Subject: Re: I/O maps and user-level device drivers
To: John Kohl <jtk@kolvir.arlington.ma.us>
From: Brett Lymn <blymn@awadi.com.AU>
List: tech-kern
Date: 12/12/1995 16:35:28
According to John Kohl:
>
>This is incorrect; my reference [1] says that ports which have no bitmap
>position (i.e. their bit offset into the bitmap is beyond the end of
>the bitmap) are protected from access.
>
John is correct - I used the same reference as he but got the meaning
of the bit around the wrong way. Intel say that a 0 means you can use
the port and a 1 will cause an exception - I skipped that bit and
assumed it was the other way round, so when I got to the bit about a
short table behaving as if all the bits were set I took this to mean
all access was allowed whereas it _really_ means all access denied.
What can I say? DOH!!!!
>
>[1] Nelson, Ross. Microsoft's 80386/80486 Programming Guide, 2nd
>Edition. Microsoft Press, Redmond, WA, 1991.
>
--
Brett Lymn, Computer Systems Administrator, AWA Defence Industries
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