In this tutorial, we’ll walk you through the process of building a custom Linux kernel tailored specifically for the BeagleBone Black platform. By following these steps, you’ll be able to create a customized embedded Linux distribution optimized for your project’s requirements.

Pre-requisite

Host Machine Environment

$ uname -a
Linux elinlinux 5.4.0-169-generic #187-Ubuntu SMP Thu Nov 23 14:53:38 UTC 2023 aarch64 aarch64 aarch64 GNU/Linux

Target Machine Environment

Board: BeagleBone Black
processor: Sitara XAM3359AZCZ100 Cortex A8 ARM

FTDI USB to Serial cable

build_kernel_result

Which can be found at: http://www.ftdichip.com/Support/Documents/DataSheets/Cables/DS_TTL-232R_CABLES.pdf

Toolchain

Create workspace

Create a working area to place the tools and components of the system.

cd ~
mkdir beaglebone_workspace
cd beaglebone_workspace

Install require packages

Make sure that your host machine is up to date and install the essential tools, and other tools required for cross compilation.

sudo apt-get update
sudo apt-get upgrade
sudo apt-get install build-essential
sudo apt-get install flex bison
sudo apt-get install lzop 
sudo apt-get install u-boot-tools

GCC Cross Compiler

sudo apt-get install gcc-arm-linux-gnueabihf

GCC libc source

mkdir arm-toolchain
cd arm-toolchain
wget -c https://releases.linaro.org/components/toolchain/binaries/latest-7/arm-linux-gnueabihf/gcc-linaro-7.5.0-2019.12-x86_64_arm-linux-gnueabihf.tar.xz
tar xf gcc-linaro-7.5.0-2019.12-x86_64_arm-linux-gnueabihf.tar.xz

Partition Manager

sudo apt-get install gparted

BootLoader (U-boot)

Das U-boot source: https://github.com/u-boot/u-boot

Download u-boot (u-boot-2023.10)

Choose a u-boot version to download.

wget -c https://github.com/u-boot/u-boot/archive/refs/tags/v2023.10.tar.gz

Configure U-Boot

make ARCH=arm CROSS_COMPILE=arm-linux-gnueabihf- am335x_boneblack_vboot_defconfig

Compile U-boot

make ARCH=arm CROSS_COMPILE=arm-linux-gnueabihf- -j4

Refer U-Boot: Building with GCC for more information.

`MLO` and `u-boot.img`

After the BootLoader has been compiled, run the ls command to make sure that you have the executables MLO and u-boot.img. The MLO file is the first stage BootLoader, and u-boot.img is the second stage BootLoader also known as the Bootstrap Loader.

Configure `Linux Kernel` for `BeagleBone Black`

Beaglebone Linux Kernel source: https://github.com/beagleboard/linux

Download Linux kernel

Choose a linux kernel version on your demand.

wget -c https://github.com/beagleboard/linux/archive/refs/tags/5.10.168-ti-r76.tar.gz
tar -xvf 5.10.168-ti-r76.tar.gz

Kernel Configuration for BeagleBone Black

sudo make ARCH=arm CROSS_COMPILE=arm-linux-gnueabihf- bb.org_defconfig

Build the Kernel

sudo make ARCH=arm CROSS_COMPILE=arm-linux-gnueabihf- uImage dtbs LOADADDR=0x80008000 -j4

Result

build_kernel_result

Build modules

sudo make ARCH=arm CROSS_COMPILE=arm-linux-gnueabihf- -j4 modules

Refer admin-guide for more information.

Preparing the MicroSD Card

Create two partitions

One partition for booting the kernel, and another one for the Root File System.

Use gparted for partitioning.
Create a new partition with 50 MiB for the size. Change the file system type to fat32 and label it boot.
Add a second partition with 1000 MiB for the size, label it rootfs, and make sure that the file type is ext4.

partition

Root File System

Download Busybox

cd ~/beaglebone_workspace
wget -c https://github.com/mirror/busybox/archive/refs/tags/1_36_0.tar.gz
tar -xvf 1_36_0.tar.gz

Configure BusyBox

cd busybox-1_36_0
make ARCH=arm CROSS_COMPILE=arm-linux-gnueabihf- defconfig

make ARCH=arm CROSS_COMPILE=arm-linux-gnueabihf- menuconfig

Enable Build static binary (no shared libs) option

menuconfig

Build BusyBox

Install Busybox into the rootfs partition of your SD card

The build automatically generates a file “busybox.links”, which is used by ‘make install’ to create symlinks to the BusyBox binary for all compiled in commands. This uses the CONFIG_PREFIX environment variable to specify where to install, and installs hardlinks or symlinks depending on the configuration preferences. (You can also manually run the install script at “applets/install.sh”).

Refer busybox: readme for more information.

make ARCH=arm CROSS_COMPILE=arm-linux-gnueabihf- CONFIG_PREFIX=/media/<username>/rootfs/ install

Create required directories and files

create directories and files required by the Linux Kernel to boot the system

dev/

mkdir dev
sudo mknod dev/console c 5 1
sudo mknod dev/null c 1 3
sudo mknod dev/zero c 1 5

lib/ and usr/lib/

Copy the libraries from the arm toolchain into the root file system lib.

sudo cp -r ~/beaglebone_workspace/arm-toolchain/gcc-linaro-7.5.0-2019.12-x86_64_arm-linux-gnueabihf/arm-linux-gnueabihf/libc/lib/* ./lib/

sudo cp -r ~/beaglebone_workspace/arm-toolchain/gcc-linaro-7.5.0-2019.12-x86_64_arm-linux-gnueabihf/arm-linux-gnueabihf/libc/lib/* ./lib/

Create additional directories for mounting virtual file systems.

sudo mkdir proc sys root

etc/

sudo mkdir etc etc/init.d

etc/inittab

After the kernel boots, it spawns the first user process, called the init. init is a background process that runs unitil the system is shut down. This process requires a configuration file called etc/inittab, which contains actions the system needs to perform at a given runlevel.

sudo vi etc/inittab

Copy the following into the etc/inittab file:

::sysinit:/etc/init.d/rcS
::respawn:-/bin/sh
::askfirst:-/bin/sh

For more setting options, please refer IBM: inittab File.

etc/fstab

vi etc/fstab

Copy the following into etc/fstab:

proc    /proc    proc   defaults  0 0
sysfs   /sys     sysfs  defaults  0 0

For more setting options, please refer man: fstab.

etc/hostname and etc/passwd

Write hostname into it.

sudo vi etc/hostname

sudo vi etc/passwd

Copy root::0:0:root:/root:/bin/sh into it.

init.d/rcS

Create the file init.d/rcS to setup the system.

sudo vi etc/init.d/rcS

#!/bin/sh
#   ---------------------------------------------
#   Common settings
#   ---------------------------------------------
# Replace <YOUR_HOSTNAME> with your hostname!
HOSTNAME=<YOUR_HOSTNAME>
VERSION=1.0.0

hostname $HOSTNAME

#   ---------------------------------------------
#   Prints execution status.
#
#   arg1 : Execution status
#   arg2 : Continue (0) or Abort (1) on error
#   ---------------------------------------------
status ()
{
       if [ $1 -eq 0 ] ; then
               echo "[SUCCESS]"
       else
               echo "[FAILED]"

               if [ $2 -eq 1 ] ; then
                       echo "... System init aborted."
                       exit 1
               fi
       fi
}

#   ---------------------------------------------
#   Get verbose
#   ---------------------------------------------
echo ""
echo "    System initialization..."
echo ""
echo "    Hostname       : $HOSTNAME"
echo "    Filesystem     : v$VERSION"
echo ""
echo ""
echo "    Kernel release : `uname -s` `uname -r`"
echo "    Kernel version : `uname -v`"
echo ""

#   ---------------------------------------------
#   MDEV Support
#   (Requires sysfs support in the kernel)
#   ---------------------------------------------
echo -n " Mounting /proc             : "
mount -n -t proc /proc /proc
status $? 1

echo -n " Mounting /sys              : "
mount -n -t sysfs sysfs /sys
status $? 1

echo -n " Mounting /dev              : "
mount -n -t tmpfs mdev /dev
status $? 1

echo -n " Mounting /dev/pts          : "
mkdir /dev/pts
mount -t devpts devpts /dev/pts
status $? 1

echo -n " Enabling hot-plug          : "
echo "/sbin/mdev" > /proc/sys/kernel/hotplug
status $? 0

echo -n " Populating /dev            : "
mkdir /dev/input
mkdir /dev/snd

mdev -s
status $? 0

#   ---------------------------------------------
#   Mount the default file systems
#   ---------------------------------------------
echo -n " Mounting other filesystems : "
mount -a
status $? 0

#   ---------------------------------------------
#   Set PATH
#   ---------------------------------------------
export PATH=/bin:/sbin:/usr/bin:/usr/sbin:/usr/local/bin

#   ---------------------------------------------
#   Start other daemons
#   ---------------------------------------------
echo -n " Starting syslogd           : "
/sbin/syslogd
status $? 0

echo -n " Starting telnetd           : "
/usr/sbin/telnetd
status $? 0

#   ---------------------------------------------
#   Done!
#   ---------------------------------------------
echo ""
echo "System initialization complete."

Build directory for the kernel

After creating the above files and directories, install the kernel modules into the Root File System.

cd ~/beaglebone_workspace/linux-5.10.168-ti-r76
make ARCH=arm CROSS_COMPILE=arm-linux-gnueabihf- CONFIG_PREFIX=/media/<username>/rootfs/ modules_install

Refer admin-guide: build-directory-for-the-kernel for more information.

Boot Partition

Create a boot folder in your workspace directory and copy MLO, u-boot.img, uImage, and am335x-boneblack.dbt.

cd ~/beaglebone_workspace/
mkdir boot
cp u-boot-2023.10/MLO boot/
cp u-boot-2023.10/u-boot.img boot/
cp linux-5.10.168-ti-r76/arch/arm/boot/uImage boot/
cp linux-5.10.168-ti-r76/arch/arm/boot/dts/am335x-boneblack.dtb boot/

uEnv.txt

Go into the boot folder and create a file called uEnv.txt. This file will tell the BootLoader where to load the kernel image and the device binary tree.

vi boot/nEnv.txt

Copy the following into uEnv.txt:

uenv_addr=0x81000000
load_addr=0x82000000
dtb_addr=0x88000000
mmc_args=setenv bootargs console=ttyO0,115200n8 noinitrd root=/dev/mmcblk0p2 rw rootfstype=ext4 rootwait
sdboot=echo Booting from SD Card ...;mmc rescan;fatload mmc 0:1 ${uenv_addr} uEnv.txt;env import -t ${uenv_addr} $filesize;fatload mmc 0:1 ${load_addr} uImage;fatload mmc 0:1 ${dtb_addr} am335x-boneblack.dtb;run mmc_args;bootm ${load_addr} - ${dtb_addr} 
uenvcmd=run sdboot

Important: Leave a newline at the end of the uEnv.txt file.

Finally, copy everything from the ~/beaglebone_workspace/boot directory to the BOOT partition of your SD card.

cd ~/beaglebone_workspace/boot/
sudo cp * /media/<username>/BOOT/
sync

Connect FTDI cable with the board

Connect FTDI cable with J1 serial header on the board.

For more information, refer BBB_SRM: 7.5 Serial Header.

Boot result

After you boot up the board, the system should mount the root file system successfully and you should automatically be logged in as root #.

boot_result

Reference

How to Build a Linux Distribution for the BeagleBone Black