[Simh] EXT :Re: Unattended background SIMH process

[Paul Koning]

> On Dec 5, 2019, at 10:37 AM, Hittner, David T [US] (MS) <david.hittner at ngc.com> wrote:
> 
> Mark can correct me if I'm wrong, but I believe that most of the SIMH simulators can already save the state (from the ^E prompt) and restore using the SAVE and RESTORE commands. I think this capability was added to facilitate very long debugging sessions over a multi-day period.
> 
> It's possible that the only thing that might need to be added to SIMH to support an automatic save on a hardware power fail is the ability for the master thread to detect the power fail event and initiate an auto-save, and of course enough time to actually perform the save before the power fails. Potentially this power fail detection and auto-save from the master thread could be enabled by something like a "POWERFAIL AUTOSAVE <filename>" command.

I think the other change needed is delivery of power fail interrupts.  It could be made part of SAVE and RESTORE, or separate.  If separate, you'd do one before SAVE, and after RESTORE.

That's not an exact match, though.  In the real machine, with persistent memory such as core, the memory is preserved across power cycles but the system is otherwise reset.  So I think what you actually need is powerfail interrupt, save, then later on restore, reset, powerfail interrupt. 

	paul