https://qooah.com/2014/08/11/lg-%e5%b0%87%e6%88%90%e7%82%ba%e4%b8%8b%e4%b8%80%e9%96%93%e8%a7%a3%e9%8e%96bootloader-%e7%9a%84%e5%a4%a7%e5%bb%a0/