[LEAPSECS] 256-week / leap seconds / in the news

[Martin Burnicki]

Hi again,

one of my colleagues has a u-blox LEA M8T with firmware 3.01 available, 
and this morning, the device has output the following fields in the 
UBX-NAV_TIMELS message:


iTOW            118812000    Time Of Week [ms]
srcOfCurrLs     2            Source of Leap Second Info
                              (2 -> GPS)
currLs          18           Current GPS/UTC offset [s]
srcOfLsChange   2            Source of Leap Second Change Info
                              (2 -> GPS)
lsChange        0            Future Leap Second, if scheduled
                              (0 -> none scheduled)
timetoLsEvent   767606       Time To Next Leap Second Event [s]
                              (counting down in subsequent messages)
dateOfLsGpsWn   2185         [extended] GPS week number of the nearest
                              leap second
dateOfLsGpsDn   7            GPS day of week number for the nearest
                              leap second
valid           0x03         Validity flags (0x03 -> both currLs and
                              timetoLsEvent are valid)


GPS LS week number 2185 and day number 7 would indicate a leap second 
scheduled for the end of Sat, 2021-11-27. This must be wrong because 
2021-11-27 is not the end of June or December, but the wrong expanded 
week number is probably just due to the ambiguity of the truncated 8 bit 
week number in the UTC parameter set.

The current GPS time when this message was received was WN 2168 and TOW 
118812.
According to timetoLsEvent, the next LS would be 767606 s in the future,
which would be around WN 2168 TOW 886418,
which would be normalized to WN 2169 and TOW 281618,
which in turn means around 6 AM on 2021-08-04,
which is obviously not plausible, either.

And it differs from the other wrong date indicated by WN 2185 DN 7.

So the output is not consistent, specifically since timetoLsEvent is 
continuously counting down.

On the other hand, the field lsChange is 0, which means there is no leap 
second pending at all, and thus there's no need to evaluate the other 
fields to generate a leap second warning to other applications.


Martin
-- 
Martin Burnicki

Senior Software Engineer

MEINBERG Funkuhren GmbH & Co. KG
Email: martin.burnicki at meinberg.de
Phone: +49 5281 9309-414
Linkedin: https://www.linkedin.com/in/martinburnicki/

Lange Wand 9, 31812 Bad Pyrmont, Germany
Amtsgericht Hannover 17HRA 100322
Geschäftsführer/Managing Directors: Günter Meinberg, Werner Meinberg, 
Andre Hartmann, Heiko Gerstung
Websites: https://www.meinberg.de  https://www.meinbergglobal.com
Training: https://www.meinberg.academy

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