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    SubjectRe: [PATCH 2.6.21-rt2] PowerPC: decrementer clockevent driver
    Hello, I wrote:

    >>>>>Yes, on some implementations there can be other conditions that
    >>>>>make a decrementer exception go away; there is no contradiction
    >>>>>here (thankfully). My wording was sloppy.

    >>>>Some CPUs have the DEC exceptions basically edge triggered (yeah I know

    >>>for example?

    >>>>it sucks). That's why, among others, the IRQ soft-disable code has code
    >>>>to re-trigger DEC exceptions ASAP (by setting it to 1.. note that we
    >>>>could probably use 0 here, we've been a bit conservative).

    > Yeah, the classic decrementer is programmed off-by-one.

    >>I'm not 100% certain... Paulus thinks all the old 6xx are like that, and
    >>maybe POWER4. If I look at the oldest BookIV I can find (the 601), it

    > From the "PowerPC Operating Environment Architecture" that I've already
    > quoated t follows that POWER4-compatible decremented exception *must* be edge
    > triggered.

    ... and cleared when delivered.

    >>says that an exception is generated when the MSB transitions from 0 to
    >>1. It's not clear wether the exception sticks while that bit is 1 or is
    >>indeed considered as an "edge" event that gets cleared as soon as

    WBR, Sergei
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      Last update: 2007-05-18 15:49    [W:0.022 / U:7.384 seconds]
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