Documentation/usb/proc_usb_info.txt - linux - Git at Google

 /proc/bus/usb filesystem output
 ===============================
 (version 2010.09.13)


 The usbfs filesystem for USB devices is traditionally mounted at
 /proc/bus/usb.  It provides the /sys/kernel/debug/usb/devices file, as well as
 the /proc/bus/usb/BBB/DDD files.

 In many modern systems the usbfs filesystem isn't used at all.  Instead
 USB device nodes are created under /dev/usb/ or someplace similar.  The
 "devices" file is available in debugfs, typically as
 /sys/kernel/debug/usb/devices.


 **NOTE**: If /proc/bus/usb appears empty, and a host controller
 	  driver has been linked, then you need to mount the
 	  filesystem.  Issue the command (as root):

       mount -t usbfs none /proc/bus/usb

 	  An alternative and more permanent method would be to add

       none  /proc/bus/usb  usbfs  defaults  0  0

 	  to /etc/fstab.  This will mount usbfs at each reboot.
 	  You can then issue `cat /sys/kernel/debug/usb/devices` to extract
 	  USB device information, and user mode drivers can use usbfs
 	  to interact with USB devices.

 	  There are a number of mount options supported by usbfs.
 	  Consult the source code (linux/drivers/usb/core/inode.c) for
 	  information about those options.

 **NOTE**: The filesystem has been renamed from "usbdevfs" to
 	  "usbfs", to reduce confusion with "devfs".  You may
 	  still see references to the older "usbdevfs" name.

 For more information on mounting the usbfs file system, see the
 "USB Device Filesystem" section of the USB Guide. The latest copy
 of the USB Guide can be found at http://www.linux-usb.org/


 THE /proc/bus/usb/BBB/DDD FILES:
 --------------------------------
 Each connected USB device has one file.  The BBB indicates the bus
 number.  The DDD indicates the device address on that bus.  Both
 of these numbers are assigned sequentially, and can be reused, so
 you can't rely on them for stable access to devices.  For example,
 it's relatively common for devices to re-enumerate while they are
 still connected (perhaps someone jostled their power supply, hub,
 or USB cable), so a device might be 002/027 when you first connect
 it and 002/048 sometime later.

 These files can be read as binary data.  The binary data consists
 of first the device descriptor, then the descriptors for each
 configuration of the device.  Multi-byte fields in the device descriptor
 are converted to host endianness by the kernel.  The configuration
 descriptors are in bus endian format! The configuration descriptor
 are wTotalLength bytes apart. If a device returns less configuration
 descriptor data than indicated by wTotalLength there will be a hole in
 the file for the missing bytes.  This information is also shown
 in text form by the /sys/kernel/debug/usb/devices file, described later.

 These files may also be used to write user-level drivers for the USB
 devices.  You would open the /proc/bus/usb/BBB/DDD file read/write,
 read its descriptors to make sure it's the device you expect, and then
 bind to an interface (or perhaps several) using an ioctl call.  You
 would issue more ioctls to the device to communicate to it using
 control, bulk, or other kinds of USB transfers.  The IOCTLs are
 listed in the <linux/usbdevice_fs.h> file, and at this writing the
 source code (linux/drivers/usb/core/devio.c) is the primary reference
 for how to access devices through those files.

 Note that since by default these BBB/DDD files are writable only by
 root, only root can write such user mode drivers.  You can selectively
 grant read/write permissions to other users by using "chmod".  Also,
 usbfs mount options such as "devmode=0666" may be helpful.


 THE /sys/kernel/debug/usb/devices FILE:
 -------------------------------
 In /sys/kernel/debug/usb/devices, each device's output has multiple
 lines of ASCII output.
 I made it ASCII instead of binary on purpose, so that someone
 can obtain some useful data from it without the use of an
 auxiliary program.  However, with an auxiliary program, the numbers
 in the first 4 columns of each "T:" line (topology info:
 Lev, Prnt, Port, Cnt) can be used to build a USB topology diagram.

 Each line is tagged with a one-character ID for that line:

 T = Topology (etc.)
 B = Bandwidth (applies only to USB host controllers, which are
     virtualized as root hubs)
 D = Device descriptor info.
 P = Product ID info. (from Device descriptor, but they won't fit
     together on one line)
 S = String descriptors.
 C = Configuration descriptor info. (* = active configuration)
 I = Interface descriptor info.
 E = Endpoint descriptor info.

 =======================================================================

 /sys/kernel/debug/usb/devices output format:

 Legend:
   d = decimal number (may have leading spaces or 0's)
   x = hexadecimal number (may have leading spaces or 0's)
   s = string


 Topology info:

 T:  Bus=dd Lev=dd Prnt=dd Port=dd Cnt=dd Dev#=ddd Spd=dddd MxCh=dd
 |   |      |      |       |       |      |        |        |__MaxChildren
 |   |      |      |       |       |      |        |__Device Speed in Mbps
 |   |      |      |       |       |      |__DeviceNumber
 |   |      |      |       |       |__Count of devices at this level
 |   |      |      |       |__Connector/Port on Parent for this device
 |   |      |      |__Parent DeviceNumber
 |   |      |__Level in topology for this bus
 |   |__Bus number
 |__Topology info tag

     Speed may be:
     	1.5	Mbit/s for low speed USB
 	12	Mbit/s for full speed USB
 	480	Mbit/s for high speed USB (added for USB 2.0);
 		  also used for Wireless USB, which has no fixed speed
 	5000	Mbit/s for SuperSpeed USB (added for USB 3.0)

     For reasons lost in the mists of time, the Port number is always
     too low by 1.  For example, a device plugged into port 4 will
     show up with "Port=03".

 Bandwidth info:
 B:  Alloc=ddd/ddd us (xx%), #Int=ddd, #Iso=ddd
 |   |                       |         |__Number of isochronous requests
 |   |                       |__Number of interrupt requests
 |   |__Total Bandwidth allocated to this bus
 |__Bandwidth info tag

     Bandwidth allocation is an approximation of how much of one frame
     (millisecond) is in use.  It reflects only periodic transfers, which
     are the only transfers that reserve bandwidth.  Control and bulk
     transfers use all other bandwidth, including reserved bandwidth that
     is not used for transfers (such as for short packets).

     The percentage is how much of the "reserved" bandwidth is scheduled by
     those transfers.  For a low or full speed bus (loosely, "USB 1.1"),
     90% of the bus bandwidth is reserved.  For a high speed bus (loosely,
     "USB 2.0") 80% is reserved.


 Device descriptor info & Product ID info:

 D:  Ver=x.xx Cls=xx(s) Sub=xx Prot=xx MxPS=dd #Cfgs=dd
 P:  Vendor=xxxx ProdID=xxxx Rev=xx.xx

 where
 D:  Ver=x.xx Cls=xx(sssss) Sub=xx Prot=xx MxPS=dd #Cfgs=dd
 |   |        |             |      |       |       |__NumberConfigurations
 |   |        |             |      |       |__MaxPacketSize of Default Endpoint
 |   |        |             |      |__DeviceProtocol
 |   |        |             |__DeviceSubClass
 |   |        |__DeviceClass
 |   |__Device USB version
 |__Device info tag #1

 where
 P:  Vendor=xxxx ProdID=xxxx Rev=xx.xx
 |   |           |           |__Product revision number
 |   |           |__Product ID code
 |   |__Vendor ID code
 |__Device info tag #2


 String descriptor info:

 S:  Manufacturer=ssss
 |   |__Manufacturer of this device as read from the device.
 |      For USB host controller drivers (virtual root hubs) this may
 |      be omitted, or (for newer drivers) will identify the kernel
 |      version and the driver which provides this hub emulation.
 |__String info tag

 S:  Product=ssss
 |   |__Product description of this device as read from the device.
 |      For older USB host controller drivers (virtual root hubs) this
 |      indicates the driver; for newer ones, it's a product (and vendor)
 |      description that often comes from the kernel's PCI ID database.
 |__String info tag

 S:  SerialNumber=ssss
 |   |__Serial Number of this device as read from the device.
 |      For USB host controller drivers (virtual root hubs) this is
 |      some unique ID, normally a bus ID (address or slot name) that
 |      can't be shared with any other device.
 |__String info tag


 Configuration descriptor info:

 C:* #Ifs=dd Cfg#=dd Atr=xx MPwr=dddmA
 | | |       |       |      |__MaxPower in mA
 | | |       |       |__Attributes
 | | |       |__ConfiguratioNumber
 | | |__NumberOfInterfaces
 | |__ "*" indicates the active configuration (others are " ")
 |__Config info tag

     USB devices may have multiple configurations, each of which act
     rather differently.  For example, a bus-powered configuration
     might be much less capable than one that is self-powered.  Only
     one device configuration can be active at a time; most devices
     have only one configuration.

     Each configuration consists of one or more interfaces.  Each
     interface serves a distinct "function", which is typically bound
     to a different USB device driver.  One common example is a USB
     speaker with an audio interface for playback, and a HID interface
     for use with software volume control.


 Interface descriptor info (can be multiple per Config):

 I:* If#=dd Alt=dd #EPs=dd Cls=xx(sssss) Sub=xx Prot=xx Driver=ssss
 | | |      |      |       |             |      |       |__Driver name
 | | |      |      |       |             |      |          or "(none)"
 | | |      |      |       |             |      |__InterfaceProtocol
 | | |      |      |       |             |__InterfaceSubClass
 | | |      |      |       |__InterfaceClass
 | | |      |      |__NumberOfEndpoints
 | | |      |__AlternateSettingNumber
 | | |__InterfaceNumber
 | |__ "*" indicates the active altsetting (others are " ")
 |__Interface info tag

     A given interface may have one or more "alternate" settings.
     For example, default settings may not use more than a small
     amount of periodic bandwidth.  To use significant fractions
     of bus bandwidth, drivers must select a non-default altsetting.

     Only one setting for an interface may be active at a time, and
     only one driver may bind to an interface at a time.  Most devices
     have only one alternate setting per interface.


 Endpoint descriptor info (can be multiple per Interface):

 E:  Ad=xx(s) Atr=xx(ssss) MxPS=dddd Ivl=dddss
 |   |        |            |         |__Interval (max) between transfers
 |   |        |            |__EndpointMaxPacketSize
 |   |        |__Attributes(EndpointType)
 |   |__EndpointAddress(I=In,O=Out)
 |__Endpoint info tag

     The interval is nonzero for all periodic (interrupt or isochronous)
     endpoints.  For high speed endpoints the transfer interval may be
     measured in microseconds rather than milliseconds.

     For high speed periodic endpoints, the "MaxPacketSize" reflects
     the per-microframe data transfer size.  For "high bandwidth"
     endpoints, that can reflect two or three packets (for up to
     3KBytes every 125 usec) per endpoint.

     With the Linux-USB stack, periodic bandwidth reservations use the
     transfer intervals and sizes provided by URBs, which can be less
     than those found in endpoint descriptor.


 =======================================================================


 If a user or script is interested only in Topology info, for
 example, use something like "grep ^T: /sys/kernel/debug/usb/devices"
 for only the Topology lines.  A command like
 "grep -i ^[tdp]: /sys/kernel/debug/usb/devices" can be used to list
 only the lines that begin with the characters in square brackets,
 where the valid characters are TDPCIE.  With a slightly more able
 script, it can display any selected lines (for example, only T, D,
 and P lines) and change their output format.  (The "procusb"
 Perl script is the beginning of this idea.  It will list only
 selected lines [selected from TBDPSCIE] or "All" lines from
 /sys/kernel/debug/usb/devices.)

 The Topology lines can be used to generate a graphic/pictorial
 of the USB devices on a system's root hub.  (See more below
 on how to do this.)

 The Interface lines can be used to determine what driver is
 being used for each device, and which altsetting it activated.

 The Configuration lines could be used to list maximum power
 (in milliamps) that a system's USB devices are using.
 For example, "grep ^C: /sys/kernel/debug/usb/devices".


 Here's an example, from a system which has a UHCI root hub,
 an external hub connected to the root hub, and a mouse and
 a serial converter connected to the external hub.

 T:  Bus=00 Lev=00 Prnt=00 Port=00 Cnt=00 Dev#=  1 Spd=12   MxCh= 2
 B:  Alloc= 28/900 us ( 3%), #Int=  2, #Iso=  0
 D:  Ver= 1.00 Cls=09(hub  ) Sub=00 Prot=00 MxPS= 8 #Cfgs=  1
 P:  Vendor=0000 ProdID=0000 Rev= 0.00
 S:  Product=USB UHCI Root Hub
 S:  SerialNumber=dce0
 C:* #Ifs= 1 Cfg#= 1 Atr=40 MxPwr=  0mA
 I:  If#= 0 Alt= 0 #EPs= 1 Cls=09(hub  ) Sub=00 Prot=00 Driver=hub
 E:  Ad=81(I) Atr=03(Int.) MxPS=   8 Ivl=255ms

 T:  Bus=00 Lev=01 Prnt=01 Port=00 Cnt=01 Dev#=  2 Spd=12   MxCh= 4
 D:  Ver= 1.00 Cls=09(hub  ) Sub=00 Prot=00 MxPS= 8 #Cfgs=  1
 P:  Vendor=0451 ProdID=1446 Rev= 1.00
 C:* #Ifs= 1 Cfg#= 1 Atr=e0 MxPwr=100mA
 I:  If#= 0 Alt= 0 #EPs= 1 Cls=09(hub  ) Sub=00 Prot=00 Driver=hub
 E:  Ad=81(I) Atr=03(Int.) MxPS=   1 Ivl=255ms

 T:  Bus=00 Lev=02 Prnt=02 Port=00 Cnt=01 Dev#=  3 Spd=1.5  MxCh= 0
 D:  Ver= 1.00 Cls=00(>ifc ) Sub=00 Prot=00 MxPS= 8 #Cfgs=  1
 P:  Vendor=04b4 ProdID=0001 Rev= 0.00
 C:* #Ifs= 1 Cfg#= 1 Atr=80 MxPwr=100mA
 I:  If#= 0 Alt= 0 #EPs= 1 Cls=03(HID  ) Sub=01 Prot=02 Driver=mouse
 E:  Ad=81(I) Atr=03(Int.) MxPS=   3 Ivl= 10ms

 T:  Bus=00 Lev=02 Prnt=02 Port=02 Cnt=02 Dev#=  4 Spd=12   MxCh= 0
 D:  Ver= 1.00 Cls=00(>ifc ) Sub=00 Prot=00 MxPS= 8 #Cfgs=  1
 P:  Vendor=0565 ProdID=0001 Rev= 1.08
 S:  Manufacturer=Peracom Networks, Inc.
 S:  Product=Peracom USB to Serial Converter
 C:* #Ifs= 1 Cfg#= 1 Atr=a0 MxPwr=100mA
 I:  If#= 0 Alt= 0 #EPs= 3 Cls=00(>ifc ) Sub=00 Prot=00 Driver=serial
 E:  Ad=81(I) Atr=02(Bulk) MxPS=  64 Ivl= 16ms
 E:  Ad=01(O) Atr=02(Bulk) MxPS=  16 Ivl= 16ms
 E:  Ad=82(I) Atr=03(Int.) MxPS=   8 Ivl=  8ms


 Selecting only the "T:" and "I:" lines from this (for example, by using
 "procusb ti"), we have:

 T:  Bus=00 Lev=00 Prnt=00 Port=00 Cnt=00 Dev#=  1 Spd=12   MxCh= 2
 T:  Bus=00 Lev=01 Prnt=01 Port=00 Cnt=01 Dev#=  2 Spd=12   MxCh= 4
 I:  If#= 0 Alt= 0 #EPs= 1 Cls=09(hub  ) Sub=00 Prot=00 Driver=hub
 T:  Bus=00 Lev=02 Prnt=02 Port=00 Cnt=01 Dev#=  3 Spd=1.5  MxCh= 0
 I:  If#= 0 Alt= 0 #EPs= 1 Cls=03(HID  ) Sub=01 Prot=02 Driver=mouse
 T:  Bus=00 Lev=02 Prnt=02 Port=02 Cnt=02 Dev#=  4 Spd=12   MxCh= 0
 I:  If#= 0 Alt= 0 #EPs= 3 Cls=00(>ifc ) Sub=00 Prot=00 Driver=serial


 Physically this looks like (or could be converted to):

                       +------------------+
                       |  PC/root_hub (12)|   Dev# = 1
                       +------------------+   (nn) is Mbps.
     Level 0           |  CN.0   |  CN.1  |   [CN = connector/port #]
                       +------------------+
                           /
                          /
             +-----------------------+
   Level 1   | Dev#2: 4-port hub (12)|
             +-----------------------+
             |CN.0 |CN.1 |CN.2 |CN.3 |
             +-----------------------+
                 \           \____________________
                  \_____                          \
                        \                          \
                +--------------------+      +--------------------+
   Level 2      | Dev# 3: mouse (1.5)|      | Dev# 4: serial (12)|
                +--------------------+      +--------------------+


 Or, in a more tree-like structure (ports [Connectors] without
 connections could be omitted):

 PC:  Dev# 1, root hub, 2 ports, 12 Mbps
 |_ CN.0:  Dev# 2, hub, 4 ports, 12 Mbps
      |_ CN.0:  Dev #3, mouse, 1.5 Mbps
      |_ CN.1:
      |_ CN.2:  Dev #4, serial, 12 Mbps
      |_ CN.3:
 |_ CN.1:


                          ### END ###
	/proc/bus/usb filesystem output
	===============================
	(version 2010.09.13)


	The usbfs filesystem for USB devices is traditionally mounted at
	/proc/bus/usb. It provides the /sys/kernel/debug/usb/devices file, as well as
	the /proc/bus/usb/BBB/DDD files.

	In many modern systems the usbfs filesystem isn't used at all. Instead
	USB device nodes are created under /dev/usb/ or someplace similar. The
	"devices" file is available in debugfs, typically as
	/sys/kernel/debug/usb/devices.


	NOTE: If /proc/bus/usb appears empty, and a host controller
	driver has been linked, then you need to mount the
	filesystem. Issue the command (as root):

	mount -t usbfs none /proc/bus/usb

	An alternative and more permanent method would be to add

	none /proc/bus/usb usbfs defaults 0 0

	to /etc/fstab. This will mount usbfs at each reboot.
	You can then issue `cat /sys/kernel/debug/usb/devices` to extract
	USB device information, and user mode drivers can use usbfs
	to interact with USB devices.

	There are a number of mount options supported by usbfs.
	Consult the source code (linux/drivers/usb/core/inode.c) for
	information about those options.

	NOTE: The filesystem has been renamed from "usbdevfs" to
	"usbfs", to reduce confusion with "devfs". You may
	still see references to the older "usbdevfs" name.

	For more information on mounting the usbfs file system, see the
	"USB Device Filesystem" section of the USB Guide. The latest copy
	of the USB Guide can be found at http://www.linux-usb.org/


	THE /proc/bus/usb/BBB/DDD FILES:
	--------------------------------
	Each connected USB device has one file. The BBB indicates the bus
	number. The DDD indicates the device address on that bus. Both
	of these numbers are assigned sequentially, and can be reused, so
	you can't rely on them for stable access to devices. For example,
	it's relatively common for devices to re-enumerate while they are
	still connected (perhaps someone jostled their power supply, hub,
	or USB cable), so a device might be 002/027 when you first connect
	it and 002/048 sometime later.

	These files can be read as binary data. The binary data consists
	of first the device descriptor, then the descriptors for each
	configuration of the device. Multi-byte fields in the device descriptor
	are converted to host endianness by the kernel. The configuration
	descriptors are in bus endian format! The configuration descriptor
	are wTotalLength bytes apart. If a device returns less configuration
	descriptor data than indicated by wTotalLength there will be a hole in
	the file for the missing bytes. This information is also shown
	in text form by the /sys/kernel/debug/usb/devices file, described later.

	These files may also be used to write user-level drivers for the USB
	devices. You would open the /proc/bus/usb/BBB/DDD file read/write,
	read its descriptors to make sure it's the device you expect, and then
	bind to an interface (or perhaps several) using an ioctl call. You
	would issue more ioctls to the device to communicate to it using
	control, bulk, or other kinds of USB transfers. The IOCTLs are
	listed in the <linux/usbdevice_fs.h> file, and at this writing the
	source code (linux/drivers/usb/core/devio.c) is the primary reference
	for how to access devices through those files.

	Note that since by default these BBB/DDD files are writable only by
	root, only root can write such user mode drivers. You can selectively
	grant read/write permissions to other users by using "chmod". Also,
	usbfs mount options such as "devmode=0666" may be helpful.



	THE /sys/kernel/debug/usb/devices FILE:
	-------------------------------
	In /sys/kernel/debug/usb/devices, each device's output has multiple
	lines of ASCII output.
	I made it ASCII instead of binary on purpose, so that someone
	can obtain some useful data from it without the use of an
	auxiliary program. However, with an auxiliary program, the numbers
	in the first 4 columns of each "T:" line (topology info:
	Lev, Prnt, Port, Cnt) can be used to build a USB topology diagram.

	Each line is tagged with a one-character ID for that line:

	T = Topology (etc.)
	B = Bandwidth (applies only to USB host controllers, which are
	virtualized as root hubs)
	D = Device descriptor info.
	P = Product ID info. (from Device descriptor, but they won't fit
	together on one line)
	S = String descriptors.
	C = Configuration descriptor info. (* = active configuration)
	I = Interface descriptor info.
	E = Endpoint descriptor info.

	=======================================================================

	/sys/kernel/debug/usb/devices output format:

	Legend:
	d = decimal number (may have leading spaces or 0's)
	x = hexadecimal number (may have leading spaces or 0's)
	s = string


	Topology info:

	T: Bus=dd Lev=dd Prnt=dd Port=dd Cnt=dd Dev#=ddd Spd=dddd MxCh=dd
	\| \| \| \| \| \| \| \| \|__MaxChildren
	\| \| \| \| \| \| \| \|__Device Speed in Mbps
	\| \| \| \| \| \| \|__DeviceNumber
	\| \| \| \| \| \|__Count of devices at this level
	\| \| \| \| \|__Connector/Port on Parent for this device
	\| \| \| \|__Parent DeviceNumber
	\| \| \|__Level in topology for this bus
	\| \|__Bus number
	\|__Topology info tag

	Speed may be:
	1.5 Mbit/s for low speed USB
	12 Mbit/s for full speed USB
	480 Mbit/s for high speed USB (added for USB 2.0);
	also used for Wireless USB, which has no fixed speed
	5000 Mbit/s for SuperSpeed USB (added for USB 3.0)

	For reasons lost in the mists of time, the Port number is always
	too low by 1. For example, a device plugged into port 4 will
	show up with "Port=03".

	Bandwidth info:
	B: Alloc=ddd/ddd us (xx%), #Int=ddd, #Iso=ddd
	\| \| \| \|__Number of isochronous requests
	\| \| \|__Number of interrupt requests
	\| \|__Total Bandwidth allocated to this bus
	\|__Bandwidth info tag

	Bandwidth allocation is an approximation of how much of one frame
	(millisecond) is in use. It reflects only periodic transfers, which
	are the only transfers that reserve bandwidth. Control and bulk
	transfers use all other bandwidth, including reserved bandwidth that
	is not used for transfers (such as for short packets).

	The percentage is how much of the "reserved" bandwidth is scheduled by
	those transfers. For a low or full speed bus (loosely, "USB 1.1"),
	90% of the bus bandwidth is reserved. For a high speed bus (loosely,
	"USB 2.0") 80% is reserved.


	Device descriptor info & Product ID info:

	D: Ver=x.xx Cls=xx(s) Sub=xx Prot=xx MxPS=dd #Cfgs=dd
	P: Vendor=xxxx ProdID=xxxx Rev=xx.xx

	where
	D: Ver=x.xx Cls=xx(sssss) Sub=xx Prot=xx MxPS=dd #Cfgs=dd
	\| \| \| \| \| \| \|__NumberConfigurations
	\| \| \| \| \| \|__MaxPacketSize of Default Endpoint
	\| \| \| \| \|__DeviceProtocol
	\| \| \| \|__DeviceSubClass
	\| \| \|__DeviceClass
	\| \|__Device USB version
	\|__Device info tag #1

	where
	P: Vendor=xxxx ProdID=xxxx Rev=xx.xx
	\| \| \| \|__Product revision number
	\| \| \|__Product ID code
	\| \|__Vendor ID code
	\|__Device info tag #2


	String descriptor info:

	S: Manufacturer=ssss
	\| \|__Manufacturer of this device as read from the device.
	\| For USB host controller drivers (virtual root hubs) this may
	\| be omitted, or (for newer drivers) will identify the kernel
	\| version and the driver which provides this hub emulation.
	\|__String info tag

	S: Product=ssss
	\| \|__Product description of this device as read from the device.
	\| For older USB host controller drivers (virtual root hubs) this
	\| indicates the driver; for newer ones, it's a product (and vendor)
	\| description that often comes from the kernel's PCI ID database.
	\|__String info tag

	S: SerialNumber=ssss
	\| \|__Serial Number of this device as read from the device.
	\| For USB host controller drivers (virtual root hubs) this is
	\| some unique ID, normally a bus ID (address or slot name) that
	\| can't be shared with any other device.
	\|__String info tag



	Configuration descriptor info:

	C:* #Ifs=dd Cfg#=dd Atr=xx MPwr=dddmA
	\| \| \| \| \| \|__MaxPower in mA
	\| \| \| \| \|__Attributes
	\| \| \| \|__ConfiguratioNumber
	\| \| \|__NumberOfInterfaces
	\| \|__ "*" indicates the active configuration (others are " ")
	\|__Config info tag

	USB devices may have multiple configurations, each of which act
	rather differently. For example, a bus-powered configuration
	might be much less capable than one that is self-powered. Only
	one device configuration can be active at a time; most devices
	have only one configuration.

	Each configuration consists of one or more interfaces. Each
	interface serves a distinct "function", which is typically bound
	to a different USB device driver. One common example is a USB
	speaker with an audio interface for playback, and a HID interface
	for use with software volume control.


	Interface descriptor info (can be multiple per Config):

	I:* If#=dd Alt=dd #EPs=dd Cls=xx(sssss) Sub=xx Prot=xx Driver=ssss
	\| \| \| \| \| \| \| \| \|__Driver name
	\| \| \| \| \| \| \| \| or "(none)"
	\| \| \| \| \| \| \| \|__InterfaceProtocol
	\| \| \| \| \| \| \|__InterfaceSubClass
	\| \| \| \| \| \|__InterfaceClass
	\| \| \| \| \|__NumberOfEndpoints
	\| \| \| \|__AlternateSettingNumber
	\| \| \|__InterfaceNumber
	\| \|__ "*" indicates the active altsetting (others are " ")
	\|__Interface info tag

	A given interface may have one or more "alternate" settings.
	For example, default settings may not use more than a small
	amount of periodic bandwidth. To use significant fractions
	of bus bandwidth, drivers must select a non-default altsetting.

	Only one setting for an interface may be active at a time, and
	only one driver may bind to an interface at a time. Most devices
	have only one alternate setting per interface.


	Endpoint descriptor info (can be multiple per Interface):

	E: Ad=xx(s) Atr=xx(ssss) MxPS=dddd Ivl=dddss
	\| \| \| \| \|__Interval (max) between transfers
	\| \| \| \|__EndpointMaxPacketSize
	\| \| \|__Attributes(EndpointType)
	\| \|__EndpointAddress(I=In,O=Out)
	\|__Endpoint info tag

	The interval is nonzero for all periodic (interrupt or isochronous)
	endpoints. For high speed endpoints the transfer interval may be
	measured in microseconds rather than milliseconds.

	For high speed periodic endpoints, the "MaxPacketSize" reflects
	the per-microframe data transfer size. For "high bandwidth"
	endpoints, that can reflect two or three packets (for up to
	3KBytes every 125 usec) per endpoint.

	With the Linux-USB stack, periodic bandwidth reservations use the
	transfer intervals and sizes provided by URBs, which can be less
	than those found in endpoint descriptor.


	=======================================================================


	If a user or script is interested only in Topology info, for
	example, use something like "grep ^T: /sys/kernel/debug/usb/devices"
	for only the Topology lines. A command like
	"grep -i ^[tdp]: /sys/kernel/debug/usb/devices" can be used to list
	only the lines that begin with the characters in square brackets,
	where the valid characters are TDPCIE. With a slightly more able
	script, it can display any selected lines (for example, only T, D,
	and P lines) and change their output format. (The "procusb"
	Perl script is the beginning of this idea. It will list only
	selected lines [selected from TBDPSCIE] or "All" lines from
	/sys/kernel/debug/usb/devices.)

	The Topology lines can be used to generate a graphic/pictorial
	of the USB devices on a system's root hub. (See more below
	on how to do this.)

	The Interface lines can be used to determine what driver is
	being used for each device, and which altsetting it activated.

	The Configuration lines could be used to list maximum power
	(in milliamps) that a system's USB devices are using.
	For example, "grep ^C: /sys/kernel/debug/usb/devices".


	Here's an example, from a system which has a UHCI root hub,
	an external hub connected to the root hub, and a mouse and
	a serial converter connected to the external hub.

	T: Bus=00 Lev=00 Prnt=00 Port=00 Cnt=00 Dev#= 1 Spd=12 MxCh= 2
	B: Alloc= 28/900 us ( 3%), #Int= 2, #Iso= 0
	D: Ver= 1.00 Cls=09(hub ) Sub=00 Prot=00 MxPS= 8 #Cfgs= 1
	P: Vendor=0000 ProdID=0000 Rev= 0.00
	S: Product=USB UHCI Root Hub
	S: SerialNumber=dce0
	C:* #Ifs= 1 Cfg#= 1 Atr=40 MxPwr= 0mA
	I: If#= 0 Alt= 0 #EPs= 1 Cls=09(hub ) Sub=00 Prot=00 Driver=hub
	E: Ad=81(I) Atr=03(Int.) MxPS= 8 Ivl=255ms

	T: Bus=00 Lev=01 Prnt=01 Port=00 Cnt=01 Dev#= 2 Spd=12 MxCh= 4
	D: Ver= 1.00 Cls=09(hub ) Sub=00 Prot=00 MxPS= 8 #Cfgs= 1
	P: Vendor=0451 ProdID=1446 Rev= 1.00
	C:* #Ifs= 1 Cfg#= 1 Atr=e0 MxPwr=100mA
	I: If#= 0 Alt= 0 #EPs= 1 Cls=09(hub ) Sub=00 Prot=00 Driver=hub
	E: Ad=81(I) Atr=03(Int.) MxPS= 1 Ivl=255ms

	T: Bus=00 Lev=02 Prnt=02 Port=00 Cnt=01 Dev#= 3 Spd=1.5 MxCh= 0
	D: Ver= 1.00 Cls=00(>ifc ) Sub=00 Prot=00 MxPS= 8 #Cfgs= 1
	P: Vendor=04b4 ProdID=0001 Rev= 0.00
	C:* #Ifs= 1 Cfg#= 1 Atr=80 MxPwr=100mA
	I: If#= 0 Alt= 0 #EPs= 1 Cls=03(HID ) Sub=01 Prot=02 Driver=mouse
	E: Ad=81(I) Atr=03(Int.) MxPS= 3 Ivl= 10ms

	T: Bus=00 Lev=02 Prnt=02 Port=02 Cnt=02 Dev#= 4 Spd=12 MxCh= 0
	D: Ver= 1.00 Cls=00(>ifc ) Sub=00 Prot=00 MxPS= 8 #Cfgs= 1
	P: Vendor=0565 ProdID=0001 Rev= 1.08
	S: Manufacturer=Peracom Networks, Inc.
	S: Product=Peracom USB to Serial Converter
	C:* #Ifs= 1 Cfg#= 1 Atr=a0 MxPwr=100mA
	I: If#= 0 Alt= 0 #EPs= 3 Cls=00(>ifc ) Sub=00 Prot=00 Driver=serial
	E: Ad=81(I) Atr=02(Bulk) MxPS= 64 Ivl= 16ms
	E: Ad=01(O) Atr=02(Bulk) MxPS= 16 Ivl= 16ms
	E: Ad=82(I) Atr=03(Int.) MxPS= 8 Ivl= 8ms


	Selecting only the "T:" and "I:" lines from this (for example, by using
	"procusb ti"), we have:

	T: Bus=00 Lev=00 Prnt=00 Port=00 Cnt=00 Dev#= 1 Spd=12 MxCh= 2
	T: Bus=00 Lev=01 Prnt=01 Port=00 Cnt=01 Dev#= 2 Spd=12 MxCh= 4
	I: If#= 0 Alt= 0 #EPs= 1 Cls=09(hub ) Sub=00 Prot=00 Driver=hub
	T: Bus=00 Lev=02 Prnt=02 Port=00 Cnt=01 Dev#= 3 Spd=1.5 MxCh= 0
	I: If#= 0 Alt= 0 #EPs= 1 Cls=03(HID ) Sub=01 Prot=02 Driver=mouse
	T: Bus=00 Lev=02 Prnt=02 Port=02 Cnt=02 Dev#= 4 Spd=12 MxCh= 0
	I: If#= 0 Alt= 0 #EPs= 3 Cls=00(>ifc ) Sub=00 Prot=00 Driver=serial


	Physically this looks like (or could be converted to):

	+------------------+
	\| PC/root_hub (12)\| Dev# = 1
	+------------------+ (nn) is Mbps.
	Level 0 \| CN.0 \| CN.1 \| [CN = connector/port #]
	+------------------+
	/
	/
	+-----------------------+
	Level 1 \| Dev#2: 4-port hub (12)\|
	+-----------------------+
	\|CN.0 \|CN.1 \|CN.2 \|CN.3 \|
	+-----------------------+
	\ \____________________
	\_____ \
	\ \
	+--------------------+ +--------------------+
	Level 2 \| Dev# 3: mouse (1.5)\| \| Dev# 4: serial (12)\|
	+--------------------+ +--------------------+



	Or, in a more tree-like structure (ports [Connectors] without
	connections could be omitted):

	PC: Dev# 1, root hub, 2 ports, 12 Mbps
	\|_ CN.0: Dev# 2, hub, 4 ports, 12 Mbps
	\|_ CN.0: Dev #3, mouse, 1.5 Mbps
	\|_ CN.1:
	\|_ CN.2: Dev #4, serial, 12 Mbps
	\|_ CN.3:
	\|_ CN.1:


	### END ###