see
papers at
http://www.usb.org/developers/whitepapers/ especially
http://www.usb.org/developers/whitepapers/power_delivery_motherboards.pdf
http://www.usb.org/developers/whitepapers/white-4c.pdf
for details on the designs
I think we really have two issues,
1. The OP had a problem with not being able to run a bus powered USB device
when his host was turned off.
I presume that this was because there was no Vusb present on the bus to
power his device. Adding a powered hub will not help here because, with no
Vusb from the host, the hub will not enable (power) any down stream ports.e
There is standby power there, but because of limits on 5vsby, only low
power devices will be able to receive power from a mother board connection.
This is aleviated by a powered hub.
2. Separate issue: some hosts are reported to support some USB devices, for
wake-up, when they are supposedly powered off.
Vendors do many non standard things in the BIOS. The last I looked, this
would be one, so I have some questions on these features, if anyone want to
take the time ;=):
a. If you execute a Shutdown from the Start Menu (Turn Off on the XP
Start Menu as opposed to StandBy), can you wake your system with your mouse
or keyboard? Is the power light on, off or flashing?
Depends on the systems. Most systems will not have any lights on. Some will
still have the light on an Optical mouse on. A book pc I have has a single
light that only comes on when the system is "turned off" with a shutdown.
Does the same with Win98/2k/XP and mandrake or knoppix Linux. The keyboard
powers the system up through a complete reboot. Power off in an ATX system
is really a super standby where the system can be awakened by many events
such as WOL, WOM, and Keyboard/mouse.
b. When your system powers on, does it go through the full BIOS check,
etc?
Yes. Full startup
c. My MS keyboard has a sleep button on it, which puts the system, almost
instantly, into a sleep mode from which it can be wakened by a press of a
key. But, this is not a powered down mode, the power light is flashing, not
off, RAM is still powered and refreshed, etc. I assume this is not what we
are talking about.
Most multimedia keyboards have 2 related buttons. One is the sleep button,
the other does a power off, just like the front panel push button. Does the
same soft off function, and a full restart happens when the power button
(or power key on keyboard so equiped or configured) is pressed.
d. Do your USB keyboards and mice still power on the system when
connected through an external hub when your system is in this powered down
(but apparently not out) mode or do they need to be plugged into the root
hub, i.e. does the BIOS support hub devices or just mice, keyboards, etc.
that are directly attached?
Depends on the hub. I have 2 belkins and a "scitek (sp?)" that do support
power up. I have had others that don't
e. Do all USB ports receive power when the system is in this state, or
only ones that have a mouse, keyboard or bootable device attached?
Thanks in advance,
Seems to be power to low power devices from the mother board. Many powered
hubs will have power to any device plugged in. For example, on my cheap
Belkin hub, I have a wireless network adapter and optical mouse that are
powerered on (at least the power lights are on) as long as the hub is
powered, no matter if the computer is on, or plugged in, or the hub is
plugged into the computer. My USB2.0 hub powers off the Wireless adapter
(which at 500ma is a high power device) while my mouse stays on. Other non
pointing devices have stayed on as well (for example a powerline network
interface). The point seems to be that pointing/human interface devices
(mice and keyboards) mostly still receive power. High powered devices don't
unless on a powered hub that constantly supplies power, and other devices -
it depends on the powered hub/motherboard. I have seen in the options for
some USB 10/100 network interfaces the option to "wake on lan", so I assume
they are expecting power even in soft off. The specs are not specific on
requirements there.
