qmk-dactyl-manuform-a/keyboards/cluepad/cluepad.c

#include "cluepad.h"

void matrix_init_kb(void) {
    // put your keyboard start-up code here
    // runs once when the firmware starts up
    matrix_init_user();

    #ifdef BACKLIGHT_ENABLE
        init_backlight_pin();
    #endif

    // JTAG disable for PORT F. write JTD bit twice within four cycles.
    MCUCR |= (1<<JTD);
    MCUCR |= (1<<JTD);
};