| blob | 98be91982677e89bef390162440c0a90a479eb46 |
1 /proc/bus/usb filesystem output
2 ===============================
3 (version 2010.09.13)
6 The usbfs filesystem for USB devices is traditionally mounted at
7 /proc/bus/usb. It provides the /proc/bus/usb/devices file, as well as
8 the /proc/bus/usb/BBB/DDD files.
10 In many modern systems the usbfs filesystem isn't used at all. Instead
11 USB 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.
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):
20 mount -t usbfs none /proc/bus/usb
22 An alternative and more permanent method would be to add
24 none /proc/bus/usb usbfs defaults 0 0
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.
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.
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.
39 For more information on mounting the usbfs file system, see the
40 "USB Device Filesystem" section of the USB Guide. The latest copy
41 of the USB Guide can be found at http://www.linux-usb.org/
44 THE /proc/bus/usb/BBB/DDD FILES:
45 --------------------------------
46 Each connected USB device has one file. The BBB indicates the bus
47 number. The DDD indicates the device address on that bus. Both
48 of these numbers are assigned sequentially, and can be reused, so
49 you can't rely on them for stable access to devices. For example,
50 it's relatively common for devices to re-enumerate while they are
51 still connected (perhaps someone jostled their power supply, hub,
52 or USB cable), so a device might be 002/027 when you first connect
53 it and 002/048 sometime later.
55 These files can be read as binary data. The binary data consists
56 of first the device descriptor, then the descriptors for each
57 configuration of the device. Multi-byte fields in the device descriptor
58 are converted to host endianness by the kernel. The configuration
59 descriptors are in bus endian format! The configuration descriptor
60 are wTotalLength bytes apart. If a device returns less configuration
61 descriptor data than indicated by wTotalLength there will be a hole in
62 the file for the missing bytes. This information is also shown
63 in text form by the /proc/bus/usb/devices file, described later.
65 These files may also be used to write user-level drivers for the USB
66 devices. You would open the /proc/bus/usb/BBB/DDD file read/write,
67 read its descriptors to make sure it's the device you expect, and then
68 bind to an interface (or perhaps several) using an ioctl call. You
69 would issue more ioctls to the device to communicate to it using
70 control, bulk, or other kinds of USB transfers. The IOCTLs are
71 listed in the <linux/usbdevice_fs.h> file, and at this writing the
72 source code (linux/drivers/usb/core/devio.c) is the primary reference
73 for how to access devices through those files.
75 Note that since by default these BBB/DDD files are writable only by
76 root, only root can write such user mode drivers. You can selectively
77 grant read/write permissions to other users by using "chmod". Also,
78 usbfs mount options such as "devmode=0666" may be helpful.
82 THE /proc/bus/usb/devices FILE:
83 -------------------------------
84 In /proc/bus/usb/devices, each device's output has multiple
85 lines of ASCII output.
86 I made it ASCII instead of binary on purpose, so that someone
87 can obtain some useful data from it without the use of an
88 auxiliary program. However, with an auxiliary program, the numbers
89 in the first 4 columns of each "T:" line (topology info:
90 Lev, Prnt, Port, Cnt) can be used to build a USB topology diagram.
92 Each line is tagged with a one-character ID for that line:
94 T = Topology (etc.)
95 B = Bandwidth (applies only to USB host controllers, which are
96 virtualized as root hubs)
97 D = Device descriptor info.
98 P = Product ID info. (from Device descriptor, but they won't fit
99 together on one line)
100 S = String descriptors.
101 C = Configuration descriptor info. (* = active configuration)
102 I = Interface descriptor info.
103 E = Endpoint descriptor info.
105 =======================================================================
107 /proc/bus/usb/devices output format:
109 Legend:
110 d = decimal number (may have leading spaces or 0's)
111 x = hexadecimal number (may have leading spaces or 0's)
112 s = string
115 Topology info:
117 T: Bus=dd Lev=dd Prnt=dd Port=dd Cnt=dd Dev#=ddd Spd=dddd MxCh=dd
118 | | | | | | | | |__MaxChildren
119 | | | | | | | |__Device Speed in Mbps
120 | | | | | | |__DeviceNumber
121 | | | | | |__Count of devices at this level
122 | | | | |__Connector/Port on Parent for this device
123 | | | |__Parent DeviceNumber
124 | | |__Level in topology for this bus
125 | |__Bus number
126 |__Topology info tag
128 Speed may be:
129 1.5 Mbit/s for low speed USB
130 12 Mbit/s for full speed USB
131 480 Mbit/s for high speed USB (added for USB 2.0);
132 also used for Wireless USB, which has no fixed speed
133 5000 Mbit/s for SuperSpeed USB (added for USB 3.0)
135 For reasons lost in the mists of time, the Port number is always
136 too low by 1. For example, a device plugged into port 4 will
137 show up with "Port=03".
139 Bandwidth info:
140 B: Alloc=ddd/ddd us (xx%), #Int=ddd, #Iso=ddd
141 | | | |__Number of isochronous requests
142 | | |__Number of interrupt requests
143 | |__Total Bandwidth allocated to this bus
144 |__Bandwidth info tag
146 Bandwidth allocation is an approximation of how much of one frame
147 (millisecond) is in use. It reflects only periodic transfers, which
148 are the only transfers that reserve bandwidth. Control and bulk
149 transfers use all other bandwidth, including reserved bandwidth that
150 is not used for transfers (such as for short packets).
152 The percentage is how much of the "reserved" bandwidth is scheduled by
153 those transfers. For a low or full speed bus (loosely, "USB 1.1"),
154 90% of the bus bandwidth is reserved. For a high speed bus (loosely,
155 "USB 2.0") 80% is reserved.
158 Device descriptor info & Product ID info:
160 D: Ver=x.xx Cls=xx(s) Sub=xx Prot=xx MxPS=dd #Cfgs=dd
161 P: Vendor=xxxx ProdID=xxxx Rev=xx.xx
163 where
164 D: Ver=x.xx Cls=xx(sssss) Sub=xx Prot=xx MxPS=dd #Cfgs=dd
165 | | | | | | |__NumberConfigurations
166 | | | | | |__MaxPacketSize of Default Endpoint
167 | | | | |__DeviceProtocol
168 | | | |__DeviceSubClass
169 | | |__DeviceClass
170 | |__Device USB version
171 |__Device info tag #1
173 where
174 P: Vendor=xxxx ProdID=xxxx Rev=xx.xx
175 | | | |__Product revision number
176 | | |__Product ID code
177 | |__Vendor ID code
178 |__Device info tag #2
181 String descriptor info:
183 S: Manufacturer=ssss
184 | |__Manufacturer of this device as read from the device.
185 | For USB host controller drivers (virtual root hubs) this may
186 | be omitted, or (for newer drivers) will identify the kernel
187 | version and the driver which provides this hub emulation.
188 |__String info tag
190 S: Product=ssss
191 | |__Product description of this device as read from the device.
192 | For older USB host controller drivers (virtual root hubs) this
193 | indicates the driver; for newer ones, it's a product (and vendor)
194 | description that often comes from the kernel's PCI ID database.
195 |__String info tag
197 S: SerialNumber=ssss
198 | |__Serial Number of this device as read from the device.
199 | For USB host controller drivers (virtual root hubs) this is
200 | some unique ID, normally a bus ID (address or slot name) that
201 | can't be shared with any other device.
202 |__String info tag
206 Configuration descriptor info:
208 C:* #Ifs=dd Cfg#=dd Atr=xx MPwr=dddmA
209 | | | | | |__MaxPower in mA
210 | | | | |__Attributes
211 | | | |__ConfiguratioNumber
212 | | |__NumberOfInterfaces
213 | |__ "*" indicates the active configuration (others are " ")
214 |__Config info tag
216 USB devices may have multiple configurations, each of which act
217 rather differently. For example, a bus-powered configuration
218 might be much less capable than one that is self-powered. Only
219 one device configuration can be active at a time; most devices
220 have only one configuration.
222 Each configuration consists of one or more interfaces. Each
223 interface serves a distinct "function", which is typically bound
224 to a different USB device driver. One common example is a USB
225 speaker with an audio interface for playback, and a HID interface
226 for use with software volume control.
229 Interface descriptor info (can be multiple per Config):
231 I:* If#=dd Alt=dd #EPs=dd Cls=xx(sssss) Sub=xx Prot=xx Driver=ssss
232 | | | | | | | | |__Driver name
233 | | | | | | | | or "(none)"
234 | | | | | | | |__InterfaceProtocol
235 | | | | | | |__InterfaceSubClass
236 | | | | | |__InterfaceClass
237 | | | | |__NumberOfEndpoints
238 | | | |__AlternateSettingNumber
239 | | |__InterfaceNumber
240 | |__ "*" indicates the active altsetting (others are " ")
241 |__Interface info tag
243 A given interface may have one or more "alternate" settings.
244 For example, default settings may not use more than a small
245 amount of periodic bandwidth. To use significant fractions
246 of bus bandwidth, drivers must select a non-default altsetting.
248 Only one setting for an interface may be active at a time, and
249 only one driver may bind to an interface at a time. Most devices
250 have only one alternate setting per interface.
253 Endpoint descriptor info (can be multiple per Interface):
255 E: Ad=xx(s) Atr=xx(ssss) MxPS=dddd Ivl=dddss
256 | | | | |__Interval (max) between transfers
257 | | | |__EndpointMaxPacketSize
258 | | |__Attributes(EndpointType)
259 | |__EndpointAddress(I=In,O=Out)
260 |__Endpoint info tag
262 The interval is nonzero for all periodic (interrupt or isochronous)
263 endpoints. For high speed endpoints the transfer interval may be
264 measured in microseconds rather than milliseconds.
266 For high speed periodic endpoints, the "MaxPacketSize" reflects
267 the per-microframe data transfer size. For "high bandwidth"
268 endpoints, that can reflect two or three packets (for up to
269 3KBytes every 125 usec) per endpoint.
271 With the Linux-USB stack, periodic bandwidth reservations use the
272 transfer intervals and sizes provided by URBs, which can be less
273 than those found in endpoint descriptor.
276 =======================================================================
279 If a user or script is interested only in Topology info, for
280 example, use something like "grep ^T: /proc/bus/usb/devices"
281 for only the Topology lines. A command like
282 "grep -i ^[tdp]: /proc/bus/usb/devices" can be used to list
283 only the lines that begin with the characters in square brackets,
284 where the valid characters are TDPCIE. With a slightly more able
285 script, it can display any selected lines (for example, only T, D,
286 and P lines) and change their output format. (The "procusb"
287 Perl script is the beginning of this idea. It will list only
288 selected lines [selected from TBDPSCIE] or "All" lines from
289 /proc/bus/usb/devices.)
291 The Topology lines can be used to generate a graphic/pictorial
292 of the USB devices on a system's root hub. (See more below
293 on how to do this.)
295 The Interface lines can be used to determine what driver is
296 being used for each device, and which altsetting it activated.
298 The Configuration lines could be used to list maximum power
299 (in milliamps) that a system's USB devices are using.
300 For example, "grep ^C: /proc/bus/usb/devices".
303 Here's an example, from a system which has a UHCI root hub,
304 an external hub connected to the root hub, and a mouse and
305 a serial converter connected to the external hub.
307 T: Bus=00 Lev=00 Prnt=00 Port=00 Cnt=00 Dev#= 1 Spd=12 MxCh= 2
308 B: Alloc= 28/900 us ( 3%), #Int= 2, #Iso= 0
309 D: Ver= 1.00 Cls=09(hub ) Sub=00 Prot=00 MxPS= 8 #Cfgs= 1
310 P: Vendor=0000 ProdID=0000 Rev= 0.00
311 S: Product=USB UHCI Root Hub
312 S: SerialNumber=dce0
313 C:* #Ifs= 1 Cfg#= 1 Atr=40 MxPwr= 0mA
314 I: If#= 0 Alt= 0 #EPs= 1 Cls=09(hub ) Sub=00 Prot=00 Driver=hub
315 E: Ad=81(I) Atr=03(Int.) MxPS= 8 Ivl=255ms
317 T: Bus=00 Lev=01 Prnt=01 Port=00 Cnt=01 Dev#= 2 Spd=12 MxCh= 4
318 D: Ver= 1.00 Cls=09(hub ) Sub=00 Prot=00 MxPS= 8 #Cfgs= 1
319 P: Vendor=0451 ProdID=1446 Rev= 1.00
320 C:* #Ifs= 1 Cfg#= 1 Atr=e0 MxPwr=100mA
321 I: If#= 0 Alt= 0 #EPs= 1 Cls=09(hub ) Sub=00 Prot=00 Driver=hub
322 E: Ad=81(I) Atr=03(Int.) MxPS= 1 Ivl=255ms
324 T: Bus=00 Lev=02 Prnt=02 Port=00 Cnt=01 Dev#= 3 Spd=1.5 MxCh= 0
325 D: Ver= 1.00 Cls=00(>ifc ) Sub=00 Prot=00 MxPS= 8 #Cfgs= 1
326 P: Vendor=04b4 ProdID=0001 Rev= 0.00
327 C:* #Ifs= 1 Cfg#= 1 Atr=80 MxPwr=100mA
328 I: If#= 0 Alt= 0 #EPs= 1 Cls=03(HID ) Sub=01 Prot=02 Driver=mouse
329 E: Ad=81(I) Atr=03(Int.) MxPS= 3 Ivl= 10ms
331 T: Bus=00 Lev=02 Prnt=02 Port=02 Cnt=02 Dev#= 4 Spd=12 MxCh= 0
332 D: Ver= 1.00 Cls=00(>ifc ) Sub=00 Prot=00 MxPS= 8 #Cfgs= 1
333 P: Vendor=0565 ProdID=0001 Rev= 1.08
334 S: Manufacturer=Peracom Networks, Inc.
335 S: Product=Peracom USB to Serial Converter
336 C:* #Ifs= 1 Cfg#= 1 Atr=a0 MxPwr=100mA
337 I: If#= 0 Alt= 0 #EPs= 3 Cls=00(>ifc ) Sub=00 Prot=00 Driver=serial
338 E: Ad=81(I) Atr=02(Bulk) MxPS= 64 Ivl= 16ms
339 E: Ad=01(O) Atr=02(Bulk) MxPS= 16 Ivl= 16ms
340 E: Ad=82(I) Atr=03(Int.) MxPS= 8 Ivl= 8ms
343 Selecting only the "T:" and "I:" lines from this (for example, by using
344 "procusb ti"), we have:
346 T: Bus=00 Lev=00 Prnt=00 Port=00 Cnt=00 Dev#= 1 Spd=12 MxCh= 2
347 T: Bus=00 Lev=01 Prnt=01 Port=00 Cnt=01 Dev#= 2 Spd=12 MxCh= 4
348 I: If#= 0 Alt= 0 #EPs= 1 Cls=09(hub ) Sub=00 Prot=00 Driver=hub
349 T: Bus=00 Lev=02 Prnt=02 Port=00 Cnt=01 Dev#= 3 Spd=1.5 MxCh= 0
350 I: If#= 0 Alt= 0 #EPs= 1 Cls=03(HID ) Sub=01 Prot=02 Driver=mouse
351 T: Bus=00 Lev=02 Prnt=02 Port=02 Cnt=02 Dev#= 4 Spd=12 MxCh= 0
352 I: If#= 0 Alt= 0 #EPs= 3 Cls=00(>ifc ) Sub=00 Prot=00 Driver=serial
355 Physically this looks like (or could be converted to):
357 +------------------+
358 | PC/root_hub (12)| Dev# = 1
359 +------------------+ (nn) is Mbps.
360 Level 0 | CN.0 | CN.1 | [CN = connector/port #]
361 +------------------+
362 /
363 /
364 +-----------------------+
365 Level 1 | Dev#2: 4-port hub (12)|
366 +-----------------------+
367 |CN.0 |CN.1 |CN.2 |CN.3 |
368 +-----------------------+
369 \ \____________________
370 \_____ \
371 \ \
372 +--------------------+ +--------------------+
373 Level 2 | Dev# 3: mouse (1.5)| | Dev# 4: serial (12)|
374 +--------------------+ +--------------------+
378 Or, in a more tree-like structure (ports [Connectors] without
379 connections could be omitted):
381 PC: Dev# 1, root hub, 2 ports, 12 Mbps
382 |_ CN.0: Dev# 2, hub, 4 ports, 12 Mbps
383 |_ CN.0: Dev #3, mouse, 1.5 Mbps
384 |_ CN.1:
385 |_ CN.2: Dev #4, serial, 12 Mbps
386 |_ CN.3:
387 |_ CN.1:
390 ### END ###