Autonomous and Critical Embedded Systems

PhD Defense Farouk Hebbache

Farouk Hebbache defends his PhD thesis entitled « Work-Conserving Dynamic TDM-Based Memory Arbitration for Multi-Criticality Real-Time Systems » today.

The defense jury is comprised of :

  • Alain Mérigot, Professor, University Paris-Saclay
  • Steven Derrien, Professor, University of Rennes 1
  • Frédéric Pétrot, Professor, Grenoble INP Ensimag
  • Claire Pagetti, Research Engineer, ONERA
  • Christine Rochange, Professor, Paul Sabatier University
  • Florian Brandner, Associate Professor, Télécom Paris (co-supervisor)
  • Mathieu Jan, Engineer-Researcher, CEA List (co-supervisor)

Multi-core architectures pose many challenges in real-time systems, which arise from contention between concurrent accesses to shared memory. Among the available memory arbitration policies, Time-Division Multiplexing (TDM) ensures a predictable behavior by bounding access latencies and guaranteeing bandwidth to tasks independently from the other tasks. To do so, TDM guarantees exclusive access to the shared memory in a fixed time window. TDM, however, provides a low resource utilization as it is non-work-conserving. Besides, it is very inefficient for resources having highly variable latencies, such as sharing the access to a DRAM memory. The constant length of a TDM slot is, hence, highly pessimistic and causes an underutilization of the memory. To address these limitations, we present dynamic arbitration schemes that are based on TDM. However, instead of arbitrating at the level of TDM slots, our approach operates at the granularity of clock cycles by exploiting slack time accumulated from preceding requests. This allows the arbiter to reorder memory requests, exploit the actual access latencies of requests, and thus improve memory utilization. We demonstrate that our policies are analyzable as they preserve the guarantees of TDM in the worst case, while our experiments show an improved memory utilization.

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