🚀 go-pugleaf

In article <25...@boulder.Colorado.EDU> a...@boulder.Colorado.EDU (Alan T. Krantz) writes:
>>
>>If you want another shot, here's a "simple" one.  Put a PUSH in
>>register 0, and start the CPU at 0.  What happens?  No fair trying it
>>on a real PDP-10.  You can assume the CPU is a bare machine, but this
>>will work OK under timesharing on Tenex, TOPS-20, or ITS systems.
>
>
>That's an easy one - if I understand the question correctly. The Dec-10
>(tops-10) had a linear address space (including the registers) so if the
>pc was 0 - it executed the data in register 0 as an instruction.

Good - you got the first instruction.  Don't forget the overflow from
the index register field into the indirect bit at pc 17.
>This is a simple trivia question - but what does the following code do:
>
>	move	1,[movei 1,@1]
>	jrst	1

I much preferred:

	movsi	0,20		;That's octal 20 - loads the indirect bit
	jrst	0

Because address evaluation had to be complete before instruction decoding
and PC incrementing, and because the -10 had indefinite indirection, this
would turn off most of the console's lights.  The PC display would be 0,
the instruction display would be off except for the indirect bit glowing
at about half brightness, and the data lights (if the console address switches
were set to 0) would have just the indirect bit.

Pretty dull, actually.  A multiport diagnostic I wrote that beat on memory
from processor, disk (RP02) and drum (RM10B) was really neat with the
computer room lights turned off.


As for alorithms in Algol - if you want that, read CACM.  If you want folklore,
then you may have to deal with assembler.  Besides, how can you cleanly
describe in Algol-60 (sorry, that's the only one I know (knew?)) the rotate
instructions?  Or ILDB/IDPB?  Or TRCE?  Criticizing assembly code when us
old fogies start rhapsodizing about our all-time favorite machine is living
dangerously

As for DDT, I'm please to say that DDT lives!  Thanks to several old PDP-10
hackers at Alliant, our OS debugger is near a relative to PDP-10 DDT.  It's
main shortcoming is the lack of the builtin assembler.  Never did understand
that code on the -10.
-- 

| A pride of lions              | Eric J Werme                   |
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