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    SubjectRe: [PATCH] i386: Selectable Frequency of the Timer Interrupt
    Date
    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).

    Cheers,
    COn
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