刚同步的aosp，怎么切换到指定分支？
我用的是
repo branch ......[No branch]
repo init -b android-5.1.1_r9
repo start android-5.1.1_r9 --all
之后，报了错：
Starting android-5.1.1_r9: 1% (4/371) error: in start android-5.1.1_r9 --all: [Errno 2] No such file or directory: u'/home/lhb/aosp/build/.git/HEAD'
error: manifest missing or unreadable -- please run init