[Simh] TMXR/UC15 documentation?

[Lars Brinkhoff]

Mark Pizzolato wrote:
>> It's mostly used to allow direct access to PDP-11 main memory.
> Mostly???  What else besides memory access?

First, we don't know everything yet.  It's not exactly documented.  I
expect details to reveal themselves as we progress.

I believe it could also be used to access memory mapped I/O registers.

> Is the access from the PDP10 side done by programmed I/O
> (i.e. referencing addresses in the Unibus address space), or by some
> DMA engine which allowed transfers from the PDP10's memory to the
> PDP11's and back?

No DMA.  Just instructions doing regular memory accesses.

> Given this explanation, it would seem that you're merely looking for a
> shared memory model, and not really a point-to-point WAN situation.

Yes, it's shared memory.

> What PDP11 model(s) were involved?  Was there a PDP11 memory map
> involved?

I 11/10, 11/20, 11/40, 11/45.  The device accesses physical memory
addresses, so if a PDP-11 has an MMU that's not visible.

The Rubin 10-11 has a memory mapping mechanism that translates PDP-10
addresses to a 3-bit Unibus number, an 18-bit Unibus base address, and a
10-bit address limit.  The latter can be used to set the size of the
mapping from a full ITS page (1024 36-bit words), down to a single
PDP-11 word.  There are 256 mappings, one for each ITS page in a 256K
range.

> You've got the software which ran on the PDP11's?

For most of them.

> What devices existed on the PDP11's?

I'll be happy to go into details!

Unibus number 0: PDP-11/10 with 12K memory, around 20 32K frame buffers
for bitmapped displays, video switch, audio switch, and keyboards.  And
the elevator button.  This 11 is our top priority.

Unibus number 1: PDP-11/20 with 28K, attached to a XGP laser printer.

Unibus number 2: GT40 with 8K attached to the CONS Lisp machine.

Unibus number 3: CHEOPS, hardware assist for a chess program.

Unibus number 4: PDP-11/45 with 32K, custom hardware with eight vector
displays.  Used by the MIT Logo group.

Unibus number 5: PDP-11/45 with 32K, and roboics equipment.

Unibus number 6: PDP-11/40 with 28K, and equipment for computer vision
research.

Unibus number 7: Unknown PDP-11 model with 8K and a Chaosnet interface.

The memory sizes are what ITS maps in.  It could actually be more.

> Given that what you've got is one way with only the PDP11's memory
> being accessed and no interrupts it would seem that a KA10 with a set
> of PDP10 Unibus(s), with each connected directly to a different PDP11
> system, you could model this pretty easily.

Right, it's not a complicated device.  I have the PDP-10 side
implemented, and ITS seems happy with it.  It creates mapping as needed,
and tries to read and write memory locations.  For now writes are
ignored and reads return zero (except the mappings).

So, uness there's any support code in SIMH for something like this,
we'll invent our own bus interfaces.