[Top][All Lists]

[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

Re: [gpsd-dev] Meaning of negative PPS offset?

From: Gary E. Miller
Subject: Re: [gpsd-dev] Meaning of negative PPS offset?
Date: Tue, 26 Aug 2014 13:21:53 -0700

Yo Greg!

On Tue, 26 Aug 2014 15:52:46 -0400
Greg Troxel <address@hidden> wrote:

> "Gary E. Miller" <address@hidden> writes:
> >> which is I think what you are saying.   So the bug is that in
> >> cases we are saying.
> >> 
> >>    n - N = -40ms
> >
> > Which makes no sense.  The NMEA at time X never preceeds the PPS
> > for time X.
> As I understand it, this discussion is happening because of a device
> which is sending NMEA in advance of the PPS edge.

I finally got that far back in my email.  The GR-601W, which has a known
kernel driver glitch.  It should be special cased as it is kernel driver
specific.  No other known USB device, of any driver, support PPS.

> >>  Or perhaps even to only capture PPS when it's within 200 ms
> >> of the system clock.
> >
> > Which fails for older and slower GPS.
> I meant system clock, not NMEA.

So did I.

>  So it would work when the device was
> synced via NTP coarsely.

Which was removed as a contraint with the latest patches.

> (I didn't quote most of your message, because I basically am in
> agreement with it - I knew my example times were not really quite
> right, but that they weren't critical to the point.)

Fair enough, except similar constants have been tried in the code
and failed, so best to be explicit they are WAGs.

> So the real issue is to find out if this device that seems to have
> premature NMEA really does do that.

GR-601W, which I have right here.

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

Attachment: signature.asc
Description: PGP signature

reply via email to

[Prev in Thread] Current Thread [Next in Thread]