Documentation/input/gamepad.rst

   1 ---------------------------
   2 Linux Gamepad Specification
   3 ---------------------------
   4
   5 :Author: 2013 by David Herrmann <dh.herrmann@gmail.com>
   6
   7
   8 Introduction
   9 ~~~~~~~~~~~~
  10 Linux provides many different input drivers for gamepad hardware. To avoid
  11 having user-space deal with different button-mappings for each gamepad, this
  12 document defines how gamepads are supposed to report their data.
  13
  14 Geometry
  15 ~~~~~~~~
  16 As "gamepad" we define devices which roughly look like this::
  17
  18             ____________________________              __
  19            / [__ZL__]          [__ZR__] \               |
  20           / [__ TL __]        [__ TR __] \              | Front Triggers
  21        __/________________________________\__         __|
  22       /                                  _   \          |
  23      /      /\           __             (N)   \         |
  24     /       ||      __  |MO|  __     _       _ \        | Main Pad
  25    |    <===DP===> |SE|      |ST|   (W) -|- (E) |       |
  26     \       ||    ___          ___       _     /        |
  27     /\      \/   /   \        /   \     (S)   /\      __|
  28    /  \________ | LS  | ____ |  RS | ________/  \       |
  29   |         /  \ \___/ /    \ \___/ /  \         |      | Control Sticks
  30   |        /    \_____/      \_____/    \        |    __|
  31   |       /                              \       |
  32    \_____/                                \_____/
  33
  34        |________|______|    |______|___________|
  35          D-Pad    Left       Right   Action Pad
  36                  Stick       Stick
  37
  38                    |_____________|
  39                       Menu Pad
  40
  41 Most gamepads have the following features:
  42
  43   - Action-Pad
  44     4 buttons in diamonds-shape (on the right side). The buttons are
  45     differently labeled on most devices so we define them as NORTH,
  46     SOUTH, WEST and EAST.
  47   - D-Pad (Direction-pad)
  48     4 buttons (on the left side) that point up, down, left and right.
  49   - Menu-Pad
  50     Different constellations, but most-times 2 buttons: SELECT - START
  51     Furthermore, many gamepads have a fancy branded button that is used as
  52     special system-button. It often looks different to the other buttons and
  53     is used to pop up system-menus or system-settings.
  54   - Analog-Sticks
  55     Analog-sticks provide freely moveable sticks to control directions. Not
  56     all devices have both or any, but they are present at most times.
  57     Analog-sticks may also provide a digital button if you press them.
  58   - Triggers
  59     Triggers are located on the upper-side of the pad in vertical direction.
  60     Not all devices provide them, but the upper buttons are normally named
  61     Left- and Right-Triggers, the lower buttons Z-Left and Z-Right.
  62   - Rumble
  63     Many devices provide force-feedback features. But are mostly just
  64     simple rumble motors.
  65
  66 Detection
  67 ~~~~~~~~~
  68
  69 All gamepads that follow the protocol described here map BTN_GAMEPAD. This is
  70 an alias for BTN_SOUTH/BTN_A. It can be used to identify a gamepad as such.
  71 However, not all gamepads provide all features, so you need to test for all
  72 features that you need, first. How each feature is mapped is described below.
  73
  74 Legacy drivers often don't comply to these rules. As we cannot change them
  75 for backwards-compatibility reasons, you need to provide fixup mappings in
  76 user-space yourself. Some of them might also provide module-options that
  77 change the mappings so you can advise users to set these.
  78
  79 All new gamepads are supposed to comply with this mapping. Please report any
  80 bugs, if they don't.
  81
  82 There are a lot of less-featured/less-powerful devices out there, which re-use
  83 the buttons from this protocol. However, they try to do this in a compatible
  84 fashion. For example, the "Nintendo Wii Nunchuk" provides two trigger buttons
  85 and one analog stick. It reports them as if it were a gamepad with only one
  86 analog stick and two trigger buttons on the right side.
  87 But that means, that if you only support "real" gamepads, you must test
  88 devices for _all_ reported events that you need. Otherwise, you will also get
  89 devices that report a small subset of the events.
  90
  91 No other devices, that do not look/feel like a gamepad, shall report these
  92 events.
  93
  94 Events
  95 ~~~~~~
  96
  97 Gamepads report the following events:
  98
  99 - Action-Pad:
 100
 101   Every gamepad device has at least 2 action buttons. This means, that every
 102   device reports BTN_SOUTH (which BTN_GAMEPAD is an alias for). Regardless
 103   of the labels on the buttons, the codes are sent according to the
 104   physical position of the buttons.
 105
 106   Please note that 2- and 3-button pads are fairly rare and old. You might
 107   want to filter gamepads that do not report all four.
 108
 109     - 2-Button Pad:
 110
 111       If only 2 action-buttons are present, they are reported as BTN_SOUTH and
 112       BTN_EAST. For vertical layouts, the upper button is BTN_EAST. For
 113       horizontal layouts, the button more on the right is BTN_EAST.
 114
 115     - 3-Button Pad:
 116
 117       If only 3 action-buttons are present, they are reported as (from left
 118       to right): BTN_WEST, BTN_SOUTH, BTN_EAST
 119       If the buttons are aligned perfectly vertically, they are reported as
 120       (from top down): BTN_WEST, BTN_SOUTH, BTN_EAST
 121
 122     - 4-Button Pad:
 123
 124       If all 4 action-buttons are present, they can be aligned in two
 125       different formations. If diamond-shaped, they are reported as BTN_NORTH,
 126       BTN_WEST, BTN_SOUTH, BTN_EAST according to their physical location.
 127       If rectangular-shaped, the upper-left button is BTN_NORTH, lower-left
 128       is BTN_WEST, lower-right is BTN_SOUTH and upper-right is BTN_EAST.
 129
 130 - D-Pad:
 131
 132   Every gamepad provides a D-Pad with four directions: Up, Down, Left, Right
 133   Some of these are available as digital buttons, some as analog buttons. Some
 134   may even report both. The kernel does not convert between these so
 135   applications should support both and choose what is more appropriate if
 136   both are reported.
 137
 138     - Digital buttons are reported as:
 139
 140       BTN_DPAD_*
 141
 142     - Analog buttons are reported as:
 143
 144       ABS_HAT0X and ABS_HAT0Y
 145
 146   (for ABS values negative is left/up, positive is right/down)
 147
 148 - Analog-Sticks:
 149
 150   The left analog-stick is reported as ABS_X, ABS_Y. The right analog stick is
 151   reported as ABS_RX, ABS_RY. Zero, one or two sticks may be present.
 152   If analog-sticks provide digital buttons, they are mapped accordingly as
 153   BTN_THUMBL (first/left) and BTN_THUMBR (second/right).
 154
 155   (for ABS values negative is left/up, positive is right/down)
 156
 157 - Triggers:
 158
 159   Trigger buttons can be available as digital or analog buttons or both. User-
 160   space must correctly deal with any situation and choose the most appropriate
 161   mode.
 162
 163   Upper trigger buttons are reported as BTN_TR or ABS_HAT1X (right) and BTN_TL
 164   or ABS_HAT1Y (left). Lower trigger buttons are reported as BTN_TR2 or
 165   ABS_HAT2X (right/ZR) and BTN_TL2 or ABS_HAT2Y (left/ZL).
 166
 167   If only one trigger-button combination is present (upper+lower), they are
 168   reported as "right" triggers (BTN_TR/ABS_HAT1X).
 169
 170   (ABS trigger values start at 0, pressure is reported as positive values)
 171
 172 - Menu-Pad:
 173
 174   Menu buttons are always digital and are mapped according to their location
 175   instead of their labels. That is:
 176
 177     - 1-button Pad:
 178
 179       Mapped as BTN_START
 180
 181     - 2-button Pad:
 182
 183       Left button mapped as BTN_SELECT, right button mapped as BTN_START
 184
 185   Many pads also have a third button which is branded or has a special symbol
 186   and meaning. Such buttons are mapped as BTN_MODE. Examples are the Nintendo
 187   "HOME" button, the XBox "X"-button or Sony "PS" button.
 188
 189 - Rumble:
 190
 191   Rumble is advertised as FF_RUMBLE.