PC turned itself on. PME ?

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HI guys,

I'm building up a mobo I inherited, MSI P4 (not sure of exact ID) with
an award BIOS. It's plugged into my (wireless) router, and the modem
is connected to my phone line.

Last couple of days, my wife has found it on, even though it was
switched off the night before. This is puzzling me. One thing which
may be a clue, is when I plugged the modem in, Sunday, the PC turned
on !

After looking in the BIOS, I found a power-management setting "Wake on
PME" which was enabled (now disabled !). Having looked up PME to mean
Power Management Event, I was wondering if there was something in the
modem, or router which was causing them to issue a PME signal ?

Can anyone confirm or dismiss this theory ?

Re: PC turned itself on. PME ?

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You should also look in your BIOS for Wake on Lan - perhaps the router is
sending a wake-up signal that way. You should turn off your PC at the wall
when not in use as it uses power even when 'turned off'

Re: PC turned itself on. PME ?

Jethro wrote:
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The PME signal is something that was added to the PCI bus. It is bussed,
meaning all PCI slots have access to it. Since the PCI bus is also used
for things like onboard Ethernet chips, it also means that an onboard
Ethernet chip has access too. (There may well be a similar mechanism
for PCI Express. The only reference I have there, is a connector pinout,
and I see a WAKE# pin on the connector.)

The second ingredient, is the chip in question would need a source of
standby power. PCI slots have some provision for standby power, and
definitely the onboard Ethernet chip is going to have it (it is a
common feature, to support Wake On LAN).

As for the waking functions of the Ethernet chip, there are two
types. Some chips support "wake on activity". In other words, if
they saw any packet, or if the PHY interface noticed a state change,
they might wake up. The second kind is "Magic Packet". In that case,
not just any packet will wake them. Specific data must be in the packet,
for that to happen.

http://en.wikipedia.org/wiki/Magic_packet (not the best article)

If you look in Windows, for the custom settings for the LAN chip,
you may find reference to the various waking options. If the chip
is well behaved, then disabling a couple of those settings, should
result in restful sleep :-)

Disabling PME in the BIOS, should make it more difficult for this
to happen (assuming that the BIOS interprets this literally as
an attempt to prevent any kind of wake from sleep activity). PME
terminates in some chip, like maybe the Southbridge, so I assume
a configuration bit would be present there, to either pay attention
or ignore PME, when the computer sleeps.

So there should be two levels of control available to you. BIOS and OS level.


Re: PC turned itself on. PME ?

On Wed, 23 Jan 2008 01:55:53 -0800 (PST), Jethro

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Yes the PME setting can be responsible for enabling another
PCI device to turn the system on.   Had you turned your
router, switch, or another computer this system is networked
too off?  If so, the NIC wake on link setting might have
caused it and is sometimes deactivated in the properties for
the nic in (windows, etc).  If it's the (analog dialup?)
modem, have someone call that telephone # while system is
off to see if that turns it on.  Regardless, unless there is
a separate cable from the modem to the system wake-on-ring
or lan header, turning off PME should have the correct
result... unless you needed PME enabled to turn on the
system with a different event.

Re: PC turned itself on. PME ?

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Yesterday, the PC didn't come on, so I'm assuming I was right. A
little more furtling in Windows showed me the modem had the "allow
this device to bring the computer on" flag checked. I've unchecked
that as well now.

Thanks for the (very informative) help

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