>So I've got a Q-bus system with 64KW (128KB) of RAM that is allegedly an 18
>bit backplane. When I'm in ODT I can type:
>
>_at_177770/
>And enter values for 1777772, 1777774, 1777776, and then it wraps around to
>000000.
>
>If I start at 200000 it works until 3777777 and then wraps to 2000000. So
>it seems to not cross a 64KB boundary.
That's how it's supposed to work. If you look in the tech manual for the
processors, you see that there's a 16-bit register for the "low" part
of the ODT address, and another register for the high part of the ODT address,
but there's no carry connecting the two.
> Also the boot area is 177300 ? so it
>is in the upper 4K of the 64KB address space, is it legal to have memory
>"above" the I/O page?
Absolutely. In fact, some configurations had only a 2Kbyte I/O page
to allow a little bit of extra memory, and this still works (albeit not
officially supported) under RT-11 (it was tested before the 5.7
release.)
--
Tim Shoppa Email: shoppa_at_trailing-edge.com
Trailing Edge Technology WWW: http://www.trailing-edge.com/
7328 Bradley Blvd Voice: 301-767-5917
Bethesda, MD, USA 20817 Fax: 301-767-5927
Received on Mon Apr 05 1999 - 09:23:10 BST