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+/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 /proc/bus/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 /proc/bus/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 /proc/bus/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 /proc/bus/usb/devices FILE:
+-------------------------------
+In /proc/bus/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.
+
+=======================================================================
+
+/proc/bus/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: /proc/bus/usb/devices"
+for only the Topology lines.  A command like
+"grep -i ^[tdp]: /proc/bus/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
+/proc/bus/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: /proc/bus/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 ###