Customized Android firmware

preface

Note

: The following is only compatible with Android 8.1 and below.

There are two ways to customize Android firmware:

Change the source code and compile the firmware.

Tailoring the existing firmware.

In the former method, Android can be customized from all levels, with
great freedom, but high requirements for the compilation environment
and technology, which can be referred to [Compile Android
firmware].(compile_android8.1_firmware.html). Now introduce the latter
method, which is divided into three phases: unpacking, customization
and packaging. The host operating system is Linux, and the tools used
are open source software.

Firmware format

Unified firmware "release_update.img" contains the boot loader
"loader.img" and the actual firmware data - "update.img".

   release_update.img
   |- loader.img
   `- update.img

"update.img" is a composite file containing multiple files described
by package-file. A typical package-file is:

   # NAME Relative path package-file package-file bootloader Image/MiniLoaderAll.bin parameter
   Image/parameter.txt trust
   Image/trust.img uboot
   Image/uboot.img misc
   Image/misc.img resource
   Image/resource.img kernel
   Image/kernel.img boot
   Image/boot.img recovery
   Image/recovery.img system
   Image/system.img backup RESERVED
   #update-script update-script #recover-script recover-script

package-file  update.img package description file, update.img also
contains a package-file.

Image/MiniLoaderAll.bin  Start the loader - bootloader.

Image/parameter.txt  Parameter file, can set the kernel boot
parameters, there are important partition information.

Image/trust.img  trust.img is the U-Boot as the secondary loader
package.

Image/misc.img  Image of misc partition, used to control whether
Android starts normally or enters Recovery Mode.

Image/kernel.img  Android kernel.

Image/resource.img  Resource image with kernel boot image and kernel
Device Tree Blob.

Image/boot.img  The memory boot disk (initrd) of the Android kernel,
the first root file system to be loaded after the kernel is started,
contains important initialization actions that generally do not need
to be changed.

Image/recovery.img  Android image,including Recovery Mode with kernel
and root file system of Recovery Mode.

Image/system.img  Corresponds to the Android /system partition and is
the following custom object.

Unpacking, is to extract the "update.img" from "release_update.img",
then the extracted with "package-file" statement by multiple files.

Packaging is an inverse process to synthesize the multiple files
listed in the package-file to "update.img", add to the "loader.img",
and finally generate the "release_update.img".

Tools preparation

   git clone https://github.com/TeeFirefly/rk2918_tools.git
   cd rk2918_tools
   make
   sudo cp afptool img_unpack img_maker mkkrnlimg /usr/local/bin

Unpack

Now that the firmware has been unpacked successfully, let's start
customizing it.

Pack

First, check the size of "system.img" and make necessary size
adjustments against the partition of the "parameter" file.(Refer to
the documentation

The file format parameter

)

For example, the system partition size in "parameter.txt" file, you
can find the "CMDLINE" line and then find the "system" string:

   0x00200000@0x000B0000(system)

Before @ is the size of the partition, the unit is 512 bytes, so the
size of the system partition is:

   $ echo $(( 0x00200000 * 512 / 1024 / 1024))M
   1024M

As long as the size of "system.img" does not exceed 1024M, the
parameter file does not need to be changed.

If the partition does not change, you can use the upgrade tool to
upgrade the new "system.img" directly to the "system" partition on the
development board for testing. Otherwise, you need to make new
firmware and burn it before testing.

Here are the steps required to package it into a unified firmware
"update.img":

Compose update.img:

Compose release_update.img ：

   $ img_maker -rk33 loader.img update_new.img release_update_new.img
   generate image...
   append md5sum...
   success!

"release_update_new.img" is a unified firmware file that can be
upgraded for the final generation

FAQS

Q1 :

 Where's the firmware version Settings?

A1 :

 In the parameter file, you can find the downward direction and modify
it. Note that the version number is a number, and the middle two dots
cannot be omitted.

   AND_FW_VER: 8.1