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Re: [gpsd-dev] [Thumbgps-devel] PPS over USB

From: Gary E. Miller
Subject: Re: [gpsd-dev] [Thumbgps-devel] PPS over USB
Date: Wed, 2 May 2012 13:13:10 -0700

Yo tz!

On Wed, 2 May 2012 07:09:09 -0400
tz <address@hidden> wrote:

> SkyTraq has a different version of the 638 (not just different
> firmware) that emits corrections to the pps edge to go to 10nS, and
> after a lock it will work down to 1 satellite and maintain accurate
> pps.

Got a model #?

> I don't know of any others that retain pps if they don't have a 3d
> lock.

The Garmin GPS 18 spec says:

"The accuracy of the one-pulse-per-second output is maintained only
while the GPS receiver is computing a valid position fix. "

I always took taht to mean 2D mode was good enough, but I see how 3D
mode would be more accurate timewise.

Looking for that check in the gpsd code, I do not see it in the PPS path
or in the NMEA path.  I wonder when that disappeared?  That may explain
some things...  I'll go add that back in now.

Gary E. Miller Rellim 109 NW Wilmington Ave., Suite E, Bend, OR 97701
        address@hidden  Tel:+1(541)382-8588

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