[ntp:questions] Driver Help?

Karl Denninger karl at denninger.net
Wed Jun 13 12:40:06 UTC 2007


Richard B. Gilbert wrote:
> Karl Denninger wrote:
>> Karl Denninger wrote:
>>
>>> Jason Rabel wrote:
>>>
>>>> What OS are you running, and what CDMA modem are you using? (Just 
>>>> curious)
>>>>
>>>> Also from the info you gave it looks like it is using your CDMA 
>>>> source, but
>>>> seeing the stratum at 16 I don't think you have had NTP run long 
>>>> enough to
>>>> adjust the clock into sync.
>>>>
>>>> Jason 
>>>
>>>
>>>
>>> FreeBSD 6 (and 7; I have both here); the modem is a Multitech MTCBA.
>>>
>>
>> Quick update on this.... it appears that while the timecode is being 
>> stuffed appropriately, the underlying NTPD daemon doesn't like it - 
>> after a half-hour or so (running with debug turned up) and watching it 
>> log things, it fails to lock on and resets the time source, dropping 
>> and restarting the clock.
>>
>> I assume this means it is unable to get "happy enough" with the 
>> stability of the timestamps to formulate a "solution", declares the 
>> clock "broken", and then restarts....... yes?
>>
>> The obvious question is "can a time source that outputs only with 1 
>> second resolution and only when polled generate 
>> sufficiently-high-quality reference time for the system to use it?"
>>
>> If the answer is "no", then the curtain needs to be drawn on this 
>> attempt.  If the answer is "yes", then I need to figure out how to 
>> accomplish getting better input resolution I suspect - perhaps with a 
>> helper application that polls at a higher rate of speed (e.g. several 
>> times per second) and "stuffs" timecode events into the receive buffer 
>> (e.g. via a named pipe or similar)
>>
> 
> Subject to correction by someone who knows what he's talking about the 
> answer is not just "no" but "HELL NO"!
> 
> The resolution of 1 second is a killer.  This is going to make the 
> jitter a function of exactly when each poll is received.  I doubt that 
> ntpd cares very much exactly when a poll is sent.  If this device has a 
> PPS output, it might be useable. . . .

It doesn't, which sucks.  Severely.

I will contact Multitech and see if there's a solution to this (either 
in the form of better resolution or a PPS output option somehow.)  If 
not, well, it was a nice try :->

-- 
Karl Denninger (karl at denninger.net)
http://www.denninger.net




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