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From: daveh@cbmvax.commodore.com (Dave Haynie)
Newsgroups: comp.sys.amiga.hardware,comp.sys.amiga
Subject: Re: 80386 BridgeBoard
Message-ID: <13775@cbmvax.commodore.com>
Date: 13 Aug 90 19:09:02 GMT
References: <1694@kirk.nmg.bu.oz>
Reply-To: daveh@cbmvax (Dave Haynie)
Organization: Commodore, West Chester, PA
Lines: 56

In article <1694@kirk.nmg.bu.oz> cameron@kirk.nmg.bu.oz (Cameron Stevenson) writes:

> Does anybody know if Commodore are working on an 80386 bridgeboard? 

That one I can't answer, but hypothetically, such a device is certainly 
possible.

> The main reason (at least this is what I was told) for not producing such
> a card was that the 2000 system could not keep up with the 80386. By this,
> I don't mean that the Amiga is slower than a '386 generally; just that
> software that is specifically written for the '386 would get tangled inside
> the Amiga because of the Janus software/bus speed/Amiga CPU speed.(As you
> appreciate from the tone of this explanation, I'm no hardware guru)

The only elements of a BridgeCard that are tied to the Amiga bus speed somewhat
are the BridgeCard video display and hard disk, when both of these are actually
on the Amiga system.  That's not as bad as it sounds, even with a reasonably
fast '386 running, since both display and disk on most PCs is pretty slow to
begin with.  It really depends on the problem you're interested in solving with
the BridgeCard.  Most PC software isn't all that display or disk bound, so most
software would run on such a card about as fast as on an equivalent standalone
'386.  Software that is display or disk bound would be noticably slower.

> Now with the 3000, I would expect these problems to be soluble (? able to
> be solved).

These problems certainly could be solved with an A3000-specific Bridge Card
(eg, a Zorro III device).  Some of the problems might be solved with a 
radically different Bridge Card design.  Most '386 PCs still run video and
disk at AT bus speeds, and the Zorro II bus is capable of similar speeds.  
Today's BridgeCards are slow because the 680x0 and 80x86 communicate via some
shared memory, not directly to each others' buses.  So to get a block of
data for the PC's hard disk driver, the PC sends a message via shared memory
to a disk server, PCDisk, in Amiga memory.  This task fetches a block to its
buffer (involving one DMA or CPU transfer, depending on the Amiga side disk
controller in place), then copies that into some of the BridgeCard's shared
memory.  The PC's hard disk driver then wakes up and copies this block into
PC main memory.  So you end up with several more copies than a PC would 
normally do, and to add to this, shared memory isn't all that fast.  Faster
shared memory or direct access by one CPU to the other's bus would speed up
this operation considerably.

> If I can slip the Amigas through the safety net as capable '386 machines
> (with another very good machine lurking inside the box for extra value),
> then the accountant types may be swayed. Any news?

No news, but I think that was one of the original drives behind the Bridge
Card -- it lets you get an Amiga when you really want one, but you or your
bean counters need some PC compatibility.

> Cameron Stephenson                      Telephone +61 75 951220

-- 
Dave Haynie Commodore-Amiga (Amiga 3000) "The Crew That Never Rests"
   {uunet|pyramid|rutgers}!cbmvax!daveh      PLINK: hazy     BIX: hazy
      Get that coffee outta my face, put a Margarita in its place!