C++: Building

C++: Building#

The supplied project is built with CMake. A configured build directory ships with the device, so in normal use you edit one file and run make.

The standard workflow#

Edit ~/Desktop/synergy_cpp/main.cpp. This is the file the build compiles into the program.
Build from the build directory:
```
cd ~/Desktop/synergy_cpp/build
make
```
Run the result:
```
sudo ./program
```

The executable is written to the same build directory. Rebuilds take a few seconds because only the changed file is recompiled.

Why sudo

The supplied main.cpp includes the RGB indicator library, which requires root privileges. If your program does not drive the indicator, remove that include and run the executable without sudo. Backplane access alone does not need elevated privileges.

Starting from an example#

The examples under ~/Desktop/synergy_cpp/examples/ are complete programs. To run one, copy its contents into main.cpp and rebuild:

cd ~/Desktop/synergy_cpp
cp examples/Basic/PrintModules/PrintModules.cpp main.cpp
cd build
make
sudo ./program

Keep a copy of your own main.cpp before overwriting it.

Adding your own source files#

For anything larger than a single file, add your sources to the executable in ~/Desktop/synergy_cpp/CMakeLists.txt:

add_executable(program main.cpp src/control.cpp src/alarms.cpp)

Then reconfigure and build:

cd ~/Desktop/synergy_cpp/build
cmake ..
make

cmake .. is only needed after changing CMakeLists.txt. Ordinary edits to existing source files need make alone.

Building without CMake#

The library is small enough to compile directly, which is useful if you keep your program outside the supplied project:

LIB=~/Desktop/synergy_cpp/lib/synergy
g++ -std=c++17 -O2 -I $LIB $LIB/Synergy.cpp $LIB/RPi.cpp myprogram.cpp -o myprogram

Three translation units, one include path, and no linker flags. The library uses only kernel headers and the standard library.

This form does not include the RGB indicator library. Add lib/rpi_ws281x to the include path and link libws2811.a if you need it.

Recommended compiler flags#

Flag	Purpose
`-std=c++17`	The library and examples assume a modern standard
`-O2`	Optimise, which is worthwhile in a control loop
`-Wall -Wextra`	Report the mistakes that otherwise become field faults
`-g`	Debug symbols, for use with `gdb`

Common build errors#

Synergy.h: No such file or directory : The include path does not point at the directory containing the headers.

undefined reference to 'Synergy::init()' : You compiled against the header without compiling the implementation. Both Synergy.cpp and RPi.cpp must be in the source list.

Permission denied when running : Not a build problem. See Getting Started with C++.

Debugging#

Build with debug symbols and no optimisation when stepping through code:

LIB=~/Desktop/synergy_cpp/lib/synergy
g++ -std=c++17 -g -O0 -I $LIB $LIB/Synergy.cpp $LIB/RPi.cpp myprogram.cpp -o myprogram
gdb ./myprogram

Stop the PLC before running under a debugger. Note that a breakpoint holds the SPI bus mid-transaction for as long as execution is paused, which can trigger the base controller’s own timeouts.

Next#

C++: Examples, for complete programs.