Steve,
I'm thinking the problem is not with GPS or with modulo arithmetic. I'm
in contact with Leo and others for the root cause or the scope of the
problem as reported on twitter. I'll say more later.
Per the GPS ICD, when dt_LS == dt_LSF there is no leap second to speak
of; not in recent past; not in near future. The 8-bit WN and DN fields
are not applicable to a non event.
When dt_LS != dt_LSF you know there is a nearby leap second event. You
then look at WN and DN to determine when. It could have been in the
recent past, it could be in the near future, or even in progress. By
"recent past" and "near future" I mean ±127 weeks (about ±2½ years).
Clearly this design means GPS cannot give indefinite past history of a
previous leap second(s), nor indefinite future notice of a pending leap
second(s). This is not a problem given how UTC is currently defined and
managed. BIPM has a good track record of 6 months (~26 weeks) of notice.
The official UTC spec is 1 month (~4 weeks) of notice so a 127 week GPS
limit is more than adequate.
/tvb
On 7/25/2021 8:54 AM, Steve Allen wrote:
On Sat 2021-07-24T18:50:50-0700 Tom Van Baak hath writ:
In the news:
"GPS will broadcast a 0 second leap second in 128 days"
https://news.ycombinator.com/item?id=27944776
A tweet from Leo Bodnar electronics about their NTP device
https://twitter.com/LeoBodnar/status/1419239590532206597
which famously includes highlighted text from the section of the GPS
ICD that describes the need to do modulo arithmetic along with the URL
to the new version of the firmware.
--
Steve Allen <s...@ucolick.org> WGS-84 (GPS)
UCO/Lick Observatory--ISB 260 Natural Sciences II, Room 165 Lat +36.99855
1156 High Street Voice: +1 831 459 3046 Lng -122.06015
Santa Cruz, CA 95064 https://www.ucolick.org/~sla/ Hgt +250 m
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