[Coco] CoCo 3 RAM mapping question.

[Phill Harvey-Smith]

Hi All,

I'm currently working on getting the Dragon and CoCo Diag cart working 
with the CoCo3.

This has mainly consisted of making sure the appropreate GIME registers 
are programmed correctly at startup. Note this cart pulls SLENB / DSD so 
that it's ROM can take over straight away at reset time, so that the 
tests can still be run if for example the internal ROM is dead / corrupt.

I'm currently working on the RAM test, to do this I am sequentially 
paging in the 8K block under test at $4000-$5FFF, first checking for 
mirrors so that I start at block $30 on a 128K machine, block $00 on a 
512K. This seems to work without problems until I page in block $3C, at 
which point the test fails! Tracing in MAME it seems that this has paged 
in the ECB ROM,  not what I want or expected, I had assumed that the DAT 
registers only applied to the RAM?

The tests are currently operating in 32K RAM, 16K internal rom, 16K 
external ROM (though the external is actually 8K ROM, 8K RAM but my card 
handles that). The Init1 register contans $C4, so CoCo 1/2 compatible 
mode, MMU enabled and standard SCS.

Anyone know how to resolve this?

Cheers.

Phill.

-- 
Phill Harvey-Smith, Programmer, Hardware hacker, and general eccentric !

"You can twist perceptions, but reality won't budge" -- Rush.

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