[Coco] GIME questions
kevdig at hypersurf.com
Mon Aug 16 12:14:18 EDT 2004
Wouldn't it be simpler (and smarter) to do your testing
on a deuce instead? It is a simpler beast with less ... other stuff
to get in the way of your testing your cpu replacement. It is also
easier to replace (deuce to tre ratio on EBay is at least 3 to 1).
Good luck with this project! This is a very innovative idea!
Robert Gault wrote:
> David Gacke wrote:
>> Hi Robert,
>> Sorry it wasn't clear. So far, you are correct though. I am stepping
>> thru the code with my dsPIC CPU that I'm coding, not a 6809 or 6309 and
>> am trying to figure out what I broke.
>> To try and put it simply, by looking at that startup code, what would
>> make a shadow copy of what is located at C000 appear at 4000.
>> Which GIME registers bits would I set if I wanted to do this
>> I've stepped thru the code and am not finding a broken instruction. I
>> want to fully understand how to reproduce this intentionally, maybe then
>> I can figure out what is going wrong.
>> This one has me a little bit stumped, especially since I've never really
>> done assembly on the CoCo (lots of other systems though), and I've never
>> twiddled the bits on the GIME before.
>> Thanks very much for the assistance.
> I think this will be what you want. I strongly advise you finding a link
> to this service data and more before trying to recreate the GIME chip.
> The service manual defines the GIME INIT0 register at $FF90 as follows
> bit # name function
> 7 COCO 1= Coco 1& 2 compatible
> 6 M/P 1= MMU enabled
> 5 IEN 1= Chip IRQ enabled
> 4 FEN 1= Chip FIRQ enabled
> 3 MC3 1= DRAM at XFEXX constant
> 2 MC2 1= standard SCS (ie. disk)
> 1 MC1 ROM map
> 0 MC0 ROM map
> MC1 MC0 Mapping
> 0 x 16K Internal, 16K External
> 1 0 32K Internal
> 1 1 32K External except for vectors
More information about the Coco