Keymap framework - how to define your keymap

NOTE: This is not final version, may be inconsistent with source code and changed occasionally for a while.

0. Keymap and layers

Keymap is comprised of multiple layers of key layout, you can define 16 layers at most. Layer is an array of keycodes to define actions on each physical keys. respective layers can be validated simultaneously. Layers are indexed with 0 to 15 and higher layer has precedence.

Keymap with 16 Layers               Layer: array of Keycodes
---------------------               ------------------------
      stack of layers               content of layer
       ____________ precedence               _______________________
      /           / | high                  / ESC / F1  / F2  / F3   ....
  15 /___________// |                      /-----/-----/-----/-----
  14 /___________// |                     / TAB /     /     /      ....
  13 /___________/_ |                    /-----/-----/-----/-----
   :  / : : : : : / |                   /LCtrl/     /     /      ....
   3 /___________// |               :  /  :     :     :     :
   2 /___________// |               2 `--------------------------
   1 /___________// |               1 `--------------------------
   0 /___________/  V low           0 `--------------------------

0.1 Keymap status

Keymap has its state in two parameters: 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.

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. To change default_layer will be useful when you want to switch key layout completely, say you use Colmak instead of Qwerty.

Initial state of Keymap         Change base layout              
-----------------------         ------------------              

  15                              15                            
  14                              14                            
  13                              13                            
   :                               :                            
   3                               3   ____________             
   2   ____________                2  /           /             
   1  /           /             ,->1 /___________/              
,->0 /___________/              |  0                            
|                               |                               
`--- default_layer = 0          `--- default_layer = 1          
     keymap_stat   = 0x0001          keymap_stat   = 0x0002     

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.

Overlay feature layer
---------------------      bit|status
       ____________        ---+------
  15  /           /        15 |   0
  14 /___________// -----> 14 |   1
  13 /___________/  -----> 13 |   1
   :                        : |   
   3   ____________         3 |   0
   2  /           /         2 |   0
,->1 /___________/  ----->  1 |   1
|  0                        0 |   0
|                                 |
`--- default_layer = 1            |
     keymap_stat   = 0x6002 <-----'

0.2 Layer Precedence and Transparency

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.

You can place KC_TRNS on overlay layer changes just part of layout to fall back on lower or base layer. Key with KC_TRANS doen’t has its own keycode and refers to lower valid layers for keycode, instead. See example below.

0.3 Keymap Example

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.

This is a keymap example for HHKB keyboard. This example has three layers, ‘Qwerty’ as base layer, ‘Cursor’ and ‘Mousekey’. In this example,

Fn0 is a momentary layer switching key, you can use keys on Cursor layer while holding the key.

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.

Fn2 is a toggle layer switch key, you can stay switched layer after releasing the key unlike momentary switching.

You can find other keymap definitions in file keymap.c located on project directories.

static const uint8_t PROGMEM keymaps[][MATRIX_ROWS][MATRIX_COLS] = {
    /* 0: Qwerty
     * ,-----------------------------------------------------------.
     * |Esc|  1|  2|  3|  4|  5|  6|  7|  8|  9|  0|  -|  =|  \|  `|
     * |-----------------------------------------------------------|
     * |Tab  |  Q|  W|  E|  R|  T|  Y|  U|  I|  O|  P|  [|  ]|Backs|
     * |-----------------------------------------------------------|
     * |Contro|  A|  S|  D|  F|  G|  H|  J|  K|  L|Fn1|  '|Enter   |
     * |-----------------------------------------------------------|
     * |Shift   |  Z|  X|  C|  V|  B|  N|  M|  ,|  .|  /|Shift |Fn0|
     * `-----------------------------------------------------------'
     *       |Gui|Alt  |Space                  |Alt  |Fn2|
     *       `-------------------------------------------'
     */
    KEYMAP(ESC, 1,   2,   3,   4,   5,   6,   7,   8,   9,   0,   MINS,EQL, BSLS,GRV, \
           TAB, Q,   W,   E,   R,   T,   Y,   U,   I,   O,   P,   LBRC,RBRC,BSPC, \
           LCTL,A,   S,   D,   F,   G,   H,   J,   K,   L,   FN1, QUOT,ENT, \
           LSFT,Z,   X,   C,   V,   B,   N,   M,   COMM,DOT, SLSH,RSFT,FN0, \
                LGUI,LALT,          SPC,                RALT,FN2),
    /* 1: Cursor(HHKB mode)
     * ,-----------------------------------------------------------.
     * |Pwr| F1| F2| F3| F4| F5| F6| F7| F8| F9|F10|F11|F12|Ins|Del|
     * |-----------------------------------------------------------|
     * |Caps |   |   |   |   |   |   |   |Psc|Slk|Pus|Up |   |Backs|
     * |-----------------------------------------------------------|
     * |Contro|VoD|VoU|Mut|   |   |  *|  /|Hom|PgU|Lef|Rig|Enter   |
     * |-----------------------------------------------------------|
     * |Shift   |   |   |   |   |   |  +|  -|End|PgD|Dow|Shift |   |
     * `-----------------------------------------------------------'
     *      |Gui |Alt  |Space                  |Alt  |Gui|
     *      `--------------------------------------------'
     */ 
    KEYMAP(PWR, F1,  F2,  F3,  F4,  F5,  F6,  F7,  F8,  F9,  F10, F11, F12, INS, DEL, \
           CAPS,TRNS,TRNS,TRNS,TRNS,TRNS,TRNS,TRNS,PSCR,SLCK,PAUS,UP,  TRNS,BSPC, \
           LCTL,VOLD,VOLU,MUTE,TRNS,TRNS,PAST,PSLS,HOME,PGUP,LEFT,RGHT,ENT, \
           LSFT,TRNS,TRNS,TRNS,TRNS,TRNS,PPLS,PMNS,END, PGDN,DOWN,RSFT,TRNS, \
                LGUI,LALT,          SPC,                RALT,RGUI),
    /* 2: Mousekey
     * ,-----------------------------------------------------------.
     * |Esc| F1| F2| F3| F4| F5| F6| F7| F8| F9|F10|F11|F12|Ins|Del|
     * |-----------------------------------------------------------|
     * |Tab  |   |   |   |   |   |MwL|MwD|MwU|MwR|   |   |   |Backs|
     * |-----------------------------------------------------------|
     * |Contro|   |   |   |   |   |McL|McD|McU|McR|   |   |Return  |
     * |-----------------------------------------------------------|
     * |Shift   |   |   |   |   |Mb3|Mb2|Mb1|Mb4|Mb5|   |Shift |   |
     * `-----------------------------------------------------------'
     *      |Gui |Alt  |Mb1                    |Alt  |   |
     *      `--------------------------------------------'
     * Mc: Mouse Cursor / Mb: Mouse Button / Mw: Mouse Wheel 
     */
    KEYMAP(ESC, F1,  F2,  F3,  F4,  F5,  F6,  F7,  F8,  F9,  F10, F11, F12, INS, DEL, \
           TAB, TRNS,TRNS,TRNS,TRNS,TRNS,WH_L,WH_D,WH_U,WH_R,TRNS,TRNS,TRNS,BSPC, \
           LCTL,TRNS,ACL0,ACL1,ACL2,TRNS,MS_L,MS_D,MS_U,MS_R,TRNS,QUOT,ENT, \
           LSFT,TRNS,TRNS,TRNS,TRNS,BTN3,BTN2,BTN1,BTN4,BTN5,SLSH,RSFT,TRNS, \
                LGUI,LALT,          BTN1,               RALT,TRNS),
};

static const uint16_t PROGMEM fn_actions[] = {
    ACTION_KEYMAP_MOMENTARY(1),                  // FN0
    ACTION_KEYMAP_TAP_KEY(2, KC_SCLN),           // FN1
    ACTION_KEYMAP_TOGGLE(2),                     // FN2
};

1. Keycode

See 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.

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().

1.0 Other key

• KC_NO for no aciton
• KC_TRNS for layer transparency (See above)

1.1 Normal key

• KC_A to KC_Z, KC_1 to KC_0 for alpha numeric key
• KC_MINS, KC_EQL, KC_GRV, KC_RBRC, KC_LBRC, KC_COMM, KC_DOT, KC_BSLS, KC_SLSH, KC_SCLN, KC_QUOT
• KC_ESC, KC_TAB, KC_SPC, KC_BSPC, KC_ENT, KC_DEL, KC_INS
• KC_UP, KC_DOWN, KC_RGHT, KC_LEFT, KC_PGUP, KC_PGDN, KC_HOME, KC_END
• KC_CAPS, KC_NLCK, KC_SLCK, KC_PSCR, KC_PAUS, KC_APP, KC_F1 to KC_F24
• KC_P1 to KC_P0, KC_PDOT, KC_PCMM, KC_PSLS, KC_PAST, KC_PMNS, KC_PPLS, KC_PEQL, KC_PENT for keypad.

1.2 Modifier

There are 8 modifiers which has discrimination between left and right.

• KC_LCTL and KC_RCTL for Control
• KC_LSFT and KC_RSFT for Shift
• KC_LALT and KC_RALT for Alt
• KC_LGUI and KC_RGUI for Windows key or Command key in Mac

1.3 Mousekey

• KC_MS_U, KC_MS_D, KC_MS_L, KC_MS_R for mouse cursor
• KC_WH_U, KC_WH_D, KC_WH_L, KC_WH_R for mouse wheel
• KC_BTN1, KC_BTN2, KC_BTN3, KC_BTN4, KC_BTN5 for mouse buttons

1.4 System & Media key

• KC_PWR, KC_SLEP, KC_WAKE for Power, Sleep, Wake
• KC_MUTE, KC_VOLU, KC_VOLD for audio volume control
• KC_MNXT, KC_MPRV, KC_MSTP, KC_MPLY, KC_MSEL for media control
• KC_MAIL, KC_CALC, KC_MYCM for application launch
• KC_WSCH, KC_WHOM, KC_WBAK, KC_WFWD, KC_WSTP, KC_WREF, KC_WFAV for web browser operation

1.5 Fn key

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.

1.6 Keycode Table

See keycode table in doc/keycode.txt for description of keycodes.

In regard to implementation side most of keycodes are identical with HID usage(pdf) sent to host for real and some virtual keycodes are defined to support special actions.

2. Action

See common/action.h. Action is a 16bit code and defines function to perform on events of a key like press, release, holding and tapping.

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.

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[].

Usually action codes are needed only when you want to use layer switching, or

2.1 Key action

This is a simple action that registers scancodes(HID usage in fact) to host on press event of key and unregister on release.

2.1.1 Normal key and Modifier

This action usually won’t be used expressly because you can use keycodes in KEYMAP() instead. You can define Key action on ‘A’ key and ‘left shift’ modifier with:

ACTION_KEY(KC_A)
ACTION_KEY(KC_LSHIFT)

2.1.2 Key with modifiers

This action is comprised of strokes of modifiers and a key. Macro action is needed if you want more complex key strokes. Say you want to assign a key to Shift + 1 to get charactor ’!’ or Alt + Tab to switch application windows.

ACTION_LMOD_KEY(KC_LSHIFT, KC_1)
ACTION_LMOD_KEY(KC_LALT, KC_TAB)

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.

ACTION_LMODS_KEY((MOD_BIT(KC_LALT) | MOD_BIT(KC_LSHIFT)), KC_TAB)

2.2 Layer Action

These actions operate layers of keymap.

Parameters:

• layer: 0-15
• on: { press | release | both }

2.2.0 Default Layer

default_layer is layer which always is valid and referred to when actions is not defined on other layers.

Return to Default Layer

Turns on only default layer with clearing other all layers.

ACTION_DEFAULT_LAYER

Set Default Layer

Sets ‘default layer’ to layer and turn it on.

ACTION_DEFAULT_LAYER_SET_TO(layer)
ACTION_DEFAULT_LAYER_SET(layer, on)

2.2.1 Keymap

These actions operate layer status of keymap.

Momentary Switch

Turns on layer momentary while holding, in other words turn on when key is pressed and off when released.

ACTION_KEYMAP_MOMENTARY(layer)

Toggle Switch

Turns on layer on first type and turns off on next.

ACTION_KEYMAP_TOGGLE(layer)

Momentary Switch with tap key

Turns on layer momentary while holding but registers key on tap.

ACTION_KEYMAP_TAP_KEY(layer, key)

Momentary Switch with tap toggle

Turns on layer momentary while holding but toggles it with serial taps.

ACTION_KEYMAP_TAP_TOGGLE(layer)

Invert layer

Inverts current layer state. If the layer is on it becomes off with this action.

ACTION_KEYMAP_INV(layer, on)

Turn On layer

Turns on layer state.

ACTION_KEYMAP_ON(layer, on)

Turns on layer state on press and turn off on release. This is identical to ‘Switch to layer’ action.

ACTION_KEYMAP_ON_OFF(layer)

Turn Off layer

Turns off layer state.

ACTION_KEYMAP_OFF(layer, on)

Set layer

Turn on layer only. keymap_stat = (1<<layer) [layer: 0-15]

ACTION_KEYMAP_SET(layer, on)

Turns on layer only and clear all layer on release..

ACTION_KEYMAP_SET_CLEAR(layer)

2.2.2 Overlay

TBD

In addition to actions of Keymap above these actions are also available.

Invert 4bit layer states

Invert 4bits out of 16bits of overlay status on both press and release. overlay_stat = (overlay_stat ^ bits<<(shift*4)) [bits: 0-15, shift: 0-3]

ACTION_OVERLAY_INV4(bits, shift)

2.3 Macro action

TBD

Macro action indicates complex key strokes.

MACRO( MD(LSHIFT), D(D), END )
MACRO( U(D), MU(LSHIFT), END )
MACRO( I(255), T(H), T(E), T(L), T(L), W(255), T(O), END )

2.3.1 Normal mode

• I() change interavl of stroke.
• D() press key
• U() release key
• T() type key(press and release)
• W() wait
• MD() modifier down
• MU() modifier up
• END end mark

2.3.2 Extended mode

TODO: sample impl See keyboard/hhkb/keymap.c for sample.

2.4 Function action

TBD

There are two type of action, normal Function and tappable Function. These actions call user defined function with id, opt, and key event information as arguments.

2.4.1 Function

To define normal Function action in keymap use this.

ACTION_FUNCTION(id, opt)

2.4.2 Function with tap

To define tappable Function action in keymap use this.

ACTION_FUNCTION_TAP(id, opt)

2.4.3 Implement user function

Function actions can be defined freely with C by user in callback function:

void keymap_call_function(keyrecord_t *event, uint8_t id, uint8_t opt)

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.

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.

typedef struct {
    keyevent_t  event;
    uint8_t     tap_count;
} keyrecord_t;

typedef struct {
    key_t    key;
    bool     pressed;
    uint16_t time;
} keyevent_t;

typedef struct {
    uint8_t col;
    uint8_t row;
} key_t;

TODO: sample impl See keyboard/hhkb/keymap.c for sample.

4. Layer switching Example

There are some ways to switch layer with ‘Layer’ actions.

4.1 Momentary switching

Momentary switching changes layer only while holding Fn key.

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.

ACTION_KEYMAP_MOMENTARY(1)

After switch actions of destination layer are perfomed. 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.

4.2 Toggle switching

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.

This is toggle action of ‘Layer 2’.

ACTION_KEYMAP_TOGGLE(2)

4.3 Momentary switching with Tap key

These actions switch layer only while holding Fn key and register key on tap. Tap means to press and release key quickly.

ACTION_KEYMAP_TAP_KEY(2, KC_SCLN)

With this you can place layer switching function on normal key like ‘;’ without losing its original key register function.

4.4 Momentary switching with Tap Toggle

This switches layer only while holding Fn key and toggle layer after several taps. Tap means to press and release key quickly.

ACTION_KEYMAP_TAP_TOGGLE(1)

Number of taps can be defined with TAPPING_TOGGLE in config.h, 5 by default.

Tapping

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.

Tap Key

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. It works as modifier or Fn when holding a key but registers normal key when tapping.

Action for modifier with tap key.

ACTION_LMODS_TAP_KEY(mods, key)

Action for Fn with tap key.

ACTION_KEYMAP_TAP_KEY(layer, key)

Tap Toggle

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.

ACTION_KEYMAP_TAP_TOGGLE(layer)

One Shot Modifier

This adds oneshot feature to modifier key. ‘One Shot Modifier’ is one time modifier which has effect only on following one alpha key. It works as normal modifier key when holding but oneshot modifier when tapping.

ACTION_LMODS_ONESHOT(mods)

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.

Legacy Keymap

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.

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.

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.

static const uint8_t PROGMEM fn_layer[] = {
    1,              // Fn0
    2,              // Fn1
    2,              // Fn2
};

static const uint8_t PROGMEM fn_keycode[] = {
    KC_NO,          // Fn0
    KC_NO,          // Fn1
    KC_SPC,         // Fn2
};

Terminology

• keymap
• layer
• layout
• key
• keycode
• scancode
• action
• layer transparency
• layer precedence
• register
• tap
• Fn key