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
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.
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.
22 Types are groupings of codes under a logical input construct. Each type has a
23 set of applicable codes to be used in generating events. See the Codes section
24 for details on valid codes for each type.
27 - Used as markers to separate events. Events may be separated in time or in
28 space, such as with the multitouch protocol.
31 - Used to describe state changes of keyboards, buttons, or other key-like
35 - Used to describe relative axis value changes, e.g. moving the mouse 5 units
39 - Used to describe absolute axis value changes, e.g. describing the
40 coordinates of a touch on a touchscreen.
43 - Used to describe miscellaneous input data that do not fit into other types.
46 - Used to describe binary state input switches.
49 - Used to turn LEDs on devices on and off.
52 - Used to output sound to devices.
55 - Used for autorepeating devices.
58 - Used to send force feedback commands to an input device.
61 - A special type for power button and switch input.
64 - Used to receive force feedback device status.
68 Codes define the precise type of event.
72 EV_SYN event values are undefined. Their usage is defined only by when they are
73 sent in the evdev event stream.
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.
85 - Used to synchronize and separate touch events. See the
86 multi-touch-protocol.txt document for more information.
90 EV_KEY events take the form KEY_<name> or BTN_<name>. For example, KEY_A is used
91 to represent the 'A' key on a keyboard. When a key is depressed, an event with
92 the key's code is emitted with value 1. When the key is released, an event is
93 emitted with value 0. Some hardware send events when a key is repeated. These
94 events have a value of 2. In general, KEY_<name> is used for keyboard keys, and
95 BTN_<name> is used for other types of momentary switch events.
97 A few EV_KEY codes have special meanings:
100 - These codes are used in conjunction with input trackpads, tablets, and
101 touchscreens. These devices may be used with fingers, pens, or other tools.
102 When an event occurs and a tool is used, the corresponding BTN_TOOL_<name>
103 code should be set to a value of 1. When the tool is no longer interacting
104 with the input device, the BTN_TOOL_<name> code should be reset to 0. All
105 trackpads, tablets, and touchscreens should use at least one BTN_TOOL_<name>
106 code when events are generated.
109 BTN_TOUCH is used for touch contact. While an input tool is determined to be
110 within meaningful physical contact, the value of this property must be set
111 to 1. Meaningful physical contact may mean any contact, or it may mean
112 contact conditioned by an implementation defined property. For example, a
113 touchpad may set the value to 1 only when the touch pressure rises above a
114 certain value. BTN_TOUCH may be combined with BTN_TOOL_<name> codes. For
115 example, a pen tablet may set BTN_TOOL_PEN to 1 and BTN_TOUCH to 0 while the
116 pen is hovering over but not touching the tablet surface.
118 Note: For appropriate function of the legacy mousedev emulation driver,
119 BTN_TOUCH must be the first evdev code emitted in a synchronization frame.
121 Note: Historically a touch device with BTN_TOOL_FINGER and BTN_TOUCH was
122 interpreted as a touchpad by userspace, while a similar device without
123 BTN_TOOL_FINGER was interpreted as a touchscreen. For backwards compatibility
124 with current userspace it is recommended to follow this distinction. In the
125 future, this distinction will be deprecated and the device properties ioctl
126 EVIOCGPROP, defined in linux/input.h, will be used to convey the device type.
128 * BTN_TOOL_FINGER, BTN_TOOL_DOUBLETAP, BTN_TOOL_TRIPLETAP, BTN_TOOL_QUADTAP:
129 - These codes denote one, two, three, and four finger interaction on a
130 trackpad or touchscreen. For example, if the user uses two fingers and moves
131 them on the touchpad in an effort to scroll content on screen,
132 BTN_TOOL_DOUBLETAP should be set to value 1 for the duration of the motion.
133 Note that all BTN_TOOL_<name> codes and the BTN_TOUCH code are orthogonal in
134 purpose. A trackpad event generated by finger touches should generate events
135 for one code from each group. At most only one of these BTN_TOOL_<name>
136 codes should have a value of 1 during any synchronization frame.
138 Note: Historically some drivers emitted multiple of the finger count codes with
139 a value of 1 in the same synchronization frame. This usage is deprecated.
141 Note: In multitouch drivers, the input_mt_report_finger_count() function should
142 be used to emit these codes. Please see multi-touch-protocol.txt for details.
146 EV_REL events describe relative changes in a property. For example, a mouse may
147 move to the left by a certain number of units, but its absolute position in
148 space is unknown. If the absolute position is known, EV_ABS codes should be used
149 instead of EV_REL codes.
151 A few EV_REL codes have special meanings:
153 * REL_WHEEL, REL_HWHEEL:
154 - These codes are used for vertical and horizontal scroll wheels,
159 EV_ABS events describe absolute changes in a property. For example, a touchpad
160 may emit coordinates for a touch location.
162 A few EV_ABS codes have special meanings:
165 - Used to describe the distance of a tool from an interaction surface. This
166 event should only be emitted while the tool is hovering, meaning in close
167 proximity of the device and while the value of the BTN_TOUCH code is 0. If
168 the input device may be used freely in three dimensions, consider ABS_Z
172 - Used to describe multitouch input events. Please see
173 multi-touch-protocol.txt for details.
177 EV_SW events describe stateful binary switches. For example, the SW_LID code is
178 used to denote when a laptop lid is closed.
180 Upon binding to a device or resuming from suspend, a driver must report
181 the current switch state. This ensures that the device, kernel, and userspace
184 Upon resume, if the switch state is the same as before suspend, then the input
185 subsystem will filter out the duplicate switch state reports. The driver does
186 not need to keep the state of the switch at any time.
190 EV_MSC events are used for input and output events that do not fall under other
195 EV_LED events are used for input and output to set and query the state of
196 various LEDs on devices.
200 EV_REP events are used for specifying autorepeating events.
204 EV_SND events are used for sending sound commands to simple sound output
209 EV_FF events are used to initialize a force feedback capable device and to cause
210 such device to feedback.
214 EV_PWR events are a special type of event used specifically for power
215 mangement. Its usage is not well defined. To be addressed later.
219 The guidelines below ensure proper single-touch and multi-finger functionality.
220 For multi-touch functionality, see the multi-touch-protocol.txt document for
225 REL_{X,Y} must be reported when the mouse moves. BTN_LEFT must be used to report
226 the primary button press. BTN_{MIDDLE,RIGHT,4,5,etc.} should be used to report
227 further buttons of the device. REL_WHEEL and REL_HWHEEL should be used to report
228 scroll wheel events where available.
232 ABS_{X,Y} must be reported with the location of the touch. BTN_TOUCH must be
233 used to report when a touch is active on the screen.
234 BTN_{MOUSE,LEFT,MIDDLE,RIGHT} must not be reported as the result of touch
235 contact. BTN_TOOL_<name> events should be reported where possible.
239 Legacy trackpads that only provide relative position information must report
240 events like mice described above.
242 Trackpads that provide absolute touch position must report ABS_{X,Y} for the
243 location of the touch. BTN_TOUCH should be used to report when a touch is active
244 on the trackpad. Where multi-finger support is available, BTN_TOOL_<name> should
245 be used to report the number of touches active on the trackpad.
249 BTN_TOOL_<name> events must be reported when a stylus or other tool is active on
250 the tablet. ABS_{X,Y} must be reported with the location of the tool. BTN_TOUCH
251 should be used to report when the tool is in contact with the tablet.
252 BTN_{STYLUS,STYLUS2} should be used to report buttons on the tool itself. Any
253 button may be used for buttons on the tablet except BTN_{MOUSE,LEFT}.
254 BTN_{0,1,2,etc} are good generic codes for unlabeled buttons. Do not use
255 meaningful buttons, like BTN_FORWARD, unless the button is labeled for that
256 purpose on the device.