Re: MMU prototyping

From: Jim Brain <brain_at_jbrain.com>
Date: Wed, 23 May 2018 11:46:23 -0500
Message-ID: <6d8a9396-9f70-3748-c545-40315a18593a@jbrain.com>
On 5/23/2018 4:55 AM, smf wrote:
> On 23/05/2018 00:41, Jim Brain wrote:
>
>> I guess it depends on what one defines as a "hack".  This unit simply 
>> engages the GAME line anytime a memory access that should be outside 
>> the C64 is requested.  I think that is standard behavior.
>
> I don't believe you were supposed to change GAME & EXROM dynamically, 
> although a handful of projects do for better or worse.
Ah, then I am a hack, in the grand spirit of hacks :-)
>
> When aren't you asserting GAME?
_game is asserted:

  * PHI2 is HIGH AND
  * Address[15:12] != 0 AND
  * Address[15:12] != D AND
  * the current PAGE!= 0

PAGE is an 8 bit (soon to be 16 bit) value denoting which 4kB page is 
mapped into the selected page of main system RAM.



-- 

Jim Brain
brain@jbrain.com
www.jbrain.com
Received on 2018-05-23 19:00:07

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