Re: [chrony-users] Setting up Chrony with PPS

[Bill Unruh <unruh@xxxxxxxxxxxxxx>]

William G. Unruh   |  Canadian Institute for|     Tel: +1(604)822-3273
Physics&Astronomy  |     Advanced Research  |     Fax: +1(604)822-5324
UBC, Vancouver,BC  |   Program in Cosmology |     unruh@xxxxxxxxxxxxxx
Canada V6T 1Z1     |      and Gravity       |  www.theory.physics.ubc.ca/

On Thu, 18 Feb 2016, Deven Hickingbotham wrote:

> Rob,
>
> Thanks for replying.
>
> A little more info: my system is a Raspberry Pi 2 B.  I have been able to get 
> ntp to work with pps via GPIO pin 4.  Had to recompile ntp to activate the 
> pps support.
>
> Don't let the above fool you into thinking I know what I am doing.  I have 
> some level of expertise with programming, but system level Linux stuff is a 
> mystery to me.  IOW, real clear step by step instructions are greatly 
> appreciated!
>
> > If either module is being loaded, you should see a device (e.g. pps0) in
> > /sys/class/pps. If your GPS has a lock and the pps kernel module is
> > configured properly, you should see timestamps updating every second, e.g.
>
> Yes, the /sys/class/pps/pps0 path exists and contains these files: subsystem 
> (folder), assert, clear, dev, echo, mode, name, path, and uevent.
>
> > $cat /sys/class/pps/pps0/assert
> > 1455831692.018636856#178
> >
> > Are you seeing those?
>
> Yes, but just one timestamp per execution:
>
> pi@gps ~ $ cat /sys/class/pps/pps0/assert
> 1455835119.289108505#4272

Yes, as should be, assuming that it was about 33 sec between the one above and
below, and then about 3 sec. 
However I am worried that you are getting such differences in ms. What GPS
device are you using? Are you sure its PPS is working? Or is your computer
really that far off in its clock rate?


> pi@gps ~ $ cat /sys/class/pps/pps0/assert
> 1455835154.690359907#4305
> pi@gps ~ $ cat /sys/class/pps/pps0/assert
> 1455835157.936493770#4308
> pi@gps ~ $ cat /sys/class/pps/pps0/assert
> 1455835160.102904599#4310

Have a look at the clear line to see if it is more regular (the ms should be
more or less the same 
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