David,
Something like this was done in NTPv3 (xntpd) and it turned out to be a
bad idea. The poll interval is determined by the time constant, which
for PPS and other low-stratum sources is relatively small. If a backup
is switched in at a poll interval much larger than this, it takes awhile
for the time constant and backup poll interval to stabilize and
meanwhile the Nyquist limit is exceeded. In NTPv3 this sometimes
resulted in an evil twitch until things calmed down.
It gets worse in the general case where sources of unequal stratum are
configured. The algorithms can result in more than one stratum survivor
is present and the combine algorithm uses them all. They must all run
the same poll interval or evil twitches can result. All in all, to do
what you suggest requires an intricate evaluation of what already is a
complicated and fragile algorithm, so this might not happen soon.
Dave
Thanks, Dave. It's a pity it can't work easily, but (for me) it's not a
show stopper, as I have four GPS/PPS sources here.
73,
David
_______________________________________________
questions mailing list
[email protected]
http://lists.ntp.org/listinfo/questions
