[Simh] B5500 idle detection

[Richard Cornwell]

Hi Dave,

> I have just started using the new Burroughs B5500 emulator with MCP
> XIII. Thanks to Paul Kimpel's and Richard Cornwell's sites, the PDFs
> at bitsavers.org, and considerable head scratching, I now have it
> running the timesharing MCP, and CANDE listening on port 2000. It's
> wonderful to be able to play with this classic architecture and an OS
> that was written entirely in ALGOL nearly ten years before UNIX.
> Before Multics, even.
> 
> Anyway. The only problem is that my laptop's CPU fan is constantly
> spinning at eleven. I have "set cpu idle" in my initialisation file,
> and "show cpu" reports "idle enabled", but CPU usage is constantly at
> 100%.
> 
> Have I missed some undocumented "set" option?

  Idle detection should be working. Unless something has changed in SCP
  since I released the simulator. Idle detection is based on detecting
  the following tight loop that MCP uses when it has nothing to do.

   ITI
   TUS
   OPDC ...
   LOR
   OPDC ...
   NEQ
   LITC 10  or LITC 1
   BBC      or LBC

   Once it finds this loop it sees if the CPU executes a TUS at that
   address. 

   I verified that it is detecting the IDLE loop, however it does not
   seem to be entering idle state. Perhaps something changed in SCP. 

Rich


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Richard Cornwell
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