[time-nuts] Linux PPS clues?
Ilia Platone
info at iliaplatone.com
Thu Oct 20 03:52:10 EDT 2016
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
>
>
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--
Ilia Platone
via Ferrara 54
47841
Cattolica (RN), Italy
Cell +39 349 1075999
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