[Simh] RK Word Count register question

[Johnny Billquist]

On 2015-12-26 22:56, Johnny Billquist wrote:
> 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.

Doh! Too many bits in there. 22 bit address should be 17 777 410 of 
course. :-)

	Johnny

>
>      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
>> _______________________________________________
>> Simh mailing list
>> Simh at trailing-edge.com
>> http://mailman.trailing-edge.com/mailman/listinfo/simh
>
>


-- 
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