[HECnet] KLH10 not idling host CPU

[Johnny Eriksson]

Mark Abene <phiber at phiber.com> wrote:

> I'm posting this here in the hopes that there are other KLH10 emulator
> users on HECnet.

There are, I am one of them.

> I've been using KLH10 with the tap patches for years and years, and idling
> has always worked fine. At some point over the recent couple of years,
> idling stopped working for me on linux (I run ubuntu 16.04.4 LTS with
> latest updates as of yesterday, on a 64-bit intel machine). My CPU is stuck
> at 100% utilization, without even starting an emulated OS (I run TOPS-20).
> In fact, as soon as I type "GO" in KLH10 and before doing anything else,
> the CPU immediately shoots to 100%. Is anyone else seeing this? In older
> versions of ubuntu/linux this didn't happen.

Handful of points:

* the idling is done by modifying the idle loop in the guest operating
  system to interact with the KLH10 idler device, not by identifying
  the idle loop like SIMH does.

* until the OS is up and running, there is no idling.  In other words,
  while at the BOOT> prompt there will be a loop consuming 100% CPU
  waiting for terminal input.  This is normal, and it has always been
  that way.

* if you have had the same TOPS20 system running, with idling, earlier
  everything points at your host os (ubuntu) no longer cooperating with
  KLH10.  I myself run (mostly) FreeBSD, and I have never had problems
  with idling the TOPSxx systems.

* for TOPS10, there are a couple of more things to consider, one of them
  is that the idler device by default is at device code 700, which can't
  be accessed from the mode the -10 idle code runs in.  Using 740 works.

I would look for what has changed in your host os (ubuntu) regarding
system timers and such.  Your setup *should* work.

> Thanks,
> Mark

--Johnny