[time-nuts] TymServe 2100 1995 Issue - A Kludgy Fix

Martin Burnicki martin.burnicki at burnicki.net
Thu May 7 06:05:17 EDT 2015


Brian Inglis wrote:
> The next rollover is about April 2019, but this can happen any time
> an older receiver's internal date representation used for GPS to UTC
> conversion overflows. Looks like Tymserve 2100 picked about Sep 1995
> for its date epoch so it hits now.
>
> Newer GPS receivers support the extra 3 bits added to GPS extended
> week allowing 8192 weeks (157 years) between rollovers - 2137 is the
> next big rollover problem, but NavStar will likely not be sending the
> same data on the same frequency then.

There are also GPS receivers out there which use (and have been using) 
an extended week number internally instead of hardcoded limit for the 10 
bit week number.

As long as there's a backup battery is OK then there's nothing to do for 
the user to get the correct epoch. If the backup battery is disconnected 
or fails then you can just send the current date to the device, and the 
firmware computes the extended week number, including the epoch of the 
GPS week number.

Martin


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