Creating a library for use with the roboRIO

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Hey all,

I’m creating device drivers to use the pixy2 [1] camera with the roboRIO. Kentridge Robotics ported the Pixy2 Arduino library [2] to make Pixy2JavaAPI [3]. I’ve chosen to use swig [4] to generate Java bindings for the libpixyusb2 [5] library. I have been able to write a Bash script to call swig and gcc to compile libpixyusb2, but I’m having a very difficult time creating a Gradle build system that. Some of its jobs include:

  • Call Swig to generate interface bindings.
  • Compile libpixyusb2 as libpixyusb2_cpp_api, and link it to libusb, producing a .so or a .dll.
  • Compile libpixyusb2_java_app, and include the libpixyusb2_cpp_api shared object inside the JAR.

Thus far, my build system is able to do these things, and run a piece of sample code, but, despite countless hours of research, I have not been able to compile the C portion for the roboRIO, through Gradle.

I have found that WPILib’s own GradleRIO [6] leverages their native-utils [7] libraries. native-utils looks promising, however I have not found any way to successfully use it to invoke arm-frc2019-linux-gnueabi-g++. I have also found Pathfinder V2 [8] to be a good example of a library that is built for roboRIO as well as desktop:

Koopa@CometObservatory MINGW64 ~/Documents/Projects/Java/Robot/Pathfinder (master)
$ ./gradlew tasks
buildDependentsPathfinderjniLinuxathenaDebugSharedLibrary - Build dependents of shared library 'pathfinderjni:linuxathena:debug:sharedLibrary'.
buildDependentsPathfinderjniLinuxathenaDebugStaticLibrary - Build dependents of static library 'pathfinderjni:linuxathena:debug:staticLibrary'.
buildDependentsPathfinderjniLinuxathenaReleaseSharedLibrary - Build dependents of shared library 'pathfinderjni:linuxathena:release:sharedLibrary'.
buildDependentsPathfinderjniLinuxathenaReleaseStaticLibrary - Build dependents of static library 'pathfinderjni:linuxathena:release:staticLibrary'.
buildDependentsPathfinderjniLinuxraspbianDebugSharedLibrary - Build dependents of shared library 'pathfinderjni:linuxraspbian:debug:sharedLibrary'.
buildDependentsPathfinderjniLinuxraspbianDebugStaticLibrary - Build dependents of static library 'pathfinderjni:linuxraspbian:debug:staticLibrary'.
buildDependentsPathfinderjniLinuxraspbianReleaseSharedLibrary - Build dependents of shared library 'pathfinderjni:linuxraspbian:release:sharedLibrary'.
buildDependentsPathfinderjniLinuxraspbianReleaseStaticLibrary - Build dependents of static library 'pathfinderjni:linuxraspbian:release:staticLibrary'.
buildDependentsPathfinderjniWindowsx86-64DebugSharedLibrary - Build dependents of shared library 'pathfinderjni:windowsx86-64:debug:sharedLibrary'.
buildDependentsPathfinderjniWindowsx86-64DebugStaticLibrary - Build dependents of static library 'pathfinderjni:windowsx86-64:debug:staticLibrary'.
buildDependentsPathfinderjniWindowsx86-64ReleaseSharedLibrary - Build dependents of shared library 'pathfinderjni:windowsx86-64:release:sharedLibrary'.
buildDependentsPathfinderjniWindowsx86-64ReleaseStaticLibrary - Build dependents of static library 'pathfinderjni:windowsx86-64:release:staticLibrary'.
buildDependentsPathfinderjniWindowsx86DebugSharedLibrary - Build dependents of shared library 'pathfinderjni:windowsx86:debug:sharedLibrary'.
buildDependentsPathfinderjniWindowsx86DebugStaticLibrary - Build dependents of static library 'pathfinderjni:windowsx86:debug:staticLibrary'.
buildDependentsPathfinderjniWindowsx86ReleaseSharedLibrary - Build dependents of shared library 'pathfinderjni:windowsx86:release:sharedLibrary'.
buildDependentsPathfinderjniWindowsx86ReleaseStaticLibrary - Build dependents of static library 'pathfinderjni:windowsx86:release:staticLibrary'.

I have tried to use Pathfinder’s Gradle code in my own library, but I haven’t had any success, I believe because their code uses the old software model [9]. As it stands, my build code uses the new C++ plugins [10], and I have not found a way to do what I currently do in the old software model.


To reiterate, I am creating a library that utilizes Java and C++ in tandem, but I am unable to configure the Gradle build system to compile for the roboRIO, rather than desktop. The WIP library is currently located here. I would be more than happy to clarify any pieces of what I have done, what hasn’t worked, or what I’m trying to accomplish. Much thanks for any guidance.

1 Like

The WPILib “blessed” way to build and distribute a JNI library is by making a “vendordep”. Take a look at the vendordep template.

Thanks @pietroglyph. The conclusion to this issue that was reached in the FRC Discord server is that, using the new C++ Gradle plugin, it is not possible to cross compile to the roboRIO. I’ve released everything I have to my repo, and will probably use the I2C library for my team’s robot code, because I’m more or less out of ideas, and the work going into this is exceeding what there is to benefit from using USB.

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