[Simh] TOPS-20 V4.1 Idling

[Mark Pizzolato - Info Comm]

On Monday, May 11, 2015 at 12:48 PM, Cory Smelosky wrote:
> Okay, I should include all the information needed now. ;)
> 
> With CPU IDLE set, with CPU set to TOPS-20 (running 4.1 running the TSU02
> monitor) SIMH continues to use 100% CPU.
> 
> Does anyone have pre-existing patches to support idling or do I need to
> provide a disk image to help identify it?
> 
> Alternatively...some people here probably already know the idle instruction.
> ;)
> 
> PDP-10 simulator V4.0-0 Beta        git commit id: 3b8c318b
> 
> ( Interestingly, SET THROTTLE 20 causes >30% CPU usage, whilst 15 is 5%
> which is just slightly above it being set to 12.  This doesn't seem linear. ;) )

This is a known problem.  It arises from the fact that TOPS-20 has a clock tick size of 1ms which is likely smaller (or at best equal to) than the tick size of the host system.

That said, I've got a project which, when complete "should" get reasonable idling behavior for this OS on almost any host system.

For now, I think you are on a reasonable track using throttling.  When you use throttling, simulated time (in the OS) won't track wall time at all though.


Please follow up on this the pre-existing issue: https://github.com/simh/simh/issues/80

That will be where testing will be solicited.

Thanks.

- Mark