[time-nuts] GPS week rollover

[paul swed]

Quite a good thread.
The old rollover is a real pain in the .... Especially on the old receivers
circa 1990s.
Whats useful is the method for calculating the week mentioned. Granted
there are tools online that help. But the math associated with reversing
the date now is clearer using the Julian date. May tinker in excel as I
think there are date macros and such available.
The output needed for the old receivers is now - 1024 weeks given as a date.
On some of the really old ones I think it may be 2 rollovers at this point.

Regards
Paul
WB8TSL

On Wed, May 6, 2015 at 8:19 AM, Pete Stephenson <pete at heypete.com> wrote:

> On Wed, May 6, 2015 at 6:48 AM, Mark Sims <holrum at hotmail.com> wrote:
> > Well,  a big one will be in 2017 when all our Tbolts roll over.    I
> have included some code in the next version of Lady Heather to compensate.
> If it detects a year from the unit before 2015,  it converts the date/time
> to Julian,  adds 1024 weeks worth of seconds,  and then converts the
> date/time back to Gregorian.  You can also specify a user defined rollover
> adjustment (in seconds).  One issue that I have seen is the Tbolt
> occasionally spitting out a bogo-year and triggering a false/premature
> rollover...  still trying to track that down.
> >
> > People using Tbolts for things like NTP servers will have to implement a
> similar fix...
>
> I assume the Tbolt rollover will be problematic for those who start
> their Tbolt completely cold (no time, almanac, or ephemeris) and
> without any non-GPS input, but how will the Tbolt behave in situations
> where the user initializes the Tbolt with the then-correct
> post-rollover date and time? For example, one might use Tboltmon and a
> wristwatch to set the approximate time on the unit and then let it
> figure out the precise time from GPS.
>
> Also, will the rollover cause time-of-day problems for running Tbolts?
> That is, would they "ride through" the rollover and continue to
> provide the correct date and time as expected (that is, they recognize
> that a rollover occurred and keep working normally so long as they're
> not cold-reset) or would they immediately jump back to December 14,
> 1997 (the Thunderbolt "zero" date)? According to
> <https://www.febo.com/pipermail/time-nuts/2014-September/086664.html>
> it looks like they'll output the incorrect date as they cross over the
> rollover point. That's not good.
>
> --
> Pete Stephenson
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