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Cross-compiling for Charge SOM

Another way to integrate custom applications into the firmware image is to cross-compile the application for Charge SOM and include it in the image. A pre-requisite for this is to have the latest firmware image as a developer build. Always keep in mind, if you want to build a new EVerest module it must be compatible to the EVerest release within the firmware. Please have a look at the official EVerest documentation, how to checkout a dedicated EVerest release.

  1. On an Ubuntu or Debian-based Linux distribution, install the cross-compilers for Charge SOM.

    sudo apt install build-essential libc6-arm64-cross gcc-aarch64-linux-gnu binutils-arm-linux-gnueabihf gcc-arm-linux-gnueabihf g++-arm-linux-gnueabihf

  2. Download chargebyte's digital certificate and use it to extract the root filesystem from the firmware image. The digital certificate is the same between Charge SOM and Charge Control C.

    rauc extract --keyring=<chargebyte_certificate>.crt <shipped_firmware>.image bundle-staging

    Note

    Alternatively, if the above command does not work, you can use the following command:
    unsquashfs -d bundle-staging <shipped_firmware>.image

    But this will not verify the signature of the firmware image.

  3. Mount the ext4 root filesystem image as a loop device.

    sudo mkdir -p /mnt/rootfs
sudo mount bundle-staging/core-image-minimal-chargesom.ext4 /mnt/rootfs

  4. Create a new directory in the folder where the new module was created (my-module) and create a new file called toolchain.cmake. This file is used to set the toolchain for the cross-compilation.

    cd my-module
mkdir toolchain
cd toolchain
touch toolchain.cmake

  5. Store the following lines in the toolchain.cmake file:

    .. literalinclude:: ../../includes/_static/files/toolchain.cmake

  6. Create a new build directory in "my-module" and navigate to it.

    mkdir build
cd build

  7. Run the following command inside to configure the build.

    cmake -DCMAKE_TOOLCHAIN_FILE=../toolchain/toolchain.cmake -DCMAKE_SYSROOT=/mnt/rootfs ..

  8. When this ends successfully, start cross-compiling using make:

    make install -j$(nproc)

  9. Test that the resulting binaries are compiled for Charge SOM as a target:

    file dist/libexec/everest/modules/MyModule/MyModule

    The output should be something like:

    dist/libexec/everest/modules/MyModule/MyModule: ELF 64-bit LSB pie executable, ARM aarch64, version 1 (SYSV),
dynamically linked, interpreter /lib/ld-linux-aarch64.so.1, BuildID[sha1]=ad2342fdd3b8fb1949fc3e13b77382d3da72f28a, for GNU/Linux 3.7.0, stripped

  10. The resulting binary and manifest file can be copied to the previously mounted root filesystem.

    cp dist/libexec/everest/modules/MyModule /mnt/rootfs/usr/libexec/everest/modules/

  11. umount the loop device.

    sudo umount /mnt/rootfs

  12. Make sure that the customized filesystem is in a clean state.

    fsck.ext4 -f bundle-staging/core-image-minimal-chargesom.ext4

  13. Follow the steps under the section :ref:`firmware_customization` to install your PKI certificate, pack the modified root filesystem image again into the firmware update image, and test the new firmware image.