qmk_firmware/keyboards/handwired/splittest/keymaps/serial_halfduplex/keymap.c

#include QMK_KEYBOARD_H

const uint16_t PROGMEM keymaps[][MATRIX_ROWS][MATRIX_COLS] = {[0] = LAYOUT(KC_L, KC_R)};

void keyboard_post_init_user(void) {
    // Customise these values to desired behaviour
    debug_enable   = true;
    debug_matrix   = true;
    debug_keyboard = true;
    // debug_mouse=true;
}