[plug] UPS's

Steve Baker sbaker at icg.net.au
Mon Nov 6 18:18:46 WST 2000

----- Original Message -----
From: "Colin Muller" <colin at durbanet.co.za>
To: <plug at plug.linux.org.au>
Sent: Monday, 6 November 2000 17:56
Subject: Re: [plug] UPS's

> I'd really appreciate it if someone could tell me (or a pointer to one)
> what happens at point 5 below in a well-designed setup (and how it
> happens):
> 1. Power fails, UPS continues providing power
> 2. Power not being restored, UPS lets computer know via serial line and
> PM software that power is getting low.
> 3. Computer shuts down (or as Matt suggested, goes into single-user
> mode)
> 4. Power is restored.
> 5. ???
> Obviously, the ideal would be that in 5, the computer powers up again
> (or returns to networked multi-user mode). How is this achieved?
> Colin

Most newer ATX motherboards have an option in the BIOS to tell the system to
boot when they detect activity in certain places - the keyboard being the
most common, serial line (usually on a modem) being the other with a
practical use.  One time my PC at home fired itself up unexpectedly when
someone rang my modem line by mistake (it's one digit off my regular phone
no).  I was in the room at the time doing something else, and wondered what
the hell was going on.  I saw the modem lights blinking and immediately
disabled the wakup on IRQ 4.

It should be easy to get this sort of thing working on a newer PC with a
smart UPS - I'm not familiar with other hardware (such as Sun etc) which
also have a soft power switch.  Older PC's will just be on once the power is
restored to the UPS.

But a bigger problem is - what if the power is only on for say 10 minutes,
or even less, before going off again?  This time the batteries in the UPS
are already very low, and the system might not have time to power down
properly before losing power.  It might not even have time to finish coming
up properly.  Intelligent UPS's should not restore power to their dependent
devices until there is enough juice to guarantee a complete startup and
shutdown cycle.

"Ummmm..." -- Heisenberg.

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