Phasing of Periodic Tasks Distributed over Real-time Fieldbus

  • Sang-Hun Lee Hyundai Mobis 17-2, 240 Mabuk-ro, Giheung-gu, Yongin-si, Gyeounggi-do 16891, Korea
  • Hyun-Wook Jin
  • Kanghee Kim Department of Smart Systems Software Soongsil University 369 Sangdo-ro, Dongjak-gu, Seoul 06978, Korea
  • Sangil Lee Agency for Defense Development Songpa P.O.Box 132, Seoul 05661, Korea


In designing a distributed hard real-time system, it is important to reduce the end-to-end delay of each real-time message in order to ensure quick responses to external inputs and a high degree of synchronization among cooperating actuators. In order to provide a real-time guarantee for each message, the related literature has focused on the analysis of end-to-end delays based on worst-case task phasing. However, such analyses are too pessimistic because they do not assume a global clock. With the assumption that task phases can be managed by using a global clock provided by emerging real-time fieldbuses, such as EtherCAT, we can try to calculate the optimal task phasing that yields the minimal worst-case end-to-end delay. In this study, we propose a heuristic to manage the phase offsets in the distributed tasks to reduce the theoretical end-to-end delay bound. The proposed heuristic reduces the search time for a solution by identifying time intervals where actual communication occurs among inter-dependent tasks. Furthermore, to analyze the distribution of endto- end delays in different phases, we implemented a simulation tool. The simulation results showed that the proposed heuristic can reduce worst-case end-to-end delay as well as jitter in end-to-end delays.


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How to Cite
LEE, Sang-Hun et al. Phasing of Periodic Tasks Distributed over Real-time Fieldbus. INTERNATIONAL JOURNAL OF COMPUTERS COMMUNICATIONS & CONTROL, [S.l.], v. 12, n. 5, p. 645-660, sep. 2017. ISSN 1841-9844. Available at: <>. Date accessed: 05 july 2020. doi:


task phasing, end-to-end delay, real-time, fieldbus, EtherCAT