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


From: Gary E. Miller
Subject: Re: [gpsd-dev] PPS not showing in gpsmon/gpsd on RPi 3
Date: Sat, 23 Apr 2016 22:29:49 -0700

Yo Oliver!

On Sun, 24 Apr 2016 01:39:46 +0100
Oliver Jowett <address@hidden> wrote:

> > > Also note that you need _write_ access to the pps device, not just
> > > read.  
> >
> > Got a citation for that?
> >  
> 
> http://git.savannah.gnu.org/cgit/gpsd.git/tree/ppsthread.c#n266
> 
> I don't know that it is required, only that gpsd does try to open it
> read-write, which would explain Eric's permission error.


Then two issues:

1. why does it work for me on Pi2/Wheezy, but not Eric on Pi3/Jessie.

2. Is rw needed?

I see that on my Pi2 the /dev/pps0 is root:root 660, so openening
rw is not an issue for me.  But gpsd better be root at open() time.

address@hidden:~# ls -lrt /dev/pps*
crw-rw---- 1 root root 244, 0 Dec 31  1969 /dev/pps0

Looking at https://tools.ietf.org/html/rfc2783 I see why we need to write.

gpsd writes to /dev/pps0 to tell the pps driver what mode bits we want set.

See section 3.3 of the RFC.

RGDS
GARY
---------------------------------------------------------------------------
Gary E. Miller Rellim 109 NW Wilmington Ave., Suite E, Bend, OR 97703
        address@hidden  Tel:+1 541 382 8588

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