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1 Introduction

Complexity of embedded and real-time systems increases from year to year and can only be handled by providing state-of-the-art programming languages. Usually software for those systems is written in C and even assembly language. This implies in-depth knowledge of the underlying hardware and the real-time operating system (RTOS) used. To handle complex software effectively a high abstraction layer of the programming language is needed. The Java Language provides an appropriate abstraction layer but is not designed for resource limited embedded systems and systems with real-time requirements. Thus the Java Language Specification [1] and the Java Virtual Machine Specification [2] need to be enhanced. In order to add real-time capabilities this is done by several specifications. Implementations of these specifications were not available until December 2001 when TimeSys [13] released the first reference implementation of the Sun's Real-Time Specification for Java (RTSJ) [3]. The Real-Time Core Extensions (RTCE) [4] are a competing specification by the Real-time Java Working Group.

In this paper we focus on real-time software such as control software for industrial automation. In this area there are systems running real-time software as well as non-real-time parts like graphical user interfaces on the same machine (e.g. the SICOMP industrial microcomputers [15]). On the other hand there are small controllers with very limited resources. Since RTCE fits better for these systems--this will be explained later--we implemented RTCE instead of RTSJ.

Designing real-time systems requires an overall system view. You cannot look at single parts like the Java Virtual Machine separately (assuming a common single processor system is used; hardware related topics are excluded). Therefore the paper starts with a definition of real-time systems, which are targeted. Based on that, current real-time operating system architectures are described in a nutshell. After an overview over the current real-time Java approaches the concept of the JaRTS Java real-time Java compiler will be discussed. Since real-time tasks run in a separate runtime environment the communication between real-time and non-real-time parts is shown in detail. Finally benchmarking results comparing JaRTS to other solutions are presented before we conclude.

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Next: 2 Real-time systems Up: JaRTS: A Portable Implementation Previous: JaRTS: A Portable Implementation
Urs Gleim 2002-05-29