Re: [gpsd-dev] gpsd for time sync on Ubuntu remix too hard for normals - how to improve?

[Hal Murray]

address@hidden said:
> Time quality as you think about it does not matter here.  If we could sync to
> within 50 ms, that is completely good enough.  We are talking about lining up
> a ~13s transmission window and a 2s guard time with other stations.  People
> who set their computers manually to WWV can succeed. 

I assume the time accuracy determines how far the receiver has to search.  
Does that take a significant amount of CPU time?  Or do you just have to stay 
within the guard band?

If your target is 50 ms, I see two problems.

The first is that some old but popular receivers have 100 ms error band after 
you correct the offset.  Sample here:
  http://users.megapathdsl.net/~hmurray/ntp/GPSSiRF-off.gif
My model is that they have a 100 ms clock internally that drives the 
scheduler, or something like that.

The other is that the offset correction probably depends on the brand/model of 
GPS unit you are using.  More likely on the chip set behind the label.

At any rate, you setup recipe may need a setup section for each type of GPS 
unit and/or you may want a list of known-good units.

Things may get a lot easier of you can relax your goals to 100 ms.


-- 
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