A buffer-aware worst-case timing analysis of wormhole NoC is proposed in this paper to integrate the impact of buffer size on the different dependencies relationship between flows, i.e. direct and indirect blocking flows, and consequently the timing performance. First, more accurate definitions of direct and indirect blocking flows sets have been introduced to take into account the buffer size impact. Then, the modeling and worst-case timing analysis of wormhole NoC have been detailed, based on Network Calculus formalism and the newly defined blocking flows sets. This introduced approach has been illustrated in the case of a realistic NoC case study to show the trade off between latency and buffer size. The comparative analysis of our proposed Buffer-aware timing analysis with conventional approaches is conducted and noticeable enhancements in terms of maximum latency have been proved. NoC, WCRT, buffer size, direct blocking, indirect blocking, Netwok Calculus I. INTRODUCTION Among several routing techniques, the wormhole routing [1] has become the most implemented routing technique in Networks On Chip (NOC) and multicomputers, and recently in other applications domains like satellites e.g. the Spacewire [2] network based on Wormhole routing has been integrated in new generation satellites. This success is incontestably due to its simplicity and its significants interests to make the message latency distance-insensitive in contention-free networks while reducing the storage buffers in intermediate routers. However, the key argument against using wormhole routing in hard real time context lies in its non deterministic behavior due to possible contentions, which can lead to deadlock situation e.g. no message can be transmitted because all the system queues are busy. Hence, achieving a real time behavior with low latency over wormhole based networks still needs the use of additional mechanisms. Various solutions are recently offered to overcome these limitations as the integration of virtual channels allowing the messages to bypass each other in case of conflict, and the implementation of deadlock-free routing algorithms based generally on deterministic approaches, such as Round Robin. Even-though these solutions eliminate the deadlock when using the wormhole routing, there are not sufficient to prove that traffic deadline constraints are effectively respected to fulfill the real time applications requirements. This may occur when simultaneous traffic flows attempt to share the same resource which can lead to a chain blocking situation e.g. a blocked packet can block another packet which in turn blocks other packets, and so on. Hence, the real-time packet schedulablity has to be proved and the response-time based schedulablity tests are usually used in such a distributed system, where the critical resource is not the computational power but the transmission medium bandwidth utilization. In Wormhole routing networks, this latter depends mainly on flows contentions scenarios, which make the exact Worst Case Response Time (WCRT) calculus very complex due to the huge possibilities of flows arrivals and blocking. In order to handle this problem, many approaches have been proposed in the literature to compute the maximum
Finally, the authors in REF have started the exploration of the buffer size impact on the interference patterns.
Buffer-aware Worst Case Timing Analysis of Wormhole Network On Chip
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