Subject: Re: SIMH runs NetBSD/vax
To: Chuck Dickman <>
From: Anders Magnusson <>
List: port-vax
Date: 03/13/2002 10:16:09
> Anders Magnusson wrote:
> > 
> > >
> > > I noticed that the kernel is busy-waiting when idle. Can this not be
> > > improved? I am used to the Motorola 68000 which has a WAIT instruction
> > > that halts the CPU until an interrupt occurs...
> > >
> > Unfortunately no, the vax do not have any such instruction, busy-wait
> > is the only solution.
> > 
> > -- Ragge
> I have used the SIMH pdp-11 simulator and noticed that although the software
> (2.11BSD) uses the WAIT instruction. The processor load does not decrease.
> So it seems that even when the simulated processor is idle, the simulator
> is not. This is using Linux/386. I would like to have a pdp-11 running BSD
> or RT-11 in a window and then ignore them, but I always have to halt the
> simulator or the host machine performance is like mud.
That would probably be simple to fix. The P11 PDP11 simulator uses the 
wait instruction in the named way so it actually idles when the cpu calls
wait. It's probably not difficult to add that to simh either.

-- Ragge