Android: Alternative boot modes

Bootloader is a low-level program which manages boot modes and then calls kernel to load the OS or recovery kernel to load recovery ramdisk.

You know that bootloader controls boot modes. In this article I will tell you about them. Here they are:

  1. Android OS boot
  2. Recovery menu
  3. Fasboot mode
  4. EDL
Android

In this article I won’t tell you about default boot mode (boot to Android OS), but you will be able to read about it in my next articles.

What is recovery menu

Stock recovery menu

The recovery menu is a special ramdisk that is located separately from the system image itself and doesn’t depend on it. The principle of operation is similar to the BIOS in computers. Recovery corresponds to the memory partition of the same name.

This software is designed to restore the system by resetting the settings (formatting the data, cache and internal memory partitions or the so-called “hard reset”) in the event of a system failure, in rare cases with an endless boot (bootloop).

Manufacturers build in primitive recovery menus, in which it is only possible to perform a hard reset. To get full control of your phone device, you should install a custom recovery with a wide range of functions. The leader among the unofficial recovery menus is TWRP (TeamWin Recovery Project) and its mods.

In my next articles I will tell about custom recovery menus and its’ features.

What is fastboot

Xiaomi’s fastboot logo

Fastboot is a special boot mode in which the user is able to flash a smartphone via ADB / FASTBOOT utilities on a PC. In this mode, you can delete standard applications, install a new firmware, roll back access to factory settings.

What is EDL

EDL (Emergency DownLoad Mode) gives permission for low-level firmware. You can sew even the most necessary sections, such as aboot, which reacts to a combination of button presses and calls the bootloader. In EDL mode, the device will appear to be off. So don’t get scared and follow the instructions below. Restore bricks with especially heavy indicators only through the Test points.

Test points are a points at the device’s motherboard, by connecting them and power on the device, it will be booted in EDL.

To exit EDL, you need to hold down the power button, after which the phone should boot into the system.

How to enter EDL

1st variant

Boot into EDL by connecting the test points. This method is very risky and used in service centers. I highly recommend to trust the specialists, because if you don’t have a tools for this method, you can burn the device’s board.

2nd variant

You must have worked fastboot and unlocked bootloader.

  1. Turn the device to fastboot mode (usually power + volume down buttons)
  2. Connect it to the PC
  3. Install ADB drivers and Qcom/MTK Loader drivers
  4. Install ADB utility (Fastboot utility is included)
  5. Open terminal and type fastboot oem edl command

Phone will be looked like powered off, but actually, it will be in EDL.

Sources

This article is based on my previously made article in VK Unix Power group.
Source

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