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C. Pitter:
"Time-Predictable Java Chip-Multiprocessor";
Supervisor, Reviewer: H. Grünbacher, M. Schoeberl; Institut für Technische Informatik - E182, 2009.

Embedded systems are frequently used in real-time applications. Such applications must undergo timing analysis to ensure the timing constraints are met and the mission succeeds. Static worst-case execution time (WCET) analysis yields safe and precise upper bounds of tasks for a given hardware platform. It is preferred to measurement-based analysis methods because it guarantees to consider all possible execution times. The purpose of this thesis is to design a novel chip-multiprocessor (CMP) solution for the development of Java real-time applications. This chipmultiprocessor system consists of a global physical memory accessible to all processors. A memory arbiter resolves concurrent access of multiple CPUs to the main memory. This architecture enables simple communication by accessing shared data objects. This thesis investigates if a shared memory multiprocessor can serve as a hardware platform for real-time applications. The great challenge is that tasks running on different CPUs of a CMP influence each others´ execution times when accessing memory. Therefore, the system´s arbiter must limit these interdependencies to be able to analyze WCETs of individual tasks. An adaptation of a static WCET tool for use with the multiprocessor architecture shall permit straightforward WCET analysis results. In this study, the proposed CMP design is implemented using field-programmable gate array technology. Three different arbitration policies are developed: a fixed priority, a fair-based, and a time-sliced arbiter. Timing analysis approaches are carried out for the specified memory arbiters. Various CMP configurations with varying number of CPUs are evaluated, analyzed, and compared with respect to their real-time and average-case performance. Different benchmarks are used for executing programs on real hardware. Results of this study have revealed that only the time-sliced memory arbitration scheme allows a calculation of viable WCET bounds of Java applications. A comparison of different CMP configurations shows that dynamic arbitration mechanisms are less predictable in the temporal domain but show better average-case program performance. The principal conclusion of this research demonstrates that timing analysis is possible for homogeneous multiprocessor systems with a shared memory.