Phasing of Periodic Tasks Distributed over Real-time Fieldbus
- Authors
- Lee, S. -H.; Jin, H. -W.; Kim, K.; Lee, S.
- Issue Date
- Oct-2017
- Publisher
- CCC PUBL-AGORA UNIV
- Keywords
- task phasing; end-to-end delay; real-time; fieldbus; EtherCAT
- Citation
- INTERNATIONAL JOURNAL OF COMPUTERS COMMUNICATIONS & CONTROL, v.12, no.5, pp.645 - 660
- Journal Title
- INTERNATIONAL JOURNAL OF COMPUTERS COMMUNICATIONS & CONTROL
- Volume
- 12
- Number
- 5
- Start Page
- 645
- End Page
- 660
- URI
- http://scholarworks.bwise.kr/ssu/handle/2018.sw.ssu/6225
- DOI
- 10.15837/ijccc.2017.5.2894
- ISSN
- 1841-9836
- Abstract
- 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 end-to-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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