All of these functions are available in the `*_kb()` or `*_user()` variety. `kb` ones should only be used in the `<keyboard>/<keyboard>.c` file, and `user` ones should only be used in the `keymap.c`. The keyboard ones call the user ones - it's necessary to keep these calls to allow the keymap functions to work correctly.
## `void matrix_init_*(void)`
This function gets called when the matrix is initiated, and can contain start-up code for your keyboard/keymap.
## `void matrix_scan_*(void)`
This function gets called at every matrix scan, which is basically as often as the MCU can handle. Be careful what you put here, as it will get run a lot.
This function gets called on every keypress/release, and is where you can define custom functionality. The return value is whether or not QMK should continue processing the keycode - returning `false` stops the execution.
The `keycode` variable is whatever is defined in your keymap, eg `MO(1)`, `KC_L`, etc. and can be switch-cased to execute code whenever a particular code is pressed.
The `record` variable contains infomation about the actual press:
```
keyrecord_t record {
keyevent_t event {
keypos_t key {
uint8_t col
uint8_t row
}
bool pressed
uint16_t time
}
}
```
The conditional `if (record->event.pressed)` can tell if the key is being pressed or released, and you can execute code based on that.
## `void led_set_*(uint8_t usb_led)`
This gets called whenever there is a state change on your host LEDs \(eg caps lock, scroll lock, etc\). The LEDs are defined as:
```
#define USB_LED_NUM_LOCK 0
#define USB_LED_CAPS_LOCK 1
#define USB_LED_SCROLL_LOCK 2
#define USB_LED_COMPOSE 3
#define USB_LED_KANA 4
```
and can be tested against the `usb_led` with a conditional like `if (usb_led & (1<<USB_LED_CAPS_LOCK))` - if this is true, you can turn your LED on, otherwise turn it off.
Jack Humbert
8 years ago
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