Date: Sat, 31 Oct 1998 10:53:15 -0800 From: John Polstra <jdp@polstra.com> To: hardware@FreeBSD.ORG Subject: Mixing 8- and 16-bit shared memory ISA cards Message-ID: <199810311853.KAA22693@austin.polstra.com>
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I have a question for you old farts who still remember ISA. I'm
trying to turn an old 486 box into an ethernet <-> frame relay router.
It has a 16-bit SMC 8013 card with shared memory, and also an 8-bit
ET Inc. card with shared memory. I have this vague recollection that
you can run into problems with a mix like that in an ISA machine. In
particular, I seem to recall something along the lines that each 128K
chunk of the address space (a0000-bffff, c0000-dffff, e0000-fffff) has
to do either all 8-bit accesses or all 16-bit accesses, but not a mix
of the two.
Is that correct? Is it true for FreeBSD systems, or was it just an
MS-DOS thing? Is such a mix guaranteed not to work, or does it just
sometimes not work?
Also, is the address chunk e0000-effff generally available on ISA
486 systems (non-IBM)? I know it used to be reserved for the Basic
ROM on ancient IBM machines.
Finally, what about the range a0000-bffff that is generally used by
video cards? The docs for my card (an old 1 MB Orchid ProDesigner ISA
card) say that it uses that whole range. But I am only using it in
text mode with the syscons driver. Will it still take up that whole
address range in that case, or will part of the address space be free
for other cards?
John
--
John Polstra jdp@polstra.com
John D. Polstra & Co., Inc. Seattle, Washington USA
"Nobody ever went broke underestimating the taste of the American public."
-- H. L. Mencken
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