[Coco] CoCo 3 MMU test for all

[Robert Gault]

Roger Taylor wrote:
><snip>
> I wanted to avoid patching the LOADM command to handle hardware port 
> poking since there's so many types of Disk ROMs in use.  LOADM could be 
> in another location depending on the maker or version/revision of the 
> ROM.  It's much safer to first see if all 128k/512k CoCo 3's add a 
> %01000000 to MMU reads so I that can include that value and expect LOADM 
> to verify it back.

This reads like you should first LOADM in a test program to correctly 
test the amount of RAM present and if adequate then auto LOADM the 
target program.

You can't determine the amount of memory by reading the MMU registers. 
You give them values and test memory at the block the MMU register alters.