[TUHS] First Unix that could run on a PDP-11 with QBUS

Noel Chiappa jnc at mercury.lcs.mit.edu
Mon Jul 28 23:27:17 AEST 2014

    > From: Dave Horsfall <dave at horsfall.org>

    > I recall that there were other differences as well, but only minor. In
    > my paper in AUUGN titled "Unix on the LSI-11/23" it will reveal all
    > about porting V6 to the thing.

I did a google for that, but couldn't find it. Is it available anywhere
online? (I'd love to read it.) I seem to recall vaguely that AUUGN stuff were
online, but if so, I'm not sure why the search didn't turn it up.

    > I vaguely remember that the LTC had to be disabled during the boot
    > process, for example, with an external switch.

I think you might be right, which means the simulated 11/23 I tested on
wasn't quite right - but keep reading!

I remember being worried about this when I started doing the V6 11/23 version
a couple of months back, because I remembered the 11/03's didn't have a
programmable clock, just a switch. So I was reading through the 11/23
documentation (I had used 11/23s, but on this point my memory had faded),
trying to see if they too did not have a programmable clock.

As best I can currently make out, the answer is 'yes/no, depending on the
exact model'! E.g. the 11/23-PLUS _does_ seem to have a programmable clock
(see pg. 610 of the 1982 edition of "microcomputers and memories"), but the
base 11/23 _apparently_ does not.

Anyway, the simulated 11/23 (on Ersatz11) does have the LTC (I just checked,
and 'lks' contains '0177546', so it thinks it has one :-).

But this will be easy to code around; if no link clock is found (in main.c),
I'd probably set 'lks' to point somewhere harmless (054, say - I'm using
050/052 to hold the pointer to the CSW, and the software CSW if there isn't a
hardware one). That way I can limit the changes to be in main.c, I won't have
to futz with clock.c too.


PS: On at least the 11/40 (and maybe the /45 too), the line clock was an
option! It was a single-height card, IIRC.

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