[Simh] RK Word Count register question

[Johnny Billquist]

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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-- 
Johnny Billquist                  || "I'm on a bus
                                   ||  on a psychedelic trip
email: bqt at softjar.se             ||  Reading murder books
pdp is alive!                     ||  tryin' to stay hip" - B. Idol