[ntp:questions] Loop Filter Gains vs. Polling Interval

Mischanko, Edward T Edward.Mischanko at arcelormittal.com
Mon May 16 19:53:37 UTC 2011


Dave, 

How do I adjust the loop time constant so that it is shorter??

>> The integral component should be retained.  The effect of having too 
>> long a loop time constant should be that the system fails to track
clock 
>> wander, so would be more vulnerable to temperature changes or
forgetting 
>> to disable power management of clock frequency.

-----Original Message-----
On Behalf Of David Woolley
Sent: Monday, May 16, 2011 2:01 AM
To: questions at lists.ntp.org
Subject: Re: [ntp:questions] Loop Filter Gains vs. Polling Interval

Mischanko, Edward T wrote:
> Can anyone tell me, does the sensitivity for frequency adjustment
lessen
> as the polling interval increases?  I ask because I'm observing that
my

They are linked, but I have a feeling that the loop time constant is not

clamped, even though the poll interval is.  The aim is to always achieve

a certain level of oversampling.  At the very least, the intent is to 
vary the time constant and then choose a poll interval that is 
appropriate for that.

> offset increases and the frequency adjustment decreases to the point I
> fall out of sync at polling intervals above 256.  What am I doing
wrong?

The integral component should be retained.  The effect of having too 
long a loop time constant should be that the system fails to track clock

wander, so would be more vulnerable to temperature changes or forgetting

to disable power management of clock frequency.

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