If someone want to add gpio pin or uart without compile the source code.The sunxi-tools can help you.

At first You may need fex2bin and bin2fex:

$ git clone git://github.com/linux-sunxi/sunxi-tools.git
$ cd sunxi-tools
$ make
$ With the using of ls, you can find the fex2bin and bin2fex.

Second copy the script.bin from Android OS:

$ adb shell
$ mkdir /mnt/tmp
$ mount -t vfat /dev/block/nanda /mnt/tmp
$ exit
$ adb pull /mnt/tmp/script.bin 

Note : Attention it's different from Linux.

Then convert the script.bin to script.fex:

$ chmod 777 script.bin
$ ./bin2fex script.bin > ./script.fex
$ gedit script.fex

Now, you can edit the script.fex. Don't forget saving the file when you leave it.

Finally,convert the script.fex to script.bin and push it back to the CB

$ ./fex2bin script.fex > ./script.bin
$ adb push script.bin /mnt/tmp
$ adb shell
$ umount /mnt/tmp
$ reboot

It will restart the CB. The new script.bin will come into effect.

You can edit the script.bin directly
Firstly, you must connect network and install compilation Tools:

$ git clone git://github.com/linux-sunxi/sunxi-tools.git
$ cd sunxi-tools
$ make

With the using of ls, you can find the files: fex2bin and bin2fex.

Copy the script.bin.(boot from sdcard):

$ mkdir /mnt/mmcp1
$ mount /dev/mmcblk0p1 /mnt/mmcp1  (the script.bin is in /dev/nanda if you boot from nand )
$ cp /mnt/mmcp1/script.bin ./

Convert the script.bin to script.fex:

$ chmod 777 script.bin
$ ./bin2fex script.bin > ./script.fex
$ vi script.fex

Now, you can edit the script.fex.Don't forget saving the file when you leave it.

Convert the script.fex to script.bin and push it back.

$ ./fex2bin script.fex > ./script.bin
$cp ./script.bin /mnt/mmcp1/
$umount /mnt/mmcp1
$reboot

It will restart the CB. The new script.bin will come into effect.

Note:When the script.bin is invalid.You must enter the u-boot command line and input

$setenv boot_normal fatload nand 0 43000000 script.bin\;boota 40007800
$saveenv
$reset