Re: [gpsd-users] Using gpio-based kernelpps with gpsd

[Gary E. Miller]

Yo Robert!

On Thu, 16 Jul 2015 16:35:37 +0000
Robert Calhoun <address@hidden> wrote:

> Thank you, Gary! Running gpsd itself works. It still tries first to
> find the time pulse on the serial port but then it takes the
> gpio-based pps passed as an arg:

If you look at the gpsd INSTALL doc you'll find how to associate the
/dev/ppsX directly with the serial port to save the extra effort.

> gpsd seemed happy with the kpps signal but I could not get chronyd to
> accept
> KPPS data via gpsd's SHM1 interface.

Hard to say what you did wrong as you do not say what your config was.
Did you follow the gpsd INSTALL and time service doc for you setup?

I suspect the nut of your problem was no folloinw the INSTALL and 
connecting the PPS to the serial port.  Or adjusting the sample config
since you failed to do so.

> I ended up using chronyd's build-in PPS driver, but the debug logging
> in gpsd was very helpful in verifying that I'd written the driver
> correctly. 

I suggest you do not do that.  A lot of GPS emit PPS when they have
an invalid time.  chronyd does not have the logic gpsd has for pps
fitlering.  Plus you lose a lot of the gpsd tools for monitoring
the PPS.

> # Here are the refclock configs from chrony.conf:
> refclock SHM 0 offset 0.0 delay 0.2 refid GPSD
> refclock PPS /dev/pps0 lock GPSD refid KPPS
> 
> 
> The end result:

> #* KPPS                          0   4   377     8  +4549ns[+7908ns]
> +/- 3666ns

4 uSec is about what I would expect on a RasPi, so that is good.

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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