[HECnet] Speaking of IDLE

[Steve Davidson]

-----Original Message-----
From: owner-hecnet at Update.UU.SE 
[mailto:owner-hecnet at Update.UU.SE] On Behalf Of Paul_Koning at Dell.com
Sent: Monday, June 04, 2012 20:58
To: hecnet at Update.UU.SE
Subject: Re: [HECnet] Speaking of IDLE


On Jun 4, 2012, at 6:22 PM, Johnny Billquist wrote:

On 2012-06-04 13:52, Brian Hechinger wrote:
Anyone know how it works? I'd really like to get it 
working on Solaris.

Simple. For a VAX, simh tries to detect the instruction 
sequence that the OS do in the idle loop. That's why it 
depends on which OS you are running on the emulated machine.

For a PDP-11 it is (supposedly) simpler, since hopefully 
the idle loop 
of the OS uses the PDP-11 WAIT instruction, but that 
actually depends 
on which OS we're talking about. Not sure that RT-11 do, 
for instance. 
(I have some vague memory of discussing this with someone a 
few years 
ago, and coming to the realization that not all PDP-11 
software might 
be using the WAIT.)

For other hardware and OS combinations, the answers might 
differ even more.

The doc says that RT and Unix do it differently (no WAIT).   I 
haven't seen the Unix code but I did see the one for RT (F/B 
version), and indeed, no WAIT instruction there.   I'm not 
sure why not.   RT11 S/J seems to just be full of spin loops, 
no central idle of any kind that I can see.

	paul



Paul,

I think that depends on whether or not the idle loop pattern (for the
console light display) is being used.   The lights pattern most certainly
makes use of the WAIT instruction.   The SJ monitor is a completely
different beast than FB and friends - no question about it!

-Steve