[Simh] Simulating the PDP-15/76 Unichannel

[Mark Pizzolato - Info Comm]

On Tuesday, March 17, 2015 at 8:52 PM, Christian Gauger-Cosgrove wrote:
> --> Actually running this configuration will either mean making SIMH
> multithreaded (please do, I'd like to see SIMH get the ability to dink around
> the "sim>" console as long as one pleases, without stopping the emulated
> CPU processing; just as the Hercules emulator does), or
> timeslicing/timesharing the execution (like the FPPs on the '8 and '15 work, if
> I presume correctly).

FYI:  The existing simh framework has a remote console capability which can be used to "dink around" in "reasonable" ways with a running simulator.  The dinking can either be done without stopping instruction execution or execution can be stopped while dinking and then resumed with CONT (which will happen automatically after a configurable timeout).

The remote console capabilities are implemented without the simulator being multi-threaded.  

Meanwhile, some simulators have some functionality which does run in multiple threads.  This occurs with VAX and PDP MSCP and TMSCP as well as RP disks devices.  These devices perform I/O in a separate thread and when that I/O completes device events are queued to the simh event queue and interrupts occur in ways similar to how real hardware functioned.  Multi-threaded I/O is only used on host platforms which have working pthreads libraries available.  These include at least Windows, OS/X, Linux and IA64 VMS.

- Mark