Buildroot - Create a Custom Project

Change directory into the project directory:

$ cd ~/project_1

Make directory br2_external_tree and change directory into it:

​$ mkdir my_br2_tree$ cd my_br2_tree

For this tutorial, we’ll name our br2_external directory my_br2_tree. For your custom project you would choose a unique name for the directory.

Create a configs directory:

$ mkdir configs

The configs directory is used to store Buildroot default configuration (_defconfig) files in the br2_external tree.

Create files Config.in and external.mk:

​$ touch Config.in$ touch external.mk

Both Config.in and external.mk will remain empty for this tutorial. They can be used to define package recipes or other custom configuration options or make logic.

Using your favorite text editor, create a text file named external.desc with the contents shown below:

name: my_br2_tree
desc: Example br2_external tree

Buildroot uses the external.desc text file to identify and differentiate multiple br2_external directories. Therefore, the names must be unique.

name defines the name for the br2_external directory. It is mandatory. Buildroot uses name to set the variable BR2_EXTERNAL_$(NAME)_PATH to the absolute path of the my_br2_tree directory.

desc provides a short description for the br2_external directory and is used to display information about the directory. It is optional.

Create a configs directory:

$ mkdir -p board/company_1/board_1

The board directory can be used to store board-specific configuration files such as the kernel configuration, the root filesystem overlay, or any other configuration file for which Buildroot allows you to set the location (by using the BR2_EXTERNAL_$(NAME)_PATH variable).

Change directory into the Buildroot directory:

​$ cd ~/project_1/buildroot

Tell Buildroot where the external tree(s) are located and start graphical configuration:

​ $ make BR2_EXTERNAL=~/project_1/buildroot-external-microchip:~/project_1/my_br2_tree menuconfig

This command to the make utility will set the BR2_EXTERNAL variable to the path of the external tree(s). If there are multiple external trees (as this tutorial does), separate the paths by a colon (“:”).

Highlight Target options and press ENTER.

​You may notice that the default architecture settings are for i386. You will be changing this to the SAMA5D2 Series ARM®-based MPU architecture.

Set the Target Options for the ATSAMA5D27-SOM1-EK1 Evaluation Kit.

After completing the settings, the Target Options submenu will look like:

Move back to the top menu by typing ESC-ESC.

Highlight Build Options and press ENTER.

Enter location to save Buildroot configuration.

The first line below the Commands —> entry is the save location of the Buildroot default configuration files. Enter:

$(BR2_EXTERNAL_my_br2_tree_PATH)/configs/project_1_defconfig

Observe the location of the Download Directory.

The second line below the Commands —> entry is the save location of the target packages and files that Buildroot will download for the build. This directory will contain all of the upstream projects as a compressed archive (*.tar.gz) files.

We see the default location $(TOPDIR)/dl is entered. Recall that you can type the make printvars command:

to see the expanded directory.

Observe the location of the Host Directory.

 The third line below the Commands —> entry is the save location of the packages and files Buildroot will download, build, and run on the host. This includes the cross-compilation toolchain when building the internal Buildroot toolchain.

We see the default location $(BASE_DIR)/host is entered. Recall that you can type the make printvars command:

to see the expanded directory.

After completing the settings, the "Build Options" submenu will look like:

Move back to the top menu by typing ESC-ESC.

Highlight Toolchain and press ENTER.

 The Toolchain submenu opens as shown in the figure below.

Observe the Toolchain type, Buildroot toolchain, and Buildroot custom toolchain vendor name. Buildroot has selected, by default, an Internal Toolchain Backend.

Select Toolchain type ( ).

Select External toolchain.

Once selected, the menu will expand.

Step a: Select Toolchain ( ) and select Linaro ARM 2018.05.

Step b: Select Toolchain Origin ( ) and select Toolchain to be downloaded and installed.

After completing the settings, the Toolchain submenu will look like this:

Move back to the top menu by typing ESC-ESC.

Highlight System Configuration and press ENTER.

Observe System Configuration options that are selected by default.

You can enter the name of the target’s hostname and system banner:

You can choose the INIT system:

You can enable/disable root login, set the root password, and enable a login prompt.

Note that the default selection the root login has been enabled with no password required.

Enable the generation of a binary image that can be flashed onto an SD Memory card for the ATSAMA5D27-SOM1-EK1 Evaluation Kit.

Select the last line of the system configuration: Custom scripts to run after creating filesystem images and enter the text string:

support/scripts/genimage.sh

This shell script is located in the main Buildroot directory.

Once entered, a new configuration option is displayed: Extra arguments passed to custom scripts and enter the text string:

-c $(BR2_EXTERNAL_MCHP_PATH)/board/microchip/sama5d27_som1_ek/genimage.cfg

This configuration file is located in the buildroot-external-microchip files.

After completing the settings, the System Configuration submenu will look like:

Move back to the top menu by typing ESC-ESC.

Highlight Kernel and press ENTER.

Observe Kernel options that are selected by default.

 By default, the Linux kernel is not selected.

Select Linux Kernel.

Once selected, the menu will expand.

Tell Buildroot which kernel source code and version to download:

Step a: Select Kernel Version and check Custom Git Repository.

Step b: Select URL of custom repository and enter:

https://github.com/linux4sam/linux-at91.git

Step c: Select Custom Repository Version and enter linux4sam_6.0.

Tell Buildroot which kernel default configuration file to use:

Step a: Select Kernel configuration and select Using an in-tree defconfig file.

Step b: Select Defconfig name and enter sama5.

Tell Buildroot to build a device tree:

Step a: Select Build a Device Tree Blob (BTD).

Step b: Select In-tree Device Tree Source file names and enter:

at91-sama5d27_som1_ek

After completing the settings, the Kernel submenu will look like:

Move back to the top menu by typing ESC-ESC.

Highlight Target packages and press ENTER.

At this step, you would select the software packages you require for your custom project.

Move back to the top menu by typing ESC-ESC.

Highlight Filesystem images and press ENTER.

By default, no filesystem is selected. This is by design as your choice of file system depends on your project hardware memory architecture and type.

Select [ ] ext2/3/4 root filesystem.

Once selected, the menu will expand.

Select ext2/3/4 variant ( ) and select Ext4.

After completing the settings, the Filesystem Images submenu will look like:

Move back to the top menu by typing ESC-ESC.

Highlight Bootloaders and press ENTER.

 The Bootloaders submenu opens as shown in the figure below.

Select AT91 Bootstrap 3.

Once selected, the menu will expand.

Step a: Select AT91 Bootstrap 3 version.

Select Custom Git Repository.

Step b: Select URL of custom repository.

Enter:

https://github.com/linux4sam/at91bootstrap.git

Step c: Select Custom repository version.

Enter:

v3.8.12

Step d: Select AT91 Bootstrap 3 configuration.

Select Using a defconfig.

Step e: Select Defconfig name.

Enter:

sama5d27_som1_eksd_uboot

This completes the selections for the AT91Bootstrap bootloader.

Select U-Boot.

Once selected, the menu will expand.

Step a: Select Build system.

Select Kconfig.

Step b: Select U-Boot Version.\

Select Custom Git repository.

Step c: Select URL of Custom Repository.

Enter:

https://github.com/linux4sam/u-boot-at91.git

Step d: Select Custom Repository Version.

Enter:

linux4sam_6.0

Step e: Select U-Boot configuration.

Select Using an in-tree board defconfig file.

Step f: Select Board defconfig.

Enter:

sama5d27_som1_ek_mmc

Step g: Select U-Boot needs dtc.

Step h: Select Environment Image - - - -.

Once the entry has been selected, the - - - - changes to a - - - > indicating that more information can be entered.

Select ( ) Source files for environment and enter:

$(BR2_EXTERNAL_MCHP_PATH)/board/microchip/sama5d27_som1_ek/uboot-env.txt

Select ( ) Size of environment and enter:

0x4000

This completes the selections for the U-Boot bootloader.

After completing the settings, the Filesystem Images submenu will look like:

Move back to the top menu by typing ESC-ESC.

Highlight host utilities and press ENTER.

Select host dosfstools.

The host dosfstools utility for creating and checking DOS FAT filesystem. It is needed by the genimage to assist in generating flash images.

Select host genimage.

The host genimage utility to generate flash images from a given root filesystem tree.

Select host mtools.

The host mtools utility to access DOS disks from Unix without mounting them. It is needed by the genimage to assist in generating flash images.

Select host u-boot tools.

Once selected, the menu will expand.

Select [ ] Flattend Image Tree (FIT) support.

The host u-boot tools are companion tools for the U-Boot bootloader.

After completing the settings, the Host Utilities submenu will look like:

Move back to the top menu by typing ESC-ESC.

Highlight Legacy config options and press ENTER.

The Legacy config options submenu opens.

Feel free to browse. However, as mentioned, it is for backward compatibility. Generally, you will have no selections unless absolutely necessary.

Move back to the top menu by typing ESC-ESC.

Highlight External options and press ENTER.

 The External Options submenu opens as shown in the figure below.

Observe there are two entries, one for each of the br2_external trees that Buildroot was told about.

Select MCHP —>.

You are now viewing the available packages in the buildroot-external-microchip directory.

Select [ ] dt-overlay-at91.

Once selected, the menu will expand.

Select ( ) platform name and enter:

sama5d27_som1_ek

After completing the settings, the External Options submenu will look like:

Move back to the top menu by typing ESC-ESC.

Save your configuration by selecting < Save >.

You may exit by selecting < Exit > or typing ESC-ESC.

At this point, your project-specific configuration is stored as .config in the ~/project_1/buildroot directory.

To save your project-specific configuration as a default configuration (_defconfig) file:

Issue the command:

​$ make savedefconfig

Recall that you told Buildroot, under the Build options submenu, the location to save the _defconfig file:

$(BR2_EXTERNAL_my_br2_tree_PATH)/configs/project_1_defconfig

Change directory to ~/project_1/my_br2_tree/configs and observe that it is there.