[Coco] CoCo3 memory expansion questions

[RETRO Innovations]

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

Jim