JOP: A Java Optimized Processor for Embedded Real-Time Systems

Compared to software development for desktop systems, current software design practice for embedded systems is still archaic. C/C++ and even assembler are used on top of a small real-time operating system. Many of the benefits of Java, such as safe object references, the notion of concurrency as a first-class language construct, and its portability, have the potential to make embedded systems much safer and simpler to program. However, Java technology is seldom used in embedded systems, due to the lack of acceptable real-time performance. This thesis presents a Java processor designed for time-predictable execution of real-time tasks. JOP (Java Optimized Processor) is the implementation of the Java virtual machine in hardware. JOP is intended for applications in embedded real-time systems and the primary implementation technology is in a field programmable gate array. This research demonstrates that a hardware implementation of the Java virtual machine results in a small design for resource-constrained devices. Architectural advancements in modern processor designs increase average performance with features such as pipelines, caches and branch prediction. However, these features complicate worst-case execution time (WCET) analysis and lead to very conservative WCET estimates. This thesis tackles this problem from the architectural perspective – by introducing a processor architecture in which simpler and more accurate WCET analysis is more important than average case performance. This thesis evaluates the issues surrounding the use of standard Java for real-time applications. In order to overcome some of the issues with standard Java, a profile for real-time Java is defined. Tight integration of the real-time scheduler with the supporting processor result in an efficient platform for Java in embedded real-time systems. The proposed processor and the Java real-time profile have been used with success to implement several commercial real-time applications.