[ntp:questions] Extracting ntpq like information programmatically

David Woolley 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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