PPS interface.  I read assert events (e.g.
> 1398449188.001000242#1741672) and compute  timestamp and event deltas.  If
> the t delta is<  .9 something horrible must have happened and if it's>  1
> some didn't happen assuming the event count delta is always 1.
> I wonder if this is a reasonable approach or if I'm being lazily
> optimistic.  I just started (and I haven't added a join with the valid fix
> indicator yet) but I've had two missing pulses in the last 24 hours.
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