linux/Documentation/usb/proc_usb_info.txt
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   1/proc/bus/usb filesystem output
   2===============================
   3(version 2010.09.13)
   4
   5
   6The usbfs filesystem for USB devices is traditionally mounted at
   7/proc/bus/usb.  It provides the /proc/bus/usb/devices file, as well as
   8the /proc/bus/usb/BBB/DDD files.
   9
  10In many modern systems the usbfs filesystem isn't used at all.  Instead
  11USB device nodes are created under /dev/usb/ or someplace similar.  The
  12"devices" file is available in debugfs, typically as
  13/sys/kernel/debug/usb/devices.
  14
  15
  16**NOTE**: If /proc/bus/usb appears empty, and a host controller
  17          driver has been linked, then you need to mount the
  18          filesystem.  Issue the command (as root):
  19
  20      mount -t usbfs none /proc/bus/usb
  21
  22          An alternative and more permanent method would be to add
  23
  24      none  /proc/bus/usb  usbfs  defaults  0  0
  25
  26          to /etc/fstab.  This will mount usbfs at each reboot.
  27          You can then issue `cat /proc/bus/usb/devices` to extract
  28          USB device information, and user mode drivers can use usbfs
  29          to interact with USB devices.
  30
  31          There are a number of mount options supported by usbfs.
  32          Consult the source code (linux/drivers/usb/core/inode.c) for
  33          information about those options.
  34
  35**NOTE**: The filesystem has been renamed from "usbdevfs" to
  36          "usbfs", to reduce confusion with "devfs".  You may
  37          still see references to the older "usbdevfs" name.
  38
  39For more information on mounting the usbfs file system, see the
  40"USB Device Filesystem" section of the USB Guide. The latest copy
  41of the USB Guide can be found at http://www.linux-usb.org/
  42
  43
  44THE /proc/bus/usb/BBB/DDD FILES:
  45--------------------------------
  46Each connected USB device has one file.  The BBB indicates the bus
  47number.  The DDD indicates the device address on that bus.  Both
  48of these numbers are assigned sequentially, and can be reused, so
  49you can't rely on them for stable access to devices.  For example,
  50it's relatively common for devices to re-enumerate while they are
  51still connected (perhaps someone jostled their power supply, hub,
  52or USB cable), so a device might be 002/027 when you first connect
  53it and 002/048 sometime later.
  54
  55These files can be read as binary data.  The binary data consists
  56of first the device descriptor, then the descriptors for each
  57configuration of the device.  Multi-byte fields in the device and
  58configuration descriptors, but not other descriptors, are converted
  59to host endianness by the kernel.  This information is also shown
  60in text form by the /proc/bus/usb/devices file, described later.
  61
  62These files may also be used to write user-level drivers for the USB
  63devices.  You would open the /proc/bus/usb/BBB/DDD file read/write,
  64read its descriptors to make sure it's the device you expect, and then
  65bind to an interface (or perhaps several) using an ioctl call.  You
  66would issue more ioctls to the device to communicate to it using
  67control, bulk, or other kinds of USB transfers.  The IOCTLs are
  68listed in the <linux/usbdevice_fs.h> file, and at this writing the
  69source code (linux/drivers/usb/core/devio.c) is the primary reference
  70for how to access devices through those files.
  71
  72Note that since by default these BBB/DDD files are writable only by
  73root, only root can write such user mode drivers.  You can selectively
  74grant read/write permissions to other users by using "chmod".  Also,
  75usbfs mount options such as "devmode=0666" may be helpful.
  76
  77
  78
  79THE /proc/bus/usb/devices FILE:
  80-------------------------------
  81In /proc/bus/usb/devices, each device's output has multiple
  82lines of ASCII output.
  83I made it ASCII instead of binary on purpose, so that someone
  84can obtain some useful data from it without the use of an
  85auxiliary program.  However, with an auxiliary program, the numbers
  86in the first 4 columns of each "T:" line (topology info:
  87Lev, Prnt, Port, Cnt) can be used to build a USB topology diagram.
  88
  89Each line is tagged with a one-character ID for that line:
  90
  91T = Topology (etc.)
  92B = Bandwidth (applies only to USB host controllers, which are
  93    virtualized as root hubs)
  94D = Device descriptor info.
  95P = Product ID info. (from Device descriptor, but they won't fit
  96    together on one line)
  97S = String descriptors.
  98C = Configuration descriptor info. (* = active configuration)
  99I = Interface descriptor info.
 100E = Endpoint descriptor info.
 101
 102=======================================================================
 103
 104/proc/bus/usb/devices output format:
 105
 106Legend:
 107  d = decimal number (may have leading spaces or 0's)
 108  x = hexadecimal number (may have leading spaces or 0's)
 109  s = string
 110
 111
 112Topology info:
 113
 114T:  Bus=dd Lev=dd Prnt=dd Port=dd Cnt=dd Dev#=ddd Spd=dddd MxCh=dd
 115|   |      |      |       |       |      |        |        |__MaxChildren
 116|   |      |      |       |       |      |        |__Device Speed in Mbps
 117|   |      |      |       |       |      |__DeviceNumber
 118|   |      |      |       |       |__Count of devices at this level
 119|   |      |      |       |__Connector/Port on Parent for this device
 120|   |      |      |__Parent DeviceNumber
 121|   |      |__Level in topology for this bus
 122|   |__Bus number
 123|__Topology info tag
 124
 125    Speed may be:
 126        1.5     Mbit/s for low speed USB
 127        12      Mbit/s for full speed USB
 128        480     Mbit/s for high speed USB (added for USB 2.0);
 129                  also used for Wireless USB, which has no fixed speed
 130        5000    Mbit/s for SuperSpeed USB (added for USB 3.0)
 131
 132    For reasons lost in the mists of time, the Port number is always
 133    too low by 1.  For example, a device plugged into port 4 will
 134    show up with "Port=03".
 135
 136Bandwidth info:
 137B:  Alloc=ddd/ddd us (xx%), #Int=ddd, #Iso=ddd
 138|   |                       |         |__Number of isochronous requests
 139|   |                       |__Number of interrupt requests
 140|   |__Total Bandwidth allocated to this bus
 141|__Bandwidth info tag
 142
 143    Bandwidth allocation is an approximation of how much of one frame
 144    (millisecond) is in use.  It reflects only periodic transfers, which
 145    are the only transfers that reserve bandwidth.  Control and bulk
 146    transfers use all other bandwidth, including reserved bandwidth that
 147    is not used for transfers (such as for short packets).
 148
 149    The percentage is how much of the "reserved" bandwidth is scheduled by
 150    those transfers.  For a low or full speed bus (loosely, "USB 1.1"),
 151    90% of the bus bandwidth is reserved.  For a high speed bus (loosely,
 152    "USB 2.0") 80% is reserved.
 153
 154
 155Device descriptor info & Product ID info:
 156
 157D:  Ver=x.xx Cls=xx(s) Sub=xx Prot=xx MxPS=dd #Cfgs=dd
 158P:  Vendor=xxxx ProdID=xxxx Rev=xx.xx
 159
 160where
 161D:  Ver=x.xx Cls=xx(sssss) Sub=xx Prot=xx MxPS=dd #Cfgs=dd
 162|   |        |             |      |       |       |__NumberConfigurations
 163|   |        |             |      |       |__MaxPacketSize of Default Endpoint
 164|   |        |             |      |__DeviceProtocol
 165|   |        |             |__DeviceSubClass
 166|   |        |__DeviceClass
 167|   |__Device USB version
 168|__Device info tag #1
 169
 170where
 171P:  Vendor=xxxx ProdID=xxxx Rev=xx.xx
 172|   |           |           |__Product revision number
 173|   |           |__Product ID code
 174|   |__Vendor ID code
 175|__Device info tag #2
 176
 177
 178String descriptor info:
 179
 180S:  Manufacturer=ssss
 181|   |__Manufacturer of this device as read from the device.
 182|      For USB host controller drivers (virtual root hubs) this may
 183|      be omitted, or (for newer drivers) will identify the kernel
 184|      version and the driver which provides this hub emulation.
 185|__String info tag
 186
 187S:  Product=ssss
 188|   |__Product description of this device as read from the device.
 189|      For older USB host controller drivers (virtual root hubs) this
 190|      indicates the driver; for newer ones, it's a product (and vendor)
 191|      description that often comes from the kernel's PCI ID database.
 192|__String info tag
 193
 194S:  SerialNumber=ssss
 195|   |__Serial Number of this device as read from the device.
 196|      For USB host controller drivers (virtual root hubs) this is
 197|      some unique ID, normally a bus ID (address or slot name) that
 198|      can't be shared with any other device.
 199|__String info tag
 200
 201
 202
 203Configuration descriptor info:
 204
 205C:* #Ifs=dd Cfg#=dd Atr=xx MPwr=dddmA
 206| | |       |       |      |__MaxPower in mA
 207| | |       |       |__Attributes
 208| | |       |__ConfiguratioNumber
 209| | |__NumberOfInterfaces
 210| |__ "*" indicates the active configuration (others are " ")
 211|__Config info tag
 212
 213    USB devices may have multiple configurations, each of which act
 214    rather differently.  For example, a bus-powered configuration
 215    might be much less capable than one that is self-powered.  Only
 216    one device configuration can be active at a time; most devices
 217    have only one configuration.
 218
 219    Each configuration consists of one or more interfaces.  Each
 220    interface serves a distinct "function", which is typically bound
 221    to a different USB device driver.  One common example is a USB
 222    speaker with an audio interface for playback, and a HID interface
 223    for use with software volume control.
 224
 225
 226Interface descriptor info (can be multiple per Config):
 227
 228I:* If#=dd Alt=dd #EPs=dd Cls=xx(sssss) Sub=xx Prot=xx Driver=ssss
 229| | |      |      |       |             |      |       |__Driver name
 230| | |      |      |       |             |      |          or "(none)"
 231| | |      |      |       |             |      |__InterfaceProtocol
 232| | |      |      |       |             |__InterfaceSubClass
 233| | |      |      |       |__InterfaceClass
 234| | |      |      |__NumberOfEndpoints
 235| | |      |__AlternateSettingNumber
 236| | |__InterfaceNumber
 237| |__ "*" indicates the active altsetting (others are " ")
 238|__Interface info tag
 239
 240    A given interface may have one or more "alternate" settings.
 241    For example, default settings may not use more than a small
 242    amount of periodic bandwidth.  To use significant fractions
 243    of bus bandwidth, drivers must select a non-default altsetting.
 244
 245    Only one setting for an interface may be active at a time, and
 246    only one driver may bind to an interface at a time.  Most devices
 247    have only one alternate setting per interface.
 248
 249
 250Endpoint descriptor info (can be multiple per Interface):
 251
 252E:  Ad=xx(s) Atr=xx(ssss) MxPS=dddd Ivl=dddss
 253|   |        |            |         |__Interval (max) between transfers
 254|   |        |            |__EndpointMaxPacketSize
 255|   |        |__Attributes(EndpointType)
 256|   |__EndpointAddress(I=In,O=Out)
 257|__Endpoint info tag
 258
 259    The interval is nonzero for all periodic (interrupt or isochronous)
 260    endpoints.  For high speed endpoints the transfer interval may be
 261    measured in microseconds rather than milliseconds.
 262
 263    For high speed periodic endpoints, the "MaxPacketSize" reflects
 264    the per-microframe data transfer size.  For "high bandwidth"
 265    endpoints, that can reflect two or three packets (for up to
 266    3KBytes every 125 usec) per endpoint.
 267
 268    With the Linux-USB stack, periodic bandwidth reservations use the
 269    transfer intervals and sizes provided by URBs, which can be less
 270    than those found in endpoint descriptor.
 271
 272
 273=======================================================================
 274
 275
 276If a user or script is interested only in Topology info, for
 277example, use something like "grep ^T: /proc/bus/usb/devices"
 278for only the Topology lines.  A command like
 279"grep -i ^[tdp]: /proc/bus/usb/devices" can be used to list
 280only the lines that begin with the characters in square brackets,
 281where the valid characters are TDPCIE.  With a slightly more able
 282script, it can display any selected lines (for example, only T, D,
 283and P lines) and change their output format.  (The "procusb"
 284Perl script is the beginning of this idea.  It will list only
 285selected lines [selected from TBDPSCIE] or "All" lines from
 286/proc/bus/usb/devices.)
 287
 288The Topology lines can be used to generate a graphic/pictorial
 289of the USB devices on a system's root hub.  (See more below
 290on how to do this.)
 291
 292The Interface lines can be used to determine what driver is
 293being used for each device, and which altsetting it activated.
 294
 295The Configuration lines could be used to list maximum power
 296(in milliamps) that a system's USB devices are using.
 297For example, "grep ^C: /proc/bus/usb/devices".
 298
 299
 300Here's an example, from a system which has a UHCI root hub,
 301an external hub connected to the root hub, and a mouse and
 302a serial converter connected to the external hub.
 303
 304T:  Bus=00 Lev=00 Prnt=00 Port=00 Cnt=00 Dev#=  1 Spd=12   MxCh= 2
 305B:  Alloc= 28/900 us ( 3%), #Int=  2, #Iso=  0
 306D:  Ver= 1.00 Cls=09(hub  ) Sub=00 Prot=00 MxPS= 8 #Cfgs=  1
 307P:  Vendor=0000 ProdID=0000 Rev= 0.00
 308S:  Product=USB UHCI Root Hub
 309S:  SerialNumber=dce0
 310C:* #Ifs= 1 Cfg#= 1 Atr=40 MxPwr=  0mA
 311I:  If#= 0 Alt= 0 #EPs= 1 Cls=09(hub  ) Sub=00 Prot=00 Driver=hub
 312E:  Ad=81(I) Atr=03(Int.) MxPS=   8 Ivl=255ms
 313
 314T:  Bus=00 Lev=01 Prnt=01 Port=00 Cnt=01 Dev#=  2 Spd=12   MxCh= 4
 315D:  Ver= 1.00 Cls=09(hub  ) Sub=00 Prot=00 MxPS= 8 #Cfgs=  1
 316P:  Vendor=0451 ProdID=1446 Rev= 1.00
 317C:* #Ifs= 1 Cfg#= 1 Atr=e0 MxPwr=100mA
 318I:  If#= 0 Alt= 0 #EPs= 1 Cls=09(hub  ) Sub=00 Prot=00 Driver=hub
 319E:  Ad=81(I) Atr=03(Int.) MxPS=   1 Ivl=255ms
 320
 321T:  Bus=00 Lev=02 Prnt=02 Port=00 Cnt=01 Dev#=  3 Spd=1.5  MxCh= 0
 322D:  Ver= 1.00 Cls=00(>ifc ) Sub=00 Prot=00 MxPS= 8 #Cfgs=  1
 323P:  Vendor=04b4 ProdID=0001 Rev= 0.00
 324C:* #Ifs= 1 Cfg#= 1 Atr=80 MxPwr=100mA
 325I:  If#= 0 Alt= 0 #EPs= 1 Cls=03(HID  ) Sub=01 Prot=02 Driver=mouse
 326E:  Ad=81(I) Atr=03(Int.) MxPS=   3 Ivl= 10ms
 327
 328T:  Bus=00 Lev=02 Prnt=02 Port=02 Cnt=02 Dev#=  4 Spd=12   MxCh= 0
 329D:  Ver= 1.00 Cls=00(>ifc ) Sub=00 Prot=00 MxPS= 8 #Cfgs=  1
 330P:  Vendor=0565 ProdID=0001 Rev= 1.08
 331S:  Manufacturer=Peracom Networks, Inc.
 332S:  Product=Peracom USB to Serial Converter
 333C:* #Ifs= 1 Cfg#= 1 Atr=a0 MxPwr=100mA
 334I:  If#= 0 Alt= 0 #EPs= 3 Cls=00(>ifc ) Sub=00 Prot=00 Driver=serial
 335E:  Ad=81(I) Atr=02(Bulk) MxPS=  64 Ivl= 16ms
 336E:  Ad=01(O) Atr=02(Bulk) MxPS=  16 Ivl= 16ms
 337E:  Ad=82(I) Atr=03(Int.) MxPS=   8 Ivl=  8ms
 338
 339
 340Selecting only the "T:" and "I:" lines from this (for example, by using
 341"procusb ti"), we have:
 342
 343T:  Bus=00 Lev=00 Prnt=00 Port=00 Cnt=00 Dev#=  1 Spd=12   MxCh= 2
 344T:  Bus=00 Lev=01 Prnt=01 Port=00 Cnt=01 Dev#=  2 Spd=12   MxCh= 4
 345I:  If#= 0 Alt= 0 #EPs= 1 Cls=09(hub  ) Sub=00 Prot=00 Driver=hub
 346T:  Bus=00 Lev=02 Prnt=02 Port=00 Cnt=01 Dev#=  3 Spd=1.5  MxCh= 0
 347I:  If#= 0 Alt= 0 #EPs= 1 Cls=03(HID  ) Sub=01 Prot=02 Driver=mouse
 348T:  Bus=00 Lev=02 Prnt=02 Port=02 Cnt=02 Dev#=  4 Spd=12   MxCh= 0
 349I:  If#= 0 Alt= 0 #EPs= 3 Cls=00(>ifc ) Sub=00 Prot=00 Driver=serial
 350
 351
 352Physically this looks like (or could be converted to):
 353
 354                      +------------------+
 355                      |  PC/root_hub (12)|   Dev# = 1
 356                      +------------------+   (nn) is Mbps.
 357    Level 0           |  CN.0   |  CN.1  |   [CN = connector/port #]
 358                      +------------------+
 359                          /
 360                         /
 361            +-----------------------+
 362  Level 1   | Dev#2: 4-port hub (12)|
 363            +-----------------------+
 364            |CN.0 |CN.1 |CN.2 |CN.3 |
 365            +-----------------------+
 366                \           \____________________
 367                 \_____                          \
 368                       \                          \
 369               +--------------------+      +--------------------+
 370  Level 2      | Dev# 3: mouse (1.5)|      | Dev# 4: serial (12)|
 371               +--------------------+      +--------------------+
 372
 373
 374
 375Or, in a more tree-like structure (ports [Connectors] without
 376connections could be omitted):
 377
 378PC:  Dev# 1, root hub, 2 ports, 12 Mbps
 379|_ CN.0:  Dev# 2, hub, 4 ports, 12 Mbps
 380     |_ CN.0:  Dev #3, mouse, 1.5 Mbps
 381     |_ CN.1:
 382     |_ CN.2:  Dev #4, serial, 12 Mbps
 383     |_ CN.3:
 384|_ CN.1:
 385
 386
 387                         ### END ###
 388
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