quoted

quoted

I do the check there because I was having problems where, if the HDEC
goes negative before we do the partition switch, we would 
occasionally
not get the HDEC interrupt at all until the next time HDEC went
negative, ~ 8.4 seconds later.

Yikes - so HDEC is edge and doesn't even keep the interrupt line up?
That sounds like a serious hardware limitation. What if you only use
HDEC and it triggers while interrupts are off in a critical section?
Is the hardware really that broken?

If HDEC expires when interrupts are off, the HDEC interrupt stays
pending until interrupts get re-enabled.  I'm not sure exactly what
the conditions are that cause an HDEC interrupt to get lost, but they
seem to involve at least a partition switch.

On some CPUs, if the top bit of the decrementer is 0 again when you 
re-enable
the interrupt, the interrupt is lost (so it is actually 
level-triggered).
The arch books talk a bit about this AFAIR.


Segher