Re: [PATCH 2.6.21-rt2] PowerPC: decrementer clockevent driver

[Segher Boessenkool <segher@kernel.crashing.org>]

> > > +     * 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

-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/