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From: peterson@utah-cs.UUCP (John W Peterson)
Newsgroups: net.micro.68k
Subject: Re: Use of high-order byte of addresses in 680x0 software
Message-ID: <3570@utah-cs.UUCP>
Date: Wed, 11-Dec-85 14:55:43 EST
Article-I.D.: utah-cs.3570
Posted: Wed Dec 11 14:55:43 1985
Date-Received: Fri, 13-Dec-85 08:33:35 EST
References: <310@amiga.UUCP> <39700008@ISM780B.UUCP> <349@amiga.amiga.UUCP> <307@l5.uucp>, <608@calgary.UUCP>
Organization: Univ of Utah CS Dept
Lines: 10

When we originally implemented PSL (Portable Standard Lisp) on the
Apollo's, we too saw that 16M machine with the "nifty typed pointers".
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.

Moral - don't do it.