Hello everyone, Is there a run-time parameter in NTP that defines the maximum rate at which the clock can be adjusted (slewed?).
Is there a run-time parameter in NTP that defines the maximum rate at which the previous parameter can change? Here's why I ask: I'm working with a standard that deals with 27 MHz clocks, and that standard states that the frequency must not change faster than 75 mHz per second. I'll try and think aloud, in case someone can see through my confusion. Consider H : a 26,999,900 Hz clock. Thus H has an offset of 100 Hz = 3.7 ppm In other words, H "misses" 100 ticks every second. I'd have to add 100 / 27e6 = 3.7 µs every second to keep H from drifting away from the correct time. But I can't make that change all of a sudden, I can only change 0.075 Hz more (2.78 ns) every second. The 1st second, I'd add 2.78 ns. The 2nd second, I'd add 5.56 ns. The Nth second, I'd add 2.78*N ns. Until I reach 3.7 µs for N = 1333 Then I'd have to correct the amount H drifted while the adjustment slowly crept to the correct value. NB: my OS is Linux 2.6 http://www.ntp.org/ntpfaq/NTP-s-algo.htm#Q-CLOCK-DISCIPLINE http://www.die.net/doc/linux/man/man8/adjtimex.8.html # ntpq -p remote refid st t when poll reach delay offset jitter ======================================================================== *10.11.12.66 LOCAL(1) 13 u 24 32 377 0.123 0.004 0.003 # adjtimex -p mode: 0 offset: 3 frequency: 4483200 maxerror: 66258 esterror: 1 status: 1 time_constant: 5 precision: 1 tolerance: 33554432 tick: 10000 raw time: 1174319208s 988507us = 1174319208.988507 Apparently, the value of HZ has an influence on these values? Would I improve precision if I changed HZ from 100 to 250? Regards. _______________________________________________ questions mailing list [email protected] https://lists.ntp.isc.org/mailman/listinfo/questions
