1/proc/bus/usb filesystem output
2===============================
3(version 2003.05.30)
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
10
11**NOTE**: If /proc/bus/usb appears empty, and a host controller
12	  driver has been linked, then you need to mount the
13	  filesystem.  Issue the command (as root):
14
15      mount -t usbfs none /proc/bus/usb
16
17	  An alternative and more permanent method would be to add
18
19      none  /proc/bus/usb  usbfs  defaults  0  0
20
21	  to /etc/fstab.  This will mount usbfs at each reboot.
22	  You can then issue `cat /proc/bus/usb/devices` to extract
23	  USB device information, and user mode drivers can use usbfs
24	  to interact with USB devices.
25
26	  There are a number of mount options supported by usbfs.
27	  Consult the source code (linux/drivers/usb/core/inode.c) for
28	  information about those options.
29
30**NOTE**: The filesystem has been renamed from "usbdevfs" to
31	  "usbfs", to reduce confusion with "devfs".  You may
32	  still see references to the older "usbdevfs" name.
33
34For more information on mounting the usbfs file system, see the
35"USB Device Filesystem" section of the USB Guide. The latest copy
36of the USB Guide can be found at http://www.linux-usb.org/
37
38
39THE /proc/bus/usb/BBB/DDD FILES:
40--------------------------------
41Each connected USB device has one file.  The BBB indicates the bus
42number.  The DDD indicates the device address on that bus.  Both
43of these numbers are assigned sequentially, and can be reused, so
44you can't rely on them for stable access to devices.  For example,
45it's relatively common for devices to re-enumerate while they are
46still connected (perhaps someone jostled their power supply, hub,
47or USB cable), so a device might be 002/027 when you first connect
48it and 002/048 sometime later.
49
50These files can be read as binary data.  The binary data consists
51of first the device descriptor, then the descriptors for each
52configuration of the device.  That information is also shown in
53text form by the /proc/bus/usb/devices file, described later.
54
55These files may also be used to write user-level drivers for the USB
56devices.  You would open the /proc/bus/usb/BBB/DDD file read/write,
57read its descriptors to make sure it's the device you expect, and then
58bind to an interface (or perhaps several) using an ioctl call.  You
59would issue more ioctls to the device to communicate to it using
60control, bulk, or other kinds of USB transfers.  The IOCTLs are
61listed in the <linux/usbdevice_fs.h> file, and at this writing the
62source code (linux/drivers/usb/core/devio.c) is the primary reference
63for how to access devices through those files.
64
65Note that since by default these BBB/DDD files are writable only by
66root, only root can write such user mode drivers.  You can selectively
67grant read/write permissions to other users by using "chmod".  Also,
68usbfs mount options such as "devmode=0666" may be helpful.
69
70
71
72THE /proc/bus/usb/devices FILE:
73-------------------------------
74In /proc/bus/usb/devices, each device's output has multiple
75lines of ASCII output.
76I made it ASCII instead of binary on purpose, so that someone
77can obtain some useful data from it without the use of an
78auxiliary program.  However, with an auxiliary program, the numbers
79in the first 4 columns of each "T:" line (topology info:
80Lev, Prnt, Port, Cnt) can be used to build a USB topology diagram.
81
82Each line is tagged with a one-character ID for that line:
83
84T = Topology (etc.)
85B = Bandwidth (applies only to USB host controllers, which are
86    virtualized as root hubs)
87D = Device descriptor info.
88P = Product ID info. (from Device descriptor, but they won't fit
89    together on one line)
90S = String descriptors.
91C = Configuration descriptor info. (* = active configuration)
92I = Interface descriptor info.
93E = Endpoint descriptor info.
94
95=======================================================================
96
97/proc/bus/usb/devices output format:
98
99Legend:
100  d = decimal number (may have leading spaces or 0's)
101  x = hexadecimal number (may have leading spaces or 0's)
102  s = string
103
104
105Topology info:
106
107T:  Bus=dd Lev=dd Prnt=dd Port=dd Cnt=dd Dev#=ddd Spd=ddd MxCh=dd
108|   |      |      |       |       |      |        |       |__MaxChildren
109|   |      |      |       |       |      |        |__Device Speed in Mbps
110|   |      |      |       |       |      |__DeviceNumber
111|   |      |      |       |       |__Count of devices at this level
112|   |      |      |       |__Connector/Port on Parent for this device
113|   |      |      |__Parent DeviceNumber
114|   |      |__Level in topology for this bus
115|   |__Bus number
116|__Topology info tag
117
118    Speed may be:
119    	1.5	Mbit/s for low speed USB
120	12	Mbit/s for full speed USB
121	480	Mbit/s for high speed USB (added for USB 2.0)
122
123
124Bandwidth info:
125B:  Alloc=ddd/ddd us (xx%), #Int=ddd, #Iso=ddd
126|   |                       |         |__Number of isochronous requests
127|   |                       |__Number of interrupt requests
128|   |__Total Bandwidth allocated to this bus
129|__Bandwidth info tag
130
131    Bandwidth allocation is an approximation of how much of one frame
132    (millisecond) is in use.  It reflects only periodic transfers, which
133    are the only transfers that reserve bandwidth.  Control and bulk
134    transfers use all other bandwidth, including reserved bandwidth that
135    is not used for transfers (such as for short packets).
136
137    The percentage is how much of the "reserved" bandwidth is scheduled by
138    those transfers.  For a low or full speed bus (loosely, "USB 1.1"),
139    90% of the bus bandwidth is reserved.  For a high speed bus (loosely,
140    "USB 2.0") 80% is reserved.
141
142
143Device descriptor info & Product ID info:
144
145D:  Ver=x.xx Cls=xx(s) Sub=xx Prot=xx MxPS=dd #Cfgs=dd
146P:  Vendor=xxxx ProdID=xxxx Rev=xx.xx
147
148where
149D:  Ver=x.xx Cls=xx(sssss) Sub=xx Prot=xx MxPS=dd #Cfgs=dd
150|   |        |             |      |       |       |__NumberConfigurations
151|   |        |             |      |       |__MaxPacketSize of Default Endpoint
152|   |        |             |      |__DeviceProtocol
153|   |        |             |__DeviceSubClass
154|   |        |__DeviceClass
155|   |__Device USB version
156|__Device info tag #1
157
158where
159P:  Vendor=xxxx ProdID=xxxx Rev=xx.xx
160|   |           |           |__Product revision number
161|   |           |__Product ID code
162|   |__Vendor ID code
163|__Device info tag #2
164
165
166String descriptor info:
167
168S:  Manufacturer=ssss
169|   |__Manufacturer of this device as read from the device.
170|      For USB host controller drivers (virtual root hubs) this may
171|      be omitted, or (for newer drivers) will identify the kernel
172|      version and the driver which provides this hub emulation.
173|__String info tag
174
175S:  Product=ssss
176|   |__Product description of this device as read from the device.
177|      For older USB host controller drivers (virtual root hubs) this
178|      indicates the driver; for newer ones, it's a product (and vendor)
179|      description that often comes from the kernel's PCI ID database.
180|__String info tag
181
182S:  SerialNumber=ssss
183|   |__Serial Number of this device as read from the device.
184|      For USB host controller drivers (virtual root hubs) this is
185|      some unique ID, normally a bus ID (address or slot name) that
186|      can't be shared with any other device.
187|__String info tag
188
189
190
191Configuration descriptor info:
192
193C:* #Ifs=dd Cfg#=dd Atr=xx MPwr=dddmA
194| | |       |       |      |__MaxPower in mA
195| | |       |       |__Attributes
196| | |       |__ConfiguratioNumber
197| | |__NumberOfInterfaces
198| |__ "*" indicates the active configuration (others are " ")
199|__Config info tag
200
201    USB devices may have multiple configurations, each of which act
202    rather differently.  For example, a bus-powered configuration
203    might be much less capable than one that is self-powered.  Only
204    one device configuration can be active at a time; most devices
205    have only one configuration.
206
207    Each configuration consists of one or more interfaces.  Each
208    interface serves a distinct "function", which is typically bound
209    to a different USB device driver.  One common example is a USB
210    speaker with an audio interface for playback, and a HID interface
211    for use with software volume control.
212
213
214Interface descriptor info (can be multiple per Config):
215
216I:* If#=dd Alt=dd #EPs=dd Cls=xx(sssss) Sub=xx Prot=xx Driver=ssss
217| | |      |      |       |             |      |       |__Driver name
218| | |      |      |       |             |      |          or "(none)"
219| | |      |      |       |             |      |__InterfaceProtocol
220| | |      |      |       |             |__InterfaceSubClass
221| | |      |      |       |__InterfaceClass
222| | |      |      |__NumberOfEndpoints
223| | |      |__AlternateSettingNumber
224| | |__InterfaceNumber
225| |__ "*" indicates the active altsetting (others are " ")
226|__Interface info tag
227
228    A given interface may have one or more "alternate" settings.
229    For example, default settings may not use more than a small
230    amount of periodic bandwidth.  To use significant fractions
231    of bus bandwidth, drivers must select a non-default altsetting.
232
233    Only one setting for an interface may be active at a time, and
234    only one driver may bind to an interface at a time.  Most devices
235    have only one alternate setting per interface.
236
237
238Endpoint descriptor info (can be multiple per Interface):
239
240E:  Ad=xx(s) Atr=xx(ssss) MxPS=dddd Ivl=dddss
241|   |        |            |         |__Interval (max) between transfers
242|   |        |            |__EndpointMaxPacketSize
243|   |        |__Attributes(EndpointType)
244|   |__EndpointAddress(I=In,O=Out)
245|__Endpoint info tag
246
247    The interval is nonzero for all periodic (interrupt or isochronous)
248    endpoints.  For high speed endpoints the transfer interval may be
249    measured in microseconds rather than milliseconds.
250
251    For high speed periodic endpoints, the "MaxPacketSize" reflects
252    the per-microframe data transfer size.  For "high bandwidth"
253    endpoints, that can reflect two or three packets (for up to
254    3KBytes every 125 usec) per endpoint.
255
256    With the Linux-USB stack, periodic bandwidth reservations use the
257    transfer intervals and sizes provided by URBs, which can be less
258    than those found in endpoint descriptor.
259
260
261=======================================================================
262
263
264If a user or script is interested only in Topology info, for
265example, use something like "grep ^T: /proc/bus/usb/devices"
266for only the Topology lines.  A command like
267"grep -i ^[tdp]: /proc/bus/usb/devices" can be used to list
268only the lines that begin with the characters in square brackets,
269where the valid characters are TDPCIE.  With a slightly more able
270script, it can display any selected lines (for example, only T, D,
271and P lines) and change their output format.  (The "procusb"
272Perl script is the beginning of this idea.  It will list only
273selected lines [selected from TBDPSCIE] or "All" lines from
274/proc/bus/usb/devices.)
275
276The Topology lines can be used to generate a graphic/pictorial
277of the USB devices on a system's root hub.  (See more below
278on how to do this.)
279
280The Interface lines can be used to determine what driver is
281being used for each device, and which altsetting it activated.
282
283The Configuration lines could be used to list maximum power
284(in milliamps) that a system's USB devices are using.
285For example, "grep ^C: /proc/bus/usb/devices".
286
287
288Here's an example, from a system which has a UHCI root hub,
289an external hub connected to the root hub, and a mouse and
290a serial converter connected to the external hub.
291
292T:  Bus=00 Lev=00 Prnt=00 Port=00 Cnt=00 Dev#=  1 Spd=12  MxCh= 2
293B:  Alloc= 28/900 us ( 3%), #Int=  2, #Iso=  0
294D:  Ver= 1.00 Cls=09(hub  ) Sub=00 Prot=00 MxPS= 8 #Cfgs=  1
295P:  Vendor=0000 ProdID=0000 Rev= 0.00
296S:  Product=USB UHCI Root Hub
297S:  SerialNumber=dce0
298C:* #Ifs= 1 Cfg#= 1 Atr=40 MxPwr=  0mA
299I:  If#= 0 Alt= 0 #EPs= 1 Cls=09(hub  ) Sub=00 Prot=00 Driver=hub
300E:  Ad=81(I) Atr=03(Int.) MxPS=   8 Ivl=255ms
301
302T:  Bus=00 Lev=01 Prnt=01 Port=00 Cnt=01 Dev#=  2 Spd=12  MxCh= 4
303D:  Ver= 1.00 Cls=09(hub  ) Sub=00 Prot=00 MxPS= 8 #Cfgs=  1
304P:  Vendor=0451 ProdID=1446 Rev= 1.00
305C:* #Ifs= 1 Cfg#= 1 Atr=e0 MxPwr=100mA
306I:  If#= 0 Alt= 0 #EPs= 1 Cls=09(hub  ) Sub=00 Prot=00 Driver=hub
307E:  Ad=81(I) Atr=03(Int.) MxPS=   1 Ivl=255ms
308
309T:  Bus=00 Lev=02 Prnt=02 Port=00 Cnt=01 Dev#=  3 Spd=1.5 MxCh= 0
310D:  Ver= 1.00 Cls=00(>ifc ) Sub=00 Prot=00 MxPS= 8 #Cfgs=  1
311P:  Vendor=04b4 ProdID=0001 Rev= 0.00
312C:* #Ifs= 1 Cfg#= 1 Atr=80 MxPwr=100mA
313I:  If#= 0 Alt= 0 #EPs= 1 Cls=03(HID  ) Sub=01 Prot=02 Driver=mouse
314E:  Ad=81(I) Atr=03(Int.) MxPS=   3 Ivl= 10ms
315
316T:  Bus=00 Lev=02 Prnt=02 Port=02 Cnt=02 Dev#=  4 Spd=12  MxCh= 0
317D:  Ver= 1.00 Cls=00(>ifc ) Sub=00 Prot=00 MxPS= 8 #Cfgs=  1
318P:  Vendor=0565 ProdID=0001 Rev= 1.08
319S:  Manufacturer=Peracom Networks, Inc.
320S:  Product=Peracom USB to Serial Converter
321C:* #Ifs= 1 Cfg#= 1 Atr=a0 MxPwr=100mA
322I:  If#= 0 Alt= 0 #EPs= 3 Cls=00(>ifc ) Sub=00 Prot=00 Driver=serial
323E:  Ad=81(I) Atr=02(Bulk) MxPS=  64 Ivl= 16ms
324E:  Ad=01(O) Atr=02(Bulk) MxPS=  16 Ivl= 16ms
325E:  Ad=82(I) Atr=03(Int.) MxPS=   8 Ivl=  8ms
326
327
328Selecting only the "T:" and "I:" lines from this (for example, by using
329"procusb ti"), we have:
330
331T:  Bus=00 Lev=00 Prnt=00 Port=00 Cnt=00 Dev#=  1 Spd=12  MxCh= 2
332T:  Bus=00 Lev=01 Prnt=01 Port=00 Cnt=01 Dev#=  2 Spd=12  MxCh= 4
333I:  If#= 0 Alt= 0 #EPs= 1 Cls=09(hub  ) Sub=00 Prot=00 Driver=hub
334T:  Bus=00 Lev=02 Prnt=02 Port=00 Cnt=01 Dev#=  3 Spd=1.5 MxCh= 0
335I:  If#= 0 Alt= 0 #EPs= 1 Cls=03(HID  ) Sub=01 Prot=02 Driver=mouse
336T:  Bus=00 Lev=02 Prnt=02 Port=02 Cnt=02 Dev#=  4 Spd=12  MxCh= 0
337I:  If#= 0 Alt= 0 #EPs= 3 Cls=00(>ifc ) Sub=00 Prot=00 Driver=serial
338
339
340Physically this looks like (or could be converted to):
341
342                      +------------------+
343                      |  PC/root_hub (12)|   Dev# = 1
344                      +------------------+   (nn) is Mbps.
345    Level 0           |  CN.0   |  CN.1  |   [CN = connector/port #]
346                      +------------------+
347                          /
348                         /
349            +-----------------------+
350  Level 1   | Dev#2: 4-port hub (12)|
351            +-----------------------+
352            |CN.0 |CN.1 |CN.2 |CN.3 |
353            +-----------------------+
354                \           \____________________
355                 \_____                          \
356                       \                          \
357               +--------------------+      +--------------------+
358  Level 2      | Dev# 3: mouse (1.5)|      | Dev# 4: serial (12)|
359               +--------------------+      +--------------------+
360
361
362
363Or, in a more tree-like structure (ports [Connectors] without
364connections could be omitted):
365
366PC:  Dev# 1, root hub, 2 ports, 12 Mbps
367|_ CN.0:  Dev# 2, hub, 4 ports, 12 Mbps
368     |_ CN.0:  Dev #3, mouse, 1.5 Mbps
369     |_ CN.1:
370     |_ CN.2:  Dev #4, serial, 12 Mbps
371     |_ CN.3:
372|_ CN.1:
373
374
375                         ### END ###
376