The Object Management Group's (OMG) Model Driven Architecture (MDA) strategy envisages a world where models play a more direct role in software production, being amenable to manipulation and transformation by machine. Model Driven Engineering (MDE) is wider in scope than MDA. MDE combines process and analysis with architecture. This article sets out a framework for model driven engineering, which can be used as a point of reference for activity in this area. It proposes an organisation of the modelling 'space' and how to locate models in that space. It discusses different kinds of mappings between models. It explains why process and architecture are tightly connected. It discusses the importance and nature of tools. It identifies the need for defining families of languages and transformations, and for developing techniques for generating/configuring tools from such definitions. It concludes with a call to align metamodelling with formal language engineering techniques.

Model Driven Engineering

This survey covers hard real-time scheduling algorithms and schedulability analysis techniques for homogeneous multiprocessor systems. It reviews the key results in this field from its origins in the late 1960s to the latest research published in late 2009. The survey outlines fundamental results about multiprocessor real-time scheduling that hold independent of the scheduling algorithms employed. It provides a taxonomy of the different scheduling methods, and considers the various performance metrics that can be used for comparison purposes. A detailed review is provided covering partitioned, global, and hybrid scheduling algorithms, approaches to resource sharing, and the latest results from empirical investigations. The survey identifies open issues, key research challenges, and likely productive research directions.

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A survey of hard real-time scheduling for multiprocessor systems

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Power Electronics Converters Applications And Design

Despite early attempts to use Ethernet in the industrial context, only recently has it attracted a lot of attention as a support for industrial communication. A number of vendors are offering industrial communication products based on Ethernet and TCP/IP as a means to interconnect field devices to the first level of automation. Others restrict their offer to communication between automation devices such as programmable logic controllers and provide integration means to existing fieldbuses. This paper first details the requirements that an industrial network has to fulfill. It then shows how Ethernet has been enhanced to comply with the real-time requirements in particular in the industrial context. Finally, we show how the requirements that cannot be fulfilled at layer 2 of the OSI model can be addressed in the higher layers adding functionality to existing standard protocols.

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Ethernet-Based Real-Time and Industrial Communications

Since the first results published in 1973 by Liu and Layland on the Rate Monotonic (RM) and Earliest Deadline First (EDF) algorithms, a lot of progress has been made in the schedulability analysis of periodic task sets. Unfortunately, many misconceptions still exist about the properties of these two scheduling methods, which usually tend to favor RM more than EDF. Typical wrong statements often heard in technical conferences and even in research papers claim that RM is easier to analyze than EDF, it introduces less runtime overhead, it is more predictable in overload conditions, and causes less jitter in task execution.Since the above statements are either wrong, or not precise, it is time to clarify these issues in a systematic fashion, because the use of EDF allows a better exploitation of the available resources and significantly improves system's performance.This paper compares RM against EDF under several aspects, using existing theoretical results, specific simulation experiments, or simple counterexamples to show that many common beliefs are either false or only restricted to specific situations.

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Rate monotonic vs. EDF: judgment day

The research on real-time software systems has produced algorithms that allow to effectively schedule system resources while guaranteeing the deadlines of the application and to group tasks in a very short number of non-preemptive sets which require much less RAM memory for stack. Unfortunately, up to now the research focus has been on time guarantees rather than the optimization of RAM usage. Furthermore, these techniques do not apply to multiprocessor architectures which are likely to be widely used in future microcontrollers. This paper presents a fast and simple algorithm for sharing resources in multiprocessor systems, together with an innovative procedure for assigning preemption thresholds to tasks. This allows to guarantee the schedulability of hard real-time task sets while minimizing RAM usage. The experimental part shows the effectiveness of a simulated annealing-based tool that allows to find a near-optimal task allocation. When used in conjunction with our preemption threshold assignment algorithm, our tool further reduces the RAM usage in multiprocessor systems.

Minimizing memory utilization of real-time task sets in single and multi-processor systems-on-a-chip

Ethernet was not originally developed to meet the requirements of real-time industrial automation systems and it was commonly considered unsuited for applications at the field level. Hence, several techniques were developed to make this protocol exhibit real-time behavior, some of them requiring specialized hardware, others providing soft-real-time guarantees only, or others achieving hard real-time guarantees with different levels of bandwidth efficiency. More recently, there has been an effort to support quality-of-service (QoS) negotiation and enforcement but there is not yet an Ethernet-based data link protocol capable of providing dynamic QoS management to further exploit the variable requirements of dynamic applications. This paper presents the FTT-Ethernet protocol, which efficiently supports hard-real-time operation in a flexible way, seamlessly over shared or switched Ethernet. The FTT-Ethernet protocol employs an efficient master/multislave transmission control technique and combines online scheduling with online admission control, to guarantee continued real-time operation under dynamic communication requirements, together with data structures and mechanisms that are tailored to support dynamic QoS management. The paper includes a sample application, aiming at the management of video streams, which highlights the protocol's ability to support dynamic QoS management with real-time guarantees.

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FTT-Ethernet: a flexible real-time communication protocol that supports dynamic QoS management on Ethernet-based systems

Despite having been designed to interconnect office equipment such as computers and printers, since its early daysEthernet has also been considered for use in the industrial domain. However, it was not originally developed to meet the requirements of real-time industrial automation systems and it was commonly considered unsuited for applications at the field level, i.e.to interconnect sensors, actuators and controllers. Therefore, along its 30 years of existence, several proposals have been presented to make this protocol exhibit real-timebehaviour. Nevertheless, these proposals either require specialised hardware, or are suited to soft-real-time operation only, or are bandwidth or response-time inefficient. This paper presents an overview about the work previously done towards real-time communication on Ethernet. Then, it presents a new protocol, FTT-Ethernet, which relies on common network adapters and on a new transmission control named master/multi-slave that efficiently supports hard-real-time operation in a flexible way.

The FTT-ethernet protocol: merging flexibility, timeliness and efficiency

The new generation of embedded systems for automotive applications can take advantage of low-cost multiprocessor system-on a chip architectures. The real-time software applications running on these systems require realtime processor scheduling, and also require the management of the communication and synchronization of tasks executing on different processors with limited blocking time. Conventional real-time technologies, like the Rate Monotonic scheduling algorithm together with the Multiprocessor Priority Ceiling Protocol (MPCP) can be used to this purpose. In earlier work, we proposed the Multiprocessor Stack Resource Policy (MSRP) for scheduling tasks and sharing resources in multiprocessor on a chip architectures. In this paper we present an experimental evaluation that compares the performance of our algorithm with a solution based on Rate Monotonic and MPCP in the con text of the Janus multiple processor architecture. The evaluation of the algorithm has been triggered by our ongoing research in the automotive domain. We report on two sets of experiments: the first addresses a range of generic task configurations to see if one of the algorithms can clearly outperform the other The results show MSRP to be better for random task periods but are probably not conclusive. Later we focus on a more application-specific (also more restrictive) architecture design representing a typical automotive application: a power-train controller In this case, MSRP clearly performs better The performance gap between the two policies can be further increased when considering that MSRP is much simpler to implement, it has a lower overhead, and it allows RAM memory optimization.

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A comparison of MPCP and MSRP when sharing resources in the Janus multiple-processor on a chip platform

This paper presents a dynamic configurable kernel architecture designed for supporting a simple implementation, integration and evaluation of scheduling algorithms. The main goal of the proposed architecture is to provide a platform for fast prototyping scheduling algorithms both for the CPU and for the devices. The kernel is fully modular in terms of scheduling policies, aperiodic servers, and concurrency control protocols, allowing applications to be developed independently from a particular system configuration. Finally, the system is compliant with the POSIX 1003.13 PSE52 specifications to simplify porting of application code developed for other POSIX compliant kernels.

Paolo Gai

Papers

Minimizing memory utilization of real-time task sets in single and multi-processor systems-on-a-chip

FTT-Ethernet: a flexible real-time communication protocol that supports dynamic QoS management on Ethernet-based systems

The FTT-ethernet protocol: merging flexibility, timeliness and efficiency

A comparison of MPCP and MSRP when sharing resources in the Janus multiple-processor on a chip platform

A new kernel approach for modular real-time systems development