[Coco] Help with some HiRes CoCo 3 MMU settings

Mark McDougall msmcdoug at iinet.net.au
Wed Dec 7 07:06:21 EST 2016

On 7/12/2016 3:23 PM, Glen Hewlett wrote:

> With Mame’s debugger I can see
> the banks of memory have wiped out my graphics screen and my program
> and filled it all with a bunch of $CD values in my RAM.  Does this
> sound familiar to anyone maybe you know what I’m missing or doing
> wrong that would cause such a thing to happen.

$CD is the value I see in MAME/MESS for uninitialised RAM. Sounds like 
your banks are being inadvertently switched.

I can't see anything immediately obvious in your setup. Similar code to 
what I use for setting up my video; pages $38/$39 @$0000 (which I think 
is the default anyway).

I'd place watchpoints on the MMU bank/task registers ($FFA0-$FFA3) and 
see if anything is hitting them that shouldn't be. Otherwise a 
watchpoint on your codespace will reveal that page being explicitly 
overwritten, as opposed to being switched out. Shouldn't be difficult to 
track down using a watchpoint!?!


Mark McDougall

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