Yocto + RPI4

README.MD

Quick Start Guide: Building Yocto for Raspberry Pi 4

This guide sets up Yocto for a Raspberry Pi 4, using the scarthgap branch and enabling SSH access via Dropbear. It also includes steps for setting up Wi-Fi credentials, using the ghcr.io/crops/poky:ubuntu-22.04 Docker image, and configuring Shared State Cache for faster builds.

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Prerequisites

1. Docker: Ensure Docker is installed and running:

   sudo apt update
   sudo apt install docker.io
   sudo systemctl start docker
   sudo systemctl enable docker

2. Docker Permissions: Add your user to the Docker group:

   sudo usermod -aG docker $USER
   newgrp docker

3. Balena Etcher: Download and install Balena Etcher to flash images onto the SD card.

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Step 1: Set Up CROPS Environment

1. Pull the CROPS Docker Image:

   docker pull ghcr.io/crops/poky:ubuntu-22.04

2. Create a Working Directory:

   mkdir ~/yocto-work

3. Start the CROPS Container: Run the following command to start the container with your working directory mounted:

   docker run --rm -it -v ~/yocto-work:/workdir ghcr.io/crops/poky:ubuntu-22.04 --workdir=/workdir

   This opens a shell in the CROPS environment with access to your ~/yocto-work directory as /workdir inside the container.

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Step 2: Set Up Yocto Environment Inside CROPS

1. Clone Yocto and Required Layers: Inside the CROPS container, run:

   cd /workdir
   git clone -b scarthgap git://git.yoctoproject.org/poky.git
   cd poky
   git clone -b scarthgap git://git.yoctoproject.org/meta-raspberrypi
   git clone -b scarthgap git://git.openembedded.org/meta-openembedded

2. Source the Yocto Build Environment:

   source oe-init-build-env

3. Configure Layer Paths: Open conf/bblayers.conf and add paths to the meta-raspberrypi and meta-openembedded layers:

   BBLAYERS ?= " \
       /workdir/poky/meta \
       /workdir/poky/meta-poky \
       /workdir/poky/meta-yocto-bsp \
       /workdir/poky/meta-raspberrypi \
       /workdir/poky/meta-openembedded/meta-oe \
       /workdir/poky/meta-openembedded/meta-networking \
       /workdir/poky/meta-openembedded/meta-python \
   "
   

4. Configure Build Settings: In conf/local.conf, set up the target machine, enable SSH, add Dropbear, configure SSTATE, and add Wi-Fi support:

   MACHINE = "raspberrypi4"
   DISTRO_FEATURES:append = " wifi"
   IMAGE_INSTALL:append = " wpa-supplicant dropbear"
   
   # Configure Shared State Cache (SSTATE) Mirrors
   SSTATE_MIRRORS ?= "file://.* https://sstate.yoctoproject.org/dev/PATH;downloadfilename=PATH"
   
   # Enable Hash Equivalence for faster rebuilds
   ENABLE_CACHE = "1"
   BB_HASHSERVE = "auto"
   BB_HASHSERVE_UPSTREAM = "hashserv.yoctoproject.org:8687"
   

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Step 3: Configure Wi-Fi Credentials

1. Create wpa_supplicant.conf: In the poky directory, create a wpa_supplicant.conf file with your Wi-Fi network credentials:

   ctrl_interface=DIR=/var/run/wpa_supplicant GROUP=netdev
   update_config=1
   
   network={
       ssid="YourNetworkSSID"
       psk="YourNetworkPassword"
       key_mgmt=WPA-PSK
   }
   

2. Copy wpa_supplicant.conf to the Yocto Root Filesystem: To ensure the Raspberry Pi uses your Wi-Fi credentials on boot, modify local.conf to include the wpa_supplicant.conf file in the root filesystem:

   FILES_${PN}-base += "/etc/wpa_supplicant.conf"
   

3. Add wpa_supplicant.conf to the Image Recipe: To include this file during the build, edit your image recipe or create a new .bbappend file (e.g., core-image-base.bbappend) in your layer to copy wpa_supplicant.conf:

   install -m 644 ${WORKDIR}/wpa_supplicant.conf ${D}/etc/wpa_supplicant.conf

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Step 4: Build the Yocto Image

1. Run Bitbake to Build the Image: Inside the CROPS container, use bitbake to build the desired image (e.g., core-image-base):

   bitbake core-image-base

   This process may take some time. The output image file will be located in the tmp/deploy/images/raspberrypi4 directory within your Yocto build directory.

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Step 5: Flash the Image to the SD Card

1. Locate the Output Image: The built image should be in:

   /workdir/poky/build/tmp/deploy/images/raspberrypi4/core-image-base-raspberrypi4.wic
   

2. Use Balena Etcher to Write the Image to the SD Card:

   • Open Balena Etcher.
   • Select the .wic image file located in the directory above.
   • Select your SD card as the target.
   • Click "Flash!" and wait for the process to complete.

3. Insert the SD Card into the Raspberry Pi 4: Once flashing is complete, insert the SD card into your Raspberry Pi 4, connect power, and it should boot with the configured SSH access and Wi-Fi credentials.