[Simh] [Simh-dev] Idling around

[Mark Pizzolato]

--- Andrew Warkentin <andreww at datanet.ab.ca> wrote:

> 
> >--- Bob Supnik <bob at supnik.org> wrote:
> >  
> >
> >>4. Then, each simulator will need a simulator specific idle 
> >>algorithm.  For the PDP-11, it's the WAIT instruction (which
> won't 
> >>work for RT11, I believe); for the Interdata systems, it's wait 
> >>state.  For the PDP-8, PDP-15, H316, and GRI-909, I'm proposing
> to 
> >>use the standard keyboard wait loop:
> >>
> >>	KSF/JMP *-1 or its equivalent
> >>
> >>as the idle loop.
> >>
> >>    
> >>
> That wouldn't work for XVM/RSX on the PDP-15. Its idle loop is just
> a 
> JMP 4265, located at address 4265.

In the VAX case, in addition to the special cases for each
OS/execution environment, I had any unconditional branch where the
destination address was the PC of the current instruction be an idle
loop indicator.  In vax_cpu.c this is simply:

case BRB:
     BRAHCHB (brdisp);
     if (PC == fault_PC)
        YIELD();

repeated for each unconditional branching instruction.