Update RootFS

LVGL application ################

LVGL application ################

This section provides information about the steps to follow to get a custom application using LVGL running on the board.

Update RootFS

Depending on the application, it might be necessary to update the rootfs. Let's take as example the compilation of LVGL with DRM. The system must have libdrm installed.

cd output
make menuconfig

To search for a string pattern in the configuration, press / followed by the desired pattern. For example, search for libdrm. You should find BR2_PACKAGE_LIBDRM set to [=n]. The Location field indicates where to find this option. By pressing the corresponding number key (9-0), you can navigate directly to the option.

In the Search Results window, the Depends on section lists the required packages or options that need to be enabled (or disabled) to make the target package configurable. For any package you wish to add, these dependencies must be met; otherwise, the option will remain hidden.

When the package configuration is completed, build the environment to add the packages (make in output folder).

To verify the library was installed, we can find it in the target sysroot:

find build/ -name "*libdrm*"

You should see the include folder and the .so files.

Generate SDK and set up environment

Generate an SDK that you can use to cross-compile the application for the target (RPi4).

make sdk

A .tar.gz is generated in output/images. This is the SDK!

To use it, extract it anywhere.

mkdir -p ~/sdk
tar -xzf images/aarch64-buildroot-linux-gnu_sdk-buildroot.tar.gz -C ~/sdk
cd ..

To set up the environment

mkdir application && cd application
touch setup-build-env.sh && chmod +x setup-build-env.sh

The script setup-build-env.sh looks like this:

#!/bin/bash

SDK_PATH="$HOME/sdk/aarch64-buildroot-linux-gnu_sdk-buildroot"

export PATH="${SDK_PATH}/bin:${PATH}"

export SYSROOT="${SDK_PATH}/aarch64-buildroot-linux-gnu/sysroot"

export CROSS_COMPILE="aarch64-buildroot-linux-gnu-"

export CC="${CROSS_COMPILE}gcc"
export CXX="${CROSS_COMPILE}g++"
export LD="${CROSS_COMPILE}ld"
export AR="${CROSS_COMPILE}ar"
export AS="${CROSS_COMPILE}as"

export CFLAGS="--sysroot=${SYSROOT}"
export LDFLAGS="--sysroot=${SYSROOT}"

Build the application

The environment is now set up, and we're ready to build an application using the lv_benchmarkrepository that is inspired fromlv_port_linux.

Navigate back to the root of the project and clone the repository:

git clone --recurse-submodules https://github.com/EDGEMTech/lv_benchmark.git

The application is configured to run on fbdev. You can either maintain the default configuration or modify it according to your preferences.

Compile the application

cd lv_benchmark
cmake -B build -S . -DCMAKE_C_COMPILER=${CROSS_COMPILE}gcc -DCMAKE_CXX_COMPILER=${CROSS_COMPILE}g++ -DCMAKE_SYSROOT=${SYSROOT} -DCMAKE_C_FLAGS="--sysroot=${SYSROOT}" -DCMAKE_CXX_FLAGS="--sysroot=${SYSROOT}"
make -j $(nproc) -C build

Verify that the output executable was compiled with the correct toolchain:

file bin/lvgl-app
cd ../..

The output should contain these information:

• ARM aarch64
  • interpreter /lib/ld-linux-aarch64.so.1

Set a rootfs overlay

In Buildroot, a rootfs overlay (or root filesystem overlay) is a mechanism that allows you to add custom files, directories, and configurations directly into the root filesystem of the target image during the build process. It is a way to extend or modify the content of the root filesystem without altering the base packages or recompiling everything.

Create the rootfs overlay structure and include the executable of the built application.

mkdir -p resources/board/rootfs_overlay/usr/bin
cp application/lv_benchmark/bin/lvgl-app resources/board/rootfs_overlay/usr/bin/

Update the configuration.

cd output
make menuconfig

Find the rootfs overlay option System configuration > Root filesystem overlay directories and use the relative path to the rootfs overlay with your application (../resources/board/rootfs_overlay) and save the configuration.

Now use make command to apply the rootfs overlay and confirm the sysroot was updated as expected.

find . -name lvgl-app

Flash the image and run the benchmark application on the board.