Date: Sun, 1 Nov 1998 00:51:35 -0800 (PST) From: dan@math.berkeley.edu (Dan Strick) To: grog@lemis.com Cc: dan@math.berkeley.edu, dg@root.com, hardware@FreeBSD.ORG, jdp@polstra.com Subject: Re: Mixing 8- and 16-bit shared memory ISA cards Message-ID: <199811010851.AAA18074@math.berkeley.edu>
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> > It affects all machines with ISA busses, not just early x86. > > What's the reason for it? I don't remember the details, but I think one of the ISA signal lines is asserted by the ISA card to indicate if it wants to do 8 or 16 bit transfers. For some reason that I don't remember, all the devices in a single segment of the I/O space may simultaneously assert their preference/requirement when any one of them is queried. This is probably just a consequence of cheap bus design. Therefore you want all the cards in the same I/O space segment to use the same transfer width. I vaguely recall that the penalty for mixing types is that the 16 bit cards end up doing 8 bit bus transfers (i.e. slowly). Dan Strick dan@math.berkeley.edu To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-hardware" in the body of the message
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