Re: [gpsd-dev] Port to QNX: PPS without SHM?

[Hal Murray]

address@hidden said:
> It's a Trimble Condor C2626. We are using a Diamond Systems Hercules III
> that has a built-in socket for this device.

I'm not familiar with that device.  I'd like to learn how good the serial 
port is for timing.

When you get things setup so that they are working well enough to collect 
data, please turn on loopstats and peerstats and collect data for a day or so.

The serial port on some GPS devices is really horrible for timing.  A fixed 
offset is not a problem.  That can be fixed with fudging.  The problem occurs 
if the offset isn't stable.  If it varies from sample to sample, that can be 
reduced by averaging over a collection of samples.  But if the offset changes 
over a timescale of hours, you can't correct by averaging and you can't pick 
a good fudge factor.

http://users.megapathdsl.net/~hmurray/ntp/GPSSiRF-off.gif



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