event-codes.rst 16 KB

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  1. .. _input-event-codes:
  2. =================
  3. Input event codes
  4. =================
  5. The input protocol uses a map of types and codes to express input device values
  6. to userspace. This document describes the types and codes and how and when they
  7. may be used.
  8. A single hardware event generates multiple input events. Each input event
  9. contains the new value of a single data item. A special event type, EV_SYN, is
  10. used to separate input events into packets of input data changes occurring at
  11. the same moment in time. In the following, the term "event" refers to a single
  12. input event encompassing a type, code, and value.
  13. The input protocol is a stateful protocol. Events are emitted only when values
  14. of event codes have changed. However, the state is maintained within the Linux
  15. input subsystem; drivers do not need to maintain the state and may attempt to
  16. emit unchanged values without harm. Userspace may obtain the current state of
  17. event code values using the EVIOCG* ioctls defined in linux/input.h. The event
  18. reports supported by a device are also provided by sysfs in
  19. class/input/event*/device/capabilities/, and the properties of a device are
  20. provided in class/input/event*/device/properties.
  21. Event types
  22. ===========
  23. Event types are groupings of codes under a logical input construct. Each
  24. type has a set of applicable codes to be used in generating events. See the
  25. Codes section for details on valid codes for each type.
  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. * EV_KEY:
  30. - Used to describe state changes of keyboards, buttons, or other key-like
  31. devices.
  32. * EV_REL:
  33. - Used to describe relative axis value changes, e.g. moving the mouse 5 units
  34. to the left.
  35. * EV_ABS:
  36. - Used to describe absolute axis value changes, e.g. describing the
  37. coordinates of a touch on a touchscreen.
  38. * EV_MSC:
  39. - Used to describe miscellaneous input data that do not fit into other types.
  40. * EV_SW:
  41. - Used to describe binary state input switches.
  42. * EV_LED:
  43. - Used to turn LEDs on devices on and off.
  44. * EV_SND:
  45. - Used to output sound to devices.
  46. * EV_REP:
  47. - Used for autorepeating devices.
  48. * EV_FF:
  49. - Used to send force feedback commands to an input device.
  50. * EV_PWR:
  51. - A special type for power button and switch input.
  52. * EV_FF_STATUS:
  53. - Used to receive force feedback device status.
  54. Event codes
  55. ===========
  56. Event codes define the precise type of event.
  57. EV_SYN
  58. ------
  59. EV_SYN event values are undefined. Their usage is defined only by when they are
  60. sent in the evdev event stream.
  61. * SYN_REPORT:
  62. - Used to synchronize and separate events into packets of input data changes
  63. occurring at the same moment in time. For example, motion of a mouse may set
  64. the REL_X and REL_Y values for one motion, then emit a SYN_REPORT. The next
  65. motion will emit more REL_X and REL_Y values and send another SYN_REPORT.
  66. * SYN_CONFIG:
  67. - TBD
  68. * SYN_MT_REPORT:
  69. - Used to synchronize and separate touch events. See the
  70. multi-touch-protocol.txt document for more information.
  71. * SYN_DROPPED:
  72. - Used to indicate buffer overrun in the evdev client's event queue.
  73. Client should ignore all events up to and including next SYN_REPORT
  74. event and query the device (using EVIOCG* ioctls) to obtain its
  75. current state.
  76. EV_KEY
  77. ------
  78. EV_KEY events take the form KEY_<name> or BTN_<name>. For example, KEY_A is used
  79. to represent the 'A' key on a keyboard. When a key is depressed, an event with
  80. the key's code is emitted with value 1. When the key is released, an event is
  81. emitted with value 0. Some hardware send events when a key is repeated. These
  82. events have a value of 2. In general, KEY_<name> is used for keyboard keys, and
  83. BTN_<name> is used for other types of momentary switch events.
  84. A few EV_KEY codes have special meanings:
  85. * BTN_TOOL_<name>:
  86. - These codes are used in conjunction with input trackpads, tablets, and
  87. touchscreens. These devices may be used with fingers, pens, or other tools.
  88. When an event occurs and a tool is used, the corresponding BTN_TOOL_<name>
  89. code should be set to a value of 1. When the tool is no longer interacting
  90. with the input device, the BTN_TOOL_<name> code should be reset to 0. All
  91. trackpads, tablets, and touchscreens should use at least one BTN_TOOL_<name>
  92. code when events are generated.
  93. * BTN_TOUCH:
  94. BTN_TOUCH is used for touch contact. While an input tool is determined to be
  95. within meaningful physical contact, the value of this property must be set
  96. to 1. Meaningful physical contact may mean any contact, or it may mean
  97. contact conditioned by an implementation defined property. For example, a
  98. touchpad may set the value to 1 only when the touch pressure rises above a
  99. certain value. BTN_TOUCH may be combined with BTN_TOOL_<name> codes. For
  100. example, a pen tablet may set BTN_TOOL_PEN to 1 and BTN_TOUCH to 0 while the
  101. pen is hovering over but not touching the tablet surface.
  102. Note: For appropriate function of the legacy mousedev emulation driver,
  103. BTN_TOUCH must be the first evdev code emitted in a synchronization frame.
  104. Note: Historically a touch device with BTN_TOOL_FINGER and BTN_TOUCH was
  105. interpreted as a touchpad by userspace, while a similar device without
  106. BTN_TOOL_FINGER was interpreted as a touchscreen. For backwards compatibility
  107. with current userspace it is recommended to follow this distinction. In the
  108. future, this distinction will be deprecated and the device properties ioctl
  109. EVIOCGPROP, defined in linux/input.h, will be used to convey the device type.
  110. * BTN_TOOL_FINGER, BTN_TOOL_DOUBLETAP, BTN_TOOL_TRIPLETAP, BTN_TOOL_QUADTAP:
  111. - These codes denote one, two, three, and four finger interaction on a
  112. trackpad or touchscreen. For example, if the user uses two fingers and moves
  113. them on the touchpad in an effort to scroll content on screen,
  114. BTN_TOOL_DOUBLETAP should be set to value 1 for the duration of the motion.
  115. Note that all BTN_TOOL_<name> codes and the BTN_TOUCH code are orthogonal in
  116. purpose. A trackpad event generated by finger touches should generate events
  117. for one code from each group. At most only one of these BTN_TOOL_<name>
  118. codes should have a value of 1 during any synchronization frame.
  119. Note: Historically some drivers emitted multiple of the finger count codes with
  120. a value of 1 in the same synchronization frame. This usage is deprecated.
  121. Note: In multitouch drivers, the input_mt_report_finger_count() function should
  122. be used to emit these codes. Please see multi-touch-protocol.txt for details.
  123. EV_REL
  124. ------
  125. EV_REL events describe relative changes in a property. For example, a mouse may
  126. move to the left by a certain number of units, but its absolute position in
  127. space is unknown. If the absolute position is known, EV_ABS codes should be used
  128. instead of EV_REL codes.
  129. A few EV_REL codes have special meanings:
  130. * REL_WHEEL, REL_HWHEEL:
  131. - These codes are used for vertical and horizontal scroll wheels,
  132. respectively. The value is the number of detents moved on the wheel, the
  133. physical size of which varies by device. For high-resolution wheels
  134. this may be an approximation based on the high-resolution scroll events,
  135. see REL_WHEEL_HI_RES. These event codes are legacy codes and
  136. REL_WHEEL_HI_RES and REL_HWHEEL_HI_RES should be preferred where
  137. available.
  138. * REL_WHEEL_HI_RES, REL_HWHEEL_HI_RES:
  139. - High-resolution scroll wheel data. The accumulated value 120 represents
  140. movement by one detent. For devices that do not provide high-resolution
  141. scrolling, the value is always a multiple of 120. For devices with
  142. high-resolution scrolling, the value may be a fraction of 120.
  143. If a vertical scroll wheel supports high-resolution scrolling, this code
  144. will be emitted in addition to REL_WHEEL or REL_HWHEEL. The REL_WHEEL
  145. and REL_HWHEEL may be an approximation based on the high-resolution
  146. scroll events. There is no guarantee that the high-resolution data
  147. is a multiple of 120 at the time of an emulated REL_WHEEL or REL_HWHEEL
  148. event.
  149. EV_ABS
  150. ------
  151. EV_ABS events describe absolute changes in a property. For example, a touchpad
  152. may emit coordinates for a touch location.
  153. A few EV_ABS codes have special meanings:
  154. * ABS_DISTANCE:
  155. - Used to describe the distance of a tool from an interaction surface. This
  156. event should only be emitted while the tool is hovering, meaning in close
  157. proximity of the device and while the value of the BTN_TOUCH code is 0. If
  158. the input device may be used freely in three dimensions, consider ABS_Z
  159. instead.
  160. - BTN_TOOL_<name> should be set to 1 when the tool comes into detectable
  161. proximity and set to 0 when the tool leaves detectable proximity.
  162. BTN_TOOL_<name> signals the type of tool that is currently detected by the
  163. hardware and is otherwise independent of ABS_DISTANCE and/or BTN_TOUCH.
  164. * ABS_MT_<name>:
  165. - Used to describe multitouch input events. Please see
  166. multi-touch-protocol.txt for details.
  167. EV_SW
  168. -----
  169. EV_SW events describe stateful binary switches. For example, the SW_LID code is
  170. used to denote when a laptop lid is closed.
  171. Upon binding to a device or resuming from suspend, a driver must report
  172. the current switch state. This ensures that the device, kernel, and userspace
  173. state is in sync.
  174. Upon resume, if the switch state is the same as before suspend, then the input
  175. subsystem will filter out the duplicate switch state reports. The driver does
  176. not need to keep the state of the switch at any time.
  177. EV_MSC
  178. ------
  179. EV_MSC events are used for input and output events that do not fall under other
  180. categories.
  181. A few EV_MSC codes have special meaning:
  182. * MSC_TIMESTAMP:
  183. - Used to report the number of microseconds since the last reset. This event
  184. should be coded as an uint32 value, which is allowed to wrap around with
  185. no special consequence. It is assumed that the time difference between two
  186. consecutive events is reliable on a reasonable time scale (hours).
  187. A reset to zero can happen, in which case the time since the last event is
  188. unknown. If the device does not provide this information, the driver must
  189. not provide it to user space.
  190. EV_LED
  191. ------
  192. EV_LED events are used for input and output to set and query the state of
  193. various LEDs on devices.
  194. EV_REP
  195. ------
  196. EV_REP events are used for specifying autorepeating events.
  197. EV_SND
  198. ------
  199. EV_SND events are used for sending sound commands to simple sound output
  200. devices.
  201. EV_FF
  202. -----
  203. EV_FF events are used to initialize a force feedback capable device and to cause
  204. such device to feedback.
  205. EV_PWR
  206. ------
  207. EV_PWR events are a special type of event used specifically for power
  208. management. Its usage is not well defined. To be addressed later.
  209. Device properties
  210. =================
  211. Normally, userspace sets up an input device based on the data it emits,
  212. i.e., the event types. In the case of two devices emitting the same event
  213. types, additional information can be provided in the form of device
  214. properties.
  215. INPUT_PROP_DIRECT + INPUT_PROP_POINTER
  216. --------------------------------------
  217. The INPUT_PROP_DIRECT property indicates that device coordinates should be
  218. directly mapped to screen coordinates (not taking into account trivial
  219. transformations, such as scaling, flipping and rotating). Non-direct input
  220. devices require non-trivial transformation, such as absolute to relative
  221. transformation for touchpads. Typical direct input devices: touchscreens,
  222. drawing tablets; non-direct devices: touchpads, mice.
  223. The INPUT_PROP_POINTER property indicates that the device is not transposed
  224. on the screen and thus requires use of an on-screen pointer to trace user's
  225. movements. Typical pointer devices: touchpads, tablets, mice; non-pointer
  226. device: touchscreen.
  227. If neither INPUT_PROP_DIRECT or INPUT_PROP_POINTER are set, the property is
  228. considered undefined and the device type should be deduced in the
  229. traditional way, using emitted event types.
  230. INPUT_PROP_BUTTONPAD
  231. --------------------
  232. For touchpads where the button is placed beneath the surface, such that
  233. pressing down on the pad causes a button click, this property should be
  234. set. Common in clickpad notebooks and macbooks from 2009 and onwards.
  235. Originally, the buttonpad property was coded into the bcm5974 driver
  236. version field under the name integrated button. For backwards
  237. compatibility, both methods need to be checked in userspace.
  238. INPUT_PROP_SEMI_MT
  239. ------------------
  240. Some touchpads, most common between 2008 and 2011, can detect the presence
  241. of multiple contacts without resolving the individual positions; only the
  242. number of contacts and a rectangular shape is known. For such
  243. touchpads, the semi-mt property should be set.
  244. Depending on the device, the rectangle may enclose all touches, like a
  245. bounding box, or just some of them, for instance the two most recent
  246. touches. The diversity makes the rectangle of limited use, but some
  247. gestures can normally be extracted from it.
  248. If INPUT_PROP_SEMI_MT is not set, the device is assumed to be a true MT
  249. device.
  250. INPUT_PROP_TOPBUTTONPAD
  251. -----------------------
  252. Some laptops, most notably the Lenovo 40 series provide a trackstick
  253. device but do not have physical buttons associated with the trackstick
  254. device. Instead, the top area of the touchpad is marked to show
  255. visual/haptic areas for left, middle, right buttons intended to be used
  256. with the trackstick.
  257. If INPUT_PROP_TOPBUTTONPAD is set, userspace should emulate buttons
  258. accordingly. This property does not affect kernel behavior.
  259. The kernel does not provide button emulation for such devices but treats
  260. them as any other INPUT_PROP_BUTTONPAD device.
  261. INPUT_PROP_ACCELEROMETER
  262. ------------------------
  263. Directional axes on this device (absolute and/or relative x, y, z) represent
  264. accelerometer data. Some devices also report gyroscope data, which devices
  265. can report through the rotational axes (absolute and/or relative rx, ry, rz).
  266. All other axes retain their meaning. A device must not mix
  267. regular directional axes and accelerometer axes on the same event node.
  268. Guidelines
  269. ==========
  270. The guidelines below ensure proper single-touch and multi-finger functionality.
  271. For multi-touch functionality, see the multi-touch-protocol.txt document for
  272. more information.
  273. Mice
  274. ----
  275. REL_{X,Y} must be reported when the mouse moves. BTN_LEFT must be used to report
  276. the primary button press. BTN_{MIDDLE,RIGHT,4,5,etc.} should be used to report
  277. further buttons of the device. REL_WHEEL and REL_HWHEEL should be used to report
  278. scroll wheel events where available.
  279. Touchscreens
  280. ------------
  281. ABS_{X,Y} must be reported with the location of the touch. BTN_TOUCH must be
  282. used to report when a touch is active on the screen.
  283. BTN_{MOUSE,LEFT,MIDDLE,RIGHT} must not be reported as the result of touch
  284. contact. BTN_TOOL_<name> events should be reported where possible.
  285. For new hardware, INPUT_PROP_DIRECT should be set.
  286. Trackpads
  287. ---------
  288. Legacy trackpads that only provide relative position information must report
  289. events like mice described above.
  290. Trackpads that provide absolute touch position must report ABS_{X,Y} for the
  291. location of the touch. BTN_TOUCH should be used to report when a touch is active
  292. on the trackpad. Where multi-finger support is available, BTN_TOOL_<name> should
  293. be used to report the number of touches active on the trackpad.
  294. For new hardware, INPUT_PROP_POINTER should be set.
  295. Tablets
  296. -------
  297. BTN_TOOL_<name> events must be reported when a stylus or other tool is active on
  298. the tablet. ABS_{X,Y} must be reported with the location of the tool. BTN_TOUCH
  299. should be used to report when the tool is in contact with the tablet.
  300. BTN_{STYLUS,STYLUS2} should be used to report buttons on the tool itself. Any
  301. button may be used for buttons on the tablet except BTN_{MOUSE,LEFT}.
  302. BTN_{0,1,2,etc} are good generic codes for unlabeled buttons. Do not use
  303. meaningful buttons, like BTN_FORWARD, unless the button is labeled for that
  304. purpose on the device.
  305. For new hardware, both INPUT_PROP_DIRECT and INPUT_PROP_POINTER should be set.