> > You need to state these things carefully. A complete power-off does > > reset/disconnect USB devices. However, turning off your computer > > might not do a complete power-off; it may well leave suspend current > > available. If that's true, USB devices won't be disconnected. > > Examples, please. Thinkpad X32 certainly does not provide power on USB > when turned off. I think Alan's point applies more directly to things like ACPI S4 state than ACPI S5 (off) ... it's quite legit for USB controllers to maintain VBUS power even after entering D3cold, which they'll often do in S4 sleep. EHCI for example is carefully specified in terms of what registers are powered through PCI VAUX, and it's designed to support remote wakeup from D3cold. VAUX provides suspend current to the various USB devices that are connected, which can initiate remote wakeup by pulling D+ high for long enough (maybe 20 msec). - Dave
