quoted

quoted

+     * 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...

quoted

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