Customize the Android firmware¶
Introduction¶
To customize Android firmware, there are two methods:
Modify source code, then compile and package to new firmware.
Patch based on existing firmware.
The former can customize Android on any level freely, but require compiling environment with high performance, and personal knowledgeable skill in Linux kernel and Android. Please see the detail in Build_android.We introduce the latter one here. It is divided in three stages: extract, customize and package. We use Linux as the host OS, and utilities which are all open source.
Firmware Format¶
Our new update image, release_update.img here, contains bootloader loader.img and the actual firmware data update.img. That is, release_undate.img is a wrapper of loader.img and update.img.
release_update.img
|- loader.img
`- update.img
update.img is a composite file, which contains multiple files described by package-file. A typical package-file is:
# NAME Relative path
#
#HWDEF HWDEF
package-file package-file
bootloader rk3128MiniLoaderAll(L)_V2.20.bin
parameter rk312x.parameter.txt
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
Package description of update.img. In update.img, there is a copy of package-file.
rk3128MiniLoaderAll(L)_V2.20.bin, Image/uboot.img
Bootloader
rk312x.parameter.txt
parameter file, which can specify kernel command line. The command line has rich information, such as partition of the flash storage.
Image/misc.img
Image of misc partition. It is a boot mode selector. If it is empty (all zero), system boots normally. If it contains recovery command, system boots into recovery mode with corresponding command and arguments.
Image/kernel.img
Android Linux kernel.
Image/resource.img
Resource image, has kernel startup logo and DTB (Device Tree Blob) inside.
Image/boot.img
Android initial ram disk, which is the first root filesystem to load and has important system initialization.
Image/recovery.img
Image of Android recovery mode, has kernel and recovery mode root filesystem inside.
Image/system.img
Image of Android’s system partition, which will has extensive customization below
Extracting firmware, will involve in extracting update.img from release_update.img, and then extract files described by package-file inside update.img. Packaging is just the reverse, which packs the files described by package-file into update.img, and then mix with loader.img into the final image file - 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¶
Extract the release_update.img
$ cd /path/to/your/firmware/dir
$ img_unpack Fireprime_Android5.1.img img
Extract the update.img
$ cd img
$ afptool -unpack update.img update
Check file...OK
------- UNPACK -------
package-file 0x00000800 0x00000285
rk3128MiniLoaderAll(L)_V2.20.bin 0x00001000 0x0004694E
rk312x.parameter.txt 0x00048000 0x000005A1
Image/misc.img 0x00048800 0x0000C000
Image/kernel.img 0x00055000 0x00578E3C
Image/resource.img 0x005CE000 0x0001C400
Image/uboot.img 0x005EA800 0x0011F6CF
Image/boot.img 0x005EA800 0x0011F6CF
Image/recovery.img 0x0070A000 0x0040F6AE
Image/system.img 0x00B19800 0x180EF000
RESERVED 0x00000000 0x00000000
update-script 0x18C09000 0x000003A5
recover-script 0x18C09800 0x0000010A
UnPack OK!
View the file tree under the update directory
$ cd update/
$ tree
.
├── Image
│ ├── boot.img
│ ├── kernel.img
│ ├── misc.img
│ ├── recovery.img
│ ├── resource.img
│ ├── uboot.img
│ └── system.img
├── package-file
├── recover-script
├── RESERVED
├── rk312x.parameter.txt
├── rk3128MiniLoaderAll(L)_V2.20.bin
└── update-script
The firmware is extracted successfully. Let’s start to customize.
Customize¶
Customize the system.img¶
system.img is an image file with ext4 filesystem format, which can be mounted into system to modify directly:
sudo mkdir -p /mnt/system
sudo mount -o loop Image/system.img /mnt/system
cd /mnt/system
# Add or delete apks inside. Pay attention to the free space. You canno add too many apks.
# Edit complete. Unmount it.
cd /
sudo umount /mnt/system
Please note, the free space of system.img is nearly zero. If you want more, you have to expand it, and change partition settings in parameter file accordingly.Here is an example of how the expand the image. Before expanding, run mount to make sure that system.img is not mounted (Unmount it if it is):
# Add 128M disk space
dd if=/dev/zero bs=1M count=128 >> Image/system.img
# Update filesystem records
e2fsck -f Image/system.img
resize2fs Image/system.img
Pack¶
First, you need to check the size of system.img. Make sure it is matched with partition setting in parameter file. If not, modify the parameter file to adjust the partitions.For example, you can find the “CMDLINE” line in parameter file rk312x.parameter.txt, which has the string “system”:
0x00180000@0x00092000(system)
The number before symbol @, is the size of the partition, in unit of 512 bytes (traditional disk sector size). Therefore this system partition has a size of:
$ echo $(( 0x00180000 * 512 / 1024 / 1024))M
768M
If size of system.img does not go beyond 768M, there is no need to change parameter file. If the partitions do not changed, you can flash the new system.img to the device for a test. Otherwise, you need to package a new firmware, flash it and test.Here are the steps to package update.img:
Pack update.img ：
# The current directory is still update/, which has package-file. All files listed in package-file are available.
# Copy the parameter file, which is the default one used by afptool.
$ cp rk312x.parameter.txt parameter
$ afptool -pack . ../update_new.img
------ PACKAGE ------
Add file: ./package-file
Add file: ./rk3128MiniLoaderAll(L)_V2.20.bin
Add file: ./rk312x.parameter.txt
Add file: ./Image/uboot.img
Add file: ./Image/misc.img
Add file: ./Image/kernel.img
Add file: ./Image/resource.img
Add file: ./Image/boot.img
Add file: ./Image/recovery.img
Add file: ./Image/system.img
Add file: ./RESERVED
Add file: ./update-script
Add file: ./recover-script
Add CRC...
------ OK ------
Pack OK!
Package release_update.img ：
$ img_maker -rk31 loader.img update_new.img release_update_new.img
generate image...
append md5sum...
success!
Congratulations, release_update_new.img is the final firmware image file ready to flash.