Path: utzoo!utgpu!jarvis.csri.toronto.edu!cs.utexas.edu!rutgers!bpa!cbmvax!daveh
From: daveh@cbmvax.commodore.com (Dave Haynie)
Newsgroups: comp.sys.amiga.hardware
Subject: Re: Our friends on the inside (of the Amiga, not Commodore)
Message-ID: <9852@cbmvax.commodore.com>
Date: 27 Feb 90 09:06:05 GMT
References: <12036@venera.isi.edu>
Reply-To: daveh@cbmvax.cbm.commodore.com (Dave Haynie)
Organization: Commodore, West Chester, PA
Lines: 54

In article <12036@venera.isi.edu> rod@venera.isi.edu (Rodney Doyle Van Meter III) writes:

>I know Agnus has something to do with the difference between chip and
>fast RAM. Chip is the only memory that can be displayed on the screen,
>is that right? What exactly does Agnus do?

Agnus in her current form is a memory controller and address generator
for everything that happens on the Chip bus.  She contains the blitter
and copper logic as well, and also creates all the video and chip clocks.

>Paula has something to do with controlling interrupts and devices?

Paula contains the logic for analog joysticks, the floppy disk data
separator, all four sound channels, and the interrupt mixer/control.

>Who are Gary and Denise, sprites and voice synthesis?

Denise does the actual video display, based on addresses generated
by Agnus.  She contains the color registers, CLUT with HAM weirdness,
etc.

Gary is a gate array that provides chip selects to everything on the
motherboard, some address decoding assistance to Agnus, Chip bus buffer
control, some floppy disk decoding functions, and anything else that
seemed appropriate to stuff in there.

>Besides the fatter Agnus, what does the Extended Chip Set provide?

Some extended video modes based around 35ns pixels.

>Will ECS run with a system clock of 25-33 MHz?

ECS runs from a nominally 28MHz clock, which gets divided down in various
ways to provide pixel clocks and the nominally 7MHz clock which feeds the
processor in a standard 68000 based Amiga.

>Has Commodore given any thought to an asynchronous system? 

Asynchronous is what way?  The A2500/30 is an example of a system from
Commodore that uses a processor clock (at 25MHz) that's completely unrelated
to the Chip subsystem clocks.  I've always called this an asynchronous
system.

>What tremendously hairy bag of ugly worms (to mix a metaphor) does this
>open up?

The chance for metastability.  Much care must be taken to avoid this in
such a design. 

>		--Rod
-- 
Dave Haynie Commodore-Amiga (Systems Engineering) "The Crew That Never Rests"
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                    Too much of everything is just enough