[HECnet] Speaking of IDLE

[Johnny Billquist]

On 2012-06-05 03:24, Steve Davidson wrote:


-----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!

Well, there are more ways to spin a cat... Or spin the lights in this case. WAIT is one way to show something on the front panel. Loading the display register is another.
RT-11 is in fact using the Switch Register at 177570 to display things on the front panel.
Look at RMONFB.MAC, around line 4800, to see the code.
(Every time I read the RT-11 sources, I feel a little dirty... No offense meant for the RT-11 fans around here or anywhere.)

It's all conditionalized on LIGH$T, and there is not even the option if you are running the SJ monitor...

	Johnny

-- 
Johnny Billquist                                   || "I'm on a bus
                                                                  ||   on a psychedelic trip
email: bqt at softjar.se                         ||   Reading murder books
pdp is alive!                                         ||   tryin' to stay hip" - B. Idol