A Clean Architecture-based, nearly pure C project for real-time robotics applications on Raspberry Pi.

The goal of this project is to demonstrate that real-time control with high precision (e.g., on the order of several microseconds), typically considered infeasible on a general-purpose operating system, is in fact achievable.

• Raspberry Pi 3 B+ with Ubuntu Server 22.04 LTS installed.
  • Other versions of Raspberry Pi or OS may work but have not been tested.
• SSH access configured with a key file.
  • Required for automated uploading of code.
• CMake installed on the Raspberry Pi.

Edit the /boot/firmware/cmdline.txt file to include the following settings:

console=serial0,115200 multipath=off dwc_otg.lpm_enable=0 console=tty1 root=LABEL=writable rootfstype=ext4 rootwait fixrtc isolcpus=2,3 quiet loglevel=5 logo.nologo

The most critical setting is isolcpus=2,3, which isolates CPU cores for the application—this is essential for real-time performance. quiet loglevel=5 logo.nologo is optional, but recommended to reduce boot time.

Simply run the upload script. This script performs the following actions:

1. Prompts for target hostname and path if not previously configured
2. Uses rsync to copy files to the target Raspberry Pi, excluding files listed in config/.rsyncignore
3. Executes the installation process on the Raspberry Pi

The installation process:

1. Creates a build directory and compiles the project using CMake
2. Copies the systemd service file to /etc/systemd/system/
3. Reloads the systemd daemon
4. Enables the service to run on startup
5. Restarts the service
6. Syncs the filesystem to ensure changes are written

You can also:

• Use ./upload reset to clean the target directory before uploading

The following is a recommended /etc/ssh/sshd_config configuration for faster SSH access:

Include /etc/ssh/sshd_config.d/*.conf
PubkeyAuthentication yes
PasswordAuthentication no
KbdInteractiveAuthentication no
GSSAPIAuthentication no
UsePAM no
X11Forwarding no
PrintMotd no
UseDNS no
AcceptEnv LANG LC_*

Warning: This configuration disables password authentication. If you are using password authentication, make sure to generate a key pair and add the public key to the Raspberry Pi's ~/.ssh/authorized_keys file.

The following system configurations are recommended to reduce boot time.

Disable the following services:

sudo systemctl disable snapd                                # Disable snapd
sudo systemctl mask snapd
sudo systemctl disable systemd-networkd-wait-online.service # Skip network wait
sudo systemctl mask systemd-networkd-wait-online.service
sudo touch /etc/cloud/cloud-init.disabled                   # Disable cloud-init
sudo systemctl disable snap.lxd.activate.service            # Disable LXD
sudo systemctl disable hciuart.service                      # Disable Bluetooth

Edit the /boot/firmware/config.txt file with the following content:

[all]
kernel=vmlinuz
cmdline=cmdline.txt
initramfs initrd.img followkernel
disable_splash=1  # Disable the splash screen
boot_delay=0      # Eliminate boot delay

[pi4]
max_framebuffers=2
arm_boost=1

[all]
dtparam=audio=on
dtparam=i2c_arm=on
dtparam=spi=on
disable_overscan=1
hdmi_drive=2
enable_uart=1
camera_auto_detect=1
display_auto_detect=1
arm_64bit=1
dtoverlay=dwc2

[cm4]
dtoverlay=dwc2,dr_mode=host

[all]

Before optimization, the boot time was approximately 2 minutes and 7 seconds:

$ systemd-analyze
Startup finished in 10.991s (kernel) + 1min 56.018s (userspace) = 2min 7.009s
graphical.target reached after 1min 52.216s in userspace

After optimization, the boot time was reduced to approximately 22 seconds:

Startup finished in 9.801s (kernel) + 12.304s (userspace) = 22.105s
graphical.target reached after 12.237s in userspace

• BCM2835 ARM Peripherals
• AXI Monitor
• SPI Register Control