Based on kernel version 2.6.26. Page generated on 2008-07-16 21:12 EST.
1 What: /sys/bus/usb/devices/.../power/autosuspend 2 Date: March 2007 3 KernelVersion: 2.6.21 4 Contact: Alan Stern <stern[AT]rowland.harvard[DOT]edu> 5 Description: 6 Each USB device directory will contain a file named 7 power/autosuspend. This file holds the time (in seconds) 8 the device must be idle before it will be autosuspended. 9 0 means the device will be autosuspended as soon as 10 possible. Negative values will prevent the device from 11 being autosuspended at all, and writing a negative value 12 will resume the device if it is already suspended. 13 14 The autosuspend delay for newly-created devices is set to 15 the value of the usbcore.autosuspend module parameter. 16 17 What: /sys/bus/usb/devices/.../power/level 18 Date: March 2007 19 KernelVersion: 2.6.21 20 Contact: Alan Stern <stern[AT]rowland.harvard[DOT]edu> 21 Description: 22 Each USB device directory will contain a file named 23 power/level. This file holds a power-level setting for 24 the device, one of "on", "auto", or "suspend". 25 26 "on" means that the device is not allowed to autosuspend, 27 although normal suspends for system sleep will still 28 be honored. "auto" means the device will autosuspend 29 and autoresume in the usual manner, according to the 30 capabilities of its driver. "suspend" means the device 31 is forced into a suspended state and it will not autoresume 32 in response to I/O requests. However remote-wakeup requests 33 from the device may still be enabled (the remote-wakeup 34 setting is controlled separately by the power/wakeup 35 attribute). 36 37 During normal use, devices should be left in the "auto" 38 level. The other levels are meant for administrative uses. 39 If you want to suspend a device immediately but leave it 40 free to wake up in response to I/O requests, you should 41 write "0" to power/autosuspend. 42 43 What: /sys/bus/usb/devices/.../power/persist 44 Date: May 2007 45 KernelVersion: 2.6.23 46 Contact: Alan Stern <stern[AT]rowland.harvard[DOT]edu> 47 Description: 48 If CONFIG_USB_PERSIST is set, then each USB device directory 49 will contain a file named power/persist. The file holds a 50 boolean value (0 or 1) indicating whether or not the 51 "USB-Persist" facility is enabled for the device. Since the 52 facility is inherently dangerous, it is disabled by default 53 for all devices except hubs. For more information, see 54 Documentation/usb/persist.txt. 55 56 What: /sys/bus/usb/device/.../power/connected_duration 57 Date: January 2008 58 KernelVersion: 2.6.25 59 Contact: Sarah Sharp <sarah.a.sharp[AT]intel[DOT]com> 60 Description: 61 If CONFIG_PM and CONFIG_USB_SUSPEND are enabled, then this file 62 is present. When read, it returns the total time (in msec) 63 that the USB device has been connected to the machine. This 64 file is read-only. 65 Users: 66 PowerTOP <power[AT]bughost[DOT]org> 67 http://www.lesswatts.org/projects/powertop/ 68 69 What: /sys/bus/usb/device/.../power/active_duration 70 Date: January 2008 71 KernelVersion: 2.6.25 72 Contact: Sarah Sharp <sarah.a.sharp[AT]intel[DOT]com> 73 Description: 74 If CONFIG_PM and CONFIG_USB_SUSPEND are enabled, then this file 75 is present. When read, it returns the total time (in msec) 76 that the USB device has been active, i.e. not in a suspended 77 state. This file is read-only. 78 79 Tools can use this file and the connected_duration file to 80 compute the percentage of time that a device has been active. 81 For example, 82 echo $((100 * `cat active_duration` / `cat connected_duration`)) 83 will give an integer percentage. Note that this does not 84 account for counter wrap. 85 Users: 86 PowerTOP <power[AT]bughost[DOT]org> 87 http://www.lesswatts.org/projects/powertop/