Subject: Re: I/O maps and user-level device drivers
To: John Kohl <email@example.com>
From: Brett Lymn <firstname.lastname@example.org.AU>
Date: 12/12/1995 16:35:28
According to John Kohl:
>This is incorrect; my reference  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!!!!
> Nelson, Ross. Microsoft's 80386/80486 Programming Guide, 2nd
>Edition. Microsoft Press, Redmond, WA, 1991.
Brett Lymn, Computer Systems Administrator, AWA Defence Industries
"Upgrading your memory gives you MORE RAM!" - ad in MacWAREHOUSE catalogue.