From: ewaniu@ee.ualberta.ca (Darren Ewaniuk)
Subject: Re: AA chipset in the A3000 -> I expect it!
Followup-To: comp.sys.amiga.advocacy
Organization: University Of Alberta, Edmonton Canada
Date: Thu, 3 Sep 1992 04:39:37 GMT

Mike_Noreen%cave@sweden.eu.net (Mike Noreen) writes:

>In a message dated Wed  1 Sep 92 16:18, Mks@cbmvax.commodore.com (michael S
>wrote:

> MS> Well, guys, it does not.  The Custom Chip accesses to CHIP RAM is 16-
> MS> bits.
> MS> The number of pins == 16-bits.  The controller (AGNUS) does not
> MS> handle
> MS> more nor does it do page mode.

Very true.  However, if you build your own memory, then you can make it as
wide as you want and control it how you want.  Since the custom chip set
behaves as bus master when accessing chip RAM, it doesn't matter what your
processor is when the custom chips are using chip RAM, as long as it is the
required bus size.  All the hardware designer has to do is provide the
interface for the processor to that 32-bit RAM.  You could even have
(internal) 32-bit burst mode ram on a 68000 system from the point of
view of the custom chip set, which is all that matters.  Sure, you may have
to access that RAM as two slow 16-bit fetches when accessing it from the
68000 CPU, but the custom chips see it as 32-bit and can use it as such.
The key is of course that you'd need NEW memory and would have to scrap
whatever you have on board, or at least find a way to use it other than
as chip RAM.

>Well yes offcourse the Agnus -being a 16-bit chip- accesses the chip RAM
>through a 16-bit bus. Nobody thought you could simply replace Agnus with
><whatever the new agnus might be called>.
>But since the CPU has 32-bit access to chip-ram, would it not be possible
>to put the AA-chips on a board in the CPU-slot?

32-bit processor access to that RAM is irrelevant.  RAM accessed 32 bits
at a time by the chip bus itself is what's relevant.  You could build
it onto a 16-bit bus, say even a Zorro II card theoretically.

>And let the old Agnus et al
>become redundant?

This is the tough part.
You forget how dependant the Amiga is on the custom chip set.  Not only
does Paula handle sound, she also handles interrupts, the floppy drive,
and the serial port.  Put a replacement in, and you have to pull out Paula
and put in a massive jumper from the new board to where she was.  Denise?
She handles the joystick ports in addition to the video.  Another jumper.
Agnus?  She can get scrapped and get put on the new board.  Add more
chip RAM?  Gary's got to be notified of this and get replaced and moved
to your new board.  Since he handles floppies too, here comes another jumper.
Of course, if chip RAM gets bigger than 16 bits, then you scrap that off
the motherboard too.  And then for sure every custom chip will have to
be pulled off the motherboard and replaced, even ones which didn't change,
because you'd have to put them on a new chip bus.
What have you got?  A BIG mess.  Nothing that Commodore will touch.
It's better off to replace the whole motherboard than try to upgrade the
chipset this far.

>I'm merely speculating, and you are offcourse in a much better position to
>know than I, but it could be done, couldn't it?

Anybody in the position to know couldn't tell you.
-- 
    //  /|      O  __       __  Amiga C=   Darren Ewaniuk               
\\ //  /_| |\/| | |   |  | |__  Users of   ewaniu@ee.ualberta.ca   -or-
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Newsgroups: comp.sys.amiga.misc