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SubjectRe: [PATCH 2.6.21-rt2] PowerPC: decrementer clockevent driver
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>>> +     * 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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