Re: C64 2 Mhz Hack
Date: 2001-02-26 07:09:32

On Sun, 25 Feb 101 wrote:

> Hallo allemaal,
> I have two question that possibly fits in this discussion:
> The SCPU uses its own memory to maintain maximum speed. But the the content 
> has to be copied in some or another way to the original memory
> - how is this done? Probably DMA?


> - what range is copied and how does the mechanism know?

All 64k.  I'm not aware of how often. :)

The V2 spcu's can 'optimise' and only copy certain regions to the c64.

> We already discussed replacing a non 6502 CPU by 6502 + Hardware. I prooved 
> it can be done. Now to find a way to be able to use fast memory.
> This triggered another question: the 65816 can run on 20 MHz. The SIMMs 
> SCPU uses ar mostly of the 70 ns type. 20 Mhz means 25 ns cycles. How does 
> that fit? Either someone is cheating or I missed something. I hope the last 
> and that someone can tell the trick.

the rams used in the scpu are 32 bits wide.  You can access 8 bits in a
4bank interleave. :)  That gives us the ability to access 70ns/4 ;)

It's quite possible to access a byte every cycle, minus the time needed to
set new dram rows up.

> Groetjes, Ruud

Greetings, David

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