1.在工程（SDK）目录执行：./build.sh -h
可以看到有很多编译项目，有U-boot、Kernel、loader、Rootfs等、
Available options:
BoardConfig*.mk -switch to specified board config
lunch -list current SDK boards and switch to specified board config
uboot -build uboot
spl -build spl （作用是引导系统启动，负责装载操作系统到RAM中，还包括很多系统命令）
loader -build loader （）
kernel -build kernel （内核）
modules -build kernel modules
toolchain -build toolchain
rootfs -build default rootfs, currently build buildroot as default
buildroot -build buildroot rootfs
ramboot -build ramboot image
multi-npu_boot -build boot image for multi-npu board
yocto -build yocto rootfs
debian -build debian10 buster/x11 rootfs
distro -build debian10 buster/wayland rootfs
pcba -build pcba
recovery -build recovery
all -build uboot, kernel, rootfs, recovery image
cleanall -clean uboot, kernel, rootfs, recovery
firmware -pack all the image we need to boot up system
updateimg -pack update image
otapackage -pack ab update otapackage image (update_ota.img)
sdpackage -pack update sdcard package image (update_sdcard.img)
save -save images, patches, commands used to debug
allsave -build all & firmware & updateimg & save
check -check the environment of building
info -see the current board building information
app/<pkg> -build packages in the dir of app/*
external/<pkg> -build packages in the dir of external/*
2. 查看某一模块的详细编译命令：
输入：./build.sh -h uboot //可以查看 uboot 的详细编译命令；
： ./build.sh -h kernel //可以查看 kernel 的详细编译命令；
//类似的也可以查看其他模块的详细编译命令；
3.具体编译某一模块：
：./build.sh kernel //编译kernel
： ./build.sh Recovery //编译Recovery
： ./build.sh uboot //编译uboot
3.u-boot 配置、Kernel 配置、Recovery 配置，暂时不需要研究，会编译就行；
