Building the Bootloader from Source

This guide will walk you through building the bootloader for the Mecha Comet platform from source. The bootloader is responsible for initializing the hardware and loading the operating system.

Prerequisites

Before you begin, Its recommended to have the following:

• A host machine running Linux (Ubuntu 20.04 recommended).

1. Setting Up the Environment

Create a Working Directory

First, create a dedicated directory on your host machine to keep everything organized for the bootloader build:

$ mkdir mecha-bootloader-bin
$ cd mecha-bootloader-bin

This directory will store all the necessary files and binaries for the bootloader.

All steps outlined below should be performed on the host machine unless explicitly stated otherwise.

2. Building U-Boot

U-Boot is an open-source bootloader responsible for initializing the hardware and loading the operating system.

If you want to explore more about U-Boot, you can refer to the U-Boot Documentation.

Clone the U-Boot Repository

On the host machine, clone the U-Boot repository:

$ git clone https://github.com/chiragp-mecha/u-boot
$ cd u-boot/

If you're using Ubuntu’s toolchain, make sure to install the necessary cross-compilation tools:

$ sudo apt-get install gcc-aarch64-linux-gnu
$ export ARCH=arm64
$ export CROSS_COMPILE=/usr/bin/aarch64-linux-gnu-

This sets the architecture to ARM64 and configures the cross-compilation toolchain for U-Boot.

Install Required Dependencies

Install the libraries needed for U-Boot, specifically those for cryptographic functions:

$ sudo apt-get install libgnutls28-dev libghc-gnutls-dev

Build U-Boot

To build U-Boot on your host machine, run:

$ make clean
$ make mecha_comet_defconfig
$ make -j10

• make clean: Cleans up any previous build files.
• make mecha_comet_defconfig: Loads the default configuration for the Mecha Comet board.
• make -j10: Builds U-Boot using 10 threads for faster compilation.

3. Building the ARM Trusted Firmware (ATF)

ARM Trusted Firmware (ATF) handles low-level initialization, security, and power management tasks.

Clone the ATF Repository

Clone the ATF repository on your host machine:

$ cd ..
$ git clone https://github.com/nxp-imx/imx-atf
$ cd imx-atf/

Checkout the Required Version

You can either check out the required branch or a specific commit:

$ git checkout -b lf_v2.8

Or:

$ git checkout 99195a23d3aef485fb8f10939583b1bdef18881c

Build the Firmware

To build the firmware on your host machine:

$ make PLAT=mecha-comet bl31

• PLAT=mecha-comet: Specifies the platform for which the firmware is being built.
• bl31: Builds the BL31 firmware, which manages secure boot and system initialization.

If you encounter linker errors, try clearing the LDFLAGS:

$ unset LDFLAGS
$ make PLAT=mecha-comet bl31

4. Downloading LPDDR4 Training Binaries

If your platform requires memory training firmware for initializing LPDDR4 RAM, you need to download and extract the appropriate binaries:

$ cd ..
$ mkdir firmware-mecha
$ cd firmware-mecha
$ wget https://www.nxp.com/lgfiles/NMG/MAD/YOCTO/firmware-imx-8.20.bin
$ chmod a+x firmware-imx-8.20.bin
$ ./firmware-imx-8.20.bin

This will extract the required firmware for memory initialization.

5. Creating the Boot Image

Now, you'll need to combine the bootloader components into a single bootable image.

Clone the imx-mkimage Repository

On your host machine, clone the imx-mkimage repository:

$ cd ..
$ git clone https://github.com/nxp-imx/imx-mkimage
$ cd imx-mkimage/

Checkout the Required Version

You can check out the required branch or a specific commit:

$ git checkout -b lf-6.1.1_1.0.0

Or:

$ git checkout d489494622585a47b4be88988595b0e4f9598f39

Copy the Required Binaries

Copy the relevant binaries from the previously built components into the iMX8M/ directory:

$ cp ../u-boot/spl/u-boot-spl.bin iMX8M/
$ cp ../u-boot/u-boot-nodtb.bin iMX8M/
$ cp ../u-boot/arch/arm/dts/mecha-comet.dtb iMX8M/
$ cp ../u-boot/tools/mkimage iMX8M/mkimage_uboot
$ cp ../imx-atf/build/mecha-comet/release/bl31.bin iMX8M/
$ cp ../firmware-mecha/firmware-imx-8.5/firmware/ddr/synopsys/lpddr4_pmu_train_* iMX8M/

Build the Boot Image

On your host machine, to build the bootable image:

$ make SOC=mecha-comet flash_evk

• SOC=mecha-comet: Specifies the target SoC (System on Chip).
• flash_evk: Creates the final bootable image.

The generated boot image will be available as ./iMX8M/flash.bin.

6. Flashing U-Boot to eMMC

Once the boot image is built, you will need to flash it onto the Mecha Comet’s eMMC storage. You can use the uuu tool to do this.

form your host machine trigger following command

$ sudo uuu -b emmc_all flash.bin

• uuu: A flashing tool for NXP-based platforms.
• b emmc_all: Specifies the target device (eMMC).
• flash.bin: The boot image you generated.

Conclusion

By following these steps, you will have successfully built and flashed the bootloader for the Mecha Comet platform. The system is now ready to boot and load an operating system.