linux/Documentation/input/event-codes.txt
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   1The input protocol uses a map of types and codes to express input device values
   2to userspace. This document describes the types and codes and how and when they
   3may be used.
   4
   5A single hardware event generates multiple input events. Each input event
   6contains the new value of a single data item. A special event type, EV_SYN, is
   7used to separate input events into packets of input data changes occurring at
   8the same moment in time. In the following, the term "event" refers to a single
   9input event encompassing a type, code, and value.
  10
  11The input protocol is a stateful protocol. Events are emitted only when values
  12of event codes have changed. However, the state is maintained within the Linux
  13input subsystem; drivers do not need to maintain the state and may attempt to
  14emit unchanged values without harm. Userspace may obtain the current state of
  15event code values using the EVIOCG* ioctls defined in linux/input.h. The event
  16reports supported by a device are also provided by sysfs in
  17class/input/event*/device/capabilities/, and the properties of a device are
  18provided in class/input/event*/device/properties.
  19
  20Event types:
  21===========
  22Event types are groupings of codes under a logical input construct. Each
  23type has a set of applicable codes to be used in generating events. See the
  24Codes section for details on valid codes for each type.
  25
  26* EV_SYN:
  27  - Used as markers to separate events. Events may be separated in time or in
  28    space, such as with the multitouch protocol.
  29
  30* EV_KEY:
  31  - Used to describe state changes of keyboards, buttons, or other key-like
  32    devices.
  33
  34* EV_REL:
  35  - Used to describe relative axis value changes, e.g. moving the mouse 5 units
  36    to the left.
  37
  38* EV_ABS:
  39  - Used to describe absolute axis value changes, e.g. describing the
  40    coordinates of a touch on a touchscreen.
  41
  42* EV_MSC:
  43  - Used to describe miscellaneous input data that do not fit into other types.
  44
  45* EV_SW:
  46  - Used to describe binary state input switches.
  47
  48* EV_LED:
  49  - Used to turn LEDs on devices on and off.
  50
  51* EV_SND:
  52  - Used to output sound to devices.
  53
  54* EV_REP:
  55  - Used for autorepeating devices.
  56
  57* EV_FF:
  58  - Used to send force feedback commands to an input device.
  59
  60* EV_PWR:
  61  - A special type for power button and switch input.
  62
  63* EV_FF_STATUS:
  64  - Used to receive force feedback device status.
  65
  66Event codes:
  67===========
  68Event codes define the precise type of event.
  69
  70EV_SYN:
  71----------
  72EV_SYN event values are undefined. Their usage is defined only by when they are
  73sent in the evdev event stream.
  74
  75* SYN_REPORT:
  76  - Used to synchronize and separate events into packets of input data changes
  77    occurring at the same moment in time. For example, motion of a mouse may set
  78    the REL_X and REL_Y values for one motion, then emit a SYN_REPORT. The next
  79    motion will emit more REL_X and REL_Y values and send another SYN_REPORT.
  80
  81* SYN_CONFIG:
  82  - TBD
  83
  84* SYN_MT_REPORT:
  85  - Used to synchronize and separate touch events. See the
  86    multi-touch-protocol.txt document for more information.
  87
  88* SYN_DROPPED:
  89  - Used to indicate buffer overrun in the evdev client's event queue.
  90    Client should ignore all events up to and including next SYN_REPORT
  91    event and query the device (using EVIOCG* ioctls) to obtain its
  92    current state.
  93
  94EV_KEY:
  95----------
  96EV_KEY events take the form KEY_<name> or BTN_<name>. For example, KEY_A is used
  97to represent the 'A' key on a keyboard. When a key is depressed, an event with
  98the key's code is emitted with value 1. When the key is released, an event is
  99emitted with value 0. Some hardware send events when a key is repeated. These
 100events have a value of 2. In general, KEY_<name> is used for keyboard keys, and
 101BTN_<name> is used for other types of momentary switch events.
 102
 103A few EV_KEY codes have special meanings:
 104
 105* BTN_TOOL_<name>:
 106  - These codes are used in conjunction with input trackpads, tablets, and
 107    touchscreens. These devices may be used with fingers, pens, or other tools.
 108    When an event occurs and a tool is used, the corresponding BTN_TOOL_<name>
 109    code should be set to a value of 1. When the tool is no longer interacting
 110    with the input device, the BTN_TOOL_<name> code should be reset to 0. All
 111    trackpads, tablets, and touchscreens should use at least one BTN_TOOL_<name>
 112    code when events are generated.
 113
 114* BTN_TOUCH:
 115    BTN_TOUCH is used for touch contact. While an input tool is determined to be
 116    within meaningful physical contact, the value of this property must be set
 117    to 1. Meaningful physical contact may mean any contact, or it may mean
 118    contact conditioned by an implementation defined property. For example, a
 119    touchpad may set the value to 1 only when the touch pressure rises above a
 120    certain value. BTN_TOUCH may be combined with BTN_TOOL_<name> codes. For
 121    example, a pen tablet may set BTN_TOOL_PEN to 1 and BTN_TOUCH to 0 while the
 122    pen is hovering over but not touching the tablet surface.
 123
 124Note: For appropriate function of the legacy mousedev emulation driver,
 125BTN_TOUCH must be the first evdev code emitted in a synchronization frame.
 126
 127Note: Historically a touch device with BTN_TOOL_FINGER and BTN_TOUCH was
 128interpreted as a touchpad by userspace, while a similar device without
 129BTN_TOOL_FINGER was interpreted as a touchscreen. For backwards compatibility
 130with current userspace it is recommended to follow this distinction. In the
 131future, this distinction will be deprecated and the device properties ioctl
 132EVIOCGPROP, defined in linux/input.h, will be used to convey the device type.
 133
 134* BTN_TOOL_FINGER, BTN_TOOL_DOUBLETAP, BTN_TOOL_TRIPLETAP, BTN_TOOL_QUADTAP:
 135  - These codes denote one, two, three, and four finger interaction on a
 136    trackpad or touchscreen. For example, if the user uses two fingers and moves
 137    them on the touchpad in an effort to scroll content on screen,
 138    BTN_TOOL_DOUBLETAP should be set to value 1 for the duration of the motion.
 139    Note that all BTN_TOOL_<name> codes and the BTN_TOUCH code are orthogonal in
 140    purpose. A trackpad event generated by finger touches should generate events
 141    for one code from each group. At most only one of these BTN_TOOL_<name>
 142    codes should have a value of 1 during any synchronization frame.
 143
 144Note: Historically some drivers emitted multiple of the finger count codes with
 145a value of 1 in the same synchronization frame. This usage is deprecated.
 146
 147Note: In multitouch drivers, the input_mt_report_finger_count() function should
 148be used to emit these codes. Please see multi-touch-protocol.txt for details.
 149
 150EV_REL:
 151----------
 152EV_REL events describe relative changes in a property. For example, a mouse may
 153move to the left by a certain number of units, but its absolute position in
 154space is unknown. If the absolute position is known, EV_ABS codes should be used
 155instead of EV_REL codes.
 156
 157A few EV_REL codes have special meanings:
 158
 159* REL_WHEEL, REL_HWHEEL:
 160  - These codes are used for vertical and horizontal scroll wheels,
 161    respectively.
 162
 163EV_ABS:
 164----------
 165EV_ABS events describe absolute changes in a property. For example, a touchpad
 166may emit coordinates for a touch location.
 167
 168A few EV_ABS codes have special meanings:
 169
 170* ABS_DISTANCE:
 171  - Used to describe the distance of a tool from an interaction surface. This
 172    event should only be emitted while the tool is hovering, meaning in close
 173    proximity of the device and while the value of the BTN_TOUCH code is 0. If
 174    the input device may be used freely in three dimensions, consider ABS_Z
 175    instead.
 176
 177* ABS_MT_<name>:
 178  - Used to describe multitouch input events. Please see
 179    multi-touch-protocol.txt for details.
 180
 181EV_SW:
 182----------
 183EV_SW events describe stateful binary switches. For example, the SW_LID code is
 184used to denote when a laptop lid is closed.
 185
 186Upon binding to a device or resuming from suspend, a driver must report
 187the current switch state. This ensures that the device, kernel, and userspace
 188state is in sync.
 189
 190Upon resume, if the switch state is the same as before suspend, then the input
 191subsystem will filter out the duplicate switch state reports. The driver does
 192not need to keep the state of the switch at any time.
 193
 194EV_MSC:
 195----------
 196EV_MSC events are used for input and output events that do not fall under other
 197categories.
 198
 199EV_LED:
 200----------
 201EV_LED events are used for input and output to set and query the state of
 202various LEDs on devices.
 203
 204EV_REP:
 205----------
 206EV_REP events are used for specifying autorepeating events.
 207
 208EV_SND:
 209----------
 210EV_SND events are used for sending sound commands to simple sound output
 211devices.
 212
 213EV_FF:
 214----------
 215EV_FF events are used to initialize a force feedback capable device and to cause
 216such device to feedback.
 217
 218EV_PWR:
 219----------
 220EV_PWR events are a special type of event used specifically for power
 221mangement. Its usage is not well defined. To be addressed later.
 222
 223Device properties:
 224=================
 225Normally, userspace sets up an input device based on the data it emits,
 226i.e., the event types. In the case of two devices emitting the same event
 227types, additional information can be provided in the form of device
 228properties.
 229
 230INPUT_PROP_DIRECT + INPUT_PROP_POINTER:
 231--------------------------------------
 232The INPUT_PROP_DIRECT property indicates that device coordinates should be
 233directly mapped to screen coordinates (not taking into account trivial
 234transformations, such as scaling, flipping and rotating). Non-direct input
 235devices require non-trivial transformation, such as absolute to relative
 236transformation for touchpads. Typical direct input devices: touchscreens,
 237drawing tablets; non-direct devices: touchpads, mice.
 238
 239The INPUT_PROP_POINTER property indicates that the device is not transposed
 240on the screen and thus requires use of an on-screen pointer to trace user's
 241movements.  Typical pointer devices: touchpads, tablets, mice; non-pointer
 242device: touchscreen.
 243
 244If neither INPUT_PROP_DIRECT or INPUT_PROP_POINTER are set, the property is
 245considered undefined and the device type should be deduced in the
 246traditional way, using emitted event types.
 247
 248INPUT_PROP_BUTTONPAD:
 249--------------------
 250For touchpads where the button is placed beneath the surface, such that
 251pressing down on the pad causes a button click, this property should be
 252set. Common in clickpad notebooks and macbooks from 2009 and onwards.
 253
 254Originally, the buttonpad property was coded into the bcm5974 driver
 255version field under the name integrated button. For backwards
 256compatibility, both methods need to be checked in userspace.
 257
 258INPUT_PROP_SEMI_MT:
 259------------------
 260Some touchpads, most common between 2008 and 2011, can detect the presence
 261of multiple contacts without resolving the individual positions; only the
 262number of contacts and a rectangular shape is known. For such
 263touchpads, the semi-mt property should be set.
 264
 265Depending on the device, the rectangle may enclose all touches, like a
 266bounding box, or just some of them, for instance the two most recent
 267touches. The diversity makes the rectangle of limited use, but some
 268gestures can normally be extracted from it.
 269
 270If INPUT_PROP_SEMI_MT is not set, the device is assumed to be a true MT
 271device.
 272
 273Guidelines:
 274==========
 275The guidelines below ensure proper single-touch and multi-finger functionality.
 276For multi-touch functionality, see the multi-touch-protocol.txt document for
 277more information.
 278
 279Mice:
 280----------
 281REL_{X,Y} must be reported when the mouse moves. BTN_LEFT must be used to report
 282the primary button press. BTN_{MIDDLE,RIGHT,4,5,etc.} should be used to report
 283further buttons of the device. REL_WHEEL and REL_HWHEEL should be used to report
 284scroll wheel events where available.
 285
 286Touchscreens:
 287----------
 288ABS_{X,Y} must be reported with the location of the touch. BTN_TOUCH must be
 289used to report when a touch is active on the screen.
 290BTN_{MOUSE,LEFT,MIDDLE,RIGHT} must not be reported as the result of touch
 291contact. BTN_TOOL_<name> events should be reported where possible.
 292
 293For new hardware, INPUT_PROP_DIRECT should be set.
 294
 295Trackpads:
 296----------
 297Legacy trackpads that only provide relative position information must report
 298events like mice described above.
 299
 300Trackpads that provide absolute touch position must report ABS_{X,Y} for the
 301location of the touch. BTN_TOUCH should be used to report when a touch is active
 302on the trackpad. Where multi-finger support is available, BTN_TOOL_<name> should
 303be used to report the number of touches active on the trackpad.
 304
 305For new hardware, INPUT_PROP_POINTER should be set.
 306
 307Tablets:
 308----------
 309BTN_TOOL_<name> events must be reported when a stylus or other tool is active on
 310the tablet. ABS_{X,Y} must be reported with the location of the tool. BTN_TOUCH
 311should be used to report when the tool is in contact with the tablet.
 312BTN_{STYLUS,STYLUS2} should be used to report buttons on the tool itself. Any
 313button may be used for buttons on the tablet except BTN_{MOUSE,LEFT}.
 314BTN_{0,1,2,etc} are good generic codes for unlabeled buttons. Do not use
 315meaningful buttons, like BTN_FORWARD, unless the button is labeled for that
 316purpose on the device.
 317
 318For new hardware, both INPUT_PROP_DIRECT and INPUT_PROP_POINTER should be set.
 319
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