[Coco] CoCo3 memory expansion questions

[Neil Cherry]

On 2/4/19 12:54 PM, RETRO Innovations wrote:
> On 2/4/2019 5:35 AM, Francis Swygert wrote:
>> Date: Sun, 3 Feb 2019 13:03:10 -0500
>> From: Neil Cherry <ncherry at linuxha.com>
>>
>> Actually there is a very cool 'hack' for the SWTPC which uses a pairof 74189s (64bit 
>> RAM). It allows each process to have it's own memory.
>> Unfortunately I'm not sure if OS9 supported DAT ram. This gave the
>> 6809 access to 1M in 8K pages.
>>
>> =======================================
>> That's similar to what the CoCo3 GIME does. I believe it uses 8K pages of memory 
>> switched in and out... if not someone will correct me!
> That is very true.  It supports 2 (two) mappings of the 64kB space, called "tasks".  With 
> the GIME, you can map an 8kB page anywhere in 512kB RAM.
>> Could be a different page size, but it's a big chunk of memory, I do recall that...I 
>> wonder if you could implement something on a separate board?
> 
> CoCoMEM Jr does exactly that.  It implements the GIME registers for MMU, extending them to 
> 8 bits (to allow mapping up to 2MB of RAM) and adds more "tasks" to the system beyond the 
> initial 2 (It extends to 4096 tasks).
> 
> Right now, I've asked a few folks to ensure Nitros9 LII runs on the unit.  When that 
> happens, it should be pretty easy to port to another 6809-based machine

Very cool. :-)

-- 
Linux Home Automation         Neil Cherry       ncherry at linuxha.com
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