Subject: Re: SIMH runs NetBSD/vax
To: None <>
From: Matthias Buelow <>
List: port-vax
Date: 03/16/2002 05:31:32
"Chuck Dickman" <> writes:

>Anders Magnusson wrote:
>> 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.
>I looked over SIMH and it seems to react to the WAIT instruction by
>a state in which instructions are not decoded until an acception occurs,
>but it still polls for keyboard input and simulated device activity.
>The simulator control program does not seem to have been designed with
>idling in mind.

Concerning the proposals of recognizing an idle loop...
I highly doubt to be able to unambiguously detect a
sequence of instructions which in the kernel implements
an idle loop... what if the same kind of instructions
happens to be coded in an application program or somewhere
else?  A dedicated microcoded "illegal" op, i.e., which
is then trapped and implemented in microcode would probably
be a lot more towards correctness than heuristically guessing
something in some code seemingly specific sequence...