[LEAPSECS] aircraft GPS receivers hit by leap second bug

Martin Burnicki martin.burnicki at burnicki.net
Fri Jun 14 03:16:11 EDT 2019


Tom Van Baak wrote:
>> What I meant is that if you try to derive the date of the last recent
>> leap second from WNlsf if the 2 offsets *are* the same, the result is
>> ambiguous since you don't know if you are in a +/- 128 weeks interval,
>> or if another 256 weeks interval has passed. That's exactly what we are
>> observing right now.
> Let me explain a cute trick. The ± 128 or modulo-256 week ambiguity that
> you mention is certainly true, as well as the 19.x year 1024 week GPS WNRO
> that we all know.
> But look one step deeper. Each 8-bit week number and 3-bit day number used
> to describe the most recent or pending leap second must necessarily be the
> last day of a calendar month, per UTC rules, yes? It turns out this fact
> can be used to resolve the ambiguity that you speak of.

This is really cute! If you permit, I'll see if we can add this to our
driver software packages.



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