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Keymap framework - how to define your keymap

NOTE: This is updated for QMK but this is still work in progress. This may still be inconsistent with the source code.

QMK is based on TMK. Understanding the essential changes made should help you understand variable names etc.

TMK vs. QMK

Firmware	TMK	QMK
Maintainer	hasu	Jack Humbert et al.
Build path customization	`TMK_DIR = ...`	`include .../Makefile`
`keymaps` data	3D array of `uint8_t` holding keycode	3D array of `uint16_t` holding action code
`fn_actions` data	1D array of `uint16_t` holding action code	1D array of `uint16_t` holding action code

Since QMK is based on TMK and uses major portion of TMK code as is, understanding the essential changes made should help you understand the code.

0. Keymap and layers

In QMK, const uint16_t PROGMEM keymaps[][MATRIX_ROWS][MATRIX_COLS] holds multiple layers of keymap information in 16 bit data holding the action code. You can define 32 layers at most.

For trivial key definitions, the higher 8 bits of the action code are all 0 and the lower 8 bits holds the USB HID usage code generated by the key as keycode.

Respective layers can be validated simultaneously. Layers are indexed with 0 to 31 and higher layer has precedence.

Keymap: 32 Layers                   Layer: action code matrix
-----------------                   ---------------------
stack of layers                     array_of_action_code[row][column]
       ____________ precedence               _______________________
      /           / | high                  / ESC / F1  / F2  / F3   ....
  31 /___________// |                      /-----/-----/-----/-----
  30 /___________// |                     / TAB /  Q  /  W  /  E   ....
  29 /___________/  |                    /-----/-----/-----/-----
   :   _:_:_:_:_:__ |               :   /LCtrl/  A  /  S  /  D   ....
   :  / : : : : : / |               :  /  :     :     :     :
   2 /___________// |               2 `--------------------------
   1 /___________// |               1 `--------------------------
   0 /___________/  V low           0 `--------------------------

Sometimes, the action code stored in keymap may be referred as keycode in some documents due to the TMK history.

0.1 Keymap layer status

Keymap layer has its state in two 32 bit parameters:

default_layer_state indicates a base keymap layer(0-31) which is always valid and to be referred.
layer_state () has current on/off status of the layer on its each bit.

Keymap has its state in two parameter default_layer indicates a base keymap layer(0-31) 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 switch key layout completely, say you want Colmak instead of Qwerty.

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

  31                               31
  30                               30
  29                               29
   :                                :
   :                                :   ____________
   2   ____________                 2  /           /
   1  /           /              ,->1 /___________/
,->0 /___________/               |  0
|                                |
`--- default_layer = 0           `--- default_layer = 1
     layer_state   = 0x00000001       layer_state   = 0x00000002

On the other hand, you shall change layer_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
       ____________        ---+------
  31  /           /        31 |   0
  30 /___________// -----> 30 |   1
  29 /___________/  -----> 29 |   1
   :                        : |   :
   :   ____________         : |   :
   2  /           /         2 |   0
,->1 /___________/  ----->  1 |   1
|  0                        0 |   0
|                                 +
`--- default_layer = 1            |
     layer_state   = 0x60000002 <-'

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_TRANS on overlay layer changes just part of layout to fall back on lower or base layer. Key with KC_TRANS (KC_TRNS and _______ are the alias) doesn’t has its own keycode and refers to lower valid layers for keycode, instead. See example below.

0.3 Keymap Example

Keymap in this QMK is static const uint16_t PROGMEM 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. It holds the 16 bit quantum keycode (action code).

Please note that keymap in the TMK, which QMK was forked from, is static const uint8_t PROGMEM keymaps[] C array which holds the 8 bit keycode (~USB HID usage code).

This is a keymap example for HHKB keyboard. This example has three layers, ‘QWERTY’ as base layer, ‘FN’ and ‘MOUSE’.

In this example,

MO(layer) is a momentary layer switching key.

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

/*
 * dbroqua HHKB Layout
 */
#include "hhkb.h"

#define BASE 0
#define FN 1
#define MOUSE 2

const uint16_t PROGMEM keymaps[][MATRIX_ROWS][MATRIX_COLS] = {
    /* BASE Level: Default Layer
     * ,-----------------------------------------------------------------------------------------.
     * | Esc |  1  |  2  |  3  |  4  |  5  |  6  |  7  |  8  |  9  |  0  |  -  |  =  |  \  |  `  |
     * |-----------------------------------------------------------------------------------------+
     * | Tab    |  Q  |  W  |  E  |  R  |  T  |  Y  |  U  |  I  |  O  |  P  |  [  |  ]  |  Bksp  |
     * |-----------------------------------------------------------------------------------------+
     * | Ctrl    |  A  |  S  |  D  |  F  |  G  |  H  |  J  |  K  |  L  |  ;  |  '  |    Enter    |
     * |-----------------------------------------------------------------------------------------+
     * | Shift     |  Z  |  X  |  C  |  V  |  B  |  N  |  M  |  ,  |  .  |  /  | Shift     | fn  |
     * +-----------------------------------------------------------------------------------------+
     *         | Gui |  Alt   |               Space               | AltGr |Mouse|
     *         `----------------------------------------------------------------´
     */
    [BASE] = KEYMAP(
        KC_ESC,   KC_1,  KC_2,  KC_3,  KC_4,  KC_5,  KC_6,  KC_7,  KC_8,     KC_9,    KC_0,     KC_MINS,  KC_EQL,    KC_BSLS,  KC_GRV, \
        KC_TAB,   KC_Q,  KC_W,  KC_E,  KC_R,  KC_T,  KC_Y,  KC_U,  KC_I,     KC_O,    KC_P,     KC_LBRC,  KC_RBRC,   KC_BSPC,          \
        KC_LCTL,  KC_A,  KC_S,  KC_D,  KC_F,  KC_G,  KC_H,  KC_J,  KC_K,     KC_L,    KC_SCLN,  KC_QUOT,  KC_ENT,                      \
        KC_LSFT,  KC_Z,  KC_X,  KC_C,  KC_V,  KC_B,  KC_N,  KC_M,  KC_COMM,  KC_DOT,  KC_SLSH,  KC_RSFT,  MO(FN),                    \
                        KC_LGUI, KC_LALT,  /*        */ KC_SPC, KC_RALT, MO(MOUSE)
    ),

    /* FN Layer
     * ,-----------------------------------------------------------------------------------------.
     * | Pwr |  F1  | F2  | F3  | F4  | F5  | F6  | F7  | F8  | F9  | F0  | F11 | F12 | Ins | Del|
     * |-----------------------------------------------------------------------------------------+
     * | Caps   |     |     |     |     |     |     |     |PrtSc| Slck| Paus|  Up |     |        |
     * |-----------------------------------------------------------------------------------------+
     * |         | Vol-| Vol+| Mute|     |     | *   | /   | Home| PgUp| Left |Right|            |
     * |-----------------------------------------------------------------------------------------+
     * |           | Prev| Play| Next|     |     | +   | -   | End |PgDwn| Down|           |     |
     * +-----------------------------------------------------------------------------------------+
     *         |     |        |                                   | Stop  |     |
     *         `----------------------------------------------------------------´
     */
    [FN] = KEYMAP(
        KC_PWR,   KC_F1,    KC_F2,    KC_F3,    KC_F4,    KC_F5,    KC_F6,    KC_F7,    KC_F8,    KC_F9,    KC_F10,   KC_F11,   KC_F12,   KC_INS,   KC_DEL, \
        KC_CAPS,  KC_TRNS,  KC_TRNS,  KC_TRNS,  KC_TRNS,  KC_TRNS,  KC_TRNS,  KC_TRNS,  KC_PSCR,  KC_SLCK,  KC_PAUS,  KC_UP,    KC_TRNS,  KC_TRNS,          \
        KC_TRNS,  KC_VOLD,  KC_VOLU,  KC_MUTE,  KC_TRNS,  KC_TRNS,  KC_PAST,  KC_PSLS,  KC_HOME,  KC_PGUP,  KC_LEFT,  KC_RGHT,  KC_TRNS,                    \
        KC_TRNS,  KC_MPRV,  KC_MPLY,  KC_MNXT,  KC_TRNS,  KC_TRNS,  KC_PPLS,  KC_PMNS,  KC_END,   KC_PGDN,  KC_DOWN,  KC_TRNS,  KC_TRNS,                    \
                        KC_TRNS, KC_TRNS,           KC_TRNS,                KC_MSTP, KC_TRNS
    ),

    /* MOUSE Layer
     * ,-----------------------------------------------------------------------------------------.
     * |     |      |     |     |     |     |     |     |     |     |     |     |     |     |    |
     * |-----------------------------------------------------------------------------------------+
     * |        |     | WUp |     |     |     |     |     |     |     | Btn1|  Up | Btn2|        |
     * |-----------------------------------------------------------------------------------------+
     * |         | WLt | WDn | WRt |     |     |     |     |     |     | Left |Right|            |
     * |-----------------------------------------------------------------------------------------+
     * |           |     |     |     |     |     |     |     |     | Btn3| Down|           |     |
     * +-----------------------------------------------------------------------------------------+
     *         |     |        |                                   |       |     |
     *         `----------------------------------------------------------------´
     */
    [MOUSE] = KEYMAP(
        KC_TRNS,  KC_TRNS,  KC_TRNS,  KC_TRNS,  KC_TRNS,  KC_TRNS,  KC_TRNS,  KC_TRNS,  KC_TRNS,  KC_TRNS,  KC_TRNS,  KC_TRNS,  KC_TRNS,  KC_TRNS,   KC_TRNS, \
        KC_TRNS,  KC_TRNS,  KC_WH_U,  KC_TRNS,  KC_TRNS,  KC_TRNS,  KC_TRNS,  KC_TRNS,  KC_TRNS,  KC_TRNS,  KC_BTN1,  KC_MS_U,  KC_BTN2,  KC_TRNS,          \
        KC_TRNS,  KC_WH_L,  KC_WH_D,  KC_WH_R,  KC_TRNS,  KC_TRNS,  KC_TRNS,  KC_TRNS,  KC_TRNS,  KC_TRNS,  KC_MS_L,  KC_MS_R,  KC_TRNS,                    \
        KC_TRNS,  KC_TRNS,  KC_TRNS,  KC_TRNS,  KC_TRNS,  KC_TRNS,  KC_TRNS,  KC_TRNS,  KC_TRNS,  KC_BTN3,  KC_MS_D,  KC_TRNS,  KC_TRNS,                    \
                        KC_TRNS, KC_TRNS,           KC_TRNS,                KC_TRNS, KC_TRNS
    )
};

const uint16_t PROGMEM fn_actions[] = {

};

const macro_t *action_get_macro(keyrecord_t *record, uint8_t id, uint8_t opt)
{
  // MACRODOWN only works in this function
      switch(id) {
        case 0:
          if (record->event.pressed) {
            register_code(KC_RSFT);
          } else {
            unregister_code(KC_RSFT);
          }
        break;
      }
    return MACRO_NONE;
};

1. Keycode

See tmk_core/common/keycode.h or keycode table below for the detail. Keycode is internal 8bit code to indicate action performed on key in keymap. Keycodes are based on HID Usage Keyboard/Keypad Page(0x07) plus special codes in the 0xA5-DF range.

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.

keymaps[]

In KEYMAP() macro, TMK recommends you to keep prefix part KC_ of keycode to keep keymap compact. For example, just use A instead you place KC_A in KEYMAP(). But this doesn’t apply for QMK.

The KEYMAP() macro defines correspondence between the physical key location to the electrical key connection.

Some keycodes has 7-letter short name such as KC_COMM in addition to descriptive name KC_COMMA, you’ll prefer short one in KEYMAP().

1.0 Other key

KC_NO for no action
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

You don’t need to use this functionality under QMK since this is a backward compatibility functionality. Unlike TMK, you can write action code itself directly in static const uint16_t PROGMEM keymaps[] C array using MO(layer), etc.

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. Only 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][HID_usage](pdf) sent to host for real and some virtual keycodes are defined to support special actions. [HID_usage]: http://www.usb.org/developers/hidpage/Hut1_12v2.pdf

2. Action

See 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.

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.

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[].

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.

Parameters

mods: { MOD_LCTL, MOD_LSFT, MOD_LALT, MOD_LGUI, MOD_RCTL, MOD_RSFT, MOD_RALT, MOD_RGUI }
key: keycode

2.1.1 Normal key and Modifier

This action usually won’t be used expressly in keymap because you can just use keycodes in KEYMAP() instead.

You can define these actions on ‘A’ key and ‘left shift’ modifier with:

ACTION_KEY(KC_A)
ACTION_KEY(KC_LSFT)

2.1.2 Modified key

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 character ‘!’ or Alt + Tab to switch application windows.

ACTION_MODS_KEY(MOD_LSFT, KC_1)
ACTION_MODS_KEY(MOD_LALT, KC_TAB)

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.

ACTION_MODS_KEY(MOD_LALT | MOD_LSFT, KC_TAB)

2.1.3 Multiple Modifiers

Registers multiple modifiers with pressing a key. To specify multiple modifiers use |.

ACTION_MODS(MOD_ALT | MOD_LSFT)

2.1.3 Modifier with Tap key(Dual role)

Works as a modifier key while holding, but registers a key on tap(press and release quickly).

ACTION_MODS_TAP_KEY(MOD_RCTL, KC_ENT)

2.2 Layer Action

These actions operate layers of keymap.

Parameters

You can specify a target layer of action and when the action is executed. Some actions take a bit value for bitwise operation.

layer: 0-31
on: { ON_PRESS | ON_RELEASE | ON_BOTH }
bits: 4-bit value and 1-bit mask bit

2.2.1 Default Layer

Default Layer is a layer which always is valid and referred to when actions is not defined on other overlay layers.

This sets Default Layer to given parameter layer and activate it.

ACTION_DEFAULT_LAYER_SET(layer)

2.2.2 Momentary

Turns on layer momentarily while holding, in other words it activates when key is pressed and deactivate when released.

ACTION_LAYER_MOMENTARY(layer)

2.2.3 Toggle Switch

Turns on layer with first type(press and release) and turns off with next.

ACTION_LAYER_TOGGLE(layer)

2.2.4 Momentary Switch with tap key

Turns on layer momentary while holding, but registers key on tap(press and release quickly).

ACTION_LAYER_TAP_KEY(layer, key)

2.2.5 Momentary Switch with tap toggle

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

ACTION_LAYER_TAP_TOGGLE(layer)

2.2.6 Invert state of layer

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

ACTION_LAYER_INVERT(layer, on)

2.2.7 Turn On layer

Turns on layer state.

ACTION_LAYER_ON(layer, on)

Turns on layer state on press and turns off on release.

ACTION_LAYER_ON_OFF(layer)

2.2.8 Turn Off layer

Turns off layer state.

ACTION_LAYER_OFF(layer, on)

Turns off layer state on press and activates on release.

ACTION_LAYER_OFF_ON(layer)

2.2.9 Set layer

Turn on layer only. layer_state = (1<<layer) [layer: 0-31]

ACTION_LAYER_SET(layer, on)

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

ACTION_LAYER_SET_CLEAR(layer)

2.2.10 Bitwise operation

part indicates which part of 32bit layer state(0-7). bits is 5-bit value. on indicates when the action is executed.

ACTION_LAYER_BIT_AND(part, bits, on)
ACTION_LAYER_BIT_OR(part, bits, on)
ACTION_LAYER_BIT_XOR(part, bits, on)
ACTION_LAYER_BIT_SET(part, bits, on)

These actions works with parameters as following code.

uint8_t shift = part*4;
uint32_t mask = (bits&0x10) ? ~(0xf<<shift) : 0;
uint32_t layer_state = layer_state <bitop> ((bits<<shift)|mask);

Default Layer also has bitwise operations, they are executed when key is released.

ACTION_DEFAULT_LAYER_BIT_AND(part, bits)
ACTION_DEFAULT_LAYER_BIT_OR(part, bits)
ACTION_DEFAULT_LAYER_BIT_XOR(part, bits)
ACTION_DEFAULT_LAYER_BIT_SET(part, bits)

2.3 Macro action

TBD

Macro action indicates complex key strokes.

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

2.3.1 Macro Commands

I() change interval of stroke.
D() press key
U() release key
T() type key(press and release)
W() wait
END end mark

2.3.2 Examples

TODO: sample implementation See keyboards/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. Function 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 implementation See keyboards/hhkb/keymap.c for sample.

2.5 Backlight Action

These actions control the backlight.

2.5.1 Change backlight level

Increase backlight level.

ACTION_BACKLIGHT_INCREASE()

Decrease backlight level.

ACTION_BACKLIGHT_DECREASE()

Step through backlight levels.

ACTION_BACKLIGHT_STEP()

Turn a specific backlight level on or off.

ACTION_BACKLIGHT_LEVEL(1)

2.5.2 Turn on / off backlight

Turn the backlight on and off without changing level.

ACTION_BACKLIGHT_TOGGLE()

2.6 Swap-Hands Action

The swap-hands action allows support for one-handed keyboards without requiring a separate layer. Set ONEHAND_ENABLE in the Makefile and define a hand_swap_config entry in your keymap. Now whenever the ACTION_SWAP_HANDS command key is pressed the keyboard is mirrored. For instance, to type “Hello, World” on QWERTY you would type ^Ge^s^s^w^c W^wr^sd

2.6.1 Configuration

The configuration table is a simple 2-dimensional array to map from column/row to new column/row. Example hand_swap_config for Planck:

const keypos_t hand_swap_config[MATRIX_ROWS][MATRIX_COLS] = {
  {{11, 0}, {10, 0}, {9, 0}, {8, 0}, {7, 0}, {6, 0}, {5, 0}, {4, 0}, {3, 0}, {2, 0}, {1, 0}, {0, 0}},
  {{11, 1}, {10, 1}, {9, 1}, {8, 1}, {7, 1}, {6, 1}, {5, 1}, {4, 1}, {3, 1}, {2, 1}, {1, 1}, {0, 1}},
  {{11, 2}, {10, 2}, {9, 2}, {8, 2}, {7, 2}, {6, 2}, {5, 2}, {4, 2}, {3, 2}, {2, 2}, {1, 2}, {0, 2}},
  {{11, 3}, {10, 3}, {9, 3}, {8, 3}, {7, 3}, {6, 3}, {5, 3}, {4, 3}, {3, 3}, {2, 3}, {1, 3}, {0, 3}},
};

Note that the array indices are reversed same as the matrix and the values are of type keypos_t which is {col, row} and all values are zero-based. In the example above, hand_swap_config[2][4] (third row, fifth column) would return {7, 2} (third row, eighth column).

2.6.2 Advanced Swap Commands

ACTION_SWAP_HANDS() Swaps hands when pressed, returns to normal when released (momentary).
ACTION_SWAP_HANDS_TOGGLE() Toggles swap on and off with every keypress.
ACTION_SWAP_HANDS_TAP_TOGGLE() Toggles with a tap; momentary when held.
ACTION_SWAP_HANDS_TAP_KEY(key) Sends key with a tap; momentary swap when held.
ACTION_SWAP_HANDS_ON_OFF() Alias for ACTION_SWAP_HANDS()
ACTION_SWAP_HANDS_OFF_ON() Momentarily turns off swap.
ACTION_SWAP_HANDS_ON() Turns on swapping and leaves it on.
ACTION_SWAP_HANDS_OFF() Turn off swapping and leaves it off. Good for returning to a known state.

3. Layer switching Example

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

3.1 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 lower layers or default layer temporarily with this action.

ACTION_LAYER_MOMENTARY(1)

Note that after switching on press the actions on destination layer(Layer 1) are performed. 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.

3.2 Toggle switching

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.

This performs toggle switching action of ‘Layer 2’.

ACTION_LAYER_TOGGLE(2)

3.3 Momentary switching with Tap key

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.

ACTION_LAYER_TAP_KEY(2, KC_SCLN)

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.

3.4 Momentary switching with Tap Toggle

This switches layer only while holding a key but toggle layer with several taps. Tap means to press and release key quickly.

ACTION_LAYER_TAP_TOGGLE(1)

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

3.5 Momentary switching with Modifiers

This registers modifier key(s) simultaneously with layer switching.

ACTION_LAYER_MODS(2, MOD_LSFT | MOD_LALT)

4. Tapping

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.

4.1 Tap Key

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. It works as modifier when holding the key but registers normal key when tapping.

Modifier with tap key:

ACTION_MODS_TAP_KEY(MOD_RSFT, KC_GRV)

Layer switching with tap key:

ACTION_LAYER_TAP_KEY(2, KC_SCLN)

When user hold a key after tap, it repeat the tapped key rather to hold a modifier key. If you prefer to hold a modifier instead, define TAPPING_FORCE_HOLD in config.h. See https://github.com/qmk/qmk_firmware/issues/889 for the detail.

4.2 Tap Toggle

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.

ACTION_LAYER_TAP_TOGGLE(1)

4.3 Oneshot Modifier

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. The behavior of oneshot modifiers is similar to the sticky keys functionality found in most operating systems.

ACTION_MODS_ONESHOT(MOD_LSFT)

Oneshot layer key:

ACTION_LAYER_ONESHOT(MY_LAYER)

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.

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.

Most implementations of sticky keys allow you to lock a modifier by double tapping the modifier. The layer then remains locked untill the modifier is tapped again. To enable this behaviour for oneshot modifiers set ONESHOT_TAP_TOGGLE to the number taps required. The feature is disabled if ONESHOT_TAP_TOGGLE<2 or not defined.

4.4 Tap Toggle Mods

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.

ACTION_MODS_TAP_TOGGLE(MOD_LSFT)

5. Legacy Keymap

In QMK, tmk_core/common/keymap.c is missing and its replacement quantum/keymap_common.c lacks Legacy Keymap support.

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.

In the following legacy keymap 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.

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
};

Under QMK, these can be realized using action code ACTION_LAYER_TAP_KEY(1, KC_NO), ACTION_LAYER_TAP_KEY(2, KC_NO), and ACTION_LAYER_TAP_KEY(2, KC_SPC) in the keymaps directly.

6. Terminology

TBD ### keymap is comprised of multiple layers. ### layer is matrix of keycodes. ### key is physical button on keyboard or logical switch on software. ### keycode is codes used on firmware. ### action is a function assigned on a key. ### layer transparency Using transparent keycode one layer can refer key definition on other lower layer. ### layer precedence Top layer has higher precedence than lower layers. ### tapping is to press and release a key quickly. ### Fn key is key which executes a special action like layer switching, mouse key, macro or etc. ### dual role key http://en.wikipedia.org/wiki/Modifier_key#Dual-role_keys

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Keymap framework - how to define your keymap

TMK vs. QMK

0. Keymap and layers

0.1 Keymap layer status

0.2 Layer Precedence and Transparency

0.3 Keymap Example

1. Keycode

1.0 Other key

1.1 Normal key

1.2 Modifier

1.3 Mousekey

1.4 System & Media key

1.5 Fn key

1.6 Keycode Table

2. Action

2.1 Key Action

Parameters

2.1.1 Normal key and Modifier

2.1.2 Modified key

2.1.3 Multiple Modifiers

2.1.3 Modifier with Tap key(Dual role)

2.2 Layer Action

Parameters

2.2.1 Default Layer

2.2.2 Momentary

2.2.3 Toggle Switch

2.2.4 Momentary Switch with tap key

2.2.5 Momentary Switch with tap toggle

2.2.6 Invert state of layer

2.2.7 Turn On layer

2.2.8 Turn Off layer

2.2.9 Set layer

2.2.10 Bitwise operation

2.3 Macro action

2.3.1 Macro Commands

2.3.2 Examples

2.4 Function action

2.4.1 Function

2.4.2 Function with tap

2.4.3 Implement user function

2.5 Backlight Action

2.5.1 Change backlight level

2.5.2 Turn on / off backlight

2.6 Swap-Hands Action

2.6.1 Configuration

2.6.2 Advanced Swap Commands

3. Layer switching Example

3.1 Momentary switching

3.2 Toggle switching

3.3 Momentary switching with Tap key

3.4 Momentary switching with Tap Toggle

3.5 Momentary switching with Modifiers

4. Tapping

4.1 Tap Key

4.2 Tap Toggle

4.3 Oneshot Modifier

4.4 Tap Toggle Mods

5. Legacy Keymap

6. Terminology

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