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. Likewise all trackpads, tablets, and 141 touchscreens should export only one BTN_TOOL_<name> at a time. To not break 142 existing userspace, it is recommended to not switch tool in one EV_SYN frame 143 but first emitting the old BTN_TOOL_<name> at 0, then emit one SYN_REPORT 144 and then set the new BTN_TOOL_<name> at 1. 145 146* BTN_TOUCH: 147 148 BTN_TOUCH is used for touch contact. While an input tool is determined to be 149 within meaningful physical contact, the value of this property must be set 150 to 1. Meaningful physical contact may mean any contact, or it may mean 151 contact conditioned by an implementation defined property. For example, a 152 touchpad may set the value to 1 only when the touch pressure rises above a 153 certain value. BTN_TOUCH may be combined with BTN_TOOL_<name> codes. For 154 example, a pen tablet may set BTN_TOOL_PEN to 1 and BTN_TOUCH to 0 while the 155 pen is hovering over but not touching the tablet surface. 156 157Note: For appropriate function of the legacy mousedev emulation driver, 158BTN_TOUCH must be the first evdev code emitted in a synchronization frame. 159 160Note: Historically a touch device with BTN_TOOL_FINGER and BTN_TOUCH was 161interpreted as a touchpad by userspace, while a similar device without 162BTN_TOOL_FINGER was interpreted as a touchscreen. For backwards compatibility 163with current userspace it is recommended to follow this distinction. In the 164future, this distinction will be deprecated and the device properties ioctl 165EVIOCGPROP, defined in linux/input.h, will be used to convey the device type. 166 167* BTN_TOOL_FINGER, BTN_TOOL_DOUBLETAP, BTN_TOOL_TRIPLETAP, BTN_TOOL_QUADTAP: 168 169 - These codes denote one, two, three, and four finger interaction on a 170 trackpad or touchscreen. For example, if the user uses two fingers and moves 171 them on the touchpad in an effort to scroll content on screen, 172 BTN_TOOL_DOUBLETAP should be set to value 1 for the duration of the motion. 173 Note that all BTN_TOOL_<name> codes and the BTN_TOUCH code are orthogonal in 174 purpose. A trackpad event generated by finger touches should generate events 175 for one code from each group. At most only one of these BTN_TOOL_<name> 176 codes should have a value of 1 during any synchronization frame. 177 178Note: Historically some drivers emitted multiple of the finger count codes with 179a value of 1 in the same synchronization frame. This usage is deprecated. 180 181Note: In multitouch drivers, the input_mt_report_finger_count() function should 182be used to emit these codes. Please see multi-touch-protocol.txt for details. 183 184EV_REL 185------ 186 187EV_REL events describe relative changes in a property. For example, a mouse may 188move to the left by a certain number of units, but its absolute position in 189space is unknown. If the absolute position is known, EV_ABS codes should be used 190instead of EV_REL codes. 191 192A few EV_REL codes have special meanings: 193 194* REL_WHEEL, REL_HWHEEL: 195 196 - These codes are used for vertical and horizontal scroll wheels, 197 respectively. The value is the number of detents moved on the wheel, the 198 physical size of which varies by device. For high-resolution wheels 199 this may be an approximation based on the high-resolution scroll events, 200 see REL_WHEEL_HI_RES. These event codes are legacy codes and 201 REL_WHEEL_HI_RES and REL_HWHEEL_HI_RES should be preferred where 202 available. 203 204* REL_WHEEL_HI_RES, REL_HWHEEL_HI_RES: 205 206 - High-resolution scroll wheel data. The accumulated value 120 represents 207 movement by one detent. For devices that do not provide high-resolution 208 scrolling, the value is always a multiple of 120. For devices with 209 high-resolution scrolling, the value may be a fraction of 120. 210 211 If a vertical scroll wheel supports high-resolution scrolling, this code 212 will be emitted in addition to REL_WHEEL or REL_HWHEEL. The REL_WHEEL 213 and REL_HWHEEL may be an approximation based on the high-resolution 214 scroll events. There is no guarantee that the high-resolution data 215 is a multiple of 120 at the time of an emulated REL_WHEEL or REL_HWHEEL 216 event. 217 218EV_ABS 219------ 220 221EV_ABS events describe absolute changes in a property. For example, a touchpad 222may emit coordinates for a touch location. 223 224A few EV_ABS codes have special meanings: 225 226* ABS_DISTANCE: 227 228 - Used to describe the distance of a tool from an interaction surface. This 229 event should only be emitted while the tool is hovering, meaning in close 230 proximity of the device and while the value of the BTN_TOUCH code is 0. If 231 the input device may be used freely in three dimensions, consider ABS_Z 232 instead. 233 - BTN_TOOL_<name> should be set to 1 when the tool comes into detectable 234 proximity and set to 0 when the tool leaves detectable proximity. 235 BTN_TOOL_<name> signals the type of tool that is currently detected by the 236 hardware and is otherwise independent of ABS_DISTANCE and/or BTN_TOUCH. 237 238* ABS_PROFILE: 239 240 - Used to describe the state of a multi-value profile switch. An event is 241 emitted only when the selected profile changes, indicating the newly 242 selected profile value. 243 244* ABS_MT_<name>: 245 246 - Used to describe multitouch input events. Please see 247 multi-touch-protocol.txt for details. 248 249* ABS_PRESSURE/ABS_MT_PRESSURE: 250 251 - For touch devices, many devices converted contact size into pressure. 252 A finger flattens with pressure, causing a larger contact area and thus 253 pressure and contact size are directly related. This is not the case 254 for other devices, for example digitizers and touchpads with a true 255 pressure sensor ("pressure pads"). 256 257 A device should set the resolution of the axis to indicate whether the 258 pressure is in measurable units. If the resolution is zero, the 259 pressure data is in arbitrary units. If the resolution is non-zero, the 260 pressure data is in units/gram. For example, a value of 10 with a 261 resolution of 1 represents 10 gram, a value of 10 with a resolution of 262 1000 represents 10 microgram. 263 264EV_SW 265----- 266 267EV_SW events describe stateful binary switches. For example, the SW_LID code is 268used to denote when a laptop lid is closed. 269 270Upon binding to a device or resuming from suspend, a driver must report 271the current switch state. This ensures that the device, kernel, and userspace 272state is in sync. 273 274Upon resume, if the switch state is the same as before suspend, then the input 275subsystem will filter out the duplicate switch state reports. The driver does 276not need to keep the state of the switch at any time. 277 278EV_MSC 279------ 280 281EV_MSC events are used for input and output events that do not fall under other 282categories. 283 284A few EV_MSC codes have special meaning: 285 286* MSC_TIMESTAMP: 287 288 - Used to report the number of microseconds since the last reset. This event 289 should be coded as an uint32 value, which is allowed to wrap around with 290 no special consequence. It is assumed that the time difference between two 291 consecutive events is reliable on a reasonable time scale (hours). 292 A reset to zero can happen, in which case the time since the last event is 293 unknown. If the device does not provide this information, the driver must 294 not provide it to user space. 295 296EV_LED 297------ 298 299EV_LED events are used for input and output to set and query the state of 300various LEDs on devices. 301 302EV_REP 303------ 304 305EV_REP events are used for specifying autorepeating events. 306 307EV_SND 308------ 309 310EV_SND events are used for sending sound commands to simple sound output 311devices. 312 313EV_FF 314----- 315 316EV_FF events are used to initialize a force feedback capable device and to cause 317such device to feedback. 318 319EV_PWR 320------ 321 322EV_PWR events are a special type of event used specifically for power 323management. Its usage is not well defined. To be addressed later. 324 325Device properties 326================= 327 328Normally, userspace sets up an input device based on the data it emits, 329i.e., the event types. In the case of two devices emitting the same event 330types, additional information can be provided in the form of device 331properties. 332 333INPUT_PROP_DIRECT + INPUT_PROP_POINTER 334-------------------------------------- 335 336The INPUT_PROP_DIRECT property indicates that device coordinates should be 337directly mapped to screen coordinates (not taking into account trivial 338transformations, such as scaling, flipping and rotating). Non-direct input 339devices require non-trivial transformation, such as absolute to relative 340transformation for touchpads. Typical direct input devices: touchscreens, 341drawing tablets; non-direct devices: touchpads, mice. 342 343The INPUT_PROP_POINTER property indicates that the device is not transposed 344on the screen and thus requires use of an on-screen pointer to trace user's 345movements. Typical pointer devices: touchpads, tablets, mice; non-pointer 346device: touchscreen. 347 348If neither INPUT_PROP_DIRECT or INPUT_PROP_POINTER are set, the property is 349considered undefined and the device type should be deduced in the 350traditional way, using emitted event types. 351 352INPUT_PROP_BUTTONPAD 353-------------------- 354 355For touchpads where the button is placed beneath the surface, such that 356pressing down on the pad causes a button click, this property should be 357set. Common in Clickpad notebooks and Macbooks from 2009 and onwards. 358 359Originally, the buttonpad property was coded into the bcm5974 driver 360version field under the name integrated button. For backwards 361compatibility, both methods need to be checked in userspace. 362 363INPUT_PROP_SEMI_MT 364------------------ 365 366Some touchpads, most common between 2008 and 2011, can detect the presence 367of multiple contacts without resolving the individual positions; only the 368number of contacts and a rectangular shape is known. For such 369touchpads, the SEMI_MT property should be set. 370 371Depending on the device, the rectangle may enclose all touches, like a 372bounding box, or just some of them, for instance the two most recent 373touches. The diversity makes the rectangle of limited use, but some 374gestures can normally be extracted from it. 375 376If INPUT_PROP_SEMI_MT is not set, the device is assumed to be a true MT 377device. 378 379INPUT_PROP_TOPBUTTONPAD 380----------------------- 381 382Some laptops, most notably the Lenovo 40 series provide a trackstick 383device but do not have physical buttons associated with the trackstick 384device. Instead, the top area of the touchpad is marked to show 385visual/haptic areas for left, middle, right buttons intended to be used 386with the trackstick. 387 388If INPUT_PROP_TOPBUTTONPAD is set, userspace should emulate buttons 389accordingly. This property does not affect kernel behavior. 390The kernel does not provide button emulation for such devices but treats 391them as any other INPUT_PROP_BUTTONPAD device. 392 393INPUT_PROP_ACCELEROMETER 394------------------------ 395 396Directional axes on this device (absolute and/or relative x, y, z) represent 397accelerometer data. Some devices also report gyroscope data, which devices 398can report through the rotational axes (absolute and/or relative rx, ry, rz). 399 400All other axes retain their meaning. A device must not mix 401regular directional axes and accelerometer axes on the same event node. 402 403Guidelines 404========== 405 406The guidelines below ensure proper single-touch and multi-finger functionality. 407For multi-touch functionality, see the multi-touch-protocol.rst document for 408more information. 409 410Mice 411---- 412 413REL_{X,Y} must be reported when the mouse moves. BTN_LEFT must be used to report 414the primary button press. BTN_{MIDDLE,RIGHT,4,5,etc.} should be used to report 415further buttons of the device. REL_WHEEL and REL_HWHEEL should be used to report 416scroll wheel events where available. 417 418Touchscreens 419------------ 420 421ABS_{X,Y} must be reported with the location of the touch. BTN_TOUCH must be 422used to report when a touch is active on the screen. 423BTN_{MOUSE,LEFT,MIDDLE,RIGHT} must not be reported as the result of touch 424contact. BTN_TOOL_<name> events should be reported where possible. 425 426For new hardware, INPUT_PROP_DIRECT should be set. 427 428Trackpads 429--------- 430 431Legacy trackpads that only provide relative position information must report 432events like mice described above. 433 434Trackpads that provide absolute touch position must report ABS_{X,Y} for the 435location of the touch. BTN_TOUCH should be used to report when a touch is active 436on the trackpad. Where multi-finger support is available, BTN_TOOL_<name> should 437be used to report the number of touches active on the trackpad. 438 439For new hardware, INPUT_PROP_POINTER should be set. 440 441Tablets 442------- 443 444BTN_TOOL_<name> events must be reported when a stylus or other tool is active on 445the tablet. ABS_{X,Y} must be reported with the location of the tool. BTN_TOUCH 446should be used to report when the tool is in contact with the tablet. 447BTN_{STYLUS,STYLUS2} should be used to report buttons on the tool itself. Any 448button may be used for buttons on the tablet except BTN_{MOUSE,LEFT}. 449BTN_{0,1,2,etc} are good generic codes for unlabeled buttons. Do not use 450meaningful buttons, like BTN_FORWARD, unless the button is labeled for that 451purpose on the device. 452 453For new hardware, both INPUT_PROP_DIRECT and INPUT_PROP_POINTER should be set. 454