On Tue, 12 Jul 2005 22:39, Con Kolivas wrote: > On Tue, 12 Jul 2005 22:10, Vojtech Pavlik wrote: > > The PIT crystal runs at 14.3181818 MHz (CGA dotclock, found on ISA, ...) > > and is divided by 12 to get PIT tick rate > > > > 14.3181818 MHz / 12 = 1193182 Hz > > > > The reality is that the crystal is usually off by 50-100 ppm from the > > standard value, depending on temperature. > > > > HZ ticks/jiffie 1 second error (ppm) > > --------------------------------------------------- > > 100 11932 1.000015238 15.2 > > 200 5966 1.000015238 15.2 > > 250 4773 1.000057143 57.1 > > 300 3977 0.999931429 -68.6 > > 333 3583 0.999964114 -35.9 > > 500 2386 0.999847619 -152.4 > > 1000 1193 0.999847619 -152.4 > > > > Some HZ values indeed fit the tick frequency better than others, up to > > 333 the error is lost in the physical error of the crystal, for 500 and > > 1000, it definitely is larger, and thus noticeable. > > > > Some (less round and nice) values of HZ would fit even better: > > > > HZ ticks/jiffie 1 second error (ppm) > > --------------------------------------------------- > > 82 14551 1.000000152 0.2 > > Most interesting... Would 838 Hz be a much better choice than 1000 then? > (apart from the ugliness). Duh I should have looked lower where you suggested 864, sorry. 864 1381 1.000001829 1.8 Cheers, Con
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