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