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Add Packages and Services on eLxr

The Modalix image is built on eLxr, a Debian-derived distribution. You add software to a board the Debian way: as packages that you install with apt. This page shows how to install a package, how to package your own service, and what a firmware update does to your changes.

Not yet validated on hardware

This page is written from the public SiMa.ai repositories. The example package was built and installed in a Debian container. The steps have not been run on a board as they are written here.

Install a Package​

  1. Connect the board to a network that reaches the package repositories.

  2. Update the package lists:

    sima@modalix:~$ sudo apt update

  3. Install the package. For example, to install the I2C tools:

    sima@modalix:~$ sudo apt install i2c-tools

SiMa.ai delivers its own software to the board as Debian packages. To list the SiMa.ai packages on a board:

sima@modalix:~$ dpkg -l | grep simaai

Package Your Own Service​

To run your own program as a service, build a Debian package for it. The package installs the files, and its post-installation script enables the service. This example packages a program named my-app.

  1. On your build host, create this directory tree. Put your program in usr/bin/my-app. It must run on the board, so build it for arm64. See Build the BSP from Source for the build container.

    my-app/
    ├── DEBIAN/
    │   ├── control
    │   └── postinst
    ├── lib/systemd/system/my-app.service
    └── usr/bin/my-app

  2. Write DEBIAN/control. Depends lists the packages that your program needs:

    Package: my-app
    Version: 1.0.0
    Section: utils
    Priority: optional
    Architecture: arm64
    Depends: python3
    Maintainer: Your Name <you@example.com>
    Description: Example service for a Modalix board

  3. Write the unit file, lib/systemd/system/my-app.service:

    [Unit]
    Description=My application
    After=network.target

    [Service]
    Type=simple
    ExecStart=/usr/bin/my-app
    Restart=on-failure
    RestartSec=5

    [Install]
    WantedBy=multi-user.target

  4. Write DEBIAN/postinst. It enables and starts the service when the package is installed:

    #!/bin/sh
    set -e
    if [ -d /run/systemd/system ]; then
        systemctl daemon-reload
        systemctl enable my-app.service
        systemctl restart my-app.service
    fi

  5. Make the script and the program executable, and build the package:

    sima-user@sima-user-machine:~$ chmod 0755 my-app/DEBIAN/postinst my-app/usr/bin/my-app
    sima-user@sima-user-machine:~$ dpkg-deb --root-owner-group --build my-app my-app_1.0.0_arm64.deb

  6. Copy the package to the board and install it. apt also installs the packages that it depends on:

    sima-user@sima-user-machine:~$ scp my-app_1.0.0_arm64.deb sima@<board-ip>:/tmp/
    sima@modalix:~$ sudo apt install /tmp/my-app_1.0.0_arm64.deb

  7. Check that the service runs, and read its log:

    sima@modalix:~$ systemctl status my-app.service
    sima@modalix:~$ journalctl -u my-app.service

For a complete package of this kind, see the MIPI camera utility in the SiMa.ai Insight repository.

What a Firmware Update Does to Your Changes​

sima-cli update works differently in each release line, so your packages are treated differently.

Platform releaseWhat the update doesYour packages and services
2.1Upgrades the SiMa.ai packages in place. It does not write a new image.Not confirmed. Check them after an update.
3.0 and laterWrites a complete root filesystem to the inactive slot, and boots from it.Kept in an overlay on /data, unless the update clears the overlay. If it does, install them again.
  • In release 2.1, the update resets the U-Boot environment. Set dtbos and any other variable that you changed again after the update.
  • Recovering a board, or writing a complete image to it, removes your packages in every release.
  • Keep your .deb files and a list of what you installed, so that you can install them again.
  • In release 3.0 and later, sima-cli update --inspect shows what the overlay holds.

Platform release 3.0 is not released yet. Its behavior is described here from the system update guide of sima-cli, and can change.

Not Covered​

  • Building a complete eLxr image that already contains your packages. See eLxr or Yocto.
  • Publishing your packages in your own package repository.

Next Steps​