🚀 go-pugleaf

I'm planning to buy a 486 machine soon, and I'd like to be able to use the
IBM RT apa16 graphics adapter and monitor in it as a second monitor.  The
apa16 card is memory mapped at addresses D80000 to D9FFFF on the ISA bus;
this address range is normally used by RAM.  Is there any way to get this
address range to pass through to the ISA bus instead of referencing system
memory?  What if I put the card on an EISA bus?  I'm guessing it will
respond to any address with the low 24 bits in the range D80000 to D9FFFF.
Is there a way to map some part of memory above 16 MB to pass through onto
the EISA bus?

I haven't said specifically what hardware because I haven't decided yet.  If
this makes a difference (some motherboards can do what I want, some can't)
I'd like to know.

(For PC users wondering how this card worked in the RT: the RT maps the
entire I/O bus into a 16 MB memory segment which does not overlap RAM.  For
DMA, I/O bus addresses get translated to RAM addresses.)


--
    John Carr (jfc@athena.mit.edu)