[Coco] Help with some HiRes CoCo 3 MMU settings

Glen Hewlett glen.hewlett at sympatico.ca
Wed Dec 7 09:15:13 EST 2016

Thanks for the confirmation of my code, I thought  I was doing everything correct. I've been trying so many things over the last few days to try and figure this out. 

Good idea to get mame to use the watch points. 

I'm trying learn how to use IRQs and I have a feeling that more is going on then just my IRQ

I setup my IRQ WITH. JMP command and my IRQ address at $FEF7 and disabled FIRQ and use
   ANDCC  #$EF

But maybe some other interrupts are happening.  That I'm not taking into account. 

Like you said using the watchpoint with mame should help me figure out what is going on. 

Thanks again,

> On Dec 7, 2016, at 7:06 AM, Mark McDougall <msmcdoug at iinet.net.au> wrote:
>> 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!?!
> Regards,
> -- 
> Mark McDougall
> <http://retroports.blogspot.com.au>
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