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/proc/bus/usb filesystem output

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

(version 2002.03.18)

The /proc filesystem for USB devices provides /proc/bus/usb/drivers

and /proc/bus/usb/devices, as well as /proc/bus/usb/BBB/DDD files.

**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/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.  That 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  file, and at this writing the

source code (linux/drivers/usb/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/drivers FILE:

-------------------------------

Each of the USB device drivers linked into your kernel (statically,

or dynamically using "modprobe") is listed in the "drivers" file.

Here's an example from one system:

         usbdevfs

         hub

  0- 15: usblp

         usbnet

         serial

         usb-storage

         pegasus

If you see this file, "usbdevfs" and "hub" will always be listed,

since those are part of the "usbcore" framework.

Drivers that use the USB major number (180) to provide character devices

will include a range of minor numbers, as shown above for the "usblp"

(actually "printer.o") module.  USB device drivers can of course use any

major number, but it's easy to use the USB range since there's explicit

support for subdividing it in the USB device driver framework.

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=ddd 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)

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

|__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=dddms

|   |        |            |         |__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.

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 ###