[Simh] New simulator - VAX-11/782

[Matt Burke]

>> On May 20, 2017, at 12:00 PM, Paul Koning <paulkoning at comcast.net> wrote:
>>
>> Interesting.  So you have the two CPUs as two processes?  I wonder if doing them as threads in a single process might be more straightforward.  I did an implementation of dual CPU CDC 6000 emulation that way (an extension to Tom Hunter's DtCyber).  Posix threads (pthread) work nicely, and semaphores (which aren't strictly part of pthreads but are often found alongside such implementations) often come in handy as well.
>>
>>  
Yes that's correct. The reason I implemented the VAX-11/782 in this way
is that it more closely replicates the arrangement of the physical
hardware. The real VAX-11/782 is two separate VAX-11/780 systems and the
only connection between them is the MA780 shared memory. For the
VAX-11/782 multi-processing configuration, the secondary VAX-11/780
(attached processor) boots from the shared memory and does not interact
with the console. For the VAX-11/784 each VAX-11/780 system boots from
it's own system disk and interacts with the console normally.
Multi-processing is then achieved via user written code that interacts
via the MA780 shared memory. It would be difficult to simulate the
VAX-11/784 via threads. The other reason for this choosing this
implementation is that it requires minimal changes to the existing VAX
simulator code.

Matt