1. Setup ARM Cross Compiler

1.1 Download and uncompress the ARM Cross Compiler

1. FriendlyARM has an open source Android package which contains a working cross compiler. You can set it up in the "PATH" variable:

   export PATH=/opt/FriendlyARM/s5p4418/android/prebuilts/gcc/linux-x86/arm/arm-eabi-4.6/bin:$PATH
   arm-eabi-gcc -v

   The “/opt/FriendlyARM/s5p4418/android” is where Android source code package is located.
   When you use this compiler please specify the option "CROSS_COMPILE=arm-eabi-".

2 Build U-Boot from sources

2.1 Download and Build U-Boot

• Download the U-Boot source code and compile it. Please note the github's branch is s5p4418-nanopi2:

  git clone https://github.com/friendlyarm/uboot_nanopi2.git
  cd uboot_nanopi2
  git checkout s5p4418-nanopi2
  make s5p4418_nanopi2_config
  make CROSS_COMPILE=arm-eabi-

  After your compilation succeeds a u-boot.bin will be generated. If you want to test it please flash it to your installation MicroSD card via fastboot.
  Warning: you cannot update this MicroSD card by commanding "dd". This command which will cause trouble when booting the NanoPi2. 

2.2 Prepare mkimage

• You need the mkimage utility to compile a U-Boot source code package. Please make sure this utility works well on your host before you start compiling a uImage.
  You can install this utility by either commanding "sudo apt-get install u-boot-tools" or following the commands below:

  cd uboot_nanopi2
  make tools
  mkdir -p /usr/local/sbin && cp -v tools/mkimage /usr/local/sbin

3 Build Linux Kernel

3.1 Download and Build Linux kernel

• Download Kernel Source Code

  git clone https://github.com/friendlyarm/linux-3.4.y.git
  cd linux-3.4.y
  git checkout s5p4418-nanopi2

  The NanoPi2's kernel source code lies in the "s5p4418-nanopi2" branch.
• Compile Android Kernel

  make nanopi2_android_defconfig
  touch .scmversion
  make CROSS_COMPILE=arm-eabi- uImage
  

• Compile Debian Kernel

  make nanopi2_linux_defconfig
  touch .scmversion
  make CROSS_COMPILE=arm-eabi- uImage

  After your compilation succeeds a uImage will be generated in the "arch/arm/boot/" directory.

3.2 Compile Kernel Modules

• Android contains kernel modules which are in the "/lib/modules" directory in the system section. If you want to add your own modules to the kernel or you changed your kernel configurations you need to recompile these new modules. Compile Original Kernel Modules:

  cd linux-3.4.y
  make CROSS_COMPILE=arm-eabi- modules

  Here we have two new modules and we can compile them by following the commands below:

  cd /opt/FriendlyARM/s5p4418/android
  ./vendor/friendly-arm/build/common/build-modules.sh

  The "/opt/FriendlyARM/s5p4418/android" directory points to the top directory of Android source code. You can get more details by specifying option "-h". After your compilation succeeds new modules will be generated

4 Compile Android

• Install Cross Compiler
  We recommend installing 64 bit Ubuntu 14.04 on your PC host.

  sudo apt-get install zlib1g-dev:i386
  sudo apt-get install bison g++-multilib git gperf libxml2-utils make python-networkx zip
  sudo apt-get install flex libncurses5-dev zlib1g-dev gawk minicom

  For more details please refer to https://source.android.com/source/initializing.html
• Download Source Code
  You need to use repo to get the Android source code. Please refer to https://source.android.com/source/downloading.html

  mkdir android && cd android
  repo init -u https://github.com/friendlyarm/android_manifest.git -b nanopi2-kitkat
  repo sync

  The "android" directory is the working directory. To initialize repo you can do "HTTPS clone URL".
• Compile System Package

  source build/envsetup.sh
  lunch aosp_nanopi2-userdebug
  make -j8

  After your compilation succeeds an image will be generated in the "out/target/product/nanopi2/" directory.