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 Extract the release_update.img $ cd /path/to/your/firmware/dir $ img_unpack Firefly-RK3399_20161027.img img rom version: 6.0.1 build time: 2016-10-27 14:58:18 chip: 33333043 checking md5sum....OK Extract the update.img $ cd img $ afptool -unpack update.img update Check file...OK ------- UNPACK ------- package-file 0x00000800 0x00000280 Image/MiniLoaderAll.bin 0x00001000 0x0003E94E Image/parameter.txt 0x00040000 0x00000350 Image/trust.img 0x00040800 0x00400000 Image/uboot.img 0x00440800 0x00400000 Image/misc.img 0x00840800 0x0000C000 Image/resource.img 0x0084C800 0x0003FE00 Image/kernel.img 0x0088C800 0x00F5D00C Image/boot.img 0x017EA000 0x0014AD24 Image/recovery.img 0x01935000 0x013C0000 Image/system.img 0x02CF5000 0x2622A000 RESERVED 0x00000000 0x00000000 UnPack OK! View the file tree under the update directory $ cd update/ $ tree . ├── Image │ ├── boot.img │ ├── kernel.img │ ├── MiniLoaderAll.bin │ ├── misc.img │ ├── parameter.txt │ ├── recovery.img │ ├── resource.img │ ├── system.img │ ├── trust.img │ └── uboot.img ├── package-file └── RESERVED 1 directory, 12 files Now that the firmware has been unpacked successfully, let's start customizing it. Customize Customize the system.img "System.img" is an ext4 file format image file that can be mounted directly to the system for modification: sudo mkdir -p /mnt/system sudo mount -o loop Image/system.img /mnt/system cd /mnt/system # Notice how much space is left when modify inside,and don't add too much APK. # After modification, uninstall. cd / sudo umount /mnt/system Note: The remaining space of the "system.img" is basically 0. If the file is not deleted, the capacity of "system.img" needs to be expanded, and the partition Settings in the parameter file are adjusted accordingly according to the final file size. The following is an example of how to extend the space. Before extending, run mount to see how the system is mounted and ensure that system.img has been unmounted: # Increase the space by 128M dd if=/dev/zero bs=1M count=128 >> Image/system.img # Extend file system information e2fsck -f Image/system.img resize2fs Image/system.img 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: # The current directory is still update/, with package-file and all files listed in package-file. # Copy the parameter file to paramter, because it is used by default by afptool. $ cp Image/parameter.txt parameter $ afptool -pack . ../update_new.img ------ PACKAGE ------ Add file: ./package-file Add file: ./Image/MiniLoaderAll.bin Add file: ./Image/parameter.txt Add file: ./Image/trust.img Add file: ./Image/uboot.img Add file: ./Image/misc.img Add file: ./Image/resource.img Add file: ./Image/kernel.img Add file: ./Image/boot.img Add file: ./Image/recovery.img Add file: ./Image/system.img Add file: ./RESERVED Add CRC... ------ OK ------ Pack OK! 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: 6.0.1