JTRON: a hybrid architecture integrating an object-oriented and real-time system

Although Java as expected to have a wide range of embedded applications, there exist some problems in applying Java to real-time systems. It is practical to have a hybrid architecture, in which the Java runtime environment is implemented on a real-time operating system (OS), where those parts of the application requiring real-time properties are implemented in the real-time OS, while those parts requiring GUI features, extensions of features and replacement of programs should be implemented in the Java runtime environment. In this paper, we present interface specifications between Java threads and real-time tasks based the hybrid architecture we have built, called the JTRON (Java on The industrial Real-time Operating system Nucleus) specification, and experiences based on application development using its implementation. First, cooperative computation models between Java threads and real-time tasks in the architecture are described. Based on these models, we categorize three types of communication interfaces between Java threads and real-time tasks: the real-time/OS attachment class, shared objects with explicit locking mechanisms, and stream-based communication. By standardizing the interface, not only Java programs but also real-time programs become portable and reusable. Two of the three types of interface can also be applied to other real-time OSs.