> Does the device draw more power or does the host or is the device bus powered? This device is USB bus powered. I am not sure I know whether the addtional power comes from device itself or hub/controller. Besides raising question in forum, is there any recommanded reading material for USB power? specifically for Linux is best. Thanks! Samuel 2010/6/30 Oliver Neukum <oneukum@xxxxxxx>: > Am Mittwoch, 30. Juni 2010, 15:49:00 schrieb Samuel Xu: >> Thanks Oliver Neukum!You solved lots of puzzle in my mind!! >> Some further questions: >> >> Q5: I still can't fully understand how autosuspension saving power. If >> a device driver only saves the device state and do not fill any >> device's physical registering to communicate with device, (hi, please > > OK, I see. A USB device is physically suspended by sending a control > message to the hub the device is plugged into. The core USB code > does that after it has given the device driver an opportunity to prepare > the device for suspension. > >> sleep), then suspend() return ok . I guess the HW device should >> continue to consume power as normarlly, since HW device knows nothing >> about the suspension request from host system. Is it mean there are >> some physical power supply change in USB bus for autosuspension >> callback? Or autosuspend means a special USB package broadcast in USB >> bus after suspend() callback return, USB device who received it must >> do some power saving work per USB SPEC? > > It changes a feature on a port which is propagated down. > >> Q6: Does it mean the most power-optimal usb system is: everything >> marked it can be autosuspend, including hubs and usb devices? there >> isn't any squeeze potential for usb power any more? > > For optimal power consumption anything that can be suspended should > be suspended. You will find that in practice many devices crash if asked to > suspend. > >> Q7: A more specific question is: If a device running on Linux is >> already enabled autosuspend and idle now, while it is physically >> consumes more power than running on Windows when idle. Is there >> anything known issue can cause this power difference? Is there any >> know advantage for USB windows power management, e.g for more mechnism >> than autosuspend? > > Does the device draw more power or does the host or is the device bus powered? > > Regards > Oliver > -- 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
