Path: utzoo!utgpu!water!watmath!clyde!bellcore!rutgers!mailrus!ames!vsi1!wyse!mips!mash
From: mash@mips.COM (John Mashey)
Newsgroups: comp.sys.m68k
Subject: Re: quad-aligning the 68020 stack
Keywords: 68020 stack longword alignment quad
Message-ID: <2759@winchester.mips.COM>
Date: 11 Aug 88 02:26:47 GMT
References: <2194@uhccux.uhcc.hawaii.edu> <4431@cbmvax.UUCP> <2727@winchester.mips.COM> <4434@cbmvax.UUCP>
Reply-To: mash@winchester.UUCP (John Mashey)
Organization: MIPS Computer Systems, Sunnyvale, CA
Lines: 30

In article <4434@cbmvax.UUCP> ford@kenobi.cts.com (Mike "Ford" Ditto) writes:
>In article <4431@cbmvax.UUCP> ditto@cbmvax.UUCP (That's me) wrote:
>>For real 32-bit 68020 systems, I am a firm believer in keeping all
>>stacks and structures longword aligned at all times.
>
>In article <2727@winchester.mips.COM> mash@winchester.UUCP (John Mashey) writes:
>>Right philosophy, but consider thinking further ahead to 64-bit objects,
>>at least.
> [ ... ]
>
>I don't see a real reason for this.  Admittedly, the older 68000 compilers
>that only aligned to 16 bits were a mistake, but that is because the 68000
>has a 32-bit archetecture.  I can't imagine an extention to the 68000
>archetecture that will have objects larger than 32 bits (other than floats)
>nor an object-code-compatible chip with a wider-than-32-bits data bus.
>64-bit chips and memories are certainly on their way to popularity, but
>they really don't have much affect on 680x0 performance decisions, or
>vice-versa.

No major disagreement, i.e., the main motivation was for the broadest
possible portability  (as I have no personal interest in improving
in the speed of 68K-based systems :-).  In some systems that
one might design with external caches, it might be a performance or cost
improvement if 64-bit things were usually on the correct boundaries.
(Very minor). 
-- 
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