Subject: Re: SIMH runs NetBSD/vax
To: Chuck Dickman <>
From: Lars Brinkhoff <>
List: port-vax
Date: 03/13/2002 07:48:31
"Chuck Dickman" <> writes:
> 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.
> 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 even if the VAX had such an instruction, SIMH
> might not do the right thing.

That's right.  SIMH mostly ignores the PDP-11 WAIT instruction.
Sometimes I hack the simulator to sleep for a short while instead,
which seems to work well.  It's only a couple of lines to add.

Lars Brinkhoff     Linux, GCC, PDP-10,
Brinkhoff Consulting    HTTP programming