[Simh] VAX 8200/8250

[Matt Burke]

On 06/04/2019 23:50, Timothy Stark wrote:
> Does simh use threads to handle MP processors?  I have other SIMH versions (vaxmp and turbovax) that uses threads to take advantage of CPU cores. 
>
> I looked through your 782 code and did not see any threads handle that vaxmp and turbovax uses.
>
For the VAX 8300/8350 I just run both processors in the same thread and
alternate between them on each instruction cycle. Things get a lot more
complicated when threads are involved because you have to think about
locking and synchronisation.

The VAX-11/782 is quite different as you actually run two separate
copies of the VAX-11/780 simulator and they communicate with each other
using a shared memory interconnect (simulated by shared memory on the
host operating system). One VAX-11/780 runs as the master and this is
the one that you interact with. It has access to all the I/O devices
such as disks/tapes. The other VAX-11/780 is non-interactive and can
only process workloads which are handed over from the master. This is
asymmetric multiprocessing.

Matt