Connected by DROID on Verizon Wireless
-----Original message-----
From: Bruce Lane <[email protected]>
To: [email protected]
Sent: Fri, Oct 21, 2011 20:44:07 GMT+00:00
Subject: Re: [time-nuts] Epoch rollover ?
Good day,
*********** REPLY SEPARATOR ***********
On 21-Oct-11 at 13:18 Dennis Ferguson wrote:
On 21 Oct, 2011, at 11:53 , [email protected] wrote:
Bruce, the most common cause of a GPS receiver getting the date
incorrect is due to cross-correlation. And cross-correlation is usually
the result of too much gain in the GPS antenna's LNA.
(snippage)
I would be more likely to believe this if the setup had not been working
just fine for the last four years. ;-)
No, based on what I've read, I'm definitely inclined to believe it's a
1024-week rollover thing.
(more snippage)
Some of the heuristics I've heard of are these (or maybe combinations of
these):
- Assume the date must be more recent than when the firmware was
compiled.
By itself this leaves the device with a 1024 week rollover problem,
but
the 1024 weeks are counted from the date the firmware was compiled
rather
than from the GPS epoch.
(still more...)
This idea fascinates me, as it is, potentially, the easiest to correct
AND the unit itself is vintage mid-90's. This would also explain why the
thing stayed working for a while after the last 1024-week roll.
I think I'll pull out the firmware, see if I can find the compile date
in a dump of the EPROM, change said date, and put the whole thing back
together. At worst, I'll end up with the same situation I have now. At
best, it'll fix it.
No matter what, I'll post the results. Dennis, thanks much! I hadn't
even considered that line of thinking.
Bruce Lane, Owner & Head Hardware Heavy,
Blue Feather Technologies (http://www.bluefeathertech.com)
Assoc. member, AZA & AAZK for many moons.
"Salvadore Dali's computer has surreal ports..."
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