[Coco] MMU testing utility

[Dave Philipsen]

When you say 'CRM' are you referring to bit 3 of $ff90, or what?

Dave

> On Sep 22, 2017, at 10:22 PM, RETRO Innovations <go4retro at go4retro.com> wrote:
> 
>> On 9/22/2017 5:03 PM, Tormod Volden wrote:
>>> On Fri, Sep 22, 2017 at 7:24 PM, RETRO Innovations wrote:
>>> Many thanks.
>>> 
>>> Since you're here, I wanted to ask:
>>> 
>>> On your MMU design, since you're on the cart port, how do you prevent a
>>> write to your cart from "bleeding through" to the internal RAM?  I see how
>>> SLENB can be used to move the RAM off the bus for reads, but I don't how it
>>> will prevent a write from happening. Of course, by redirecting all reads to
>>> your cart, the only issue is graphics, correct?  How do you handle that?
>> You can't fully prevent it from the cartridge port (without internal
>> surgery on the machine). However if you have 64K internally, the upper
>> 32K are safe since the bleed-through won't happen in SAM map type 0.
> Hmm, I'll have to look into SAM mode 0, didn't know it handled RAM in a special way.
> 
> Another question:
> 
> In your design, when CRM is enabled and the user access $fexx page, what actual RAM address do you map them into?  On a 32kB or smaller machine, I assume not the mainboard RAM.  But, do you pin the access to the $ffa7 value?
> 
> And, for others:
> 
> what does the GIME do?  where does it map $fexx when I enable CRM bit?
> 
> 
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