18 Mar
2015
18 Mar
'15
10:29 a.m.
On 2015-03-18 17:57, John Wilson wrote:
On Wed, Mar 18, 2015 at 11:16:02AM -0400, Noel Chiappa
wrote:
(And it's not giving you more RAM. PMI memory already gives you 4M minus
the I/O page)
Johnny
The UNIBUS map will not respond to UNIBUS cycles
in the address range
assigned to the UNIBUS memory.
Just to state the obvious: I assume the whole point of this "Unibus fence"
concept is really for things that *aren't* memory. Mixing in some Unibus
memory that's slower than PMI etc. and needs to use real addresses for DMA
(vs. mapped ones) seems like a giant hassle for just 6.5% more RAM, so I
figure it's really for bus windows or ROM boards or frame buffers or any
oddball device that looks like memory and is too big to fit in the I/O page.