[time-nuts] Noob question, NTP stratum 1.

[Achim Gratz]

Achim Gratz writes:
> [I can post plots, but at ~500kiB I think I should rather ask for
> permission first.]

Permission granted, so here it is, data is for the last week plus today.

Keeping the CPU temp constant actually doesn't do much good, since the
crystal is at a lower temperature.  Lacking that measurement I use the
CPU load and a simple thermal resistance model to estimate the
environmental and crystal temperature.  The CPU temperature measurement
is also coarsely quantized (all data collection is triggered from the
PPS pulse), but it seems to be the result of some kind of delta-sigma
conversion, so it actually just needs a bit of filtering to come out
surprisingly detailed.

Note that the time values are asinh(t) scaled, which is a fancy way of
saying linear through zero and logarithmic elsewhere.

Measured CPU load and temperature (raw and filtered), modeled crystal
temperature and reconstructed environmental temperature:
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PPS statistics (raw and filtered, overlaid with temperature):
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NTP loop statistics:
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NTP frequency error vs. predicted frequency error:
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The spike two days ago was an update and the requisite reboot, the spike
yesterday was me putting another rasPi on top of the box this rasPi is
in and then putting an airgap inbetween the two, later the window was
open for the night.  This box does double duty as an ADS-B receiver, so
would pull around 30%?50% load on its own.


Regards,
Achim.
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