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