Path: utzoo!utgpu!news-server.csri.toronto.edu!rpi!zaphod.mps.ohio-state.edu!wuarchive!uunet!cbmvax!daveh
From: daveh@cbmvax.commodore.com (Dave Haynie)
Newsgroups: comp.sys.amiga.hardware
Subject: Re: 68030+68040 on A3000: is it possible?
Message-ID: <21214@cbmvax.commodore.com>
Date: 3 May 91 14:22:34 GMT
References: <24561@well.sf.ca.us>
Reply-To: daveh@cbmvax.commodore.com (Dave Haynie)
Distribution: comp
Organization: Commodore, West Chester, PA
Lines: 33

In article <24561@well.sf.ca.us> cassiel@well.sf.ca.us (Paul Theodoropoulos) writes:

>   At the back of AmigaWorld's April '91 issue, in the section devoted
>to rumors, speculation, etc., there was an intrigueing idea proposed:
>Designing an 040 board that would allow the 030/882 to continue functioning,
>essentially as coprocessors to the 040. They stated that all that would be
>needed to implement this would be to "tweak" the system software so that
>it would recognize both chips were aboard.

That will certainly work, though implying software overhead is no more than
a "tweak" grossly oversimplifies the problem.  My guess is that, for the first
such systems anyone does this way, AmigaOS will run on the 68040, while the
68030 will be used as some kind of I/O processor or something, not actual
somewhat-symmetric multiprocessing.

>Unfortunately, as i understand it the Fast Slot on the A3000 motherboard
>is a bus master slot - it disables the 030. 

Yes and no.  The only way to allow a Coprocessor device to access motherboard
resources is for it to master the motherboard bus.  You can't have both
processors running a cycle at the same time on the bus, of course.  This
hardly means that the 68030 is disabled, it just gets kicked off the bus
when the coprocessor device wants the bus.  The 68040, for example, is normally
off its processor bus, requesting bus access when it wants to use the bus.
This meshes quite well with the 68030's habit of acting as a default bus
master.  Any time the coprocessor device is running from cache or any private
memory it has, the 68030 can run free.  This is very typical of tightly coupled
multiprocessor systems.

-- 
Dave Haynie Commodore-Amiga (Amiga 3000) "The Crew That Never Rests"
   {uunet|pyramid|rutgers}!cbmvax!daveh      PLINK: hazy     BIX: hazy
      "That's me in the corner, that's me in the spotlight" -R.E.M.