David and others, The adaptive poll algorithm evolved over many years and many variations. A summary follows.
1. The poll will not be less than the maximum of the peer poll and minpoll. The maximum poll will not be greater than maxpoll. This is to protect the network. 2. The time constant will not be less than minpoll nor greater than maxpoll of the system peer. This is to allow the user to constrain the time constant for some purpose. Note that if the maxpoll is different as the system peer changes, some swish and sway must be expected. That's why the ACTS driver is disabled if other peers are active. 3. Subject to the above constraints, a jiggle counter increments by the value of the time constant when the current clock offset is less than twice the clock jitter and otherwise decrements by twice this value. If the jiggle counter exceeds +30, the time constant increments by one. If it falls below -30 it decrements by one and in both cases the jiggle counter is reset to zero. The design is intended to 1. Always poll at twice the Nyquist rate with any time constant. Serious audiophiles and DSP engineers will recognize the needfor this. 2. The poll value here is the exponent of two to yield the actual poll interval. This is chosen to match the Allan deviation characteristic which results in straight lines in log-log coordinates. 3. The time constant increases slowly to higher intervals and decreases quickly to lower intervals. 4. The time constant adapts more rapidly at higher polls and more slowly at the lower intervals. I hope this explains the behavior you report. Dave David Woolley wrote: > Mike K Smith wrote: > >> Looks like I should be reducing maxpoll. I guess the design of NTP is > > > As I understand it, the loop time constant determines the poll interval, > but the poll interval doesn't constrain the loop time constant, so > reducing maxpoll will not make the system significantly more responsive > to anything except a complete failure of a time source. > >> optimised for clocks with predictable drift rates, and a sudden >> variation in drift rate takes longer to correct. >> _______________________________________________ questions mailing list [email protected] https://lists.ntp.org/mailman/listinfo/questions
