Achim Gratz <strom...@nexgo.de>:
> > Therefore I *deduce* that the PLL correction (the one NTP does, not
> > the in-kernel one Hal tells us is associated with PPS) requires a
> > monotonically increasing clock. It's the simplest explanation for the
> > way libntp/systime.c works, and it explains *everything* that has puzzled
> > me about that code.
>
> The thing the PLL (more specifically the loop filter) should care about
> is that the error estimate it makes is unbiased and has a (relatively)
> white spectrum. That's exactly what doesn't happen when you have a
> clock that jumps and you try to read it several times inbetween those
> jumps.
Is "unbiased and has a (relatively) white spectrum" equivalent to
looking like symmetrical digital white noise around actual UTC, if you
knew what it was?
(I'm asking this question because my inituitions about analog-level
signal processing are still weak.)
--
<a href="http://www.catb.org/~esr/";>Eric S. Raymond</a>
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