Path: utzoo!attcan!uunet!ispi!jbayer
From: jbayer@ispi.UUCP (id for use with uunet/usenet)
Newsgroups: comp.unix.xenix
Subject: Re: Memory-mapped device IO
Summary: Memory mapped i/o
Message-ID: <155@ispi.UUCP>
Date: 7 Aug 88 16:10:41 GMT
References: <7816@cup.portal.com> <11650007@hpubvwa.HP.COM>
Organization: Intelligent Software Products, Inc.
Lines: 25

In article <11650007@hpubvwa.HP.COM>, jeffh@hpubvwa.HP.COM (Jeff Harrell) writes:
> Memory-mapped I/O is best implemented on the Motorola chips. INTEL
> didn't even get that right!
> 

Wrong, wrong, wrong.  This statement shows that you do not know what memory-
mapped I/O is.

This reminds me of an old debate I read in some computer magazine back
in the dark ages when people were still putting computer kits together.  I
saw the discussion when somebody boasted that their SWTP 6800 (South West
Technical Products) had memory mapped I/O and the IMSI 8080 did not.  The
same ignorance applies.

Memory mapped I/O is any I/O which accesses memory addresses instead of using
special instructions to access the device.  Taken to the extreme even access
to normal memory can be considered to be memory mapped I/O.  ANY COMPUTER WHICH
ACCESSES MEMORY CAN HAVE MEMORY MAPPED I/O.  Possibly Intel didn't get some-
thing right, but it wasn't memory-mapped I/O.  

Jonathan Bayer
Intelligent Software Products, Inc.
19 Virginia Ave.
Rockville Centre, NY   11570
uunet!ispi!jbayer