[time-nuts] Z3801A gps week rollover

Magnus Danielson magnus at rubidium.dyndns.org
Fri Sep 9 03:06:29 EDT 2016


On 09/08/2016 11:53 PM, Hal Murray wrote:
> petervince1952 at gmail.com said:
>> Can I just ask why the Z3801As are  having week roll-over problems now - I
>> didn't think it was 2048 weeks since GPS "zero-hour" until late on the 6th
>> of April 2019?
> It's probably 1024 weeks since a date was built into the firmware.
> It's like the year 2000 problem.  If you aren't worried about old people and
> I tell you somebody was born in 03, you can assume that's 2003 rather than
> 1903.  For GPS, a handy value for the cutoff is the date the firmware was
> built.  Any date that looks like it is older than the firmware is probably
> off by a rollover.

We had this discussion in NTP context, and people where saying "We won't 
fix receiver problems" and where not helpful. When I explained how GPS 
time actually worked and just showing how the receivers was attempting 
to correct the GPS signal behaviors they realized that 1024 week 
wrap-around is more of a GPS generic problem and accepting time modulus 
1024 weeks was not too hard. I don't know if that ever made it into the 
code thought.


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