Grant <emailgrant@xxxxxxxxx> writes: >>> Can I disable VBUS while keeping the rest of USB functional for a >>> device that does not require bus power? >> >> unfortunately not, your device would see a disconnection. The reason is >> that even though you don't really put any load on the bus, the PHY still >> samples VBUS levels to know when the session is valid (VBUS > 4.4V). > > > Is that part of the USB spec or is it a Linux driver convention? You know you can just download the spec and find out such things for yourself instead of having others spell it out for you? Anyway, from section 7.2 "Power Distribution" of the USB 2.0 spec: No device shall supply (source) current on V BUS at its upstream facing port at any time. From V BUS on its upstream facing port, a device may only draw (sink) current. They may not provide power to the pull-up resistor on D+/D- unless V BUS is present (see Section 7.1.5). When V BUS is removed, the device must remove power from the D+/D- pull-up resistor within 10 seconds. So your device can work at most 10 seconds after VBUS is disconnected. Bjørm -- 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
