[ntp:questions] SIRF time output wobble, GPS or NTP fault?

Ron Frazier (NTP) timekeepingntplist at c3energy.com
Thu Mar 8 18:57:43 UTC 2012


On 3/8/2012 11:58 AM, David J Taylor wrote:
> "Ron Frazier (NTP)" <timekeepingntplist at c3energy.com> wrote in message 
> news:4F58DFB2.3060009 at c3energy.com...
>> Hi David,
>>
>> I would look at the file, but I'm running Windows at the moment, and 
>> I can't figure out how to extract a .tar.gz file from here.  Can you 
>> email me the C file?  I have about 15 things going on with the PC 
>> right now and I don't want to reboot into Linux.  I could possibly do 
>> that later if I need to.
>>
>> Sincerely,
>>
>> Ron
>
> Will do.
>
> Cheers,
> David
>


Thanks David.  I got the C file and looked at it.  I can see what you 
mean.  They are doing validity checks on GPRMC, GPGLL, GPGGA, and GPZDG, 
but not GPZDA.  I'm not very knowledgeable on C, but can usually read 
the basic meaning of code.  This is a bit harder to figure out than I 
thought.  I may have to spend more time later on it.  I don't know what 
they're doing with the validity check, but I presume a failure would 
force the system to seek another clock, if one is available.  I'm going 
back to GPGGA for testing.  I'm pretty sure this will increase the 
jitter in the NMEA stream.  So, that presents me with an interesting 
dilemma.  Have low jitter data with no validity check when GPS is 
working, or higher jitter data with a validity check in case GPS fails.  
Interesting paradox.

I cannot figure out how to make this GPS output GPZDG.

Psychologically speaking, with this particular equipment, being under + 
/ - 10 ms sounds really cool.

Sincerely,

Ron


-- 

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Ron Frazier
timekeepingdude AT c3energy.com



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