Path: utzoo!utgpu!news-server.csri.toronto.edu!cs.utexas.edu!swrinde!zaphod.mps.ohio-state.edu!wuarchive!uunet!cbmvax!daveh
From: daveh@cbmvax.commodore.com (Dave Haynie)
Newsgroups: comp.sys.amiga.hardware
Subject: Re: RAMs for ehe A3000
Message-ID: <22124@cbmvax.commodore.com>
Date: 3 Jun 91 16:53:40 GMT
References: <618.28484461@busker.fidonet.org>
Reply-To: daveh@cbmvax.commodore.com (Dave Haynie)
Organization: Commodore, West Chester, PA
Lines: 40

In article <618.28484461@busker.fidonet.org> DAN.BENDIKSEN@f601.n105.z1.FIDONET.ORG (DAN BENDIKSEN) writes:

> >The speed of the memory cycle is determined by the memory controller,
> >RAMSEY in this case.  

>Ok then, is it possible to increase the speed of the A3000 beyond 25 mhz? 
>Or, would it be possible to increase the speed of RAM accesses. I am most 
>interested in the possibilities of running an 040 at >40 mhz.

The A3000's motherboard/system bus will go at either 16MHz or 25MHz, period.
Nothing is expected to run at any other clock speed.  A coprocessor device that
goes faster than the motherboard should have its own private memory and/or 
cache and sync-up to the motherboard, like an A2000 coprocessor device does.
Zorro III bus devices can run about as fast as they like, though when they 
access the A3000 motherboard, the transaction speed is limited by the A3000
motherboard clock.

>One other thing... The chip RAM speed. Does the CPU still access it at 7.14 
>mhz, or has chip RAM also been increased to 25 mhz for CPU accesses?

No, the CPU access speed is the same, just 32 bits wide rather than 16 bits 
wide as on the A2000 and A500.  It doesn't make sense to refer to Chip RAM
access as "7.16MHz" or "25MHz", since they really doesn't say anything about
what's happening.  The CPU always runs at 25MHz (in a 25MHz system), it just
takes waits states when accessing Chip RAM.  The Chip bus is synchronous to 
Agnus.  It runs a 560ns cycle, consisting of two 280ns memory accesses, one 
of which the CPU can use if the blitter, copper, or video fetch don't lock it 
out.  The only way to let the CPU in for more cycles is to double the memory
speed during the CPU access window.  That would require a 140ns cycle and a
faster Agnus.  That's not quite attainable yet.  When 60ns DRAMs become as 
cheap as 80ns, that may be something to consider.  Software has done more for
system performance that this would, anyway, by moving as much as possible into
Fast RAM.  Fast RAM will always be faster than Chip to the CPU, no matter what
you do.  As of 2.0, the only things that go in Chip RAM are those that have to
go in Chip RAM.

-- 
Dave Haynie Commodore-Amiga (Amiga 3000) "The Crew That Never Rests"
   {uunet|pyramid|rutgers}!cbmvax!daveh      PLINK: hazy     BIX: hazy
	"This is my mistake.  Let me make it good." -R.E.M.