# Frequently Asked Keymap Questions
This page covers questions people often have about keymaps. If you haven't you should read [Keymap Overview](keymap.html) first.
## What Keycodes Can I Use?
See [Basic Keycodes](keycodes.html) and [Quantum Keycodes](quantum_keycodes.html) for most of the keys you can define.
Keycodes are actually defined in [common/keycode.h](https://github.com/qmk/qmk_firmware/blob/master/tmk_core/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](https://github.com/tmk/tmk_keyboard/issues/168) and
- http://en.wikipedia.org/wiki/Magic_SysRq_key
- http://en.wikipedia.org/wiki/System_request
## 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: http://geekhack.org/index.php?topic=14290.msg1327264#msg1327264
## Oneshot modifier
Solves my personal 'the' problem. I often got 'the' or 'THe' wrongly instead of 'The'. Oneshot Shift mitgates this for me.
https://github.com/tmk/tmk_keyboard/issues/67
## 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.
- https://github.com/tmk/tmk_core/blob/master/doc/keymap.md#31-momentary-switching
- http://geekhack.org/index.php?topic=57008.msg1492604#msg1492604
- https://github.com/tmk/tmk_keyboard/issues/248
## Mechanical Lock Switch Support
This feature is for *mechanical lock switch* like [this Alps one](http://deskthority.net/wiki/Alps_SKCL_Lock). You can enable it by adding this to your `config.h`:
```
#define LOCKING_SUPPORT_ENABLE
#define LOCKING_RESYNC_ENABLE
```
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.
http://deskthority.net/workshop-f7/tmk-keyboard-firmware-collection-t4478-120.html#p195620
On **Windows** you can use `AltGr` key or **Alt code**.
- http://en.wikipedia.org/wiki/AltGr_key
- http://en.wikipedia.org/wiki/Alt_code
On **Mac** OS defines `Option` key combinations.
- http://en.wikipedia.org/wiki/Option_key#Alternative_keyboard_input
On **Xorg** you can use `compose` key, instead.
- http://en.wikipedia.org/wiki/Compose_key
And see this for **Unicode** input.
- http://en.wikipedia.org/wiki/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.
https://opensource.apple.com/source/IOHIDFamily/IOHIDFamily-606.1.7/IOHIDFamily/AppleHIDUsageTables.h
## Media control keys in Mac OSX
#### KC_MNXT and KC_MPRV does not work on Mac
Use `KC_MFFD`(`KC_MEDIA_FAST_FORWARD`) and `KC_MRWD`(`KC_MEDIA_REWIND`) instead of `KC_MNXT` and `KC_MPRV`.
See https://github.com/tmk/tmk_keyboard/issues/195
## 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).
https://opensource.apple.com/source/IOHIDFamily/IOHIDFamily-606.1.7/IOHIDFamily/Cosmo_USB2ADB.c
And `IOHIDConsumer::dispatchConsumerEvent` handles Consumer page usages.
https://opensource.apple.com/source/IOHIDFamily/IOHIDFamily-606.1.7/IOHIDFamily/IOHIDConsumer.cpp
## 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
https://pqrs.org/osx/karabiner/seil.html
## 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.
https://github.com/tekezo/Karabiner/issues/403#issuecomment-102559237
See these for the deail of this problem.
https://github.com/tmk/tmk_keyboard/issues/213
https://github.com/tekezo/Karabiner/issues/403
## 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
*
* https://github.com/tmk/tmk_core/blob/master/doc/keymap.md#213-modifier-with-tap-keydual-role
* https://en.wikipedia.org/wiki/Modifier_key#Dual-role_keys
*/
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,TRNS,TRNS,TRNS,TRNS,TRNS,TRNS,TRNS,TRNS,TRNS,\
TRNS,TRNS,TRNS,TRNS,TRNS,TRNS,TRNS,TRNS,TRNS,TRNS,TRNS,TRNS,TRNS, \
TRNS,TRNS,TRNS,TRNS,TRNS,TRNS,TRNS,TRNS,TRNS,TRNS,TRNS,TRNS,FN5, TRNS, \
TRNS,TRNS,TRNS, TRNS, TRNS,FN7, FN6, FN8),
};
const uint16_t PROGMEM fn_actions[] = {
[0] = ACTION_MODS_TAP_KEY(MOD_RSFT, KC_UP),
[1] = ACTION_MODS_TAP_KEY(MOD_RGUI, KC_DOWN),
[2] = ACTION_MODS_TAP_KEY(MOD_RALT, KC_LEFT),
[3] = ACTION_MODS_TAP_KEY(MOD_RCTL, KC_RIGHT),
[4] = ACTION_LAYER_MOMENTARY(1),
[5] = ACTION_MODS_TAP_KEY(MOD_RSFT, KC_PGUP),
[6] = ACTION_MODS_TAP_KEY(MOD_RGUI, KC_PGDN),
[7] = ACTION_MODS_TAP_KEY(MOD_RALT, KC_HOME),
[8] = ACTION_MODS_TAP_KEY(MOD_RCTL, KC_END),
};
```
Dual-role key: https://en.wikipedia.org/wiki/Modifier_key#Dual-role_keys
## Eject on Mac OSX
`KC_EJCT` keycode works on OSX. https://github.com/tmk/tmk_keyboard/issues/250
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
___TO BE IMPROVED___
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.
https://github.com/tmk/tmk_core/blob/master/common/action_util.c#L57
## Timer functionality
It's possible to start timers and read values for time-specific events - here's an example:
```c
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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