Path: utzoo!attcan!telly!lethe!torsqnt!news-server.csri.toronto.edu!cs.utexas.edu!uunet!cbmvax!daveh
From: daveh@cbmvax.commodore.com (Dave Haynie)
Newsgroups: comp.sys.amiga
Subject: Re: Amiga Chips/Comp.Sys.Amiga.Tech
Message-ID: <16730@cbmvax.commodore.com>
Date: 21 Dec 90 17:26:49 GMT
References: <39640@nigel.ee.udel.edu> <37123@cup.portal.com>
Reply-To: daveh@cbmvax.commodore.com (Dave Haynie)
Organization: Commodore, West Chester, PA
Lines: 34

In article <37123@cup.portal.com> Lee_Robert_Willis@cup.portal.com writes:

>DISCLAIMER: When it comes to Hardware, I'm dumb as dirt.

>On a related topic, I've read here that with a 68030 or 40 CPU, it would
>be faster to draw the graphics using the CPU, because the custom chips
>still run at 8Mhz.

Depends.  Agnus, et. al. access the bus roughly the same as a 7.16MHz 68030
would with 0 wait states, which is to say, twice the speed of a 7.16MHz
68000.  No matter what CPU you have in your system, the CPU can't access
chipram faster than the speed of a 7.16MHz 68000.  Basically, the chips 
run a cycle on the chip bus every two clock, but only allow the CPU in on
alternate cycles, if at all.  On the A3000, this is still the case, but
since the CPU his Chip memory with twice the number of bits as does Agnus,
CPU and Agnus access are basically equivalent.

>Why can't the custom chips simply be made to run at a faster clock rate?
>(i.e. a 68030 can run at 16, 25, 50Mhz, why can't Agnus et. al.?)

Today's chips are running at their limit.  For the same basic reasons Moto
had to redesign the 68000 to get to 16MHz or the 68030 to get beyond 33MHz,
we would have to redesign the custom chips to go faster.  We have an additional
constraint -- Moto can charge $200 or more if they like for their faster parts,
we have to keep things down to a cost point that'll allow us to actually put
them in Amigas.

>Lee		Lee_Robert_Willis@cup.portal.com


-- 
Dave Haynie Commodore-Amiga (Amiga 3000) "The Crew That Never Rests"
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		"I can't drive 55"	-Sammy Hagar