[time-nuts] Garmin GPS12XL V3.51

[Bob kb8tq]

Hi

The “fix” for this (adding 3 more bits) was worked out and announced back in 2004. The new
generation of sats will be transmitting a longer week number. The gotcha is that the old sats
are still up there doing their thing. They are built in a way that you can’t just shoot a firmware
patch into space and add more bits to the transmitted message. 

The original plan was that the new message would be on the air well before the rollover event
that just happened. Even then, there was some debate about how many devices would be able
to use the “new” message. The whole implement / debug / deploy / patch cycle is not something
that happens overnight. 

On all of our older gear, there pretty much are no patches for any of this. Doing a patch that 
resets the magic “built on” date is pretty trivial compared to doing more bits in the message. 
We don’t even have simple patches for this gear …..

Bob


> On Apr 10, 2019, at 1:49 AM, Forrest Christian (List Account) <lists at packetflux.com> wrote:
> 
> I realize that this doesn't help old receivers, but I'm sort of
> surprised that this wasn't addressed as the GPS system has had various
> additions made to it such as WAAS.  Even 3-4 bits allocated to this
> purpose in one of the datastreams would move us out beyond any
> reasonable expectation of the life of the current GPS protocol.
> 
> Does anyone know if any of the global GNSS alternatives (aka GLONASS,
> etc.) have similar limitations?
> 
> On Tue, Apr 9, 2019 at 7:01 AM Tom Van Baak <tvb at leapsecond.com> wrote:
>> 
>>> There's another relatively simple clue in the old GPS signal: the leap
>>> second count! A device manufacturer could teach it what the leap second
>>> count was at manufacturing time, and how to predict a lower bound on the
>>> leap second count in the future (with a suitable safety margin / fudge
>>> factor) which should allow it to live a bit more than 20 years.
>> 
>> The idea was proposed 20+ years ago, Trimble even has a patent on it. Details here:
>> 
>> http://leapsecond.com/notes/gpswnro.htm
>> 
>> But it turns out not to work. Earth rotation is too difficult to predict 20, 40, or 60 years into the future. There was talk that the GPS receiver failures in 2015 were related to this algorithm. Look for any threads with subjects like: TS2100, TymServe 2100, 1995 rollover, Trimble ACE, Heol Design in:
>> 
>> http://lists.febo.com/pipermail/time-nuts_lists.febo.com/2015-May/
>> http://lists.febo.com/pipermail/time-nuts_lists.febo.com/2015-June/
>> 
>> /tvb
>> 
>> ----- Original Message -----
>> From: "Tony Finch" <dot at dotat.at>
>> To: "Discussion of precise time and frequency measurement" <time-nuts at lists.febo.com>
>> Sent: Tuesday, April 09, 2019 4:08 AM
>> Subject: Re: [time-nuts] Garmin GPS12XL V3.51
>> 
>> 
>>> Leo Bodnar <leo at leobodnar.com> wrote:
>>> 
>>>> Assume that the device does not have any reliable long term non-volatile
>>>> memory that you can update.
>>> 
>>>> In the absence of any clues your only reliable piece of knowledge is
>>>> that the cold start date is somewhere after the date of manufacturing
>>>> or, most often, firmware compilation date.
>>> 
>>> There's another relatively simple clue in the old GPS signal: the leap
>>> second count! A device manufacturer could teach it what the leap second
>>> count was at manufacturing time, and how to predict a lower bound on the
>>> leap second count in the future (with a suitable safety margin / fudge
>>> factor) which should allow it to live a bit more than 20 years.
>>> 
>>> Tony.
>>> --
>>> f.anthony.n.finch  <dot at dotat.at>  http://dotat.at/
>>> Gibraltar Point to North Foreland: Northeasterly 5 or 6, occasionally 7 in
>>> south. Moderate. Showers at first in south. Good, occasionally moderate at
>>> first.
>>> 
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>> 
>> 
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> 
> 
> 
> -- 
> - Forrest
> 
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