From a regular user to a full-fledged developer based on Xiaomi Redmi Note 4 (codenamed “mido”) opens up endless opportunities for customization and deep understanding of Android. This smartphone, released in 2017 on the Qualcomm Snapdragon 625 processor, became legendary due to its community and availability of modifications. This is where you can master the basic principles of Android development, learn how to compile cores and create your own assemblies of the operating system.
Unlike more modern devices with locked bootloaders and strict integrity checks, the Redmi Note 4 remains the perfect testing ground, USB-It is critical to understand that the process of turning a device into a development tool requires unlocking the bootloader, which is officially authorized by Xiaomi, but entails a reset of all data. Risk-readiness and careful follow-up to instructions are key qualities of the future modder.
Before you start diving into the world of fastboot and recovery, you need to understand the responsibility. Any interference with the software code of the device can lead to its inoperability, although in the case of mido, the chances of recovery (bricking is rare here) are extremely high. This article will be your guide to setting up the environment, installing the necessary drivers and the first steps in writing code for a particular hardware.
Preparation of working environment and tools
The first step in the development process is to create a stable environment for interaction with the device, you need a computer running Windows, Linux or macOS, which will be installed specialized tools, the basis of the entire process is the Platform Tools package, containing the utilities ADB (Android Debug Bridge) and Fastboot. Without them, communication with the phone at a low level is impossible.
You also need to install current drivers for Qualcomm and Xiaomi. In Windows, driver signature conflicts often arise, so be ready to manually install through Device Manager. To compile code and work with repositories, you will need Git and, preferably, an installed Android Studio environment or at least a JDK (Java Development Kit), since many scripts are written in Java or require its libraries.
- 📦 Download and unpack. SDK Platform Tools to the root folder of the disk (for example, C:\platform-tools) ease of use.
- 💻 Install Qualcomm drivers HS-USB QDLoader 9008 in case you need to recover through the EDL regime.
- 🔗 Use original or quality USB-cable that supports data transfer, not just charging.
After installing all the components, check the connection. Turn on Developer Mode on your phone by going to Settings → About Phone and quickly clicking 7 times on MIUI Version. Then activate Debugging on USB from the Developer Menu. Connect your smartphone to your PC and type in the command line:
adb devicesIf you see the serial number of the device and the status of the device, it means that the connection is successfully established. If the status is unauthorized, look at the phone screen and confirm the fingerprint. RSA-key.
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When working on Linux, add the user to the plugdev group to avoid problems with access rights to the user. USB-port without having to run the terminal from root.
Unlocking the bootloader and obtaining superuser rights
The foundation for any development on Android devices is the unlocked bootloader. In Xiaomi smartphones, this process is strictly regulated: it requires a binding Mi Account to the device and a wait of 7 to 30 days. This is a security measure, which, however, should not frighten the future developer. Once the permission in the Mi Unlock Tool application on the PC, the bootloader will be unlocked and the data on the phone deleted.
The next step is to install the custom TWRP (Team Win Recovery Project) Recovery Mode. Xiaomi's standard recovery mode does not allow you to make changes to system partitions. TWRP gives you access to the file system, the ability to make full backups (Nandroid) and install a modified bootloader. Redmi Note 4 is updated with TWRP versions that support encryption and full work with A/B partitions (although it uses a single partition scheme).
⚠️ Warning: Once the bootloader is unlocked, some security features such as Widevine will stop working. L1 (lost HD Netflix and banking apps may require additional manipulation to run.
The most common way to get Root rights is to use Magisk, which is embedded in the boot image (boot.img) system-safely, without modifying the system partition directly, which hides the rights from the applications and maintains integrity. OTA-Updates (with proper configuration).
☑️ Checklist before firmware
The TWRP installation process is as follows in the command line:
fastboot flash recovery twrp-3.x.x-x-mido.img
fastboot boot twrp-3.x.x-x-mido.imgThe second command loads the Recovery temporarily to install Magisk immediately, preventing the stock system from overwrite recovery back.
Set up Android Development Environment (Android Studio and SDK)
To build applications or modify system components, you will need a full-fledged integrated development environment. Android Studio is Google’s official tool that includes an emulator, code editor, debugger and SDK manager. To work with Redmi Note 4, it is important to install the appropriate versions of Build Tools and Platform SDK, corresponding to the versions of Android installed on the device (usually Android 7 Nougat or custom Android 10-12).
Inside the development environment, you need to configure remote debugging, which allows you to run a written application directly on a connected Redmi Note 4, track logs in real time and analyze resource consumption by the Snapdragon 625 processor. Logs are the main source of information when searching for bugs in code.
- 🛠 Install the plugin ADB Idea or use built-in tools to quickly access commands ADB.
- 📱 Set up adb wireless for debugging over Wi-Fi to get rid of wires while testing the interface.
- 📊 Use Android Profiler to monitor your CPU, Memory and Network activity of your application on a real device.
The focus is on setting up Gradle, the build automation system that drives dependencies and compilation. For the Redmi Note 4, which doesn’t have the power of the 2026 flagship, optimizing code and resources is critical to smooth operation.
Compilation of own kernel and work with source code
The pinnacle of a developer’s skill on Xiaomi is building a native kernel (Kernel). The Linux kernel is a bridge between hardware (hardware) and the operating system. For Redmi Note 4, the kernel source code is available on GitHub thanks to Xiaomi’s openness policy. Compiling its kernel allows you to implement CPU overclocking, improve power consumption or add support for new file systems.
The process requires a cross-compiler (toolchain) installation, usually a Linaro GCC or Google Clang. You will need to download the source (kernel source) for your particular version of MIUI or custom firmware, configure a configuration file (defconfig) and start the build process. This is a resource-intensive task that can take from 30 minutes to several hours on a weak PC.
The main stages of work with the core:
- Cloning of a source code repository through a git clone.
- Configure environment variables for cross-compilation (ARCH=arm64, CROSS_COMPILE=..).
- Edit configuration files to turn drivers on or off.
- Compilation and packaging of the result in Image.gz-dtb format.
⚠️ Warning: An improperly assembled core can cause a cyclic bootloop or a phone to fail completely. Always have a working image on hand to recover from the Fastboot.
Where do I look for the source?
Once compiled successfully, the finished kernel is sewn into the boot section, giving you complete control over how the operating system interacts with the hardware of your smartphone.
Comparison of System Modification Methods
As you develop, you'll encounter different approaches to change the behavior of the system, and understanding the differences between them is essential to choosing the right tool for a particular task. Below is a table comparing the main interventions.
| Method | Level of access | Risk of data loss | Difficulty |
|---|---|---|---|
| ADB Commands | Customized | Low. | Low. |
| Magisk Modules | System (Root) | Low. | Medium |
| Custom ROM | Complete. | High-pitched | Tall. |
| Kernel Compilation | Hardware. | critical | Expert |
Using ADB allows you to remove system applications and change some settings without superuser rights. Magisk acts as a patch, modifying memory on the fly when booting, which retains the ability to receive updates. Custom ROM (like LineageOS or Pixel Experience) completely replaces the operating system, requiring a clean installation.
The choice of method depends on your goal. If you just want to remove advertising, enough ADB. If you want deep customization of interface and functions, you need custom firmware. To manage CPU frequencies and temperature limits, only work with the core.
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Start with the least invasive methods (ADB, Magisk), moving to ROM firmware and kernel compilation only as your competencies grow.
Debugging, Logging and Error Search
Development is not just about creating code, it's about constantly finding bugs. In Android, the main tool for doing this is logcat. It outputs all system logs, application error messages, and kernel service records in real time. For a developer on Redmi Note 4, the ability to read logs is the number one skill.
To filter out the noise you want, use filtering commands. For example, to see only messages from your app with the MyApp tag and Error importance level, use the command:
adb logcat -s MyApp:EIt's also useful to use Monkey, a stress testing utility that generates random taps and events to test the app's resilience to the user's chaotic behavior. On Redmi Note 4, this helps identify performance problems when there's a shortage of RAM.
- 📝 Use adb bugreport to create a full snapshot of the system state that can be analyzed later.
- 🔍 We use Regex in Logcat filters to accurately search for the right lines in thousands of messages.
- ⏱ Monitor the time of staff drawing (GPU rendering) in the developer settings to find bottlenecks in the interface.
Remember that active logging can slow down the device and quickly land the battery. In production builds, debugging should be turned off.
Safety and return to runoff
Every developer must be able to not only break, but also fix. A return to factory status (Stock ROM) is required before selling a device, before going to a service center, or if the experiments have gone too far. For Xiaomi, there are two main methods: through Recovery (if it works) and through Fastboot.
The most reliable way is to use the Fastboot ROM image, which is a full system shot that is recorded cleanly, erasing all partitions. The Redmi Note 4 is the Global and China versions.
⚠️ Note: When switching from Chinese to Global (and vice versa) via Fastboot, make sure to use the command flash_all_lock with caution, as regions may be incompatible, leading to a region-wide lockdown.
The recovery process looks like this:
- Download the Fastboot ROM archive for mido.
- Unpack the archive and launch the script flash_all.bat (Windows or flash_all.sh (Linux/Mac).
- Wait for the process to be completed without turning off the cable.
After that, your Redmi Note 4 will look like it just left the store, with no trace of your developer activity.