Re: Increasing Hub Power to charge a mobile phone battery ?

[Alan Stern <stern@xxxxxxxxxxxxxxxxxxx>]

On Mon, 12 Mar 2007, Gordon McLellan wrote:

> My phone, a Nextel i830 (motorola) draws as much as 750mA when
> charging a low battery and transmitting at the same time.
> 
> I've modified the datacable to try to charge from USB, but the
> per-port current limit quickly kicks in and puts an end to it.
> 
> As I understand it, the 500mA as per the usb 2.0 spec is only
> available after a device enumerates as needing that much current.
> The default of 100mA is all that will be allowed, unless the device
> specifically asks for more.   I don't think my phone enumerates as a
> high power device, since I'm not able to draw more than 100mA.   I

You don't have to guess.  Look in /proc/bus/usb/devices.

> don't think there's anything that can be done on the host side to
> enable more current, the limits are probably imposed at the microcode
> level, inside the USB host interface chip.

As far as I know, the chip's only limit is 500 mA.  You should be able to 
tell if a device is violating a current limit, though; there would be an 
"overcurrent change" message in the system log.

> On older computers, those having only usb 1.1 ports, you might be able
> to get the full 500, or more, since I don't think current-limiting
> routines were imposed until 2.0 came around.

Alan Stern


-------------------------------------------------------------------------
Take Surveys. Earn Cash. Influence the Future of IT
Join SourceForge.net's Techsay panel and you'll get the chance to share your
opinions on IT & business topics through brief surveys-and earn cash
http://www.techsay.com/default.php?page=join.php&p=sourceforge&CID=DEVDEV
_______________________________________________
Linux-usb-users@xxxxxxxxxxxxxxxxxxxxx
To unsubscribe, use the last form field at:
https://lists.sourceforge.net/lists/listinfo/linux-usb-users