Frequently Asked Keymap Questions

This page covers questions people often have about keymaps. If you haven't you should read Keymap Overview first.

What Keycodes Can I Use?

See Basic Keycodes and Quantum Keycodes for most of the keys you can define.

Keycodes are actually defined in common/keycode.h.

KC_SYSREQ isn't working

Use keycode for Print Screen(KC_PSCREEN or KC_PSCR) instead of KC_SYSREQ. Key combination of 'Alt + Print Screen' is recognized as 'System request'.

See issue #168 and

Power key doesn't work

Use KC_PWR instead of KC_POWER or vice versa.

  • KC_PWR works with Windows and Linux, not with OSX.
  • KC_POWER works with OSX and Linux, not with Windows.

More info:

Oneshot modifier

Solves my personal 'the' problem. I often got 'the' or 'THe' wrongly instead of 'The'. Oneshot Shift mitgates this for me.

Modifier/Layer stuck

Modifier keys or layers can be stuck unless layer switching is configured properly. For Modifier keys and layer actions you have to place KC_TRANS on same position of destination layer to unregister the modifier key or return to previous layer on release event.

Mechanical Lock Switch Support

This feature is for mechanical lock switch like this Alps one. You can enable it by adding this to your config.h:


After enabling this feature use keycodes KC_LCAP, KC_LNUM and KC_LSCR in your keymap instead.

Old vintage mechanical keyboards occasionally have lock switches but modern ones don't have. You don't need this feature in most case and just use keycodes KC_CAPS, KC_NLCK and KC_SLCK.

Input special charactors other than ASCII like Cédille 'Ç'

NO UNIVERSAL METHOD TO INPUT THOSE WORKS OVER ALL SYSTEMS. You have to define MACRO in way specific to your OS or layout.

See this post for example MACRO code.

On Windows you can use AltGr key or Alt code.

On Mac OS defines Option key combinations.

On Xorg you can use compose key, instead.

And see this for Unicode input.

Apple/Mac keyboard Fn

Not supported.

Apple/Mac keyboard sends keycode for Fn unlike most of other keyboards. I think you can send Apple Fn key using Apple venter specific Page 0xff01 and usage 0x0003. But you have to change HID Report Descriptor for this, of course.

Media control keys in Mac OSX

KC_MNXT and KC_MPRV does not work on Mac


Keys supported in Mac OSX?

You can know which keycodes are supported in OSX from this source code.

usb_2_adb_keymap array maps Keyboard/Keypad Page usages to ADB scancodes(OSX internal keycodes).

And IOHIDConsumer::dispatchConsumerEvent handles Consumer page usages.

JIS keys in Mac OSX

Japanese JIS keyboard specific keys like 無変換(Muhenkan), 変換(Henkan), ひらがな(hiragana) are not recognized on OSX. You can use Seil to enable those keys, try following options.

  • Enable NFER Key on PC keyboard
  • Enable XFER Key on PC keyboard
  • Enable KATAKANA Key on PC keyboard

RN-42 Bluetooth doesn't work with Karabiner

Karabiner - Keymapping tool on Mac OSX - ignores inputs from RN-42 module by default. You have to enable this option to make Karabiner working with your keyboard.

See these for the deail of this problem.

Esc and `~ on a key

Use GRAVE_ESC or KC_GESC in your keymap.

Arrow on Right Modifier keys with Dual-Role

This turns right modifer keys into arrow keys when the keys are tapped while still modifiers when the keys are hold. In TMK the dual-role function is dubbed TAP.

#include "keymap_common.h"

/* Arrow keys on right modifier keys with TMK dual role feature
const uint8_t PROGMEM keymaps[][MATRIX_ROWS][MATRIX_COLS] = {
    /* 0: qwerty */
    [0] = KEYMAP( \
        ESC, 1,   2,   3,   4,   5,   6,   7,   8,   9,   0,   MINS,EQL, NUHS,BSPC, \
        TAB, Q,   W,   E,   R,   T,   Y,   U,   I,   O,   P,   LBRC,RBRC,BSLS, \
        LCTL,A,   S,   D,   F,   G,   H,   J,   K,   L,   SCLN,QUOT,ENT,  \
        LSFT,NUBS,Z,   X,   C,   V,   B,   N,   M,   COMM,DOT, SLSH,FN0, ESC, \
        FN4, LGUI,LALT,          SPC,                     APP, FN2, FN1, FN3),
    [1] = KEYMAP( \
        GRV, F1,  F2,  F3,  F4,  F5,  F6,  F7,  F8,  F9,  F10, F11, F12, TRNS,TRNS, \
        TRNS,TRNS,TRNS,          TRNS,                    TRNS,FN7, FN6, FN8),

const uint16_t PROGMEM fn_actions[] = {

Dual-role key:

Eject on Mac OSX

KC_EJCT keycode works on OSX. It seems Windows 10 ignores the code and Linux/Xorg recognizes but has no mapping by default.

Not sure what keycode Eject is on genuine Apple keyboard actually. HHKB uses F20 for Eject key(Fn+f) on Mac mode but this is not same as Apple Eject keycode probably.

What's weak_mods and real_mods in action_util.c


real_mods is intended to retains state of real/physical modifier key state, while weak_mods retains state of virtual or temprary modifiers which should not affect state real modifier key.

Let's say you hold down physical left shift key and type ACTION_MODS_KEY(LSHIFT, KC_A),

with weak_mods,

  • (1) hold down left shift: real_mods |= MOD_BIT(LSHIFT)
  • (2) press ACTION_MODS_KEY(LSHIFT, KC_A): weak_mods |= MOD_BIT(LSHIFT)
  • (3) release ACTION_MODS_KEY(LSHIFT, KC_A): waek_mods &= ~MOD_BIT(LSHIFT) real_mods still keeps modifier state.

without weak mods,

  • (1) hold down left shift: real_mods |= MOD_BIT(LSHIFT)
  • (2) press ACTION_MODS_KEY(LSHIFT, KC_A): real_mods |= MOD_BIT(LSHIFT)
  • (3) release ACTION_MODS_KEY(LSHIFT, KC_A): real_mods &= ~MOD_BIT(LSHIFT) here real_mods lost state for 'physical left shift'.

weak_mods is ORed with real_mods when keyboard report is sent.

Timer functionality

It's possible to start timers and read values for time-specific events - here's an example:

static uint16_t key_timer;
key_timer = timer_read();

if (timer_elapsed(key_timer) < 100) {
  // do something if less than 100ms have passed
} else {
  // do something if 100ms or more have passed

It's best to declare the static uint16_t key_timer; at the top of the file, outside of any code blocks you're using it in.

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