From owner-freebsd-hardware  Sat Oct 31 21:02:47 1998
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To: Greg Lehey <grog@lemis.com>
cc: John Polstra <jdp@polstra.com>, hardware@FreeBSD.ORG
Subject: Re: Mixing 8- and 16-bit shared memory ISA cards 
In-reply-to: Your message of "Sun, 01 Nov 1998 15:25:39 +1030."
             <19981101152539.R28493@freebie.lemis.com> 
From: David Greenman <dg@root.com>
Reply-To: dg@root.com
Date: Sat, 31 Oct 1998 21:03:38 -0800
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>>    It affects all machines with ISA busses, not just early x86.
>
>What's the reason for it?

   Reason? Because it's PC hardware, that's why. :-) I think it has something
to do with timing of the top 8bits of (the 24bit) address decoding and when
the 8/16 bit select line is valid. The result is that the 8/16 bit selection
ends up being segmented into 128KB chunks. ...something like that.

-DG

David Greenman
Co-founder/Principal Architect, The FreeBSD Project

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