[Coco] MMU testing utility

[RETRO Innovations]

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?


-- 
RETRO Innovations, Contemporary Gear for Classic Systems
www.go4retro.com
store.go4retro.com