>>> In article <[EMAIL PROTECTED]>, Spoon <[EMAIL PROTECTED]> writes:
Spoon> Hello everyone, Is there a run-time parameter in NTP that defines the Spoon> maximum rate at which the clock can be adjusted (slewed?). There is probably a "tinker" variable to do this. Be amazingly careful when messing with these. But I don't think you will need to - see below. Spoon> Here's why I ask: Spoon> I'm working with a standard that deals with 27 MHz clocks, and that Spoon> standard states that the frequency must not change faster than 75 mHz Spoon> per second. If ntpd has the correct drift adjustment, you should be in good shape. Under what exact conditions must the "don't change faster than 75mHz/sec" be met? Spoon> I'll try and think aloud, in case someone can see through my Spoon> confusion. Spoon> Consider H : a 26,999,900 Hz clock. Spoon> Thus H has an offset of 100 Hz = 3.7 ppm Spoon> In other words, H "misses" 100 ticks every second. If left uncorrected, yes. Spoon> I'd have to add 100 / 27e6 = 3.7 µs every second to keep H from Spoon> drifting away from the correct time. Once ntpd has achieved "state 4", ntpd will calculate the drift and will automatically handle this. Spoon> But I can't make that change all of a sudden, I can only change 0.075 Spoon> Hz more (2.78 ns) every second. ntpd will apply the correction on a per-tick basis, not all at once, once a second. Are you comfortable that the specs of the machines you are using will keep time well enough that their clocks can be kept in-sync by limiting adjustment to 75mHz/sec? Spoon> Would I improve precision if I changed HZ from 100 to 250? Exactly what do you mean by "precision"? Have you seen http://ntp.isc.org/Support/NTPRelatedDefinitions ? And have you read about the problems you can cause by having HZ at a value other than 100? Particularly with Linux kernels? H _______________________________________________ questions mailing list [email protected] https://lists.ntp.isc.org/mailman/listinfo/questions
