Re: [gpsd-users] Disable or restart PPS in gpsd?

[Gary E. Miller]

Yo Alexander!

On Wed, 03 Sep 2014 12:59:41 -0700
Alexander Carver <address@hidden> wrote:

> > Just do not expect any patches on such an old gpsd.
> 
> Of course not.  As I said I can compile a new version which is fine by
> me, I just can't go up on the kernel right now since a newer image is
> not available in the stable branch.  I may at a later time investigate
> the backports which I understand may potentially be up to 3.14.

I do not think there is anything in newer kernels to affect this.

> > Sounds like you just want KPPS off in gpsd.  So just compile it
> > without pps support.
> 
> If I disable KPPS in gpsd will it still create the pps0 device or will
> it skip that part?

Creating pps0 is how KPPS works.  No KPPS, then no pps0 from gpsd.

> If it skips that, how do I share the port with
> ldattach and gpsd?

gpsd never uses ldattach.  Port sharing of a GPS is problematic as 
autobaud and auto configure will get confused between two GPS clients.

Just have ntpd read the GPS by way of gpsd.

> > What sort of jitter difference are you seeing?
> 
> Jitter using the PPS ATOM driver is nominally 6 microseconds.  Jitter
> using SHM(1) from gpsd is up to 5 milliseconds.  So about 1000 times
> worse.  And this assumes that KPPS doesn't go belly up for some
> reason.

Something wrong with your setup then.  No way gpsd adds 1000x jitter.
I routinely see around 1 microSec using gpsd and SHM().  Even better
with chronyd.


> Right now, SHM(0) isn't even reporting, gpsd is spewing KPPS errors,
> but ntpd's ATOM is happily ticking away with 1 microsecond jitter and
> less than 5 microseconds offset.

Likely because only one can use the port at a time.

>  I used another one of my machines
> as a second preferred peer for seconds counting which is why ATOM is
> still running even though SHM(0) is dead.  SHM(1) does not work at
> all if ntpd's ATOM is configured and when I only use SHM(0,1) with no
> ATOM, SHM(1) shows the bad jitter compared to ATOM's jitter.

You gotta pick ntpd or gpsd to run the GPS.  You can't share and get
good timing.

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