Path: utzoo!attcan!uunet!husc6!cmcl2!nrl-cmf!ames!pasteur!ucbvax!trwind.ind.trw.COM!karl
From: karl@trwind.ind.trw.COM (Karl Auerbach)
Newsgroups: comp.protocols.tcp-ip.ibmpc
Subject: Re: Western Digital board
Message-ID: <8805111451.AA21000@trwind.ind.TRW.COM>
Date: 11 May 88 14:51:44 GMT
Sender: daemon@ucbvax.BERKELEY.EDU
Organization: The Internet
Lines: 21

One thing to watch out for with shared memory boards -- a number of
AT clones do not honor the I/O CH RDY line on the bus.  This signal
is used by the memory to hold-off the processor for a little while.
This is typically necessary when the on-board hardware is using its
port into the shared memory.  The consequence of not honoring I/O CH RDY
is that the AT processor can pick up bad data because it fails to
wait when told to do so.

To build a shared memory board that does not have sensitivity to 
machines with this "feature" requires that the shared memory be
essentially zero wait, which is increasingly difficult as machines
get faster and faster and as LAN controller chips become more like
I/O channels.  Zero wait tends to imply that the raw memory speed
is enough to satisfy both the LAN controller and the PC procesor
simultaneously -- in other words we're talking about expensive,
probably static, memory.

~I hope the folks who clone micro-channels do a better job than those
who built clone AT buses.

				--karl--