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10-ros-remote.md

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Guide to Cross Compilation for a Raspberry Pi

  1. Start
  2. Setup XCS and RPi
  3. Setup RPi Network and SSH
  4. Setup RPi Peripherals
  5. Setup Cross-compile environment
  6. Cross-compile and Install Userland
  7. Cross-compile and Install OpenCV
  8. Cross-compile and Install ROS
  9. Compile and Install OpenCV
  10. Compile and Install ROS
  11. > Remote ROS (RPi node and XCS master)
  12. ROS package development (RPi/XCS)
  13. Compile and Install WiringPi

11. Remote ROS (RPi node and XCS master)

TO BE UPDATED. GUIDE MIGHT STILL WORK.

When all previous steps are followed the setup should currently be able to:

  • (cross) compile aribtrary c(++)-code
  • (cross) compile OpenCV code
  • (cross) compile ROS code
  • Run the native-compiled code in the VM
  • Run the cross-compiled code on the RPi
  • Update and synchronise the RPi
  • Call OpenCV and ROS functions from Python
  • Start/Stop ROS-nodes on both the VM and RPi

The next step is to setup extend the communication functions between the RPi and VM, such that we can run roscore in the VM and connect a node from the RPi.

ROS_MASTER_URI

ROS nodes connect to a master (roscore) via a tcp-connection. This allows a ROS system to have external nodes, hence we should be able to connect the RPi to our VM.

Unfortunally there is a challenge: the VM is configured to be attached to the NAT, therefore it is not visible by any device in the network except the HOST~$. As a result, the RPi is cannot detect the VM and hence cannot connect to the ROS-master (roscore) running in the VM.

The nodes in a ROS system connect to an IP address by communicating with a specific port (by default 11311). When the calls to this port on the HOST~$ are forwarded to our VM and the ROS-master is set to the ip-address of the HOST~$ we can circumvent this problem and have external nodes communicating with the RPi. The setup then becomes:

Overview of setup with ROS

  • HOST has an IP named HOST_IP
  • HOST forwards port 2222 to 22 in the VM (see Installation)
  • HOST forwards port 11311 to 11311 in the VM
  • VM has a (local) IP named VM_IP. This IP is only accessible by the HOST
  • VM runs SSH at port 22
  • VM runs roscore at port 11311.
  • VM runs internal a ROS-node called subscriber which connects to HOST_IP:11311 (and therefore roscore)
  • VM communicated with the natdnsresolver of the host in order to resolve dns-names such as rpizw-hessel.local.
  • RPi has an IP named RPi_IP
  • RPi runs SSH at port 22
  • RPi runs internal a ROS-node called publisher which connects to HOST_IP:11311 (and therefore roscore)
  • HOST and RPi are connected to the same network and are able to connect to each other.

HOST-VM Port forwarding

In a similar manner as the SSH-setting (see Installation), a forward rule in VirtualBox needs to be set. After selecting the VM in VirtualBox:

  1. Machine > Settings > Network > Advanced > Port Forwarding > New Rule
    • Name: ROS_MASTER
    • Protocol: TCP
    • Host IP: (leave empty)
    • Host Port: 11311
    • Guest IP: (leave empty)
    • Guest Port: 11311

Compilation

  1. Compile for VM

    XCS~$ source ~/rpicross_notes/scripts/ros-native
XCS~$ mkdir -p ~/build/ros/chatter
XCS~$ cd ~/build/ros/chatter
XCS~$ cmake ~/rpicross_notes/ros/chatter
XCS~$ make

  2. Compile for RPi

    XCS~$ source ~/rpicross_notes/scripts/ros-cross
XCS~$ mkdir -p ~/ros/chatter_cross
XCS~$ cd ~/ros/chatter_cross
XCS~$ cmake \
    -DCMAKE_TOOLCHAIN_FILE=/home/pi/rpicross_notes/rpi-generic-toolchain.cmake \
    ~/rpicross_notes/ros/chatter
XCS~$ make
XCS~$ ~/rpicross_notes/scripts/sync-ros.sh

Testing

  1. First we need to determine the (external) IP (or hostname) of the HOST~$ on which the VM is active. This is the IP on which the ROS-master will be reachable. When using an unix system, the hostname can be determined by:

    HOST~$ hostname
  Hessels-MacBook-Pro.local

    While the IP of the host can also be used, in different networks different IPs might be active. Using the hostname of the HOST~$ eliminates this potential issue.

  2. Open three terminals in the VM:

    1. Source ROS-files and start roscore

      XCS~$ source ~/rpicross_notes/scripts/ros-native <hostname> <rpiname>
XCS~$ roscore

      The values <hostname> and <rpiname> need to be set in order for the RPi to connect properly to the VM via the HOST. This scripts fetches the IP of <hostname>, updates ROS_MASTER_URI locally, sends the update via ~/ros/rossetup-rpi to <rpiname> and finally sources ROS files on the VM. For my setup the full command is:

      XCS~$ source ~/rpicross_notes/scripts/ros-native Hessels-MacBook-Pro.local rpizero-local

      Note that roscore complains about the IP of ROS_MASTER_URI as it differs from the IP of the VM. More about this in issue #7 .

    2. After starting ROS, start the subscriber-node

      XCS~$ source ~/rpicross_notes/scripts/ros-native <hostname>
XCS~$ rosrun chatter subscriber

      Note that we do not need to update the RPi anymore.

    3. Start publisher on rpi

      XCS~$ ssh rpizero-local
RPI~$ source ~/ros/rossetup-rpi
RPI~$ rosrun chatter publisher

      The contents of ~/ros/rossetup-rpi are created by copying and adapting ~/rpicross_notes/ros/rossetup-rpi in the VM.

  3. When succesfull, you should see:

    1. Publisher (RPi): 
      RPI~$ rosrun chatter publisher
  [ INFO] [1490361500.794854734]: hello world 0
  [ INFO] [1490361500.894476970]: hello world 1
  [ INFO] [1490361500.994248202]: hello world 2
  [ INFO] [1490361501.094246431]: hello world 3
  [ INFO] [1490361501.194246659]: hello world 4
  [ INFO] [1490361501.294338885]: hello world 5
  [ INFO] [1490361501.394404112]: hello world 6
  [ INFO] [1490361501.494347342]: hello world 7
  [ INFO] [1490361501.594348570]: hello world 8
  ...
    2. Subscriber (VM): 
      XCS~$ rosrun chatter subscriber
  [ INFO] [1490361501.387607575]: I heard: [hello world 5]
  [ INFO] [1490361501.486619994]: I heard: [hello world 6]
  [ INFO] [1490361501.588621491]: I heard: [hello world 7]
  [ INFO] [1490361501.688693481]: I heard: [hello world 8]
  ...

    Note that some packages are lost..

Simplify life

It can become quite tedious to constantly source the ros-files. Luckily we can do this by adding the source command to ~/.bashrc. Upon a ssh-call, ~/.bashrc is loaded by the unix OS, hence the ROS binairies will be sourced automatically.

  1. Add source-command to ~/.bashrc in the VM

    XCS~$ nano ~/.bashrc

    Add the following to the bottom of the file

    # Load ROS biniaries and setup ROS_MASTER_URI
source ~/rpicross_notes/scripts/ros-native Hessels-MacBook-Pro.local

  2. Add source-command to ~/.bashrc on the RPi

    XCS~$ ssh rpizero-local
RPI~$ nano ~/.bashrc

    Add the following to the bottom of the file

    # Load ROS biniaries
source ~/ros/rossetup-rpi

So, the steps to execute the example become:

  1. Open three terminals in the VM:

    1. Start ros

      XCS~$ roscore

      If ROS_MASTER_URI has changed, or the RPi has not yet been configured, an initial call before roscore is required:

      XCS~$ source ~/rpicross_notes/scripts/ros-native Hessels-MacBook-Pro.local rpizero-local
XCS~$ roscore

    2. Start subscriber in the second terminal

      XCS~$ rosrun chatter subscriber

    3. Start publisher on RPi

      XCS~$ ssh rpizero-local
RPI~$ rosrun chatter publisher