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Chase Douglasb1e064b2011-04-12 23:29:07 -07001The 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
20Types:
21==========
22Types are groupings of codes under a logical input construct. Each type has a
23set of applicable codes to be used in generating events. See the Codes section
24for 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
66Codes:
67==========
68Codes 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
Jeff Brown9fb0f142011-04-12 23:29:38 -070088* 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
Chase Douglasb1e064b2011-04-12 23:29:07 -070094EV_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
223Guidelines:
224==========
225The guidelines below ensure proper single-touch and multi-finger functionality.
226For multi-touch functionality, see the multi-touch-protocol.txt document for
227more information.
228
229Mice:
230----------
231REL_{X,Y} must be reported when the mouse moves. BTN_LEFT must be used to report
232the primary button press. BTN_{MIDDLE,RIGHT,4,5,etc.} should be used to report
233further buttons of the device. REL_WHEEL and REL_HWHEEL should be used to report
234scroll wheel events where available.
235
236Touchscreens:
237----------
238ABS_{X,Y} must be reported with the location of the touch. BTN_TOUCH must be
239used to report when a touch is active on the screen.
240BTN_{MOUSE,LEFT,MIDDLE,RIGHT} must not be reported as the result of touch
241contact. BTN_TOOL_<name> events should be reported where possible.
242
243Trackpads:
244----------
245Legacy trackpads that only provide relative position information must report
246events like mice described above.
247
248Trackpads that provide absolute touch position must report ABS_{X,Y} for the
249location of the touch. BTN_TOUCH should be used to report when a touch is active
250on the trackpad. Where multi-finger support is available, BTN_TOOL_<name> should
251be used to report the number of touches active on the trackpad.
252
253Tablets:
254----------
255BTN_TOOL_<name> events must be reported when a stylus or other tool is active on
256the tablet. ABS_{X,Y} must be reported with the location of the tool. BTN_TOUCH
257should be used to report when the tool is in contact with the tablet.
258BTN_{STYLUS,STYLUS2} should be used to report buttons on the tool itself. Any
259button may be used for buttons on the tablet except BTN_{MOUSE,LEFT}.
260BTN_{0,1,2,etc} are good generic codes for unlabeled buttons. Do not use
261meaningful buttons, like BTN_FORWARD, unless the button is labeled for that
262purpose on the device.