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Documentation / input / event-codes.txt




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Based on kernel version 3.16. Page generated on 2014-08-06 21:40 EST.

1	The input protocol uses a map of types and codes to express input device values
2	to userspace. This document describes the types and codes and how and when they
3	may be used.
4	
5	A single hardware event generates multiple input events. Each input event
6	contains the new value of a single data item. A special event type, EV_SYN, is
7	used to separate input events into packets of input data changes occurring at
8	the same moment in time. In the following, the term "event" refers to a single
9	input event encompassing a type, code, and value.
10	
11	The input protocol is a stateful protocol. Events are emitted only when values
12	of event codes have changed. However, the state is maintained within the Linux
13	input subsystem; drivers do not need to maintain the state and may attempt to
14	emit unchanged values without harm. Userspace may obtain the current state of
15	event code values using the EVIOCG* ioctls defined in linux/input.h. The event
16	reports supported by a device are also provided by sysfs in
17	class/input/event*/device/capabilities/, and the properties of a device are
18	provided in class/input/event*/device/properties.
19	
20	Event types:
21	===========
22	Event types are groupings of codes under a logical input construct. Each
23	type has a set of applicable codes to be used in generating events. See the
24	Codes 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	
66	Event codes:
67	===========
68	Event codes define the precise type of event.
69	
70	EV_SYN:
71	----------
72	EV_SYN event values are undefined. Their usage is defined only by when they are
73	sent 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	
94	EV_KEY:
95	----------
96	EV_KEY events take the form KEY_<name> or BTN_<name>. For example, KEY_A is used
97	to represent the 'A' key on a keyboard. When a key is depressed, an event with
98	the key's code is emitted with value 1. When the key is released, an event is
99	emitted with value 0. Some hardware send events when a key is repeated. These
100	events have a value of 2. In general, KEY_<name> is used for keyboard keys, and
101	BTN_<name> is used for other types of momentary switch events.
102	
103	A 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	
124	Note: For appropriate function of the legacy mousedev emulation driver,
125	BTN_TOUCH must be the first evdev code emitted in a synchronization frame.
126	
127	Note: Historically a touch device with BTN_TOOL_FINGER and BTN_TOUCH was
128	interpreted as a touchpad by userspace, while a similar device without
129	BTN_TOOL_FINGER was interpreted as a touchscreen. For backwards compatibility
130	with current userspace it is recommended to follow this distinction. In the
131	future, this distinction will be deprecated and the device properties ioctl
132	EVIOCGPROP, 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	
144	Note: Historically some drivers emitted multiple of the finger count codes with
145	a value of 1 in the same synchronization frame. This usage is deprecated.
146	
147	Note: In multitouch drivers, the input_mt_report_finger_count() function should
148	be used to emit these codes. Please see multi-touch-protocol.txt for details.
149	
150	EV_REL:
151	----------
152	EV_REL events describe relative changes in a property. For example, a mouse may
153	move to the left by a certain number of units, but its absolute position in
154	space is unknown. If the absolute position is known, EV_ABS codes should be used
155	instead of EV_REL codes.
156	
157	A 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	
163	EV_ABS:
164	----------
165	EV_ABS events describe absolute changes in a property. For example, a touchpad
166	may emit coordinates for a touch location.
167	
168	A 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	
181	EV_SW:
182	----------
183	EV_SW events describe stateful binary switches. For example, the SW_LID code is
184	used to denote when a laptop lid is closed.
185	
186	Upon binding to a device or resuming from suspend, a driver must report
187	the current switch state. This ensures that the device, kernel, and userspace
188	state is in sync.
189	
190	Upon resume, if the switch state is the same as before suspend, then the input
191	subsystem will filter out the duplicate switch state reports. The driver does
192	not need to keep the state of the switch at any time.
193	
194	EV_MSC:
195	----------
196	EV_MSC events are used for input and output events that do not fall under other
197	categories.
198	
199	A few EV_MSC codes have special meaning:
200	
201	* MSC_TIMESTAMP:
202	  - Used to report the number of microseconds since the last reset. This event
203	    should be coded as an uint32 value, which is allowed to wrap around with
204	    no special consequence. It is assumed that the time difference between two
205	    consecutive events is reliable on a reasonable time scale (hours).
206	    A reset to zero can happen, in which case the time since the last event is
207	    unknown.  If the device does not provide this information, the driver must
208	    not provide it to user space.
209	
210	EV_LED:
211	----------
212	EV_LED events are used for input and output to set and query the state of
213	various LEDs on devices.
214	
215	EV_REP:
216	----------
217	EV_REP events are used for specifying autorepeating events.
218	
219	EV_SND:
220	----------
221	EV_SND events are used for sending sound commands to simple sound output
222	devices.
223	
224	EV_FF:
225	----------
226	EV_FF events are used to initialize a force feedback capable device and to cause
227	such device to feedback.
228	
229	EV_PWR:
230	----------
231	EV_PWR events are a special type of event used specifically for power
232	mangement. Its usage is not well defined. To be addressed later.
233	
234	Device properties:
235	=================
236	Normally, userspace sets up an input device based on the data it emits,
237	i.e., the event types. In the case of two devices emitting the same event
238	types, additional information can be provided in the form of device
239	properties.
240	
241	INPUT_PROP_DIRECT + INPUT_PROP_POINTER:
242	--------------------------------------
243	The INPUT_PROP_DIRECT property indicates that device coordinates should be
244	directly mapped to screen coordinates (not taking into account trivial
245	transformations, such as scaling, flipping and rotating). Non-direct input
246	devices require non-trivial transformation, such as absolute to relative
247	transformation for touchpads. Typical direct input devices: touchscreens,
248	drawing tablets; non-direct devices: touchpads, mice.
249	
250	The INPUT_PROP_POINTER property indicates that the device is not transposed
251	on the screen and thus requires use of an on-screen pointer to trace user's
252	movements.  Typical pointer devices: touchpads, tablets, mice; non-pointer
253	device: touchscreen.
254	
255	If neither INPUT_PROP_DIRECT or INPUT_PROP_POINTER are set, the property is
256	considered undefined and the device type should be deduced in the
257	traditional way, using emitted event types.
258	
259	INPUT_PROP_BUTTONPAD:
260	--------------------
261	For touchpads where the button is placed beneath the surface, such that
262	pressing down on the pad causes a button click, this property should be
263	set. Common in clickpad notebooks and macbooks from 2009 and onwards.
264	
265	Originally, the buttonpad property was coded into the bcm5974 driver
266	version field under the name integrated button. For backwards
267	compatibility, both methods need to be checked in userspace.
268	
269	INPUT_PROP_SEMI_MT:
270	------------------
271	Some touchpads, most common between 2008 and 2011, can detect the presence
272	of multiple contacts without resolving the individual positions; only the
273	number of contacts and a rectangular shape is known. For such
274	touchpads, the semi-mt property should be set.
275	
276	Depending on the device, the rectangle may enclose all touches, like a
277	bounding box, or just some of them, for instance the two most recent
278	touches. The diversity makes the rectangle of limited use, but some
279	gestures can normally be extracted from it.
280	
281	If INPUT_PROP_SEMI_MT is not set, the device is assumed to be a true MT
282	device.
283	
284	INPUT_PROP_TOPBUTTONPAD:
285	-----------------------
286	Some laptops, most notably the Lenovo *40 series provide a trackstick
287	device but do not have physical buttons associated with the trackstick
288	device. Instead, the top area of the touchpad is marked to show
289	visual/haptic areas for left, middle, right buttons intended to be used
290	with the trackstick.
291	
292	If INPUT_PROP_TOPBUTTONPAD is set, userspace should emulate buttons
293	accordingly. This property does not affect kernel behavior.
294	The kernel does not provide button emulation for such devices but treats
295	them as any other INPUT_PROP_BUTTONPAD device.
296	
297	Guidelines:
298	==========
299	The guidelines below ensure proper single-touch and multi-finger functionality.
300	For multi-touch functionality, see the multi-touch-protocol.txt document for
301	more information.
302	
303	Mice:
304	----------
305	REL_{X,Y} must be reported when the mouse moves. BTN_LEFT must be used to report
306	the primary button press. BTN_{MIDDLE,RIGHT,4,5,etc.} should be used to report
307	further buttons of the device. REL_WHEEL and REL_HWHEEL should be used to report
308	scroll wheel events where available.
309	
310	Touchscreens:
311	----------
312	ABS_{X,Y} must be reported with the location of the touch. BTN_TOUCH must be
313	used to report when a touch is active on the screen.
314	BTN_{MOUSE,LEFT,MIDDLE,RIGHT} must not be reported as the result of touch
315	contact. BTN_TOOL_<name> events should be reported where possible.
316	
317	For new hardware, INPUT_PROP_DIRECT should be set.
318	
319	Trackpads:
320	----------
321	Legacy trackpads that only provide relative position information must report
322	events like mice described above.
323	
324	Trackpads that provide absolute touch position must report ABS_{X,Y} for the
325	location of the touch. BTN_TOUCH should be used to report when a touch is active
326	on the trackpad. Where multi-finger support is available, BTN_TOOL_<name> should
327	be used to report the number of touches active on the trackpad.
328	
329	For new hardware, INPUT_PROP_POINTER should be set.
330	
331	Tablets:
332	----------
333	BTN_TOOL_<name> events must be reported when a stylus or other tool is active on
334	the tablet. ABS_{X,Y} must be reported with the location of the tool. BTN_TOUCH
335	should be used to report when the tool is in contact with the tablet.
336	BTN_{STYLUS,STYLUS2} should be used to report buttons on the tool itself. Any
337	button may be used for buttons on the tablet except BTN_{MOUSE,LEFT}.
338	BTN_{0,1,2,etc} are good generic codes for unlabeled buttons. Do not use
339	meaningful buttons, like BTN_FORWARD, unless the button is labeled for that
340	purpose on the device.
341	
342	For new hardware, both INPUT_PROP_DIRECT and INPUT_PROP_POINTER should be set.
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