• Install Raspbian Lite. We currently use Debian 10 (Buster).

• Change password by using

  passwd pi

• Activate SSH

  sudo systemctl enable ssh
  sudo systemctl start ssh

• Install and configure NTP

• Install tmux

   sudo apt install tmux

• "Install" the RTI Connext libraries under /usr/local/lib/ by copying the arm-folder from the Main PC under opt/rti_connext_dds-6.0.0/lib/armv6vfphLinux3.xgcc4.7.2/. This can of course only be done after the ARM libraries have been installed on the Main Computer. 

It should look like this afterward:

pi@raspberrypi-06:~ $ find /usr/local/lib/rti_connext_dds-6.0.0/armv6vfphLinux3.xgcc4.7.2/
/usr/local/lib/rti_connext_dds-6.0.0/armv6vfphLinux3.xgcc4.7.2/
/usr/local/lib/rti_connext_dds-6.0.0/armv6vfphLinux3.xgcc4.7.2/libnddscppd.so
/usr/local/lib/rti_connext_dds-6.0.0/armv6vfphLinux3.xgcc4.7.2/libnddscd.so
/usr/local/lib/rti_connext_dds-6.0.0/armv6vfphLinux3.xgcc4.7.2/libnddstransporttcpzd.a
/usr/local/lib/rti_connext_dds-6.0.0/armv6vfphLinux3.xgcc4.7.2/libnddscpp2z.a
/usr/local/lib/rti_connext_dds-6.0.0/armv6vfphLinux3.xgcc4.7.2/librtidlcppz.a
/usr/local/lib/rti_connext_dds-6.0.0/armv6vfphLinux3.xgcc4.7.2/librtimonitoringd.so
/usr/local/lib/rti_connext_dds-6.0.0/armv6vfphLinux3.xgcc4.7.2/libnddstransporttcp.so
/usr/local/lib/rti_connext_dds-6.0.0/armv6vfphLinux3.xgcc4.7.2/libnddscpp2.so
/usr/local/lib/rti_connext_dds-6.0.0/armv6vfphLinux3.xgcc4.7.2/libnddscpp2d.so
/usr/local/lib/rti_connext_dds-6.0.0/armv6vfphLinux3.xgcc4.7.2/librtimonitoringz.a
/usr/local/lib/rti_connext_dds-6.0.0/armv6vfphLinux3.xgcc4.7.2/libnddstransporttcpd.so
/usr/local/lib/rti_connext_dds-6.0.0/armv6vfphLinux3.xgcc4.7.2/libnddscz.a
/usr/local/lib/rti_connext_dds-6.0.0/armv6vfphLinux3.xgcc4.7.2/libnddscppzd.a
/usr/local/lib/rti_connext_dds-6.0.0/armv6vfphLinux3.xgcc4.7.2/libnddsc.so
/usr/local/lib/rti_connext_dds-6.0.0/armv6vfphLinux3.xgcc4.7.2/libnddstransporttcpz.a
/usr/local/lib/rti_connext_dds-6.0.0/armv6vfphLinux3.xgcc4.7.2/librtidlcpp.so
/usr/local/lib/rti_connext_dds-6.0.0/armv6vfphLinux3.xgcc4.7.2/libnddscpp.so
/usr/local/lib/rti_connext_dds-6.0.0/armv6vfphLinux3.xgcc4.7.2/libnddscore.so
/usr/local/lib/rti_connext_dds-6.0.0/armv6vfphLinux3.xgcc4.7.2/librtimonitoringzd.a
/usr/local/lib/rti_connext_dds-6.0.0/armv6vfphLinux3.xgcc4.7.2/libnddscorez.a
/usr/local/lib/rti_connext_dds-6.0.0/armv6vfphLinux3.xgcc4.7.2/libnddscppz.a
/usr/local/lib/rti_connext_dds-6.0.0/armv6vfphLinux3.xgcc4.7.2/libnddscored.so
/usr/local/lib/rti_connext_dds-6.0.0/armv6vfphLinux3.xgcc4.7.2/librtidlcppd.so
/usr/local/lib/rti_connext_dds-6.0.0/armv6vfphLinux3.xgcc4.7.2/libnddsjava.so
/usr/local/lib/rti_connext_dds-6.0.0/armv6vfphLinux3.xgcc4.7.2/libnddscpp2zd.a
/usr/local/lib/rti_connext_dds-6.0.0/armv6vfphLinux3.xgcc4.7.2/libnddsczd.a
/usr/local/lib/rti_connext_dds-6.0.0/armv6vfphLinux3.xgcc4.7.2/libnddscorezd.a
/usr/local/lib/rti_connext_dds-6.0.0/armv6vfphLinux3.xgcc4.7.2/libnddsjavad.so
/usr/local/lib/rti_connext_dds-6.0.0/armv6vfphLinux3.xgcc4.7.2/librtimonitoring.so
/usr/local/lib/rti_connext_dds-6.0.0/armv6vfphLinux3.xgcc4.7.2/librtidlcz.a
/usr/local/lib/rti_connext_dds-6.0.0/armv6vfphLinux3.xgcc4.7.2/librtidlcppzd.a
/usr/local/lib/rti_connext_dds-6.0.0/armv6vfphLinux3.xgcc4.7.2/librtidlc.so
/usr/local/lib/rti_connext_dds-6.0.0/armv6vfphLinux3.xgcc4.7.2/librtidlcd.so
/usr/local/lib/rti_connext_dds-6.0.0/armv6vfphLinux3.xgcc4.7.2/librtidlczd.a

'Register' the Libraries

Make the libraries available. Insert /usr/local/lib/rti_connext_dds-6.0.0/armv6vfphLinux3.xgcc4.7.2 into /etc/ld.so.conf. Then run

sudo ldconfig

Configure Bootup Behaviour

Copy the file git:software/vehicle_raspberry_firmware/bootloader_raspberry.bash to /root/bootloader_raspberry.bash on the Raspberry.

Enable autostart, using sudo nano /etc/rc.local and insert

tmux new-session -d -s "bootloader_raspberry" "bash /root/bootloader_raspberry.bash"

NTP configuration

See the NUC NTP-Configuration.

ID-Related Settings

Edit the /etc/hostname file to give the Raspberry a unique name. The name should correspond to the vehicle ID, for example raspberrypi-06 or raspberrypi-42.

Create a DHCP reservation for the Raspberry on the router. The vehicle ID is derived from the IP. The IP is 192.168.1.1XX where XX are the digits of the vehicle ID.

Read-Only Filesystem

One crucial aspect regarding the Raspberry Pi is, that the vehicle will be turned off by using the switch on the bottom, mostly. That will directly cut off the power supply of the RPI. In order to avoid damage to the OS, it is important to configure the filesystem to be read-only. For that, follow the instructions on https://kofler.info/raspbian-lite-fuer-den-read-only-betrieb/ . (As alternative https://www.mehr4u.de/raspberry-pi-mit-readonly-filesystem.html may also be used. Vehicle 20 is created by following the first link but using fastboot noswap ro instead of fastboot noswap.)

In order to make NTP working properly with a read-only filesystem, it is also necessary to copy the following file

cp /lib/systemd/system/ntp.service /etc/systemd/system/ntp.service

and to comment out PrivateTmp=true in

/etc/systemd/system/ntp.service

sudo mount -o remount,rw /
sudo mount -o remount,rw /boot

Applying RT-Patch

Because the vehicle needs to be real-time capable, a real-time patch (RT-Patch) should be applied to the underlying Linux Kernel.

Follow these instructions to build the kernel. It is recommended to use the section Cross-Compiling instead of Local Building to speed up the process (e.g. ~15 minutes vs. ~2 hours). Additionally, there has to be done several annotations:

• Get Sources: 
  • Make sure that there exists a real-time patch for the current kernel version. You can see this version by looking at the first lines of the makefile residing in the cloned directory, e.g., by using
    head Makefile -n 4
    The currently existing real-time patches can be found here.
• Before Build sources
  • Download the RT-Patch matching your kernel version and patch the kernel according to these instructions. (Execute the patch-command in the root directory of the cloned git repository.)
• Build sources
  
  • Run the commands which depend on the RPi version.
  • Run make menuconfig, navigate to General Setup > Preemption Model, choose Fully Preemptible Kernel (RT) and save.
  • Run the lastly given make command.
    • Make sure to use the parameter -j n to configure how many threads are used for this command in order to speed up this process as explained.
    • It might happen that you are asked to set up the .config file again which you already configured in the last step. (The console will show something like *Restart config... and asks you questions.) Then press strg+c and replace the command by
      make ARCH=arm menuconfig CROSS_COMPILE=arm-linux-gnueabihf- zImage modules dtbs
      Now, the menu will open again, but you can quit that by only ?saving? and leaving the menu. Afterwards, the process should start building as usual.

Troubleshooting

It might happen that the system clock is not automatically synchronizing via NTP if it differs too much from the real-time. Firstly, take care that your timezone is set correctly:

sudo raspi-config

In the opening UI go to: 4 Localisation Options → I2 Change Time Zone → None of the above → UTC

Furthermore, you can force NTP to set the time once. Therefore, stop the service, force it, and restart it again :

sudo /etc/init.d/ntp stop
sudo ntpd -qg
sudo /etc/init.d/ntp start

Afterwards, NTP should synchronize automatically.

Repeating the process for several vehicles

In order to create identical vehicles it might be useful to clone the SD-cards by using Clonezilla. Afterwards, only the ID-Related Settings have to be adapted at the cloned SD-card.

Cross Compilation and Software Distribution

The vehicle Raspberry software is cross-compiled from the master PC. The build script git:software/vehicle_raspberry_firmware/build.bash creates an archive of the compiled software and other required files and publishes it via Apache. The bootloader_raspberry.bash autostart script on the Raspberry downloads and runs this software.

ARP Table Generation

Because unsuccessful ARP requests sometimes block communication a static ARP table is sometimes useful. To generate one one needs to switch on all participants, ping each one from the main PC and then output the arp table on the main pc with e.g. https://man7.org/linux/man-pages/man8/ip-neighbour.8.html (newer) or arp -a (old).
The info can then be used to feed a script that sets up the arp entries statically for the participants. Currently this is done in https://git.rwth-aachen.de/CPM/Project/Lab/software/-/blob/feature/fastdds/mid_level_controller/package/start.bash and the static arp table is part of the package.