U-Boot

U-Boot (Universal Boot Loader) is the primary bootloader for the Mecha Comet. It initializes the hardware, manages the secure boot environment, and loads the Linux kernel into memory.

Why U-Boot?

On the Mecha Comet (powered by the NXP i.MX 8M Plus), U-Boot is essential for:

• Hardware Initialization: Setting up the LPDDR4 memory, storage (eMMC/SD), and peripheral controllers.
• Hardware Variants: Automatically handling configurations for the 4GB RAM model.
• Secure Foundations: Coordinating with ARM Trusted Firmware (ATF) to establish a secure platform before the OS starts.
• Recovery & Configuration: Providing a low-level environment for system recovery and boot parameter adjustment.

Prerequisites

Building U-Boot requires a Linux host system (e.g., Ubuntu 22.04+) with the ARM64 cross-compilation toolchain.

1. Install Build Dependencies

sudo apt update
sudo apt install -y build-essential libgnutls28-dev bison flex libssl-dev \
device-tree-compiler python3-setuptools swig wget git efitools uuid-dev

2. Set Up Toolchain

sudo apt install gcc-aarch64-linux-gnu
export ARCH=arm64
export CROSS_COMPILE=aarch64-linux-gnu-

3. Firmware Components

U-Boot for i.MX8MP requires external binaries:

• ARM Trusted Firmware (ATF): Available from nxp-imx/imx-atf.
• NXP DDR Firmware: Proprietary binaries for LPDDR4 training.

Build Guide

This guide describes the manual build process based on the mecha-org/u-boot repository (branch imx/lf_v2025.04).

1. Prepare Source and Firmware

# Clone U-Boot
git clone -b imx/lf_v2025.04 https://github.com/mecha-org/u-boot
cd u-boot

# Clone and Build ATF (for bl31.bin)
git clone https://github.com/nxp-imx/imx-atf
cd imx-atf
make PLAT=imx8mp bl31
cp build/imx8mp/release/bl31.bin ../
cd ..

2. Configure and Compile

Select the configuration corresponding to your hardware variant.

make mecha-comet-imx8mp-4gb_defconfig
make -j$(nproc)

3. Final Image Creation

The final bootable image (flash.bin) is assembled using the imx-mkimage tool. This tool combines the U-Boot SPL, the main U-Boot image, the ATF bl31.bin, and the NXP DDR firmware.