Building Yocto Kirkstone BSP Distribution

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This document describes how Embedian builds a customized version of NXP’s i.MX8M Mini official Yocto Kirkstone BSP release for Embedian’s SMARC-iMX8MM product platform. The approach is to pull from Embedian’s Github repository and build that using bitbake. The reason why we use this approach is that it allows co-development. The build output is comprised of binary images, feed packages, and an SDK for SMARC-iMX8MM specific development.

NXP makes their i.MX series official bsp build scripts available via the following GIT repository:

Freescale community BSP release build script is available via the following repository:

It is this repository that actually pulls in the meta-imx/meta-bsp project to perform the Linux BSP builds for NXP’s i.MX8M Mini ARM Cortext-A53 chips.

Overview of the meta-embedian Yocto Layer

The supplied meta-embedian Yocto compliant layer has the following organization:

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|-- conf
|   |-- layer.conf
|   |-- machine
|       |-- include
|       |   |-- imx8mp-emb.inc
|       |-- pitximx8mp2g.conf
|       |-- pitximx8mp4g.conf
|       |-- pitximx8mp6g.conf
|       |-- smarcimx8qm8g.conf
|       |-- smarcimx8qm4g.conf
|       |-- smarcimx8mp6g.conf
|       |-- smarcimx8mp4g.conf
|       |-- smarcimx8mp2g.conf
|       |-- smarcimx8mq4g.conf
|       |-- smarcimx8mq2g.conf
|       |-- smarcimx8mm4g.conf
|       |-- smarcimx8mm2g.conf
|       |-- smarcfimx7d2g.conf
|       |-- smarcfimx7d.conf
|       |-- smarcfimx7s.conf
|       |-- smarcfimx6qp2g.conf
|       |-- smarcfimx6qp1g.conf
|       |-- smarcfimx6q2g.conf
|       |-- smarcfimx6q1g.conf
|       |-- smarcfimx6dl1g.conf
|   |   `-- smarcfimx6solo.conf
|-- README
|-- recipes-bsp
|   |-- u-boot
|       `-- u-boot-imx_2022.04.bb
|   |-- imx-atf
|       `-- imx-atf_2.6.bbappend
|       |   |-- imx-atf
|       |   |   `-- imx8mm-atf-uart4.patch
|   |-- imx-sc-firmware
|       `-- imx-sc-firmware_%.bbappend
|       |   |-- imx-sc-firmware
|       |   |   |-- mx8qm-smarc-8g-scfw-tcm.bin
|       |   |   `-- mx8qm-smarc-4g-scfw-tcm.bin
|   |-- alsa-state
|       |   |-- alsa-state
|       |   |   `-- asound.state
|       `-- alsa-state.bbappend
|   |-- pm-utils
|       `-- pm-utils_%.bbappend
|   |-- imx-mkimage
|       `-- imx-boot_1.0.bbappend
|-- recipes-core
|   |-- busybox
|       `-- busybox_%.bbappend
|       |   |-- busybox
|       |   |   |-- ftpget.cfg
|       |   |   `-- defconfig
|   |-- base-files
|       `-- base-files_%.bbappend
|       |   |-- base-files
|       |   |   |-- issue
|       |   |   `-- issue.net
|   |-- systemd
|       `-- systemd-serialgetty.bbappend
|       |   |-- systemd-serialgetty
|       |   |   |-- disable-serialgetty.service
|       |   |   `-- disable-serialgetty.sh
|   |-- packagegroups
|       `-- packagegroup-core-tools-testapps.bbappend
|   |-- psplash
|       `-- psplash_git.bbappend
|       |   |-- files
|       |   |   |-- 0001-psplash-Change-colors-for-the-Embedian-Yocto-logo.patch
|       |   |   |-- psplash-poky.png
|       |   |   `-- psplash-bar.png
|   |-- udev
|       |   |-- files
|       |   |   |   `-- usb-power.rules  
|       `-- udev-rules-imx.bbappend
|-- recipes-kernel
|   |-- linux
|       `-- linux-imx.bb
`-- scripts
|   `-- emb_mk_yocto_sdcard

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Setting Up the Tools and Build Environment

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To build the latest NXP i.MX8M Mini meta-bsp, you first need an Ubuntu 20.04 or 22.04 LTS installation. Since bitbake does not accept building images using root privileges, please do not login as a root user when performing the instructions in this section. 

Once you have Ubuntu 20.04 or 22.04 LTS running, install the additional required support packages using the following console command:

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To get the BSP you need to have ‘repo’ installed and use it as:

Install the ‘repo’ utility:

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Download the BSP Yocto Project Environment.

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Download the Embedian Yocto build script and meta layer.

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Choose “y” to accept EULA.

This script will create and bring you to ~/kirkstone-release/build-xwayland directory.

Building the Target Platforms

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To build Embedian/NXP Yocto BSP, use the following commands:

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Once it done, you can find all required images under ~/kirkstone-release/<build directory>/tmp/deploy/images/<machine name>/

You may want to build programs that aren’t installed into a root file system so you can make them available via a feed site (described below.) To do this you can build the package directly and then build the package named package-index to add the new package to the feed site.

The following example builds the tcpdump program and makes it available on the feed site:

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Once the build(s) are completed, you will find the resulting images, rpm and licenses in folder ~/kirkstone-release/<build directory>/tmp/deploy.

deploy/images/<machine name>/* 

This folder contains the binary images for the root file system and the Embedian SMARC-iMX8MM specific version of the boot file, Image and device tree file. Specifically the images are:

deploy/images/<machine name>/imx-boot-<machine name>-sd.bin-flash_singleboot

This is boot file binary for SMARC-iMX8MM.

deploy/images/<machine name>/Image

The kernel Image for SMARC-iMX8MM.  

deploy/images/<machine name>/<device tree file>

Selecting display configuration is a matter of selecting an appropriate DTB file under deploy/images/<machine name>/<device tree file>

All available DTB files are listed in the table below.

deploy/images/<machine name>/fsl-image-validation-imx-<machine name>.*

Embedian root file system images for software development on Embedian’s SMARC-iMX8MM platforms without QT6.

deploy/images/<machine name>/fsl-image-qt6-validation-imx-<machine name>.*

Embedian root file system images for software development on Embedian’s SMARC-iMX8MM  with QT6.

deploy/deb/*

This folder contains all the packages used to construct the root file system images. They are in deb format (similar format to Debian packages) and can be dynamically installed on the target platform via a properly  constructed feed file. Here is an example of the feed file (named base- feeds.conf) that is used internally at Embedian to install upgrades onto a SMARC-iMX8MM platform without reflashing the file system:

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deploy/licenses/*

A database of all licenses used in all packages built for the system.

Setup SD Card Manually

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For these instruction, we are assuming: DISK=/dev/mmcblk0, “lsblk” is very useful for determining the device id.

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Erase SD card:

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Create Partition Layout: Leave 2MB offset for boot file. With util-linux v2.26, sfdisk was rewritten and is now based on libfdisk.

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Create Partitions:

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Format Partitions:

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Mount Partitions:

On some systems, these partitions may be auto-mounted…

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Boot file is factory default flashed at on-module eMMC flash.

Install Boot File (imx-boot-<machine name>-sd.bin-flash_evk)

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In some cases, when eMMC flash is erased or the u-boot is under development, we need a way to boot from SD card first. Users need to shunt cross the TEST# pin to ground. In this way, SMARC-iMX8MM will always boot up from SD card. 

Write flash.bin to SD card.

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The <boot file> is pre-installed in on-module eMMC flash at factory default. SMARC-iMX8MM is designed to always boot up from on-module eMMC flash and to load Image, device tree blob and root file systems based on the setting of BOOT_SEL. If users need to fuse your own flash.bin or perform u-boot upgrade. This section will instruct you how to do that.

Copy <boot file> to the second partition home directory of your SD card and boot into SD card. Go to home directory and you should see flash.bin file.

Write <boot file> to the on-module eMMC flash. (The eMMC flash is emulated as /dev/mmcblk0 in SMARC-iMX8MM)

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Install uEnv.txt based bootscript

Create “uEnv.txt” boot script: ($ vim uEnv.txt)

Copy uEnv.txt to the boot partition:

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Install Linux Kernel Image

Copy Image to the boot partition:

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Install Linux Kernel Device Tree Binary

All available DTB binary files are listed in the table below.

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Install Root Filesystem

Extract the Yocto built root filesystem to your SD card

Remove SD card:

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Setup SD Card Automatically

This section tells you how to set up an SD card automatically. It mainly uses a script to do all the steps in the above section.

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Shunt cross TEST# pin to ground and set the BOOT_SEL to ON OFF OFF. The module will boot up from SD card.  

Feed Packages

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You need to setup Apache2 web server on your development host machine first.

The Apache server default web page directory is /var/www/html .We need to populate it with a link pointing to our deb package repository.

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$ sudo ln -s /path/to/build-yocto/tmp/deploy/deb /var/www/html/deb

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The following procedure can be used on a Embedian SMARC-iMX8MM device to download and utilize the feed file show above to install the tcpdump terminal emulation program:

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# vim /etc/apt/sources.list.d/yocto.list

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Only keep the following four lines.

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deb https://<ip address>/all ./

deb http://<ip address>/armv8a ./

deb http://<ip address>/armv8a-mx8mm ./

deb http://<ip address>/smarcimx8mm4g ./

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# apt-get update

# apt-get upgrade

# apt-get install tcpdump

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Writing Bitbake Recipes

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In order to package your application and include it in the root filesystem image, you must write a BitBake recipe for it.

When starting from scratch, it is easiest to learn by example from existing recipes. 

Example HelloWorld recipe using autotools

For software that uses autotools (./configure; make; make install), writing recipes can be very simple:

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DESCRIPTION = "Hello World Recipe using autotools"
HOMEPAGE = "http://www.embedian.com/"
SECTION = "console/utils"
PRIORITY = "optional"
LICENSE = "GPL"
PR = "r0"
  
SRC_URI = "git://github.com/embedian/helloworld-autotools.git;protocol=https"
S = "${WORKDIR}/git"
  
inherit autotools

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SRC_URI specifies the location to download the source from. It can take the form of any standard URL using http://, ftp://, etc. It can also fetch from SCM systems, such as git in the example above.

PR is the package revision variable. Any time a recipe is updated that should require the package to be rebuilt, this variable should be incremented.

inherit autotools brings in support for the package to be built using autotools, and thus no other instructions on how to compile and install the software are needed unless something needs to be customized.

S is the source directory variable. This specifies where the source code will exist after it is fetched from SRC_URI and unpacked. The default value is ${WORKDIR}/${PN}-${PV}, where PN is the package name and PV is the package version. Both PN and PV are set by default using the filename of the recipe, where the filename has the format PN_PV.bb.

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Example HelloWorld recipe using a single source file

This example shows a simple case of building a helloworld.c file directly using the default compiler (gcc). Since it isn’t using autotools or make, we have to tell BitBake how to build it explicitly.

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DESCRIPTION = "HelloWorld"
SECTION = "examples"
LICENSE = "GPL"
  
SRC_URI = "file://helloworld.c"
  
S = "${WORKDIR}"
  
do_compile() {
    ${CC} ${CFLAGS} ${LDFLAGS} helloworld.c -o helloworld
}
  
do_install() {
    install -d ${D}${bindir}
    install -m 0755 helloworld ${D}${bindir}
}

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In this case, SRC_URI specifies a file that must exist locally with the recipe. Since there is no code to download and unpack, we set S to WORKDIR since that is where helloworld.c will be copied to before it is built.

WORKDIR is located at ${OETREE}/<build directory>/tmp/work/armv8a-poky-linux/<package name and version> for most packages. If the package is machine-specific (rather than generic for the armv8a architecture), it may be located in the smarcimx8mm4g-poky-linux subdirectory depending on your hardware (this applies to kernel packages, images, etc).

do_compile defines how to compile the source. In this case, we just call gcc directly. If it isn’t defined, do_compile runs make in the source directory by default.

do_install defines how to install the application. This example runs install to create a bin directory where the application will be copied to and then copies the application there with permissions set to 755.

D is the destination directory where the application is installed to before it is packaged.

${bindir} is the directory where most binary applications are installed, typically /usr/bin.

For a more in-depth explanation of BitBake recipes, syntax, and variables, see the Recipe Chapter of the OpenEmbedded User Manual.

Setup eMMC Manually

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Setting up eMMC usually is the last step at development stage after the development work is done at your SD card or NFS environments. From software point of view, eMMC is nothing but a non-removable SD card on board. For SMARC-iMX8MM, the SD card is always emulated as /dev/mmcblk1 and on-module eMMC is always emulated as /dev/mmcblk0. Setting up eMMC now is nothing but changing the device descriptor. 

This section gives a step-by-step procedure to setup eMMC flash. Users can write a shell script your own at production to simplify the steps.

First, we need to backup the final firmware from your SD card or NFS.

Prepare for eMMC binaries from SD card (or NFS):

Insert SD card into your Linux PC. For these instructions, we are assuming: DISK=/dev/mmcblk0, “lsblk” is very useful for determining the device id.

For these instruction, we are assuming: DISK=/dev/mmcblk0, “lsblk” is very useful for determining the device id.

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Mount Partitions:

On some systems, these partitions may be auto-mounted…

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for: DISK=/dev/mmcblk0

for: DISK=/dev/sdX

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Copy Image to rootfs partition

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Copy uEnv.txt to rootfs partition

Copy and paste the following contents to /media/rootfs/home/root ($ sudo vim /media/rootfs/home/root/uEnv.txt)

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Copy device tree binary to rootfs partition

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Copy boot file to rootfs partition

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Copy final root file system to rootfs partition

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Remove SD card:

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Copy Binaries to eMMC from SD card

Insert this SD card into your SMARC-iMX8MM device.

Now it will be almost the same as you did when setup your SD card, but the eMMC device descriptor is /dev/mmcblk0 now. Booting up the device from SD card (shunt cross TEST#).

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Erase eMMC:

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Create Partition Layout:

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Format Partitions:

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Mount Partitions:

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Copy binaries to boot partition

Copy uEnv.txt/Image/*.dtb to the boot partition

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Copy Linux kernel device tree binary

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Copy root file system to rootfs partition

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Unmount eMMC:

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Write boot file to eMMC

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Switch your Boot Select to eMMC (OFF ON ON) and you will be able to boot up from eMMC now.

Setup eMMC Automatically

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Boot up the module from SD card and run the following script. The Yocto images will be written into on-module eMMC.

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version 1.0a, 10/28/2024

Last updated 2024-10-28