Detailed explanation of uboot (embedded learning)

concept

U-Boot (Unified Bootloader) is an open source embedded system bootloader and a general-purpose bootloader. It is mainly used in the boot process of embedded systems, responsible for initializing hardware devices, loading the operating system kernel and starting applications.

Uboot is a kind of BootLoader; Bootloader is the collective name of boot loader, which is the first piece of code after the embedded system is powered on. Its main function is to initialize the hardware to a suitable state and load the embedded operating system into the memory. implement.

Detailed explanation

1. Boot stage:
   When the embedded system is powered on or reset, the processor will jump to the entry address of the U-Boot boot loader. U-Boot will first perform hardware initialization, including initial configuration of the processor, memory, peripherals, etc. Next, it loads the boot image file from a predefined boot device such as flash memory, SD card, network, etc.

2. Configuration and environment variables:
   U-Boot has a configuration system that include/configs/<board>.hdefines hardware platform-specific information, including processor type, peripheral configuration, clock frequency, etc., through configuration files (eg. Developers can configure according to the specific hardware platform. In addition, U-Boot also supports the configuration of environment variables, which can be used to store and transmit configuration information.

3. Load boot image files:
   U-Boot will load one or more boot image files, usually operating system kernel images. These image files can be located in local storage media (such as flash memory, SD card, etc.), or loaded through the network (such as through TFTP protocol).

4. Start the kernel:
   Once the boot image file is loaded, U-Boot will jump to the entry address of the kernel, thus giving control to the operating system. At this point, the operating system starts executing and is responsible for further initializing the system and launching user space applications.

5. Interactive Command Line Interface:
   U-Boot also provides an interactive command line interface that enables developers to debug, configure and execute a series of commands during system startup. Through the command line interface, developers can view and modify environment variables, load and run other applications, perform various system operations, and more.

6. Function extension:
   U-Boot provides a rich function extension mechanism, and developers can add custom functions according to requirements. For example, new drivers, commands, filesystem support, etc. can be added. This makes U-Boot adaptable to different hardware platforms and application scenarios.

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"uboot" for Windows

In Windows system, there is no bootloader called U-Boot. U-Boot is an open source boot loader mainly used in embedded systems, it is usually used in embedded systems, responsible for initializing hardware devices, loading operating system kernel and starting applications.

For the Windows operating system, its boot loader is called Windows Boot Manager (Windows Boot Manager). Windows Boot Manager (bootmgr for short) is part of the Windows operating system boot process responsible for loading and starting the Windows operating system.

During the boot process, the computer's BIOS (Basic Input/Output System) or UEFI (Unified Firmware Interface) passes control to bootmgr. According to the configuration information, bootmgr selects and loads the startup file of the operating system (for example, Windows NTLDR or Windows Boot Loader), and then transfers the control right to the corresponding startup file, and finally starts the Windows operating system.

It should be noted that U-Boot and Windows Boot Manager are two different boot loaders for different system environments. U-Boot is mainly used in embedded systems, while Windows Boot Manager is used to start Windows operating system.