On Sat, 7 Nov 2009, Bruno [UTF-8] Prémont wrote: > > When a hub is bus-powered, the USB specification does not allow it to > > provide more than 100 mA to each port. Since the Sandisk pen wants > > more than 100 mA, the kernel rejects its configuration. You can > > override this decision if you want by writing the appropriate config > > value to the pen's /sys/bus/usb/devices/.../bConfigurationValue file. > > That's a not so nice limitation of the spec... It would have been more > useful if the "available" power could be forwarded to a single port of > the HUB even if in that case 0ma remain for the other 3 ports. I don't know why they decided to do it like that, but the language in the spec is very clear. Section 7.2.1 says: External ports in a bus-powered hub can supply only one unit load per port regardless of the current draw on the other ports of that hub. A unit load is defined earlier to be 100 mA. Alan Stern -- To unsubscribe from this list: send the line "unsubscribe linux-usb" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
