1 .. _usb-hostside-api: 1 .. _usb-hostside-api:
2 2
3 =========================== 3 ===========================
4 The Linux-USB Host Side API 4 The Linux-USB Host Side API
5 =========================== 5 ===========================
6 6
7 Introduction to USB on Linux 7 Introduction to USB on Linux
8 ============================ 8 ============================
9 9
10 A Universal Serial Bus (USB) is used to connec 10 A Universal Serial Bus (USB) is used to connect a host, such as a PC or
11 workstation, to a number of peripheral devices 11 workstation, to a number of peripheral devices. USB uses a tree
12 structure, with the host as the root (the syst 12 structure, with the host as the root (the system's master), hubs as
13 interior nodes, and peripherals as leaves (and 13 interior nodes, and peripherals as leaves (and slaves). Modern PCs
14 support several such trees of USB devices, usu 14 support several such trees of USB devices, usually
15 a few USB 3.0 (5 GBit/s) or USB 3.1 (10 GBit/s 15 a few USB 3.0 (5 GBit/s) or USB 3.1 (10 GBit/s) and some legacy
16 USB 2.0 (480 MBit/s) busses just in case. 16 USB 2.0 (480 MBit/s) busses just in case.
17 17
18 That master/slave asymmetry was designed-in fo 18 That master/slave asymmetry was designed-in for a number of reasons, one
19 being ease of use. It is not physically possib 19 being ease of use. It is not physically possible to mistake upstream and
20 downstream or it does not matter with a type C 20 downstream or it does not matter with a type C plug (or they are built into the
21 peripheral). Also, the host software doesn't n 21 peripheral). Also, the host software doesn't need to deal with
22 distributed auto-configuration since the pre-d 22 distributed auto-configuration since the pre-designated master node
23 manages all that. 23 manages all that.
24 24
25 Kernel developers added USB support to Linux e 25 Kernel developers added USB support to Linux early in the 2.2 kernel
26 series and have been developing it further sin 26 series and have been developing it further since then. Besides support
27 for each new generation of USB, various host c 27 for each new generation of USB, various host controllers gained support,
28 new drivers for peripherals have been added an 28 new drivers for peripherals have been added and advanced features for latency
29 measurement and improved power management intr 29 measurement and improved power management introduced.
30 30
31 Linux can run inside USB devices as well as on 31 Linux can run inside USB devices as well as on the hosts that control
32 the devices. But USB device drivers running in 32 the devices. But USB device drivers running inside those peripherals
33 don't do the same things as the ones running i 33 don't do the same things as the ones running inside hosts, so they've
34 been given a different name: *gadget drivers*. 34 been given a different name: *gadget drivers*. This document does not
35 cover gadget drivers. 35 cover gadget drivers.
36 36
37 USB Host-Side API Model 37 USB Host-Side API Model
38 ======================= 38 =======================
39 39
40 Host-side drivers for USB devices talk to the 40 Host-side drivers for USB devices talk to the "usbcore" APIs. There are
41 two. One is intended for *general-purpose* dri 41 two. One is intended for *general-purpose* drivers (exposed through
42 driver frameworks), and the other is for drive 42 driver frameworks), and the other is for drivers that are *part of the
43 core*. Such core drivers include the *hub* dri 43 core*. Such core drivers include the *hub* driver (which manages trees
44 of USB devices) and several different kinds of 44 of USB devices) and several different kinds of *host controller
45 drivers*, which control individual busses. 45 drivers*, which control individual busses.
46 46
47 The device model seen by USB drivers is relati 47 The device model seen by USB drivers is relatively complex.
48 48
49 - USB supports four kinds of data transfers ( 49 - USB supports four kinds of data transfers (control, bulk, interrupt,
50 and isochronous). Two of them (control and 50 and isochronous). Two of them (control and bulk) use bandwidth as
51 it's available, while the other two (interr 51 it's available, while the other two (interrupt and isochronous) are
52 scheduled to provide guaranteed bandwidth. 52 scheduled to provide guaranteed bandwidth.
53 53
54 - The device description model includes one o 54 - The device description model includes one or more "configurations"
55 per device, only one of which is active at 55 per device, only one of which is active at a time. Devices are supposed
56 to be capable of operating at lower than th 56 to be capable of operating at lower than their top
57 speeds and may provide a BOS descriptor sho 57 speeds and may provide a BOS descriptor showing the lowest speed they
58 remain fully operational at. 58 remain fully operational at.
59 59
60 - From USB 3.0 on configurations have one or 60 - From USB 3.0 on configurations have one or more "functions", which
61 provide a common functionality and are grou 61 provide a common functionality and are grouped together for purposes
62 of power management. 62 of power management.
63 63
64 - Configurations or functions have one or mor 64 - Configurations or functions have one or more "interfaces", each of which may have
65 "alternate settings". Interfaces may be sta 65 "alternate settings". Interfaces may be standardized by USB "Class"
66 specifications, or may be specific to a ven 66 specifications, or may be specific to a vendor or device.
67 67
68 USB device drivers actually bind to interfa 68 USB device drivers actually bind to interfaces, not devices. Think of
69 them as "interface drivers", though you may 69 them as "interface drivers", though you may not see many devices
70 where the distinction is important. *Most U 70 where the distinction is important. *Most USB devices are simple,
71 with only one function, one configuration, 71 with only one function, one configuration, one interface, and one alternate
72 setting.* 72 setting.*
73 73
74 - Interfaces have one or more "endpoints", ea 74 - Interfaces have one or more "endpoints", each of which supports one
75 type and direction of data transfer such as 75 type and direction of data transfer such as "bulk out" or "interrupt
76 in". The entire configuration may have up t 76 in". The entire configuration may have up to sixteen endpoints in
77 each direction, allocated as needed among a 77 each direction, allocated as needed among all the interfaces.
78 78
79 - Data transfer on USB is packetized; each en 79 - Data transfer on USB is packetized; each endpoint has a maximum
80 packet size. Drivers must often be aware of 80 packet size. Drivers must often be aware of conventions such as
81 flagging the end of bulk transfers using "s 81 flagging the end of bulk transfers using "short" (including zero
82 length) packets. 82 length) packets.
83 83
84 - The Linux USB API supports synchronous call 84 - The Linux USB API supports synchronous calls for control and bulk
85 messages. It also supports asynchronous cal 85 messages. It also supports asynchronous calls for all kinds of data
86 transfer, using request structures called " 86 transfer, using request structures called "URBs" (USB Request
87 Blocks). 87 Blocks).
88 88
89 Accordingly, the USB Core API exposed to devic 89 Accordingly, the USB Core API exposed to device drivers covers quite a
90 lot of territory. You'll probably need to cons 90 lot of territory. You'll probably need to consult the USB 3.0
91 specification, available online from www.usb.o 91 specification, available online from www.usb.org at no cost, as well as
92 class or device specifications. 92 class or device specifications.
93 93
94 The only host-side drivers that actually touch 94 The only host-side drivers that actually touch hardware (reading/writing
95 registers, handling IRQs, and so on) are the H 95 registers, handling IRQs, and so on) are the HCDs. In theory, all HCDs
96 provide the same functionality through the sam 96 provide the same functionality through the same API. In practice, that's
97 becoming more true, but there are still differ 97 becoming more true, but there are still differences
98 that crop up especially with fault handling on 98 that crop up especially with fault handling on the less common controllers.
99 Different controllers don't 99 Different controllers don't
100 necessarily report the same aspects of failure 100 necessarily report the same aspects of failures, and recovery from
101 faults (including software-induced ones like u 101 faults (including software-induced ones like unlinking an URB) isn't yet
102 fully consistent. Device driver authors should 102 fully consistent. Device driver authors should make a point of doing
103 disconnect testing (while the device is active 103 disconnect testing (while the device is active) with each different host
104 controller driver, to make sure drivers don't 104 controller driver, to make sure drivers don't have bugs of their own as
105 well as to make sure they aren't relying on so 105 well as to make sure they aren't relying on some HCD-specific behavior.
106 106
107 .. _usb_chapter9: 107 .. _usb_chapter9:
108 108
109 USB-Standard Types 109 USB-Standard Types
110 ================== 110 ==================
111 111
112 In ``include/uapi/linux/usb/ch9.h`` you will f !! 112 In ``<linux/usb/ch9.h>`` you will find the USB data types defined in
113 in chapter 9 of the USB specification. These d !! 113 chapter 9 of the USB specification. These data types are used throughout
114 USB, and in APIs including this host side API, 114 USB, and in APIs including this host side API, gadget APIs, usb character
115 devices and debugfs interfaces. That file is i !! 115 devices and debugfs interfaces.
116 ``include/linux/usb/ch9.h``, which also contai <<
117 utility routines for manipulating these data t <<
118 are in ``drivers/usb/common/common.c``. <<
119 116
120 .. kernel-doc:: drivers/usb/common/common.c !! 117 .. kernel-doc:: include/linux/usb/ch9.h
121 :export: !! 118 :internal:
122 <<
123 In addition, some functions useful for creatin <<
124 defined in ``drivers/usb/common/debug.c``. <<
125 119
126 .. _usb_header: 120 .. _usb_header:
127 121
128 Host-Side Data Types and Macros 122 Host-Side Data Types and Macros
129 =============================== 123 ===============================
130 124
131 The host side API exposes several layers to dr 125 The host side API exposes several layers to drivers, some of which are
132 more necessary than others. These support life 126 more necessary than others. These support lifecycle models for host side
133 drivers and devices, and support passing buffe 127 drivers and devices, and support passing buffers through usbcore to some
134 HCD that performs the I/O for the device drive 128 HCD that performs the I/O for the device driver.
135 129
136 .. kernel-doc:: include/linux/usb.h 130 .. kernel-doc:: include/linux/usb.h
137 :internal: 131 :internal:
138 132
139 USB Core APIs 133 USB Core APIs
140 ============= 134 =============
141 135
142 There are two basic I/O models in the USB API. 136 There are two basic I/O models in the USB API. The most elemental one is
143 asynchronous: drivers submit requests in the f 137 asynchronous: drivers submit requests in the form of an URB, and the
144 URB's completion callback handles the next ste 138 URB's completion callback handles the next step. All USB transfer types
145 support that model, although there are special 139 support that model, although there are special cases for control URBs
146 (which always have setup and status stages, bu 140 (which always have setup and status stages, but may not have a data
147 stage) and isochronous URBs (which allow large 141 stage) and isochronous URBs (which allow large packets and include
148 per-packet fault reports). Built on top of tha 142 per-packet fault reports). Built on top of that is synchronous API
149 support, where a driver calls a routine that a 143 support, where a driver calls a routine that allocates one or more URBs,
150 submits them, and waits until they complete. T 144 submits them, and waits until they complete. There are synchronous
151 wrappers for single-buffer control and bulk tr 145 wrappers for single-buffer control and bulk transfers (which are awkward
152 to use in some driver disconnect scenarios), a 146 to use in some driver disconnect scenarios), and for scatterlist based
153 streaming i/o (bulk or interrupt). 147 streaming i/o (bulk or interrupt).
154 148
155 USB drivers need to provide buffers that can b 149 USB drivers need to provide buffers that can be used for DMA, although
156 they don't necessarily need to provide the DMA 150 they don't necessarily need to provide the DMA mapping themselves. There
157 are APIs to use used when allocating DMA buffe 151 are APIs to use used when allocating DMA buffers, which can prevent use
158 of bounce buffers on some systems. In some cas 152 of bounce buffers on some systems. In some cases, drivers may be able to
159 rely on 64bit DMA to eliminate another kind of 153 rely on 64bit DMA to eliminate another kind of bounce buffer.
160 154
161 .. kernel-doc:: drivers/usb/core/urb.c 155 .. kernel-doc:: drivers/usb/core/urb.c
162 :export: 156 :export:
163 157
164 .. kernel-doc:: drivers/usb/core/message.c 158 .. kernel-doc:: drivers/usb/core/message.c
165 :export: 159 :export:
166 160
167 .. kernel-doc:: drivers/usb/core/file.c 161 .. kernel-doc:: drivers/usb/core/file.c
168 :export: 162 :export:
169 163
170 .. kernel-doc:: drivers/usb/core/driver.c 164 .. kernel-doc:: drivers/usb/core/driver.c
171 :export: 165 :export:
172 166
173 .. kernel-doc:: drivers/usb/core/usb.c 167 .. kernel-doc:: drivers/usb/core/usb.c
174 :export: 168 :export:
175 169
176 .. kernel-doc:: drivers/usb/core/hub.c 170 .. kernel-doc:: drivers/usb/core/hub.c
177 :export: 171 :export:
178 172
179 Host Controller APIs 173 Host Controller APIs
180 ==================== 174 ====================
181 175
182 These APIs are only for use by host controller 176 These APIs are only for use by host controller drivers, most of which
183 implement standard register interfaces such as 177 implement standard register interfaces such as XHCI, EHCI, OHCI, or UHCI. UHCI
184 was one of the first interfaces, designed by I 178 was one of the first interfaces, designed by Intel and also used by VIA;
185 it doesn't do much in hardware. OHCI was desig 179 it doesn't do much in hardware. OHCI was designed later, to have the
186 hardware do more work (bigger transfers, track 180 hardware do more work (bigger transfers, tracking protocol state, and so
187 on). EHCI was designed with USB 2.0; its desig 181 on). EHCI was designed with USB 2.0; its design has features that
188 resemble OHCI (hardware does much more work) a 182 resemble OHCI (hardware does much more work) as well as UHCI (some parts
189 of ISO support, TD list processing). XHCI was 183 of ISO support, TD list processing). XHCI was designed with USB 3.0. It
190 continues to shift support for functionality i 184 continues to shift support for functionality into hardware.
191 185
192 There are host controllers other than the "big 186 There are host controllers other than the "big three", although most PCI
193 based controllers (and a few non-PCI based one 187 based controllers (and a few non-PCI based ones) use one of those
194 interfaces. Not all host controllers use DMA; 188 interfaces. Not all host controllers use DMA; some use PIO, and there is
195 also a simulator and a virtual host controller 189 also a simulator and a virtual host controller to pipe USB over the network.
196 190
197 The same basic APIs are available to drivers f 191 The same basic APIs are available to drivers for all those controllers.
198 For historical reasons they are in two layers: 192 For historical reasons they are in two layers: :c:type:`struct
199 usb_bus <usb_bus>` is a rather thin layer that 193 usb_bus <usb_bus>` is a rather thin layer that became available
200 in the 2.2 kernels, while :c:type:`struct usb_ 194 in the 2.2 kernels, while :c:type:`struct usb_hcd <usb_hcd>`
201 is a more featureful layer 195 is a more featureful layer
202 that lets HCDs share common code, to shrink dr 196 that lets HCDs share common code, to shrink driver size and
203 significantly reduce hcd-specific behaviors. 197 significantly reduce hcd-specific behaviors.
204 198
205 .. kernel-doc:: drivers/usb/core/hcd.c 199 .. kernel-doc:: drivers/usb/core/hcd.c
206 :export: 200 :export:
207 201
208 .. kernel-doc:: drivers/usb/core/hcd-pci.c 202 .. kernel-doc:: drivers/usb/core/hcd-pci.c
209 :export: 203 :export:
210 204
211 .. kernel-doc:: drivers/usb/core/buffer.c 205 .. kernel-doc:: drivers/usb/core/buffer.c
212 :internal: 206 :internal:
213 207
214 The USB character device nodes 208 The USB character device nodes
215 ============================== 209 ==============================
216 210
217 This chapter presents the Linux character devi 211 This chapter presents the Linux character device nodes. You may prefer
218 to avoid writing new kernel code for your USB 212 to avoid writing new kernel code for your USB driver. User mode device
219 drivers are usually packaged as applications o 213 drivers are usually packaged as applications or libraries, and may use
220 character devices through some programming lib 214 character devices through some programming library that wraps it.
221 Such libraries include: 215 Such libraries include:
222 216
223 - `libusb <http://libusb.sourceforge.net>`__ 217 - `libusb <http://libusb.sourceforge.net>`__ for C/C++, and
224 - `jUSB <http://jUSB.sourceforge.net>`__ for 218 - `jUSB <http://jUSB.sourceforge.net>`__ for Java.
225 219
226 Some old information about it can be seen at t 220 Some old information about it can be seen at the "USB Device Filesystem"
227 section of the USB Guide. The latest copy of t 221 section of the USB Guide. The latest copy of the USB Guide can be found
228 at http://www.linux-usb.org/ 222 at http://www.linux-usb.org/
229 223
230 .. note:: 224 .. note::
231 225
232 - They were used to be implemented via *usbf 226 - They were used to be implemented via *usbfs*, but this is not part of
233 the sysfs debug interface. 227 the sysfs debug interface.
234 228
235 - This particular documentation is incomple 229 - This particular documentation is incomplete, especially with respect
236 to the asynchronous mode. As of kernel 2. 230 to the asynchronous mode. As of kernel 2.5.66 the code and this
237 (new) documentation need to be cross-revi 231 (new) documentation need to be cross-reviewed.
238 232
239 What files are in "devtmpfs"? 233 What files are in "devtmpfs"?
240 ----------------------------- 234 -----------------------------
241 235
242 Conventionally mounted at ``/dev/bus/usb/``, u 236 Conventionally mounted at ``/dev/bus/usb/``, usbfs features include:
243 237
244 - ``/dev/bus/usb/BBB/DDD`` ... magic files ex 238 - ``/dev/bus/usb/BBB/DDD`` ... magic files exposing the each device's
245 configuration descriptors, and supporting a 239 configuration descriptors, and supporting a series of ioctls for
246 making device requests, including I/O to de 240 making device requests, including I/O to devices. (Purely for access
247 by programs.) 241 by programs.)
248 242
249 Each bus is given a number (``BBB``) based on 243 Each bus is given a number (``BBB``) based on when it was enumerated; within
250 each bus, each device is given a similar numbe 244 each bus, each device is given a similar number (``DDD``). Those ``BBB/DDD``
251 paths are not "stable" identifiers; expect the 245 paths are not "stable" identifiers; expect them to change even if you
252 always leave the devices plugged in to the sam 246 always leave the devices plugged in to the same hub port. *Don't even
253 think of saving these in application configura 247 think of saving these in application configuration files.* Stable
254 identifiers are available, for user mode appli 248 identifiers are available, for user mode applications that want to use
255 them. HID and networking devices expose these 249 them. HID and networking devices expose these stable IDs, so that for
256 example you can be sure that you told the righ 250 example you can be sure that you told the right UPS to power down its
257 second server. Pleast note that it doesn't (ye 251 second server. Pleast note that it doesn't (yet) expose those IDs.
258 252
259 /dev/bus/usb/BBB/DDD 253 /dev/bus/usb/BBB/DDD
260 -------------------- 254 --------------------
261 255
262 Use these files in one of these basic ways: 256 Use these files in one of these basic ways:
263 257
264 - *They can be read,* producing first the devi 258 - *They can be read,* producing first the device descriptor (18 bytes) and
265 then the descriptors for the current configu 259 then the descriptors for the current configuration. See the USB 2.0 spec
266 for details about those binary data formats. 260 for details about those binary data formats. You'll need to convert most
267 multibyte values from little endian format t 261 multibyte values from little endian format to your native host byte
268 order, although a few of the fields in the d 262 order, although a few of the fields in the device descriptor (both of
269 the BCD-encoded fields, and the vendor and p 263 the BCD-encoded fields, and the vendor and product IDs) will be
270 byteswapped for you. Note that configuration 264 byteswapped for you. Note that configuration descriptors include
271 descriptors for interfaces, altsettings, end 265 descriptors for interfaces, altsettings, endpoints, and maybe additional
272 class descriptors. 266 class descriptors.
273 267
274 - *Perform USB operations* using *ioctl()* req 268 - *Perform USB operations* using *ioctl()* requests to make endpoint I/O
275 requests (synchronously or asynchronously) o 269 requests (synchronously or asynchronously) or manage the device. These
276 requests need the ``CAP_SYS_RAWIO`` capabili 270 requests need the ``CAP_SYS_RAWIO`` capability, as well as filesystem
277 access permissions. Only one ioctl request c 271 access permissions. Only one ioctl request can be made on one of these
278 device files at a time. This means that if y 272 device files at a time. This means that if you are synchronously reading
279 an endpoint from one thread, you won't be ab 273 an endpoint from one thread, you won't be able to write to a different
280 endpoint from another thread until the read 274 endpoint from another thread until the read completes. This works for
281 *half duplex* protocols, but otherwise you'd 275 *half duplex* protocols, but otherwise you'd use asynchronous i/o
282 requests. 276 requests.
283 277
284 Each connected USB device has one file. The ` 278 Each connected USB device has one file. The ``BBB`` indicates the bus
285 number. The ``DDD`` indicates the device addr 279 number. The ``DDD`` indicates the device address on that bus. Both
286 of these numbers are assigned sequentially, an 280 of these numbers are assigned sequentially, and can be reused, so
287 you can't rely on them for stable access to de 281 you can't rely on them for stable access to devices. For example,
288 it's relatively common for devices to re-enume 282 it's relatively common for devices to re-enumerate while they are
289 still connected (perhaps someone jostled their 283 still connected (perhaps someone jostled their power supply, hub,
290 or USB cable), so a device might be ``002/027` 284 or USB cable), so a device might be ``002/027`` when you first connect
291 it and ``002/048`` sometime later. 285 it and ``002/048`` sometime later.
292 286
293 These files can be read as binary data. The b 287 These files can be read as binary data. The binary data consists
294 of first the device descriptor, then the descr 288 of first the device descriptor, then the descriptors for each
295 configuration of the device. Multi-byte field 289 configuration of the device. Multi-byte fields in the device descriptor
296 are converted to host endianness by the kernel 290 are converted to host endianness by the kernel. The configuration
297 descriptors are in bus endian format! The conf 291 descriptors are in bus endian format! The configuration descriptor
298 are wTotalLength bytes apart. If a device retu 292 are wTotalLength bytes apart. If a device returns less configuration
299 descriptor data than indicated by wTotalLength 293 descriptor data than indicated by wTotalLength there will be a hole in
300 the file for the missing bytes. This informat 294 the file for the missing bytes. This information is also shown
301 in text form by the ``/sys/kernel/debug/usb/de 295 in text form by the ``/sys/kernel/debug/usb/devices`` file, described later.
302 296
303 These files may also be used to write user-lev 297 These files may also be used to write user-level drivers for the USB
304 devices. You would open the ``/dev/bus/usb/BB 298 devices. You would open the ``/dev/bus/usb/BBB/DDD`` file read/write,
305 read its descriptors to make sure it's the dev 299 read its descriptors to make sure it's the device you expect, and then
306 bind to an interface (or perhaps several) usin 300 bind to an interface (or perhaps several) using an ioctl call. You
307 would issue more ioctls to the device to commu 301 would issue more ioctls to the device to communicate to it using
308 control, bulk, or other kinds of USB transfers 302 control, bulk, or other kinds of USB transfers. The IOCTLs are
309 listed in the ``<linux/usbdevice_fs.h>`` file, 303 listed in the ``<linux/usbdevice_fs.h>`` file, and at this writing the
310 source code (``linux/drivers/usb/core/devio.c` 304 source code (``linux/drivers/usb/core/devio.c``) is the primary reference
311 for how to access devices through those files. 305 for how to access devices through those files.
312 306
313 Note that since by default these ``BBB/DDD`` f 307 Note that since by default these ``BBB/DDD`` files are writable only by
314 root, only root can write such user mode drive 308 root, only root can write such user mode drivers. You can selectively
315 grant read/write permissions to other users by 309 grant read/write permissions to other users by using ``chmod``. Also,
316 usbfs mount options such as ``devmode=0666`` m 310 usbfs mount options such as ``devmode=0666`` may be helpful.
317 311
318 312
319 Life Cycle of User Mode Drivers 313 Life Cycle of User Mode Drivers
320 ------------------------------- 314 -------------------------------
321 315
322 Such a driver first needs to find a device fil 316 Such a driver first needs to find a device file for a device it knows
323 how to handle. Maybe it was told about it beca 317 how to handle. Maybe it was told about it because a ``/sbin/hotplug``
324 event handling agent chose that driver to hand 318 event handling agent chose that driver to handle the new device. Or
325 maybe it's an application that scans all the ` 319 maybe it's an application that scans all the ``/dev/bus/usb`` device files,
326 and ignores most devices. In either case, it s 320 and ignores most devices. In either case, it should :c:func:`read()`
327 all the descriptors from the device file, and 321 all the descriptors from the device file, and check them against what it
328 knows how to handle. It might just reject ever 322 knows how to handle. It might just reject everything except a particular
329 vendor and product ID, or need a more complex 323 vendor and product ID, or need a more complex policy.
330 324
331 Never assume there will only be one such devic 325 Never assume there will only be one such device on the system at a time!
332 If your code can't handle more than one device 326 If your code can't handle more than one device at a time, at least
333 detect when there's more than one, and have yo 327 detect when there's more than one, and have your users choose which
334 device to use. 328 device to use.
335 329
336 Once your user mode driver knows what device t 330 Once your user mode driver knows what device to use, it interacts with
337 it in either of two styles. The simple style i 331 it in either of two styles. The simple style is to make only control
338 requests; some devices don't need more complex 332 requests; some devices don't need more complex interactions than those.
339 (An example might be software using vendor-spe 333 (An example might be software using vendor-specific control requests for
340 some initialization or configuration tasks, wi 334 some initialization or configuration tasks, with a kernel driver for the
341 rest.) 335 rest.)
342 336
343 More likely, you need a more complex style dri 337 More likely, you need a more complex style driver: one using non-control
344 endpoints, reading or writing data and claimin 338 endpoints, reading or writing data and claiming exclusive use of an
345 interface. *Bulk* transfers are easiest to use 339 interface. *Bulk* transfers are easiest to use, but only their sibling
346 *interrupt* transfers work with low speed devi 340 *interrupt* transfers work with low speed devices. Both interrupt and
347 *isochronous* transfers offer service guarante 341 *isochronous* transfers offer service guarantees because their bandwidth
348 is reserved. Such "periodic" transfers are awk 342 is reserved. Such "periodic" transfers are awkward to use through usbfs,
349 unless you're using the asynchronous calls. Ho 343 unless you're using the asynchronous calls. However, interrupt transfers
350 can also be used in a synchronous "one shot" s 344 can also be used in a synchronous "one shot" style.
351 345
352 Your user-mode driver should never need to wor 346 Your user-mode driver should never need to worry about cleaning up
353 request state when the device is disconnected, 347 request state when the device is disconnected, although it should close
354 its open file descriptors as soon as it starts 348 its open file descriptors as soon as it starts seeing the ENODEV errors.
355 349
356 The ioctl() Requests 350 The ioctl() Requests
357 -------------------- 351 --------------------
358 352
359 To use these ioctls, you need to include the f 353 To use these ioctls, you need to include the following headers in your
360 userspace program:: 354 userspace program::
361 355
362 #include <linux/usb.h> 356 #include <linux/usb.h>
363 #include <linux/usbdevice_fs.h> 357 #include <linux/usbdevice_fs.h>
364 #include <asm/byteorder.h> 358 #include <asm/byteorder.h>
365 359
366 The standard USB device model requests, from " 360 The standard USB device model requests, from "Chapter 9" of the USB 2.0
367 specification, are automatically included from 361 specification, are automatically included from the ``<linux/usb/ch9.h>``
368 header. 362 header.
369 363
370 Unless noted otherwise, the ioctl requests des 364 Unless noted otherwise, the ioctl requests described here will update
371 the modification time on the usbfs file to whi 365 the modification time on the usbfs file to which they are applied
372 (unless they fail). A return of zero indicates 366 (unless they fail). A return of zero indicates success; otherwise, a
373 standard USB error code is returned (These are 367 standard USB error code is returned (These are documented in
374 :ref:`usb-error-codes`). 368 :ref:`usb-error-codes`).
375 369
376 Each of these files multiplexes access to seve 370 Each of these files multiplexes access to several I/O streams, one per
377 endpoint. Each device has one control endpoint 371 endpoint. Each device has one control endpoint (endpoint zero) which
378 supports a limited RPC style RPC access. Devic 372 supports a limited RPC style RPC access. Devices are configured by
379 hub_wq (in the kernel) setting a device-wide * 373 hub_wq (in the kernel) setting a device-wide *configuration* that
380 affects things like power consumption and basi 374 affects things like power consumption and basic functionality. The
381 endpoints are part of USB *interfaces*, which 375 endpoints are part of USB *interfaces*, which may have *altsettings*
382 affecting things like which endpoints are avai 376 affecting things like which endpoints are available. Many devices only
383 have a single configuration and interface, so 377 have a single configuration and interface, so drivers for them will
384 ignore configurations and altsettings. 378 ignore configurations and altsettings.
385 379
386 Management/Status Requests 380 Management/Status Requests
387 ~~~~~~~~~~~~~~~~~~~~~~~~~~ 381 ~~~~~~~~~~~~~~~~~~~~~~~~~~
388 382
389 A number of usbfs requests don't deal very dir 383 A number of usbfs requests don't deal very directly with device I/O.
390 They mostly relate to device management and st 384 They mostly relate to device management and status. These are all
391 synchronous requests. 385 synchronous requests.
392 386
393 USBDEVFS_CLAIMINTERFACE 387 USBDEVFS_CLAIMINTERFACE
394 This is used to force usbfs to claim a spe 388 This is used to force usbfs to claim a specific interface, which has
395 not previously been claimed by usbfs or an 389 not previously been claimed by usbfs or any other kernel driver. The
396 ioctl parameter is an integer holding the 390 ioctl parameter is an integer holding the number of the interface
397 (bInterfaceNumber from descriptor). 391 (bInterfaceNumber from descriptor).
398 392
399 Note that if your driver doesn't claim an 393 Note that if your driver doesn't claim an interface before trying to
400 use one of its endpoints, and no other dri 394 use one of its endpoints, and no other driver has bound to it, then
401 the interface is automatically claimed by 395 the interface is automatically claimed by usbfs.
402 396
403 This claim will be released by a RELEASEIN 397 This claim will be released by a RELEASEINTERFACE ioctl, or by
404 closing the file descriptor. File modifica 398 closing the file descriptor. File modification time is not updated
405 by this request. 399 by this request.
406 400
407 USBDEVFS_CONNECTINFO 401 USBDEVFS_CONNECTINFO
408 Says whether the device is lowspeed. The i 402 Says whether the device is lowspeed. The ioctl parameter points to a
409 structure like this:: 403 structure like this::
410 404
411 struct usbdevfs_connectinfo { 405 struct usbdevfs_connectinfo {
412 unsigned int devnum; 406 unsigned int devnum;
413 unsigned char slow; 407 unsigned char slow;
414 }; 408 };
415 409
416 File modification time is not updated by t 410 File modification time is not updated by this request.
417 411
418 *You can't tell whether a "not slow" devic 412 *You can't tell whether a "not slow" device is connected at high
419 speed (480 MBit/sec) or just full speed (1 413 speed (480 MBit/sec) or just full speed (12 MBit/sec).* You should
420 know the devnum value already, it's the DD 414 know the devnum value already, it's the DDD value of the device file
421 name. 415 name.
422 416
423 USBDEVFS_GET_SPEED <<
424 Returns the speed of the device. The speed <<
425 numerical value in accordance with enum us <<
426 <<
427 File modification time is not updated by t <<
428 <<
429 USBDEVFS_GETDRIVER 417 USBDEVFS_GETDRIVER
430 Returns the name of the kernel driver boun 418 Returns the name of the kernel driver bound to a given interface (a
431 string). Parameter is a pointer to this st 419 string). Parameter is a pointer to this structure, which is
432 modified:: 420 modified::
433 421
434 struct usbdevfs_getdriver { 422 struct usbdevfs_getdriver {
435 unsigned int interface; 423 unsigned int interface;
436 char driver[USBDEVFS_ 424 char driver[USBDEVFS_MAXDRIVERNAME + 1];
437 }; 425 };
438 426
439 File modification time is not updated by t 427 File modification time is not updated by this request.
440 428
441 USBDEVFS_IOCTL 429 USBDEVFS_IOCTL
442 Passes a request from userspace through to 430 Passes a request from userspace through to a kernel driver that has
443 an ioctl entry in the *struct usb_driver* 431 an ioctl entry in the *struct usb_driver* it registered::
444 432
445 struct usbdevfs_ioctl { 433 struct usbdevfs_ioctl {
446 int ifno; 434 int ifno;
447 int ioctl_code; 435 int ioctl_code;
448 void *data; 436 void *data;
449 }; 437 };
450 438
451 /* user mode call looks like this. 439 /* user mode call looks like this.
452 * 'request' becomes the driver->ioctl 440 * 'request' becomes the driver->ioctl() 'code' parameter.
453 * the size of 'param' is encoded in ' 441 * the size of 'param' is encoded in 'request', and that data
454 * is copied to or from the driver->io 442 * is copied to or from the driver->ioctl() 'buf' parameter.
455 */ 443 */
456 static int 444 static int
457 usbdev_ioctl (int fd, int ifno, unsign 445 usbdev_ioctl (int fd, int ifno, unsigned request, void *param)
458 { 446 {
459 struct usbdevfs_ioctl wrappe 447 struct usbdevfs_ioctl wrapper;
460 448
461 wrapper.ifno = ifno; 449 wrapper.ifno = ifno;
462 wrapper.ioctl_code = request; 450 wrapper.ioctl_code = request;
463 wrapper.data = param; 451 wrapper.data = param;
464 452
465 return ioctl (fd, USBDEVFS_IOC 453 return ioctl (fd, USBDEVFS_IOCTL, &wrapper);
466 } 454 }
467 455
468 File modification time is not updated by t 456 File modification time is not updated by this request.
469 457
470 This request lets kernel drivers talk to u 458 This request lets kernel drivers talk to user mode code through
471 filesystem operations even when they don't 459 filesystem operations even when they don't create a character or
472 block special device. It's also been used 460 block special device. It's also been used to do things like ask
473 devices what device special file should be 461 devices what device special file should be used. Two pre-defined
474 ioctls are used to disconnect and reconnec 462 ioctls are used to disconnect and reconnect kernel drivers, so that
475 user mode code can completely manage bindi 463 user mode code can completely manage binding and configuration of
476 devices. 464 devices.
477 465
478 USBDEVFS_RELEASEINTERFACE 466 USBDEVFS_RELEASEINTERFACE
479 This is used to release the claim usbfs ma 467 This is used to release the claim usbfs made on interface, either
480 implicitly or because of a USBDEVFS_CLAIMI 468 implicitly or because of a USBDEVFS_CLAIMINTERFACE call, before the
481 file descriptor is closed. The ioctl param 469 file descriptor is closed. The ioctl parameter is an integer holding
482 the number of the interface (bInterfaceNum 470 the number of the interface (bInterfaceNumber from descriptor); File
483 modification time is not updated by this r 471 modification time is not updated by this request.
484 472
485 .. warning:: 473 .. warning::
486 474
487 *No security check is made to ensure t 475 *No security check is made to ensure that the task which made
488 the claim is the one which is releasin 476 the claim is the one which is releasing it. This means that user
489 mode driver may interfere other ones.* 477 mode driver may interfere other ones.*
490 478
491 USBDEVFS_RESETEP 479 USBDEVFS_RESETEP
492 Resets the data toggle value for an endpoi 480 Resets the data toggle value for an endpoint (bulk or interrupt) to
493 DATA0. The ioctl parameter is an integer e 481 DATA0. The ioctl parameter is an integer endpoint number (1 to 15,
494 as identified in the endpoint descriptor), 482 as identified in the endpoint descriptor), with USB_DIR_IN added
495 if the device's endpoint sends data to the 483 if the device's endpoint sends data to the host.
496 484
497 .. Warning:: 485 .. Warning::
498 486
499 *Avoid using this request. It should p 487 *Avoid using this request. It should probably be removed.* Using
500 it typically means the device and driv 488 it typically means the device and driver will lose toggle
501 synchronization. If you really lost sy 489 synchronization. If you really lost synchronization, you likely
502 need to completely handshake with the 490 need to completely handshake with the device, using a request
503 like CLEAR_HALT or SET_INTERFACE. 491 like CLEAR_HALT or SET_INTERFACE.
504 492
505 USBDEVFS_DROP_PRIVILEGES 493 USBDEVFS_DROP_PRIVILEGES
506 This is used to relinquish the ability to 494 This is used to relinquish the ability to do certain operations
507 which are considered to be privileged on a 495 which are considered to be privileged on a usbfs file descriptor.
508 This includes claiming arbitrary interface 496 This includes claiming arbitrary interfaces, resetting a device on
509 which there are currently claimed interfac 497 which there are currently claimed interfaces from other users, and
510 issuing USBDEVFS_IOCTL calls. The ioctl pa 498 issuing USBDEVFS_IOCTL calls. The ioctl parameter is a 32 bit mask
511 of interfaces the user is allowed to claim 499 of interfaces the user is allowed to claim on this file descriptor.
512 You may issue this ioctl more than one tim 500 You may issue this ioctl more than one time to narrow said mask.
513 501
514 Synchronous I/O Support 502 Synchronous I/O Support
515 ~~~~~~~~~~~~~~~~~~~~~~~ 503 ~~~~~~~~~~~~~~~~~~~~~~~
516 504
517 Synchronous requests involve the kernel blocki 505 Synchronous requests involve the kernel blocking until the user mode
518 request completes, either by finishing success 506 request completes, either by finishing successfully or by reporting an
519 error. In most cases this is the simplest way 507 error. In most cases this is the simplest way to use usbfs, although as
520 noted above it does prevent performing I/O to 508 noted above it does prevent performing I/O to more than one endpoint at
521 a time. 509 a time.
522 510
523 USBDEVFS_BULK 511 USBDEVFS_BULK
524 Issues a bulk read or write request to the 512 Issues a bulk read or write request to the device. The ioctl
525 parameter is a pointer to this structure:: 513 parameter is a pointer to this structure::
526 514
527 struct usbdevfs_bulktransfer { 515 struct usbdevfs_bulktransfer {
528 unsigned int ep; 516 unsigned int ep;
529 unsigned int len; 517 unsigned int len;
530 unsigned int timeout; /* in m 518 unsigned int timeout; /* in milliseconds */
531 void *data; 519 void *data;
532 }; 520 };
533 521
534 The ``ep`` value identifies a bulk endpoin 522 The ``ep`` value identifies a bulk endpoint number (1 to 15, as
535 identified in an endpoint descriptor), mas 523 identified in an endpoint descriptor), masked with USB_DIR_IN when
536 referring to an endpoint which sends data 524 referring to an endpoint which sends data to the host from the
537 device. The length of the data buffer is i 525 device. The length of the data buffer is identified by ``len``; Recent
538 kernels support requests up to about 128KB 526 kernels support requests up to about 128KBytes. *FIXME say how read
539 length is returned, and how short reads ar 527 length is returned, and how short reads are handled.*.
540 528
541 USBDEVFS_CLEAR_HALT 529 USBDEVFS_CLEAR_HALT
542 Clears endpoint halt (stall) and resets th 530 Clears endpoint halt (stall) and resets the endpoint toggle. This is
543 only meaningful for bulk or interrupt endp 531 only meaningful for bulk or interrupt endpoints. The ioctl parameter
544 is an integer endpoint number (1 to 15, as 532 is an integer endpoint number (1 to 15, as identified in an endpoint
545 descriptor), masked with USB_DIR_IN when r 533 descriptor), masked with USB_DIR_IN when referring to an endpoint
546 which sends data to the host from the devi 534 which sends data to the host from the device.
547 535
548 Use this on bulk or interrupt endpoints wh 536 Use this on bulk or interrupt endpoints which have stalled,
549 returning ``-EPIPE`` status to a data tran 537 returning ``-EPIPE`` status to a data transfer request. Do not issue
550 the control request directly, since that c 538 the control request directly, since that could invalidate the host's
551 record of the data toggle. 539 record of the data toggle.
552 540
553 USBDEVFS_CONTROL 541 USBDEVFS_CONTROL
554 Issues a control request to the device. Th 542 Issues a control request to the device. The ioctl parameter points
555 to a structure like this:: 543 to a structure like this::
556 544
557 struct usbdevfs_ctrltransfer { 545 struct usbdevfs_ctrltransfer {
558 __u8 bRequestType; 546 __u8 bRequestType;
559 __u8 bRequest; 547 __u8 bRequest;
560 __u16 wValue; 548 __u16 wValue;
561 __u16 wIndex; 549 __u16 wIndex;
562 __u16 wLength; 550 __u16 wLength;
563 __u32 timeout; /* in millise 551 __u32 timeout; /* in milliseconds */
564 void *data; 552 void *data;
565 }; 553 };
566 554
567 The first eight bytes of this structure ar 555 The first eight bytes of this structure are the contents of the
568 SETUP packet to be sent to the device; see 556 SETUP packet to be sent to the device; see the USB 2.0 specification
569 for details. The bRequestType value is com 557 for details. The bRequestType value is composed by combining a
570 ``USB_TYPE_*`` value, a ``USB_DIR_*`` valu 558 ``USB_TYPE_*`` value, a ``USB_DIR_*`` value, and a ``USB_RECIP_*``
571 value (from ``linux/usb.h``). If wLength i 559 value (from ``linux/usb.h``). If wLength is nonzero, it describes
572 the length of the data buffer, which is ei 560 the length of the data buffer, which is either written to the device
573 (USB_DIR_OUT) or read from the device (USB 561 (USB_DIR_OUT) or read from the device (USB_DIR_IN).
574 562
575 At this writing, you can't transfer more t 563 At this writing, you can't transfer more than 4 KBytes of data to or
576 from a device; usbfs has a limit, and some 564 from a device; usbfs has a limit, and some host controller drivers
577 have a limit. (That's not usually a proble 565 have a limit. (That's not usually a problem.) *Also* there's no way
578 to say it's not OK to get a short read bac 566 to say it's not OK to get a short read back from the device.
579 567
580 USBDEVFS_RESET 568 USBDEVFS_RESET
581 Does a USB level device reset. The ioctl p 569 Does a USB level device reset. The ioctl parameter is ignored. After
582 the reset, this rebinds all device interfa 570 the reset, this rebinds all device interfaces. File modification
583 time is not updated by this request. 571 time is not updated by this request.
584 572
585 .. warning:: 573 .. warning::
586 574
587 *Avoid using this call* until some usb 575 *Avoid using this call* until some usbcore bugs get fixed, since
588 it does not fully synchronize device, 576 it does not fully synchronize device, interface, and driver (not
589 just usbfs) state. 577 just usbfs) state.
590 578
591 USBDEVFS_SETINTERFACE 579 USBDEVFS_SETINTERFACE
592 Sets the alternate setting for an interfac 580 Sets the alternate setting for an interface. The ioctl parameter is
593 a pointer to a structure like this:: 581 a pointer to a structure like this::
594 582
595 struct usbdevfs_setinterface { 583 struct usbdevfs_setinterface {
596 unsigned int interface; 584 unsigned int interface;
597 unsigned int altsetting; 585 unsigned int altsetting;
598 }; 586 };
599 587
600 File modification time is not updated by t 588 File modification time is not updated by this request.
601 589
602 Those struct members are from some interfa 590 Those struct members are from some interface descriptor applying to
603 the current configuration. The interface n 591 the current configuration. The interface number is the
604 bInterfaceNumber value, and the altsetting 592 bInterfaceNumber value, and the altsetting number is the
605 bAlternateSetting value. (This resets each 593 bAlternateSetting value. (This resets each endpoint in the
606 interface.) 594 interface.)
607 595
608 USBDEVFS_SETCONFIGURATION 596 USBDEVFS_SETCONFIGURATION
609 Issues the :c:func:`usb_set_configuration( 597 Issues the :c:func:`usb_set_configuration()` call for the
610 device. The parameter is an integer holdin 598 device. The parameter is an integer holding the number of a
611 configuration (bConfigurationValue from de 599 configuration (bConfigurationValue from descriptor). File
612 modification time is not updated by this r 600 modification time is not updated by this request.
613 601
614 .. warning:: 602 .. warning::
615 603
616 *Avoid using this call* until some usb 604 *Avoid using this call* until some usbcore bugs get fixed, since
617 it does not fully synchronize device, 605 it does not fully synchronize device, interface, and driver (not
618 just usbfs) state. 606 just usbfs) state.
619 607
620 Asynchronous I/O Support 608 Asynchronous I/O Support
621 ~~~~~~~~~~~~~~~~~~~~~~~~ 609 ~~~~~~~~~~~~~~~~~~~~~~~~
622 610
623 As mentioned above, there are situations where 611 As mentioned above, there are situations where it may be important to
624 initiate concurrent operations from user mode 612 initiate concurrent operations from user mode code. This is particularly
625 important for periodic transfers (interrupt an 613 important for periodic transfers (interrupt and isochronous), but it can
626 be used for other kinds of USB requests too. I 614 be used for other kinds of USB requests too. In such cases, the
627 asynchronous requests described here are essen 615 asynchronous requests described here are essential. Rather than
628 submitting one request and having the kernel b 616 submitting one request and having the kernel block until it completes,
629 the blocking is separate. 617 the blocking is separate.
630 618
631 These requests are packaged into a structure t 619 These requests are packaged into a structure that resembles the URB used
632 by kernel device drivers. (No POSIX Async I/O 620 by kernel device drivers. (No POSIX Async I/O support here, sorry.) It
633 identifies the endpoint type (``USBDEVFS_URB_T 621 identifies the endpoint type (``USBDEVFS_URB_TYPE_*``), endpoint
634 (number, masked with USB_DIR_IN as appropriate 622 (number, masked with USB_DIR_IN as appropriate), buffer and length,
635 and a user "context" value serving to uniquely 623 and a user "context" value serving to uniquely identify each request.
636 (It's usually a pointer to per-request data.) 624 (It's usually a pointer to per-request data.) Flags can modify requests
637 (not as many as supported for kernel drivers). 625 (not as many as supported for kernel drivers).
638 626
639 Each request can specify a realtime signal num 627 Each request can specify a realtime signal number (between SIGRTMIN and
640 SIGRTMAX, inclusive) to request a signal be se 628 SIGRTMAX, inclusive) to request a signal be sent when the request
641 completes. 629 completes.
642 630
643 When usbfs returns these urbs, the status valu 631 When usbfs returns these urbs, the status value is updated, and the
644 buffer may have been modified. Except for isoc 632 buffer may have been modified. Except for isochronous transfers, the
645 actual_length is updated to say how many bytes 633 actual_length is updated to say how many bytes were transferred; if the
646 USBDEVFS_URB_DISABLE_SPD flag is set ("short p 634 USBDEVFS_URB_DISABLE_SPD flag is set ("short packets are not OK"), if
647 fewer bytes were read than were requested then 635 fewer bytes were read than were requested then you get an error report::
648 636
649 struct usbdevfs_iso_packet_desc { 637 struct usbdevfs_iso_packet_desc {
650 unsigned int l 638 unsigned int length;
651 unsigned int a 639 unsigned int actual_length;
652 unsigned int s 640 unsigned int status;
653 }; 641 };
654 642
655 struct usbdevfs_urb { 643 struct usbdevfs_urb {
656 unsigned char t 644 unsigned char type;
657 unsigned char e 645 unsigned char endpoint;
658 int s 646 int status;
659 unsigned int f 647 unsigned int flags;
660 void * 648 void *buffer;
661 int b 649 int buffer_length;
662 int a 650 int actual_length;
663 int s 651 int start_frame;
664 int n 652 int number_of_packets;
665 int e 653 int error_count;
666 unsigned int s 654 unsigned int signr;
667 void * 655 void *usercontext;
668 struct usbdevfs_iso_packet_desc i 656 struct usbdevfs_iso_packet_desc iso_frame_desc[];
669 }; 657 };
670 658
671 For these asynchronous requests, the file modi 659 For these asynchronous requests, the file modification time reflects
672 when the request was initiated. This contrasts 660 when the request was initiated. This contrasts with their use with the
673 synchronous requests, where it reflects when r 661 synchronous requests, where it reflects when requests complete.
674 662
675 USBDEVFS_DISCARDURB 663 USBDEVFS_DISCARDURB
676 *TBS* File modification time is not update 664 *TBS* File modification time is not updated by this request.
677 665
678 USBDEVFS_DISCSIGNAL 666 USBDEVFS_DISCSIGNAL
679 *TBS* File modification time is not update 667 *TBS* File modification time is not updated by this request.
680 668
681 USBDEVFS_REAPURB 669 USBDEVFS_REAPURB
682 *TBS* File modification time is not update 670 *TBS* File modification time is not updated by this request.
683 671
684 USBDEVFS_REAPURBNDELAY 672 USBDEVFS_REAPURBNDELAY
685 *TBS* File modification time is not update 673 *TBS* File modification time is not updated by this request.
686 674
687 USBDEVFS_SUBMITURB 675 USBDEVFS_SUBMITURB
688 *TBS* 676 *TBS*
689 677
690 The USB devices 678 The USB devices
691 =============== 679 ===============
692 680
693 The USB devices are now exported via debugfs: 681 The USB devices are now exported via debugfs:
694 682
695 - ``/sys/kernel/debug/usb/devices`` ... a tex 683 - ``/sys/kernel/debug/usb/devices`` ... a text file showing each of the USB
696 devices on known to the kernel, and their c 684 devices on known to the kernel, and their configuration descriptors.
697 You can also poll() this to learn about new 685 You can also poll() this to learn about new devices.
698 686
699 /sys/kernel/debug/usb/devices 687 /sys/kernel/debug/usb/devices
700 ----------------------------- 688 -----------------------------
701 689
702 This file is handy for status viewing tools in 690 This file is handy for status viewing tools in user mode, which can scan
703 the text format and ignore most of it. More de 691 the text format and ignore most of it. More detailed device status
704 (including class and vendor status) is availab 692 (including class and vendor status) is available from device-specific
705 files. For information about the current forma 693 files. For information about the current format of this file, see below.
706 694
707 This file, in combination with the poll() syst 695 This file, in combination with the poll() system call, can also be used
708 to detect when devices are added or removed:: 696 to detect when devices are added or removed::
709 697
710 int fd; 698 int fd;
711 struct pollfd pfd; 699 struct pollfd pfd;
712 700
713 fd = open("/sys/kernel/debug/usb/devices", 701 fd = open("/sys/kernel/debug/usb/devices", O_RDONLY);
714 pfd = { fd, POLLIN, 0 }; 702 pfd = { fd, POLLIN, 0 };
715 for (;;) { 703 for (;;) {
716 /* The first time through, this call w 704 /* The first time through, this call will return immediately. */
717 poll(&pfd, 1, -1); 705 poll(&pfd, 1, -1);
718 706
719 /* To see what's changed, compare the 707 /* To see what's changed, compare the file's previous and current
720 contents or scan the filesystem. ( 708 contents or scan the filesystem. (Scanning is more precise.) */
721 } 709 }
722 710
723 Note that this behavior is intended to be used 711 Note that this behavior is intended to be used for informational and
724 debug purposes. It would be more appropriate t 712 debug purposes. It would be more appropriate to use programs such as
725 udev or HAL to initialize a device or start a 713 udev or HAL to initialize a device or start a user-mode helper program,
726 for instance. 714 for instance.
727 715
728 In this file, each device's output has multipl 716 In this file, each device's output has multiple lines of ASCII output.
729 717
730 I made it ASCII instead of binary on purpose, 718 I made it ASCII instead of binary on purpose, so that someone
731 can obtain some useful data from it without th 719 can obtain some useful data from it without the use of an
732 auxiliary program. However, with an auxiliary 720 auxiliary program. However, with an auxiliary program, the numbers
733 in the first 4 columns of each ``T:`` line (to 721 in the first 4 columns of each ``T:`` line (topology info:
734 Lev, Prnt, Port, Cnt) can be used to build a U 722 Lev, Prnt, Port, Cnt) can be used to build a USB topology diagram.
735 723
736 Each line is tagged with a one-character ID fo 724 Each line is tagged with a one-character ID for that line::
737 725
738 T = Topology (etc.) 726 T = Topology (etc.)
739 B = Bandwidth (applies only to USB hos 727 B = Bandwidth (applies only to USB host controllers, which are
740 virtualized as root hubs) 728 virtualized as root hubs)
741 D = Device descriptor info. 729 D = Device descriptor info.
742 P = Product ID info. (from Device desc 730 P = Product ID info. (from Device descriptor, but they won't fit
743 together on one line) 731 together on one line)
744 S = String descriptors. 732 S = String descriptors.
745 C = Configuration descriptor info. (* 733 C = Configuration descriptor info. (* = active configuration)
746 I = Interface descriptor info. 734 I = Interface descriptor info.
747 E = Endpoint descriptor info. 735 E = Endpoint descriptor info.
748 736
749 /sys/kernel/debug/usb/devices output format 737 /sys/kernel/debug/usb/devices output format
750 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ 738 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
751 739
752 Legend:: 740 Legend::
753 d = decimal number (may have leading spaces 741 d = decimal number (may have leading spaces or 0's)
754 x = hexadecimal number (may have leading spa 742 x = hexadecimal number (may have leading spaces or 0's)
755 s = string 743 s = string
756 744
757 745
758 746
759 Topology info 747 Topology info
760 ^^^^^^^^^^^^^ 748 ^^^^^^^^^^^^^
761 749
762 :: 750 ::
763 751
764 T: Bus=dd Lev=dd Prnt=dd Port=dd Cnt= 752 T: Bus=dd Lev=dd Prnt=dd Port=dd Cnt=dd Dev#=ddd Spd=dddd MxCh=dd
765 | | | | | | 753 | | | | | | | | |__MaxChildren
766 | | | | | | 754 | | | | | | | |__Device Speed in Mbps
767 | | | | | | 755 | | | | | | |__DeviceNumber
768 | | | | | |__C 756 | | | | | |__Count of devices at this level
769 | | | | |__Connector 757 | | | | |__Connector/Port on Parent for this device
770 | | | |__Parent DeviceNumb 758 | | | |__Parent DeviceNumber
771 | | |__Level in topology for th 759 | | |__Level in topology for this bus
772 | |__Bus number 760 | |__Bus number
773 |__Topology info tag 761 |__Topology info tag
774 762
775 Speed may be: 763 Speed may be:
776 764
777 ======= ============================== 765 ======= ======================================================
778 1.5 Mbit/s for low speed USB 766 1.5 Mbit/s for low speed USB
779 12 Mbit/s for full speed USB 767 12 Mbit/s for full speed USB
780 480 Mbit/s for high speed USB (add !! 768 480 Mbit/s for high speed USB (added for USB 2.0);
>> 769 also used for Wireless USB, which has no fixed speed
781 5000 Mbit/s for SuperSpeed USB (add 770 5000 Mbit/s for SuperSpeed USB (added for USB 3.0)
782 ======= ============================== 771 ======= ======================================================
783 772
784 For reasons lost in the mists of time, the Por 773 For reasons lost in the mists of time, the Port number is always
785 too low by 1. For example, a device plugged i 774 too low by 1. For example, a device plugged into port 4 will
786 show up with ``Port=03``. 775 show up with ``Port=03``.
787 776
788 Bandwidth info 777 Bandwidth info
789 ^^^^^^^^^^^^^^ 778 ^^^^^^^^^^^^^^
790 779
791 :: 780 ::
792 781
793 B: Alloc=ddd/ddd us (xx%), #Int=ddd, 782 B: Alloc=ddd/ddd us (xx%), #Int=ddd, #Iso=ddd
794 | | | 783 | | | |__Number of isochronous requests
795 | | |__Number 784 | | |__Number of interrupt requests
796 | |__Total Bandwidth allocated to th 785 | |__Total Bandwidth allocated to this bus
797 |__Bandwidth info tag 786 |__Bandwidth info tag
798 787
799 Bandwidth allocation is an approximation of ho 788 Bandwidth allocation is an approximation of how much of one frame
800 (millisecond) is in use. It reflects only per 789 (millisecond) is in use. It reflects only periodic transfers, which
801 are the only transfers that reserve bandwidth. 790 are the only transfers that reserve bandwidth. Control and bulk
802 transfers use all other bandwidth, including r 791 transfers use all other bandwidth, including reserved bandwidth that
803 is not used for transfers (such as for short p 792 is not used for transfers (such as for short packets).
804 793
805 The percentage is how much of the "reserved" b 794 The percentage is how much of the "reserved" bandwidth is scheduled by
806 those transfers. For a low or full speed bus 795 those transfers. For a low or full speed bus (loosely, "USB 1.1"),
807 90% of the bus bandwidth is reserved. For a h 796 90% of the bus bandwidth is reserved. For a high speed bus (loosely,
808 "USB 2.0") 80% is reserved. 797 "USB 2.0") 80% is reserved.
809 798
810 799
811 Device descriptor info & Product ID info 800 Device descriptor info & Product ID info
812 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ 801 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
813 802
814 :: 803 ::
815 804
816 D: Ver=x.xx Cls=xx(s) Sub=xx Prot=xx 805 D: Ver=x.xx Cls=xx(s) Sub=xx Prot=xx MxPS=dd #Cfgs=dd
817 P: Vendor=xxxx ProdID=xxxx Rev=xx.xx 806 P: Vendor=xxxx ProdID=xxxx Rev=xx.xx
818 807
819 where:: 808 where::
820 809
821 D: Ver=x.xx Cls=xx(sssss) Sub=xx Prot 810 D: Ver=x.xx Cls=xx(sssss) Sub=xx Prot=xx MxPS=dd #Cfgs=dd
822 | | | | | 811 | | | | | | |__NumberConfigurations
823 | | | | | 812 | | | | | |__MaxPacketSize of Default Endpoint
824 | | | | |__D 813 | | | | |__DeviceProtocol
825 | | | |__DeviceSu 814 | | | |__DeviceSubClass
826 | | |__DeviceClass 815 | | |__DeviceClass
827 | |__Device USB version 816 | |__Device USB version
828 |__Device info tag #1 817 |__Device info tag #1
829 818
830 where:: 819 where::
831 820
832 P: Vendor=xxxx ProdID=xxxx Rev=xx.xx 821 P: Vendor=xxxx ProdID=xxxx Rev=xx.xx
833 | | | |__Product 822 | | | |__Product revision number
834 | | |__Product ID code 823 | | |__Product ID code
835 | |__Vendor ID code 824 | |__Vendor ID code
836 |__Device info tag #2 825 |__Device info tag #2
837 826
838 827
839 String descriptor info 828 String descriptor info
840 ^^^^^^^^^^^^^^^^^^^^^^ 829 ^^^^^^^^^^^^^^^^^^^^^^
841 :: 830 ::
842 831
843 S: Manufacturer=ssss 832 S: Manufacturer=ssss
844 | |__Manufacturer of this device as 833 | |__Manufacturer of this device as read from the device.
845 | For USB host controller drivers 834 | For USB host controller drivers (virtual root hubs) this may
846 | be omitted, or (for newer drive 835 | be omitted, or (for newer drivers) will identify the kernel
847 | version and the driver which pr 836 | version and the driver which provides this hub emulation.
848 |__String info tag 837 |__String info tag
849 838
850 S: Product=ssss 839 S: Product=ssss
851 | |__Product description of this dev 840 | |__Product description of this device as read from the device.
852 | For older USB host controller d 841 | For older USB host controller drivers (virtual root hubs) this
853 | indicates the driver; for newer 842 | indicates the driver; for newer ones, it's a product (and vendor)
854 | description that often comes fr 843 | description that often comes from the kernel's PCI ID database.
855 |__String info tag 844 |__String info tag
856 845
857 S: SerialNumber=ssss 846 S: SerialNumber=ssss
858 | |__Serial Number of this device as 847 | |__Serial Number of this device as read from the device.
859 | For USB host controller drivers 848 | For USB host controller drivers (virtual root hubs) this is
860 | some unique ID, normally a bus 849 | some unique ID, normally a bus ID (address or slot name) that
861 | can't be shared with any other 850 | can't be shared with any other device.
862 |__String info tag 851 |__String info tag
863 852
864 853
865 854
866 Configuration descriptor info 855 Configuration descriptor info
867 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ 856 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
868 :: 857 ::
869 858
870 C:* #Ifs=dd Cfg#=dd Atr=xx MPwr=dddmA 859 C:* #Ifs=dd Cfg#=dd Atr=xx MPwr=dddmA
871 | | | | | |__MaxPower 860 | | | | | |__MaxPower in mA
872 | | | | |__Attributes 861 | | | | |__Attributes
873 | | | |__ConfiguratioNumber 862 | | | |__ConfiguratioNumber
874 | | |__NumberOfInterfaces 863 | | |__NumberOfInterfaces
875 | |__ "*" indicates the active configu 864 | |__ "*" indicates the active configuration (others are " ")
876 |__Config info tag 865 |__Config info tag
877 866
878 USB devices may have multiple configurations, 867 USB devices may have multiple configurations, each of which act
879 rather differently. For example, a bus-powere 868 rather differently. For example, a bus-powered configuration
880 might be much less capable than one that is se 869 might be much less capable than one that is self-powered. Only
881 one device configuration can be active at a ti 870 one device configuration can be active at a time; most devices
882 have only one configuration. 871 have only one configuration.
883 872
884 Each configuration consists of one or more int 873 Each configuration consists of one or more interfaces. Each
885 interface serves a distinct "function", which 874 interface serves a distinct "function", which is typically bound
886 to a different USB device driver. One common 875 to a different USB device driver. One common example is a USB
887 speaker with an audio interface for playback, 876 speaker with an audio interface for playback, and a HID interface
888 for use with software volume control. 877 for use with software volume control.
889 878
890 Interface descriptor info (can be multiple per 879 Interface descriptor info (can be multiple per Config)
891 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ 880 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
892 :: 881 ::
893 882
894 I:* If#=dd Alt=dd #EPs=dd Cls=xx(sssss 883 I:* If#=dd Alt=dd #EPs=dd Cls=xx(sssss) Sub=xx Prot=xx Driver=ssss
895 | | | | | | 884 | | | | | | | | |__Driver name
896 | | | | | | 885 | | | | | | | | or "(none)"
897 | | | | | | 886 | | | | | | | |__InterfaceProtocol
898 | | | | | | 887 | | | | | | |__InterfaceSubClass
899 | | | | | |__Interface 888 | | | | | |__InterfaceClass
900 | | | | |__NumberOfEndpoints 889 | | | | |__NumberOfEndpoints
901 | | | |__AlternateSettingNumber 890 | | | |__AlternateSettingNumber
902 | | |__InterfaceNumber 891 | | |__InterfaceNumber
903 | |__ "*" indicates the active altsett 892 | |__ "*" indicates the active altsetting (others are " ")
904 |__Interface info tag 893 |__Interface info tag
905 894
906 A given interface may have one or more "altern 895 A given interface may have one or more "alternate" settings.
907 For example, default settings may not use more 896 For example, default settings may not use more than a small
908 amount of periodic bandwidth. To use signific 897 amount of periodic bandwidth. To use significant fractions
909 of bus bandwidth, drivers must select a non-de 898 of bus bandwidth, drivers must select a non-default altsetting.
910 899
911 Only one setting for an interface may be activ 900 Only one setting for an interface may be active at a time, and
912 only one driver may bind to an interface at a 901 only one driver may bind to an interface at a time. Most devices
913 have only one alternate setting per interface. 902 have only one alternate setting per interface.
914 903
915 904
916 Endpoint descriptor info (can be multiple per 905 Endpoint descriptor info (can be multiple per Interface)
917 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ 906 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
918 907
919 :: 908 ::
920 909
921 E: Ad=xx(s) Atr=xx(ssss) MxPS=dddd Iv 910 E: Ad=xx(s) Atr=xx(ssss) MxPS=dddd Ivl=dddss
922 | | | | |_ 911 | | | | |__Interval (max) between transfers
923 | | | |__EndpointM 912 | | | |__EndpointMaxPacketSize
924 | | |__Attributes(EndpointTyp 913 | | |__Attributes(EndpointType)
925 | |__EndpointAddress(I=In,O=Out) 914 | |__EndpointAddress(I=In,O=Out)
926 |__Endpoint info tag 915 |__Endpoint info tag
927 916
928 The interval is nonzero for all periodic (inte 917 The interval is nonzero for all periodic (interrupt or isochronous)
929 endpoints. For high speed endpoints the trans 918 endpoints. For high speed endpoints the transfer interval may be
930 measured in microseconds rather than milliseco 919 measured in microseconds rather than milliseconds.
931 920
932 For high speed periodic endpoints, the ``Endpo 921 For high speed periodic endpoints, the ``EndpointMaxPacketSize`` reflects
933 the per-microframe data transfer size. For "h 922 the per-microframe data transfer size. For "high bandwidth"
934 endpoints, that can reflect two or three packe 923 endpoints, that can reflect two or three packets (for up to
935 3KBytes every 125 usec) per endpoint. 924 3KBytes every 125 usec) per endpoint.
936 925
937 With the Linux-USB stack, periodic bandwidth r 926 With the Linux-USB stack, periodic bandwidth reservations use the
938 transfer intervals and sizes provided by URBs, 927 transfer intervals and sizes provided by URBs, which can be less
939 than those found in endpoint descriptor. 928 than those found in endpoint descriptor.
940 929
941 Usage examples 930 Usage examples
942 ~~~~~~~~~~~~~~ 931 ~~~~~~~~~~~~~~
943 932
944 If a user or script is interested only in Topo 933 If a user or script is interested only in Topology info, for
945 example, use something like ``grep ^T: /sys/ke 934 example, use something like ``grep ^T: /sys/kernel/debug/usb/devices``
946 for only the Topology lines. A command like 935 for only the Topology lines. A command like
947 ``grep -i ^[tdp]: /sys/kernel/debug/usb/device 936 ``grep -i ^[tdp]: /sys/kernel/debug/usb/devices`` can be used to list
948 only the lines that begin with the characters 937 only the lines that begin with the characters in square brackets,
949 where the valid characters are TDPCIE. With a 938 where the valid characters are TDPCIE. With a slightly more able
950 script, it can display any selected lines (for 939 script, it can display any selected lines (for example, only T, D,
951 and P lines) and change their output format. 940 and P lines) and change their output format. (The ``procusb``
952 Perl script is the beginning of this idea. It 941 Perl script is the beginning of this idea. It will list only
953 selected lines [selected from TBDPSCIE] or "Al 942 selected lines [selected from TBDPSCIE] or "All" lines from
954 ``/sys/kernel/debug/usb/devices``.) 943 ``/sys/kernel/debug/usb/devices``.)
955 944
956 The Topology lines can be used to generate a g 945 The Topology lines can be used to generate a graphic/pictorial
957 of the USB devices on a system's root hub. (S 946 of the USB devices on a system's root hub. (See more below
958 on how to do this.) 947 on how to do this.)
959 948
960 The Interface lines can be used to determine w 949 The Interface lines can be used to determine what driver is
961 being used for each device, and which altsetti 950 being used for each device, and which altsetting it activated.
962 951
963 The Configuration lines could be used to list 952 The Configuration lines could be used to list maximum power
964 (in milliamps) that a system's USB devices are 953 (in milliamps) that a system's USB devices are using.
965 For example, ``grep ^C: /sys/kernel/debug/usb/ 954 For example, ``grep ^C: /sys/kernel/debug/usb/devices``.
966 955
967 956
968 Here's an example, from a system which has a U 957 Here's an example, from a system which has a UHCI root hub,
969 an external hub connected to the root hub, and 958 an external hub connected to the root hub, and a mouse and
970 a serial converter connected to the external h 959 a serial converter connected to the external hub.
971 960
972 :: 961 ::
973 962
974 T: Bus=00 Lev=00 Prnt=00 Port=00 Cnt= 963 T: Bus=00 Lev=00 Prnt=00 Port=00 Cnt=00 Dev#= 1 Spd=12 MxCh= 2
975 B: Alloc= 28/900 us ( 3%), #Int= 2, 964 B: Alloc= 28/900 us ( 3%), #Int= 2, #Iso= 0
976 D: Ver= 1.00 Cls=09(hub ) Sub=00 Pro 965 D: Ver= 1.00 Cls=09(hub ) Sub=00 Prot=00 MxPS= 8 #Cfgs= 1
977 P: Vendor=0000 ProdID=0000 Rev= 0.00 966 P: Vendor=0000 ProdID=0000 Rev= 0.00
978 S: Product=USB UHCI Root Hub 967 S: Product=USB UHCI Root Hub
979 S: SerialNumber=dce0 968 S: SerialNumber=dce0
980 C:* #Ifs= 1 Cfg#= 1 Atr=40 MxPwr= 0mA 969 C:* #Ifs= 1 Cfg#= 1 Atr=40 MxPwr= 0mA
981 I: If#= 0 Alt= 0 #EPs= 1 Cls=09(hub 970 I: If#= 0 Alt= 0 #EPs= 1 Cls=09(hub ) Sub=00 Prot=00 Driver=hub
982 E: Ad=81(I) Atr=03(Int.) MxPS= 8 Iv 971 E: Ad=81(I) Atr=03(Int.) MxPS= 8 Ivl=255ms
983 972
984 T: Bus=00 Lev=01 Prnt=01 Port=00 Cnt= 973 T: Bus=00 Lev=01 Prnt=01 Port=00 Cnt=01 Dev#= 2 Spd=12 MxCh= 4
985 D: Ver= 1.00 Cls=09(hub ) Sub=00 Pro 974 D: Ver= 1.00 Cls=09(hub ) Sub=00 Prot=00 MxPS= 8 #Cfgs= 1
986 P: Vendor=0451 ProdID=1446 Rev= 1.00 975 P: Vendor=0451 ProdID=1446 Rev= 1.00
987 C:* #Ifs= 1 Cfg#= 1 Atr=e0 MxPwr=100mA 976 C:* #Ifs= 1 Cfg#= 1 Atr=e0 MxPwr=100mA
988 I: If#= 0 Alt= 0 #EPs= 1 Cls=09(hub 977 I: If#= 0 Alt= 0 #EPs= 1 Cls=09(hub ) Sub=00 Prot=00 Driver=hub
989 E: Ad=81(I) Atr=03(Int.) MxPS= 1 Iv 978 E: Ad=81(I) Atr=03(Int.) MxPS= 1 Ivl=255ms
990 979
991 T: Bus=00 Lev=02 Prnt=02 Port=00 Cnt= 980 T: Bus=00 Lev=02 Prnt=02 Port=00 Cnt=01 Dev#= 3 Spd=1.5 MxCh= 0
992 D: Ver= 1.00 Cls=00(>ifc ) Sub=00 Pro 981 D: Ver= 1.00 Cls=00(>ifc ) Sub=00 Prot=00 MxPS= 8 #Cfgs= 1
993 P: Vendor=04b4 ProdID=0001 Rev= 0.00 982 P: Vendor=04b4 ProdID=0001 Rev= 0.00
994 C:* #Ifs= 1 Cfg#= 1 Atr=80 MxPwr=100mA 983 C:* #Ifs= 1 Cfg#= 1 Atr=80 MxPwr=100mA
995 I: If#= 0 Alt= 0 #EPs= 1 Cls=03(HID 984 I: If#= 0 Alt= 0 #EPs= 1 Cls=03(HID ) Sub=01 Prot=02 Driver=mouse
996 E: Ad=81(I) Atr=03(Int.) MxPS= 3 Iv 985 E: Ad=81(I) Atr=03(Int.) MxPS= 3 Ivl= 10ms
997 986
998 T: Bus=00 Lev=02 Prnt=02 Port=02 Cnt= 987 T: Bus=00 Lev=02 Prnt=02 Port=02 Cnt=02 Dev#= 4 Spd=12 MxCh= 0
999 D: Ver= 1.00 Cls=00(>ifc ) Sub=00 Pro 988 D: Ver= 1.00 Cls=00(>ifc ) Sub=00 Prot=00 MxPS= 8 #Cfgs= 1
1000 P: Vendor=0565 ProdID=0001 Rev= 1.08 989 P: Vendor=0565 ProdID=0001 Rev= 1.08
1001 S: Manufacturer=Peracom Networks, In 990 S: Manufacturer=Peracom Networks, Inc.
1002 S: Product=Peracom USB to Serial Con 991 S: Product=Peracom USB to Serial Converter
1003 C:* #Ifs= 1 Cfg#= 1 Atr=a0 MxPwr=100m 992 C:* #Ifs= 1 Cfg#= 1 Atr=a0 MxPwr=100mA
1004 I: If#= 0 Alt= 0 #EPs= 3 Cls=00(>ifc 993 I: If#= 0 Alt= 0 #EPs= 3 Cls=00(>ifc ) Sub=00 Prot=00 Driver=serial
1005 E: Ad=81(I) Atr=02(Bulk) MxPS= 64 I 994 E: Ad=81(I) Atr=02(Bulk) MxPS= 64 Ivl= 16ms
1006 E: Ad=01(O) Atr=02(Bulk) MxPS= 16 I 995 E: Ad=01(O) Atr=02(Bulk) MxPS= 16 Ivl= 16ms
1007 E: Ad=82(I) Atr=03(Int.) MxPS= 8 I 996 E: Ad=82(I) Atr=03(Int.) MxPS= 8 Ivl= 8ms
1008 997
1009 998
1010 Selecting only the ``T:`` and ``I:`` lines fr 999 Selecting only the ``T:`` and ``I:`` lines from this (for example, by using
1011 ``procusb ti``), we have 1000 ``procusb ti``), we have
1012 1001
1013 :: 1002 ::
1014 1003
1015 T: Bus=00 Lev=00 Prnt=00 Port=00 Cnt 1004 T: Bus=00 Lev=00 Prnt=00 Port=00 Cnt=00 Dev#= 1 Spd=12 MxCh= 2
1016 T: Bus=00 Lev=01 Prnt=01 Port=00 Cnt 1005 T: Bus=00 Lev=01 Prnt=01 Port=00 Cnt=01 Dev#= 2 Spd=12 MxCh= 4
1017 I: If#= 0 Alt= 0 #EPs= 1 Cls=09(hub 1006 I: If#= 0 Alt= 0 #EPs= 1 Cls=09(hub ) Sub=00 Prot=00 Driver=hub
1018 T: Bus=00 Lev=02 Prnt=02 Port=00 Cnt 1007 T: Bus=00 Lev=02 Prnt=02 Port=00 Cnt=01 Dev#= 3 Spd=1.5 MxCh= 0
1019 I: If#= 0 Alt= 0 #EPs= 1 Cls=03(HID 1008 I: If#= 0 Alt= 0 #EPs= 1 Cls=03(HID ) Sub=01 Prot=02 Driver=mouse
1020 T: Bus=00 Lev=02 Prnt=02 Port=02 Cnt 1009 T: Bus=00 Lev=02 Prnt=02 Port=02 Cnt=02 Dev#= 4 Spd=12 MxCh= 0
1021 I: If#= 0 Alt= 0 #EPs= 3 Cls=00(>ifc 1010 I: If#= 0 Alt= 0 #EPs= 3 Cls=00(>ifc ) Sub=00 Prot=00 Driver=serial
1022 1011
1023 1012
1024 Physically this looks like (or could be conve 1013 Physically this looks like (or could be converted to)::
1025 1014
1026 +------------------+ 1015 +------------------+
1027 | PC/root_hub (12)| 1016 | PC/root_hub (12)| Dev# = 1
1028 +------------------+ 1017 +------------------+ (nn) is Mbps.
1029 Level 0 | CN.0 | CN.1 | 1018 Level 0 | CN.0 | CN.1 | [CN = connector/port #]
1030 +------------------+ 1019 +------------------+
1031 / 1020 /
1032 / 1021 /
1033 +-----------------------+ 1022 +-----------------------+
1034 Level 1 | Dev#2: 4-port hub (12)| 1023 Level 1 | Dev#2: 4-port hub (12)|
1035 +-----------------------+ 1024 +-----------------------+
1036 |CN.0 |CN.1 |CN.2 |CN.3 | 1025 |CN.0 |CN.1 |CN.2 |CN.3 |
1037 +-----------------------+ 1026 +-----------------------+
1038 \ \________________ 1027 \ \____________________
1039 \_____ 1028 \_____ \
1040 \ 1029 \ \
1041 +--------------------+ +- 1030 +--------------------+ +--------------------+
1042 Level 2 | Dev# 3: mouse (1.5)| | 1031 Level 2 | Dev# 3: mouse (1.5)| | Dev# 4: serial (12)|
1043 +--------------------+ +- 1032 +--------------------+ +--------------------+
1044 1033
1045 1034
1046 1035
1047 Or, in a more tree-like structure (ports [Con 1036 Or, in a more tree-like structure (ports [Connectors] without
1048 connections could be omitted):: 1037 connections could be omitted)::
1049 1038
1050 PC: Dev# 1, root hub, 2 ports, 12 Mb 1039 PC: Dev# 1, root hub, 2 ports, 12 Mbps
1051 |_ CN.0: Dev# 2, hub, 4 ports, 12 Mb 1040 |_ CN.0: Dev# 2, hub, 4 ports, 12 Mbps
1052 |_ CN.0: Dev #3, mouse, 1.5 Mbp 1041 |_ CN.0: Dev #3, mouse, 1.5 Mbps
1053 |_ CN.1: 1042 |_ CN.1:
1054 |_ CN.2: Dev #4, serial, 12 Mbp 1043 |_ CN.2: Dev #4, serial, 12 Mbps
1055 |_ CN.3: 1044 |_ CN.3:
1056 |_ CN.1: 1045 |_ CN.1:
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