1. Directories
 doc/		Reference documentation.
 build/	Build scripts.
 tools/	The tools, include common and vendor specific.
 u-boot/	The source code of u-boot.
 linux/	The source code of linux kernel.
2. Download source code
 mkdir xprj
 cd xprj
 git clone https://github.com/wowotechX/doc.git
 git clone https://github.com/wowotechX/build.git
 git clone https://github.com/wowotechX/tools.git
 git clone https://github.com/wowotechX/u-boot.git
 git clone https://github.com/wowotechX/linux.git
3. Download toolchain compilers
 cd ./build
 make env_prepare
 Then the build script will download the suitable toolchain
 according to your board(assigned by config.mk) and your host
 environment.
 NOTE: mostly, you just need do it once.
4. Install neccessary package(Based Ubuntu)
 # udev
 sudo apt-get install libudev-dev
 # update dtc tools
 sudo apt-get remove device-tree-compiler
 sudo apt-get install device-tree-compiler
 # if not work, then build it from source code
 sudo apt-get install flex
 sudo apt-get install bison
 git clone https://kernel.org/pub/scm/utils/dtc/dtc.git -b 1.4.1
 cd dtc
 make
 make install
 export PATH=$HOME/bin/:$PATH
5. Preparation building
 cd ./build
 make libusb
 make dfu
 NOTE: mostly, you just need do it once.
6. Build u-boot, linux kernel, busybox, initramfs, uImage, etc.
 cd ./build
 make u-boot
 make kernel
 make busybox
 make initramfs
 make uImage
7. Download and run u-boot through USB DFU tools.
 a. press ADFU key, and reboot the board to ADFU mode.
 b. press ADFU key, download and run SPL, util it enter ADFU mode again
 make spl-run # at ./build directory, a help command
 c. release ADFU key, download and run u-boot.
 make uboot-run # at ./build directory, a help command
 You will see the command line in UART console. Enjoy it!
 Known issues:
 These operations cannot work on "Ubuntu 64bit" host. Instead, you should
 do another more operations:
 >. Connect the bubblegum96 board to PC using USB cable.
 a. press ADFU key, and reboot the board to ADFU mode.
 >. Disconnect the USB cable, then re-connect it.
 Okay, do what you should do according to the upper steps!!
8. Boot Linux kernel(stand alone, or with initramfs)
 a. press ADFU key, and reboot the board to ADFU mode.
 b. press ADFU key, download and run SPL, util it enter ADFU mode again
 make spl-run # at ./build directory, a help command
 c. release ADFU key, download and run FIT uImage
 make kernel-run # at ./build directory, a help command
 If with initramfs, you will see the command line based on busybox
 in UART console. Enjoy it!