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SubjectRe: ioport range of 8259 aka pic1
On Tue, 6 Nov 2001, Randy.Dunlap wrote:

> The Intel chipset specs say that PIC1 uses:
> (all hex:) 20-21, 24-25, 28-29, 2c-2d, 30-31, 34-35, 38-39, 3c-3d.
> Some of the older chipset specs say that all of these other than
> 20-21 are just aliases of 20-21 (like the 440MX spec).
> Later specs don't say this (as in all of the 800-model ICH0/ICH2
> specs).

These are chipset implementation details (i.e. address decoder's
shortcomings) only. An 8259A only uses two I/O ports; in PC/AT systems,
these are 0x20, 0x21 and 0xa0, 0xa1 for the two PICs, respectively. Since
the 0x00-0xff range is assigned to motherboard devices, there is no
problem with leaving aliases free -- they are never used by Linux. You
still need to verify your extra devices are really present there.

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

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