[TUHS] Re: A Census of /etc and /sys Prior to V4

[segaloco via TUHS <tuhs@tuhs.org>]

> > ac and mq EAE registers are still in use in s2-bits binaries
> > but have been replaced by s1-bits.
> 
> Interesting. How did you work that out, BTW?

Regarding the EAE registers, in as19.s[1], there is this set of mappings:

012717;000000;01;177570 /csw
015176;000000;01;177300 /div
003270;000000;01;177302 /ac
051750;000000;01;177304 /mq
052224;000000;01;177306 /mul
073470;000000;01;177310 /sc
074620;000000;01;177311 /sr
054752;000000;01;177312 /nor
047000;000000;01;177314 /lsh
004500;000000;01;177316 /ash

Among others, here we have the mappings for ac, mq, mul, and div.

In the disassembled source of df(I) from s2-bits[2], at the second 9 label, ac, mq, div, and mul are used to perform a division by 10 (I think, my PDP-11-fu isn't *that* strong yet):

9:
	clr	ac
	mov	$10.,div
	mov	ac,-(sp)
	tst	mq
	beq	2f
	jsr	pc,9b

In the disassembler output (I used pdp11dasm[3]) these values were all the same addresses as the above table from as(I).

In the source df.s under the V2/cmd section[4], this is instead replaced by use of the dvd opcode:

9:
	clr	r2
	dvd	$10.,r2
	mov	r3,-(sp)
	mov	r2,r3
	beq	2f
	jsr	pc,9b

I've seen this sort of thing consistently as I comb through files in s2-bits, using stuff from s1-bits and V5 as references.

[1] - https://www.tuhs.org/cgi-bin/utree.pl?file=V2/cmd/as19.s
[2] - https://gitlab.com/segaloco/v2src/-/raw/master/cmd/df.s
[3] - https://github.com/caldwell/pdp11dasm
[4] - https://www.tuhs.org/cgi-bin/utree.pl?file=V2/cmd/df.s

- Matt G.