Re: [chrony-dev] Frequency synchronization without phase

[Dan Drown <dan-ntp@xxxxxxxxx>]

Quoting Miroslav Lichvar <mlichvar@xxxxxxxxxx>:
> On Wed, Dec 28, 2016 at 05:57:15PM -0600, Dan Drown wrote:
> > That looks like this (green=Linux system's clock, purple=TCXO's measurement
> > of Linux system's clock).
> > https://dan.drown.org/odroid/run7/tcxo-acc-1024.png
> >
> > I've adjusted the starting offset to be within 50ppb, but the TCXO drifts
> > off and the difference widens to over 300ppb after 3 days.
>
> Would a high-pass filter help?

I suspect this TCXO drifting is actually a hardware problem, my TCXO  
is already out of spec at above 3.6ppm[1].  My current theory is I  
toasted it during assembly a soldering iron set too hot.  I'm having a  
pair of boards assembled by a place that has a proper reflow oven to  
see if that helps.

[1] https://dan.drown.org/odroid/latest/chan2.png

> > Here's how tempcomp.log vs tracking.log looks:
> > https://dan.drown.org/odroid/latest/tempcomp.png
>
> This looks awesome :).

I especially like this[2] graph, comparing frequency stability of  
tracking.log offsets: odroid (tempcomp enabled) vs BBB (normal).   
Odroid's initial point at 64s is 2e-9 (2ppb).

[2]https://dan.drown.org/odroid/latest/adev-bbb.png

> > Unrelated to tempcomp, I'm also trying out the new asymmetry code because
> > I'm on a recent git version.  I assume the offset value in statistics.log is
> > corrected for asymmetry while the offset value in measurements.log is not.
>
> Yes.
>
> > I've added the two offsets to my graphs:
> > https://dan.drown.org/odroid/run9/remote-statistics.96.126.122.39.png
> > https://dan.drown.org/odroid/run9/remote-statistics.216.239.35.0.png
> > https://dan.drown.org/odroid/run9/remote-statistics.216.239.35.4.png
>
> This looks pretty good to me. At this moment it nicely shows how
> updating the minimum measured delay shifts the offset line.
>
> The graphs don't show it anymore, but IIRC when I looked at it the
> first time one of the sources had the statistics offset overlapping
> the bottom offset-rtt/2 line and I was not sure how would that happen.
> It looked like the minimum measured delay was zero or maybe even
> negative, or it was shifted by the offset option. If you still have
> the old data, I'd be interested to see a separate graph of the delay.

I forgot that measurements.log offset had the opposite sign from  
statistics.log.  Correcting that in the graphs to show the same sign  
fixed that problem :)

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