Yocto and Raspberry Pi Project Setup (WSL2 on Windows 10)

1. Install Required Packages

# Update package repositories
sudo apt update

# Install packages required for Yocto build
sudo apt install -y 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 python3-subunit zstd liblz4-tool file \
locales libacl1 libssl-dev libncurses5-dev u-boot-tools

# Generate locale
sudo locale-gen en_US.UTF-8

2. Download the Poky Sources

git clone git://git.yoctoproject.org/poky (this really takes time)

3. Checkout the Latest Branch/Release

cd poky
git checkout kirkstone

4. Add a Package to the Root File System

Edit your local.conf file and add the desired package:

IMAGE_INSTALL += "recipe-name"

For example, to add usbutils for lsusb, use:

IMAGE_INSTALL += "usbutils"

Alternatively, you can append it:

IMAGE_INSTALL_append = " usbutils"

5. Where to Get Other Layers

• OpenEmbedded Layer Index
• Yocto Project Layers

6. Poky Source Tree Structure

• bitbake: Contains all Python scripts used by the bitbake command.
• documentation: Source files for Yocto Project documentation.
• meta: Contains the core metadata.
• meta-poky: Configuration for the Poky reference distribution.
• meta-skeleton: Template recipes for BSP and kernel development.
• meta-yocto-bsp: Maintains BSPs for the Beaglebone, EdgeRouter, and generic IA machines.
• scripts: Scripts for environment setup, development tools, and flashing generated images.
• LICENSE: The license under which Poky is distributed (GPLv2 and MIT).

7. Raspberry Pi Layer Setup

• Clone the Raspberry Pi meta-layer:

git clone git://git.yoctoproject.org/meta-raspberrypi
cd meta-raspberrypi
git checkout kirkstone

Dependencies

• meta-openembedded: Required dependencies for the Raspberry Pi layer.

git clone git://git.openembedded.org/meta-openembedded
cd meta-openembedded
git checkout kirkstone

Layers Needed:

• meta-oe
• meta-multimedia
• meta-networking
• meta-python

8. Directory Structure After Cloning

~/embd_linux/
├── poky
├── meta-raspberrypi
└── meta-openembedded

9. Building the Image

1. Run the environment script to set up the Yocto Environment and create the build directory:

source poky/oe-init-build-env build_pi

2. Add meta-openembedded layers (meta-oe, meta-multimedia, meta-networking, meta-python) and the meta-raspberrypi layer to build_pi/conf/bblayers.conf.

  BBLAYERS ?= " \
  ${TOPDIR}/../poky/meta \
  ${TOPDIR}/../poky/meta-poky \
  ${TOPDIR}/../poky/meta-yocto-bsp \
  ${TOPDIR}/../meta-openembedded/meta-oe \
  ${TOPDIR}/../meta-openembedded/meta-multimedia \
  ${TOPDIR}/../meta-openembedded/meta-networking \
  ${TOPDIR}/../meta-openembedded/meta-python \
  ${TOPDIR}/../meta-raspberrypi \
  "

3. Configure local.conf for Raspberry Pi 3: Edit the build_pi/conf/local.conf file to set up the Raspberry Pi and enable UART, SPI, I2C, SSH, and Ethernet:

# Set the target machine
MACHINE = "raspberrypi3"

# Enable UART
ENABLE_UART = "1"

# Enable SSH server
EXTRA_IMAGE_FEATURES += " ssh-server-openssh"

# Include Ethernet, SPI, and I2C tools
IMAGE_INSTALL += " i2c-tools spi-tools python3-serial dhcp-client iproute2"

# Add support for systemd
DISTRO_FEATURES += " systemd"
VIRTUAL-RUNTIME_init_manager = "systemd"

BB_GIT_CLONE_FOR_SRC_URI = "1"
BB_FETCH_TIMEOUT = "60000"
GIT_CONFIG[user.timeout] = "60000"
BB_GIT_SHALLOW = "1"
GIT_SHALLOW_pn-linux-raspberrypi = "1"
BB_NUMBER_THREADS = "8"
PARALLEL_MAKE = "-j8"

4. To see available images:

ls ../meta-raspberrypi/recipes-*/images/

11. Images Overview

• rpi-hwup-image.bb: Based on core-image-minimal.
• rpi-basic-image.bb: Based on rpi-hwup-image.bb with added features (e.g., splash screen).
• rpi-test-image.bb: Based on rpi-basic-image.bb, includes packages from meta-raspberrypi.

12. Build Image:

bitbake core-image-minimal

13. Raspberry Pi Information

• Broadcom BCM2837
  • CPU: 1.2GHz 64-bit quad-core ARMv8 Cortex-A53
  • GPU: Broadcom VideoCore IV
  • SDRAM: 1024 MiB

14. Booting Sequence in Raspberry Pi

1. GPU Core: First stage bootloader, stored in ROM on the SoC.
2. bootcode.bin
3. start.elf
4. config.txt
5. cmdline.txt
6. kernel7.img

15. Image Location

The built images can be found at:

tmp/deploy/images/raspberrypi3/core-image-minimal-raspberrypi3-20241004105158.rootfs.wic.bz2

16. IMAGE_ROOTFS_EXTRA_SPACE

This variable adds extra free space to the root filesystem image. The value is specified in kilobytes.

Default Value: 0

For example, to add an additional 4 GB of space:

IMAGE_ROOTFS_EXTRA_SPACE = "4194304"