qmk_firmware/keyboards/handwired/2x5keypad/keymaps/default/keymap.c

#include QMK_KEYBOARD_H

#define WIN_TAB LGUI(KC_TAB)
#define WIN_LOCK LGUI(KC_L)

enum layers {
  NORMAL_LAYER = 0,
  MEDIA_LAYER,
  TBD_LAYER2,
  TBD_LAYER3
};


const uint16_t PROGMEM keymaps[][MATRIX_ROWS][MATRIX_COLS] = {

    [NORMAL_LAYER]=
	LAYOUT(TO(1),    WIN_TAB, KC_HOME, KC_UP,   KC_END, 
	       WIN_LOCK, KC_MUTE, KC_LEFT, KC_DOWN, KC_RGHT),

    [MEDIA_LAYER]=
	LAYOUT(TO(2),    KC_CALC, KC_MPRV, KC_MNXT, KC_VOLU, 
	       KC_TRNS,  KC_TRNS, KC_MSTP, KC_MPLY, KC_VOLD),

    [TBD_LAYER2]=
	LAYOUT(TO(3),    KC_TRNS, KC_TRNS, KC_TRNS, KC_TRNS, 
	       KC_TRNS,  KC_TRNS, KC_TRNS, KC_TRNS, KC_TRNS),

    [TBD_LAYER3]=
	LAYOUT(TO(0),    KC_TRNS, KC_TRNS, KC_TRNS, KC_TRNS, 
	       KC_TRNS,  KC_TRNS, KC_TRNS, KC_TRNS, KC_TRNS)
};


/* DISABLED
void matrix_init_user(void) {
}

void matrix_scan_user(void) {
}

bool process_record_user(uint16_t keycode, keyrecord_t *record) {
	return true;
}
*/


layer_state_t layer_state_set_user(layer_state_t state)
{
    turn_off_leds();

    switch (biton32(state))
    {
    case NORMAL_LAYER:
	break;

    case MEDIA_LAYER:
	turn_on_led(RED_LED);
	break;

    case TBD_LAYER2:
	turn_on_led(BLUE_LED);
	break;

    case TBD_LAYER3:
	turn_on_led(GREEN_LED);
	break;
	}
    return state;
}