[Coco] CoCo 3 MMU test for all
operator at coco3.com
Mon Jan 21 15:52:57 EST 2008
At 09:01 AM 1/21/2008, you wrote:
>Roger Taylor wrote:
>>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
It's already working as intended without doing any of that,
actually. Now that I know that bit #6 of the MMU registers in a
128k/512k CoCo is always set high (Whether or not it's legal to read
or use the bit or not, it's there)... I make LOADM store the desired
block # there + %01000000 and LOADM naturally sees that (extra bit)
when it verifies the write. My desired blocks are in the $30-$3F
range which makes it safe for both 128k/512k. I don't touch anything
out of that range if my game is 128k. :) Now, if it's a 512k game,
512k will be *required*. An automatic VDG title screen would also
appear telling the user what type of CoCo is required if the game
uses more than 128k.
I may or may not have to assemble a separate file for 1- and 2-meg
systems. Whatever the upper 2 bits are when those people do a
PEEK(65441) may hold the answer I need.
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