[time-nuts] Warped back to 1993

[Bob Camp]

Hi

On Aug 11, 2013, at 5:32 PM, Hal Murray <hmurray at megapathdsl.net> wrote:

> 
> lists at rtty.us said:
>> The issue with the fudge option is that you need to engage it at exactly the
>> right point. Put another way, there's a period between it failing and your
>> entering a fudge that the NTP server is down.
> 
> Yup.  But if you are running along and suddenly your GPS breaks, you might be 
> able to fix it by editing a config file and not needing to install any new 
> software or wait for the bug to get fixed.

If you only "fix" it modulo 1024 when instructed, there isn't the same downside as a "change it all over the place" sort of solution.


> 
>> With a couple lines of auto correct code in there, it would (essentially)
>> never fail. If you are running a GPS, you enable the auto-correction and
>> forget about it. My guess is that many GPS devices will eventually suffer
>> from the wrap around
> 
> Agreed.
> 
> 
>> The  only way they could avoid it would be some sort of external correction
>> (like continuous firmware updates) or a "no reverse" on the year. Both
>> approaches have their drawbacks…..
> 
> There is another option that may be good-enough for some/many of us.  That is 
> a way to tell the GPS unit the date.

That *assumes* that the GPS firmware will accept a date as an input. The firmware would need to be able to do this.

> 
> If a GPS device knows the rough date, it can get the right answer.
> 
> Most GPS units have a battery and 32KHz clock to keep track of the time so 
> they can get started (much) quicker on power up: warm start vs cold start.  
> This isn't quite "no reverse", but it's pretty close.
> 
> 1024 weeks is 20 years, so the batteries are probably old by the time this 
> gets interesting.  But even an old tired battery might keep a clock ticking 
> for a few minutes/hours.  That might cover rearranging cables or a 
> not-too-long power outage.
> 
> But after the unit has been powered off too long (relative to the battery) or 
> after you replace the battery, you need some way to set the date.
> 
> My Z3801A has been happy since I told it the date.  I don't know if it has 
> been powered off since then.  I should probably try the experiment.

Z3805's and later have multiple receivers in them. Different firmware will / may fail at different times.

Bob

> 
> 
> 
> -- 
> These are my opinions.  I hate spam.
> 
> 
> 
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