[time-nuts] Warped back to 1993

Bob Camp lists at rtty.us
Sun Aug 11 16:00:49 EDT 2013


Hi

I'd claim that the modulo 1024 wrap is a "known issue" with GPS. I would not force the correction on all users. I'd just make it an optional item. This obviously also applies to things like LH and other TimeNut stuff. As we try to keep the gear going much longer than the original designers anticipated, and as manufacturers drop firmware support, we're going to need a generic solution for the issue. "Forcing" manufacturers to fix stuff long after it's gone obsolete isn't the answer….

Bob

On Aug 11, 2013, at 3:45 PM, Martin Burnicki <martin.burnicki at burnicki.net> wrote:

> Bob Camp wrote:
>> Hi
>> 
>> 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.
> 
> The question is whether you know in advance *when* the problem will occur.
> 
> If you observe that your GPS sends a wrong date you are already after the point where the bug started to occur, so you can safely add a fudge value to get this working for the next 1024 weeks.
> 
>> 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. 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…..
> 
> Unless you know the source code of the firmware you can only assume what is the reason for the wrong date being sent. I'm not sure whether a piece of software like ntpd should try to work around all possible kinds of firmware bugs in all possible types of GPS receivers.
> 
> Martin
> 
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