qmk_firmware/keyboards/planck/planck.c

#include "quantum.h"

__attribute__ ((weak))
void matrix_init_kb(void) {
	// Turn status LED on, with the exception of THK
	#if defined(__AVR_ATmega32U4__)
	gpio_set_pin_output(E6);
	gpio_write_pin_high(E6);
	#endif

	matrix_init_user();
}

#ifdef ENCODER_ENABLE
bool encoder_update_kb(uint8_t index, bool clockwise) {
    if (!encoder_update_user(index, clockwise)) { return false; }
    if (get_highest_layer(layer_state) > 0) {
        if (clockwise) {
            tap_code_delay(KC_VOLU, 10);
        } else {
            tap_code_delay(KC_VOLD, 10);
        }
    } else {
        if (clockwise) {
            tap_code(KC_PGDN);
        } else {
            tap_code(KC_PGUP);
        }
    }
    return true;
}
#endif