[time-nuts] Re: question about GPS time

[Gary Myers]

I'd say most receivers do, even my old Motorola. Software wise you can
offset to TAI time using Lady Heather.

On 2024-03-28 12:51, Jim Harman via time-nuts wrote:

> The u-blox receivers have UBX messages that provide the current GPS and UTC
> time as well as information about the number of leap seconds that have
> occurred and the time, date, and direction of any upcoming leap second.
> 
> On Thu, Mar 28, 2024 at 3:01 PM David Bridgham via time-nuts <
> time-nuts at lists.febo.com> wrote:
> 
> On 3/28/24 2:03 PM, Tom Van Baak via time-nuts wrote:
> 
> If a second needs to be added to UTC it is named 23:59:60 
> 
> This brings to mind a question I've been meaning to ask one of these
> days.  I guess today is a good day.
> 
> I was contemplating building a system that would keep its internal time
> in TAI.  That makes more sense to me than jumping the internal time
> around to keep up with leap seconds; that conversion, if needed, can be
> done in a UI library.
> 
> In support of this, I was looking over GPS receiver data-sheets to see
> what I had to work with.  The GPSes I found all liked to report times in
> UTC, rather than TAI or GPS time.  Hmmm.  But one thing I noticed was
> that the seconds field of that UTC time report was defined to be
> [00..59].  Uhhh, so what do they do when a leap second comes along?
> Does the GPS receiver double up with :59 or maybe it rolls over to :00
> and doubles that one up?  Neither of those are very good answers.  Or
> maybe the documentation is just wrong and the receiver actually does the
> right thing and report :60.  I suppose documenting it wrong is better
> than doing it wrong.
> 
> So while I'm curious about that, my real question is whether there's a
> way to get GPS time out of a GPS receiver.  Or, lacking that, is there a
> way to reliably get the information out of a GPS receiver as to what
> leap-second offset it's currently using to calculate the UTC that it's
> reporting.  Yeah, I *should* be able to figure that out with my own
> leap-second database but how can I be sure that the GPS is really using
> the same list of leap-seconds that I have?  Better if it just tells me.
> Better still if I could get GPS time without the leap-second offset
> applied.
> 
> Thanks,
> Dave
> 
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