tmk_core/doc/keymap.md

   1 Keymap framework - how to define your keymap
   2 ============================================
   3 ***NOTE: This is not final version, may be inconsistent with source code and changed occasionally for a while.***
   4
   5 ## 0. Keymap and layers
   6 The **keymap** is an array composed of one or more layers.
   7 Each **layer** is an array of **keycodes**, defining **actions** for each physical key.
   8 Layers can be activated and deactivated independently. Multiple layers may be active at once, resulting in the currently-active **layer state**. Each layer has an index between 0-31. As active layers are stacked together, higher layers take precedence over lower layers.
   9
  10     Keymap: 32 Layers                   Layer: Keycode matrix
  11     -----------------                   ---------------------
  12     stack of layers                     array_of_keycode[row][column]
  13            ____________ precedence               _______________________
  14           /           / | high                  / ESC / F1  / F2  / F3   ....
  15       31 /___________// |                      /-----/-----/-----/-----
  16       30 /___________// |                     / TAB /  Q  /  W  /  E   ....
  17       29 /___________/  |                    /-----/-----/-----/-----
  18        :   _:_:_:_:_:__ |               :   /LCtrl/  A  /  S  /  D   ....
  19        :  / : : : : : / |               :  /  :     :     :     :
  20        2 /___________// |               2 `--------------------------
  21        1 /___________// |               1 `--------------------------
  22        0 /___________/  V low           0 `--------------------------
  23
  24 **Note:** The keymap array is limited to **32 layers**.
  25
  26
  27
  28 ### 0.1 Layer state
  29 The current keymap layer state is determined by two parameters: the *default layer*, and the individual *layer states*. Changing the default layer is useful for switching key layouts completely; for example, switching to Dvorak, Colemak or Workman instead of QWERTY. Individual layer states, on the other hand, can be used to overlay the base layer with other functions such as navigation keys, function keys (F1-F12), media keys or other actions.
  30
  31 Because the default layer is really just a special case affecting the overall layer state, it is important to first understand how the layer state is determined.
  32
  33 #### 0.1.1 The layer state
  34 The **layer state** indicates the current on/off status of all layers. It is defined in the firmware by a 32-bit integer, `layer_state`, which stores each layer's on/off status in a single bit: 0 for off, 1 for on. As layers are activated and deactivated, their respective bits are flipped, changing the value of `layer_state`.
  35
  36     Overlay feature layer
  37     ---------------------      bit|status
  38            ____________        ---+------
  39       31  /           /        31 |   0
  40       30 /___________// -----> 30 |   1
  41       29 /___________/  -----> 29 |   1
  42        :                        : |   :
  43        :   ____________         : |   :
  44        2  /           /         2 |   0
  45     ,->1 /___________/  ----->  1 |   1
  46     |  0                        0 |   0
  47     |                                 +
  48     `--- default_layer = 1            |
  49          layer_state   = 0x60000002 <-'
  50
  51 #### 0.1.2 The default layer
  52 The **default layer** is the base keymap layer (0-31) which is always active and considered the "bottom" of the stack. When the firmware boots, the default layer is the only active layer. It is set to layer 0 by default, though this can be changed ~~in *config.h*~~ via Boot Magic settings.
  53
  54     Initial state of Keymap          Change base layout
  55     -----------------------          ------------------
  56
  57       31                               31
  58       30                               30
  59       29                               29
  60        :                                :
  61        :                                :   ____________
  62        2   ____________                 2  /           /
  63        1  /           /              ,->1 /___________/
  64     ,->0 /___________/               |  0
  65     |                                |
  66     `--- default_layer = 0           `--- default_layer = 1
  67          layer_state   = 0x00000001       layer_state   = 0x00000002
  68
  69 Note that the `default_layer_state` variable only determines the lowest value to which `layer_state` may be set, and that `default_layer_state` is used by the core firmware when determining the starting value of `layer_state` before applying changes. In other words, the default layer will *always* be set to *on* in `layer_state`.
  70
  71 The default layer is defined in the firmware by the `default_layer_state` variable, which is identical in format to the `layer_state` variable exlpained above. The value may be changed using the following functions:
  72
  73 - `default_layer_state_set(state)` sets the state to the specified 32-bit integer value.
  74 - AND/OR/XOR functions set the state based on a boolean logic comparison between the current state and the specified 32-bit integer value:
  75     - `default_layer_state_and(state)`
  76     - `default_layer_state_or(state)`
  77     - `default_layer_state_xor(state)`
  78
  79 For example, to set layer 3 as the default layer:
  80
  81 ```C
  82 // convert 3 to a 32-bit unsigned long value, and set the default layer
  83 default_layer_state_set(1UL<<3);
  84 ```
  85
  86
  87
  88 ### 0.2 Layer Precedence and Transparency
  89 Note that ***higher layers have priority in the layer stack***. The firmware starts at the topmost active layer, and works down to the bottom to find the an active keycode. Once the search encounters any keycode other than **`KC_TRNS`** (transparent) on an active layer, the search is halted and the remaining lower layers aren't examined, even if they are active.
  90
  91 **Note:** a layer must be activated before it may be included in the stack search.
  92
  93 `KC_TRNS` is a special placeholder which can be used on overlay layers. This allows for the creation of "partial" layers which fall back on the lower layers, eliminating a good deal of repetition in keymap files.
  94
  95
  96
  97 ### 0.3 Keymap Example
  98 The keymap is defined in the **`keymaps[]`** array, a 2-dimensional array of rows and columns corresponding to positions in the keyboard matrix. But most often the layers are defined using C macros to allow for easier reading and editing of the keymap files. To use complex actions you need to define `Fn` keycodes in the **`fn_actions[]`** array.
  99
 100 This is a keymap example for the [HHKB](http://en.wikipedia.org/wiki/Happy_Hacking_Keyboard) keyboard.
 101 This example has three layers: the QWERTY base layer, and two overlay layers for cursor and mousekey control, respectively.
 102 In this example,
 103
 104  `Fn0` is a **momentary layer switching** key--you can use keys on the Cursor layer while holding the key.
 105
 106  `Fn1` is a momentary layer switching key with tapping function--tapping the key as one would normally use it, sends the semicolon **';'** keycode, while holding the key down switches layers.
 107
 108  `Fn2` is a **toggle layer switch** key--pressing the key toggles the layer on until you press it again.
 109
 110 You can find other keymap definitions in file `keymap.c` located on project directories.
 111
 112     static const uint8_t PROGMEM keymaps[][MATRIX_ROWS][MATRIX_COLS] = {
 113         /* 0: Qwerty
 114          * ,-----------------------------------------------------------.
 115          * |Esc|  1|  2|  3|  4|  5|  6|  7|  8|  9|  0|  -|  =|  \|  `|
 116          * |-----------------------------------------------------------|
 117          * |Tab  |  Q|  W|  E|  R|  T|  Y|  U|  I|  O|  P|  [|  ]|Backs|
 118          * |-----------------------------------------------------------|
 119          * |Contro|  A|  S|  D|  F|  G|  H|  J|  K|  L|Fn1|  '|Enter   |
 120          * |-----------------------------------------------------------|
 121          * |Shift   |  Z|  X|  C|  V|  B|  N|  M|  ,|  .|  /|Shift |Fn0|
 122          * `-----------------------------------------------------------'
 123          *       |Gui|Alt  |Space                  |Alt  |Fn2|
 124          *       `-------------------------------------------'
 125          */
 126         KEYMAP(ESC, 1,   2,   3,   4,   5,   6,   7,   8,   9,   0,   MINS,EQL, BSLS,GRV, \
 127                TAB, Q,   W,   E,   R,   T,   Y,   U,   I,   O,   P,   LBRC,RBRC,BSPC, \
 128                LCTL,A,   S,   D,   F,   G,   H,   J,   K,   L,   FN1, QUOT,ENT, \
 129                LSFT,Z,   X,   C,   V,   B,   N,   M,   COMM,DOT, SLSH,RSFT,FN0, \
 130                     LGUI,LALT,          SPC,                RALT,FN2),
 131         /* 1: Cursor(HHKB mode)
 132          * ,-----------------------------------------------------------.
 133          * |Pwr| F1| F2| F3| F4| F5| F6| F7| F8| F9|F10|F11|F12|Ins|Del|
 134          * |-----------------------------------------------------------|
 135          * |Caps |   |   |   |   |   |   |   |Psc|Slk|Pus|Up |   |Backs|
 136          * |-----------------------------------------------------------|
 137          * |Contro|VoD|VoU|Mut|   |   |  *|  /|Hom|PgU|Lef|Rig|Enter   |
 138          * |-----------------------------------------------------------|
 139          * |Shift   |   |   |   |   |   |  +|  -|End|PgD|Dow|Shift |   |
 140          * `-----------------------------------------------------------'
 141          *      |Gui |Alt  |Space                  |Alt  |Gui|
 142          *      `--------------------------------------------'
 143          */
 144         KEYMAP(PWR, F1,  F2,  F3,  F4,  F5,  F6,  F7,  F8,  F9,  F10, F11, F12, INS, DEL, \
 145                CAPS,TRNS,TRNS,TRNS,TRNS,TRNS,TRNS,TRNS,PSCR,SLCK,PAUS,UP,  TRNS,BSPC, \
 146                LCTL,VOLD,VOLU,MUTE,TRNS,TRNS,PAST,PSLS,HOME,PGUP,LEFT,RGHT,ENT, \
 147                LSFT,TRNS,TRNS,TRNS,TRNS,TRNS,PPLS,PMNS,END, PGDN,DOWN,RSFT,TRNS, \
 148                     LGUI,LALT,          SPC,                RALT,RGUI),
 149         /* 2: Mousekey
 150          * ,-----------------------------------------------------------.
 151          * |Esc| F1| F2| F3| F4| F5| F6| F7| F8| F9|F10|F11|F12|Ins|Del|
 152          * |-----------------------------------------------------------|
 153          * |Tab  |   |   |   |   |   |MwL|MwD|MwU|MwR|   |   |   |Backs|
 154          * |-----------------------------------------------------------|
 155          * |Contro|   |   |   |   |   |McL|McD|McU|McR|   |   |Return  |
 156          * |-----------------------------------------------------------|
 157          * |Shift   |   |   |   |   |Mb3|Mb2|Mb1|Mb4|Mb5|   |Shift |   |
 158          * `-----------------------------------------------------------'
 159          *      |Gui |Alt  |Mb1                    |Alt  |   |
 160          *      `--------------------------------------------'
 161          * Mc: Mouse Cursor / Mb: Mouse Button / Mw: Mouse Wheel
 162          */
 163         KEYMAP(ESC, F1,  F2,  F3,  F4,  F5,  F6,  F7,  F8,  F9,  F10, F11, F12, INS, DEL, \
 164                TAB, TRNS,TRNS,TRNS,TRNS,TRNS,WH_L,WH_D,WH_U,WH_R,TRNS,TRNS,TRNS,BSPC, \
 165                LCTL,TRNS,ACL0,ACL1,ACL2,TRNS,MS_L,MS_D,MS_U,MS_R,TRNS,QUOT,ENT, \
 166                LSFT,TRNS,TRNS,TRNS,TRNS,BTN3,BTN2,BTN1,BTN4,BTN5,SLSH,RSFT,TRNS, \
 167                     LGUI,LALT,          BTN1,               RALT,TRNS),
 168     };
 169
 170     static const uint16_t PROGMEM fn_actions[] = {
 171         ACTION_LAYER_MOMENTARY(1),                  // FN0
 172         ACTION_LAYER_TAP_KEY(2, KC_SCLN),           // FN1
 173         ACTION_LAYER_TOGGLE(2),                     // FN2
 174     };
 175
 176
 177
 178
 179 ## 1. Keycode
 180 See [`common/keycode.h`](../common/keycode.h) or keycode table below for the detail. Keycode is internal **8bit code** to indicate action performed on key in keymap. Keycode has `KC_` prefixed symbol respectively. Most of keycodes like `KC_A` have simple action registers key to host on press and unregister on release, while some of other keycodes has some special actions like `Fn` keys, Media control keys, System control keys and Mousekeys.
 181
 182  ***In `KEYMAP()` macro you should omit prefix part `KC_` of keycode to keep keymap compact.*** For example, just use `A` instead you place `KC_A` in `KEYMAP()`. Some keycodes has 4-letter **short name** in addition to descriptive name, you'll prefer short one in `KEYMAP()`.
 183
 184 ### 1.0 Other key
 185 - `KC_NO` for no action
 186 - `KC_TRNS` for layer transparency (See above)
 187
 188 ### 1.1 Normal key
 189 - `KC_A` to `KC_Z`, `KC_1` to `KC_0` for alpha numeric key
 190 - `KC_MINS`, `KC_EQL`, `KC_GRV`, `KC_RBRC`, `KC_LBRC`, `KC_COMM`, `KC_DOT`, `KC_BSLS`, `KC_SLSH`, `KC_SCLN`, `KC_QUOT`
 191 - `KC_ESC`, `KC_TAB`, `KC_SPC`, `KC_BSPC`, `KC_ENT`, `KC_DEL`, `KC_INS`
 192 - `KC_UP`, `KC_DOWN`, `KC_RGHT`, `KC_LEFT`, `KC_PGUP`, `KC_PGDN`, `KC_HOME`, `KC_END`
 193 - `KC_CAPS`, `KC_NLCK`, `KC_SLCK`, `KC_PSCR`, `KC_PAUS`, `KC_APP`, `KC_F1` to `KC_F24`
 194 - `KC_P1` to `KC_P0`, `KC_PDOT`, `KC_PCMM`, `KC_PSLS`, `KC_PAST`, `KC_PMNS`, `KC_PPLS`, `KC_PEQL`, `KC_PENT` for keypad.
 195
 196 ### 1.2 Modifier
 197 There are 8 modifiers which has discrimination between left and right.
 198
 199 - `KC_LCTL` and `KC_RCTL` for Control
 200 - `KC_LSFT` and `KC_RSFT` for Shift
 201 - `KC_LALT` and `KC_RALT` for Alt
 202 - `KC_LGUI` and `KC_RGUI` for Windows key or Command key in Mac
 203
 204 ### 1.3 Mousekey
 205 - `KC_MS_U`, `KC_MS_D`, `KC_MS_L`, `KC_MS_R` for mouse cursor
 206 - `KC_WH_U`, `KC_WH_D`, `KC_WH_L`, `KC_WH_R` for mouse wheel
 207 - `KC_BTN1`, `KC_BTN2`, `KC_BTN3`, `KC_BTN4`, `KC_BTN5` for mouse buttons
 208
 209 ### 1.4 System & Media key
 210 - `KC_PWR`, `KC_SLEP`, `KC_WAKE` for Power, Sleep, Wake
 211 - `KC_MUTE`, `KC_VOLU`, `KC_VOLD` for audio volume control
 212 - `KC_MNXT`, `KC_MPRV`, `KC_MSTP`, `KC_MPLY`, `KC_MSEL` for media control
 213 - `KC_MAIL`, `KC_CALC`, `KC_MYCM` for application launch
 214 - `KC_WSCH`, `KC_WHOM`, `KC_WBAK`, `KC_WFWD`, `KC_WSTP`, `KC_WREF`, `KC_WFAV` for web browser operation
 215
 216 ### 1.5 Fn key
 217 `KC_FNnn` are keycodes for `Fn` key which not given any actions at the beginning unlike most of keycodes has its own inborn action. To use these keycodes in `KEYMAP()` you need to assign action you want at first. Action of `Fn` key is defined in `fn_actions[]` and its index of the array is identical with number part of `KC_FNnn`. Thus `KC_FN0` keycode indicates the action defined in first element of the array. ***32 `Fn` keys can be defined at most.***
 218
 219 ### 1.6 Keycode Table
 220  See keycode table in [`doc/keycode.txt`](./keycode.txt) for description of keycodes.
 221
 222  In regard to implementation side most of keycodes are identical with [HID usage][HID_usage](pdf) sent to host for real and some virtual keycodes are defined to support special actions.
 223 [HID_usage]: http://www.usb.org/developers/hidpage/Hut1_12v2.pdf
 224
 225
 226
 227 ## 2. Action
 228 See [`common/action_code.h`](../common/action_code.h). Action is a **16bit code** and defines function to perform on events of a key like press, release, holding and tapping.
 229
 230 Most of keys just register 8bit scancode to host, but to support other complex features needs 16bit extended action codes internally. However, using 16bit action codes in keymap results in double size in memory compared to using just keycodes. To avoid this waste 8bit keycodes are used in `KEYMAP()` instead of action codes.
 231
 232 ***You can just use keycodes of `Normal key`, `Modifier`, `Mousekey` and `System & Media key` in keymap*** to indicate corresponding actions instead of using action codes. While ***to use other special actions you should use keycode of `Fn` key defined in `fn_actions[]`.***
 233
 234
 235 ### 2.1 Key Action
 236 This is a simple action that registers scancodes(HID usage in fact) to host on press event of key and unregister on release.
 237
 238 #### Parameters
 239 + **mods**: { ` MOD_LCTL`, ` MOD_LSFT`, ` MOD_LALT`, ` MOD_LGUI`,
 240               ` MOD_RCTL`, ` MOD_RSFT`, ` MOD_RALT`, ` MOD_RGUI` }
 241 + **key**: keycode
 242
 243
 244 #### 2.1.1 Normal key and Modifier
 245 ***This action usually won't be used expressly in keymap*** because you can just use keycodes in `KEYMAP()` instead.
 246
 247 You can define these actions on *'A'* key and *'left shift'* modifier with:
 248
 249     ACTION_KEY(KC_A)
 250     ACTION_KEY(KC_LSFT)
 251
 252 #### 2.1.2 Modified key
 253 This action is comprised of strokes of modifiers and a key. `Macro` action is needed if you want more complex key strokes.
 254
 255 Say you want to assign a key to `Shift + 1` to get character *'!'* or `Alt + Tab` to switch application windows.
 256
 257     ACTION_MODS_KEY(MOD_LSFT, KC_1)
 258     ACTION_MODS_KEY(MOD_LALT, KC_TAB)
 259
 260 Or `Alt,Shift + Tab` can be defined. `ACTION_MODS_KEY(mods, key)` requires **4-bit modifier state** and a **keycode** as arguments. See `keycode.h` for `MOD_BIT()` macro.
 261
 262     ACTION_MODS_KEY(MOD_LALT | MOD_LSFT, KC_TAB)
 263
 264 #### 2.1.3 Multiple Modifiers
 265 Registers multiple modifiers with pressing a key. To specify multiple modifiers use `|`.
 266
 267     ACTION_MODS(MOD_ALT | MOD_LSFT)
 268
 269 #### 2.1.3 Modifier with Tap key([Dual role][dual_role])
 270 Works as a modifier key while holding, but registers a key on tap(press and release quickly).
 271
 272
 273     ACTION_MODS_TAP_KEY(MOD_RCTL, KC_ENT)
 274
 275
 276
 277 ### 2.2 Layer Action
 278 These actions operate layers of keymap.
 279
 280 #### Parameters
 281 You can specify a **target layer** of action and **when the action is executed**. Some actions take a **bit value** for bitwise operation.
 282
 283
 284 + **layer**: `0`-`31`
 285 + **on**: { `ON_PRESS` | `ON_RELEASE` | `ON_BOTH` }
 286 + **bits**: 4-bit value and 1-bit mask bit
 287
 288
 289 #### 2.2.1 Default Layer
 290 Default Layer is a layer which always is valid and referred to when actions is not defined on other overlay layers.
 291
 292 This sets Default Layer to given parameter `layer` and activate it.
 293
 294     ACTION_DEFAULT_LAYER_SET(layer)
 295
 296
 297 #### 2.2.2 Momentary
 298 Turns on `layer` momentarily while holding, in other words it activates when key is pressed and deactivate when released.
 299
 300     ACTION_LAYER_MOMENTARY(layer)
 301
 302
 303 #### 2.2.3 Toggle Switch
 304 Turns on `layer` with first type(press and release) and turns off with next.
 305
 306     ACTION_LAYER_TOGGLE(layer)
 307
 308
 309 #### 2.2.4 Momentary Switch with tap key
 310 Turns on `layer` momentary while holding, but registers key on tap(press and release quickly).
 311
 312     ACTION_LAYER_TAP_KEY(layer, key)
 313
 314
 315 #### 2.2.5 Momentary Switch with tap toggle
 316 Turns on `layer` momentary while holding and toggles it with serial taps.
 317
 318     ACTION_LAYER_TAP_TOGGLE(layer)
 319
 320
 321 #### 2.2.6 Invert state of layer
 322 Inverts current state of `layer`. If the layer is on it becomes off with this action.
 323
 324     ACTION_LAYER_INVERT(layer, on)
 325
 326
 327 #### 2.2.7 Turn On layer
 328 Turns on layer state.
 329
 330     ACTION_LAYER_ON(layer, on)
 331
 332 Turns on layer state on press and turns off on release.
 333
 334     ACTION_LAYER_ON_OFF(layer)
 335
 336
 337 #### 2.2.8 Turn Off layer
 338 Turns off layer state.
 339
 340     ACTION_LAYER_OFF(layer, on)
 341
 342 Turns off layer state on press and activates on release.
 343
 344     ACTION_LAYER_OFF_ON(layer)
 345
 346
 347 #### 2.2.9 Set layer
 348 Turn on layer only.
 349 `layer_state = (1<<layer) [layer: 0-31]`
 350
 351     ACTION_LAYER_SET(layer, on)
 352
 353 Turns on layer only and clear all layer on release..
 354
 355     ACTION_LAYER_SET_CLEAR(layer)
 356
 357
 358 #### 2.2.10 Bitwise operation
 359
 360 **part** indicates which part of 32bit layer state(0-7). **bits** is 5-bit value. **on** indicates when the action is executed.
 361
 362     ACTION_LAYER_BIT_AND(part, bits, on)
 363     ACTION_LAYER_BIT_OR(part, bits, on)
 364     ACTION_LAYER_BIT_XOR(part, bits, on)
 365     ACTION_LAYER_BIT_SET(part, bits, on)
 366
 367 These actions works with parameters as following code.
 368
 369     uint8_t shift = part*4;
 370     uint32_t mask = (bits&0x10) ? ~(0xf<<shift) : 0;
 371     uint32_t layer_state = layer_state <bitop> ((bits<<shift)|mask);
 372
 373
 374 Default Layer also has bitwise operations, they are executed when key is released.
 375
 376     ACTION_DEFAULT_LAYER_BIT_AND(part, bits)
 377     ACTION_DEFAULT_LAYER_BIT_OR(part, bits)
 378     ACTION_DEFAULT_LAYER_BIT_XOR(part, bits)
 379     ACTION_DEFAULT_LAYER_BIT_SET(part, bits)
 380
 381
 382
 383 ### 2.3 Macro action
 384 ***TBD***
 385
 386 `Macro` action indicates complex key strokes.
 387
 388     MACRO( D(LSHIFT), D(D), END )
 389     MACRO( U(D), U(LSHIFT), END )
 390     MACRO( I(255), T(H), T(E), T(L), T(L), W(255), T(O), END )
 391
 392 #### 2.3.1 Macro Commands
 393 - **MACRO()**
 394 - **MACRO_NONE**
 395
 396 - **I()**   change interval of stroke.
 397 - **D()**   press key
 398 - **U()**   release key
 399 - **T()**   type key(press and release)
 400 - **W()**   wait
 401 - **SM()**  store modifier state
 402 - **RM()**  restore modifier state
 403 - **CM()**  clear modifier state
 404 - **END**   end mark
 405
 406 #### 2.3.2 Examples
 407 ***TBD***
 408
 409     const macro_t *action_get_macro(keyrecord_t *record, uint8_t id, uint8_t opt)
 410     {
 411         switch (id) {
 412             case HELLO:
 413                 return (record->event.pressed ?
 414                         MACRO( I(0), T(H), T(E), T(L), T(L), W(255), T(O), END ) :
 415                         MACRO_NONE );
 416             case ALT_TAB:
 417                 return (record->event.pressed ?
 418                         MACRO( D(LALT), D(TAB), END ) :
 419                         MACRO( U(TAB), END ));
 420         }
 421         return MACRO_NONE;
 422     }
 423
 424
 425
 426
 427 ### 2.4 Function action
 428 ***TBD***
 429
 430 There are two type of action, normal `Function` and tappable `Function`.
 431 These actions call user defined function with `id`, `opt`, and key event information as arguments.
 432
 433 #### 2.4.1 Function
 434 To define normal `Function` action in keymap use this.
 435
 436     ACTION_FUNCTION(id, opt)
 437
 438 #### 2.4.2 Function with tap
 439 To define tappable `Function` action in keymap use this.
 440
 441     ACTION_FUNCTION_TAP(id, opt)
 442
 443 #### 2.4.3 Implement user function
 444 `Function` actions can be defined freely with C by user in callback function:
 445
 446     void keymap_call_function(keyrecord_t *event, uint8_t id, uint8_t opt)
 447
 448 This C function is called every time key is operated, argument `id` selects action to be performed and `opt` can be used for option. Function `id` can be 0-255 and `opt` can be 0-15.
 449
 450  `keyrecord_t` is comprised of key event and tap count. `keyevent_t` indicates which and when key is pressed or released. From `tap_count` you can know tap state, 0 means no tap. These information will be used in user function to decide how action of key is performed.
 451
 452     typedef struct {
 453         keyevent_t  event;
 454         uint8_t     tap_count;
 455     } keyrecord_t;
 456
 457     typedef struct {
 458         key_t    key;
 459         bool     pressed;
 460         uint16_t time;
 461     } keyevent_t;
 462
 463     typedef struct {
 464         uint8_t col;
 465         uint8_t row;
 466     } key_t;
 467
 468 ***TODO: sample implementation***
 469 See `keyboard/hhkb/keymap.c` for sample.
 470
 471
 472
 473 ### 2.5 Backlight Action
 474 These actions control the backlight.
 475
 476 #### 2.5.1 Change backlight level
 477 Increase backlight level.
 478
 479     ACTION_BACKLIGHT_INCREASE()
 480
 481 Decrease backlight level.
 482
 483     ACTION_BACKLIGHT_DECREASE()
 484
 485 Step through backlight levels.
 486
 487     ACTION_BACKLIGHT_STEP()
 488
 489 Turn a specific backlight level on or off.
 490
 491     ACTION_BACKLIGHT_LEVEL(1)
 492
 493 #### 2.5.2 Turn on / off backlight
 494 Turn the backlight on and off without changing level.
 495
 496     ACTION_BACKLIGHT_TOGGLE()
 497
 498
 499
 500 ## 3. Layer switching Example
 501 There are some ways to switch layer with 'Layer' actions.
 502
 503 ### 3.1 Momentary switching
 504 Momentary switching changes layer only while holding Fn key.
 505
 506 This action makes 'Layer 1' active(valid) on key press event and inactive on release event. Namely you can overlay a layer on lower layers or default layer temporarily with this action.
 507
 508     ACTION_LAYER_MOMENTARY(1)
 509
 510
 511 Note that after switching on press the actions on destination layer(Layer 1) are performed.
 512 ***Thus you shall need to place an action to go back on destination layer***, or you will be stuck in destination layer without way to get back. Usually you need to place same action or 'KC_TRNS` on destination layer to get back.
 513
 514
 515 ### 3.2 Toggle switching
 516 Toggle switching performed after releasing a key. With this action you can keep staying on the destination layer until you type the key again to return.
 517
 518 This performs toggle switching action of 'Layer 2'.
 519
 520     ACTION_LAYER_TOGGLE(2)
 521
 522
 523
 524 ### 3.3 Momentary switching with Tap key
 525 These actions switch a layer only while holding a key but register the key on tap. **Tap** means to press and release a key quickly.
 526
 527     ACTION_LAYER_TAP_KEY(2, KC_SCLN)
 528
 529 With this you can place a layer switching action on normal key like ';' without losing its original key register function. This action allows you to have layer switching action without necessity of a dedicated key. It means you can have it even on home row of keyboard.
 530
 531
 532
 533 ### 3.4 Momentary switching with Tap Toggle
 534 This switches layer only while holding a key but toggle layer with several taps. **Tap** means to press and release key quickly.
 535
 536     ACTION_LAYER_TAP_TOGGLE(1)
 537
 538 Number of taps can be configured with `TAPPING_TOGGLE` in `config.h`, `5` by default.
 539
 540
 541
 542 ### 3.5 Momentary switching with Modifiers
 543 This registers modifier key(s) simultaneously with layer switching.
 544
 545     ACTION_LAYER_MODS(2, MOD_LSFT | MOD_LALT)
 546
 547
 548
 549 ## 4. Tapping
 550 Tapping is to press and release a key quickly. Tapping speed is determined with setting of `TAPPING_TERM`, which can be defined in `config.h`, 200ms by default.
 551
 552 ### 4.1 Tap Key
 553 This is a feature to assign normal key action and modifier including layer switching to just same one physical key. This is a kind of [Dual role key][dual_role]. It works as modifier when holding the key but registers normal key when tapping.
 554
 555 Modifier with tap key:
 556
 557     ACTION_MODS_TAP_KEY(MOD_RSFT, KC_GRV)
 558
 559 Layer switching with tap key:
 560
 561     ACTION_LAYER_TAP_KEY(2, KC_SCLN)
 562
 563 [dual_role]: http://en.wikipedia.org/wiki/Modifier_key#Dual-role_keys
 564
 565
 566 ### 4.2 Tap Toggle
 567 This is a feature to assign both toggle layer and momentary switch layer action to just same one physical key. It works as momentary layer switch when holding a key but toggle switch with several taps.
 568
 569     ACTION_LAYER_TAP_TOGGLE(1)
 570
 571
 572 ### 4.3 Oneshot Modifier
 573 This runs onetime effects which modify only on just one following key. It works as normal modifier key when holding down while oneshot modifier when tapping.
 574
 575     ACTION_MODS_ONESHOT(MOD_LSFT)
 576
 577 Say you want to type 'The', you have to push and hold Shift key before type 't' then release it before type 'h' and 'e', otherwise you'll get 'THe' or 'the' unintentionally. With Oneshot Modifier you can tap Shift then type 't', 'h' and 'e' normally, you don't need to holding Shift key properly here. This mean you can release Shift before 't' is pressed down.
 578
 579 Oneshot effect is cancel unless following key is pressed down within `ONESHOT_TIMEOUT` of `config.h`. No timeout when it is `0` or not defined.
 580
 581
 582 ### 4.4 Tap Toggle Mods
 583 Similar to layer tap toggle, this works as a momentary modifier when holding, but toggles on with several taps. A single tap will 'unstick' the modifier again.
 584
 585     ACTION_MODS_TAP_TOGGLE(MOD_LSFT)
 586
 587
 588
 589
 590 ## 5. Legacy Keymap
 591 This was used in prior version and still works due to legacy support code in `common/keymap.c`. Legacy keymap doesn't support many of features that new keymap offers. ***It is not recommended to use Legacy Keymap for new project.***
 592
 593 To enable Legacy Keymap support define this macro in `config.h`.
 594
 595     #define USE_LEGACY_KEYMAP
 596
 597 Legacy Keymap uses two arrays `fn_layer[]` and `fn_keycode[]` to define Fn key. The index of arrays corresponds with postfix number of `Fn` key. Array `fn_layer[]` indicates destination layer to switch and `fn_keycode[]` has keycodes to send when tapping `Fn` key.
 598
 599 In following setting example, `Fn0`, `Fn1` and `Fn2` switch layer to 1, 2 and 2 respectively. `Fn2` registers `Space` key when tapping while `Fn0` and `Fn1` doesn't send any key.
 600
 601     static const uint8_t PROGMEM fn_layer[] = {
 602         1,              // Fn0
 603         2,              // Fn1
 604         2,              // Fn2
 605     };
 606
 607     static const uint8_t PROGMEM fn_keycode[] = {
 608         KC_NO,          // Fn0
 609         KC_NO,          // Fn1
 610         KC_SPC,         // Fn2
 611     };
 612
 613
 614 ## 6. Terminology
 615 ***TBD***
 616 ### keymap
 617 is comprised of multiple layers.
 618 ### layer
 619 is matrix of keycodes.
 620 ### key
 621 is physical button on keyboard or logical switch on software.
 622 ### keycode
 623 is codes used on firmware.
 624 ### action
 625 is a function assigned on a key.
 626 ### layer transparency
 627 Using transparent keycode one layer can refer key definition on other lower layer.
 628 ### layer precedence
 629 Top layer has higher precedence than lower layers.
 630 ### tapping
 631 is to press and release a key quickly.
 632 ### Fn key
 633 is key which executes a special action like layer switching, mouse key, macro or etc.
 634 ### dual role key
 635 <http://en.wikipedia.org/wiki/Modifier_key#Dual-role_keys>