Abstract

Abstract
In this paper we survey the most relevant results for the priority--based schedulability analysis of real-time tasks, both for the fixed and dynamic priority assignment schemes. We give emphasis to the worst-case response time analysis in non-preemptive contexts, which is fundamental for the communication schedulability analysis. We define an architecture to support priority-based scheduling of messages at the application process level of a specific fieldbus communication network, the PROFIBUS. The proposed architecture improves the worst-case messages’ response time, overcoming the limitation of the first-come-first-served (FCFS) PROFIBUS queue implementations. © Springer-Verlag Berlin Heidelberg 1999.

Abstract
Due to the increased availability of low cost network technology, the use of networks to interconnect sensors, actuators and controllers is becoming widely accepted for the implementation of feedback control systems. Such type of feedback implementation, wherein the control loops are closed through a real-time network, are called Network Controlled Systems (NCS). When implementing a NCS, the underlying communication network must provide a timely communication service, which must be the adequate to fulfil the control application requirements. Therefore, the assessment of the network responsiveness to the real-time requirements of the control application is a fundamental issue. Both PROFIBUS and CAN networks are usually considered suitable to support small-scale NCS, due to their real-time capabilities. However, their temporal responsiveness is highly dependent on both the timing characteristics of the supported message streams, such as its periodicity and the related message lengths. In this paper, we compare the timing properties of both CAN and PROFIBUS control networks. Basically, we assess their capability to support Network Controlled Systems, through the evaluation of the related worst-case message's response time. A small example of a NCS is then used to assess the capability of the CAN control network to fulfil control application requirements.

Abstract
This paper presents the application of a CAN network to the integration of sensors and actuators in an unmanned airship called HELIX, based on the architecture of distributed processing proposed by [4]. Initially, a study of the viability of several communication networks used in vehicles (such as CAN, VAN, C2D and FIP, etc.) was accomplished [6]. The preliminary study concluded that the behavior of CAN was better for this application when compared to other types of networks analyzed. In the present work, a detailed study of the employability of a CAN network in the HELIX project was accomplished, including situations not considered in the preliminary analysis, such as the presence of Jitter in the group of messages, the high load of messages over the network, and the consideration of presence of transmission errors. As the CAN networks offers good properties for transmission of messages with temporal requirements, a schedulability analysis was accomplished for the transmission of messages and a numeric example is presented in an illustrative way to the present problem.

Abstract
This chapter discusses the analysis of an enhanced collision resolution algorithm for the shared Ethernet networks, referred as the high priority binary exponential backoff (h-BEB). Such an algorithm allows for the coexistence of the Ethernet standard devices together with the modified (real-time) devices in the same network segment. Both the analytical and the simulation timing analysis show that the h-BEB algorithm assures a maximum access delay that is significantly smaller than that for the case of the standard Ethernet stations. Analyses of two cases were done. The analytical study for a heavily loaded network scenario shows that the maximum access delay for 95% of the messages is smaller than 1,86 ms. While, for more realistic load scenarios (intermediate load cases), the simulation analysis shows that the maximum access delay for 98% of the messages is always smaller than 1 ms. It also shows a nearly constant message transfer jitter, which is one order of magnitude smaller than the maximum access delay for 98% of the messages. The algorithm enables the traffic separation between the standard and the modified (real-time) stations, and is therefore able to guarantee a real-time communication behavior in the unconstrained traffic environments.

Abstract
The goal of this paper is to provide a methodology for the pre-run-time schedulability analysis of Fieldbus networks, based on the evaluation of the worst-case response time. A comparison of the well-known Fieldbusses Profibus and FIP is made.