Motorola Oncore UT wrong date

[Jonathan Peakall]

Hi All,

My nixie clock that uses a Motorola Oncore UT for a time base started
shwing the time incorrectly yesterday, with time off by one hour.
Hooking up to the debug output I see that the GPS thinks the date is
1/14/2000. With my automatic DST routine, the clock is set wrong by an
hour. Or rather, it is set right for that date, but since that isn't the
date...

I have done several hard starts with the same result. I am waiting until
the synch bit is set so as far as the GPS is concerned the data is
valid. I have a 3D fix. The RTC has no back up power so a hard restart
will blank the current date and time. It synchs up quickly as it has
always done.

Any thoughts?

Jonathan

[Paolo Cravero]

[not a solution, but info worth sharing]

Hi Jonathan,

when I read your description my thoughts went back to that time my Garmin Geko 201 (small GPS tracker) recorded a date 15 years back in time.

Digging around I discovered that GPS/NMEA carry a 10 bit "week" information, which makes a rollover every 1024 weeks. But quoting a search result (written in 2013):

The last rollover (and the first since GPS went live in 1980)
was 0000 22 August 1999; the next would fall in 2019, but plans are
afoot to upgrade the satellite counters to 13 bits; this will delay
the next rollover until 2173

So what you are seeing is not due to a week rollover, even though my Geko 201 showed the problem in 2010 (and others too).

Perhaps Motorola hardcoded a "starting date" that matched a week number and counted from that point. Then a software variable has overflowed or 1024 have passed and you're back to "Oncore UT day 0".

If the delta_days is constant you might add it to your code right after reading the date information? You might discover is it some integer number falling within powers of 2. :-)

Paolo

PS: Garmin has issued a firmware update for the Geko 201. But I doubt I will get a new firmware in 2019...

[Jonathan Peakall]

Thanks for the thoughts. I am going to program up a data dump from the unit and see if I can find anything. For the moment I have simply corrected the UTC offset manually, which means reprogramming twice a year. So odd, over a decade of use with no problems. I checked my DST code and it is correct, the date is the issue.  ANother odd aspect: The date is incrementing every day. It was starting with 1/14/2000 now it says 1/16/2000. Hmmm...

Jonathan

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[Andy Tefft]

Given the age of these units, RAM space was probably at a premium and the routine in the firmware that converts from GPS time to human readable time is overflowing a variable. Perhaps an undiscovered bug or a limitation that the programmers didn't figure would matter this far down the road.

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