[ntp:questions] Re: Bought a GPS receiver--What next?

Richard B. Gilbert rgilbert88 at comcast.net
Tue Nov 2 01:59:45 UTC 2004


W. D. wrote:

>Hi Harlan,
>
>At 17:39 11/1/2004, Harlan Stenn wrote:
>  
>
>>Would you please add this info to the oncore configuration page at:
>>    
>>
>
>Um, this request is being addressed to whom?
>
>What exactly do you mean by 'this info'?
>
>
>  
>
>>http://ntp.isc.org/Support/ConfiguringMotorolaOncoreRefclocks
>>    
>>
>
>Yeppers--saw that page.  It's gibberish to me.  It looks like
>the shorthand notes for a procedure that someone has executed
>at some point.  For someone who hasn't run through this
>once before, it's more confusing than helpful.
>  
>
That page is describing how to use the Motorola protocol (computer to 
Oncore, Oncore to computer) to set up the Oncore in Timing Mode.  It 
would be of more use to someone trying to write an Oncore driver than to 
someone setting up ntpd to use an Oncore as a reference clock.

>  
>
>>or if not, say if it is OK for somebody else to add it?
>>
>>Also see:
>>
>>http://ntp.isc.org/Support/ConfiguringMotorolaOncoreRefclocksDev
>>    
>>
>
>
>Well, it looks like there is some controversy whether the 
>PPS pulse really starts at the 'real' beginning of a 
>1 second epoch.  It's way above my head at this point.
>
>  
>
We had a long discussion on the topic here a few weeks ago.  The long 
and the short of it is that Motorola should have written a much better 
manual.  The chapter on how it all works leaves far too much room to 
read between the lines.  The leading edge of the PPS signal marks the 
exact "top of the second".  The receiver adjusts its measurement epoch 
to keep it within one millisecond of the top of the second..  There are 
facilities built into the Motorola command set to allow adjusting the 
"top of the second" for cable delays and other systematic errors.





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