Custom Yocto image for RaspberryPi 4

Prerequisite

• RaspberryPi 4
• Sd-card (Me:32G)
• Linux OS (Me:Debian 12)

Dependencies

sudo apt update
sudo apt install bc build-essential chrpath cpio diffstat gawk git python texinfo wget gdisk

Get started

clone poky (reference distribution) kirkstone branch (LTS)

mkdir yocto && cd yocto
git clone -b kirkstone http://git.yoctoproject.org/git/poky
cd poky 

clone raspberrypi meta-layer kirkstone branch as well

git clone -b kirkstone git://git.yoctoproject.org/meta-raspberrypi 

Set the target machine, by default is "qemux86-64".

# MACHINE ??= "qemux86-64"
MACHINE ??= "raspberrypi4"

Enable UART for serial console, add following variable to "conf/local.conf"

ENABLE_UART = "1"

for preparing build environment and use bitbake source "oe-init-build-env" script. the "oe-init-build-env" will create a "build" folder and change auto. dir. to it. run following commad:

. oe-init-build-env

list supported raspberrypi boards run following commad:

ls poky/meta-raspberrypi/conf/machine

install python3 in the image, add the following to local.conf

IMAGE_INSTALL:append = " python3"

Shell environment set up for builds, saved under "conf-notes.txt" file

cat meta/conf/conf-notes.txt

Extract bz2, run following command.

bunzip2 eddaaf-image-minimal-raspberrypi4-64-20240526073202.rootfs.wic.bz2

Flash image to Sd-card, run following command. Note:Be carefull of using this command.

sudo dd if=eddaaf-image-minimal-raspberrypi4-64-20240526073202.rootfs.wic of=/dev/sda bs=4M status=progress

Basic Yocto layer (Create and add layer)

Show existing layers, run following command

bitbake-layers show-layers

create layer (supposed from build dir), run following command

bitbake-layers create-layer ../meta-eddaaf

Add layer to build configuration, run following command

bitbake-layers add-layer ../meta-eddaaf

create a directory inside "meta-eddaaf"

Basic Yocto Recipes (Write and add the Recipe)

create a recipe, run following commands

mkdir meta-eddaaf/recipes-eddaaf
mkdir meta-eddaaf/recipes-eddaaf/helloworld
mkdir meta-eddaaf/recipes-eddaaf/helloworld/files
touch meta-eddaaf/recipes-eddaaf/helloworld/files/main.cpp
touch meta-eddaaf/recipes-eddaaf/helloworld/helloworld_0.1.bb

File structure (tree)

├── conf\
│   └── layer.conf\
├── COPYING.MIT\
├── README\
├── recipes-eddaaf\
│   └── hello-world-cpp\
│       ├── files\
│       │   └── main.cpp\
│       └── hello_world_cpp.bb\
└── recipes-example\
    └── example\
        └── example_0.1.bb\

Some common terms used in recipes:

${WORKDIR} - this is the location inside of your build (after you run source oe-init-build-env) and is referring to: build/tmp/work/<machine_architecture>/<recipe_name>/<recipe_version>
${PN} - Package name, i.e., name of the recipe. Same as the name you gave your .bb file.
${PV} - Package version, i.e., version of the recipe.
SRC_URI = “the file your recipe is built off of.” This can be a .zip, .c, or whichever file you need to build your recipe with.
md5, sha256 - these can be found by typing “openssl md5 <file_name>” into the command line.

Basic Yocto image (customizing images using .bb)

create image based on core-image-minimal

mkdir /meta-eddaaf/recipes-eddaaf/images
touch /meta-eddaaf/recipes-eddaaf/images/eddaaf-image-minimal.bb

copy to eddaf-image-minimal.bb

SUMMARY = "A small image just capable of allowing a device to boot."

IMAGE_INSTALL = "packagegroup-core-boot ${CORE_IMAGE_EXTRA_INSTALL} helloworld"
IMAGE_FEATURES += " ssh-server-dropbear"

IMAGE_LINGUAS = " "

LICENSE = "MIT"

inherit core-image

IMAGE_ROOTFS_SIZE ?= "8192"
IMAGE_ROOTFS_EXTRA_SPACE:append = "${@bb.utils.contains("DISTRO_FEATURES", "systemd", " + 4096", "", d)}"