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Building BeagleBone Systems with Yocto

11 Jan 2018

Building systems for BeagleBone Black and BeagleBone Green boards using tools from the Yocto Project.

Yocto is a set of tools for building a custom embedded Linux distribution. The systems are usually targeted at particular applications like commercial products.

Yocto uses what it calls meta-layers to define the configuration for a system build. Within each meta-layer are recipes, classes and configuration files that support the primary build tool, a python framework called bitbake.

The Yocto system, while very powerful, does have a substantial learning curve. You may want to look at another popular tool for building embedded systems Buildroot.

The meta-bbb layer generates some basic systems with packages that support C, C++, Qt5, Perl and Python development, the languages and tools I commonly use. Other languages are supported of course.

I use this layer as a template when starting new BeagleBone projects.

System Info

The Yocto version is 2.4 the [rocko] branch.

The default 4.14 Linux kernel comes from the linux-stable repository. Recipes for 4.9 and 4.4 LTS kernels are also available.)

The u-boot version is 2017.09.

These are sysvinit systems using eudev.

The Qt version is 5.9.2. There is no X11 and no desktop installed. Qt GUI applications can be run using the linuxfb platform plugin.

A light-weight X11 desktop can be added with minimal changes to the build configuration. For instance X11 is needed to run Java GUI apps or browser kiosk applications.

Python 3.5.3 is installed.

I have not added any display dtbs to the 4.14 kernels yet. No requests.

For the 4.9 and 4.4 kernels, device tree binaries are built that support

  1. HDMI (bbb-hdmi.dtb) not for the BBG
  2. No HDMI (bbb-nohdmi.dtb)
  3. 4DCape 4.3-inch resistive touchscreen cape (bbb-4dcape43t.dtb)
  4. 4DCape 7-inch resistive touchscreen cape (bbb-4dcape70t.dtb)
  5. Newhaven 5-inch capacitive touchscreen cape (bbb-nh5cape.dtb)
  6. Newhaven 7-inch capacitive touchscreen cape (bbb-nhd7cape.dtb)

The DTBs are easy enough to switch between using a u-boot script file uEnv.txt

spidev on SPI bus 1, I2C1 and I2C2 and UART4 are configured for use from the P9 header.

There are some simple loopback test programs included in the console image.

spiloop is a utility for testing the spidev driver.

serialecho is a utility for testing uarts.

Ubuntu Setup

I primarily use 16.04 64-bit servers for builds. Other versions should work.

You will need at least the following packages installed

build-essential
chrpath
diffstat
gawk
libncurses5-dev
texinfo

For 16.04 you also need to install the python 2.7 package

python2.7

And then create some links for it in /usr/bin

sudo ln -sf /usr/bin/python2.7 /usr/bin/python
sudo ln -sf /usr/bin/python2.7 /usr/bin/python2

For all versions of Ubuntu, you should change the default Ubuntu shell from dash to bash by running this command from a shell

sudo dpkg-reconfigure dash

Choose No to dash when prompted.

Fedora Setup

I have also used a Fedora 27 64-bit workstation.

The extra packages I needed were

chrpath
perl-bignum
perl-Thread-Queue
texinfo

and the package group

Development Tools

Fedora already uses bash as the shell.

Clone the repositories

~$ git clone -b rocko git://git.yoctoproject.org/poky.git poky-rocko

~$ cd poky-rocko
~/poky-rocko$ git clone -b rocko git://git.openembedded.org/meta-openembedded
~/poky-rocko$ git clone -b rocko https://github.com/meta-qt5/meta-qt5.git

I usually keep these repositories separated since they can be shared between projects and different boards.

Clone the meta-bbb repository

Create a sub-directory for the meta-bbb repository before cloning

~$ mkdir ~/bbb
~$ cd ~/bbb
~/bbb$ git clone -b rocko git://github.com/jumpnow/meta-bbb

The meta-bbb/README.md file has the last commits from the dependency repositories that I tested. You can always checkout those commits explicitly if you run into problems.

Initialize the build directory

Much of the following are only the conventions that I use. All of the paths to the meta-layers are configurable.

First setup a build directory. I tend to do this on a per board and/or per project basis so I can quickly switch between projects. For this example I’ll put the build directory under ~/bbb/ with the meta-bbb layer.

You could manually create the directory structure like this

~$ mkdir -p ~/bbb/build/conf

Or you could use the Yocto environment script oe-init-build-env like this passing in the path to the build directory

~$ source poky-rocko/oe-init-build-env ~/bbb/build

The Yocto environment script will create the build directory if it does not already exist.

Customize the configuration files

There are some sample configuration files in the meta-bbb/conf directory.

Copy them to the build/conf directory (removing the ‘-sample’)

~/bbb$ cp meta-bbb/conf/local.conf.sample build/conf/local.conf
~/bbb$ cp meta-bbb/conf/bblayers.conf.sample build/conf/bblayers.conf

If you used the oe-init-build-env script to create the build directory, it generated some generic configuration files in the build/conf directory. It is okay to copy over them.

You may want to customize the configuration files before your first build.

Edit bblayers.conf

In bblayers.conf file replace ${HOME} with the appropriate path to the meta-layer repositories on your system if you modified any of the paths in the previous instructions.

For example, if your directory structure does not look exactly like this, you will need to modify bblayers.conf

~/poky-rocko/
     meta-openembedded/
     meta-qt5/
     ...

~/bbb/
    meta-bbb/
    build/
        conf/

Edit local.conf

The variables you may want to customize are the following:

The defaults for all of these work fine. Adjustments are optional.

TMPDIR

This is where temporary build files and the final build binaries will end up. Expect to use at least 35GB. You probably want at least 50GB available.

The default location is in the build directory, in this example ~/bbb/build/tmp.

If you specify an alternate location as I do in the example conf file make sure the directory is writable by the user running the build.

DL_DIR

This is where the downloaded source files will be stored. You can share this among configurations and build files so I created a general location for this outside the project directory. Make sure the build user has write permission to the directory you decide on.

The default location is in the build directory, ~/bbb/build/sources.

SSTATE_DIR

This is another Yocto build directory that can get pretty big, greater then 5GB. I often put this somewhere else other then my home directory as well.

The default location is in the build directory, ~/bbb/build/sstate-cache.

Run the build

You need to source the Yocto environment into your shell before you can use bitbake. The oe-init-build-env will not overwrite your customized conf files.

~$ source poky-rocko/oe-init-build-env ~/bbb/build

### Shell environment set up for builds. ###

You can now run 'bitbake '

Common targets are:
    core-image-minimal
    core-image-sato
    meta-toolchain
    meta-toolchain-sdk
    adt-installer
    meta-ide-support

You can also run generated qemu images with a command like 'runqemu qemux86'
scott@octo:~/bbb/build$

I don’t use those Common targets, but instead use my own custom image recipes.

There are two custom images available in the meta-bbb layer. The recipes for the images can be found in meta-bbb/images/

You should add your own custom images to this same directory.

console-image

A basic console developer image. See the recipe meta-bbb/images/console-image.bb for specifics, but some of the installed programs are

gcc/g++ and associated build tools
git
ssh/scp server and client
python3 with a number of modules

The console-image has a line

inherit core-image

which is poky-rocko/meta/classes/core-image.bbclass and pulls in some required base packages. This is useful to know if you create your own image recipe.

qt5-image

This image includes the console-image and adds Qt5 runtime libraries.

installer-image

This is a minimal image meant only to run from an SD card and whose only purpose is to perform an eMMC installation.

Build

To build the console-image run the following command

~/bbb/build$ bitbake console-image

You may occasionally run into build errors related to packages that either failed to download or sometimes out of order builds. The easy solution is to clean the failed package and rerun the build again.

For instance if the build for zip failed for some reason, I would run this

~/bbb/build$ bitbake -c cleansstate zip
~/bbb/build$ bitbake zip

And then continue with the full build.

~/bbb/build$ bitbake console-image

To build the qt5-image it would be

~/bbb/build$ bitbake qt5-image

Or the installer-image

~/bbb/build$ bitbake installer-image

The cleansstate command (with two s’s) works for image recipes as well.

The image files won’t get deleted from the TMPDIR until the next time you build.

Copying the binaries to an SD card

After the build completes, the bootloader, kernel and rootfs image files can be found in <TMPDIR>/deploy/images/beaglebone/.

The meta-bbb/scripts directory has some helper scripts to format and copy the files to a microSD card.

mk2parts.sh

This script will partition an SD card with the minimal 2 partitions required for the boards.

Insert the microSD into your workstation and note where it shows up.

lsblk is convenient for finding the microSD card.

For example

scott@octo:~/bbb/meta-bbb$ lsblk
NAME    MAJ:MIN RM   SIZE RO TYPE MOUNTPOINT
sda       8:0    0 931.5G  0 disk
|-sda1    8:1    0  93.1G  0 part /
|-sda2    8:2    0  93.1G  0 part /home
|-sda3    8:3    0  29.8G  0 part [SWAP]
|-sda4    8:4    0     1K  0 part
|-sda5    8:5    0   100G  0 part /oe5
|-sda6    8:6    0   100G  0 part /oe6
|-sda7    8:7    0   100G  0 part /oe7
|-sda8    8:8    0   100G  0 part /oe8
|-sda9    8:9    0   100G  0 part /oe9
`-sda10   8:10   0 215.5G  0 part /oe10
sdb       8:16   1   7.4G  0 disk
|-sdb1    8:17   1    64M  0 part
`-sdb2    8:18   1   7.3G  0 part

I would use sdb for the format and copy script parameters on this machine.

It doesn’t matter if some partitions from the SD card are mounted. The mk2parts.sh script will unmount them.

BE CAREFUL with this script. It will format any disk on your workstation.

~$ cd ~/bbb/meta-bbb/scripts
~/bbb/meta-bbb/scripts$ sudo ./mk2parts.sh sdb

You only have to format the SD card once.

/media/card

You will need to create a mount point on your workstation for the copy scripts to use.

~$ sudo mkdir /media/card

You only have to create this directory once.

copy_boot.sh

This script copies the bootloaders (MLO and u-boot) to the boot partition of the SD card.

The script also copies a uEnv.txt file to the boot partition if it finds one in either

<TMPDIR>/deploy/images/beaglebone/

or in the local directory where the script is run from.

If you are just starting out, you might just want to do this

~/bbb/meta-bbb/scripts$ cp uEnv.txt-example uEnv.txt

This copy_boot.sh script needs to know the TMPDIR to find the binaries. It looks for an environment variable called OETMP.

For instance, if I had this in the local.conf

TMPDIR = "/oe7/bbb/tmp-rocko"

Then I would export this environment variable before running copy_boot.sh

~/bbb/meta-bbb/scripts$ export OETMP=/oe7/bbb/tmp-rocko

Then run the copy_boot.sh script passing the location of SD card

~/bbb/meta-bbb/scripts$ ./copy_boot.sh sdb

This script should run very fast.

copy_rootfs.sh

This script copies the zImage Linux kernel, the device tree binaries and the rest of the operating system to the root file system partition of the SD card.

The script accepts an optional command line argument for the image type, for example console or qt5. The default is console if no argument is provided.

The script also accepts a hostname argument if you want the host name to be something other then the default beaglebone.

Here’s an example of how you’d run copy_rootfs.sh

~/bbb/meta-bbb/scripts$ ./copy_rootfs.sh sdb console

or

~/bbb/meta-bbb/scripts$ ./copy_rootfs.sh sdb qt5 bbb

The copy_rootfs.sh script will take longer to run and depends a lot on the quality of your SD card. With a good Class 10 card it should take less then 30 seconds.

The copy scripts will NOT unmount partitions automatically. If an SD card partition is already mounted, the script will complain and abort. This is for safety, mine mostly, since I run these scripts many times a day on different machines and the SD cards show up in different places.

Here’s a realistic example session where I want to copy already built images to a second SD card that I just inserted.

~$ sudo umount /dev/sdb1
~$ sudo umount /dev/sdb2
~$ export OETMP=/oe7/bbb/tmp-rocko
~$ cd bbb/meta-bbb/scripts
~/bbb/meta-bbb/scripts$ ./copy_boot.sh sdb
~/bbb/meta-bbb/scripts$ ./copy_rootfs.sh sdb console bbb2

Both copy_boot.sh and copy_rootfs.sh are simple scripts meant to be modified for custom use.

Booting from the SD card

The default behavior of the beaglebone is to boot from the eMMC first if it finds a bootloader there.

Holding the S2 switch down when the bootloader starts will cause the BBB to try booting from the SD card first. The S2 switch is above the SD card holder.

If you are using a cape, the S2 switch is usually inaccessible or at least awkward to reach. From the back of the board a temporary jump of P8.43 to ground when the bootloader starts will do the same thing as holding the S2 switch.

If you prefer to always boot from the SD card you can erase any existing bootloader from the eMMC with something like the following

root@beaglebone:~# dd if=/dev/zero of=/dev/mmcblk1 bs=4096 count=4096

On a system that booted from an SD card, /dev/mmcblk0 is the SD card and /dev/mmcblk1 is the eMMC.

Installing to the eMMC

Normally you will want to use the eMMC over the SD card since the eMMC is a little faster.

You need a running system to install to the eMMC, since it is not accessible otherwise.

Suppose you wanted to install the console-image onto the eMMC.

First make sure you build both the console-image and the installer-image using bitbake.

First edit the meta-bbb/scripts/emmc-uEnv.txt file to be the uEnv.txt you want when using the eMMC. Normally you will only need to modify the fdtfile variable for the dtb you want.

Then when copying to the SD card, use these steps

scott@octo:~$ export OETMP=<your-tmp-dir>
scott@octo:~$ cd bbb/meta-bbb/scripts
scott@octo:~/bbb/meta-bbb/scripts$ ./copy_boot.sh sdb
scott@octo:~/bbb/meta-bbb/scripts$ ./copy_rootfs.sh sdb installer [<hostname>]
scott@octo:~/bbb/meta-bbb/scripts$ ./copy_emmc_install.sh sdb console

When you boot from the SD card this time, it will automatically launch the eMMC installation of the console-image.

When the BBB LEDs stop flashing in cylon-mode, the eMMC installation is complete.

It should take a little over a minute from the time you apply power.

Power off, pull the SD card and reboot.

Modifying uEnv.txt

The uEnv.txt bootloader configuration script is where the kernel dtb is specified.

The uEnv.txt file is located on the first partition of the SD card or eMMC.

You can modify the uEnv.txt file at installation by adding a uEnv.txt file to the meta-bbb/scripts directory.

~/bbb/meta-bbb/scripts$ cp uEnv.txt-example uEnv.txt

And then edit the file. The copy_boot.sh script will pick it up and use it.

For the uEnv.txt file that installs onto the eMMC, edit this file directly

scott@octo:~/bbb/meta-bbb/scripts/emmc-uEnv.txt

Be careful not to lose this line in the eMMC version of uEnv.txt

bootpart=1:2

It differs from SD card uEnv.txt files which uses

bootpart=0:2

You can also edit uEnv.txt on a running BBB system.

You first need to mount the bootloader partition

root@bbb:~# mount /dev/mmcblk0p1 /mnt

root@bbb:~# ls -l /mnt
total 466
-rwxr-xr-x 1 root root  64408 Aug 10  2015 MLO
-rwxr-xr-x 1 root root 410860 Aug 10  2015 u-boot.img
-rwxr-xr-x 1 root root    931 Aug 10  2015 uEnv.txt

You can edit /etc/fstab if you want the bootloader partition mounted all the time.

Some custom package examples

spiloop is a spidev test application installed in /usr/bin.

The bitbake recipe that builds and packages spiloop is here

meta-bbb/recipes-misc/spiloop/spiloop_1.0.bb

Use it to test the spidev driver before and after placing a jumper between pins P9.29 and P9.30.

serialecho is a similar test app for serial ports.

The bitbake recipe that builds and packages serialecho is here

meta-bbb/recipes-misc/serialecho/serialecho.bb

Use it to test UART4 after placing a jumper between pins P9.11 and P9.13.

tspress is a Qt5 GUI application installed with the qt5-image.

The bitbake recipe is here

meta-bbb/recipes-qt/tspress/tspress.bb

Adding additional packages

To display the list of available packages from the meta- repositories included in bblayers.conf

~$ source poky-rocko/oe-init-build-env ~/bbb/build
~/bbb/build$ bitbake -s

Once you have the package name, you can choose to either

  1. Add the new package to the console-image or qt5-image.

  2. Create a new image file and either include the console-image the way the qt5-image does or create a complete new image recipe.

The new package needs to get included directly in the IMAGE_INSTALL variable or indirectly through another variable in the image file.

Customizing the Kernel

See this post for some ways to go about customizing and rebuilding the BBB kernel or generating a new device tree binary.

Customizing U-Boot

See this post for similar notes on working with u-boot for the BBB.

Package Management

The package manager for these systems is opkg. The other choices are rpm or apt. You can change the package manager with the PACKAGE_CLASSES variable in local.conf.

opkg is the most lightweight of the Yocto package managers and the one that builds packages the quickest.

To add or upgrade packages to the system, you might be interested in using the build workstation as a remote package repository.

Full System Upgrades

For deployed production systems, you might prefer full system upgrades using an A/B rootfs strategy. This keeps upgrades atomic instead of spread out over multiple packages. It also allows for easy rollback when required.

An implementation of this idea is described here An upgrade strategy for embedded Linux systems.

There is a emmc-upgrader package in the meta-bbb layer that will add this capability to your systems.