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Re: [gpsd-users] Support for PPS on 10Hz Devices

From: Gary E. Miller
Subject: Re: [gpsd-users] Support for PPS on 10Hz Devices
Date: Sun, 15 Sep 2013 21:17:38 -0700

Yo Andrew!

On Mon, 16 Sep 2013 08:53:26 +0800
Andrew Yong <address@hidden> wrote:

> Hi Anthony,
> > On 16 Sep, 2013, at 4:23 am, Anthony Stirk <address@hidden> wrote:
> > 
> > I might be out of turn here but isn't the PPS output still 1Hz
> > regardless of the NMEA output frequency ?
> Yep, the PPS still comes in at 1Hz, but for some reason GPSD doesn't
> pick it up.

How do you know it is coming if you can't see it?  What RS-232
pin is it coming in on?  Have you tried high debugging levels in 
gpsd to see hat gpsd is seeing?
> I recall seeing a patch to the code base to specifically support the
> Garmin 5Hz LVC. 

Yes, applied a long time ago and it ws working last time someone checked.

> Perhaps GPSD is overwhelmed with the 10Hz output, or just is
> expecting 1Hz NMEA?

NMEA is all over the map.  Even on a 5HZ GPS some sentences are only
output every 5 seconds, or less.  None of it applies to PPS.  All PPS
cares is that there is a good fix and the pulse is seen.

> > I did noticed when using the Adafruit module it seems to fire PPS
> > on both the rising and falling, i.e I was getting 2 pulse per
> > second. Switched it for a ublox which seems to work better (by
> > better I mean 1 pulse per second).

gpsd can handle a wide variety of 'PPS' inputs.  There are no reports
of anything out there it does not handle.
> I can customize the PPS pulse duration; it's set to 100ms by default.
> Should I get that decreased or increased for better compatibility
> with GPSD's PPS detection?

gpsd can handle everything from a pulse so small the UART does not see
both edges to a 2HZ square wave where each edge is on the second.  100
milli Sec is good because there is no ambiguity on which edge, but 1
milli Sec to 200 milli Sec would be equally good.  Just let it be.

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

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