[ntp:questions] Running GPS under NTP

dhavey dhavey at gmail.com
Sun Dec 14 19:14:41 UTC 2008


On Dec 11, 9:03 pm, "David J Taylor" <david-tay... at blueyonder.neither-
this-part.nor-this-bit.co.uk> wrote:
> dhavey wrote:
>
> []
>
> > I am seeing 2000 - 4000 micro-second offsets from the serial port
> > experiments.
> > Here is a graph:
> >http://cs.ucsb.edu/~dhavey/gps/offset.pdf
>
> I wouldn't worry about a couple of milliseconds, but I am surprised by how
> much it seems to vary throughout the day - almost 3:1 from 1ms average at
> 30,000 seconds to 3ms average at 65,000 seconds - if I'm reading your
> graph correctly.  Caused by other activity on that PC?  Surely not by
> temperature?
>
> David


I was using libserial to send the serial data.  I think it may have
been doing some buffering.  I am using low level c functions now.  I'm
still seeing about 2000 usecs of offset but I don't know how much
variance I will see throughout the day yet because I just finished
writing it ;)
I'll post a graph tomorrow with the results for today.




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