[time-nuts] TymServe 2100 1995 Issue - A Kludgy Fix

Tom Van Baak tvb at LeapSecond.com
Wed May 6 13:38:07 EDT 2015


Hi Hal,

> Why is that so hard?

Depends if you want a quick hack (easy) or a solid solution (hard).

> If I understand things correctly, the time (UTC) is correct because the GPS 
> receiver is using the current GPS-UTC offset.  But the date is off by 1024 
> weeks.  (or some multiple of that)

You don't know if the UTC time is correct until the receiver locks to GPS and waits up to 12.5 minutes to get UTC-GPS corrections. At that point you have some to high confidence. Before that point it's a guess. That guess depends very much on the implementation of the receiver; what they hardcode, what they cache, soft resets, hard resets, NVRAM clear, etc.

As much as I cringe when I hear that telecoms often use GPS time instead of UTC, I have come to understand the wisdom of that decision.

> All you need for "external information" is the date when the fixup software 
> was compiled.  Call that the build-date.  Then the recipe is:
>  t = dateAndTimeFromGPS
>  while t < build-date
>      t += 1024 weeks
> 
> That won't solve the problem forever but it will give you another 20 years, 
> and you can restart the timer anytime you want by rebuilding and reinstalling 
> the fixup software.

Good, you understand my point. You need "external information" and "That won't solve the problem forever" and oh, well, yeah, duh, just "rebuild and reinstall the fixup software" anytime there's trouble in the future.

To me this is replacing a broken GPS receiver algorithm with a broken Arduino hack. You're not solving anything except pushing a problem to the next unsuspecting user or customer. Worse yet, now instead of being part of a group of N people sharing the same TymServe problem, you are a group of 1 with both a TymServe problem and an Arduino problem.

> I think the problems with leap-seconds are also non-problems because the 
> broken firmware will be working with the correct/current GPS-UTC offset.  I 
> don't remember any problems like that 2 years ago.

Re-read the TymServe field service bulletin. It's not about when leap seconds happen. The issue with TymServe is more like when leap seconds don't happen!

/tvb



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