How can I switch to a particular version of Android after I checkout out the source code?

If I check out the android source code like this:

repo init -u git://android.git.kernel.org/platform/manifest.git

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How can I switch to a particular version of android ? e.g. 1.6?

Thank you.

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From http://source.android.com/source/downloading.html:

To check out a branch other than "master", specify it with -b:
$ repo init -u git://android.git.kernel.org/platform/manifest.git -b froyo