rpicross_notes

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

13. Compile and Install WiringPi

TO BE UPDATED. GUIDE MIGHT STILL WORK.

Library to control GPIO / PWM on the Raspberry Pi using wiringPi

Steps on this page are derived from http://wiringpi.com/download-and-install/

Required Packages

No additional packages are required

Compilation & Synchronisation

Note: As compilation-process of the library polls several hardware features, the library itself cannot be crosscompiled and needs to be build on the RPi itself.

1. Download code in src dir of rootfs.

    XCS~$ cd ~/rpi/rootfs/usr/src
    XCS~$ git clone git://git.drogon.net/wiringPi
   

2. Copy the PkgConfig .pc file for wiringPi from this repository to rootfs. The upcoming build process does not create it, while it is needed for cmake to build and cross-compile code depending on wiringPi.

    XCS~$ cp ~/rpicross_notes/hello/wiringpi/wiringpi.pc ~/rpi/rootfs/usr/share/pkgconfig/
   

3. Sync rootfs to RPi

    XCS~$ ~/rpicross-notes/scripts/sync—vm-rpi.sh
   

4. Build on RPi

    XCS~$ ssh rpizer-local
    RPI~$ cd /usr/src/wiringPi
    RPI~$ sudo ./build
   

5. Sync updates to VM

    XCS~$ ~/rpicross-notes/scripts/sync-rpi-xcs.sh
   

Testing

Testing the compiled and installed wiringPi libraries with a PWM signal.

Prerequisites:

• Toolchain installed
• Repository initialised
• WiringPi installed and synchronised
• wiringpi.pc installed

Steps:

1. To see a fading LED, you should connect a LED to GPIO18. How to connect the LED is described here.

2. Build the code with the rpi-generic-toolchain

    XCS~$ mkdir -p ~/rpi/build/hello/wiringpi
    XCS~$ cd ~/rpi/build/hello/wiringpi
    XCS~$ cmake \
     -D CMAKE_TOOLCHAIN_FILE=/home/pi/rpicross_notes/rpi-generic-toolchain.cmake \
     ~/rpicross_notes/hello/wiringpi
    XCS~$ make
   

3. Sync and run.

    XCS~$ scp wpi rpizero-local:~/
    XCS~$ ssh -X rpizero-local
    RPI~$ sudo ./wpi
     Raspberry Pi wiringPi PWM test program
     Iteration:  5/ 5 - Brightness:    0/1024
     Done
   

Note application utilising X server.

When an application uses both wiringPi and requires Xserver to run the application, errors might be encountered when using sudo:

...
    X11 connection rejected because of wrong authentication.
...

This error means that the created connection to Xserver does not allow root to setup a window. Presumably, the original connection to the RPi was created by the user pi:

XCS~$ ssh -X pi@rpizero-local

When connecting via SSH as root does not pose a (security) problem, this might solve the problem:

XCS~$ ssh -X root@rpizero-local

Proper solution

Luckily, a simple and more secure solution exists:

XCS~$ ssh -X pi@rpizero-local
RPi~$ su -pc ./flashcam

This will execute the application with root-privileges, while maintaining the current environment variables (and hence the XAUTHORITY settings of the pi user).

Deprecated solution..

A more secure way is to allow root to use the same XAUTHORITY settings as the pi-user:

1. Setup SSH connection and start editing bashrc of root :

    XCS~$ ssh -X pi@rpizero-local
    RPi~$ su - root
    RPi~root$ nano ~/.bashrc
   

2. Add the following line to the file:

    export XAUTHORITY=/home/user/.Xauthority
   

3. Logout

    RPi~root$ exit
   

4. Run application

    RPi~$ su
    RPi~root$ ./flashcam
    RPi~root$ exit
   

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