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 **Keymap** is comprised of multiple layers of key layout, you can define **16** layers at most.
   7 **Layer** is an array of **keycodes** to define **actions** on each physical keys.
   8 respective layers can be validated simultaneously. Layers are indexed with 0 to 15 and higher layer has precedence.
   9
  10     Keymap with 16 Layers               Layer: array of Keycodes
  11     ---------------------               ------------------------
  12           stack of layers               content of layer
  13            ____________ precedence               _______________________
  14           /           / | high                  / ESC / F1  / F2  / F3   ....
  15       15 /___________// |                      /-----/-----/-----/-----
  16       14 /___________// |                     / TAB /     /     /      ....
  17       13 /___________/_ |                    /-----/-----/-----/-----
  18        :  / : : : : : / |                   /LCtrl/     /     /      ....
  19        3 /___________// |               :  /  :     :     :     :
  20        2 /___________// |               2 `--------------------------
  21        1 /___________// |               1 `--------------------------
  22        0 /___________/  V low           0 `--------------------------
  23
  24
  25
  26 ### 0.1 Keymap status
  27 Keymap has its state in two parameters:
  28 **`default_layer`** indicates a base keymap layer(0-15) which is always valid and to be referred, **`keymap_stat`** is 16bit variable which has current on/off status of layers on its each bit.
  29
  30 Keymap layer '0' is usually `default_layer` and which is the only valid layer and other layers is initially off after boot up firmware, though, you can configured them in `config.h`.
  31 To change `default_layer` will be useful when you want to switch key layout completely, say you use Colmak instead of Qwerty.
  32
  33     Initial state of Keymap         Change base layout
  34     -----------------------         ------------------
  35
  36       15                              15
  37       14                              14
  38       13                              13
  39        :                               :
  40        3                               3   ____________
  41        2   ____________                2  /           /
  42        1  /           /             ,->1 /___________/
  43     ,->0 /___________/              |  0
  44     |                               |
  45     `--- default_layer = 0          `--- default_layer = 1
  46          keymap_stat   = 0x0001          keymap_stat   = 0x0002
  47
  48 On the other hand, you shall change `keymap_state` to overlay base layer with some layers for feature such as navigation keys, function key(F1-F12), media keys or special actions.
  49
  50     Overlay feature layer
  51     ---------------------      bit|status
  52            ____________        ---+------
  53       15  /           /        15 |   0
  54       14 /___________// -----> 14 |   1
  55       13 /___________/  -----> 13 |   1
  56        :                        : |
  57        3   ____________         3 |   0
  58        2  /           /         2 |   0
  59     ,->1 /___________/  ----->  1 |   1
  60     |  0                        0 |   0
  61     |                                 |
  62     `--- default_layer = 1            |
  63          keymap_stat   = 0x6002 <-----'
  64
  65
  66
  67 ### 0.2 Layer Precedence and Transparency
  68 Note that ***higher layer has higher priority on stack of layers***, namely firmware falls down from top layer to bottom to look up keycode. Once it spots keycode other than **`KC_TRNS`**(transparent) on a layer it stops searching and lower layers aren't referred.
  69
  70 You can place `KC_TRNS` on overlay layer changes just part of layout to fall back on lower or base layer.
  71 Key with `KC_TRANS` doen't has its own keycode and refers to lower valid layers for keycode, instead.
  72 See example below.
  73
  74
  75 ### 0.3 Keymap Example
  76 Keymap is **`keymaps[]`** C array in fact and you can define layers in it with **`KEYMAP()`** C macro and keycodes. To use complex actions you need to define `Fn` keycode in **`fn_actions[]`** array.
  77
  78 This is a keymap example for [HHKB](http://en.wikipedia.org/wiki/Happy_Hacking_Keyboard) keyboard.
  79 This example has three layers, 'Qwerty' as base layer, 'Cursor' and  'Mousekey'.
  80 In this example,
  81
  82  `Fn0` is a **momentary layer switching** key, you can use keys on Cursor layer while holding the key.
  83
  84  `Fn1` is a momentary layer switching key with tapping feature, you can get semicolon **';'** with taping the key and switch layers while holding the key. The word **'tap'** or **'tapping'** mean to press and release a key quickly.
  85
  86  `Fn2` is a **toggle layer switch** key, you can stay switched layer after releasing the key unlike momentary switching.
  87
  88 You can find other keymap definitions in file `keymap.c` located on project directories.
  89
  90     static const uint8_t PROGMEM keymaps[][MATRIX_ROWS][MATRIX_COLS] = {
  91         /* 0: Qwerty
  92          * ,-----------------------------------------------------------.
  93          * |Esc|  1|  2|  3|  4|  5|  6|  7|  8|  9|  0|  -|  =|  \|  `|
  94          * |-----------------------------------------------------------|
  95          * |Tab  |  Q|  W|  E|  R|  T|  Y|  U|  I|  O|  P|  [|  ]|Backs|
  96          * |-----------------------------------------------------------|
  97          * |Contro|  A|  S|  D|  F|  G|  H|  J|  K|  L|Fn1|  '|Enter   |
  98          * |-----------------------------------------------------------|
  99          * |Shift   |  Z|  X|  C|  V|  B|  N|  M|  ,|  .|  /|Shift |Fn0|
 100          * `-----------------------------------------------------------'
 101          *       |Gui|Alt  |Space                  |Alt  |Fn2|
 102          *       `-------------------------------------------'
 103          */
 104         KEYMAP(ESC, 1,   2,   3,   4,   5,   6,   7,   8,   9,   0,   MINS,EQL, BSLS,GRV, \
 105                TAB, Q,   W,   E,   R,   T,   Y,   U,   I,   O,   P,   LBRC,RBRC,BSPC, \
 106                LCTL,A,   S,   D,   F,   G,   H,   J,   K,   L,   FN1, QUOT,ENT, \
 107                LSFT,Z,   X,   C,   V,   B,   N,   M,   COMM,DOT, SLSH,RSFT,FN0, \
 108                     LGUI,LALT,          SPC,                RALT,FN2),
 109         /* 1: Cursor(HHKB mode)
 110          * ,-----------------------------------------------------------.
 111          * |Pwr| F1| F2| F3| F4| F5| F6| F7| F8| F9|F10|F11|F12|Ins|Del|
 112          * |-----------------------------------------------------------|
 113          * |Caps |   |   |   |   |   |   |   |Psc|Slk|Pus|Up |   |Backs|
 114          * |-----------------------------------------------------------|
 115          * |Contro|VoD|VoU|Mut|   |   |  *|  /|Hom|PgU|Lef|Rig|Enter   |
 116          * |-----------------------------------------------------------|
 117          * |Shift   |   |   |   |   |   |  +|  -|End|PgD|Dow|Shift |   |
 118          * `-----------------------------------------------------------'
 119          *      |Gui |Alt  |Space                  |Alt  |Gui|
 120          *      `--------------------------------------------'
 121          */
 122         KEYMAP(PWR, F1,  F2,  F3,  F4,  F5,  F6,  F7,  F8,  F9,  F10, F11, F12, INS, DEL, \
 123                CAPS,TRNS,TRNS,TRNS,TRNS,TRNS,TRNS,TRNS,PSCR,SLCK,PAUS,UP,  TRNS,BSPC, \
 124                LCTL,VOLD,VOLU,MUTE,TRNS,TRNS,PAST,PSLS,HOME,PGUP,LEFT,RGHT,ENT, \
 125                LSFT,TRNS,TRNS,TRNS,TRNS,TRNS,PPLS,PMNS,END, PGDN,DOWN,RSFT,TRNS, \
 126                     LGUI,LALT,          SPC,                RALT,RGUI),
 127         /* 2: Mousekey
 128          * ,-----------------------------------------------------------.
 129          * |Esc| F1| F2| F3| F4| F5| F6| F7| F8| F9|F10|F11|F12|Ins|Del|
 130          * |-----------------------------------------------------------|
 131          * |Tab  |   |   |   |   |   |MwL|MwD|MwU|MwR|   |   |   |Backs|
 132          * |-----------------------------------------------------------|
 133          * |Contro|   |   |   |   |   |McL|McD|McU|McR|   |   |Return  |
 134          * |-----------------------------------------------------------|
 135          * |Shift   |   |   |   |   |Mb3|Mb2|Mb1|Mb4|Mb5|   |Shift |   |
 136          * `-----------------------------------------------------------'
 137          *      |Gui |Alt  |Mb1                    |Alt  |   |
 138          *      `--------------------------------------------'
 139          * Mc: Mouse Cursor / Mb: Mouse Button / Mw: Mouse Wheel
 140          */
 141         KEYMAP(ESC, F1,  F2,  F3,  F4,  F5,  F6,  F7,  F8,  F9,  F10, F11, F12, INS, DEL, \
 142                TAB, TRNS,TRNS,TRNS,TRNS,TRNS,WH_L,WH_D,WH_U,WH_R,TRNS,TRNS,TRNS,BSPC, \
 143                LCTL,TRNS,ACL0,ACL1,ACL2,TRNS,MS_L,MS_D,MS_U,MS_R,TRNS,QUOT,ENT, \
 144                LSFT,TRNS,TRNS,TRNS,TRNS,BTN3,BTN2,BTN1,BTN4,BTN5,SLSH,RSFT,TRNS, \
 145                     LGUI,LALT,          BTN1,               RALT,TRNS),
 146     };
 147
 148     static const uint16_t PROGMEM fn_actions[] = {
 149         ACTION_KEYMAP_MOMENTARY(1),                  // FN0
 150         ACTION_KEYMAP_TAP_KEY(2, KC_SCLN),           // FN1
 151         ACTION_KEYMAP_TOGGLE(2),                     // FN2
 152     };
 153
 154
 155
 156
 157 ## 1. Keycode
 158 See [`common/keycode.h`](../common/keycode.h) or keycode table below for the detail. Keycode is internal **8bit code** to inidicate 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 contorl keys, System control keys and Mousekeys.
 159
 160  ***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()`.
 161
 162 ### 1.0 Other key
 163 - `KC_NO` for no aciton
 164 - `KC_TRNS` for layer transparency (See above)
 165
 166 ### 1.1 Normal key
 167 - `KC_A` to `KC_Z`, `KC_1` to `KC_0` for alpha numeric key
 168 - `KC_MINS`, `KC_EQL`, `KC_GRV`, `KC_RBRC`, `KC_LBRC`, `KC_COMM`, `KC_DOT`, `KC_BSLS`, `KC_SLSH`, `KC_SCLN`, `KC_QUOT`
 169 - `KC_ESC`, `KC_TAB`, `KC_SPC`, `KC_BSPC`, `KC_ENT`, `KC_DEL`, `KC_INS`
 170 - `KC_UP`, `KC_DOWN`, `KC_RGHT`, `KC_LEFT`, `KC_PGUP`, `KC_PGDN`, `KC_HOME`, `KC_END`
 171 - `KC_CAPS`, `KC_NLCK`, `KC_SLCK`, `KC_PSCR`, `KC_PAUS`, `KC_APP`, `KC_F1` to `KC_F24`
 172 - `KC_P1` to `KC_P0`, `KC_PDOT`, `KC_PCMM`, `KC_PSLS`, `KC_PAST`, `KC_PMNS`, `KC_PPLS`, `KC_PEQL`, `KC_PENT` for keypad.
 173
 174 ### 1.2 Modifier
 175 There are 8 modifiers which has discrimination between left and right.
 176
 177 - `KC_LCTL` and `KC_RCTL` for Control
 178 - `KC_LSFT` and `KC_RSFT` for Shift
 179 - `KC_LALT` and `KC_RALT` for Alt
 180 - `KC_LGUI` and `KC_RGUI` for Windows key or Command key in Mac
 181
 182 ### 1.3 Mousekey
 183 - `KC_MS_U`, `KC_MS_D`, `KC_MS_L`, `KC_MS_R` for mouse cursor
 184 - `KC_WH_U`, `KC_WH_D`, `KC_WH_L`, `KC_WH_R` for mouse wheel
 185 - `KC_BTN1`, `KC_BTN2`, `KC_BTN3`, `KC_BTN4`, `KC_BTN5` for mouse buttons
 186
 187 ### 1.4 System & Media key
 188 - `KC_PWR`, `KC_SLEP`, `KC_WAKE` for Power, Sleep, Wake
 189 - `KC_MUTE`, `KC_VOLU`, `KC_VOLD` for audio volume control
 190 - `KC_MNXT`, `KC_MPRV`, `KC_MSTP`, `KC_MPLY`, `KC_MSEL` for media control
 191 - `KC_MAIL`, `KC_CALC`, `KC_MYCM` for application launch
 192 - `KC_WSCH`, `KC_WHOM`, `KC_WBAK`, `KC_WFWD`, `KC_WSTP`, `KC_WREF`, `KC_WFAV` for web browser operation
 193
 194 ### 1.5 Fn key
 195 `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` keyocde indicates the action defined in first element of the array. ***32 `Fn` keys can be defined at most.***
 196
 197 ### 1.6 Keycode Table
 198  See keycode table in [`doc/keycode.txt`](./keycode.txt) for description of keycodes.
 199
 200  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.
 201 [HID_usage]: http://www.usb.org/developers/devclass_docs/Hut1_11.pdf
 202
 203
 204
 205 ## 2. Action
 206 See [`common/action.h`](../common/action.h). Action is a **16bit code** and defines function to perform on events of a key like press, release, holding and tapping.
 207
 208 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 against using jsut keycodes. To avoid this waste 8bit keycodes are used in `KEYMAP` instead of action codes.
 209
 210 ***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[]`.***
 211
 212 Usually action codes are needed only when you want to use layer switching, or
 213
 214 ### 2.1 Key action
 215 This is a simple action that registers scancodes(HID usage in fact) to host on press event of key and unregister on release.
 216
 217 #### 2.1.1 Normal key and Modifier
 218 This action usually won't be used expressly because you can use keycodes in `KEYMAP()` instead.
 219 You can define `Key` action on *'A'* key and *'left shift'* modifier with:
 220
 221     ACTION_KEY(KC_A)
 222     ACTION_KEY(KC_LSHIFT)
 223
 224 #### 2.1.2 Key with modifiers
 225 This action is comprised of strokes of modifiers and a key. `Macro` action is needed if you want more complex key strokes.
 226 Say you want to assign a key to `Shift + 1` to get charactor *'!'* or `Alt + Tab` to switch application windows.
 227
 228     ACTION_LMOD_KEY(KC_LSHIFT, KC_1)
 229     ACTION_LMOD_KEY(KC_LALT, KC_TAB)
 230
 231 Or `Alt,Shift + Tab` can be defined. `ACTION_LMODS_KEY()` requires **4-bit modifier state** and a **keycode** as arguments. See `keycode.h` for `MOD_BIT()` macro.
 232
 233     ACTION_LMODS_KEY((MOD_BIT(KC_LALT) | MOD_BIT(KC_LSHIFT)), KC_TAB)
 234
 235
 236
 237 ### 2.2 Layer Action
 238 These actions operate layers of keymap.
 239
 240 Parameters:
 241 - layer: 0-15
 242 - on: { press | release | both }
 243
 244
 245 #### 2.2.0 Default Layer
 246 `default_layer` is layer which always is valid and referred to when actions is not defined on other layers.
 247
 248 ##### Return to Default Layer
 249 Turns on only `default layer` with clearing other all layers.
 250
 251     ACTION_DEFAULT_LAYER
 252
 253 ##### Set Default Layer
 254 Sets 'default layer' to layer and turn it on.
 255
 256     ACTION_DEFAULT_LAYER_SET_TO(layer)
 257     ACTION_DEFAULT_LAYER_SET(layer, on)
 258
 259
 260 #### 2.2.1 Keymap
 261 These actions operate layer status of keymap.
 262
 263 ##### Momentary Switch
 264 Turns on layer momentary while holding, in other words turn on when key is pressed and off when released.
 265
 266     ACTION_KEYMAP_MOMENTARY(layer)
 267
 268
 269 ##### Toggle Switch
 270 Turns on layer on first type and turns off on next.
 271
 272     ACTION_KEYMAP_TOGGLE(layer)
 273
 274
 275 ##### Momentary Switch with tap key
 276 Turns on layer momentary while holding but registers key on tap.
 277
 278     ACTION_KEYMAP_TAP_KEY(layer, key)
 279
 280
 281 ##### Momentary Switch with tap toggle
 282 Turns on layer momentary while holding but toggles it with serial taps.
 283
 284     ACTION_KEYMAP_TAP_TOGGLE(layer)
 285
 286
 287 ##### Invert layer
 288 Inverts current layer state. If the layer is on it becomes off with this action.
 289
 290     ACTION_KEYMAP_INV(layer, on)
 291
 292
 293 ##### Turn On layer
 294 Turns on layer state.
 295
 296     ACTION_KEYMAP_ON(layer, on)
 297
 298 Turns on layer state on press and turn off on release. This is identical to **'Switch to layer'** action.
 299
 300     ACTION_KEYMAP_ON_OFF(layer)
 301
 302
 303 ##### Turn Off layer
 304 Turns off layer state.
 305
 306     ACTION_KEYMAP_OFF(layer, on)
 307
 308
 309 ##### Set layer
 310 Turn on layer only.
 311 `keymap_stat = (1<<layer) [layer: 0-15]`
 312
 313     ACTION_KEYMAP_SET(layer, on)
 314
 315 Turns on layer only and clear all layer on release..
 316
 317     ACTION_KEYMAP_SET_CLEAR(layer)
 318
 319
 320 #### 2.2.2 Overlay
 321 ***TBD***
 322
 323 In addition to actions of `Keymap` above these actions are also available.
 324
 325 ##### Invert 4bit layer states
 326 Invert 4bits out of 16bits of overlay status on both press and release.
 327 `overlay_stat = (overlay_stat ^ bits<<(shift*4)) [bits: 0-15, shift: 0-3]`
 328
 329     ACTION_OVERLAY_INV4(bits, shift)
 330
 331
 332
 333 ### 2.3 Macro action
 334 ***TBD***
 335
 336 `Macro` action indicates complex key strokes.
 337
 338     MACRO( MD(LSHIFT), D(D), END )
 339     MACRO( U(D), MU(LSHIFT), END )
 340     MACRO( I(255), T(H), T(E), T(L), T(L), W(255), T(O), END )
 341
 342 #### 2.3.1 Normal mode
 343 - **I()**   change interavl of stroke.
 344 - **D()**   press key
 345 - **U()**   release key
 346 - **T()**   type key(press and release)
 347 - **W()**   wait
 348 - **MD()**  modifier down
 349 - **MU()**  modifier up
 350 - **END**   end mark
 351
 352 #### 2.3.2 Extended mode
 353
 354 ***TODO: sample impl***
 355 See `keyboard/hhkb/keymap.c` for sample.
 356
 357
 358 ### 2.4 Function action
 359 ***TBD***
 360
 361 There are two type of action, normal `Function` and tappable `Function`.
 362 These actions call user defined function with `id`, `opt`, and key event information as arguments.
 363
 364 #### 2.4.1 Function
 365 To define normal `Function` action in keymap use this.
 366
 367     ACTION_FUNCTION(id, opt)
 368
 369 #### 2.4.2 Function with tap
 370 To define tappable `Function` action in keymap use this.
 371
 372     ACTION_FUNCTION_TAP(id, opt)
 373
 374 #### 2.4.3 Implement user function
 375 `Function` actions can be defined freely with C by user in callback function:
 376
 377     void keymap_call_function(keyrecord_t *event, uint8_t id, uint8_t opt)
 378
 379 This C function is called every time key is operated, argument `id` selects action to be performed and `opt` can be used for option. Functon `id` can be 0-255 and `opt` can be 0-15.
 380
 381  `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.
 382
 383     typedef struct {
 384         keyevent_t  event;
 385         uint8_t     tap_count;
 386     } keyrecord_t;
 387
 388     typedef struct {
 389         key_t    key;
 390         bool     pressed;
 391         uint16_t time;
 392     } keyevent_t;
 393
 394     typedef struct {
 395         uint8_t col;
 396         uint8_t row;
 397     } key_t;
 398
 399 ***TODO: sample impl***
 400 See `keyboard/hhkb/keymap.c` for sample.
 401
 402
 403
 404
 405
 406 ## 4. Layer switching Example
 407 There are some ways to switch layer with 'Layer' actions.
 408
 409 ### 4.1 Momentary switching
 410 Momentary switching changes layer only while holding Fn key.
 411
 412 This action makes 'Layer 1' active(valid) on key press event and inactive on release event. Namely you can overlay a layer on base layer temporarily with this.
 413
 414     ACTION_KEYMAP_MOMENTARY(1)
 415
 416
 417 After switch actions of destination layer are perfomed.
 418 ***Thus you shall need to place action to come back on destination layer***, or you will be stuck in destination layer without way to get back. Usually you need to palce same action or 'KC_TRNS` on destination layer to get back.
 419
 420
 421 ### 4.2 Toggle switching
 422 Toggle switching changes layer after press then release. With this you can keep staying on the layer until you press the key again to return.
 423
 424 This is toggle action of 'Layer 2'.
 425
 426     ACTION_KEYMAP_TOGGLE(2)
 427
 428
 429
 430 ### 4.3 Momentary switching with Tap key
 431 These actions switch layer only while holding `Fn` key and register key on tap. **Tap** means to press and release key quickly.
 432
 433     ACTION_KEYMAP_TAP_KEY(2, KC_SCLN)
 434
 435 With this you can place layer switching function on normal key like ';' without losing its original key register function.
 436
 437
 438
 439 ### 4.4 Momentary switching with Tap Toggle
 440 This switches layer only while holding `Fn` key and toggle layer after several taps. **Tap** means to press and release key quickly.
 441
 442     ACTION_KEYMAP_TAP_TOGGLE(1)
 443
 444 Number of taps can be defined with `TAPPING_TOGGLE` in `config.h`, `5` by default.
 445
 446
 447
 448 ## Tapping
 449 Tapping is to press and release key quickly. Tapping speed is determined with setting of `TAPPING_TERM`, which can be defined in `config.h`, 200ms by default.
 450
 451 ### Tap Key
 452 This is feature to assign normal key action and modifier including `Fn` to just one physical key. This is a kind of [Dual role modifier][dual_role]. It works as modifier or `Fn` when holding a key but registers normal key when tapping.
 453
 454 Action for modifier with tap key.
 455
 456     ACTION_LMODS_TAP_KEY(mods, key)
 457
 458 Action for `Fn` with tap key.
 459
 460     ACTION_KEYMAP_TAP_KEY(layer, key)
 461
 462 [dual_role]: http://en.wikipedia.org/wiki/Modifier_key#Dual-role_modifier_keys
 463
 464
 465 ### Tap Toggle
 466 This is feature to assign both toggle layer and momentary switch layer action to just one physical key. It works as mementary switch when holding a key but toggle switch when tapping.
 467
 468     ACTION_KEYMAP_TAP_TOGGLE(layer)
 469
 470
 471 ### One Shot Modifier
 472 This adds oneshot feature to modifier key. 'One Shot Modifier' is one time modifier which has effect only on following one alpha key.
 473 It works as normal modifier key when holding but oneshot modifier when tapping.
 474
 475     ACTION_LMODS_ONESHOT(mods)
 476
 477 Say you want to type 'The', you have to push and hold Shift before type 't' then release Shift before type 'h' and 'e' or you'll get 'THe'. With One Shot Modifier you can tap Shift then type 't', 'h' and 'e' normally, you don't need to holding Shift key properly  here.
 478
 479
 480
 481
 482 ## Legacy Keymap
 483 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.
 484
 485 In comparison with new keymap how to define Fn key is different. It uses two arrays `fn_layer[]` and `fn_keycode[]`. 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.
 486
 487 In following setting example, `Fn0`, `Fn1` and `Fn2` switch layer to 1, 2 and 2 respectively. `Fn2` registers `Space` key when tap while `Fn0` and `Fn1` doesn't send any key.
 488
 489     static const uint8_t PROGMEM fn_layer[] = {
 490         1,              // Fn0
 491         2,              // Fn1
 492         2,              // Fn2
 493     };
 494
 495     static const uint8_t PROGMEM fn_keycode[] = {
 496         KC_NO,          // Fn0
 497         KC_NO,          // Fn1
 498         KC_SPC,         // Fn2
 499     };
 500
 501
 502 ## Terminology
 503 - keymap
 504 - layer
 505 - layout
 506 - key
 507 - keycode
 508 - scancode
 509 - action
 510 - layer transparency
 511 - layer precedence
 512 - register
 513 - tap
 514 - Fn key