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Holistic Scheduling and Analysis for Mixed Time/Event-Triggered Distributed Embedded Systems

This discussion paper presents a comprehensive approach to the holistic scheduling and timing analysis of mixed Time-Triggered (TT) and Event-Triggered (ET) distributed embedded systems. It explores the fundamental scheduling strategies and emphasizes the importance of considering both task execution and message timing to ensure predictable system behavior. The paper discusses system architecture, the classification of tasks and messages, and offers a fixed-point solution for schedulability analysis. Experimental results demonstrate successful optimization of system performance, focusing on bus access and task scheduling strategies.

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Holistic Scheduling and Analysis for Mixed Time/Event-Triggered Distributed Embedded Systems

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  1. Holistic Scheduling and Analysis of Mixed Time/Event-Triggered Distributed Embedded SystemTraian Pop, Petru Eles, Zebo Peng EE249 Discussion Paper Review Haiyang Zheng 11/19/2002

  2. Introduction • Embedded systems are usually hard real-time applications. • Predictable behaviors for safety issues. • Implementation as distributed systems. • The holistic schedulability analysis of tasks and communication scheduling is necessary.

  3. How to schedule? • Two basic approaches for scheduling: • Time-triggered (TT) • Event-triggered (ET) • There is no single best approach. • A mixed solution has more flexibility for potentially efficient and optimized implementations.

  4. System Architecture

  5. Application Model • A task belongs either to the TT or ET domain. • A message belongs either to the static (ST) or the dynamic (DYN) domain. • Each task has a worst case execution time and a deadline. A TT task has a period. An ET task has a unique priority. • All tasks belonging to a task graph have the same period, the period of the task graph. • The period of message is the same as the sender task. DYN messages have priorities.

  6. Holistic Scheduling • Two important aspects: • Interference from the statically scheduled TT tasks and ST messages is considered. • The schedulability of ET tasks and DYN messages has priority. • Assumption: • TT tasks talk with ST messages only and ET tasks talk with DYN messages only.

  7. Fixed Point Solution Schedulability Analysis of ET subsystem

  8. Influence of Static Schedule

  9. Static Schedule Construction and Holistic Analysis • Schedule the TT tasks in such a position between earliest available time and last available time to reduce the cost. • Schedule the ST messages in the first available bus-slot of the sender node. • Limited backtracking mechanism is used to explore alternative solution.

  10. System optimization • Partition the system functionality into TT and ET activities. • Determine the optimal structure of the bus access cycle.

  11. Bus access optimization

  12. Experimental Results

  13. Conclusion • A holistic scheduling and timing analysis approach for mixed TT/ET system is given. • A static cyclic schedule is constructed in such a way that it fits the schedulability requirements of the ET tasks. • System optimization issues are discussed. • A bus access optimization example is studied and the result is positive.

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