Path: utzoo!utgpu!news-server.csri.toronto.edu!cs.utexas.edu!uunet!cbmvax!daveh
From: daveh@cbmvax.commodore.com (Dave Haynie)
Newsgroups: comp.sys.amiga.hardware
Subject: Re: Concurrent operation of A2620 with 68k
Message-ID: <17075@cbmvax.commodore.com>
Date: 3 Jan 91 18:30:29 GMT
References: <3528@bruce.cs.monash.OZ.AU>
Reply-To: daveh@cbmvax.commodore.com (Dave Haynie)
Distribution: comp
Organization: Commodore, West Chester, PA
Lines: 35

In article <3528@bruce.cs.monash.OZ.AU> zik@bruce.cs.monash.OZ.AU (Michael Saleeba) writes:
>What I'd
>really like is to be able to run AmigaOS on the 68000, but set the 68020
>running also. My approach would be to run my new OS in the 4Mb of 32 bit RAM 
>local to the A2620, and try to communicate with the 68k using message
>passing and semaphores.

[...]

>Sounds neat, but will it work? What I'd really like is for someone to tell
>me that all I need to do to set both processors running concurrently is
>to manipulate autoconfig device x or location y. 

Unfortunately, that won't work, at least not without hacking the A2620.  The
A2620 grabs the A2000 bus when the machine first powers up.  If you select 
68000 mode via the A2620 ROM menu, what really happens is that a bit in a
special configuration register gets set.  This bit gets the 68020 out of the
way by forcing the whole A2620 board into reset.  It certainly could have been
done in a way that would have allowed both CPUs to run at once.  However, the
guy who was originally working on the A2620 never considered that, or never
considered it useful.  When I took over, I put in the "get the 68000 back"
mechanism, but it was too late in the project to go mucking much with the 
design.  We were far more concerned with making the A2620 work, period, than
adding any features.  It just turned out that the 68000 mode, the way I did
it, was practically for free, and took only a few minutes to come up with.

> Michael Saleeba - sortof postgraduate student - Monash University - Australia
>    "Why is it that the people who like fast computers also like fast cars?"

And coffee.  Speed is addictive, in its many forms...
-- 
Dave Haynie Commodore-Amiga (Amiga 3000) "The Crew That Never Rests"
   {uunet|pyramid|rutgers}!cbmvax!daveh      PLINK: hazy     BIX: hazy
	"Don't worry, 'bout a thing. 'Cause every little thing, 
	 gonna be alright"		-Bob Marley