A Linux PC in required to cross compile the Kernel image.
This procedure has been tested on:
Using an Intel PC is required to install these packages
Here we will illustrate how to compile the source available on the Microchip website site and repository:
Open a terminal on your Linux PC and download the Linux Kernel sources from the main stream repository:
Extract the Kernel sources from the compressed file by typing:
Move inside the new folder:
Create with git a new branch of Linux Kernel sources called acme 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 the new branch acme:
git init; git add .; git commit -m "linux-5.4-at91"; 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):
and apply it by typing:
patch -p1 < linux-4.19.x.patch
Set the defconfig:
make ARCH=arm CROSS_COMPILE=arm-linux-gnueabi- acme-acqua_defconfig
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.
make ARCH=arm savedefconfig
defconfig contains your configuration. You could rename and copy it in
cp defconfig arch/arm/configs/my_defconfig
Now compile the device tree file requested by your board by selecting one of the following commands:
make ARCH=arm CROSS_COMPILE=arm-linux-gnueabi- acme-acqua.dtb
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
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
Write the Linux Kernel image and the device tree blob in the first microSD partition:
sudo cp arch/arm/boot/zImage /media/$USER/boot sudo cp arch/arm/boot/dts/acme-acqua.dtb /media/$USER/boot/at91-sama5d3_acqua.dtb
Write the Linux Kernel modules inside the second microSD partition:
sudo rsync -avc modules/lib/. /media/$USER/rootfs/lib/.
At the first access to the board command line update the module dependencies by typing this 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