#MMU and mapped memory?
12-Jun-94 22:17:43
Sb: #152153-#MMU and mapped memory?
Fm: Black Belt Systems 76004,1771
To: Alan K. Adamson 72370,613
Yep, you're out in the weeds.
Here's the problem, in a legume shell:
MMU's "map" addresses as they come out of the central processor (68000,
68040, etc) on the way to memory (both chip and fast) and I/o devices, in
the Amiga hardware design.
However, display memory is actually displayed by _another_ processor, one
of those you've heard about when the Amiga is described as having a form
of hardware multiprocessing, and that processor goes directly to chip
memory, and NOT tru the MMU. So, if you remap "chip" memory to somewhere
else, the CPU will dutifully read and write from and to that spot. The
display processor hardware, not having been channeled thru the MMU (which
is often, but not always, actually physically INSIDE the CPU), will still
fetch the "display information" from the same place.
What you end up with is a screenfull of "stuff" that the CPU hasn't done
anything to; so it's trash and you see nothing useful.
"You can't get there from here".
–Ben
…via AutoPilot