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RPi4 custom image

This chapter offers a detailed guide for creating a custom image for the Raspberry Pi 4 (RPi4). Key Buildroot components and concepts will be introduced. The process outlined here can be adapted for use with other boards. For advanced features not covered in this guide, please consult the Buildroot manual

This guide was done on Ubuntu 22.04

Prepare the workspace

The workspace is structured to utilize Buildroot without any modifications. Execute the following commands:

mkdir rpi4_buildroot_lvgl && cd rpi4_buildroot_lvgl
mkdir resources && cd resources
mkdir board
mkdir configs
touch Config.in && touch external.desc && touch external.mk
echo "name: rpi4_lvgl" >> external.desc
echo "desc: rpi4 lvgl custom build" >> external.desc
cd ..

Each folder utility will be explained throughout the guide.

Get Buildroot

First, according to the Builroot Manual, Buildroot requires certain packages to be installed before starting the build. Lets install them using Ubuntu's package manager.

sudo apt install sed make binutils gcc g++ bash patch gzip bzip2 perl tar \
        cpio python3 unzip rsync wget libncurses-dev

Now that we have satisfied all the prerequisites lets download a stable release of Buildroot.

git clone --branch 2024.08 --depth 1 https://github.com/buildroot/buildroot.git

Create RPi4 image

Let's see if there is already a configuration for RPi4 in Buildroot:

cd buildroot
make list-defconfigs | grep rasp

There is a build available for RPi4 62 bits: raspberrypi4_64_defconfig.

You can also find all the configurations in the Buildroot repository buildroot > configs

Start with this configuration as a base, but this configuration needs to be changed to meet lvgl requirements. So let's copy this base and keep it out of Buildroot.

# move to the project root
cp buildroot/configs/raspberrypi4_64_defconfig resources/configs/raspberrypi4_lvgl_defconfig

Create a new file build.sh at the root of the project with this content:

#!/bin/bash
SCRIPTPATH="$( cd "$(dirname "$0")" >/dev/null 2>&1 ; pwd -P )"

cd $SCRIPTPATH
mkdir -p output
cd buildroot
make defconfig O=../output BR2_DEFCONFIG=../resources/configs/raspberrypi4_lvgl_defconfig

Make this file executable.

chmod +x build.sh
./build.sh

Running this script creates an output folder that contains everything the process will generate:

  • Fetched resources

  • Toolchain

  • Images

This helps maintain a clean Buildroot directory. When the script is executed, an (almost) empty folder named output is created, as the build process has not yet begun.

Let's modify the configuration with menuconfig.

cd output
make menuconfig

Change these configurations:

  • Sytem host name to lvgl-buildroot under system_configuration > System hostname.

  • Root password to lvgl-buildroot under system_configuration > Root password.

  • Enable SSH in target-packages > Networking applications > openssh

Build the image

make

What happened?

Let's explore the contents of the output folder and what it contains.

build

This folder contains the intermediate files and build artifacts for the various packages that are being compiled. Each package has its own subdirectory within the build folder, where the build process takes place. It includes files such as configuration files, source code, and object files that are generated as part of the build process.

host

The host folder contains files and binaries that are built for the host system rather than the target system. This includes tools and utilities that are needed to build packages or to run the build system itself. It may contain compilers, build tools, and libraries that are required to support the build process for the target.

images

This directory holds the final output images generated for the target system, such as filesystem images, kernel images, or bootloader images. Depending on the configuration, you may find files like rootfs.tar, zImage, uImage, or others that are ready to be deployed onto the target hardware.

target

The target folder contains the files that are specifically intended for the target system. This includes the root filesystem and any additional files that will be included in the target environment. The structure within this folder often mimics the directory structure of a standard Linux system, containing directories like bin, lib, etc, usr, and others, which hold the binaries, libraries, configuration files, and other necessary components for the target system to function properly.

Flash the image

Insert the SD card into the laptop and check its mount point. It is typically labeled as sda or sdb, but you can use the lsblk command to confirm this information.

If it is mounted on /dev/sda, run the following command

sudo dd if=images/sdcard.img of=/dev/sda

As mentioned in images, the output image is in images and named sdcard.img.

Connect an Ethernet cable to the RPi4 and ensure the laptop and the RPi4 are on the same network.

You can use ifconfig or ip a to find your IP address. Then, use nmap or any tool to scan the network and find the IP address of the RPi4.

nmap -sn <YOUR_IP_ADDRESS>/24 | grep lvgl

All of this can be done with the UART instead of SSH if you don't want to connect the RPi4 to the network.