Path: utzoo!attcan!uunet!cbmvax!daveh
From: daveh@cbmvax.commodore.com (Dave Haynie)
Newsgroups: comp.sys.amiga.tech
Subject: Re: MC68881/2 Support (hello, Dave Haynie)
Message-ID: <12390@cbmvax.commodore.com>
Date: 7 Jun 90 17:19:17 GMT
References: <1181@metaphor.Metaphor.COM> <11996@cbmvax.commodore.com> <664.266d2e99@waikato.ac.nz>
Reply-To: daveh@cbmvax (Dave Haynie)
Organization: Commodore, West Chester, PA
Lines: 42

In article <664.266d2e99@waikato.ac.nz> hamish@waikato.ac.nz writes:
>In article <11996@cbmvax.commodore.com>, valentin@cbmvax.commodore.com (Valentin Pepelea) writes:

>> The 68040 does not have a floating point coprocessor, nor the coprocessor
>> interface of the 68020 & 68030. 

>The 68040 DOES have a floating point coprocessor. 

You're arguing trivia here, for the most part.  The 68040 doesn't have a 
floating point coprocessor, at least in the traditional sense.  It does that
idea one better by having an internal floating point execution unit which is
a first class processing unit with some of it's own buses and everything.  That
makes it much faster than a coprocessor, which is an external device that sits
next to an integer processor and generally relies on that processor's integer
unit to feed it instructions and data via some special protocol.  All of which
makes things slower.

From the programmer's point of view, though, you have the better part of a 
68882 in the 68040, assuming the factor of 10 or so increase on hardwared
instructions doesn't present a problem.  With an F-line math package to 
cover the missing 68882 codes, you wouldn't know any difference other than
speed.  But in truth, there is no coprocessor.

>Compare this to the 68030. Are you going to say that it doesn't have an MMU,
>even though its in the same boat? ie subset of 68851, on same piece of silicon.

Valentin was saying it didn't have a floating point coprocessor, not that it
didn't have a floating point unit.  The 68851 connected to the 68020 uses the
coprocessor protocol to manage it's registers and all, while the 68030 does
this all internally, without dropping though the coprocessor protocol.  So
I would say the 68030 has an MMU, but I wouldn't say the 68030 has an MMU
coprocessor.

Like I said, trivia.

>> Valentin

>|  Hamish Marson                        |  Internet  hamish@waikato.ac.nz    |
-- 
Dave Haynie Commodore-Amiga (Amiga 3000) "The Crew That Never Rests"
   {uunet|pyramid|rutgers}!cbmvax!daveh      PLINK: hazy     BIX: hazy
	"I have been given the freedom to do as I see fit" -REM