[Ham-Computers] RE: Computer - Power Management Query

Thu, 2 Jan 2003 11:21:19 -0800

First, the basic answers to your questions...

LED on M/B - Can be one of two things...1) a power LED to remind you that
power is *ALWAYS* supplied to the M/B when the A/C is plugged in (and
*hardware* switch on, if supplied), or 2) a *link* indicator for the
on-board NIC.

IR Mouse light - if mouseport based, "wake on mouse" is enabled in BIOS.  If
USB based, the USB bus is supplying +5v when in "soft-off" (to support "wake
on" functions).

LED on hub - signifies that a your PC is connected and accepting data even
when off (usually for a "Wake On Lan" (WOL) signal)

As far as the BIOS settings go, yes, you can probably change these settings.
They will probably listed as "Wake-on-LAN" and "Wake-on-Mouse" or something
similar.  If the mouse is USB, it may not be possible as the root USB bus is
powered in "soft-off" (see below).

The nitty-gritty...

Most current motherboards are built to "ATX" power specs (developed by
Intel).  With ATX style systems, power is *ALWAYS* fed to certain components
to monitor for "wake" conditions.  With ATX style systems, the powerswitch
on the front of the PC is a "soft" switch (momentary) and switches the
system from "on" and "soft-off" states.  Often, a physical "hard" switch is
wired on the power supply itself, but this is not required by spec (my PC
Power & Cooling 400W supply has no hard switch).  Using this switch will
fully power down the system a "hard-off" state.  During the "soft-off"
state, the system CPU is powered-down, but the motherboard chipset circuitry
is "on" and handling power management functions.

As mentioned above, one of the possible "wake" conditions is mouse movement
or clicks.  Many "power management" keyboards have "power-on" and "sleep"
buttons.  Since power is required to operate these devices, the
keyboard/mouse and USB busses remain powered when the system is "soft-off".
This would explain why your IR Mouse LED is on...it's still powered.

Another possible "wake" condition is a "WOL" signal from the network.  This
allows system administrators in a large network environment the ability to
perform system maintenance on a remote system even though a worker
"turned-off" the system.  As long as the system is only in a "soft-off"
state, a WOL signal will power-up the system.  Hence the reason your hub
indicates a link even with the PC "turned off".

Operating Systems interface with ATX-style motherboard's power management
via Advanced Configuration and Power Interface (ACPI) controls.  The ACPI
spec was co-developed by  several companies (MS, Compaq, Intel, Toshiba,
Phoenix) and allows OS' to properly perform hardware configurations (e.g.
Plug-n-Pray) and to handle power management functions (such as Standby,
Hibernate, display controls, etc).  Prior to ACPI was Advanced Power
Management (APM).  Most older motherboards since the 80486 support APM and
most ACPI compliant boards are backwards compatibile with APM.

The "Energy Star" spec requires that a device consume no more that 5 watts
of power in the "soft-off" state.  That's 1 amp at +5v.  Considering that a
typical mouse only uses 50ma and a NIC's WOL circuit consumes probably the
same, it's safe to assume that a PC can meet the Energy Star spec in
"soft-off" and still have "wake" functionality.

You can get more on the ACPI spec at http://www.acpi.info.

73,

  - Aaron Hsu, NN6O (ex-KD6DAE)
    {nn6o}@arrl.net
    {athsu}@unistudios.com
    No-QRO Int'l #1,000,006
    . -..- - .-. .-   ".... . .- ...- -.--"

-----Original Message-----
From: [email protected] [mailto:[email protected]]
Sent: Wednesday, January 01, 2003 4:41 PM
To: [email protected]
Subject: [Ham-Computers] Computer - Power Management Query

Does anyone know a web address or can explain modern power management 
methods. eg

Just upgraded to a Pentium IV ASUS S370 motherboard and notice the following

when the computer is connected to the mains power socket :

1.  LED on Motherboard continuously ON.
2.  IR Mouse light always ON.
3.  LAN connection always shows ON on the LAN Hub.

I presume this is modern accepted "Low Power" Consumption convention because

no reference in Manual - is the above a MODE and can it be changed in the
BIAS - 
it confuses me. 

One should therefore always disconnect computer from the power before making

any hardware changes.

Dont want to consume too much bandwidth with this slightly off topic subject
but if 
anyone can point me in the right direction would appreciate it.

Regards

Eddie
VK2BEH