[ntp:questions] systems won't synchronize no matter what

David J Taylor david-taylor at blueyonder.co.uk.invalid
Sat Oct 30 17:18:01 UTC 2010


> Because it's not a bug.  There are different ways of controlling clock 
> adjustments (Phase Locked Loop vs Frequency Locked Loop), and the 
> FreeBSD kernel will switch between them depending on how often adjtime() 
> is being invoked.  The only real issue is that logging about it can be 
> annoying, but I think newer versions of ntpd have changed the log level 
> to only display the message if debugging is enabled.  See:
>
>  https://support.ntp.org/bugs/show_bug.cgi?id=452
>
>  http://www.ece.udel.edu/~mills/database/papers/nano/nano.pdf
>
> "In operation, PLL mode is preferred at small update intervals and time 
> constants and FLL mode at large intervals and time constants. The 
> optimum crossover point between the PLL and FLL modes, as determined by 
> simulation and analysis, is the Allan intercept. As a compromise, the 
> PLL/FLL algorithm operates in PLL mode for update intervals of 256 s and 
> smaller and in FLL mode for intervals of 1024 s and larger. Between 256 
> s and 1024 s the mode is specified by the API. This behavior parallels 
> the NTP daemon behavior, except that in the latter the weight given the 
> FLL prediction is linearly interpolated from zero at 256 s to unity at 
> 1024 s."
>
> Regards,
> -- 
> -Chuck

Thanks, Chuck, you learn something every day!

Cheers,
David 




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