Yocto on Beaglebone Black

Want to use Yocto on Beaglebone Black. No problem!

What is the Yocto Project?

Yocto is an Open Source project that enables users to create custom GNU Linux systems on embedded. This project began in 2010 as a collaboration of hardware vendors. The development environment includes debuggers, Application toolkit generator, and emulation environments. The core system recipes are available from the OpenEmbedded Project. The Yocto kernel and build profiles have been community test and include architectures for:

• ARM
• PPC
• MIPS
• x86
• x86-64
• An Eclipse plugin is also available

Covered in this project:

• Workstation setup
• Building images
• partitioning and copying image to SD
• Boot from SD

Setting Up the Workstation

Ubuntu or Debian

I personally, do not like Ubuntu. However, for the purposes of this project, the team members requested I perform this work at the middle school level and requested Ubuntu. So, for the purposes of this project, you could use Ubuntu - even though I highly recommend against it. Keep in mind some dependencies may be on your system but updated. This may work. Otherwise use a container or virtual machine. Then, you won't need to have Ubuntu on your machine. :)

You will need at least 50 gb of free disk space that is running Ubuntu 14.04 or greater.

Build Host

BUILD HOST is based on the OpenEmbedded Project. This project uses bitbake to construct images.

Reference Build Host POKY = Bitbake + OpenEmbedded

The OpenEmbedded build system is able to run on Ubuntu that has the following versions for Git, tar, and Python.

Dependencies – OpenEmbedded

Git 1.7.8 or greater

tar 1.24 or greater

Python 2.7.3 or greater excluding Python 3.x, which is not supported.

Dependencies - Build Host Packages¶

These packages installed on the build host using an Ubuntu System

• bc
• libsdl1.2-dev
• build-essential
• pkg-config
• chrpath
• socat
• diffstat
• subversion
• gawk
• texi2html
• git
• texinfo
• libncurses5-dev
• u-boot-tools

Again, if you use Ubuntu, you can use sudo. Debian does not come with sudo, so just apt-get as you normally do - as superuser su whatever.

sudo apt-get install bc build-essential chrpath diffstat gawk git libncurses5-dev pkg-config socat subversion texi2html texinfo u-boot-tools

Repositories

YOCTO RELEASE

Clone the Yocto Project repository poky jethro. Below is an example from an Ubuntu build host that clones the poky repository and then checks out the latest Yocto Project Release:

git clone -b jethro git://git.yoctoproject.org/poky.git poky-jethro

META-OPENEMBEDDED

Clone the OpenEmbedded repo.

git clone -b jethro git://git.openembedded.org/meta-openembedded

META-BEAGLEBOARD repository

Clone the official Beagleboard repo. Before cloning, create a sub directory and change to that directory.

mkdir bbb 
cd bbb
git clone git://github.com/beagleboard/meta-beagleboard

Building Images¶

Now that you have your system requirements in order, you can give the Yocto Project a try. This section presents steps that let you do the following:

Initialize the Build Directory

The build directory can be either manually created or created using the oe-init-build-env script.

1. Manually - Configure these paths to the meta layers per your standards.

2. With the script oe-init-build-env

Customize the config files

When using oe-init-build-env to create the build directory, some configuration files are generated in the build/conf directory.

Editing bblayers.conf

The directory structure in bblayers.conf should look like this

~/poky-jethro/

meta-openembedded

~/bbb/

meta-beagleboard

build/

conf/

Editing local.conf

There are 3 variables to edit in local.conf

Editing these are not necessary but optional.

DL_DIR – Where downloaded sources are stored

SSTATE_DIR – This is usually 5gb and can be moved from home

TMP_DIR – Where the temporary build and final binaries are found

Initialize the Build Environment:

Run the oe-init-build-env environment setup script to use bitbake. This defines the OpenEmbedded build environment for the build host and will not overwrite the customized conf files.

source oe-init-build-env

Note: Use bitbake in the build directory.

Run the Build

core-image-sato

Change directory to the build directory to use bitbake.

To build the core-image, run the command:

bitbake core-image-sato

Note: Depending on your workstation specifications and internet connect, this could take awhile.

Build Errors

If you have build errors due to package download failure, clean the failed package and rerun the build.

bitbake -c cleanstate.file 
bitbake file

Resume the full or long build

bitbake core-image-sato

The cleansstate command works for image recipes also.

Copy to the SD card

The core or long build can take some time, depending on your internet speed and hardware. There is a difference when copying a long build or a minimal build to the SD card, as well.

Partition the SD card

Partition the SD card with at least 2 partitions using gparted, fdisk, or another tool.

sudo apt-get install gparted

Insert the SD card into the workstation.

sudo gparted

Use lsblk or df -h to find the microSD card.

Warning: This will format any disk on your workstation. Select the specified SD card listed when using lsblk or df -h. In some cases, the SD card may be mmcblk0 or sdb. Double check to make sure the correct device is being formatted.

Partition 1:

Set the “boot” flag for the first partition.

• type: FAT32
• size: around 30MB
• label: BOOT
• flags: boot and lba

Partition2:

• type: ext4
• size: around 200MB, or remaining SD-card space
• label: ROOT

After partitioning is completed, we are ready to copy the files to the SD-card.

Long Build

After completing the build, the following images are the most important found in the <TMPDIR>/deploy/images/beaglebone:

bootloader kernel rootfs

• MLO-beaglebone

The second stage bootloader (the first stage bootloader is implemented in ROM code on the AM335x chip and cannot be altered in software)

• u-boot-beaglebone.img

The third stage u-boot bootloader (the “main” bootloader)

Copy the boot loaders. The media or SD may be something like /media/bbb/BOOT/MLO. Check your system for the location to copy to the SD.

sudo cp -v MLO-beaglebone /media/bbb/BOOT/MLO  
sudo cp -v u-boot-beaglebone.img /media/bbb/BOOT/u-boot.img

• zImage

The Linux kernel image (zImage is a special format used with u-boot bootloader) zImage is found in root/boot/

• core-image-base-begalebone.tar.bz2 or something similar

This archive contains the root file system.

sudo tar x -C /media/root -f core-image-sato-beaglebone.tar.bz2 /media/bbb/root

After completing the copying process, unmount the SD partitions. Then, insert the micro SD card into the Beaglebone. and continue to the section below on how to boot the Beaglebone.

*Minimal RootFS Instructions

If you build a minimal rootfs:

• Install modules-beaglebone.tgz.

sudo tar x -C /media/root -f modules-beaglebone.tgz /media/bbb/root

• If you used core-image-base, rootfs already includes the kernel, modules and Device tree files needed to work with the u-boot default configuration
• Install the kernel uImage to /boot in rootfs and install the device tree files into rootfs /boot. Include zImage-4.4-r4am335x-boneblack-xxx.dtb

sudo cp uImage-beaglebone.bin /media/root/boot/uImage 
sudo cp uImage-am335x-bone.dtb /media/root/boot/am335x-bone.dtb  
sudo cp uImage-am335x-boneblack.dtb /media/root/boot/am335x-boneblack.dtb

After completing the copying process, unmount the SD partitions. Then, insert the micro SD card into the Beaglebone. and continue to the section below on how to boot the Beaglebone.

Reference: https://www.yoctoproject.org/downloads/bsps/daisy16/beaglebone

Boot from the SD card

Connect the microHDMI cable to the Beaglebone Black. Connect the HDMI end to an HDMI output device such as a television or monitor.

The Beaglebone Black has Debian preloaded. You can flash the image to the onboard eMMC so the SD will boot or boot holding down the S2 switch. There are 4 different ways of booting up: eMMC boot, SD boot, Serial boot, and USB boot.

For SD boot, hold the S2 switch on the Beaglebone Black for at least 5 seconds. The lights on the Beaglebone will indicate the BBB is booting.

Login

To login, use the keypad and type the username at the prompt.

Username: root

Password:

The Yocto default username is root. By default, there is no password. After entering root as the username, select the enter key to login.

Conclusion

By using Yocto, you can create customized images using recipes. Once your customization is complete, your images can be used across multiple platforms using Yocto.

Linux® is a registered trademark of Linus Torvalds.

Yocto Project™ is a registered trademark of the Linux Foundation.