Yocto for embedded systems ¶

Embedded systems have more limitations than usual workstations such as limited disk space or memory.

Because of that, there is a need to create a minimal operating systems with as few packages as possible and properly configure them to work within an environment with fewer resources.

Yocto is a collaborative project to create Linux-based systems designed for embedded products.

To get started, install Poky. See also: crops/poky.

$ sudo apt install gawk wget git diffstat unzip texinfo gcc build-essential chrpath socat cpio python3 python3-pip python3-pexpect xz-utils debianutils iputils-ping python3-git python3-jinja2 libegl1-mesa libsdl1.2-dev python3-subunit mesa-common-dev zstd liblz4-tool file locales
$ git clone -b <poky_version> git://git.yoctoproject.org/poky.git
$ source poky/oe-init-build-env # load

Configuration files ¶

Configuration files are in the conf folder.

$ nano conf/local.conf
# add or remove packages from the image
IMAGE_INSTALL_append = " xxx"
IMAGE_INSTALL_remove = " xxx"
# Enable GUI/...
DISTRO_FEATURES_append = " feature-name" 

Bitbake ¶

Bitbake is a multipurpose build engine.

$ bitbake core-image-minimal   # build an image
$ bitbake -c <some_task> [...] # run a specific task

When building images, it stores the generated image files in <build_folder>/tmp/deploy/images.

Image recipe ¶

You create multiple image recipes.

$ cat recipes-core/images/custom-image.bb

DESCRIPTION = "Custom Image"
LICENSE = "CLOSED"
PR = "r0"

inherit core-image

# see https://layers.openembedded.org/layerindex/branch/master/recipes/
# if there are from openembedded-core everything is fine
# otherwise, edit: conf/bblayers.conf
IMAGE_INSTALL_append = " vim"

$ cat conf/local.conf
...
IMAGE_INSTALL_append = " custom-image"
$ bitbake custom-image

Petalinux is a build-system built on Yocto, and leveraging yocto components and tools for Xilinx platforms.

$ # assuming PETALINUX was download from Xilinx website
$ source <PETALINUX_DIR>/settings.sh
$ petalinux-util --version      # OK

$ petalinux-create [...]
$ petalinux-config [...]
$ petalinux-build

➡️ images/linux for the output.

• Layers (priority/...)
• Recipes
• Devtool
• Steps: download (fetch), compile, generate packages, generate image (sdk? rootfs?)

• IPK/OPKG files
  • swupdate, entware
• SSTATE
• Yocto native recipes generate tools for our host that will be used to compile the target recipes
• bitbake -c xxx -x yyy

Set the password of "root" to "root"

# local.conf
INHERIT += "extrausers"
EXTRA_USERS_PARAMS = "usermod -P root root;"