Master of Computer Science by Research
School of Computer Science and Software Engineering - Faculty of Informatics
Lu, Qinghua, Real-time operating system in Java, MA thesis, School of Computer Science and Software Engineering, University of Wollongong, 2007. http://ro.uow.edu/theses/29
Real-time operating systems (RTOSes) are required to run for years, and never fail, without human intervention. Safety is the primary concern for RTOSes because they usually control physical equipment. One strand of real-time operating system (RTOS) research is looking at the question: can developing an RTOS in a safe language result in a system that an errant process can’t crash? Choosing a good programming language can significantly improve the safety of the RTOS. In this thesis, we examine the advantages and associated problems of writing RTOSes in a safe language, namely Java.
We design an RTOS named JARTOS that schedules processes on a micro-controller called TINI. The code of the JARTOS system is mainly written in Java, since Java provides both static and dynamic safety. The Java compiler handles potentially unsafe operations rather than the programmer. Also, Java includes run-time support to catch and handle run-time errors.
JARTOS is designed to be a time-sharing system, where cooperative multiprocessing is used to schedule real-time processes. JARTOS switches processes on a timer interrupt. Each process is required to execute quickly and then give up the processor. Otherwise it will be timed out. To implement a timeout, JARTOS supports a timer interrupt that regularly updates a clock and checks for timeouts. To keep the number of interrupts to a minimum, input/output is done using polling where possible. Also, interrupts code is designed to be transparent to the processes. An interrupt handler sets flags and values, and then returns to the process it interrupted.
In the context of achieving real-time performance, we look at the issues of implementing our system design in Java. We introduce how we used Java constructs to implement the design of JARTOS, and how we solved the low-level issues.
RTOSes have to guarantee that real-time processes execute within specified time dead-lines. Loss of synchronization can occur when deadlines are not met. Timing problems are often very difficult to find. In JARTOS, we designed a set of performance measurements to investigate timing problems. These performance measurements are carefully designed to provide the right information at minimal cost in performance. Performance of TINI and JARTOS are measured and discussed.
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