[Simh] Losing Time In SIMH

[Mark Pizzolato]

On Monday, January 30, 2017 at 8:19 AM, Jason Self wrote:
> I should also add that I've noticed this loss of time both when running the
> version of simh provided by my distro and when running from git master (git
> commit id: d14243c8.)

Thanks for providing this since it was going to be my first question.

As for the underlying cause of the problem, using the simulator built from the
github codebase, you can stop the simulator while booted with ^E and at the
sim> prompt enter the SHOW CLOCK command.  Some of the details provided
in that output might help explain the cause of the problem.  In particular I'd 
look at the difference between the displayed values 'Ticks' vs 'Ticks Acked'.  
That difference multiplied by the value of 'Tick Size' should be somewhere 
Close to the time lost you are observing.  If the simulator has significant loss, 
then I suspect that similar losses would have been observed on the original 
hardware.  

Other operating systems have been observed to keep good time relative to 
wall clock time on this simulator.

If the observation I suggest above doesn't hold up, please create an issue at https://github.com/simh/simh/issues and we can dig deeper into what may be
going on.

- Mark