[Simh] No recognizable idle loop

[Norman Lastovica]

SRI (for charon-vax) includes a utility that appears
to detect the idle loop in the emulated system and
somehow notifies the emulator of this and presumably
then the emulator is able to 'throttle back'. check
out:

www.emulatorsinternational.com/downloads/cvax3100.pdf

> -----Original Message-----
> From: simh-bounces at trailing-edge.com
> [mailto:simh-bounces at trailing-edge.com]On Behalf Of bsupnik at comcast.net
> Sent: Monday, April 03, 2006 11:09 AM
> To: simh at trailing-edge.com
> Subject: [Simh] No recognizable idle loop
> 
> 
> I've seen this question so many times, here's the definitive answer: 
> there is no idle job or simple idle loop in VMS.  Instead, VMS loops 
> in the scheduler (at IPL 3) waiting for interrupts or for something to 
> appear on a scheduler queue as a result of a higher priority 
> interrupt.  Here is the code from VMS 7.2:
> 
> 61$:
> JSB	G^EXE$PROC_IDLE		;SEE IF WE HAVE  CPU SPECIFIC IDLE LOOP
> BLBS	R0,61$			;NO - GO TO STANDARD LOOP
> BBC	#CPB$V_RUN,CPU$L_CAPABILITY(R3),70$ ; RUN CAPABILITY PRESENT?
> BBS	R1,G^SCH$GL_IDLE_CPUS,60$ ;LOOP UNTIL WE AREN'T IDLE
> BRB	65$
> 61$:
> BBC	#CPB$V_RUN,CPU$L_CAPABILITY(R3),80$ ; RUN CAPABILITY PRESENT?
> TSTL	G^SCH$GL_TBSH		; Class scheduler present?
> BEQL	64$			; No, see if still idle
> JSB	G^SCH$CLASS_IDLE	; Yes, see if TBS job runnable
> 64$:
> BBS	R1,G^SCH$GL_IDLE_CPUS,61$ ;LOOP UNTIL WE AREN'T IDLE
> 
> This varies from release to release as well.
> 
> /Bob Supnik
> 
> > 
> > Message: 5
> > Date: Mon, 03 Apr 2006 08:55:43 -0600
> > From: Villy Madsen <Villy.Madsen at shaw.ca>
> > Subject: [Simh] VMS Idle loop
> > To: simh at trailing-edge.com
> > Message-ID: <69d691969d7ad0.69d7ad069d6919 at shaw.ca>
> > Content-Type: text/plain; charset=us-ascii
> > 
> > Does anyone have a clue what the vax/vms idle loop looks like..
> > 
> > at one point in time I had been told it was just a
> > BRB pointing to itself
> > 
> > (so would that be brb 0 or brb -1 - it's been too many years and and I can't 
> > remember).
> > 
> > 
> > In case you are wondering, I am wondering if it would be possible to build a 
> > throttle into the simulator so that it doesn' run wide open all of 
> the time...
> > 
> > Villy
> > 
> > 
> > 
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> > End of Simh Digest, Vol 29, Issue 2
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