[time-nuts] GPSDO and holdover

[David McQuate]

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.

Dave

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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