1 .. _input-event-codes:
2
3 =================
4 Input event codes
5 =================
6
7
8 The input protocol uses a map of types and codes to express input device values
9 to userspace. This document describes the types and codes and how and when they
10 may be used.
11
12 A single hardware event generates multiple input events. Each input event
13 contains the new value of a single data item. A special event type, EV_SYN, is
14 used to separate input events into packets of input data changes occurring at
15 the same moment in time. In the following, the term "event" refers to a single
16 input event encompassing a type, code, and value.
17
18 The input protocol is a stateful protocol. Events are emitted only when values
19 of event codes have changed. However, the state is maintained within the Linux
20 input subsystem; drivers do not need to maintain the state and may attempt to
21 emit unchanged values without harm. Userspace may obtain the current state of
22 event code values using the EVIOCG* ioctls defined in linux/input.h. The event
23 reports supported by a device are also provided by sysfs in
24 class/input/event*/device/capabilities/, and the properties of a device are
25 provided in class/input/event*/device/properties.
26
27 Event types
28 ===========
29
30 Event types are groupings of codes under a logical input construct. Each
31 type has a set of applicable codes to be used in generating events. See the
32 Codes section for details on valid codes for each type.
33
34 * EV_SYN:
35
36 - Used as markers to separate events. Events may be separated in time or in
37 space, such as with the multitouch protocol.
38
39 * EV_KEY:
40
41 - Used to describe state changes of keyboards, buttons, or other key-like
42 devices.
43
44 * EV_REL:
45
46 - Used to describe relative axis value changes, e.g. moving the mouse 5 units
47 to the left.
48
49 * EV_ABS:
50
51 - Used to describe absolute axis value changes, e.g. describing the
52 coordinates of a touch on a touchscreen.
53
54 * EV_MSC:
55
56 - Used to describe miscellaneous input data that do not fit into other types.
57
58 * EV_SW:
59
60 - Used to describe binary state input switches.
61
62 * EV_LED:
63
64 - Used to turn LEDs on devices on and off.
65
66 * EV_SND:
67
68 - Used to output sound to devices.
69
70 * EV_REP:
71
72 - Used for autorepeating devices.
73
74 * EV_FF:
75
76 - Used to send force feedback commands to an input device.
77
78 * EV_PWR:
79
80 - A special type for power button and switch input.
81
82 * EV_FF_STATUS:
83
84 - Used to receive force feedback device status.
85
86 Event codes
87 ===========
88
89 Event codes define the precise type of event.
90
91 EV_SYN
92 ------
93
94 EV_SYN event values are undefined. Their usage is defined only by when they are
95 sent in the evdev event stream.
96
97 * SYN_REPORT:
98
99 - Used to synchronize and separate events into packets of input data changes
100 occurring at the same moment in time. For example, motion of a mouse may set
101 the REL_X and REL_Y values for one motion, then emit a SYN_REPORT. The next
102 motion will emit more REL_X and REL_Y values and send another SYN_REPORT.
103
104 * SYN_CONFIG:
105
106 - TBD
107
108 * SYN_MT_REPORT:
109
110 - Used to synchronize and separate touch events. See the
111 multi-touch-protocol.txt document for more information.
112
113 * SYN_DROPPED:
114
115 - Used to indicate buffer overrun in the evdev client's event queue.
116 Client should ignore all events up to and including next SYN_REPORT
117 event and query the device (using EVIOCG* ioctls) to obtain its
118 current state.
119
120 EV_KEY
121 ------
122
123 EV_KEY events take the form KEY_<name> or BTN_<name>. For example, KEY_A is used
124 to represent the 'A' key on a keyboard. When a key is depressed, an event with
125 the key's code is emitted with value 1. When the key is released, an event is
126 emitted with value 0. Some hardware send events when a key is repeated. These
127 events have a value of 2. In general, KEY_<name> is used for keyboard keys, and
128 BTN_<name> is used for other types of momentary switch events.
129
130 A few EV_KEY codes have special meanings:
131
132 * BTN_TOOL_<name>:
133
134 - These codes are used in conjunction with input trackpads, tablets, and
135 touchscreens. These devices may be used with fingers, pens, or other tools.
136 When an event occurs and a tool is used, the corresponding BTN_TOOL_<name>
137 code should be set to a value of 1. When the tool is no longer interacting
138 with the input device, the BTN_TOOL_<name> code should be reset to 0. All
139 trackpads, tablets, and touchscreens should use at least one BTN_TOOL_<name>
140 code when events are generated. Likewise all trackpads, tablets, and
141 touchscreens should export only one BTN_TOOL_<name> at a time. To not break
142 existing userspace, it is recommended to not switch tool in one EV_SYN frame
143 but first emitting the old BTN_TOOL_<name> at 0, then emit one SYN_REPORT
144 and then set the new BTN_TOOL_<name> at 1.
145
146 * BTN_TOUCH:
147
148 BTN_TOUCH is used for touch contact. While an input tool is determined to be
149 within meaningful physical contact, the value of this property must be set
150 to 1. Meaningful physical contact may mean any contact, or it may mean
151 contact conditioned by an implementation defined property. For example, a
152 touchpad may set the value to 1 only when the touch pressure rises above a
153 certain value. BTN_TOUCH may be combined with BTN_TOOL_<name> codes. For
154 example, a pen tablet may set BTN_TOOL_PEN to 1 and BTN_TOUCH to 0 while the
155 pen is hovering over but not touching the tablet surface.
156
157 Note: For appropriate function of the legacy mousedev emulation driver,
158 BTN_TOUCH must be the first evdev code emitted in a synchronization frame.
159
160 Note: Historically a touch device with BTN_TOOL_FINGER and BTN_TOUCH was
161 interpreted as a touchpad by userspace, while a similar device without
162 BTN_TOOL_FINGER was interpreted as a touchscreen. For backwards compatibility
163 with current userspace it is recommended to follow this distinction. In the
164 future, this distinction will be deprecated and the device properties ioctl
165 EVIOCGPROP, defined in linux/input.h, will be used to convey the device type.
166
167 * BTN_TOOL_FINGER, BTN_TOOL_DOUBLETAP, BTN_TOOL_TRIPLETAP, BTN_TOOL_QUADTAP:
168
169 - These codes denote one, two, three, and four finger interaction on a
170 trackpad or touchscreen. For example, if the user uses two fingers and moves
171 them on the touchpad in an effort to scroll content on screen,
172 BTN_TOOL_DOUBLETAP should be set to value 1 for the duration of the motion.
173 Note that all BTN_TOOL_<name> codes and the BTN_TOUCH code are orthogonal in
174 purpose. A trackpad event generated by finger touches should generate events
175 for one code from each group. At most only one of these BTN_TOOL_<name>
176 codes should have a value of 1 during any synchronization frame.
177
178 Note: Historically some drivers emitted multiple of the finger count codes with
179 a value of 1 in the same synchronization frame. This usage is deprecated.
180
181 Note: In multitouch drivers, the input_mt_report_finger_count() function should
182 be used to emit these codes. Please see multi-touch-protocol.txt for details.
183
184 EV_REL
185 ------
186
187 EV_REL events describe relative changes in a property. For example, a mouse may
188 move to the left by a certain number of units, but its absolute position in
189 space is unknown. If the absolute position is known, EV_ABS codes should be used
190 instead of EV_REL codes.
191
192 A few EV_REL codes have special meanings:
193
194 * REL_WHEEL, REL_HWHEEL:
195
196 - These codes are used for vertical and horizontal scroll wheels,
197 respectively. The value is the number of detents moved on the wheel, the
198 physical size of which varies by device. For high-resolution wheels
199 this may be an approximation based on the high-resolution scroll events,
200 see REL_WHEEL_HI_RES. These event codes are legacy codes and
201 REL_WHEEL_HI_RES and REL_HWHEEL_HI_RES should be preferred where
202 available.
203
204 * REL_WHEEL_HI_RES, REL_HWHEEL_HI_RES:
205
206 - High-resolution scroll wheel data. The accumulated value 120 represents
207 movement by one detent. For devices that do not provide high-resolution
208 scrolling, the value is always a multiple of 120. For devices with
209 high-resolution scrolling, the value may be a fraction of 120.
210
211 If a vertical scroll wheel supports high-resolution scrolling, this code
212 will be emitted in addition to REL_WHEEL or REL_HWHEEL. The REL_WHEEL
213 and REL_HWHEEL may be an approximation based on the high-resolution
214 scroll events. There is no guarantee that the high-resolution data
215 is a multiple of 120 at the time of an emulated REL_WHEEL or REL_HWHEEL
216 event.
217
218 EV_ABS
219 ------
220
221 EV_ABS events describe absolute changes in a property. For example, a touchpad
222 may emit coordinates for a touch location.
223
224 A few EV_ABS codes have special meanings:
225
226 * ABS_DISTANCE:
227
228 - Used to describe the distance of a tool from an interaction surface. This
229 event should only be emitted while the tool is hovering, meaning in close
230 proximity of the device and while the value of the BTN_TOUCH code is 0. If
231 the input device may be used freely in three dimensions, consider ABS_Z
232 instead.
233 - BTN_TOOL_<name> should be set to 1 when the tool comes into detectable
234 proximity and set to 0 when the tool leaves detectable proximity.
235 BTN_TOOL_<name> signals the type of tool that is currently detected by the
236 hardware and is otherwise independent of ABS_DISTANCE and/or BTN_TOUCH.
237
238 * ABS_PROFILE:
239
240 - Used to describe the state of a multi-value profile switch. An event is
241 emitted only when the selected profile changes, indicating the newly
242 selected profile value.
243
244 * ABS_MT_<name>:
245
246 - Used to describe multitouch input events. Please see
247 multi-touch-protocol.txt for details.
248
249 * ABS_PRESSURE/ABS_MT_PRESSURE:
250
251 - For touch devices, many devices converted contact size into pressure.
252 A finger flattens with pressure, causing a larger contact area and thus
253 pressure and contact size are directly related. This is not the case
254 for other devices, for example digitizers and touchpads with a true
255 pressure sensor ("pressure pads").
256
257 A device should set the resolution of the axis to indicate whether the
258 pressure is in measurable units. If the resolution is zero, the
259 pressure data is in arbitrary units. If the resolution is non-zero, the
260 pressure data is in units/gram. For example, a value of 10 with a
261 resolution of 1 represents 10 gram, a value of 10 with a resolution of
262 1000 represents 10 microgram.
263
264 EV_SW
265 -----
266
267 EV_SW events describe stateful binary switches. For example, the SW_LID code is
268 used to denote when a laptop lid is closed.
269
270 Upon binding to a device or resuming from suspend, a driver must report
271 the current switch state. This ensures that the device, kernel, and userspace
272 state is in sync.
273
274 Upon resume, if the switch state is the same as before suspend, then the input
275 subsystem will filter out the duplicate switch state reports. The driver does
276 not need to keep the state of the switch at any time.
277
278 EV_MSC
279 ------
280
281 EV_MSC events are used for input and output events that do not fall under other
282 categories.
283
284 A few EV_MSC codes have special meaning:
285
286 * MSC_TIMESTAMP:
287
288 - Used to report the number of microseconds since the last reset. This event
289 should be coded as an uint32 value, which is allowed to wrap around with
290 no special consequence. It is assumed that the time difference between two
291 consecutive events is reliable on a reasonable time scale (hours).
292 A reset to zero can happen, in which case the time since the last event is
293 unknown. If the device does not provide this information, the driver must
294 not provide it to user space.
295
296 EV_LED
297 ------
298
299 EV_LED events are used for input and output to set and query the state of
300 various LEDs on devices.
301
302 EV_REP
303 ------
304
305 EV_REP events are used for specifying autorepeating events.
306
307 EV_SND
308 ------
309
310 EV_SND events are used for sending sound commands to simple sound output
311 devices.
312
313 EV_FF
314 -----
315
316 EV_FF events are used to initialize a force feedback capable device and to cause
317 such device to feedback.
318
319 EV_PWR
320 ------
321
322 EV_PWR events are a special type of event used specifically for power
323 management. Its usage is not well defined. To be addressed later.
324
325 Device properties
326 =================
327
328 Normally, userspace sets up an input device based on the data it emits,
329 i.e., the event types. In the case of two devices emitting the same event
330 types, additional information can be provided in the form of device
331 properties.
332
333 INPUT_PROP_DIRECT + INPUT_PROP_POINTER
334 --------------------------------------
335
336 The INPUT_PROP_DIRECT property indicates that device coordinates should be
337 directly mapped to screen coordinates (not taking into account trivial
338 transformations, such as scaling, flipping and rotating). Non-direct input
339 devices require non-trivial transformation, such as absolute to relative
340 transformation for touchpads. Typical direct input devices: touchscreens,
341 drawing tablets; non-direct devices: touchpads, mice.
342
343 The INPUT_PROP_POINTER property indicates that the device is not transposed
344 on the screen and thus requires use of an on-screen pointer to trace user's
345 movements. Typical pointer devices: touchpads, tablets, mice; non-pointer
346 device: touchscreen.
347
348 If neither INPUT_PROP_DIRECT or INPUT_PROP_POINTER are set, the property is
349 considered undefined and the device type should be deduced in the
350 traditional way, using emitted event types.
351
352 INPUT_PROP_BUTTONPAD
353 --------------------
354
355 For touchpads where the button is placed beneath the surface, such that
356 pressing down on the pad causes a button click, this property should be
357 set. Common in Clickpad notebooks and Macbooks from 2009 and onwards.
358
359 Originally, the buttonpad property was coded into the bcm5974 driver
360 version field under the name integrated button. For backwards
361 compatibility, both methods need to be checked in userspace.
362
363 INPUT_PROP_SEMI_MT
364 ------------------
365
366 Some touchpads, most common between 2008 and 2011, can detect the presence
367 of multiple contacts without resolving the individual positions; only the
368 number of contacts and a rectangular shape is known. For such
369 touchpads, the SEMI_MT property should be set.
370
371 Depending on the device, the rectangle may enclose all touches, like a
372 bounding box, or just some of them, for instance the two most recent
373 touches. The diversity makes the rectangle of limited use, but some
374 gestures can normally be extracted from it.
375
376 If INPUT_PROP_SEMI_MT is not set, the device is assumed to be a true MT
377 device.
378
379 INPUT_PROP_TOPBUTTONPAD
380 -----------------------
381
382 Some laptops, most notably the Lenovo 40 series provide a trackstick
383 device but do not have physical buttons associated with the trackstick
384 device. Instead, the top area of the touchpad is marked to show
385 visual/haptic areas for left, middle, right buttons intended to be used
386 with the trackstick.
387
388 If INPUT_PROP_TOPBUTTONPAD is set, userspace should emulate buttons
389 accordingly. This property does not affect kernel behavior.
390 The kernel does not provide button emulation for such devices but treats
391 them as any other INPUT_PROP_BUTTONPAD device.
392
393 INPUT_PROP_ACCELEROMETER
394 ------------------------
395
396 Directional axes on this device (absolute and/or relative x, y, z) represent
397 accelerometer data. Some devices also report gyroscope data, which devices
398 can report through the rotational axes (absolute and/or relative rx, ry, rz).
399
400 All other axes retain their meaning. A device must not mix
401 regular directional axes and accelerometer axes on the same event node.
402
403 Guidelines
404 ==========
405
406 The guidelines below ensure proper single-touch and multi-finger functionality.
407 For multi-touch functionality, see the multi-touch-protocol.rst document for
408 more information.
409
410 Mice
411 ----
412
413 REL_{X,Y} must be reported when the mouse moves. BTN_LEFT must be used to report
414 the primary button press. BTN_{MIDDLE,RIGHT,4,5,etc.} should be used to report
415 further buttons of the device. REL_WHEEL and REL_HWHEEL should be used to report
416 scroll wheel events where available.
417
418 Touchscreens
419 ------------
420
421 ABS_{X,Y} must be reported with the location of the touch. BTN_TOUCH must be
422 used to report when a touch is active on the screen.
423 BTN_{MOUSE,LEFT,MIDDLE,RIGHT} must not be reported as the result of touch
424 contact. BTN_TOOL_<name> events should be reported where possible.
425
426 For new hardware, INPUT_PROP_DIRECT should be set.
427
428 Trackpads
429 ---------
430
431 Legacy trackpads that only provide relative position information must report
432 events like mice described above.
433
434 Trackpads that provide absolute touch position must report ABS_{X,Y} for the
435 location of the touch. BTN_TOUCH should be used to report when a touch is active
436 on the trackpad. Where multi-finger support is available, BTN_TOOL_<name> should
437 be used to report the number of touches active on the trackpad.
438
439 For new hardware, INPUT_PROP_POINTER should be set.
440
441 Tablets
442 -------
443
444 BTN_TOOL_<name> events must be reported when a stylus or other tool is active on
445 the tablet. ABS_{X,Y} must be reported with the location of the tool. BTN_TOUCH
446 should be used to report when the tool is in contact with the tablet.
447 BTN_{STYLUS,STYLUS2} should be used to report buttons on the tool itself. Any
448 button may be used for buttons on the tablet except BTN_{MOUSE,LEFT}.
449 BTN_{0,1,2,etc} are good generic codes for unlabeled buttons. Do not use
450 meaningful buttons, like BTN_FORWARD, unless the button is labeled for that
451 purpose on the device.
452
453 For new hardware, both INPUT_PROP_DIRECT and INPUT_PROP_POINTER should be set.
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