Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP
Posting-Version: version B 2.10.2 9/5/84; site ism780c.UUCP
Path: utzoo!watmath!clyde!cbosgd!ukma!psuvm.bitnet!psuvax1!burdvax!sdcrdcf!ism780c!tim
From: tim@ism780c.UUCP (Tim Smith)
Newsgroups: net.micro.68k
Subject: Re: Use of high-order byte of addresses in 680x0 software
Message-ID: <151@ism780c.UUCP>
Date: Fri, 13-Dec-85 15:57:41 EST
Article-I.D.: ism780c.151
Posted: Fri Dec 13 15:57:41 1985
Date-Received: Sat, 14-Dec-85 23:20:28 EST
References: <310@amiga.UUCP> <39700008@ISM780B.UUCP> <349@amiga.amiga.UUCP> <307@l5.uucp> <608@calgary.UUCP> <3570@utah-cs.UUCP>
Reply-To: tim@ism780c.UUCP (Tim Smith)
Organization: Interactive Systems Corp., Santa Monica, CA
Lines: 21

[ Discussion is about using upper byte of an address to contain data]

Note that I am NOT advocating immoral use of the high byte.  I am just
curious...

In article <3570@utah-cs.UUCP> peterson@utah-cs.UUCP (John W Peterson) writes:
>Boy, did we get screwed two years later when the 010's came out.  It
>took YEARS to track down all of the places where the high order byte
>contained a tag when it was used as an address.  On the particular
>machines where this happened, it would only fail if a page fault
>actually occured - thus the bugs were not repeatable and very difficult
>to isolate.
>

I don't understand.  The 68010 still only has a 24 bit address bus, so
those bits shouldn't matter.  The page fault handler has to mask them
off before deciding what virtual address to page in, but that should
be an easy thing to do.  Where else does it not work on a 68010 but
work on a 68000?
--
Tim Smith       sdcrdcf!ism780c!tim || ima!ism780!tim || ihnp4!cithep!tim