====== Kernel Porting and Configuration ======

==== Kernel Porting ====
The zipped kernel linux-sunxi-sunxi-3.4.61.tar.gz can be found on [[http://dl.cubieboard.org/parteners/waveshare/Source_Code/COMMON/|linux-sunxi-sunxi-3.4.61.tar.gz]], the kernel config file can be found on [[http://dl.cubieboard.org/parteners/waveshare/Source_Code/a20-cubieboard-dvk/kernel_configs/|cubieboard2_defconfig]]
Or can be obtained from the internet:
https://github.com/linux-sunxi/linux-sunxi/releases  ,
To avoid unexpected error while porting, please download the 3.4.61 version kernel. 

=== Extract the kernel source code ===
Assume that the source code was placed under /home/waveshare/cubieboard2/kernel directory, use the following command to extract it: 
  #cd /home/waveshare/cubieboard2/kernel
  #tar -xzvf linux-sunxi-sunxi-3.4.61.tar.gz
Now we get the original linux-sunxi-sunxi-3.4.61 source code, rename it as linux-sunxi-sunxi-3.4.61_A20, as shown in the picture below:

{{:tutorials:dvk521:documentations:a20:a20_1.jpg}}

=== Assign the cross compiler ===  
Modify the Makefile under root directory:
  #cd linux-sunxi-sunxi-3.4.61_A20
  #vi Makefile
Edit the following lines:
  export KBUILD_BUILDHOST := $(SUBARCH) 
  ARCH   ?= $(SUBARCH) 
  CROSS_COMPILE ?=
As:
  export KBUILD_BUILDHOST := $(SUBARCH)
  ARCH        ?= arm
  CROSS_COMPILE   ?= arm-linux-gnueabihf-
ARCH specifies the target platform as arm, CROSS_COMPILE assigns the cross compile tool chain. As shown in the picture below: 

{{:tutorials:dvk521:documentations:a20:a20_2.jpg}}

Note: the vim editor is recommended.

=== Clear the temp files === 
Under the root directory, enter:
  #make clean

=== Copy the default config file === 
Under the root directory, enter:
  # cp ../cubieboard2_defconfig .config
A hidden .config file will be generated under the root directory.

=== Config the kernel === 
Under the root directory, enter:
  #make menuconfig
Config the kernel on the popup window, as shown in the picture below:

{{:tutorials:dvk521:documentations:a20:a20_3.jpg}}

=== Compile the kernel === 
Under the root directory, enter:
  #make uImage 
It will take much time to complete the compiling.
When completed, the compressed kernel image will be generated under linux-sunxi-sunxi-3.4.61_A20/arch/arm/boot directory.

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