On Thu, 18 Aug 2005, Robert Marquardt wrote:
> I hope this is the correct group for this message.
>
> I have a (HID) device which has a descriptor with two configurations.
> The first configuration is high power wheras the second one is low
> power. The rest of the configurations are identical and form a valid HID
> device.
> The configurations are numbered in reverse, ie the first (hi power)
> configuration is numbered 2 and the following low power configuration is
> numbered 1.
>
> The idea behind that is to have the device be enumerated as hi or low
> power device depending on the hub it is connected to.
>
> On my SuSE Linux 9.3 though the device gets configured for hi power even
> on a low power port. Obviously Linux gets confused by the non-standard,
> but valid configurations.
Linux doesn't get confused. The problem is that power budgeting is
ignored when choosing device configurations. There's even a comment about
it in the source code:
static int choose_configuration(struct usb_device *udev)
{
int c, i;
/* NOTE: this should interact with hub power budgeting */
The current strategy is to avoid vendor-specific interface classes and
Microsoft RNDIS, and to use the first otherwise available configuration.
(The numbering is ignored totally.) That's why you end up with the
high-power config.
Note that you can set config number 1 manually, by doing
echo 1 >/sys/bus/usb/devices/your device's id/bConfigurationValue
Alan Stern
-------------------------------------------------------
SF.Net email is Sponsored by the Better Software Conference & EXPO
September 19-22, 2005 * San Francisco, CA * Development Lifecycle Practices
Agile & Plan-Driven Development * Managing Projects & Teams * Testing & QA
Security * Process Improvement & Measurement * http://www.sqe.com/bsce5sf
_______________________________________________
[email protected]
To unsubscribe, use the last form field at:
https://lists.sourceforge.net/lists/listinfo/linux-usb-users
