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    SubjectRe: [PATCH 2.6.21-rt2] PowerPC: decrementer clockevent driver
    Date
    >>> +     * We must write a positive value to the decrementer to clear
    >>> + * the interrupt on the IBM 970 CPU series. In periodic mode,
    >>> + * this happens when the decrementer gets reloaded later, but
    >>> + * in one-shot mode, we have to do it here since an event
    >>> handler
    >>> + * may skip loading the new value...
    >
    >> Nothing special about 970 here -- on *every* PowerPC,
    >> a decrementer exception exists as long as the high
    >> bit of the decrementer equals 1. BookE is different
    >> of course. Some other CPUs might deviate from the
    >> architecture as well.
    >
    > Quoting "PowerPC Operating Environment Architecture":

    <snip>

    > Otherwise, when the contents of DEC0 change, the exception effects of
    > the Decrementer become consistent with the new contents of the
    > Decrementer reasonably soon after the change.

    And that is guaranteed on all PowerPC as far as I can see.
    The main thing is that a decrementer exception won't go
    away until the high bit becomes 0.


    Segher

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