Based on kernel version 4.10.8. Page generated on 2017-04-01 14:43 EST.
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 3 may be used. 4 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. 10 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. 19 20 Event types: 21 =========== 22 Event types are groupings of codes under a logical input construct. Each 23 type has a set of applicable codes to be used in generating events. See the 24 Codes section for 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 66 Event codes: 67 =========== 68 Event codes define the precise type of event. 69 70 EV_SYN: 71 ---------- 72 EV_SYN event values are undefined. Their usage is defined only by when they are 73 sent 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 88 * 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 94 EV_KEY: 95 ---------- 96 EV_KEY events take the form KEY_<name> or BTN_<name>. For example, KEY_A is used 97 to represent the 'A' key on a keyboard. When a key is depressed, an event with 98 the key's code is emitted with value 1. When the key is released, an event is 99 emitted with value 0. Some hardware send events when a key is repeated. These 100 events have a value of 2. In general, KEY_<name> is used for keyboard keys, and 101 BTN_<name> is used for other types of momentary switch events. 102 103 A 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. 123 124 Note: For appropriate function of the legacy mousedev emulation driver, 125 BTN_TOUCH must be the first evdev code emitted in a synchronization frame. 126 127 Note: Historically a touch device with BTN_TOOL_FINGER and BTN_TOUCH was 128 interpreted as a touchpad by userspace, while a similar device without 129 BTN_TOOL_FINGER was interpreted as a touchscreen. For backwards compatibility 130 with current userspace it is recommended to follow this distinction. In the 131 future, this distinction will be deprecated and the device properties ioctl 132 EVIOCGPROP, 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. 143 144 Note: Historically some drivers emitted multiple of the finger count codes with 145 a value of 1 in the same synchronization frame. This usage is deprecated. 146 147 Note: In multitouch drivers, the input_mt_report_finger_count() function should 148 be used to emit these codes. Please see multi-touch-protocol.txt for details. 149 150 EV_REL: 151 ---------- 152 EV_REL events describe relative changes in a property. For example, a mouse may 153 move to the left by a certain number of units, but its absolute position in 154 space is unknown. If the absolute position is known, EV_ABS codes should be used 155 instead of EV_REL codes. 156 157 A 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. 162 163 EV_ABS: 164 ---------- 165 EV_ABS events describe absolute changes in a property. For example, a touchpad 166 may emit coordinates for a touch location. 167 168 A 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 - BTN_TOOL_<name> should be set to 1 when the tool comes into detectable 177 proximity and set to 0 when the tool leaves detectable proximity. 178 BTN_TOOL_<name> signals the type of tool that is currently detected by the 179 hardware and is otherwise independent of ABS_DISTANCE and/or BTN_TOUCH. 180 181 * ABS_MT_<name>: 182 - Used to describe multitouch input events. Please see 183 multi-touch-protocol.txt for details. 184 185 EV_SW: 186 ---------- 187 EV_SW events describe stateful binary switches. For example, the SW_LID code is 188 used to denote when a laptop lid is closed. 189 190 Upon binding to a device or resuming from suspend, a driver must report 191 the current switch state. This ensures that the device, kernel, and userspace 192 state is in sync. 193 194 Upon resume, if the switch state is the same as before suspend, then the input 195 subsystem will filter out the duplicate switch state reports. The driver does 196 not need to keep the state of the switch at any time. 197 198 EV_MSC: 199 ---------- 200 EV_MSC events are used for input and output events that do not fall under other 201 categories. 202 203 A few EV_MSC codes have special meaning: 204 205 * MSC_TIMESTAMP: 206 - Used to report the number of microseconds since the last reset. This event 207 should be coded as an uint32 value, which is allowed to wrap around with 208 no special consequence. It is assumed that the time difference between two 209 consecutive events is reliable on a reasonable time scale (hours). 210 A reset to zero can happen, in which case the time since the last event is 211 unknown. If the device does not provide this information, the driver must 212 not provide it to user space. 213 214 EV_LED: 215 ---------- 216 EV_LED events are used for input and output to set and query the state of 217 various LEDs on devices. 218 219 EV_REP: 220 ---------- 221 EV_REP events are used for specifying autorepeating events. 222 223 EV_SND: 224 ---------- 225 EV_SND events are used for sending sound commands to simple sound output 226 devices. 227 228 EV_FF: 229 ---------- 230 EV_FF events are used to initialize a force feedback capable device and to cause 231 such device to feedback. 232 233 EV_PWR: 234 ---------- 235 EV_PWR events are a special type of event used specifically for power 236 management. Its usage is not well defined. To be addressed later. 237 238 Device properties: 239 ================= 240 Normally, userspace sets up an input device based on the data it emits, 241 i.e., the event types. In the case of two devices emitting the same event 242 types, additional information can be provided in the form of device 243 properties. 244 245 INPUT_PROP_DIRECT + INPUT_PROP_POINTER: 246 -------------------------------------- 247 The INPUT_PROP_DIRECT property indicates that device coordinates should be 248 directly mapped to screen coordinates (not taking into account trivial 249 transformations, such as scaling, flipping and rotating). Non-direct input 250 devices require non-trivial transformation, such as absolute to relative 251 transformation for touchpads. Typical direct input devices: touchscreens, 252 drawing tablets; non-direct devices: touchpads, mice. 253 254 The INPUT_PROP_POINTER property indicates that the device is not transposed 255 on the screen and thus requires use of an on-screen pointer to trace user's 256 movements. Typical pointer devices: touchpads, tablets, mice; non-pointer 257 device: touchscreen. 258 259 If neither INPUT_PROP_DIRECT or INPUT_PROP_POINTER are set, the property is 260 considered undefined and the device type should be deduced in the 261 traditional way, using emitted event types. 262 263 INPUT_PROP_BUTTONPAD: 264 -------------------- 265 For touchpads where the button is placed beneath the surface, such that 266 pressing down on the pad causes a button click, this property should be 267 set. Common in clickpad notebooks and macbooks from 2009 and onwards. 268 269 Originally, the buttonpad property was coded into the bcm5974 driver 270 version field under the name integrated button. For backwards 271 compatibility, both methods need to be checked in userspace. 272 273 INPUT_PROP_SEMI_MT: 274 ------------------ 275 Some touchpads, most common between 2008 and 2011, can detect the presence 276 of multiple contacts without resolving the individual positions; only the 277 number of contacts and a rectangular shape is known. For such 278 touchpads, the semi-mt property should be set. 279 280 Depending on the device, the rectangle may enclose all touches, like a 281 bounding box, or just some of them, for instance the two most recent 282 touches. The diversity makes the rectangle of limited use, but some 283 gestures can normally be extracted from it. 284 285 If INPUT_PROP_SEMI_MT is not set, the device is assumed to be a true MT 286 device. 287 288 INPUT_PROP_TOPBUTTONPAD: 289 ----------------------- 290 Some laptops, most notably the Lenovo *40 series provide a trackstick 291 device but do not have physical buttons associated with the trackstick 292 device. Instead, the top area of the touchpad is marked to show 293 visual/haptic areas for left, middle, right buttons intended to be used 294 with the trackstick. 295 296 If INPUT_PROP_TOPBUTTONPAD is set, userspace should emulate buttons 297 accordingly. This property does not affect kernel behavior. 298 The kernel does not provide button emulation for such devices but treats 299 them as any other INPUT_PROP_BUTTONPAD device. 300 301 INPUT_PROP_ACCELEROMETER 302 ------------------------- 303 Directional axes on this device (absolute and/or relative x, y, z) represent 304 accelerometer data. All other axes retain their meaning. A device must not mix 305 regular directional axes and accelerometer axes on the same event node. 306 307 Guidelines: 308 ========== 309 The guidelines below ensure proper single-touch and multi-finger functionality. 310 For multi-touch functionality, see the multi-touch-protocol.txt document for 311 more information. 312 313 Mice: 314 ---------- 315 REL_{X,Y} must be reported when the mouse moves. BTN_LEFT must be used to report 316 the primary button press. BTN_{MIDDLE,RIGHT,4,5,etc.} should be used to report 317 further buttons of the device. REL_WHEEL and REL_HWHEEL should be used to report 318 scroll wheel events where available. 319 320 Touchscreens: 321 ---------- 322 ABS_{X,Y} must be reported with the location of the touch. BTN_TOUCH must be 323 used to report when a touch is active on the screen. 324 BTN_{MOUSE,LEFT,MIDDLE,RIGHT} must not be reported as the result of touch 325 contact. BTN_TOOL_<name> events should be reported where possible. 326 327 For new hardware, INPUT_PROP_DIRECT should be set. 328 329 Trackpads: 330 ---------- 331 Legacy trackpads that only provide relative position information must report 332 events like mice described above. 333 334 Trackpads that provide absolute touch position must report ABS_{X,Y} for the 335 location of the touch. BTN_TOUCH should be used to report when a touch is active 336 on the trackpad. Where multi-finger support is available, BTN_TOOL_<name> should 337 be used to report the number of touches active on the trackpad. 338 339 For new hardware, INPUT_PROP_POINTER should be set. 340 341 Tablets: 342 ---------- 343 BTN_TOOL_<name> events must be reported when a stylus or other tool is active on 344 the tablet. ABS_{X,Y} must be reported with the location of the tool. BTN_TOUCH 345 should be used to report when the tool is in contact with the tablet. 346 BTN_{STYLUS,STYLUS2} should be used to report buttons on the tool itself. Any 347 button may be used for buttons on the tablet except BTN_{MOUSE,LEFT}. 348 BTN_{0,1,2,etc} are good generic codes for unlabeled buttons. Do not use 349 meaningful buttons, like BTN_FORWARD, unless the button is labeled for that 350 purpose on the device. 351 352 For new hardware, both INPUT_PROP_DIRECT and INPUT_PROP_POINTER should be set.