U-Boot

Official website: Das U-Boot.

Das U-Boot is an open-source bootloader commonly used in embedded systems. It performs low-level hardware initialization and loads the operating system kernel (usually Linux) into memory before transferring execution to it.

U-Boot supports many processor architectures including ARM, x86, MIPS, PowerPC, and RISC-V, making it one of the most widely used bootloaders in embedded Linux systems.

Main Responsibilities

U-Boot is responsible for several tasks during the system boot process:

• Initializing basic hardware (CPU, RAM, clocks)
• Setting up memory and device configuration
• Loading the Linux kernel into RAM
• Passing boot parameters to the kernel
• Booting the operating system

Boot Process

A typical embedded Linux boot process involving U-Boot is:

1. Boot ROM executes code from a predefined storage location
2. Boot ROM loads the U-Boot bootloader
3. U-Boot initializes hardware
4. U-Boot loads the Linux kernel and device tree
5. Execution is transferred to the Linux kernel

U-Boot Features

• Interactive command-line interface
• Support for multiple boot sources (SD card, NAND, NOR, eMMC, network)
• Network boot capabilities (TFTP, DHCP)
• Flash memory management
• Environment variables for boot configuration

Common U-Boot Commands

Some commonly used commands include:

• printenv – display environment variables
• setenv – set environment variables
• saveenv – save environment variables to persistent storage
• boot / bootm / bootz – boot the kernel
• tftpboot – load images over the network

U-Boot plays a critical role in embedded Linux systems by acting as the bridge between the hardware platform and the operating system kernel.