[time-nuts] Linux PPS clues?

[Ilia Platone]

Thank you.

I quickly read the gpsd howto and it explains what I want to do using 
kpps on a raspberry. From there I can see a typical accuracy of 1uS, but 
the informations of the live graphs page are precise down to the ns: are 
these averaged?

What do you intend for granularity? Consider that I'm a newbie in 
frequency/time specific terms.

Regards,
Ilia.



On 10/20/16 07:02, Gary E. Miller wrote:
> 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
>
>
> _______________________________________________
> time-nuts mailing list -- time-nuts at febo.com
> To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
> and follow the instructions there.

-- 
Ilia Platone
via Ferrara 54
47841
Cattolica (RN), Italy
Cell +39 349 1075999