[ntp:questions] Extracting ntpq like information programmatically
david at ex.djwhome.demon.invalid
Sat Mar 30 09:55:41 UTC 2013
Mischanko, Edward T wrote:
> What can be done with ntpd's code to address the lack of speed in ramping
> down the time constant as needed to keep up with changes in the local clock?
The problem is that it only sees the effects and doesn't know the cause.
To really speed it up, you would need to, for example, monitor the
temperature near the crystal, and reduce the time constant if there was
a sudden change. However, if you had that parameter, you could also
compute a temperature compensation for the frequency and therefore do an
open loop correction.
The basic question is, given only the history of the offsets, how do you
distinguish between a slowly increasing measurement error and a slowly
increasing error in the local clock time.
I think the linear regression based systems respond faster because they
only use a finite amount of history. I'm a bit wary, though of calling
this a distinction between IIR and FIR systems, as I suspect there are
IIR elements in the local clock state even in the linear regression
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