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SubjectRe: Why is double_fault serviced by a trap gate?
On Thu, 7 Dec 2000, Andi Kleen wrote:

> Interesting. One of my ports references for PCs lists
> 0044 r/w PIT counter 3 (PS/2, EISA)
> used as fail-safe timer. generates an NMI on time out.
> for user generated NMI see at 0462.

Oh no, we don't use that. Even though we could, it's rare -- it exists
for EISA systems only and then mostly older ones (i.e. non-PCI ones).

In fact the only chipset that provides these additional NMI sources I
have docs for is the i82350 one.

> I don't know if modern PCs still provide this counter, but if yes it could
> be used for a slow NMI watchdog that only runs every 30s or so.

An ability to choose a NMI frequency, especially such a low one, would be
desirable but it is really inexistent for most IA32 systems.

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

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