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Table of Contents


Main Bazel targets

Working on the GWT frontend

Source code structure

Submitting code

Unit tests



In order to compile EduMIPS64, you need the following tools:

  • Java JDK version 8 or above.
  • Apache Ant version 1.8 or above (needed for JUnit 4 tests)
  • Bazel (

To build the user documentation, you'll need:

Bazel will download the following dependencies:

  • JUnit
  • JavaHelp
  • GWT (experimental)

If you want to use the automatic style checks (pre-commit hook), then you should have Automatic Style (astyle) installed.

This project uses Travis CI for continuous integration (

Main Bazel targets

Note that you will need to specify the command to use to generate build-time variables. This is done by appending the following parameters to all the bazel build commands: --workspace_status_command=utils/ --stamp.

  • //src/main/java/org/edumips64:slim-jar builds the jar package named edumips64-version-nodeps.jar, that does not embed the JavaHelp libraries and is oriented towards distribution package creators, that should add a dependency on JavaHelp and appropriately set the classpath in their scripts.

  • //src/test/java/org/edumips64/:all runs all unit tests (to be ran with bazel test);

  • //src/main/java/org/edumips64:standalone-jar builds the jar package named edumips64-version.jar, that embeds the JavaHelp libraries, and is oriented towards users downloading the JAR archive from the website (not through package managers).

  • //src/main/java/org/edumips64:cli-jar builds a jar package containing an experimental CLI front-end.

  • //docs/user/en:pdf builds the English PDF docs.

  • //docs/user/en:html builds the English HTML docs.

  • //docs/user/it:pdf builds the English PDF docs.

  • //docs/user/it:html builds the English HTML docs.

  • //src/main/java/org/edumips64:{devmode,gwtc} are related to the GWT frontend, see below.

Working on the GWT frontend

An experimental web frontend, based on GWT, is being developed right now. Currently, only a prototype is available. The GWT code for it is in the org.edumips64.client package. The HTML file is at src/main/java/org/edumips64/client/edumips64.html.

To work on it, run the devmode Build target, which will fire up the GWT developer console for you. Once the console is available, you'll be given a local URL where the frontend will be available.

Every time you change the GWT frontend, reloading that web page will cause the GWT console to recompile the code, thus allowing quick iteration on the web frontend code.

To create a releasable version of the JS code, use the gwtc target.

Source code structure

The source code structure follows the Gradle project layout conventions. The main package for the simulator is org.edumips64, therefore the Java code resides in src/main/java/org/edumips64, and contains 5 sub-packages, plus the entry points. is the code for the main Swing frontend entry point, while contains an experimental CLI front-end.

  • The client package contains Java code for the Web UI.
  • The core package contains all the core classes for the simulator, including important bits such as the CPU, the Memory, instructions and the Parser.
  • The img package contains a class to load images and the actual images used in the simulator.
  • The ui package contains the code for the Swing UI.
  • The utils package contains miscellaneous code, including abstractions needed to decouple the core code from packages that are not available in the GWT JRE emulation (such as

Submitting code

We use the GitHub Flow development workflow, which means that master is always fully working (the code can be built and all tests pass), and development is done in separate named branches. The good state of master is enforced by its protected status, meaning that no commits can be pushed directly to master and any pull requests for master have to pass the status checks (Travis CI building the code and executing unit tests).

Unit tests

It is expected that all new features are implemented with good unit tests coverage.

There is a suite of end-to-end tests, but any significant change to core classes should ideally come with their own separate unit tests.

Unit tests are stored in the src/test directory. The resources subdirectory contains MIPS64 programs that are executed during unit test as a form of end-to-end unit tests, whereas java contains the actual Java code that runs unit tests.

The main tests are contained in This class contains unit tests that run MIPS64 code (contained in resources). One of the common patterns in those tests is that, if something goes unexpectedly during the execution of unit tests, the MIPS64 code executes a BREAK instruction, which will trigger a BreakException in the Java code and make the test fail. Tests in can also verify other behaviors, including forwarding and correct working of the Dinero Tracefile generation logic.

Other types of test, e.g., or, will test other components in isolation.

To add a unit test, the first consideration is whether this test should be writte in assembly or in Java. Tests in assembly should typically be put in, since it contains already boilerplate for executing and verifying assembly programs. Tests which should not be written in assembly, and therefore most likely exercise only one component, should pertain to other classes, possibly even an entirely new class if required.

When writing new unit test classes, pay attention to the initialization code necessary to initialize the simulator. Look at other unit test classes to make sure your new class behaves as required.

The Swing UI code is explicitly excluded from code coverage reports because writing tests for it is quite difficult and might not be worth it since we might be migrating to a new shiny web-based frontend.