31 Mar
2008
31 Mar
'08
3:02 p.m.
On Tue, Apr 01, 2008 at 08:38:33AM +1100, Doug Jackson - pesonal email wrote:
Hi Everybody
I was reading some doco last night (specifically the DEC RL11/01 Disk
Subsystem Training Handout), and I am confused.
(That is nothing new...)
In the "Subsystem commands section", the addresses specified for DAR and
CSR are 774404, and 774400 respectively, but in the back of the
document, under the 'toggle in programs' section, the DAR and CSR are
shown as being at 174404 and 174400 respectively.
Yes.
Hmmm. I see three possibilities:
1. I have (re) discovered a documentation error - I wonder if DEC, no,
HP, no Compaq, would be happy for me to submit an amendment :-)
It's not a documentation error.
2. The hardware throws away the upper bits so both
references are
correct. Hmmm Possibly not :-)
The hardware doesn't throw away the upper bits... quite the opposite...
3. There is some other stuff happening that I
missed...
What's happening is that you have a machine with 16-bit registers, but
are working with, essentially, 18 address bits.
Look at 174400... 16 bits, so it fits inside a PDP-11 register. 774404
takes 18 bits to represent, and _is_ what ends up on the Unibus.
What's going on under the hood is that when you point to addresses near
the top few K (2K? 8K?), what goes onto the Unibus _doesn't_ trigger
an access to your RAM card - it adds two 1 bits on the Unibus and tickles
I/O cards instead.
In otherwords, if you write a program to scan all 64K that you can directly
address with a register (and not fiddling with MMU registers), you'll hit
whatever 64K bank of RAM is mapped in, until you hit the I/O page, then
it's I/O registers to 177777.
If you are at the pre-boot stage (i.e., no OS has set up your MMU or
Unibus mapping registers), you should probably refer to the handbook
for your exact processor for details about how to hit I/O registers
from console ODT or your console keypad or whatever.
Thinking back
nearly 25 years, ISTR slight differences between, say, an 11/04 and
an 11/34 about this sort of thing (because the 11/34 is a richer-
featured machine). The 11/24 has either an 18-bit or 22-bit bus
depending if you have a KT24 installed or not The 11/70 has a 22-bit
address space always, AFAIK. I don't know enough about the internals
of the 11/44 or other models like the 11/40, 11/45, 11/60, but I'm
sure there are plenty of large -11 experts here who can chime in.
You didn't say what machine you have, so I've kept things quite generic,
mostly thinking of how the 11/04 and/or 11/34 do things since they are
the most common.
At the very least, you should be able to hit the CSR and DAR from either
your front panel or console ODT and see that the board shows up.
You mention a "seek test"... is this with XXDP or are you toggling-in
a standalone test or what? Is this caution, or will the machine not
boot with a bootable pack?
-ethan
--
Ethan Dicks, A-333-S Current South Pole Weather at 31-Mar-2008 at 21:40 Z
South Pole Station
PSC 468 Box 400 Temp -59.8 F (-51.0 C) Windchill -100.6 F (-73.6 C)
APO AP 96598 Wind 17.5 kts Grid 30 Barometer 691.5 mb (10197 ft)
Ethan.Dicks at usap.gov http://penguincentral.com/penguincentral.html