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
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.
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.
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.
36 - Used as markers to separate events. Events may be separated in time or in
37 space, such as with the multitouch protocol.
41 - Used to describe state changes of keyboards, buttons, or other key-like
46 - Used to describe relative axis value changes, e.g. moving the mouse 5 units
51 - Used to describe absolute axis value changes, e.g. describing the
52 coordinates of a touch on a touchscreen.
56 - Used to describe miscellaneous input data that do not fit into other types.
60 - Used to describe binary state input switches.
64 - Used to turn LEDs on devices on and off.
68 - Used to output sound to devices.
72 - Used for autorepeating devices.
76 - Used to send force feedback commands to an input device.
80 - A special type for power button and switch input.
84 - Used to receive force feedback device status.
89 Event codes define the precise type of event.
94 EV_SYN event values are undefined. Their usage is defined only by when they are
95 sent in the evdev event stream.
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.
110 - Used to synchronize and separate touch events. See the
111 multi-touch-protocol.txt document for more information.
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
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.
130 A few EV_KEY codes have special meanings:
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.
144 BTN_TOUCH is used for touch contact. While an input tool is determined to be
145 within meaningful physical contact, the value of this property must be set
146 to 1. Meaningful physical contact may mean any contact, or it may mean
147 contact conditioned by an implementation defined property. For example, a
148 touchpad may set the value to 1 only when the touch pressure rises above a
149 certain value. BTN_TOUCH may be combined with BTN_TOOL_<name> codes. For
150 example, a pen tablet may set BTN_TOOL_PEN to 1 and BTN_TOUCH to 0 while the
151 pen is hovering over but not touching the tablet surface.
153 Note: For appropriate function of the legacy mousedev emulation driver,
154 BTN_TOUCH must be the first evdev code emitted in a synchronization frame.
156 Note: Historically a touch device with BTN_TOOL_FINGER and BTN_TOUCH was
157 interpreted as a touchpad by userspace, while a similar device without
158 BTN_TOOL_FINGER was interpreted as a touchscreen. For backwards compatibility
159 with current userspace it is recommended to follow this distinction. In the
160 future, this distinction will be deprecated and the device properties ioctl
161 EVIOCGPROP, defined in linux/input.h, will be used to convey the device type.
163 * BTN_TOOL_FINGER, BTN_TOOL_DOUBLETAP, BTN_TOOL_TRIPLETAP, BTN_TOOL_QUADTAP:
165 - These codes denote one, two, three, and four finger interaction on a
166 trackpad or touchscreen. For example, if the user uses two fingers and moves
167 them on the touchpad in an effort to scroll content on screen,
168 BTN_TOOL_DOUBLETAP should be set to value 1 for the duration of the motion.
169 Note that all BTN_TOOL_<name> codes and the BTN_TOUCH code are orthogonal in
170 purpose. A trackpad event generated by finger touches should generate events
171 for one code from each group. At most only one of these BTN_TOOL_<name>
172 codes should have a value of 1 during any synchronization frame.
174 Note: Historically some drivers emitted multiple of the finger count codes with
175 a value of 1 in the same synchronization frame. This usage is deprecated.
177 Note: In multitouch drivers, the input_mt_report_finger_count() function should
178 be used to emit these codes. Please see multi-touch-protocol.txt for details.
183 EV_REL events describe relative changes in a property. For example, a mouse may
184 move to the left by a certain number of units, but its absolute position in
185 space is unknown. If the absolute position is known, EV_ABS codes should be used
186 instead of EV_REL codes.
188 A few EV_REL codes have special meanings:
190 * REL_WHEEL, REL_HWHEEL:
192 - These codes are used for vertical and horizontal scroll wheels,
193 respectively. The value is the number of "notches" moved on the wheel, the
194 physical size of which varies by device. For high-resolution wheels (which
195 report multiple events for each notch of movement, or do not have notches)
196 this may be an approximation based on the high-resolution scroll events.
200 - If a vertical scroll wheel supports high-resolution scrolling, this code
201 will be emitted in addition to REL_WHEEL. The value is the (approximate)
202 distance travelled by the user's finger, in microns.
207 EV_ABS events describe absolute changes in a property. For example, a touchpad
208 may emit coordinates for a touch location.
210 A few EV_ABS codes have special meanings:
214 - Used to describe the distance of a tool from an interaction surface. This
215 event should only be emitted while the tool is hovering, meaning in close
216 proximity of the device and while the value of the BTN_TOUCH code is 0. If
217 the input device may be used freely in three dimensions, consider ABS_Z
219 - BTN_TOOL_<name> should be set to 1 when the tool comes into detectable
220 proximity and set to 0 when the tool leaves detectable proximity.
221 BTN_TOOL_<name> signals the type of tool that is currently detected by the
222 hardware and is otherwise independent of ABS_DISTANCE and/or BTN_TOUCH.
226 - Used to describe multitouch input events. Please see
227 multi-touch-protocol.txt for details.
232 EV_SW events describe stateful binary switches. For example, the SW_LID code is
233 used to denote when a laptop lid is closed.
235 Upon binding to a device or resuming from suspend, a driver must report
236 the current switch state. This ensures that the device, kernel, and userspace
239 Upon resume, if the switch state is the same as before suspend, then the input
240 subsystem will filter out the duplicate switch state reports. The driver does
241 not need to keep the state of the switch at any time.
246 EV_MSC events are used for input and output events that do not fall under other
249 A few EV_MSC codes have special meaning:
253 - Used to report the number of microseconds since the last reset. This event
254 should be coded as an uint32 value, which is allowed to wrap around with
255 no special consequence. It is assumed that the time difference between two
256 consecutive events is reliable on a reasonable time scale (hours).
257 A reset to zero can happen, in which case the time since the last event is
258 unknown. If the device does not provide this information, the driver must
259 not provide it to user space.
264 EV_LED events are used for input and output to set and query the state of
265 various LEDs on devices.
270 EV_REP events are used for specifying autorepeating events.
275 EV_SND events are used for sending sound commands to simple sound output
281 EV_FF events are used to initialize a force feedback capable device and to cause
282 such device to feedback.
287 EV_PWR events are a special type of event used specifically for power
288 management. Its usage is not well defined. To be addressed later.
293 Normally, userspace sets up an input device based on the data it emits,
294 i.e., the event types. In the case of two devices emitting the same event
295 types, additional information can be provided in the form of device
298 INPUT_PROP_DIRECT + INPUT_PROP_POINTER
299 --------------------------------------
301 The INPUT_PROP_DIRECT property indicates that device coordinates should be
302 directly mapped to screen coordinates (not taking into account trivial
303 transformations, such as scaling, flipping and rotating). Non-direct input
304 devices require non-trivial transformation, such as absolute to relative
305 transformation for touchpads. Typical direct input devices: touchscreens,
306 drawing tablets; non-direct devices: touchpads, mice.
308 The INPUT_PROP_POINTER property indicates that the device is not transposed
309 on the screen and thus requires use of an on-screen pointer to trace user's
310 movements. Typical pointer devices: touchpads, tablets, mice; non-pointer
313 If neither INPUT_PROP_DIRECT or INPUT_PROP_POINTER are set, the property is
314 considered undefined and the device type should be deduced in the
315 traditional way, using emitted event types.
320 For touchpads where the button is placed beneath the surface, such that
321 pressing down on the pad causes a button click, this property should be
322 set. Common in clickpad notebooks and macbooks from 2009 and onwards.
324 Originally, the buttonpad property was coded into the bcm5974 driver
325 version field under the name integrated button. For backwards
326 compatibility, both methods need to be checked in userspace.
331 Some touchpads, most common between 2008 and 2011, can detect the presence
332 of multiple contacts without resolving the individual positions; only the
333 number of contacts and a rectangular shape is known. For such
334 touchpads, the semi-mt property should be set.
336 Depending on the device, the rectangle may enclose all touches, like a
337 bounding box, or just some of them, for instance the two most recent
338 touches. The diversity makes the rectangle of limited use, but some
339 gestures can normally be extracted from it.
341 If INPUT_PROP_SEMI_MT is not set, the device is assumed to be a true MT
344 INPUT_PROP_TOPBUTTONPAD
345 -----------------------
347 Some laptops, most notably the Lenovo 40 series provide a trackstick
348 device but do not have physical buttons associated with the trackstick
349 device. Instead, the top area of the touchpad is marked to show
350 visual/haptic areas for left, middle, right buttons intended to be used
353 If INPUT_PROP_TOPBUTTONPAD is set, userspace should emulate buttons
354 accordingly. This property does not affect kernel behavior.
355 The kernel does not provide button emulation for such devices but treats
356 them as any other INPUT_PROP_BUTTONPAD device.
358 INPUT_PROP_ACCELEROMETER
359 ------------------------
361 Directional axes on this device (absolute and/or relative x, y, z) represent
362 accelerometer data. Some devices also report gyroscope data, which devices
363 can report through the rotational axes (absolute and/or relative rx, ry, rz).
365 All other axes retain their meaning. A device must not mix
366 regular directional axes and accelerometer axes on the same event node.
371 The guidelines below ensure proper single-touch and multi-finger functionality.
372 For multi-touch functionality, see the multi-touch-protocol.txt document for
378 REL_{X,Y} must be reported when the mouse moves. BTN_LEFT must be used to report
379 the primary button press. BTN_{MIDDLE,RIGHT,4,5,etc.} should be used to report
380 further buttons of the device. REL_WHEEL and REL_HWHEEL should be used to report
381 scroll wheel events where available.
386 ABS_{X,Y} must be reported with the location of the touch. BTN_TOUCH must be
387 used to report when a touch is active on the screen.
388 BTN_{MOUSE,LEFT,MIDDLE,RIGHT} must not be reported as the result of touch
389 contact. BTN_TOOL_<name> events should be reported where possible.
391 For new hardware, INPUT_PROP_DIRECT should be set.
396 Legacy trackpads that only provide relative position information must report
397 events like mice described above.
399 Trackpads that provide absolute touch position must report ABS_{X,Y} for the
400 location of the touch. BTN_TOUCH should be used to report when a touch is active
401 on the trackpad. Where multi-finger support is available, BTN_TOOL_<name> should
402 be used to report the number of touches active on the trackpad.
404 For new hardware, INPUT_PROP_POINTER should be set.
409 BTN_TOOL_<name> events must be reported when a stylus or other tool is active on
410 the tablet. ABS_{X,Y} must be reported with the location of the tool. BTN_TOUCH
411 should be used to report when the tool is in contact with the tablet.
412 BTN_{STYLUS,STYLUS2} should be used to report buttons on the tool itself. Any
413 button may be used for buttons on the tablet except BTN_{MOUSE,LEFT}.
414 BTN_{0,1,2,etc} are good generic codes for unlabeled buttons. Do not use
415 meaningful buttons, like BTN_FORWARD, unless the button is labeled for that
416 purpose on the device.
418 For new hardware, both INPUT_PROP_DIRECT and INPUT_PROP_POINTER should be set.
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