This project showcases building three simple applications for the raspberry pi, cross-compiling them using cmake:

• write-file prints a short message to the console and to a file. This is the simplest example, with no dependencies.
• hello-asound prints the version of alsa on the system. The example demonstrates linking to a library installed on the system.
• hello-portaudio tries to initialize portaudio. Another example of linking to a library, the difference this one is installed to /usr/lib.

Cross compilation has been tested on a linux machine as the host, and a Raspberry Pi 2 model B with Raspbian Stretch Lite as the target.

Howto:

1. Grab the compilers from https://github.com/raspberrypi/tools and put them somewhere on the host machine
2. Install the needed dependencies on the rpi: apt install libasound-dev libportaudio-dev
3. Mount the rpi filesystem locally on the host machine with sshfs (the cross-compilers will then be able to look for the dependencies in the mounted directory)
4. Provide the locations for the rpi-tools (see point 1) and the target sysroot (see point 3) to the rpi-toolchain.cmake script, by creating a toolchain-locations.cmake script with the definitions of the needed variables (see toolchain-locations-example.cmake for an example). Remember to never add toolchain-locations.cmake to version control.
5. Run cmake, providing the toolchain file, eg: mkdir build, then cd build and cmake ../ -DCMAKE_TOOLCHAIN_FILE=../rpi-toolchain.cmake
6. If the cmake step succeded, build the applications with make (you can also compile only one of the applications, eg: make write-file).
7. Copy the compiled executables to the mounted rpi filesystem, for example in the pi user home dir.
8. Open an ssh console session and launch the executable on the rpi.

Notes:

• The setup/deployment process can be automated, and one nice way is using Qt-creator, which works well with cmake and can define kits for cross compilation and deployment to a remote device.
• You can even build these examples on the rpi itself, you will of course need to install the dependencies but you won't otherwise need to provide a cmake toolchain file.