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Re: New Vax - future directions :-)

On 2021-07-07 20:40, Mouse wrote:
It wouldn't be hard to, for example, define a variant of PDP-11
compatability mode for which instruction fetches came from
00010000-0001ffff while data accesses used 00000000-0000ffff.
Unfortunately, the rules are more complicated than that.  Any
reference through R7 (PC) goes to the I-space, even data.

Sure.  Anything that goes to I-space on a split I/D -11 gets mapped to
0001xxxx; D-space, 0000xxxx.  If you want to emulate a non-split
system, you just map the same physical pages into both ranges.

Well, you'd need that it somehow do get translated to another address, but only under the right circumstances. And it is a bit more complicated than just "all data".

But running something like 2.11BSD would require more than just
classic VAX compatability mode, because it's more than just user
mode.  [...]
Right.  Which was part of my question why bother with the PDP-11

ZORK, of course! :)


I thought I'd seen something on a VAX system which talked about that
"old, sourceless Zork binary".  Maybe my memories are getting
conflated; that would have been decades ago by now.

Well, "current" Zork, both the MDL and FORTRAN version, are around. Do definitely not lost. And there are no problems building and running them on a VAX. It's on the PDP-11 where it's tricky. Also, the Infocom commercial Zork binaries are also around, and if you have a Z-machine interpreter you can run those too.
I wrote one for the PDP-11, which works under RSX, RT-11 and RSTS/E.
Noone have done anything under 2.11BSD as far as I can tell.

So for VAXen, there is a plethora of options available. Running the PDP-11 variant in compatible mode would be far down on my list to start with. But it's also heavily overlaid as well as dependent on split I/D space to even run.

Running that on a VAX would really be for a masochist. When I backported the latest version of DUNGEON back to RSX, I had to work out a new overlay scheme, and it's extremely complicated. And building the whole thing from sources on an 11/70 with RSX took something like four hours...

That latest version only runs on RSX-11M-PLUS by the way. RT-11 and RSTS/E users are out of luck... (Well, maybe it would be doable, but I haven't seen anyone trying.)

If it could run under 2.11, I'm moderately sure I could make it run
under NetBSD/vax, given compatability-mode-capable hardware (or
emulated hardware).  I don't suppose you'd happen to know where I might
be able to get hold of that 2.11 binary?

It's in the standard 2.11BSD distribution.


Johnny Billquist                  || "I'm on a bus
                                  ||  on a psychedelic trip
email: bqt%softjar.se@localhost             ||  Reading murder books
pdp is alive!                     ||  tryin' to stay hip" - B. Idol

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