[LAU] USB has power even when PC is shut down?

[David Olofson]

On Monday 07 May 2007 19:19, Florin Andrei wrote:
[...]
> Well, I guess this is more of a hardware question, but still, what's
> the deal with USB on these new motherboards? Is the bus still
> powered even after the system is turned off?

Yes, on some motherboards. It *might* be possible to select this in 
the BIOS setup in some cases, but I can't remember seeing that option 
anywhere yet. The boards I've seen so far either have USB power 
whenever there is AC power, or they don't.

Maybe it's wired to the suspend-to-RAM logic in some cases...?

I believe the idea is that WLAN interfaces and the like should stay 
awake, and potentially be able to wake the PC up when someone tries 
to talk to it.

A side effect is that hardware that won't cold plug properly, 
sometimes works just fine with motherboards that leave the USB power 
on. Probably a coincidence, though; driver forgets to upload firmware 
in the cold plug case, or something like that.

Also note that powered USB hubs are usually powered at all times, even 
when not connected to a host.


//David Olofson - Programmer, Composer, Open Source Advocate

.-------  http://olofson.net - Games, SDL examples  -------.
|        http://zeespace.net - 2.5D rendering engine       |
|       http://audiality.org - Music/audio engine          |
|     http://eel.olofson.net - Real time scripting         |
'--  http://www.reologica.se - Rheology instrumentation  --'