[Simh] error

[Mark Pizzolato]

On Tuesday, February 9, 2016 at 2:16 PM, Johnny Billquist wrote:
> On 2016-02-09 22:58, Mark Pizzolato wrote:
> > You may recall that older computers didn’t have a way to
> > programmatically power themselves down.
> 
> Well, this isn't about powering down, but halting...

Well, not really.  The VAX has a HALT instruction and if that was all that was needed, it could be executed.  
However nothing defines HALT to do anything but stop executing instructions.  Well sitting in an infinite loop is sort of like that, but to save power someone might want to turn the system off since none of the VAX model systems that simh simulators for has any way to programmatically influence power.

The original poster executed the operating command to shutdown the operating system.   That would imply that he didn't want it running anymore.  If he wanted it to continue running after shutting down, the operating system command to reboot the system could have been executed.

> Older and older... It's actually more of a trait of newer computers...
> Back when you had frontpanels and all that stuff, halting the computer were
> considered normal. With the disappearance of most meaningful ways to
> interact with computers at such low levels, halting the computer also went
> away, as it wasn't that useful, and the question the becomes, how would you
> restart it?
> 
> > VMS is one of those systems.
> 
> Er... VAX. VMS is an operating system. :-)
> 
> > When you shutdown a VMS system it closes all files and cleans up
> > everything going on in the operating system then it displays a message
> > which says something like “SYSTEM SHUTDOWN COMPLETE - USE THE
> CONSOLE
> > TO HALT THE SYSTEM” and then it goes into an infinite loop with
> > interrupts disabled.  The simulator detects this condition which will
> > never produce useful results from the simulated system again without
> > operator intervention and allows you to do that.
> 
> Right.
> 
> > Would you want it to behave differently?
> 
> I think simh does a reasonable thing, if you ask me. It was a mistake that the
> VAX didn't standardize how to halt or reboot the machine, but that is not
> simhs fault.

There are absolutely mechanisms to reboot each of the VAX systems which 
simh has simulators for and reboot does work fine on these simulators.

As it turns out, these mechanisms usually use the HALT instruction which 
interacts with some model specific features of the model specific console 
subsystem to effect the reboot.  So, clearly the message which VMS issues
"USE THE CONSOLE TO HALT THE SYSTEM" is actually using the word HALT 
to mean 'turn off' rather than anything which relates to the halt instruction.

> And some VAXen do have the ability to power themselves down as well...
> But it's all very model specific.

If we had a simulator for a VAX model system which had that functionality 
it would be supported.

- Mark

> >
> > *From:*Simh [mailto:simh-bounces at trailing-edge.com] *On Behalf Of
> > *Bill Cunningham
> > *Sent:* Tuesday, February 9, 2016 1:46 PM
> > *To:* simh at trailing-edge.com
> > *Subject:* [Simh] error
> >
> >      After using shutdown on my virtual VMS, it dropped to the simh
> > prompt and had this error.
> >
> > Infinite loop, PC833DC8D3 (BRB ...)
> >
> > and the same hex number were the ... is. What does that mean?
> >
> > Bill
> >
> >
> >
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> 
> --
> Johnny Billquist                  || "I'm on a bus
>                                    ||  on a psychedelic trip
> email: bqt at softjar.se             ||  Reading murder books
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