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Compiling Linux Kernel 4.19.x LTS for Arietta

This article illustrates how to generate a bootable Linux Kernel image for Arietta SOM

Step-by-step Kernel cross-compilation procedure:

This article has been tested on a Linux Ubuntu 18.04.4 PC Intel/64bit and on a Raspberry Pi 4 Raspbian Buster Lite,

Ubuntu

Install these packages

Raspberry Pi

The toolchain (gcc, g++, etc) required to compile the Linux Kernel is already installed by default on Raspbian Buster. Install just these few packages:
        sudo apt update
        sudo apt install bc bison libssl-dev
        
It is possible to use the Raspberry Pi native gcc compiler so remove: CROSS_COMPILE=arm-linux-gnueabi- from the command provided below

Open this web page https://www.kernel.org and check which is the latest Linux Kernel 4.19.x version available. In this article we will use the version 4.19.131. Change the last version number (127) with the version you found.

Open a terminal on your Linux PC and download the Linux Kernel sources from the main stream repository:

wget https://www.kernel.org/pub/linux/kernel/v4.x/linux-4.19.131.tar.xz

Extract the Kernel sources from the compressed file by typing:

tar xvfJ linux-4.19.131.tar.xz

Move inside the new folder:

cd linux-4.19.131

Create a your own personal branch of Linux Kernel sources using git to keep a trace of any changes from the Kernel mainline.

Install git on your PC:

sudo apt update
sudo apt install git

Create a local git repository and a new branch called "acme":

git init; git add .; git commit -m "Linux vanilla"; git branch acme; git checkout acme

Download the Acme Systems patch for this Kernel version. It add just the Acme boards defconfig, device trees and small fewbug fixes (don't change the version number in this case):

wget https://raw.githubusercontent.com/AcmeSystems/acmepatches/master/linux-4.19.x.patch

and apply it by typing:

patch -p1 < linux-4.19.x.patch

Then select from the following list the right Linux configuration for your board by typing one of these commands:

Arietta alone:
    make ARCH=arm CROSS_COMPILE=arm-linux-gnueabi- acme-arietta_defconfig

Arietta + XTERM-01:
    make ARCH=arm CROSS_COMPILE=arm-linux-gnueabi- acme-xterm-01_defconfig

Customize the default Linux Kernel configuration:

If you need to customize the Kernel configuration or you just want to take a look around the Kernel setup type:

make ARCH=arm menuconfig

and navigate inside the Kernel configuration using the arrow keys and following the help provided by the menuconfig interface.

Create a defconfig of your own Kernel configuration

make ARCH=arm savedefconfig

The file defconfig contains your configuration. You could rename and copy it in arch/arm/configs/

cp defconfig arch/arm/configs/my_defconfig

Generate the Device Tree Blob file (.dtb)

Now compile the device tree file requested by your board by selecting one of the following commands:

Arietta alone:
    make ARCH=arm CROSS_COMPILE=arm-linux-gnueabi- acme-arietta.dtb

Arietta + XTERM-01:
    make ARCH=arm CROSS_COMPILE=arm-linux-gnueabi- acme-xterm-01.dtb

Compile the Kernel image

Compile the Linux Kernel sources and generate the binary compressed image file to save in the first partition of microSD card.

make -j8 ARCH=arm CROSS_COMPILE=arm-linux-gnueabi- zImage
...
Image arch/arm/boot/zImage is ready

Compile the Kernel modules

The image generated contains the Linux Kernel and all the built-in device drivers (option [*] in menuconfig) compiled with it.

Al the drivers compiled as external modules (option [M] in menuconfig) need to be compiled and saved in the rootfs /lib directory on the second partition of the microSD. We didn't use any [M] flag in our defconfig so this procedure is not requested but. in case you add something. these are the commands to use to compile them:

make modules -j8 ARCH=arm CROSS_COMPILE=arm-linux-gnueabi-
make modules_install INSTALL_MOD_PATH=./modules ARCH=arm

Copy the boot files into the first microSD partition

Insert a formatted microSD with the boot loader (at91bootstrap) and the rootfs contents already created in your Linux PC and copy on it these files:

Write the Linux Kernel image and the device tree blob in the first microSD partition:

sudo cp arch/arm/boot/zImage /media/$USER/boot

Arietta alone:
    sudo cp arch/arm/boot/dts/acme-arietta.dtb /media/$USER/boot/acme-arietta.dtb

Arietta + XTERM-01:
    sudo cp arch/arm/boot/dts/acme-xterm-01.dtb /media/$USER/boot/acme-arietta.dtb

Write the Linux Kernel modules inside the second microSD partition:

sudo rsync -avc modules/lib/. /media/$USER/rootfs/lib/.

After the first boot

At the first access to the board command line update the module dependencies by typing this command:

depmod -a

Links

Usefull command

If you want to create a patch with the changes you have made on the vanilla Linux kernel use these commands:

git checkout acme
git diff master > acme.patch

To revert a patch applied type:

patch -p1 -R < ../acme.patch

Technical documentation Buy on-line

Bruna Mandolino