1 .. include:: <isonum.txt>
2
3 ============
4 Introduction
5 ============
6
7 :Copyright: |copy| 1999-2001 Vojtech Pavlik <vojtech@ucw.cz> - Sponsored by SuSE
8
9 Architecture
10 ============
11
12 Input subsystem is a collection of drivers that is designed to support
13 all input devices under Linux. Most of the drivers reside in
14 drivers/input, although quite a few live in drivers/hid and
15 drivers/platform.
16
17 The core of the input subsystem is the input module, which must be
18 loaded before any other of the input modules - it serves as a way of
19 communication between two groups of modules:
20
21 Device drivers
22 --------------
23
24 These modules talk to the hardware (for example via USB), and provide
25 events (keystrokes, mouse movements) to the input module.
26
27 Event handlers
28 --------------
29
30 These modules get events from input core and pass them where needed
31 via various interfaces - keystrokes to the kernel, mouse movements via
32 a simulated PS/2 interface to GPM and X, and so on.
33
34 Simple Usage
35 ============
36
37 For the most usual configuration, with one USB mouse and one USB keyboard,
38 you'll have to load the following modules (or have them built in to the
39 kernel)::
40
41 input
42 mousedev
43 usbcore
44 uhci_hcd or ohci_hcd or ehci_hcd
45 usbhid
46 hid_generic
47
48 After this, the USB keyboard will work straight away, and the USB mouse
49 will be available as a character device on major 13, minor 63::
50
51 crw-r--r-- 1 root root 13, 63 Mar 28 22:45 mice
52
53 This device is usually created automatically by the system. The commands
54 to create it by hand are::
55
56 cd /dev
57 mkdir input
58 mknod input/mice c 13 63
59
60 After that you have to point GPM (the textmode mouse cut&paste tool) and
61 XFree to this device to use it - GPM should be called like::
62
63 gpm -t ps2 -m /dev/input/mice
64
65 And in X::
66
67 Section "Pointer"
68 Protocol "ImPS/2"
69 Device "/dev/input/mice"
70 ZAxisMapping 4 5
71 EndSection
72
73 When you do all of the above, you can use your USB mouse and keyboard.
74
75 Detailed Description
76 ====================
77
78 Event handlers
79 --------------
80
81 Event handlers distribute the events from the devices to userspace and
82 in-kernel consumers, as needed.
83
84 evdev
85 ~~~~~
86
87 ``evdev`` is the generic input event interface. It passes the events
88 generated in the kernel straight to the program, with timestamps. The
89 event codes are the same on all architectures and are hardware
90 independent.
91
92 This is the preferred interface for userspace to consume user
93 input, and all clients are encouraged to use it.
94
95 See :ref:`event-interface` for notes on API.
96
97 The devices are in /dev/input::
98
99 crw-r--r-- 1 root root 13, 64 Apr 1 10:49 event0
100 crw-r--r-- 1 root root 13, 65 Apr 1 10:50 event1
101 crw-r--r-- 1 root root 13, 66 Apr 1 10:50 event2
102 crw-r--r-- 1 root root 13, 67 Apr 1 10:50 event3
103 ...
104
105 There are two ranges of minors: 64 through 95 is the static legacy
106 range. If there are more than 32 input devices in a system, additional
107 evdev nodes are created with minors starting with 256.
108
109 keyboard
110 ~~~~~~~~
111
112 ``keyboard`` is in-kernel input handler and is a part of VT code. It
113 consumes keyboard keystrokes and handles user input for VT consoles.
114
115 mousedev
116 ~~~~~~~~
117
118 ``mousedev`` is a hack to make legacy programs that use mouse input
119 work. It takes events from either mice or digitizers/tablets and makes
120 a PS/2-style (a la /dev/psaux) mouse device available to the
121 userland.
122
123 Mousedev devices in /dev/input (as shown above) are::
124
125 crw-r--r-- 1 root root 13, 32 Mar 28 22:45 mouse0
126 crw-r--r-- 1 root root 13, 33 Mar 29 00:41 mouse1
127 crw-r--r-- 1 root root 13, 34 Mar 29 00:41 mouse2
128 crw-r--r-- 1 root root 13, 35 Apr 1 10:50 mouse3
129 ...
130 ...
131 crw-r--r-- 1 root root 13, 62 Apr 1 10:50 mouse30
132 crw-r--r-- 1 root root 13, 63 Apr 1 10:50 mice
133
134 Each ``mouse`` device is assigned to a single mouse or digitizer, except
135 the last one - ``mice``. This single character device is shared by all
136 mice and digitizers, and even if none are connected, the device is
137 present. This is useful for hotplugging USB mice, so that older programs
138 that do not handle hotplug can open the device even when no mice are
139 present.
140
141 CONFIG_INPUT_MOUSEDEV_SCREEN_[XY] in the kernel configuration are
142 the size of your screen (in pixels) in XFree86. This is needed if you
143 want to use your digitizer in X, because its movement is sent to X
144 via a virtual PS/2 mouse and thus needs to be scaled
145 accordingly. These values won't be used if you use a mouse only.
146
147 Mousedev will generate either PS/2, ImPS/2 (Microsoft IntelliMouse) or
148 ExplorerPS/2 (IntelliMouse Explorer) protocols, depending on what the
149 program reading the data wishes. You can set GPM and X to any of
150 these. You'll need ImPS/2 if you want to make use of a wheel on a USB
151 mouse and ExplorerPS/2 if you want to use extra (up to 5) buttons.
152
153 joydev
154 ~~~~~~
155
156 ``joydev`` implements v0.x and v1.x Linux joystick API. See
157 :ref:`joystick-api` for details.
158
159 As soon as any joystick is connected, it can be accessed in /dev/input on::
160
161 crw-r--r-- 1 root root 13, 0 Apr 1 10:50 js0
162 crw-r--r-- 1 root root 13, 1 Apr 1 10:50 js1
163 crw-r--r-- 1 root root 13, 2 Apr 1 10:50 js2
164 crw-r--r-- 1 root root 13, 3 Apr 1 10:50 js3
165 ...
166
167 And so on up to js31 in legacy range, and additional nodes with minors
168 above 256 if there are more joystick devices.
169
170 Device drivers
171 --------------
172
173 Device drivers are the modules that generate events.
174
175 hid-generic
176 ~~~~~~~~~~~
177
178 ``hid-generic`` is one of the largest and most complex driver of the
179 whole suite. It handles all HID devices, and because there is a very
180 wide variety of them, and because the USB HID specification isn't
181 simple, it needs to be this big.
182
183 Currently, it handles USB mice, joysticks, gamepads, steering wheels,
184 keyboards, trackballs and digitizers.
185
186 However, USB uses HID also for monitor controls, speaker controls, UPSs,
187 LCDs and many other purposes.
188
189 The monitor and speaker controls should be easy to add to the hid/input
190 interface, but for the UPSs and LCDs it doesn't make much sense. For this,
191 the hiddev interface was designed. See Documentation/hid/hiddev.rst
192 for more information about it.
193
194 The usage of the usbhid module is very simple, it takes no parameters,
195 detects everything automatically and when a HID device is inserted, it
196 detects it appropriately.
197
198 However, because the devices vary wildly, you might happen to have a
199 device that doesn't work well. In that case #define DEBUG at the beginning
200 of hid-core.c and send me the syslog traces.
201
202 usbmouse
203 ~~~~~~~~
204
205 For embedded systems, for mice with broken HID descriptors and just any
206 other use when the big usbhid wouldn't be a good choice, there is the
207 usbmouse driver. It handles USB mice only. It uses a simpler HIDBP
208 protocol. This also means the mice must support this simpler protocol. Not
209 all do. If you don't have any strong reason to use this module, use usbhid
210 instead.
211
212 usbkbd
213 ~~~~~~
214
215 Much like usbmouse, this module talks to keyboards with a simplified
216 HIDBP protocol. It's smaller, but doesn't support any extra special keys.
217 Use usbhid instead if there isn't any special reason to use this.
218
219 psmouse
220 ~~~~~~~
221
222 This is driver for all flavors of pointing devices using PS/2
223 protocol, including Synaptics and ALPS touchpads, Intellimouse
224 Explorer devices, Logitech PS/2 mice and so on.
225
226 atkbd
227 ~~~~~
228
229 This is driver for PS/2 (AT) keyboards.
230
231 iforce
232 ~~~~~~
233
234 A driver for I-Force joysticks and wheels, both over USB and RS232.
235 It includes Force Feedback support now, even though Immersion
236 Corp. considers the protocol a trade secret and won't disclose a word
237 about it.
238
239 Verifying if it works
240 =====================
241
242 Typing a couple keys on the keyboard should be enough to check that
243 a keyboard works and is correctly connected to the kernel keyboard
244 driver.
245
246 Doing a ``cat /dev/input/mouse0`` (c, 13, 32) will verify that a mouse
247 is also emulated; characters should appear if you move it.
248
249 You can test the joystick emulation with the ``jstest`` utility,
250 available in the joystick package (see :ref:`joystick-doc`).
251
252 You can test the event devices with the ``evtest`` utility.
253
254 .. _event-interface:
255
256 Event interface
257 ===============
258
259 You can use blocking and nonblocking reads, and also select() on the
260 /dev/input/eventX devices, and you'll always get a whole number of input
261 events on a read. Their layout is::
262
263 struct input_event {
264 struct timeval time;
265 unsigned short type;
266 unsigned short code;
267 unsigned int value;
268 };
269
270 ``time`` is the timestamp, it returns the time at which the event happened.
271 Type is for example EV_REL for relative movement, EV_KEY for a keypress or
272 release. More types are defined in include/uapi/linux/input-event-codes.h.
273
274 ``code`` is event code, for example REL_X or KEY_BACKSPACE, again a complete
275 list is in include/uapi/linux/input-event-codes.h.
276
277 ``value`` is the value the event carries. Either a relative change for
278 EV_REL, absolute new value for EV_ABS (joysticks ...), or 0 for EV_KEY for
279 release, 1 for keypress and 2 for autorepeat.
280
281 See :ref:`input-event-codes` for more information about various even codes.
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