[time-nuts] Linux PPS clues?

[Gary E. Miller]

Yo Ilia!

On Thu, 20 Oct 2016 06:15:39 +0000
Ilia Platone <info at iliaplatone.com> wrote:

> I am trying to take some timestamps of events on a GPIO using an ARM 
> SBC, and noticed that the kernel linux can be interfaced to a PPS 
> signal, wanted to sync another GPIO to a GPS receiver for time 
> reference.

You should check out the gpsd time howto, and ntpsec.

http://www.catb.org/gpsd/gpsd-time-service-howto.html

https://www.ntpsec.org

> I need to know how much precise this system can be. How
> much resolution can I obtain with a cheap receiver (maximum
> quantization frequency)?

On average, on a RasPi 3, you can expect about

> Formulas are well accepted.


How about a graph, or two?  See attached.  From the histogram, I suspect the
granularity is about 200 nano sec.  From the offset graph you can
see how the offset jumps.

Here is the offset data on PPS v. the system clock:
    Percentiles......
    Min	        1% 	5%	50% 	95%	99% 	Max
    -21.645	-2.587	-0.834	-0.020 	0.991	0.991	13.557 µs

    Ranges...... 		
    90%	95% 	StdDev 	 	Mean	Units
    1.825	5.318	0.850	  	-0.006	µs

Or see a lot more live graphs here: https://pi4.rellim.com/day/


RGDS
GARY
---------------------------------------------------------------------------
Gary E. Miller Rellim 109 NW Wilmington Ave., Suite E, Bend, OR 97703
	gem at rellim.com  Tel:+1 541 382 8588
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