[HECnet] PDXVAX - 40MB Memory - VAXstation 4000/VLC?

[John Wilson]

From: "Bob Armstrong" <bob at jfcl.com>

So can E11 actually use multiple processors on the host (aka Intel) side
so that the emulated 11/74 CPUs can really run in parallel?

Exactly.   It also commits some atrocities (making CPUs wait for each other
while sending/receiving inter-CPU interrupts) to ensure that it'll still
basically work even on Linux/Windows systems which don't have enough
(available) 80x86 CPUs/cores to cover all the PDP-11/74 CPUs (and more
importantly, doesn't crash just because of occasional latency problems on a
heavily loaded host PC).   The DOS and stand-alone versions DO need enough
80x86 CPUs though, since there's no time-slicing there (there are different
atrocities there -- all I/O is done on the boot processor since DOS and the
BIOS aren't mP-safe).

The bugginess is annoying (occasional hangs) but part of the problem is
that there are no real manuals for the IIST (the inter-processor interrupt
device) and obviously I don't have access to a real mP system to test on.
So I just did the best I could.   RSX comes with sources of course, and the
IIST diag listings are in the PDP-11 fiche kit, but as always the diags
themselves mostly focus on little details (evidently the IIST used some kind
of serial bus so there's parity and other weirdness) which are hard/pointless
to emulate, and doesn't point towards whatever I'm getting wrong, so it's
not as if it's just a simple matter of ironing things out until the diag
makes it all the way through.

Anyway I would love it if more people tried out the mP feature.   There's a
chapter in the Ersatz-11 manual which tells how to turn it on, and how
to configure RSX to use it.   The more users, the more bug reports, and the
sooner the mP parts of E11 get all the kinks worked out.   It's a lot of fun to
play with!   DEC sort of pretended mP PDP-11s never happened (there was never
any official support) but only after they'd already done *all* of the work.
The mP stuff is in the real printed RSX manuals, and the diags are on the
regular XXDP packs, it's great!   And lots of fun to play with...

John Wilson
D Bit