http://files.cnblogs.com/pengdonglin137/ARM%E5%9C%B0%E5%9D%80%E9%87%8D%E6%98%A0%E5%B0%84%E7%9A%84%E9%80%9A%E4%BF%97%E8%A7%A3%E9%87%8A.pdf