之前每次修改BoardConfig.mk后，都傻傻的先make clean然后重新编译，这样浪费的时间不计其数。后来忍受不了这种效率，Google了一下，果然不出所料是可以模块独立编译的。

1、进入Android源码根目录，执行source build/envsetup.sh；

2、可以执行mm、mmm等模块编译命令了。如要编译audioflinger，则执行mmm frameworks/base/services/audioflinger/ -B即可。

3、make -snod重新生成system.img映像。

将envsetup.sh的一些注释摘下来如下：

Invoke ". build/envsetup.sh" from your shell to add the following functions to your environment:
- croot:   Changes directory to the top of the tree.
- m:       Makes from the top of the tree.
- mm:      Builds all of the modules in the current directory.
- mmm:     Builds all of the modules in the supplied directories.
- cgrep:   Greps on all local C/C++ files.
- jgrep:   Greps on all local Java files.
- resgrep: Greps on all local res/*.xml files.
- godir:   Go to the directory containing a file.

编译Android2.3所需要的toolchains：

1、安装jdk1.6：http://www.oracle.com/technetwork/java/javase/downloads/index-jsp-138363.html

设置环境变量：

export JAVA_HOME=<JDK_PATH>
export JAVA_BIN=<JDK_PATH>
export PATH=$JAVA_HOME/bin:$PATH
export CLASSPATH=.:$JAVA_HOME/lib/dt.jar:$JAVA_HOME/lib/tools.jar
export JAVA_HOME JAVA_BIN PATH CLASSPATH

2、

sudo apt-get install flex bison gperf libsdl1.2-dev libesd0-dev libwxgtk2.6-dev build-essential zip curl libncurses5-dev zlib1g-dev valgrind libreadline5-dev git-core gnupg
sudo apt-get install x11proto-core-dev libx11-dev

3、我的系统是64bits，还需要：

sudo apt-get install libc6-dev lib32ncurses5-dev ia32-libs lib32readline5-dev lib32z-dev g++-multilib