Re: Independent CPU/VIC-II setup

From: Jim Brain <brain_at_jbrain.com>
Date: Tue, 1 Jun 2021 18:09:52 -0500
Message-ID: <aa1af205-5d04-646c-7e60-d16bc25f45a9_at_jbrain.com>
On 6/1/2021 5:44 PM, smf wrote:
> On 01/06/2021 18:46, Jim Brain wrote:
>> Your comments are not in line with the original request for information.
>
> Slowing the cpu down to 1mhz when reading or writing to vic2's ram is
> going to be worse than a supercpu connected to a c64. My understanding
> of the results he wanted to achieve, it wouldn't slow the cpu down that
> much.
Reading or writing to the VIC-II RAM does not require slowing down the 
CPU to 1MHz.  If the RAM is as fast as the CPU (50nS or so), then a RAM 
access within the VIC-II space can be executed at 20MHz speeds on the 
CPU side of the VIC-cycle, assuming the VIC is not in a badline/cycle 
stealing mode.  In fact, when it's not in such a mode, the CPU has 4-10 
cycles to do as it pleases (assuming 8-20 MHz).  The only time slowdowns 
would occur is when the VIC is using both halves of the VIC cycle.
>
>
Jim
>
>

-- 
Jim Brain
brain_at_jbrain.com
www.jbrain.com
Received on 2021-06-02 02:00:03

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