On Fri, Nov 26, 2021 at 9:13 PM Mark Litwack <mlitwack@...>
wrote:
I looked at the address decoding about 3 years ago. The goal was clearly
to be able to access all the RAM. But, as you point out, if they did it
would overlay the I/O address space. I think the easiest path was to make
the full 8k of RAM appear elsewhere. This would have had advantages in
minimizing design changes to the hardware moving from the 2445/2465 base
design and options, and also minimizing changes to driver code when ported
from the 2445/2465.
Ah - somehow I totally overlooked the fact that the 2465A/2467 et al have
8K of RAM, whereas the original address mapping only allotted 2K of address
space. So the answer was staring me in the face the whole time :).
I believe option boards also have ROM, so maybe the existing option boards
rely on the location of the IO range?
