[HECnet] UPS driven OPC$CRASH?

[Thomas DeBellis]

Can anybody elaborate more on what the VMS power failure options are?  
OPC$CRASH sure looks like a crash, but what happens before the belly up?

Some time ago (at least a decade), I started looking at re-enabling the 
Tops-20's power failure code with an eye towards making some changes to 
the KLH10 micro-engine.  So clearly, at a minimum, I would have needed 
to catch a SIGPWR and then do something useful with it, which then meant 
some nosing around in APRSRV and SCHED and some other monitor code.

At one point, Tops-20 appears to actually have been able to save what it 
was doing and cleanly resume on power up; in other words, not crash.  
Some hardware was able to detect a power fail and cause an APR generated 
PI.  Any running process was dismissed, the front end was notified and 
any disk I/O was completed.  The caches were shut off.  That leaves the 
volatile structures.  Assuming you were running with core (MA20's), you 
could survive the power outage.  A power on would generate an interrupt 
which checked whether the power off handling was completed.  If so, away 
you went.

I don't ever remember ever that working at Columbia, which stands to 
reason since we were running semi-conductor memory. We only had a single 
MA20 to increase the total memory of one particular system to 3.75 MW 
(the rest was MF20).

However, the code itself is still there.  Fully supporting the power 
fail would have then involved the 20 signaling the micro-engine (perhaps 
by doing a CONO to the Idler device with a magic bit set), that it was 
done.  KLH10 would then have had save about 34 MB of memory and exit.

It wasn't clear what volatile structures in the micro-engine needed to 
be preserved, so I stopped there and turned to other things.  If the 
host operating supported sleep, maybe not much. You can't just 'sleep' 
Tops-20 because on resumption, the keep-alive counters won't have been 
updated and it will immediately crash.   It has to know the power went out.

If you don't have a UPS, you may not have a lot of time to do things.  
Depending on the power supply and capacitor usage and discharge, you 
might have only milliseconds.  I would imagine that's plenty for SSD 
storage, it might not be enough for rotating media.

> ------------------------------------------------------------------------
> On 5/30/20 1:14 PM, Supratim Sanyal wrote:
>
> Good afternoon everyone,
>
> What are you guys doing to get something like OPC$CRASH invoked when a 
> UPS signals it is on battery?
>
> I have serial connectivity to TTAx ports on a Microvax 3100-80 running 
> OVMS 7.3. Recommendations on a UPS?
>
> Generally how do you get a VAX to shut down immediately on UPS going 
> on battery?
>
> Thanks in advance
> Supratim
>
>
> ---
> Supratim Sanyal, W1XMT
> 39.19151 N, 77.23432 W
> QCOCAL::SANYAL via HECnet <http://www.update.uu.se/~bqt/hecnet.html>
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