[Simh] Simulating the PDP-15/76 Unichannel

[Mark Pizzolato - Info Comm]

On Tuesday, March 17, 2015 at 7:50 PM, Sergey Oboguev wrote:
> Unless I misread Mark's message about the RQDX3 analogy, he is suggesting
> to put PDP-15 and PDP-11 in the same SIMH thread and in the same address
> space. When PDP-11 side becomes non-idle, it can signal an event and
> become eligible for execution, in a way similar to RQDX3. The options for co-
> execution with PDP-15 side in this structure are:

Well, the intention of my suggestion was not to actually execute PIREX code in a PDP11 simulator, but to merely have the DR15 device implement the protocol (and the resulting behaviors) that the slave PDP11 system executed while running PIREX (that is what the RQDX3 simulator does when it implements MSCP).

As Christian points out, the discussion in github issue (https://github.com/simh/simh/issues/96) covers this concept as mentioned by both Christian and Bob.  I never read the detail of that issue since PDP-15 was way beyond/before my time and experience and the discussion seemed to have a good flow of its own (by most of the same folks involved in this one now).

> 1) Execute PDP-11 exclusively until it enters idle state, then resume PDP-15
> execution until PDP-11 becomes non-idle again.(This directly mirrors RQDX3
> analogy).
> 
> 2) Probably a better option (albeit dissimilar with RQDX3): co-execute PDP-11
> and PDP-15 instruction streams on the same SIMH thread. I.e. execute of
> chunk of N instructions on PDP-15 side, then execute N (or M) instructions
> on PDP-11 side, then come back to PDP-15 main loop etc., and repeat this
> alternating execution of per-CPU main loops until one of the sides becomes
> idle, at which point the other side receives 100% share unless it becomes idle
> too.

Some aspect of this idea is also explored in that github issue...

- Mark