[rc-oncore] [Bug 2872] Oncore is offset by current GPS-UTC delta at startup

bugzilla-daemon at ntp.org bugzilla-daemon at ntp.org
Wed Aug 26 07:25:59 UTC 2015


--- Comment #3 from Martin Burnicki <burnicki at ntp.org> 2015-08-26 07:25:59 UTC ---
(In reply to comment #2)
> (In reply to comment #1)
> > GPS receivers only know the current UTC to GPS time offset immediately after
> > power-up if they save the latest UTC parameter set received from the satellites
> > in a non-volatile memory while powered off.
> Martin,
> In this case the receiver has a backup battery, and a valid almanac that it
> loads and warm starts with, so either it does not load the current offset
> offset from the almanac, or does not take it into account but starts providing
> a valid signal indication (TRAIM is on in this configuration) and time that is
> offset until received again, or loaded again.

Just to be nitpicking ;-) :

The almanac parameter sets only provide the raw satellite position at a given
time. There are additional parameter sets which provide UTC correction,
ionospheric correction, etc. If the device only saves the almanac parameters
persistently then the other parameter sets might not be available at startup,
anyway, though such a behaviour wouldn't make much sense, IMO.

> At this point I just need someone who has more than the 2-3 Oncore receivers
> that I have looking for this behavior, I think.  It's not clear how widespread
> this bug is.

Some years ago I wrote a firmware for a GPS receiver, but I haven't used an
Oncore receiver myself, yet.

Eventually you should investigate on the time-nuts mailing list:

There are a couple of guys on that list who are playing around with lots of
different types of GPS receivers, and since they are "time nuts" ;-) they know
many details of the exact behaviour of those receivers.

> Majdi

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