OpenJDK for ev3dev-lang-java

Custom build of OpenJDK providing Java support for ev3dev on the following devices:

• LEGO Mindstorms EV3, featuring a ARM926EJ-S 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
OpenJDK 10	EV3	C1 JIT
OpenJDK 11	EV3	C1 JIT
OpenJDK 12 (dev)	EV3	C1 JIT

Components

The build process produces these files:

Name	File name	Summary	Where it runs	Who is it for	What is it useful for
JRI	jri-ev3.zip	Minimal runtime	Brick	Java developer	Running Java programs on ev3dev.
JDK	jdk-ev3.zip	Full JDK	Brick	ev3dev power user	Compiling Java programs directly on the brick.
JMODs	jmods-ev3.zip	Runtime precursor	Developer PC	both	Creating runtime images with more Java modules.

JRI stands for "Java Runtime Image". The term itself is not specific to this project, it is equivalent to Modular Run-Time Image. To see which modules are included in our case, take a look at the jlink commandline in scripts/zip.sh.

Building

0. Clone this repository.
1. Install Docker for your operating system.
2. Build the base cross-compilation image:

sudo docker build -t ev3dev-lang-java:jdk-stretch -f system/Dockerfile.armel system

3. Build the image with OpenJDK cross-compilation scripts:

sudo docker build -t ev3dev-lang-java:jdk-build   -f scripts/Dockerfile scripts

Next steps depend on whether you want to navigate the build yourself, or if you want the build to run automatically.

Semi-manual build

4. 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.

5. 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=11        # OpenJDK 11
export JDKVER=12        # OpenJDK 12
export JDKVM=zero       # Use Zero interpreter
export JDKVM=client     # Use ARM32 JIT
export JDKPLATFORM=ev3  # Use EV3  build flags

6. Before we can start the build process, Boot JDK must be downloaded:

./prepare.sh

7. Now we can download the OpenJDK sources:

./fetch.sh

8. The OpenJDK source tree should be ready. Now you can start the cross-build itself:

./build.sh

9. Create the zipped images:

./zip.sh

10. 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

4. 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.

5. 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.

LeJOS support

LeJOS is not supported. To create a build, it is needed to build Java dependencies for the old LEGO-provided rootfs. Also, the rootfs build compiler is needed for building OpenJDK itself. linux-devkit + CodeSourcery GCC could be used for the cross-compilation.