• 编译

$ . build/envsetup.sh
$ lunch rpi-eng
$ make -j 4

又是漫长的等待。。。

• 下载

先对SD卡进行分区，并进行格式化。需要3个分区, 第一个分区存放bootcode.bin, config.txt, start.elf, fixup.dat, cmdline.txt, kernel7.img, ramdisk7.img；第二个区公为系统分区：会写入system.img；第三个分区为data分区，用于存放运行时的配置文件等。

可以参考这个(一定要知道SD卡是属于哪个设备文件， 可以用dmesg | tail 查看）：

$ sudo fdisk /dev/sd?

Command (m for help): o
Building a new DOS disklabel with disk identifier 0x29767d95.
Changes will remain in memory only, until you decide to write them.
After that, of course, the previous content won't be recoverable.

Warning: invalid flag 0x0000 of partition table 4 will be corrected by w(rite)

Command (m for help): n
Partition type:
   p   primary (0 primary, 0 extended, 4 free)
   e   extended
Select (default p): 
Using default response p
Partition number (1-4, default 1): 
Using default value 1
First sector (2048-15523839, default 2048): 8192
Last sector, +sectors or +size{K,M,G} (8192-15523839, default 15523839): +400M 

Command (m for help): n
Partition type:
   p   primary (1 primary, 0 extended, 3 free)
   e   extended
Select (default p): 
Using default response p
Partition number (1-4, default 2): 
Using default value 2
First sector (2048-15523839, default 2048): 827392
Last sector, +sectors or +size{K,M,G} (827392-15523839, default 15523839): +112M

Command (m for help): n
Partition type:
   p   primary (2 primary, 0 extended, 2 free)
   e   extended
Select (default p): 
Using default response p
Partition number (1-4, default 3): 
Using default value 3
First sector (2048-15523839, default 2048): 1056768
Last sector, +sectors or +size{K,M,G} (1056768-15523839, default 15523839): +512M

Command (m for help): p

Disk /dev/sd?: 7948 MB, 7948206080 bytes
245 heads, 62 sectors/track, 1021 cylinders, total 15523840 sectors
Units = sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disk identifier: 0x29767d95

   Device Boot      Start         End      Blocks   Id  System
/dev/sd?1            8192      827391      409600   83  Linux
/dev/sd?2          827392     1056767      114688   83  Linux
/dev/sd?3         1056768     2105343      524288   83  Linux

Command (m for help): w
The partition table has been altered!

Calling ioctl() to re-read partition table.
Syncing disks.

可以看到/dev/sd?1为linux分区（id为83)，一定要将其改成b (FAT32)分区，不然系统无法识别，开不了机。

下面是格式化分区：

$ sudo mkfs.vfat /dev/sd?1
$ sudo mkfs.ext4 /dev/sd?3

挂载/dev/sd?1分区，将out/target/product/rpi/boot中的文件copy过去，再将kernel, ramdisk.img也copy过去：

$ sudo mount /dev/sd?1 /mnt/
$ sudo cp out/target/product/rpi/boot/* /mnt/
$ sudo cp out/target/product/rpi/kernel /mnt/kernel7.img
$ sudo cp out/target/product/rpi/ramdisk.img /mnt/ramdisk7.img
$ sudo umount /mnt
$ sync

接着将system.img写到/dev/sd?2分区中（一定要按照下面的方法进行操作，如果进行mount, cp, umount的操作，开机的时候会出现意想不到的问题，因为system.img中的文件是有SELinux context的，使用cp命令无法进行完整的将SELinux context copy过去; SELinux context可以通过ls -Z or ps -Z查看）：

$ sudo dd if=out/target/product/rpi/system.img of=/dev/sd?2
$ sync

做完这些，你就可以将TF卡插入Raspberry Pi 2B上开机运行了。