scholarly journals Phasing of Periodic Tasks Distributed over Real-time Fieldbus

2017 ◽  
Vol 12 (5) ◽  
pp. 645 ◽  
Author(s):  
Sang-Hun Lee ◽  
Hyun-Wook Jin ◽  
Kanghee Kim ◽  
Sangil Lee
Keyword(s):  
Real Time ◽  
Search Time ◽  
Periodic Tasks ◽  
Worst Case ◽  
Real Time System ◽  
Delay Bound ◽  
End To End Delay ◽  
Global Clock ◽  
End To End ◽  
Hard Real Time

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.

scholarly journals Scheduling an aperiodic flow within a real-time system using Fairness properties

2014 ◽  
Vol Volume 18, 2014 ◽  
Author(s):  
Annie Choquet-Geniet ◽  
Sadouanouan MALO
Keyword(s):  
Real Time ◽  
Acceptance Test ◽  
Periodic Tasks ◽  
Real Time System ◽  
Model Driven ◽  
Aperiodic Tasks ◽  
International Audience ◽  
Hard Real Time ◽  
Model Driven Approach ◽  
Time Systems

International audience We consider hard real-time systems composed of periodic tasks and of an aperiodic flow. Each task, either periodic or aperiodic, has a firm deadline. An aperiodic task is accepted within the system only if it can be completed before its deadline, without causing temporal failures for the periodic tasks or for the previously accepted aperiodic tasks. We propose an acceptance test, linear in the number of pending accepted aperiodic tasks. This protocol can be used provided the idle slots left by the periodic tasks are fairly distributed. We then propose a model-driven approach, based on Petri nets, to produce schedules with a fair distribution of the idle slots for systems of non independent periodic tasks. Nous considérons des systèmes temps-réel composés de tâches périodiques et d’un fluxapériodique. Toutes les tâches, périodiques comme apériodiques, sont soumises à des échéancesstrictes. Une tâche apériodique n’est acceptée que si elle ne remet pas en cause le respect deséchéances par les tâches périodiques et par les tâches apériodiques déjà acceptées. Nous proposonsun protocole d’acceptation des tâches apériodiques de complexité linéaire en le nombre de tâchesapériodiques acceptées présentes dans le système. Ce protocle est utilisable dès lors que les tempscreux sont répartis de manière équitable. Nous proposons donc une approche modèle, à base deréseaux de Petri, pour produire des séquences où les temps creux sont équitablement répartis, pourdes systèmes de tâches interdépendantes.

Analysis of forward approach for upper bounding end-to-end transmission delays over distributed real-time avionics networks

2020 ◽  
Vol 124 (1279) ◽  
pp. 1399-1435
Author(s):  
Q. Xu ◽  
X. Yang
Keyword(s):  
Real Time ◽  
Upper Bound ◽  
Data Exchange ◽  
Direct Consequence ◽  
Transmission Delay ◽  
Worst Case ◽  
Engineering Research ◽  
Transmission Delays ◽  
Global Clock ◽  
End To End

ABSTRACTDistributed real-time avionics networks have been subjected to a great evolution in terms of functionality and complexity. A direct consequence of this evolution is a continual growth of data exchange. AFDX standardised as ARINC 664 is chosen as the backbone network for those distributed real-time avionics networks as it offers high throughput and does not require global clock synchronisation. For certification reasons and engineering research, a deterministic upper bound of the end-to-end transmission delay for packets of each flow should be guaranteed. The Forward Approach (FA) is proposed for the computation of the worst-case end-to-end transmission delay. This approach iteratively estimates the maximum backlog (amount of the pending packets) in each visited switch along the transmission path, and the worst-case end-to-end transmission delay can be computed. Although it is pessimistic (overestimated), the Forward Approach can provide a tighter upper bound of the end-to-end transmission delay while considering the serialisation effect. Recently, our research finds the computation of the serialisation effect might induce an optimistic (underestimated) upper bound. In this paper, we analyse the pessimism in the Forward Approach and the optimism induced by the computation of the serialisation effect, and then we provide a new computation of the serialisation effect. We compare this new computation with the original one, the experiments show that the new computation reduces the optimism and the upper bound of the end-to-end transmission delay can be computed more accurately.

scholarly journals Online Slack-Stealing Scheduling with Modified laEDF in Real-Time Systems

Electronics ◽  
2019 ◽  
Vol 8 (11) ◽  
pp. 1286 ◽  
Author(s):  
Wonbo Jeon ◽  
Wonsop Kim ◽  
Heoncheol Lee ◽  
Cheol-Hoon Lee
Keyword(s):  
Response Time ◽  
Real Time ◽  
Execution Time ◽  
Computation Method ◽  
Periodic Tasks ◽  
Worst Case ◽  
Dynamic Priority ◽  
Look Ahead ◽  
Aperiodic Tasks ◽  
Hard Real Time

In hard real-time task systems where periodic and aperiodic tasks coexist, the object of task scheduling is to reduce the response time of the aperiodic tasks while meeting the deadline of periodic tasks. Total bandwidth server (TBS) and advanced TBS (ATBS) are used in dynamic priority systems. However, these methods are not optimal solutions because they use the worst-case execution time (WCET) or the estimation value of the actual execution time of the aperiodic tasks. This paper presents an online slack-stealing algorithm called SSML that can make significant response time reducing by modification of look-ahead earliest deadline first (laEDF) algorithm as the slack computation method. While the conventional slack-stealing method has a disadvantage that the slack amount of each frame must be calculated in advance, SSML calculates the slack when aperiodic tasks arrive. Our simulation results show that SSML outperforms the existing TBS based algorithms when the periodic task utilization is higher than 60%. Compared to ATBS with virtual release advancing (VRA), the proposed algorithm can reduce the response time up to about 75%. The performance advantage becomes much larger as the utilization increases. Moreover, it shows a small performance variation of response time for various task environments.

The Goal-Setting Model in a Multiagent Hard Real-Time System

Vestnik MEI ◽  
2018 ◽  
Vol 5 (5) ◽  
pp. 73-78
Author(s):  
Igor В. Fominykh ◽  
◽  
Sergey V. Romanchuk ◽  
Nikolay Р. Alekseev ◽  
◽  
...  
Keyword(s):  
Real Time ◽  
Goal Setting ◽  
Time System ◽  
Real Time System ◽  
Hard Real Time

scholarly journals A Proposal for End-to-End QoS Provisioning in Software-Defined Networks

2017 ◽  
Vol 7 (4) ◽  
pp. 2261 ◽  
Author(s):  
Francesco Lucrezia ◽  
Guido Marchetto ◽  
Fulvio Risso ◽  
Michele Santuari ◽  
Matteo Gerola
Keyword(s):  
Smart Grids ◽  
Service Level ◽  
End User ◽  
Delay Bound ◽  
Qos Guarantee ◽  
End To End Delay ◽  
Network Controller ◽  
Edge Network ◽  
End To End

This paper describes a framework application for the control plane of a network infrastructure; the objective is to feature end-user applications with the capability of requesting at any time a customised end-to-end Quality-of-Service profile in the context of dynamic Service-Level-Agreements. Our solution targets current and future real-time applications that require tight QoS parameters, such as a guaranteed end-to-end delay bound. These applications include, but are not limited to, health-care, mobility, education, manufacturing, smart grids, gaming and much more. We discuss the issues related to the previous Integrated Service and the reason why the RSVP protocol for guaranteed QoS did not take off. Then we present a new signaling and resource reservation framework based on the cutting-edge network controller ONOS.  Moreover, the presented system foresees the need of considering the edges of the network, where terminal applications are connected to, to be piloted by distinct logically centralised controllers. We discuss a possible inter-domain communication mechanism to achieve the end-to-end QoS guarantee.

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