Workshop 3: Construction of an embedded system with the project Buildroot

Important chars

Buildroot is technically a set of “Makefiles” defining, in depending on the options set by the user, how to compile each package selected with particular options. He builds finally a complete and coherent distribution of which each component has been compiled.

To start the process of configuration, run

make menuconfig

make xconfig)

Toolchain

➢ The toolchain designates the set of tools to be compiled which will then allow to have an environment capable of cross compiling from the architecture host (x86_64) to the target architecture (ARM).

➢ The toolchain includes a number of mandatory components as :
✓ A compiler.
✓ A linker.
✓ An assembler.

➢ Once everything is configured, the configuration tool generates a file “.config” which contains the entire configuration. This file will be read by the “Makefile” file during the build process.

To start the build process, just run:

make

Key points

➢ The main output files of the execution of the “make” command can be located in the “./output/images” folder. ➢ Buildroot generates a bootloader, a kernel image and a file system.

➢ The “make” command generally performs the following steps:

Download source files (if necessary);
Configuration, compilation and installation of the toolchain crossed;
Configuration, compilation, corrections (applying patches) and installation of selected target packages;
Construction of an image of the core;
Building a bootloader image;
Creation of a root file system (rootfs) in the formats selected.

Lab Started

From a terminal, create a directory in /home/user called “buildroot_trial” and go to it.
download latest version of buildroot there:

wget https://buildroot.org/dowloads/buildroot-2022.02.8.tar.bz2

decompress bz2

tar xf buildroot-2022.02.8.tar.bz2

move to it

cd buildroot-2022.02.8

We request a default Buildroot configuration for the target chosen. The available default configurations are visible in the “configs/” subdirectory. We choose the one for Raspberry Pi 3b/3b+:

make raspberrypi3_defconfig

then, execute make

make

Buildroot generated new files as required containing the tools u need to generate ur embedded OS

Buildroot Output

All the files produced during the compilation are in the “output/” sub-trees:

ls output

In “output/images” the compilation result files:

ls output/images

We can also observe an “output/target” sub-directory representing the complete tree that we will install on the target.

ls output/target

As the “output/target” directory contains files that do not have the correct membership, it should not be used blindly, nor copied directly to a target or exported for an NFS root mount. This is what Buildroot reminds us of by creating this famous file.

Install Boot

to see all hirerachy, in the buildroot-2022 run

lsblk

Insert a micro-SD card on the development computer (for example with a USB adapter), then relaunch the same command to see what who has appeared.

lsblk

Copy the “sdcard.img” file to your SD card using this linux command in the Buildroot folder:

sudo dd if=output/images/sdcard.img of=/dev/mmcblk0

The copy takes a little while, it’s normal, you have to fill a few hundred megabytes. Once the copy is complete, you insert the micro-SD card on a Raspberry Pi 3 to which you are connected by a serial link with a USB-Serial cable of this kind.

we can now see this messages

We do have a login prompt, and can connect:

The kernel corresponds well to the version indicated above. Let’s examine the state of memory:
we can verify the process of Raspberry Pi3 in the cpuinfo directory

cat /proc/cpuinfo