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From: daveh@cbmvax.commodore.com (Dave Haynie)
Newsgroups: comp.sys.amiga.hardware,comp.sys.amiga
Subject: Re: Is 9 megs + AT Bridgeboard possible?
Keywords: A2286, 1-meg Agnus, 8-meg RAM, C00000
Message-ID: <9663@cbmvax.commodore.com>
Date: 13 Feb 90 22:12:09 GMT
References: <931@tardis.Tymnet.COM>
Reply-To: daveh@cbmvax.cbm.commodore.com (Dave Haynie)
Followup-To: comp.sys.amiga.hardware
Organization: Commodore, West Chester, PA
Lines: 36

In article <931@tardis.Tymnet.COM> jms@tardis.Tymnet.COM (Joe Smith) writes:
>A question for Dave Haynie or other hardware types at CATS.

>Now that I have installed the 1-meg Agnus, nothing is using the address
>range at $C00000.  Does the design of the BridgeBoard allow the shared
>memory to appear at other than the auto-config range?  In particular,
>is it possible to have 1-meg of CHIP RAM, 8-megs of fast RAM, and run
>the BridgeBoard at $C00000, all at the same time?

No, the Bridge Board memory will always be autoconfigured.  It is impossible
to reliably locate any expansion card at $00C00000, because even if you were
to hack it to do so physically, the OVR* signal you'd also have to hack isn't
fast enough from the expansion bus on an A2000 to cause the extra memory to
overlay the $00C00000 memory.  And that overlaying feature won't even be there
in the future.

Second thing is, only 128K of Bridge Board memory is shared between the Bridge
and the Amiga Bus, so you'd be wasting a great deal of effort for only a little
extra memory.

>Is it feasable to change the address decode logic on the A2286 if it does
>not support this?

You'd have to hack the configuration latch on the A2286 to force the "C0" address.
Then cut away the SLAVE* signal, so the card wouldn't register a bus collision
($00C00000 space is reserved motherboard space, not expansion bus space).  The
memory couldn't be DMAed to, since the system would expect it to be on the
motherboard and turn on the bus buffers at the wrong time.  And it wouldn't
work on the A3000.  I'd recommend against it.

>Joe Smith (408)922-6220 | SMTP: jms@tardis.tymnet.com or jms@gemini.tymnet.com

-- 
Dave Haynie Commodore-Amiga (Systems Engineering) "The Crew That Never Rests"
   {uunet|pyramid|rutgers}!cbmvax!daveh      PLINK: hazy     BIX: hazy
                    Too much of everything is just enough