Short, obvious question. Is simh expecting 16-bit addresses, and running
all addresses through the mmu in the command mode, or does it actually
use 18-, or 22-bit addresses, in which case you commands are accessing
memory, and not the I/O page, which is actually 17 777 777 410, if we
talk 22-bits.
Johnny
On 2015-12-26 21:28, Will Senn wrote:
All,
I am looking at code that puts data into the RKWC register (177410). I
am getting some interesting results and I would like to know what y'all
think about the results.
The code I am analyzing is the RK05 bootloader code from "Setting up
Unix - Sixth Edition" and I have completed the analysis and am satisfied
with the understanding I have gained from that process. However,
whenever I try to examine the contents of the RK buffers after executing
instructions that modify them, they always appear to be 00000. Is this
normal?
I set out to see if the behavior was consistent.
I wrote some machine code (comments added after sim run) to put a value
into the RKWC location and HALT.
PDP-11 simulator V4.0-0 Beta git commit id: 0f43551d
sim> d 10000 012737 ; MOV 1,(PC)+
sim> d 10002 177440 ; -340
sim> d 10004 177410 ; RKWC RK word counter register
sim> d 10006 000000 ; HALT
sim> g 10000
HALT instruction, PC: 010010 (HALT)
Then I examined the buffer:
sim> ex 177410
177410: 000000
Shouldn't 177410 contain 177440?
Next, I added an instruction to move the contents of 177410 into R0
before HALTing:
Add an instruction to move the contents of 177410 into R0
PDP-11 simulator V4.0-0 Beta git commit id: 0f43551d
sim> d 10000 012737
sim> d 10002 177440
sim> d 10004 177410
sim> d 10006 013700
sim> d 10010 177410
sim> d 10012 000000
sim>
sim> g 10000
HALT instruction, PC: 010014 (HALT)
I examined RKWC and R0:
sim> ex 177410
177410: 000000
sim> ex r0
R0: 177440
Well, 177410 still contains 0, but R0 contains 177440, some improvement.
Finally, I tried loading the memory location directly:
sim> d 177410 030303
sim> ex 177410
177410: 030303
Huh? That was totally unexpected. What is going on?
Thanks,
Will
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|| on a psychedelic trip
email: [email protected] || Reading murder books
pdp is alive! || tryin' to stay hip" - B. Idol
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