Path: utzoo!attcan!uunet!husc6!mailrus!ames!pasteur!ucbvax!decwrl!sgi!wdl1!bobw
From: bobw@wdl1.UUCP (Robert Lee Wilson Jr.)
Newsgroups: comp.arch
Subject: Re: Japanese 32-bit micro can be a 68020 or 80386
Message-ID: <3490012@wdl1.UUCP>
Date: 24 May 88 18:20:32 GMT
References: <2006@sugar.UUCP>
Lines: 27

Presumably the new chip does at least something in a hard-wired way: Micro-
code can't take you all the way back to the big bang, and the PLA/ALU
don't generally talk directly to pins. The 8*86 and 68K
families are so different at bottom levels that it is hard to imagine any
PLA changes which could let the underlying hard wired stuff be even a
little efficient at both games. Either buffers are wired to make
big-endian or little-endian memory connections efficient, but not both.
Conceivably either microcode playing games with registers as they are
stored/loaded or else PLA paths could reconcile these differences, but it
seems likely to cost cycles (even for the PLA implementation) and either
a lot of your PLA or else lots of microcode space.

If the goal were a chip which, in one piece of silicon by reloading
microcode, could emulate either family, then maybe the performance
penalties would be offset by the versatility. When all you get is that the
same fundamental die can play both games, but two different pieces of
silicon are required, that level of versatility is lost.

This sounds like it might be a neat legal move around Intel's holding the
386 so closely, which might work for a while and even have advantages to
those of us who are Intel customers, but it hardly sounds like it has more
technical advantages!

Bob Wilson

(I'm not allowed to have opinions, much less to claim they represent my
employer!)