[pdp7-unix] pdp7-unix Digest, Vol 5, Issue 17

Will Senn will.senn at gmail.com
Wed Oct 23 06:09:05 AEST 2019


On 10/22/19 1:58 PM, pdp7-unix-request at minnie.tuhs.org wrote:
> First of all what you're doing is od on system (the directory) and on
> cat, so what you're seeing is a directory, not a binary.
> To look at cat, do `ln system cat cat` `od cat` `rm cat`
>
> As for opcodes, the numbers given have the lower two bits set to zero
> because they aren't actually part of the opcode field. i.e. 54 means 1011xx
>
>
> aap

Angelo,

That did the trick. Thanks. Learning all kinds of stuff today :). If the 
following looks funky, view it with fixed width font:


"cat.s
    lac 017777 i
    sad d4

...

@ ln dd ken .
@ ln system cat cat
@ od cat
000000: 237777 550407 610052 217777 350406 350407 050010 020003
000010: 000000 000000 741100 610035 050301 110104 550407 610022


237777
010 011 111 111 111 111
010 0                    "20 lac
      1                   "indirect flag
       1 111 111 111 111 "17777
lac 017777 i


550407
101 101 000 100 000 111
101 1                    "54 sad
      0                   "direct address
       1 000 100 000 111  "10407 - offset to d4 label

Having a hard time wrapping my head around the ln system cat cat command 
though! I've read The Evolution of the Unix Time-sharing System a couple 
of times and still don't understand why this makes sense:

ln dd ken ken ln ken x x rm ken

-- 
GPG Fingerprint: 68F4 B3BD 1730 555A 4462  7D45 3EAA 5B6D A982 BAAF

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