Towards an embedded real-time Java virtual machine

Sammanfattning: Most computers today are embedded, i.e. they are built into some products or system that is not perceived as a computer. It is highly desirable to use modern safe object-oriented software techniques for a rapid development of reliable systems. However, languages and run-time platforms for embedded systems have not kept up with the front line of language development. Reasons include complex and, in some cases, contradictory requirements on timing, concurrency, predictability, safety, and flexibility. A carefully tailored Java virtual machine (called IVM) is proposed as an approach to overcome these difficulties. In particular, real-time garbage collection has been considered an essential part. The set of bytecodes has been revised to require less memory and to facilitate predictable execution. To further reduce the memory footprint, the class loader can be located outside the embedded processor. Since the accomplished concurrency is crucial for the function of many embedded applications, the scheduling can be defined on the application level in Java. Finally considering future needs for flexibility and on-line configuration of embedded system, the IVM has a unique structure with which, for instance, methods being objects that can be replaced and GCed. The approach has been experimentally verified by a full prototype implementation of such a virtual machine. By making the prototype available for development of real products, this in turn has confronted the solutions with real industrial demands. It was found that the IVM can be easily integrated in typical systems today and the mentioned requirements are fulfilled. Based on experiences from more than 10 projects utilising the novel Java-oriented techniques, there are reasons to believe that the proposed approach is very promising for future flexible embedded systems.