Multicore processors have been increasing in development by the industry to meet the ever-growing processing requirements of various applications because these processors offer benefits such as reduced power consumption, more processing power and efficient parallel task execution for general purpose work- loads. However, in hard real time systems where predictability is a key aspect, the average performance of these multicore processors is even worse than the scenarios in which the same task set is executed on a single core processor. This performance degradation is due to the fact that the multicore systems have shared resources such as DRAM, BUS and caches which make the system highly unpredictable. One way to achieve predictability in such systems is to serialize the access of the cores to the shared resources such that there is no contention. Another widely emerging approach is the integration of the scratchpad memory. Using scratchpad, at run time, the code and data for the requested task is made available in the scratchpad and contention can be avoided.In this thesis, we approach the problem of shared resource arbitration at an OS-level and propose a novel scratchpad centric OS design for multi-core platforms. In the proposed OS, the predictable usage of shared resources across multiple cores represents a central design-time goal. Hence, we show (i) how contention-free execution of real-time tasks can be achieved on scratchpad-based architectures, and (ii) how a separation of application logic and I/O operations in the time domain can be enforced. To validate the proposed design, we implemented the proposed OS using a commercial-off-the-shelf (COTS) platform. Experiments show that this novel design delivers predictable temporal behavior to hard real-time tasks, and it improves performance up to 2.1x compared to traditional approaches.
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A real-time scratchpad-centric OS for multi-core embedded systems
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