已经下载了Android源码，但是现在需要想更新，便可以直接使用repo sync同步到本地。
可能会出现如下错误：
$ repo sync
remote: Counting objects: 10, done.
remote: Compressing objects: 100% (4/4), done.
remote: Total 6 (delta 2), reused 6 (delta 2)
Unpacking objects: 100% (6/6), done.
From git://github.com/richi-chen/Pandaboard-ICS-repo
3ea7f09..11ecd6d master -> origin/master
534d620..5fa74f5 omapzoom -> origin/omapzoom
error: .repo/manifests/: contains uncommitted changes
网友解决：richi 大虾：
to recover any uncommitted change, you should use 'git stash' and 'git clean -f -d'
for example: if you find it say there are uncommitted changes in .repo/manifests, you shoud 'cd .repo/manifests' and then 'git stash', 'git clean -f -d'
也就是执行以下命令：
$ cd .repo/manifests
$ git stash
$ git clean -f -d