Re: [gpsd-dev] PPS not showing in gpsmon/gpsd on RPi 3

[Oliver Jowett]

On 23 April 2016 at 16:43, Eric S. Raymond <address@hidden> wrote:

 

It's obvious why the TIOCMIWAIT isn't working.  What's unobvious is why KPPS
isn't.  The ppstest result seems to tell us that the RFC2783 interface is
up.  My conclusion is that the GPSD code is failing to use it correctly
because of something specific to Pi3/Jessie.

Sorry to be a bit vague here as I'm working from memory and it was a few months ago and I never properly worked through the details (once I worked out that PPS wasn't going to work with that hardware anyway, I shelved it), but FWIW..

IIRC I had some problems with the timing of when the PPS thread was started; in some cases it would happen after root had been dropped. I think there was a race between the pps thread opening the PPS device and the main thread dropping root.

Also note that you need _write_ access to the pps device, not just read.

Oliver