使用串口进行u-boot的烧写。
首先打开串口，使用Xmodem烧写u-boot-spl.bin成功之后，然后在烧写u-boot.img文件，可是一直显示Retry 0:Timeout on sector ACK.
具体的步骤如下：
1 Press Ctrl-A then S to start a serial download
2 Select xmodem
3 Page down to the [board-port] directory and select it (tap the space bar twice to select a directory)
4 Page down to the [sitara-board-port-uboot] directory and select it
5 Page down to the [spl] directory and select it
6 Select u-boot-spl.bin (press the space bar once to select a file) and press Enter
7 Now press the Reset button on the Beaglebone board to start xmodem download protocol of SPL
8 Press Ctrl-A then S to start serial download
9 Select xmodem
10 Select [..] to back up to the [sitara-board-port-uboot] directory
11 Page down to the u-boot.img file, select it, and press Enter
12 Press any key when minicom has completed the download
