Re: [PATCH] Re: UP APIC reenabling vs. cpu type detection o

From: Maciej W. Rozycki (
Date: Fri Feb 09 2001 - 07:06:53 EST

On Fri, 9 Feb 2001, Mikael Pettersson wrote:

> (I had a theory about inspecting the APIC_LVTPC "Delivery Status"
> field, but unfortunately it doesn't seem to get set if a counter
> overflowed while LVTPC was masked. Perhaps it's because NMIs are
> edge-triggered.)

 The delivery status bit gets only set if an interrupt got accepted (that
implies it was unmasked at the moment) but its delivery is held pending
due to some reason. It may happen when the target CPU has its interrupts
masked or the target local APIC cannot accept it due to a higher task
priority or no free slots. The semantics of the bit is the same for both
local and I/O APIC interrupts.

+  Maciej W. Rozycki, Technical University of Gdansk, Poland   +
+        e-mail:, PGP key available        +

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