Input Event Codes

상태 기반 input event 규약과 type

Linux input protocol은 type과 code의 조합으로 장치 값을 사용자 공간에 표현합니다. 하나의 hardware event는 여러 `input_event`를 만들며 각 event는 단일 데이터 항목의 새 값인 type, code, value를 담습니다. `EV_SYN`이 같은 시점에 일어난 변경들을 하나의 packet으로 구분합니다.

이 규약은 stateful입니다. Code 값이 바뀔 때만 event가 전달되지만 상태는 input subsystem이 유지하므로 driver가 자체 상태를 보관할 필요는 없고 같은 값을 다시 보내도 해가 없습니다. 사용자 공간은 `linux/input.h`의 `EVIOCG*` ioctl로 현재 상태를 조회할 수 있습니다.

.. _input-event-codes:

=================
Input event codes
=================


The input protocol uses a map of types and codes to express input device values
to userspace. This document describes the types and codes and how and when they
may be used.

A single hardware event generates multiple input events. Each input event
contains the new value of a single data item. A special event type, EV_SYN, is
used to separate input events into packets of input data changes occurring at
the same moment in time. In the following, the term "event" refers to a single
input event encompassing a type, code, and value.

The input protocol is a stateful protocol. Events are emitted only when values
of event codes have changed. However, the state is maintained within the Linux
input subsystem; drivers do not need to maintain the state and may attempt to
emit unchanged values without harm. Userspace may obtain the current state of
event code values using the EVIOCG* ioctls defined in linux/input.h. The event
reports supported by a device are also provided by sysfs in
class/input/event*/device/capabilities/, and the properties of a device are
provided in class/input/event*/device/properties.

Event types
===========

Event types are groupings of codes under a logical input construct. Each
type has a set of applicable codes to be used in generating events. See the
Codes section for details on valid codes for each type.

* EV_SYN:

  - Used as markers to separate events. Events may be separated in time or in
    space, such as with the multitouch protocol.

* EV_KEY:

  - Used to describe state changes of keyboards, buttons, or other key-like
    devices.

* EV_REL:

  - Used to describe relative axis value changes, e.g. moving the mouse 5 units
    to the left.

* EV_ABS:

  - Used to describe absolute axis value changes, e.g. describing the
    coordinates of a touch on a touchscreen.

* EV_MSC:

  - Used to describe miscellaneous input data that do not fit into other types.

* EV_SW:

  - Used to describe binary state input switches.

* EV_LED:

  - Used to turn LEDs on devices on and off.

* EV_SND:

  - Used to output sound to devices.

* EV_REP:

  - Used for autorepeating devices.

* EV_FF:

  - Used to send force feedback commands to an input device.

* EV_PWR:

  - A special type for power button and switch input.

* EV_FF_STATUS:

  - Used to receive force feedback device status.

Event codes
===========

Event codes define the precise type of event.

EV_SYN 동기화와 EV_KEY touch·tool 규칙

`SYN_DROPPED`를 받으면 client는 다음 `SYN_REPORT`까지 포함해 모든 event를 무시하고, `EVIOCG*` ioctl로 장치의 현재 상태를 다시 조회해야 합니다. 유실 packet을 부분 적용해서는 안 됩니다.

`EV_KEY` code는 keyboard에 `KEY_<name>`, 그 밖의 momentary switch에 `BTN_<name>`을 사용합니다. Value 1은 press, 0은 release, 일부 hardware가 보내는 2는 repeat입니다.

`BTN_TOOL_<name>`은 trackpad, tablet, touchscreen에서 현재 tool 종류를 나타냅니다. Tool이 상호작용하면 1, 떠나면 0입니다. 한 synchronization frame에는 최대 하나만 1이어야 하며, tool을 바꿀 때는 기존 tool=0, `SYN_REPORT`, 새 tool=1 순서가 권장됩니다.

`BTN_TOUCH`는 의미 있는 물리 접촉 동안 1입니다. Hovering pen은 `BTN_TOOL_PEN=1`, `BTN_TOUCH=0`일 수 있습니다. Legacy `mousedev` 호환을 위해 `BTN_TOUCH`는 synchronization frame에서 첫 evdev code여야 합니다.

역사적으로 `BTN_TOOL_FINGER`와 `BTN_TOUCH`를 모두 제공하면 touchpad, `BTN_TOOL_FINGER` 없이 `BTN_TOUCH`만 제공하면 touchscreen으로 해석됐습니다. 현재 사용자 공간 호환을 위해 이 구분을 따르지만 장기적으로는 `EVIOCGPROP` device property가 대체합니다. Multitouch driver는 finger-count code를 `input_mt_report_finger_count()`로 보내야 합니다.

EV_SYN
------

EV_SYN event values are undefined. Their usage is defined only by when they are
sent in the evdev event stream.

* SYN_REPORT:

  - Used to synchronize and separate events into packets of input data changes
    occurring at the same moment in time. For example, motion of a mouse may set
    the REL_X and REL_Y values for one motion, then emit a SYN_REPORT. The next
    motion will emit more REL_X and REL_Y values and send another SYN_REPORT.

* SYN_CONFIG:

  - TBD

* SYN_MT_REPORT:

  - Used to synchronize and separate touch events. See the
    multi-touch-protocol.txt document for more information.

* SYN_DROPPED:

  - Used to indicate buffer overrun in the evdev client's event queue.
    Client should ignore all events up to and including next SYN_REPORT
    event and query the device (using EVIOCG* ioctls) to obtain its
    current state.

EV_KEY
------

EV_KEY events take the form KEY_<name> or BTN_<name>. For example, KEY_A is used
to represent the 'A' key on a keyboard. When a key is depressed, an event with
the key's code is emitted with value 1. When the key is released, an event is
emitted with value 0. Some hardware send events when a key is repeated. These
events have a value of 2. In general, KEY_<name> is used for keyboard keys, and
BTN_<name> is used for other types of momentary switch events.

A few EV_KEY codes have special meanings:

* BTN_TOOL_<name>:

  - These codes are used in conjunction with input trackpads, tablets, and
    touchscreens. These devices may be used with fingers, pens, or other tools.
    When an event occurs and a tool is used, the corresponding BTN_TOOL_<name>
    code should be set to a value of 1. When the tool is no longer interacting
    with the input device, the BTN_TOOL_<name> code should be reset to 0. All
    trackpads, tablets, and touchscreens should use at least one BTN_TOOL_<name>
    code when events are generated. Likewise all trackpads, tablets, and
    touchscreens should export only one BTN_TOOL_<name> at a time. To not break
    existing userspace, it is recommended to not switch tool in one EV_SYN frame
    but first emitting the old BTN_TOOL_<name> at 0, then emit one SYN_REPORT
    and then set the new BTN_TOOL_<name> at 1.

* BTN_TOUCH:

    BTN_TOUCH is used for touch contact. While an input tool is determined to be
    within meaningful physical contact, the value of this property must be set
    to 1. Meaningful physical contact may mean any contact, or it may mean
    contact conditioned by an implementation defined property. For example, a
    touchpad may set the value to 1 only when the touch pressure rises above a
    certain value. BTN_TOUCH may be combined with BTN_TOOL_<name> codes. For
    example, a pen tablet may set BTN_TOOL_PEN to 1 and BTN_TOUCH to 0 while the
    pen is hovering over but not touching the tablet surface.

Note: For appropriate function of the legacy mousedev emulation driver,
BTN_TOUCH must be the first evdev code emitted in a synchronization frame.

Note: Historically a touch device with BTN_TOOL_FINGER and BTN_TOUCH was
interpreted as a touchpad by userspace, while a similar device without
BTN_TOOL_FINGER was interpreted as a touchscreen. For backwards compatibility
with current userspace it is recommended to follow this distinction. In the
future, this distinction will be deprecated and the device properties ioctl
EVIOCGPROP, defined in linux/input.h, will be used to convey the device type.

* BTN_TOOL_FINGER, BTN_TOOL_DOUBLETAP, BTN_TOOL_TRIPLETAP, BTN_TOOL_QUADTAP:

  - These codes denote one, two, three, and four finger interaction on a
    trackpad or touchscreen. For example, if the user uses two fingers and moves
    them on the touchpad in an effort to scroll content on screen,
    BTN_TOOL_DOUBLETAP should be set to value 1 for the duration of the motion.
    Note that all BTN_TOOL_<name> codes and the BTN_TOUCH code are orthogonal in
    purpose. A trackpad event generated by finger touches should generate events
    for one code from each group. At most only one of these BTN_TOOL_<name>
    codes should have a value of 1 during any synchronization frame.

Note: Historically some drivers emitted multiple of the finger count codes with
a value of 1 in the same synchronization frame. This usage is deprecated.

Note: In multitouch drivers, the input_mt_report_finger_count() function should
be used to emit these codes. Please see multi-touch-protocol.txt for details.

EV_REL 스크롤과 EV_ABS 거리·압력

`EV_REL`은 절대 위치를 모르는 상대 변화량입니다. Mouse가 왼쪽으로 몇 unit 움직였다는 정보가 예이며, 실제 절대 위치를 아는 장치는 `EV_ABS`를 사용해야 합니다.

High-resolution을 지원하지 않는 장치는 값이 항상 120의 배수이고, 지원 장치는 120의 일부 값을 보낼 수 있습니다. High-resolution code는 legacy `REL_WHEEL` 또는 `REL_HWHEEL`과 함께 보내며 legacy 값은 근사치일 수 있습니다. Legacy event 시점에 누적 high-resolution 값이 반드시 120의 배수일 필요는 없습니다.

`EV_ABS`는 touch 위치처럼 property의 절대값을 나타냅니다. `ABS_DISTANCE`는 tool이 hover 중이고 `BTN_TOUCH=0`일 때 표면으로부터의 거리를 보고합니다. 자유로운 3차원 위치라면 `ABS_Z`를 고려합니다.

`ABS_DISTANCE`와 무관하게 tool이 detect proximity에 들어오면 대응 `BTN_TOOL_<name>`을 1, 벗어나면 0으로 해야 합니다. `ABS_PROFILE`은 선택된 profile이 바뀔 때만 새 값을 보냅니다.

많은 touch device는 접촉 면적이 pressure와 함께 커지는 점을 이용해 contact size를 pressure로 변환하지만 true pressure sensor를 가진 digitizer나 pressure pad에는 이 관계가 적용되지 않습니다. Axis resolution 0이면 arbitrary unit, non-zero이면 units/gram입니다.

EV_REL
------

EV_REL events describe relative changes in a property. For example, a mouse may
move to the left by a certain number of units, but its absolute position in
space is unknown. If the absolute position is known, EV_ABS codes should be used
instead of EV_REL codes.

A few EV_REL codes have special meanings:

* REL_WHEEL, REL_HWHEEL:

  - These codes are used for vertical and horizontal scroll wheels,
    respectively. The value is the number of detents moved on the wheel, the
    physical size of which varies by device. For high-resolution wheels
    this may be an approximation based on the high-resolution scroll events,
    see REL_WHEEL_HI_RES. These event codes are legacy codes and
    REL_WHEEL_HI_RES and REL_HWHEEL_HI_RES should be preferred where
    available.

* REL_WHEEL_HI_RES, REL_HWHEEL_HI_RES:

  - High-resolution scroll wheel data. The accumulated value 120 represents
    movement by one detent. For devices that do not provide high-resolution
    scrolling, the value is always a multiple of 120. For devices with
    high-resolution scrolling, the value may be a fraction of 120.

    If a vertical scroll wheel supports high-resolution scrolling, this code
    will be emitted in addition to REL_WHEEL or REL_HWHEEL. The REL_WHEEL
    and REL_HWHEEL may be an approximation based on the high-resolution
    scroll events. There is no guarantee that the high-resolution data
    is a multiple of 120 at the time of an emulated REL_WHEEL or REL_HWHEEL
    event.

EV_ABS
------

EV_ABS events describe absolute changes in a property. For example, a touchpad
may emit coordinates for a touch location.

A few EV_ABS codes have special meanings:

* ABS_DISTANCE:

  - Used to describe the distance of a tool from an interaction surface. This
    event should only be emitted while the tool is hovering, meaning in close
    proximity of the device and while the value of the BTN_TOUCH code is 0. If
    the input device may be used freely in three dimensions, consider ABS_Z
    instead.
  - BTN_TOOL_<name> should be set to 1 when the tool comes into detectable
    proximity and set to 0 when the tool leaves detectable proximity.
    BTN_TOOL_<name> signals the type of tool that is currently detected by the
    hardware and is otherwise independent of ABS_DISTANCE and/or BTN_TOUCH.

* ABS_PROFILE:

  - Used to describe the state of a multi-value profile switch.  An event is
    emitted only when the selected profile changes, indicating the newly
    selected profile value.

* ABS_MT_<name>:

  - Used to describe multitouch input events. Please see
    multi-touch-protocol.txt for details.

* ABS_PRESSURE/ABS_MT_PRESSURE:

   - For touch devices, many devices converted contact size into pressure.
     A finger flattens with pressure, causing a larger contact area and thus
     pressure and contact size are directly related. This is not the case
     for other devices, for example digitizers and touchpads with a true
     pressure sensor ("pressure pads").

     A device should set the resolution of the axis to indicate whether the
     pressure is in measurable units. If the resolution is zero, the
     pressure data is in arbitrary units. If the resolution is non-zero, the
     pressure data is in units/gram. For example, a value of 10 with a
     resolution of 1 represents 10 gram, a value of 10 with a resolution of
     1000 represents 10 microgram.

Switch·timestamp·LED·sound·force-feedback event

`EV_SW`는 `SW_LID` 같은 상태형 binary switch를 나타냅니다. Driver는 device bind 시점과 suspend에서 resume할 때 현재 switch 상태를 반드시 보고해 device, kernel, userspace를 동기화해야 합니다.

Resume 후 상태가 suspend 전과 같으면 input subsystem이 duplicate report를 필터하므로 driver가 switch 상태를 따로 유지할 필요는 없습니다.

`MSC_TIMESTAMP`는 uint32 microseconds이고 wrap-around는 특별한 문제로 취급하지 않습니다. 연속 event 간 시간차는 수 시간 정도의 합리적 범위에서 신뢰할 수 있다고 가정합니다. 0으로 reset되면 마지막 event 이후 시간은 알 수 없습니다. 장치가 제공하지 않으면 driver가 임의 생성해 사용자 공간에 제공해서는 안 됩니다.

EV_SW
-----

EV_SW events describe stateful binary switches. For example, the SW_LID code is
used to denote when a laptop lid is closed.

Upon binding to a device or resuming from suspend, a driver must report
the current switch state. This ensures that the device, kernel, and userspace
state is in sync.

Upon resume, if the switch state is the same as before suspend, then the input
subsystem will filter out the duplicate switch state reports. The driver does
not need to keep the state of the switch at any time.

EV_MSC
------

EV_MSC events are used for input and output events that do not fall under other
categories.

A few EV_MSC codes have special meaning:

* MSC_TIMESTAMP:

  - Used to report the number of microseconds since the last reset. This event
    should be coded as an uint32 value, which is allowed to wrap around with
    no special consequence. It is assumed that the time difference between two
    consecutive events is reliable on a reasonable time scale (hours).
    A reset to zero can happen, in which case the time since the last event is
    unknown.  If the device does not provide this information, the driver must
    not provide it to user space.

EV_LED
------

EV_LED events are used for input and output to set and query the state of
various LEDs on devices.

EV_REP
------

EV_REP events are used for specifying autorepeating events.

EV_SND
------

EV_SND events are used for sending sound commands to simple sound output
devices.

EV_FF
-----

EV_FF events are used to initialize a force feedback capable device and to cause
such device to feedback.

EV_PWR
------

EV_PWR events are a special type of event used specifically for power
management. Its usage is not well defined. To be addressed later.

Direct·pointer·buttonpad·multitouch·sensor property

같은 event type을 내는 장치들을 더 정확히 구분하려면 device property를 사용합니다. `INPUT_PROP_DIRECT`는 좌표가 화면 좌표에 직접 매핑됨을, `INPUT_PROP_POINTER`는 화면 위 pointer가 사용자의 움직임을 추적해야 함을 뜻합니다.

`INPUT_PROP_BUTTONPAD`는 표면 아래 통합 button을 눌러 click하는 Clickpad류에 설정합니다. 2009년 이후 MacBook과 notebook에서 흔합니다. 과거 `bcm5974` version의 integrated button field도 호환을 위해 사용자 공간에서 함께 확인해야 합니다.

`INPUT_PROP_SEMI_MT`는 여러 contact의 존재와 수는 알지만 개별 위치를 분리하지 못하고 rectangle만 제공하는 일부 2008~2011 touchpad에 사용합니다. Rectangle이 모든 touch의 bounding box일 수도, 최근 두 touch만 포함할 수도 있어 제한적입니다. 이 property가 없으면 true MT로 간주합니다.

`INPUT_PROP_TOPBUTTONPAD`는 trackstick 전용 물리 button 없이 touchpad 상단을 left·middle·right 영역으로 사용하는 Lenovo 40 series 같은 장치를 표시합니다. 사용자 공간이 button을 emulate하며 kernel 동작에는 영향을 주지 않습니다.

`INPUT_PROP_ACCELEROMETER`가 설정된 node의 x/y/z axis는 accelerometer data이고 rotational rx/ry/rz는 gyroscope data일 수 있습니다. 같은 event node에 일반 directional axis와 accelerometer axis를 섞어서는 안 됩니다.

`INPUT_PROP_PRESSUREPAD`는 surface 아래 vibrator 같은 simulated haptic feedback을 제공하는 장치에만 설정합니다. 최소 5손가락을 구분하고 X/Y의 unit·resolution이 정확하며 MT protocol type B를 따라야 합니다.

해당하는 경우 `INPUT_PROP_PRESSUREPAD`는 `INPUT_PROP_BUTTONPAD`에 추가로 설정하며 이를 대체하지 않습니다.

Device properties
=================

Normally, userspace sets up an input device based on the data it emits,
i.e., the event types. In the case of two devices emitting the same event
types, additional information can be provided in the form of device
properties.

INPUT_PROP_DIRECT + INPUT_PROP_POINTER
--------------------------------------

The INPUT_PROP_DIRECT property indicates that device coordinates should be
directly mapped to screen coordinates (not taking into account trivial
transformations, such as scaling, flipping and rotating). Non-direct input
devices require non-trivial transformation, such as absolute to relative
transformation for touchpads. Typical direct input devices: touchscreens,
drawing tablets; non-direct devices: touchpads, mice.

The INPUT_PROP_POINTER property indicates that the device is not transposed
on the screen and thus requires use of an on-screen pointer to trace user's
movements.  Typical pointer devices: touchpads, tablets, mice; non-pointer
device: touchscreen.

If neither INPUT_PROP_DIRECT or INPUT_PROP_POINTER are set, the property is
considered undefined and the device type should be deduced in the
traditional way, using emitted event types.

INPUT_PROP_BUTTONPAD
--------------------

For touchpads where the button is placed beneath the surface, such that
pressing down on the pad causes a button click, this property should be
set. Common in Clickpad notebooks and Macbooks from 2009 and onwards.

Originally, the buttonpad property was coded into the bcm5974 driver
version field under the name integrated button. For backwards
compatibility, both methods need to be checked in userspace.

INPUT_PROP_SEMI_MT
------------------

Some touchpads, most common between 2008 and 2011, can detect the presence
of multiple contacts without resolving the individual positions; only the
number of contacts and a rectangular shape is known. For such
touchpads, the SEMI_MT property should be set.

Depending on the device, the rectangle may enclose all touches, like a
bounding box, or just some of them, for instance the two most recent
touches. The diversity makes the rectangle of limited use, but some
gestures can normally be extracted from it.

If INPUT_PROP_SEMI_MT is not set, the device is assumed to be a true MT
device.

INPUT_PROP_TOPBUTTONPAD
-----------------------

Some laptops, most notably the Lenovo 40 series provide a trackstick
device but do not have physical buttons associated with the trackstick
device. Instead, the top area of the touchpad is marked to show
visual/haptic areas for left, middle, right buttons intended to be used
with the trackstick.

If INPUT_PROP_TOPBUTTONPAD is set, userspace should emulate buttons
accordingly. This property does not affect kernel behavior.
The kernel does not provide button emulation for such devices but treats
them as any other INPUT_PROP_BUTTONPAD device.

INPUT_PROP_ACCELEROMETER
------------------------

Directional axes on this device (absolute and/or relative x, y, z) represent
accelerometer data. Some devices also report gyroscope data, which devices
can report through the rotational axes (absolute and/or relative rx, ry, rz).

All other axes retain their meaning. A device must not mix
regular directional axes and accelerometer axes on the same event node.

INPUT_PROP_PRESSUREPAD
----------------------

The INPUT_PROP_PRESSUREPAD property indicates that the device provides
simulated haptic feedback (e.g. a vibrator motor situated below the surface)
instead of physical haptic feedback (e.g. a hinge). This property is only set
if the device:

- can differentiate between at least 5 fingers
- uses correct resolution for the X/Y (units and value)
- follows the MT protocol type B

If the simulated haptic feedback is controllable by userspace the device must:

- support simple haptic auto and manual triggering, and
- report correct force per touch, and correct units for them (newtons or grams), and
- provide the EV_FF FF_HAPTIC force feedback effect.

Summing up, such devices follow the MS spec for input devices in
Win8 and Win8.1, and in addition may support the Simple haptic controller HID
table, and report correct units for the pressure.

Where applicable, this property is set in addition to INPUT_PROP_BUTTONPAD, it
does not replace that property.

Mouse·touchscreen·trackpad·tablet 보고 지침

Mouse는 움직일 때 `REL_{X,Y}`, primary button에 `BTN_LEFT`, 추가 button에 `BTN_{MIDDLE,RIGHT,4,5,...}`, scroll에 `REL_WHEEL`과 `REL_HWHEEL`을 사용합니다.

Touchscreen은 touch 위치에 `ABS_{X,Y}`, 활성 접촉에 `BTN_TOUCH`를 사용합니다. 접촉 때문에 `BTN_{MOUSE,LEFT,MIDDLE,RIGHT}`를 보내서는 안 되고 가능한 경우 `BTN_TOOL_<name>`을 보냅니다. 새 hardware는 `INPUT_PROP_DIRECT`를 설정합니다.

Absolute trackpad는 위치에 `ABS_{X,Y}`, 접촉에 `BTN_TOUCH`, multi-finger가 있으면 활성 touch 수에 `BTN_TOOL_<name>`을 사용합니다. 새 hardware는 `INPUT_PROP_POINTER`를 설정합니다.

Tablet은 stylus나 tool이 활성일 때 `BTN_TOOL_<name>`, 위치에 `ABS_{X,Y}`, 표면 접촉에 `BTN_TOUCH`, tool 자체 button에 `BTN_STYLUS`·`BTN_STYLUS2`를 씁니다. Tablet 본체의 unlabeled button은 `BTN_0`, `BTN_1` 같은 generic code를 쓰고 실제 label이 없는 `BTN_FORWARD` 같은 의미 있는 code를 임의로 사용하지 않습니다.

Guidelines
==========

The guidelines below ensure proper single-touch and multi-finger functionality.
For multi-touch functionality, see the multi-touch-protocol.rst document for
more information.

Mice
----

REL_{X,Y} must be reported when the mouse moves. BTN_LEFT must be used to report
the primary button press. BTN_{MIDDLE,RIGHT,4,5,etc.} should be used to report
further buttons of the device. REL_WHEEL and REL_HWHEEL should be used to report
scroll wheel events where available.

Touchscreens
------------

ABS_{X,Y} must be reported with the location of the touch. BTN_TOUCH must be
used to report when a touch is active on the screen.
BTN_{MOUSE,LEFT,MIDDLE,RIGHT} must not be reported as the result of touch
contact. BTN_TOOL_<name> events should be reported where possible.

For new hardware, INPUT_PROP_DIRECT should be set.

Trackpads
---------

Legacy trackpads that only provide relative position information must report
events like mice described above.

Trackpads that provide absolute touch position must report ABS_{X,Y} for the
location of the touch. BTN_TOUCH should be used to report when a touch is active
on the trackpad. Where multi-finger support is available, BTN_TOOL_<name> should
be used to report the number of touches active on the trackpad.

For new hardware, INPUT_PROP_POINTER should be set.

Tablets
-------

BTN_TOOL_<name> events must be reported when a stylus or other tool is active on
the tablet. ABS_{X,Y} must be reported with the location of the tool. BTN_TOUCH
should be used to report when the tool is in contact with the tablet.
BTN_{STYLUS,STYLUS2} should be used to report buttons on the tool itself. Any
button may be used for buttons on the tablet except BTN_{MOUSE,LEFT}.
BTN_{0,1,2,etc} are good generic codes for unlabeled buttons. Do not use
meaningful buttons, like BTN_FORWARD, unless the button is labeled for that
purpose on the device.

For new hardware, both INPUT_PROP_DIRECT and INPUT_PROP_POINTER should be set.