José M. Drake

Modeling distributed real-time systems with MAST 2

Abstract Switched networks have an increasingly important role in real-time communications. The IEEE Ethernet standards have defined prioritized traffic (802.1p) and other QoS mechanisms (802.1q). The Avionics Full-Duplex Switched Ethernet (AFDX) standard defines a hard real-time network based on switched Ethernet. Clock synchronization is also an important service in some real-time distributed systems because it allows a global notion of time for event timing and timing requirements. In the process of defining the new MAST 2 model, clock synchronization modeling capabilities have been added, and the network elements have been enhanced to include switches and routers. This paper introduces the schedulability model that will enable an automatic schedulability analysis of a distributed application using switched networks and clock synchronization mechanisms.

Ada-CCM: Component-Based Technology for Distributed Real-Time Systems

This paper proposes a technology for the development of distributed real-time component-based applications, which takes advantage of the features that Ada offers for the development of applications with predictable temporal behaviour, and which can be executed in embedded platforms with limited resources. The technology uses the Deployment and Configuration of Compo nent-based Distributed Applications Specification of the OMG for describing the components, the execution platforms and the applications. The framework defined in the Lightweight CCM standard of the OMG is taken as the basis of the internal architecture of the components and the applications. It has been extended with a number of features to make the temporal behaviour of the appli cations predictable. Among these extensions, the usage of CORBA has been replaced by special distributed components, called connectors, which implement the interaction between components by means of predictable and customizable communication services. Besides, special mechanisms have been introduced in the environment to make the threading characteristics of the components config urable. The technology fixes the responsibilities and the knowledge required by each actor involved in the component-based development process, and for each of them it defines the input and output artifacts that they have to manage.

Real-Time Modelling of Distributed Component-Based Applications

This paper presents a modular modelling methodology to formulate the timing behaviour of real-time distributed component-based applications. It allows to build real-time models of the platform resources and software components, which are reusable and independent of the applications that use them. The proposed methodology satisfies the completeness, opacity and composability properties, required to ensure that the complete real-time model of an application, able to predict its temporal behaviour by schedulability analysis or simulation, may be assembled by composition of the real-time models of its constituent parts. These real-time models present a dual descriptor/instance based nature. A class of component, independent of any application, is modelled as a parameterized class-type descriptor, which describes its inherent temporal behaviour and includes references to the real-time models of other hardware/software modules that it requires. An instance of the component in a concrete application context is modelled by an instance-type model, which is generated by assigning concrete values to the parameters and unsolved references of its corresponding descriptor. Instances are formed and combined by automatic tools to build complete analysis models for each specific real-time situation

Shared memory multimicroprocessor operating system with an extended Petri net model

We propose a methodology for programming multiprocessor event-driven systems. This methodology is based on two programming levels: the task level, which involves programming the basic actions that may be executed in the system as units with a single control thread; and the job level, on which parallel programs to be executed by the complete multiprocessor system are developed. We also present the structure and implementation of an operating system designed as the programming support for software development under the proposed methodology. The model that has been chosen for the representation of the system software is based on an extended Petri net, which provides a well-established conceptual model for the development of the tasks, thus allowing a totally independent and generic development. This model also facilitates job-level programming, since the Petri net is a very powerful description tool for the parallel program. >

Scheduling configuration of real-time component-based applications

This paper proposes a strategy to manage the scheduling of real-time component-based applications that is fully compatible with the concept of component viewed as a reusable and opaque software module. The strategy is used on top of the RT-CCM technology, which extends the OMG’s LwCCM technology with the purpose of building real-time distributed component-based applications that can be executed on embedded platforms and with heterogeneous communication services. The strategy is based on three services included in the RT-CCM framework, which are implemented by the containers of the components, and are in charge of supplying the threads and the synchronization artifacts that the business code of a component requires to implement its functionality. During the components configuration process, these services are used to assign the values that lead to a schedulable application to the scheduling parameters of these threads and synchronization mechanisms, without having to know the internal code of the components. The assigned values are obtained from the analysis of the real-time model of the application, which is built based on metadata provided by the components and the elements of the platform.

RT-D&C: Deployment Specification of Real-Time Component-Based Applications

This paper proposes an extension of the Deployment and Configuration of Component-based Distributed Applications Specification of the OMG (D&C) to support the development of applications with hard real-time requirements. The deployment plans of this kind of applications must include the configuration of the parameters that manage the components scheduling, in order to guarantee that the execution of the application always satisfies the specified timing constraints. The components must provide new metadata about their temporal behaviour and resource usage in order to schedule the applications in which they are used. The extension is formulated at platform independent model (PIM) level, based only on the models of component and application introduced in D&C, and on the requirements introduced by a reactive real-time paradigm. The extension is strictly compatible with the metamodel and the process defined in current D&C, adding some new modelling elements to the metamodel and new optional phases to the design application process, which are specific of applications with real-time requirements.

An Ada 2005 Technology for Distributed and Real-Time Component-Based Applications

The concept of interface in Ada 2005 significantly facilitates its usage as the basis for a software components technology. This technology, taking benefit of the resources that Ada offers for real-time systems development, would be suitable for component-based real-time applications that run on embedded platforms with limited resources. This paper proposes a model based technology for the implementation of distributed real-time component-based applications with Ada 2005. The proposed technology uses the specification of components and the framework defined in the LwCCM standard, modifying it with some key features that make the temporal behaviour of the applications executed on it, predictable, and analysable with schedulability analysis tools. Among these features, the dependency on CORBA is replaced by specialized communication components called connectors, the threads required by the components are created and managed by the environment, and interception mechanisms are placed to control their scheduling parameters in a per-transaction basis. This effort aims to lead to a new IDL to Ada mapping, a prospective standard of the OMG.

Compositional real-time models

This paper proposes a methodology for modelling the timing behaviour of hard real-time systems oriented to compositionality and reusability. When a system is built according to a modular structure, the methodology provides the system designer with capacity to build the real-time model of the system as a composition of the reusable timing models of the modules that make up the system. The modularization is applied at all levels: software, hardware and middleware. The methodology relies on a reactive modelling approach, i.e. the timing behaviour of a system is modelled by identifying and describing the timing behaviour of the activities executed in the system in response to events, coming either from the environment or from the timer. The methodology is based on the complementary concepts of model descriptor and model instance. The reusable timing model of a software or hardware module is formulated as a parameterized descriptor, which contains all the information about the internal elements of the module that is required to evaluate the behaviour of any application in which the module may be used. The analysable real-time model of a system is built by composing the model instances of the modules that form it, which are generated from their corresponding descriptors by assigning concrete values to all their parameters according to the specific configuration of the system.

Enabling Model-Driven Schedulability Analysis in the Development of Distributed Component-Based Real-Time Applications

This work presents a strategy to include temporal behaviour models in deliverable software components in order to develop hard real-time component-based distributed applications, keeping the opacity and composability features that are inherent to the components paradigm. The Deployment and Configuration of Component-based Distributed Applications Specification of the OMG has been extended to include and manage the information that is required to design, analyse, and configure component-based applications with hard real-time requirements. The real-time data added to a component interface enable the application designers to validate scheduling and design decisions without any knowledge of the component internals. Besides, real-time reusable and composable analysis models, developed according to a concrete modelling methodology, are added to each implementation of the component interface. In the context of a concrete application, they are processed by tools to generate the complete real-time analysis model of the application, which is used to evaluate the configuration parameters that guarantee its schedulability. The OMGs MARTE profile provides the conceptual and semantic framework to formulate the real-time behaviour models used in this work.

Modeling and schedulability analysis in the development of real-time distributed Ada systems

The paper proposes a model for specific Ada structures that can be integrated into our methodology for modeling and performing schedulability analysis in the development phases of distributed real-time applications written in Ada 95 and using its Annexes D and E. This methodology is based on independently modeling the platform, the logical components used, and the real-time situations of the application itself (real-time transactions, workload or timing requirements). The specific models presented in the paper provide support for the automated analysis of local and remote access to distributed services; hence, if a procedure of a remote call interface is invoked from a component assigned to a remote node, the corresponding communication model (with marshalling, transmission, dispatching, and unmarshalling of messages) is implicitly integrated into the overall model that is being analyzed.