RaspbPi HOWTO

[Gary E. Miller]

Yo Mike!

On Wed, 4 May 2016 08:58:48 -0400
Mike <bellyacres at gmail.com> wrote:

> > As the pps-gpio module is in April 2016 it has a flaw. It catches
> > only one edge of the PPS. You have a 50/50 chance you are seeing the
> > trailing edge rather than the leading edge (which is the actual top
> > of second).  A patch to fix this has been submitted to the Linux
> > kernel maintainers but not merged.  
> I've tried to figure out just how one determines exactly which edge
> is being seen.
> I'm at a loss on this one with software.  Using ppstest shows me 
> atypical output

Yup, beacuse the kernel module is broken and you only see one edge.
There is a patch to fix it, but we can't get it upstreamed.

> from nearly every example I'm seen online.  What is the definetive
> way to determine this?

Best, use an oscilloscope.  Good enough, is get a USB GPS with PPS and
compare the two PPS edges.

> The GPS device I'm using isn't a hat.  In the past I've had it
> working with gpsd and ntp classic.  I haven't a clue which edge is
> actually being seen though.

ppstest tells you which edges you are, or are not, seeing.

RGDS
GARY
---------------------------------------------------------------------------
Gary E. Miller Rellim 109 NW Wilmington Ave., Suite E, Bend, OR 97703
	gem at rellim.com  Tel:+1 541 382 8588
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