former power status

[Kerry Hoath]

This feature is not fail safe. Since the switch
is a software construct then your power supply needs to
provide sufficient standby current in order to keep the board happy.
Old computers had a dual pole single throw switch so when power was on
it stayed on so as soon as the power
came on the whole machine got power.
With the modern ATX design it is up to logic on the board and in the supply to
sense when a key is hit or network is accessed or
modem rings or button is hit and power up the machine.
Depending on how the power goes out; depends on what state the supply
is left in and how the cmos is notified that power has gone if at all.
I have seen bioses claim that they will power up a machine when
power returns; but rarely has this worked all of the time.
Usually the feature works when you don't need it to and fails silently
when you do need it.
I presume some standby current is stored in some capacitors on the board in order to save
some state info in cmos or in a circuit to tell the machine what
the previous state was. (the above sentence is speculation so
corrections but no flames accepted).
If this info is not set correctly or not stored or doesn't work for reasons of the
supply or board or mysterious circumstances the machine
won't power on.
It is possible to get this feature to work some of the time but not reliably.
get yourself a Jell-cell UPS which should
keep the box going for 30-45 minutes assuming no monitor.
You also get controlled shutdown via serial port notification;
and protection against short outages. If you do have an outage long enough to
exhaust the ups then your power on after wibble feature might save you
but don't count on it.
If it is important for a server to come back on and the
server is ATX; I get an UPS or call someone to press
a button.

Note also that if an ATX supply has power go on and off multiple times rapidly or
has power dips the surge protector can't account for;
it can lock up in such a way that requires you to
turn off the power at the wall for 30 seconds or more to reset the caps in the
supply. I don't know why this occurrs in atx supplies, I think
the switch-mode gets confused.

Regards, Kerry.
On Tue, Jun 04, 2002 at 11:55:21PM -0500, Gregory Nowak wrote:
> Hi all,
> 
> I went down this evening to add a piece of hardware, and to reconfigure my kernel. 
> 
> In my machine's cmos, there is an option asking what should be done when the power goes off and then comes back on. The choices are: stay off, turn on, or return to former power status, which means that the machine should go into whatever power state it was at when the power went off.
> 
> The last time I had some one here about 3 weeks ago who hellped me reconfigure my bios after upgrading it, the power option described above was set by me to former power status. As far as I know, it shouldn't have changed since.
> 
> Anyway, when I added my hardware this evening, I also upgraded to ext3. Since this machine is acting now as the main server (dns, mail, ETC.) for my domain, I wanted to check if the former status choice really works. So, while the box was running (all users were logged off), I hit my serge protector's power switch, causing it to shut off power to the server. When I turned the power back on after about a minute, the pc stayed off. Assuming the power option described above is still set to former power status (I have no reason to suspect otherwise), why isn't the machine powering back up when the power comes back on, and when it was left on before the power was turned off? Is there some sort of a difference between me flipping the power switch on my serge protector, and the power going off naturally? Thanks.
> Greg
> 
> 
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-- 
Kerry Hoath:  kerry at gotss.net kerry at gotss.eu.org or  kerry at gotss.spice.net.au
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