[time-nuts] Linux PPS clues?

[Chris Albertson]

On Thu, Oct 20, 2016 at 12:02 AM, Gary E. Miller <gem at rellim.com> wrote:

I think your graph only shows 1/2 of the problem.  It is the easy part
because all that code is written and likely already installed on the OP's
computer.

The other half of the problem is responding to events and getting them time
stamped with very low latency and jitter.   In other words the harder job
is actually putting to use that well sync's internal clock.    I think the
best way is to copy the design of the Linux PPS system.    Then assume the
error in time stamp is a little larger than double your graph.

But if the event time stamp code is not so well designed the results might
to 10X worse not just 2x worse.



> 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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-- 

Chris Albertson
Redondo Beach, California