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. 141 142* BTN_TOUCH: 143 144 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. 152 153Note: For appropriate function of the legacy mousedev emulation driver, 154BTN_TOUCH must be the first evdev code emitted in a synchronization frame. 155 156Note: Historically a touch device with BTN_TOOL_FINGER and BTN_TOUCH was 157interpreted as a touchpad by userspace, while a similar device without 158BTN_TOOL_FINGER was interpreted as a touchscreen. For backwards compatibility 159with current userspace it is recommended to follow this distinction. In the 160future, this distinction will be deprecated and the device properties ioctl 161EVIOCGPROP, defined in linux/input.h, will be used to convey the device type. 162 163* BTN_TOOL_FINGER, BTN_TOOL_DOUBLETAP, BTN_TOOL_TRIPLETAP, BTN_TOOL_QUADTAP: 164 165 - 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. 173 174Note: Historically some drivers emitted multiple of the finger count codes with 175a value of 1 in the same synchronization frame. This usage is deprecated. 176 177Note: In multitouch drivers, the input_mt_report_finger_count() function should 178be used to emit these codes. Please see multi-touch-protocol.txt for details. 179 180EV_REL 181------ 182 183EV_REL events describe relative changes in a property. For example, a mouse may 184move to the left by a certain number of units, but its absolute position in 185space is unknown. If the absolute position is known, EV_ABS codes should be used 186instead of EV_REL codes. 187 188A few EV_REL codes have special meanings: 189 190* REL_WHEEL, REL_HWHEEL: 191 192 - These codes are used for vertical and horizontal scroll wheels, 193 respectively. The value is the number of detents moved on the wheel, the 194 physical size of which varies by device. For high-resolution wheels 195 this may be an approximation based on the high-resolution scroll events, 196 see REL_WHEEL_HI_RES. These event codes are legacy codes and 197 REL_WHEEL_HI_RES and REL_HWHEEL_HI_RES should be preferred where 198 available. 199 200* REL_WHEEL_HI_RES, REL_HWHEEL_HI_RES: 201 202 - High-resolution scroll wheel data. The accumulated value 120 represents 203 movement by one detent. For devices that do not provide high-resolution 204 scrolling, the value is always a multiple of 120. For devices with 205 high-resolution scrolling, the value may be a fraction of 120. 206 207 If a vertical scroll wheel supports high-resolution scrolling, this code 208 will be emitted in addition to REL_WHEEL or REL_HWHEEL. The REL_WHEEL 209 and REL_HWHEEL may be an approximation based on the high-resolution 210 scroll events. There is no guarantee that the high-resolution data 211 is a multiple of 120 at the time of an emulated REL_WHEEL or REL_HWHEEL 212 event. 213 214EV_ABS 215------ 216 217EV_ABS events describe absolute changes in a property. For example, a touchpad 218may emit coordinates for a touch location. 219 220A few EV_ABS codes have special meanings: 221 222* ABS_DISTANCE: 223 224 - Used to describe the distance of a tool from an interaction surface. This 225 event should only be emitted while the tool is hovering, meaning in close 226 proximity of the device and while the value of the BTN_TOUCH code is 0. If 227 the input device may be used freely in three dimensions, consider ABS_Z 228 instead. 229 - BTN_TOOL_<name> should be set to 1 when the tool comes into detectable 230 proximity and set to 0 when the tool leaves detectable proximity. 231 BTN_TOOL_<name> signals the type of tool that is currently detected by the 232 hardware and is otherwise independent of ABS_DISTANCE and/or BTN_TOUCH. 233 234* ABS_MT_<name>: 235 236 - Used to describe multitouch input events. Please see 237 multi-touch-protocol.txt for details. 238 239* ABS_PRESSURE/ABS_MT_PRESSURE: 240 241 - For touch devices, many devices converted contact size into pressure. 242 A finger flattens with pressure, causing a larger contact area and thus 243 pressure and contact size are directly related. This is not the case 244 for other devices, for example digitizers and touchpads with a true 245 pressure sensor ("pressure pads"). 246 247 A device should set the resolution of the axis to indicate whether the 248 pressure is in measurable units. If the resolution is zero, the 249 pressure data is in arbitrary units. If the resolution is non-zero, the 250 pressure data is in units/gram. For example, a value of 10 with a 251 resolution of 1 represents 10 gram, a value of 10 with a resolution of 252 1000 represents 10 microgram. 253 254EV_SW 255----- 256 257EV_SW events describe stateful binary switches. For example, the SW_LID code is 258used to denote when a laptop lid is closed. 259 260Upon binding to a device or resuming from suspend, a driver must report 261the current switch state. This ensures that the device, kernel, and userspace 262state is in sync. 263 264Upon resume, if the switch state is the same as before suspend, then the input 265subsystem will filter out the duplicate switch state reports. The driver does 266not need to keep the state of the switch at any time. 267 268EV_MSC 269------ 270 271EV_MSC events are used for input and output events that do not fall under other 272categories. 273 274A few EV_MSC codes have special meaning: 275 276* MSC_TIMESTAMP: 277 278 - Used to report the number of microseconds since the last reset. This event 279 should be coded as an uint32 value, which is allowed to wrap around with 280 no special consequence. It is assumed that the time difference between two 281 consecutive events is reliable on a reasonable time scale (hours). 282 A reset to zero can happen, in which case the time since the last event is 283 unknown. If the device does not provide this information, the driver must 284 not provide it to user space. 285 286EV_LED 287------ 288 289EV_LED events are used for input and output to set and query the state of 290various LEDs on devices. 291 292EV_REP 293------ 294 295EV_REP events are used for specifying autorepeating events. 296 297EV_SND 298------ 299 300EV_SND events are used for sending sound commands to simple sound output 301devices. 302 303EV_FF 304----- 305 306EV_FF events are used to initialize a force feedback capable device and to cause 307such device to feedback. 308 309EV_PWR 310------ 311 312EV_PWR events are a special type of event used specifically for power 313management. Its usage is not well defined. To be addressed later. 314 315Device properties 316================= 317 318Normally, userspace sets up an input device based on the data it emits, 319i.e., the event types. In the case of two devices emitting the same event 320types, additional information can be provided in the form of device 321properties. 322 323INPUT_PROP_DIRECT + INPUT_PROP_POINTER 324-------------------------------------- 325 326The INPUT_PROP_DIRECT property indicates that device coordinates should be 327directly mapped to screen coordinates (not taking into account trivial 328transformations, such as scaling, flipping and rotating). Non-direct input 329devices require non-trivial transformation, such as absolute to relative 330transformation for touchpads. Typical direct input devices: touchscreens, 331drawing tablets; non-direct devices: touchpads, mice. 332 333The INPUT_PROP_POINTER property indicates that the device is not transposed 334on the screen and thus requires use of an on-screen pointer to trace user's 335movements. Typical pointer devices: touchpads, tablets, mice; non-pointer 336device: touchscreen. 337 338If neither INPUT_PROP_DIRECT or INPUT_PROP_POINTER are set, the property is 339considered undefined and the device type should be deduced in the 340traditional way, using emitted event types. 341 342INPUT_PROP_BUTTONPAD 343-------------------- 344 345For touchpads where the button is placed beneath the surface, such that 346pressing down on the pad causes a button click, this property should be 347set. Common in Clickpad notebooks and Macbooks from 2009 and onwards. 348 349Originally, the buttonpad property was coded into the bcm5974 driver 350version field under the name integrated button. For backwards 351compatibility, both methods need to be checked in userspace. 352 353INPUT_PROP_SEMI_MT 354------------------ 355 356Some touchpads, most common between 2008 and 2011, can detect the presence 357of multiple contacts without resolving the individual positions; only the 358number of contacts and a rectangular shape is known. For such 359touchpads, the SEMI_MT property should be set. 360 361Depending on the device, the rectangle may enclose all touches, like a 362bounding box, or just some of them, for instance the two most recent 363touches. The diversity makes the rectangle of limited use, but some 364gestures can normally be extracted from it. 365 366If INPUT_PROP_SEMI_MT is not set, the device is assumed to be a true MT 367device. 368 369INPUT_PROP_TOPBUTTONPAD 370----------------------- 371 372Some laptops, most notably the Lenovo 40 series provide a trackstick 373device but do not have physical buttons associated with the trackstick 374device. Instead, the top area of the touchpad is marked to show 375visual/haptic areas for left, middle, right buttons intended to be used 376with the trackstick. 377 378If INPUT_PROP_TOPBUTTONPAD is set, userspace should emulate buttons 379accordingly. This property does not affect kernel behavior. 380The kernel does not provide button emulation for such devices but treats 381them as any other INPUT_PROP_BUTTONPAD device. 382 383INPUT_PROP_ACCELEROMETER 384------------------------ 385 386Directional axes on this device (absolute and/or relative x, y, z) represent 387accelerometer data. Some devices also report gyroscope data, which devices 388can report through the rotational axes (absolute and/or relative rx, ry, rz). 389 390All other axes retain their meaning. A device must not mix 391regular directional axes and accelerometer axes on the same event node. 392 393Guidelines 394========== 395 396The guidelines below ensure proper single-touch and multi-finger functionality. 397For multi-touch functionality, see the multi-touch-protocol.rst document for 398more information. 399 400Mice 401---- 402 403REL_{X,Y} must be reported when the mouse moves. BTN_LEFT must be used to report 404the primary button press. BTN_{MIDDLE,RIGHT,4,5,etc.} should be used to report 405further buttons of the device. REL_WHEEL and REL_HWHEEL should be used to report 406scroll wheel events where available. 407 408Touchscreens 409------------ 410 411ABS_{X,Y} must be reported with the location of the touch. BTN_TOUCH must be 412used to report when a touch is active on the screen. 413BTN_{MOUSE,LEFT,MIDDLE,RIGHT} must not be reported as the result of touch 414contact. BTN_TOOL_<name> events should be reported where possible. 415 416For new hardware, INPUT_PROP_DIRECT should be set. 417 418Trackpads 419--------- 420 421Legacy trackpads that only provide relative position information must report 422events like mice described above. 423 424Trackpads that provide absolute touch position must report ABS_{X,Y} for the 425location of the touch. BTN_TOUCH should be used to report when a touch is active 426on the trackpad. Where multi-finger support is available, BTN_TOOL_<name> should 427be used to report the number of touches active on the trackpad. 428 429For new hardware, INPUT_PROP_POINTER should be set. 430 431Tablets 432------- 433 434BTN_TOOL_<name> events must be reported when a stylus or other tool is active on 435the tablet. ABS_{X,Y} must be reported with the location of the tool. BTN_TOUCH 436should be used to report when the tool is in contact with the tablet. 437BTN_{STYLUS,STYLUS2} should be used to report buttons on the tool itself. Any 438button may be used for buttons on the tablet except BTN_{MOUSE,LEFT}. 439BTN_{0,1,2,etc} are good generic codes for unlabeled buttons. Do not use 440meaningful buttons, like BTN_FORWARD, unless the button is labeled for that 441purpose on the device. 442 443For new hardware, both INPUT_PROP_DIRECT and INPUT_PROP_POINTER should be set. 444