[Coco] GIME questions

[Robert Gault]

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
> intentionally?
> 
> 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.
> 
> Dave
 ><snip>
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