Documentation/input/input.txt

   1                           Linux Input drivers v1.0
   2                (c) 1999-2001 Vojtech Pavlik <vojtech@ucw.cz>
   3                              Sponsored by SuSE
   4 ----------------------------------------------------------------------------
   5
   6 0. Disclaimer
   7 ~~~~~~~~~~~~~
   8   This program is free software; you can redistribute it and/or modify it
   9 under the terms of the GNU General Public License as published by the Free
  10 Software Foundation; either version 2 of the License, or (at your option)
  11 any later version.
  12
  13   This program is distributed in the hope that it will be useful, but
  14 WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
  15 or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License for
  16 more details.
  17
  18   You should have received a copy of the GNU General Public License along
  19 with this program; if not, write to the Free Software Foundation, Inc., 59
  20 Temple Place, Suite 330, Boston, MA 02111-1307 USA
  21
  22   Should you need to contact me, the author, you can do so either by e-mail
  23 - mail your message to <vojtech@ucw.cz>, or by paper mail: Vojtech Pavlik,
  24 Simunkova 1594, Prague 8, 182 00 Czech Republic
  25
  26   For your convenience, the GNU General Public License version 2 is included
  27 in the package: See the file COPYING.
  28
  29 1. Introduction
  30 ~~~~~~~~~~~~~~~
  31   This is a collection of drivers that is designed to support all input
  32 devices under Linux. While it is currently used only on for USB input
  33 devices, future use (say 2.5/2.6) is expected to expand to replace
  34 most of the existing input system, which is why it lives in
  35 drivers/input/ instead of drivers/usb/.
  36
  37   The centre of the input drivers is the input module, which must be
  38 loaded before any other of the input modules - it serves as a way of
  39 communication between two groups of modules:
  40
  41 1.1 Device drivers
  42 ~~~~~~~~~~~~~~~~~~
  43   These modules talk to the hardware (for example via USB), and provide
  44 events (keystrokes, mouse movements) to the input module.
  45
  46 1.2 Event handlers
  47 ~~~~~~~~~~~~~~~~~~
  48   These modules get events from input and pass them where needed via
  49 various interfaces - keystrokes to the kernel, mouse movements via a
  50 simulated PS/2 interface to GPM and X and so on.
  51
  52 2. Simple Usage
  53 ~~~~~~~~~~~~~~~
  54   For the most usual configuration, with one USB mouse and one USB keyboard,
  55 you'll have to load the following modules (or have them built in to the
  56 kernel):
  57
  58         input
  59         mousedev
  60         keybdev
  61         usbcore
  62         uhci_hcd or ohci_hcd or ehci_hcd
  63         usbhid
  64
  65   After this, the USB keyboard will work straight away, and the USB mouse
  66 will be available as a character device on major 13, minor 63:
  67
  68         crw-r--r--   1 root     root      13,  63 Mar 28 22:45 mice
  69
  70   This device has to be created.
  71   The commands to create it by hand are:
  72
  73         cd /dev
  74         mkdir input
  75         mknod input/mice c 13 63
  76
  77   After that you have to point GPM (the textmode mouse cut&paste tool) and
  78 XFree to this device to use it - GPM should be called like:
  79
  80         gpm -t ps2 -m /dev/input/mice
  81
  82   And in X:
  83
  84         Section "Pointer"
  85             Protocol    "ImPS/2"
  86             Device      "/dev/input/mice"
  87             ZAxisMapping 4 5
  88         EndSection
  89
  90   When you do all of the above, you can use your USB mouse and keyboard.
  91
  92 3. Detailed Description
  93 ~~~~~~~~~~~~~~~~~~~~~~~
  94 3.1 Device drivers
  95 ~~~~~~~~~~~~~~~~~~
  96   Device drivers are the modules that generate events. The events are
  97 however not useful without being handled, so you also will need to use some
  98 of the modules from section 3.2.
  99
 100 3.1.1 usbhid
 101 ~~~~~~~~~~~~
 102   usbhid is the largest and most complex driver of the whole suite. It
 103 handles all HID devices, and because there is a very wide variety of them,
 104 and because the USB HID specification isn't simple, it needs to be this big.
 105
 106   Currently, it handles USB mice, joysticks, gamepads, steering wheels
 107 keyboards, trackballs and digitizers.
 108
 109  However, USB uses HID also for monitor controls, speaker controls, UPSs,
 110 LCDs and many other purposes.
 111
 112  The monitor and speaker controls should be easy to add to the hid/input
 113 interface, but for the UPSs and LCDs it doesn't make much sense. For this,
 114 the hiddev interface was designed. See Documentation/hid/hiddev.txt
 115 for more information about it.
 116
 117   The usage of the usbhid module is very simple, it takes no parameters,
 118 detects everything automatically and when a HID device is inserted, it
 119 detects it appropriately.
 120
 121   However, because the devices vary wildly, you might happen to have a
 122 device that doesn't work well. In that case #define DEBUG at the beginning
 123 of hid-core.c and send me the syslog traces.
 124
 125 3.1.2 usbmouse
 126 ~~~~~~~~~~~~~~
 127   For embedded systems, for mice with broken HID descriptors and just any
 128 other use when the big usbhid wouldn't be a good choice, there is the
 129 usbmouse driver. It handles USB mice only. It uses a simpler HIDBP
 130 protocol. This also means the mice must support this simpler protocol. Not
 131 all do. If you don't have any strong reason to use this module, use usbhid
 132 instead.
 133
 134 3.1.3 usbkbd
 135 ~~~~~~~~~~~~
 136   Much like usbmouse, this module talks to keyboards with a simplified
 137 HIDBP protocol. It's smaller, but doesn't support any extra special keys.
 138 Use usbhid instead if there isn't any special reason to use this.
 139
 140 3.1.4 wacom
 141 ~~~~~~~~~~~
 142   This is a driver for Wacom Graphire and Intuos tablets. Not for Wacom
 143 PenPartner, that one is handled by the HID driver. Although the Intuos and
 144 Graphire tablets claim that they are HID tablets as well, they are not and
 145 thus need this specific driver.
 146
 147 3.1.5 iforce
 148 ~~~~~~~~~~~~
 149   A driver for I-Force joysticks and wheels, both over USB and RS232.
 150 It includes ForceFeedback support now, even though Immersion
 151 Corp. considers the protocol a trade secret and won't disclose a word
 152 about it.
 153
 154 3.2 Event handlers
 155 ~~~~~~~~~~~~~~~~~~
 156   Event handlers distribute the events from the devices to userland and
 157 kernel, as needed.
 158
 159 3.2.1 keybdev
 160 ~~~~~~~~~~~~~
 161   keybdev is currently a rather ugly hack that translates the input
 162 events into architecture-specific keyboard raw mode (Xlated AT Set2 on
 163 x86), and passes them into the handle_scancode function of the
 164 keyboard.c module. This works well enough on all architectures that
 165 keybdev can generate rawmode on, other architectures can be added to
 166 it.
 167
 168   The right way would be to pass the events to keyboard.c directly,
 169 best if keyboard.c would itself be an event handler. This is done in
 170 the input patch, available on the webpage mentioned below.
 171
 172 3.2.2 mousedev
 173 ~~~~~~~~~~~~~~
 174   mousedev is also a hack to make programs that use mouse input
 175 work. It takes events from either mice or digitizers/tablets and makes
 176 a PS/2-style (a la /dev/psaux) mouse device available to the
 177 userland. Ideally, the programs could use a more reasonable interface,
 178 for example evdev
 179
 180   Mousedev devices in /dev/input (as shown above) are:
 181
 182         crw-r--r--   1 root     root      13,  32 Mar 28 22:45 mouse0
 183         crw-r--r--   1 root     root      13,  33 Mar 29 00:41 mouse1
 184         crw-r--r--   1 root     root      13,  34 Mar 29 00:41 mouse2
 185         crw-r--r--   1 root     root      13,  35 Apr  1 10:50 mouse3
 186         ...
 187         ...
 188         crw-r--r--   1 root     root      13,  62 Apr  1 10:50 mouse30
 189         crw-r--r--   1 root     root      13,  63 Apr  1 10:50 mice
 190
 191 Each 'mouse' device is assigned to a single mouse or digitizer, except
 192 the last one - 'mice'. This single character device is shared by all
 193 mice and digitizers, and even if none are connected, the device is
 194 present.  This is useful for hotplugging USB mice, so that programs
 195 can open the device even when no mice are present.
 196
 197   CONFIG_INPUT_MOUSEDEV_SCREEN_[XY] in the kernel configuration are
 198 the size of your screen (in pixels) in XFree86. This is needed if you
 199 want to use your digitizer in X, because its movement is sent to X
 200 via a virtual PS/2 mouse and thus needs to be scaled
 201 accordingly. These values won't be used if you use a mouse only.
 202
 203   Mousedev will generate either PS/2, ImPS/2 (Microsoft IntelliMouse) or
 204 ExplorerPS/2 (IntelliMouse Explorer) protocols, depending on what the
 205 program reading the data wishes. You can set GPM and X to any of
 206 these. You'll need ImPS/2 if you want to make use of a wheel on a USB
 207 mouse and ExplorerPS/2 if you want to use extra (up to 5) buttons.
 208
 209 3.2.3 joydev
 210 ~~~~~~~~~~~~
 211   Joydev implements v0.x and v1.x Linux joystick api, much like
 212 drivers/char/joystick/joystick.c used to in earlier versions. See
 213 joystick-api.txt in the Documentation subdirectory for details.  As
 214 soon as any joystick is connected, it can be accessed in /dev/input
 215 on:
 216
 217         crw-r--r--   1 root     root      13,   0 Apr  1 10:50 js0
 218         crw-r--r--   1 root     root      13,   1 Apr  1 10:50 js1
 219         crw-r--r--   1 root     root      13,   2 Apr  1 10:50 js2
 220         crw-r--r--   1 root     root      13,   3 Apr  1 10:50 js3
 221         ...
 222
 223 And so on up to js31.
 224
 225 3.2.4 evdev
 226 ~~~~~~~~~~~
 227   evdev is the generic input event interface. It passes the events
 228 generated in the kernel straight to the program, with timestamps. The
 229 API is still evolving, but should be usable now. It's described in
 230 section 5.
 231
 232   This should be the way for GPM and X to get keyboard and mouse
 233 events. It allows for multihead in X without any specific multihead
 234 kernel support. The event codes are the same on all architectures and
 235 are hardware independent.
 236
 237   The devices are in /dev/input:
 238
 239         crw-r--r--   1 root     root      13,  64 Apr  1 10:49 event0
 240         crw-r--r--   1 root     root      13,  65 Apr  1 10:50 event1
 241         crw-r--r--   1 root     root      13,  66 Apr  1 10:50 event2
 242         crw-r--r--   1 root     root      13,  67 Apr  1 10:50 event3
 243         ...
 244
 245 And so on up to event31.
 246
 247 4. Verifying if it works
 248 ~~~~~~~~~~~~~~~~~~~~~~~~
 249   Typing a couple keys on the keyboard should be enough to check that
 250 a USB keyboard works and is correctly connected to the kernel keyboard
 251 driver.
 252
 253   Doing a "cat /dev/input/mouse0" (c, 13, 32) will verify that a mouse
 254 is also emulated; characters should appear if you move it.
 255
 256   You can test the joystick emulation with the 'jstest' utility,
 257 available in the joystick package (see Documentation/input/joystick.txt).
 258
 259   You can test the event devices with the 'evtest' utility available
 260 in the LinuxConsole project CVS archive (see the URL below).
 261
 262 5. Event interface
 263 ~~~~~~~~~~~~~~~~~~
 264   Should you want to add event device support into any application (X, gpm,
 265 svgalib ...) I <vojtech@ucw.cz> will be happy to provide you any help I
 266 can. Here goes a description of the current state of things, which is going
 267 to be extended, but not changed incompatibly as time goes:
 268
 269   You can use blocking and nonblocking reads, also select() on the
 270 /dev/input/eventX devices, and you'll always get a whole number of input
 271 events on a read. Their layout is:
 272
 273 struct input_event {
 274         struct timeval time;
 275         unsigned short type;
 276         unsigned short code;
 277         unsigned int value;
 278 };
 279
 280   'time' is the timestamp, it returns the time at which the event happened.
 281 Type is for example EV_REL for relative moment, EV_KEY for a keypress or
 282 release. More types are defined in include/linux/input.h.
 283
 284   'code' is event code, for example REL_X or KEY_BACKSPACE, again a complete
 285 list is in include/linux/input.h.
 286
 287   'value' is the value the event carries. Either a relative change for
 288 EV_REL, absolute new value for EV_ABS (joysticks ...), or 0 for EV_KEY for
 289 release, 1 for keypress and 2 for autorepeat.
 290