Unix Version 7 Booting

[Barry Shein]

>I am currently working on an independent research project consisting
>of placing a copy of Unix Version 7 on a MC68000 based computer at
>North Carolina State University (our license does cover this machine).
>I have a kernal which is bootable from device rx (an 8" floppy drive)
>and am having trouble getting everything operational.  This kernal is
>on a PDP 11/23 and I beleive was written for a PDP 11/45.  The boot
>loader comes up properly; the kernal displays the amount of available
>memory properly; but nothing else happens.  I get no shell prompt, nor
>am I even sure the kernal even gets to a point where it attempts to
>load the shell.  Does anyone know what the problem may be, and if the
>kernal for a PDP 11/45 will execute properly on a PDP 11/23?
>
>George B. Miler

Back when the 11/23 first came out I ported V6 to it and I do remember
one incredibly irksome difference...enabling the hardware clock is
different on the two machines (I forget the details exactly but if you
got this far you can probably figure the rest out.) It sounds a lot
like that problem (since the clock is never enabled no process
switching starts so you just hang, you never enter the scheduler.)

In fact, if I remember correctly (we're talking about a decade here)
the real problem was that you don't have to enable the 11/23 clock,
just set up the interrupt vectors. The hang may be caused by trying to
access the 11/45's hardware clock register causing infinite
non-existant memory errors, or something like that.

Maybe this will help, but the clock is one of the very few differences
between the machines at that point in the boot (also separate I&D
space, you really want to be thinking 11/34 not 11/45, the 11/23 is
almost identical to the former.)

I think there was also something obscure about whether or not a
post-in/decrement operation on the stack, upon causing a trap [for
stack expansion], yields an already in/decremented register or not,
but you probably shouldn't run into this (?)
-- 
	-Barry Shein

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