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OpenJDK for ev3dev-lang-java

A custom build of OpenJDK 9 & 10 for LEGO Mindstorms compatible bricks supported by ev3dev:

  • EV3, featuring a ARM926EJ-S CPU
  • Raspberry Pi 1, featuring a ARM1176JZF-S CPU
  • Raspberry Pi 2, featuring a Cortex-A7 CPU
  • Raspberry Pi 3, featuring a Cortex-A53 CPU

Builds for older boards should work on newer boards, the performance might just be a bit lower.

Build Status

OpenJDK version Platform VM Status
OpenJDK 9 EV3 C1 JIT openjdk9_build_ev3_linux
OpenJDK 10 EV3 C1 JIT openjdk10_build_ev3_linux
OpenJDK 11 EV3 C1 JIT openjdk11_build_ev3_linux
OpenJDK 12 (dev) EV3 C1 JIT openjdk12_build_ev3_linux

Components

The output consists of these parts:

  • JRI for the brick - jri-*.zip
    • Stripped down version of Java -- a Java Runtime Image
    • Intended for normal users.
  • Full JDK running on the brick - jdk-*.zip
    • Intended for Linux power users.
  • Brick jmods - jmods-*.zip
    • They can be used for creating custom JRIs.
    • Intended for advanced users wanting to add additional OpenJDK modules.

Building

  1. Clone/download this repo to your computer.
  2. Install Docker for your operating system.
  3. Build the jdk cross-compilation OS:
sudo docker build -t ev3dev-lang-java:jdk-stretch -f system/Dockerfile.armel  system # ONLY FOR EV3
sudo docker build -t ev3dev-lang-java:jdk-stretch -f system/Dockerfile.armhf  system # ONLY FOR RPI1. RPI2 & RPI3
  1. Build the jdk cross-compilation environment:
sudo docker build -t ev3dev-lang-java:jdk-build   -f scripts/Dockerfile scripts

Semi-manual build

  1. Run the newly prepared container. You have to mount a host directory to the the /build directory in the container, otherwise the build would get discarded. The final build needs at least 6.5 GB of free space (in the build directory).
sudo docker run --rm -it -v $BUILD_DIRECTORY:/build ev3dev-lang-java:jdk-build

Please change the $BUILD_DIRECTORY to a valid path.

  1. Select the OpenJDK version and VM you want to cross-compile (select only one for each variable):
export JDKVER=9         # OpenJDK 9
export JDKVER=10        # OpenJDK 10
export JDKVER=dev       # OpenJDK Master+dev (to-be OpenJDK 11 at the time of writing)
export JDKVM=zero       # Use Zero interpreter
export JDKVM=client     # Use ARM32 JIT
export JDKPLATFORM=ev3  # Use EV3  build flags
export JDKPLATFORM=rpi1 # Use RPi1 build flags
export JDKPLATFORM=rpi2 # Use RPi2 build flags
export JDKPLATFORM=rpi3 # Use RPi3 build flags
  1. Before we can start the build process, Boot JDK must be downloaded:
./prepare.sh
  1. Now we can download the OpenJDK sources:
./fetch.sh
  1. The OpenJDK source tree should be ready. Now you can start the cross-build itself:
./build.sh
  1. Create the zipped images:
./zip.sh
  1. If the build was successful, JDK packages were created in /build/jri-ev3.tar.gz, /build/jdk-ev3.tar.gz and /build/jmods.tar.gz. If you have mounted /build, you can access the files from the host.

Automatic build

  1. Run the newly prepared container. You have to mount a host directory to the the /build directory in the container, otherwise the build would get discarded. The final build needs at least 6.5 GB of free space (in the build directory).
sudo docker run --rm -v $BUILD_DIRECTORY:/build -e JDKVER='X' -e JDKVM='Y' -e JDKPLATFORM='Z' -e AUTOBUILD='yes' ev3dev-lang-java:jdk-build

For values of X, Y and Z see above. Please change the $BUILD_DIRECTORY to a valid path.

  1. If the build was successful, JDK packages were created in $BUILD_DIRECTORY/jri-ev3.tar.gz, $BUILD_DIRECTORY/jdk-ev3.tar.gz and $BUILD_DIRECTORY/jmods.tar.gz.

JShell on the EV3

No longer supported. JShell backend on the EV3 is a huge overkill.

OpenJDK for leJOS

LeJOS has probably reached its EOL. It is not a priority anymore to support it. linux-devkit + CodeSourcery GCC could be used for cross-compilation of it.