1.. _input-event-codes:
2
3=================
4Input event codes
5=================
6
7
8The input protocol uses a map of types and codes to express input device values
9to userspace. This document describes the types and codes and how and when they
10may be used.
11
12A single hardware event generates multiple input events. Each input event
13contains the new value of a single data item. A special event type, EV_SYN, is
14used to separate input events into packets of input data changes occurring at
15the same moment in time. In the following, the term "event" refers to a single
16input event encompassing a type, code, and value.
17
18The input protocol is a stateful protocol. Events are emitted only when values
19of event codes have changed. However, the state is maintained within the Linux
20input subsystem; drivers do not need to maintain the state and may attempt to
21emit unchanged values without harm. Userspace may obtain the current state of
22event code values using the EVIOCG* ioctls defined in linux/input.h. The event
23reports supported by a device are also provided by sysfs in
24class/input/event*/device/capabilities/, and the properties of a device are
25provided in class/input/event*/device/properties.
26
27Event types
28===========
29
30Event types are groupings of codes under a logical input construct. Each
31type has a set of applicable codes to be used in generating events. See the
32Codes 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
86Event codes
87===========
88
89Event codes define the precise type of event.
90
91EV_SYN
92------
93
94EV_SYN event values are undefined. Their usage is defined only by when they are
95sent 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
120EV_KEY
121------
122
123EV_KEY events take the form KEY_<name> or BTN_<name>. For example, KEY_A is used
124to represent the 'A' key on a keyboard. When a key is depressed, an event with
125the key's code is emitted with value 1. When the key is released, an event is
126emitted with value 0. Some hardware send events when a key is repeated. These
127events have a value of 2. In general, KEY_<name> is used for keyboard keys, and
128BTN_<name> is used for other types of momentary switch events.
129
130A 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
157Note: For appropriate function of the legacy mousedev emulation driver,
158BTN_TOUCH must be the first evdev code emitted in a synchronization frame.
159
160Note: Historically a touch device with BTN_TOOL_FINGER and BTN_TOUCH was
161interpreted as a touchpad by userspace, while a similar device without
162BTN_TOOL_FINGER was interpreted as a touchscreen. For backwards compatibility
163with current userspace it is recommended to follow this distinction. In the
164future, this distinction will be deprecated and the device properties ioctl
165EVIOCGPROP, 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
178Note: Historically some drivers emitted multiple of the finger count codes with
179a value of 1 in the same synchronization frame. This usage is deprecated.
180
181Note: In multitouch drivers, the input_mt_report_finger_count() function should
182be used to emit these codes. Please see multi-touch-protocol.txt for details.
183
184EV_REL
185------
186
187EV_REL events describe relative changes in a property. For example, a mouse may
188move to the left by a certain number of units, but its absolute position in
189space is unknown. If the absolute position is known, EV_ABS codes should be used
190instead of EV_REL codes.
191
192A 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
218EV_ABS
219------
220
221EV_ABS events describe absolute changes in a property. For example, a touchpad
222may emit coordinates for a touch location.
223
224A 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_MT_<name>:
239
240  - Used to describe multitouch input events. Please see
241    multi-touch-protocol.txt for details.
242
243* ABS_PRESSURE/ABS_MT_PRESSURE:
244
245   - For touch devices, many devices converted contact size into pressure.
246     A finger flattens with pressure, causing a larger contact area and thus
247     pressure and contact size are directly related. This is not the case
248     for other devices, for example digitizers and touchpads with a true
249     pressure sensor ("pressure pads").
250
251     A device should set the resolution of the axis to indicate whether the
252     pressure is in measurable units. If the resolution is zero, the
253     pressure data is in arbitrary units. If the resolution is non-zero, the
254     pressure data is in units/gram. For example, a value of 10 with a
255     resolution of 1 represents 10 gram, a value of 10 with a resolution of
256     1000 represents 10 microgram.
257
258EV_SW
259-----
260
261EV_SW events describe stateful binary switches. For example, the SW_LID code is
262used to denote when a laptop lid is closed.
263
264Upon binding to a device or resuming from suspend, a driver must report
265the current switch state. This ensures that the device, kernel, and userspace
266state is in sync.
267
268Upon resume, if the switch state is the same as before suspend, then the input
269subsystem will filter out the duplicate switch state reports. The driver does
270not need to keep the state of the switch at any time.
271
272EV_MSC
273------
274
275EV_MSC events are used for input and output events that do not fall under other
276categories.
277
278A few EV_MSC codes have special meaning:
279
280* MSC_TIMESTAMP:
281
282  - Used to report the number of microseconds since the last reset. This event
283    should be coded as an uint32 value, which is allowed to wrap around with
284    no special consequence. It is assumed that the time difference between two
285    consecutive events is reliable on a reasonable time scale (hours).
286    A reset to zero can happen, in which case the time since the last event is
287    unknown.  If the device does not provide this information, the driver must
288    not provide it to user space.
289
290EV_LED
291------
292
293EV_LED events are used for input and output to set and query the state of
294various LEDs on devices.
295
296EV_REP
297------
298
299EV_REP events are used for specifying autorepeating events.
300
301EV_SND
302------
303
304EV_SND events are used for sending sound commands to simple sound output
305devices.
306
307EV_FF
308-----
309
310EV_FF events are used to initialize a force feedback capable device and to cause
311such device to feedback.
312
313EV_PWR
314------
315
316EV_PWR events are a special type of event used specifically for power
317management. Its usage is not well defined. To be addressed later.
318
319Device properties
320=================
321
322Normally, userspace sets up an input device based on the data it emits,
323i.e., the event types. In the case of two devices emitting the same event
324types, additional information can be provided in the form of device
325properties.
326
327INPUT_PROP_DIRECT + INPUT_PROP_POINTER
328--------------------------------------
329
330The INPUT_PROP_DIRECT property indicates that device coordinates should be
331directly mapped to screen coordinates (not taking into account trivial
332transformations, such as scaling, flipping and rotating). Non-direct input
333devices require non-trivial transformation, such as absolute to relative
334transformation for touchpads. Typical direct input devices: touchscreens,
335drawing tablets; non-direct devices: touchpads, mice.
336
337The INPUT_PROP_POINTER property indicates that the device is not transposed
338on the screen and thus requires use of an on-screen pointer to trace user's
339movements.  Typical pointer devices: touchpads, tablets, mice; non-pointer
340device: touchscreen.
341
342If neither INPUT_PROP_DIRECT or INPUT_PROP_POINTER are set, the property is
343considered undefined and the device type should be deduced in the
344traditional way, using emitted event types.
345
346INPUT_PROP_BUTTONPAD
347--------------------
348
349For touchpads where the button is placed beneath the surface, such that
350pressing down on the pad causes a button click, this property should be
351set. Common in Clickpad notebooks and Macbooks from 2009 and onwards.
352
353Originally, the buttonpad property was coded into the bcm5974 driver
354version field under the name integrated button. For backwards
355compatibility, both methods need to be checked in userspace.
356
357INPUT_PROP_SEMI_MT
358------------------
359
360Some touchpads, most common between 2008 and 2011, can detect the presence
361of multiple contacts without resolving the individual positions; only the
362number of contacts and a rectangular shape is known. For such
363touchpads, the SEMI_MT property should be set.
364
365Depending on the device, the rectangle may enclose all touches, like a
366bounding box, or just some of them, for instance the two most recent
367touches. The diversity makes the rectangle of limited use, but some
368gestures can normally be extracted from it.
369
370If INPUT_PROP_SEMI_MT is not set, the device is assumed to be a true MT
371device.
372
373INPUT_PROP_TOPBUTTONPAD
374-----------------------
375
376Some laptops, most notably the Lenovo 40 series provide a trackstick
377device but do not have physical buttons associated with the trackstick
378device. Instead, the top area of the touchpad is marked to show
379visual/haptic areas for left, middle, right buttons intended to be used
380with the trackstick.
381
382If INPUT_PROP_TOPBUTTONPAD is set, userspace should emulate buttons
383accordingly. This property does not affect kernel behavior.
384The kernel does not provide button emulation for such devices but treats
385them as any other INPUT_PROP_BUTTONPAD device.
386
387INPUT_PROP_ACCELEROMETER
388------------------------
389
390Directional axes on this device (absolute and/or relative x, y, z) represent
391accelerometer data. Some devices also report gyroscope data, which devices
392can report through the rotational axes (absolute and/or relative rx, ry, rz).
393
394All other axes retain their meaning. A device must not mix
395regular directional axes and accelerometer axes on the same event node.
396
397Guidelines
398==========
399
400The guidelines below ensure proper single-touch and multi-finger functionality.
401For multi-touch functionality, see the multi-touch-protocol.rst document for
402more information.
403
404Mice
405----
406
407REL_{X,Y} must be reported when the mouse moves. BTN_LEFT must be used to report
408the primary button press. BTN_{MIDDLE,RIGHT,4,5,etc.} should be used to report
409further buttons of the device. REL_WHEEL and REL_HWHEEL should be used to report
410scroll wheel events where available.
411
412Touchscreens
413------------
414
415ABS_{X,Y} must be reported with the location of the touch. BTN_TOUCH must be
416used to report when a touch is active on the screen.
417BTN_{MOUSE,LEFT,MIDDLE,RIGHT} must not be reported as the result of touch
418contact. BTN_TOOL_<name> events should be reported where possible.
419
420For new hardware, INPUT_PROP_DIRECT should be set.
421
422Trackpads
423---------
424
425Legacy trackpads that only provide relative position information must report
426events like mice described above.
427
428Trackpads that provide absolute touch position must report ABS_{X,Y} for the
429location of the touch. BTN_TOUCH should be used to report when a touch is active
430on the trackpad. Where multi-finger support is available, BTN_TOOL_<name> should
431be used to report the number of touches active on the trackpad.
432
433For new hardware, INPUT_PROP_POINTER should be set.
434
435Tablets
436-------
437
438BTN_TOOL_<name> events must be reported when a stylus or other tool is active on
439the tablet. ABS_{X,Y} must be reported with the location of the tool. BTN_TOUCH
440should be used to report when the tool is in contact with the tablet.
441BTN_{STYLUS,STYLUS2} should be used to report buttons on the tool itself. Any
442button may be used for buttons on the tablet except BTN_{MOUSE,LEFT}.
443BTN_{0,1,2,etc} are good generic codes for unlabeled buttons. Do not use
444meaningful buttons, like BTN_FORWARD, unless the button is labeled for that
445purpose on the device.
446
447For new hardware, both INPUT_PROP_DIRECT and INPUT_PROP_POINTER should be set.
448