<p>Distributed real-time systems are notoriously difficult to correctly design and construct [Pam as 1985]. The fundamental principles of concurrency, deadline driven scheduling, and reaction to external stimuli which underlie such systems are inherently complex. This difficulty is further exacerbated when applications based on these principles are distributed over a network. Academic instruction in this domain is challenging: while theoretical issues can be taught with traditional "pencil and paper" techniques, real-time programming skills require experience that can be best provided by a laboratory. To this end, the Computer Science Department at Virginia Tech created and built a laboratory, known as the Reactive Systems Laboratory (RSL), specifically designed to provide these practical experiences. This paper documents the decisions, designs, and equipment used to build this laboratory. Additionally, the low-level software systems required to operate the RSL are discussed. Finally, future directions for the laboratory are considered and some conclusions are drawn based on usage to-date.</p> / Master of Science

Indiana University-Purdue University Indianapolis (IUPUI) / This thesis demonstrates a novel idea on how components in a distributed real-time & embedded (DRE) system can choose from different data interchange formats at run-time. It also quantitatively evaluates three binary data interchange protocols used in distributed real-time & embedded (DRE) systems: the Common Data Representation (CDR), which collects data "as-is" into a buffer; Binary JSON (BSON), which enables "on the fly" discovery of elements in a message; and FIX Adapted for Streaming (FAST), which is a binary compression algorithm popularly used for data exchange in financial stock market domain. We compare these three data exchange formats to determine if it is possible to minimize the data usage without compromising CPU processing times, data throughput, and data latency. The lack of such a study has made protocols such as CDR popular based on the assumption that collecting data "as-is" will consume less processing time and send with high throughput. We perform the study in the context of an Open Source Architecture for Software Instrumentation of Systems (OASIS). To perform our study, we modified its existing data interchange framework to flexibly and seamlessly integrate either format, and let the components choose a format at run-time. The experiments from our study shows that as data size increases, the throughput of CDR, BSON, and FAST decreases by 96.16%, 97.23%, and 84.41%, respectively. The increase in packaging and un-packaging times are 1985.12% and 1642.28% for FAST, compared to 3158.96% and 2312.50% for CDR, and 5077.98% and 3686.48% for BSON.

No description available.

Energy consumption is increasingly affecting battery life and cooling for real- time systems. Dynamic Voltage and frequency Scaling (DVS) has been shown to substantially reduce the energy consumption of uniprocessor real-time systems. It is worthwhile to extend the efficient DVS scheduling algorithms to distributed system with dependent tasks. The dissertation describes how to extend several effective uniprocessor DVS schedul- ing algorithms to distributed system with dependent task set. Task assignment and deadline assignment heuristics are proposed and compared with existing heuristics concerning energy-conserving performance. An admission test and a deadline com- putation algorithm are presented in the dissertation for dynamic task set to accept the arriving task in a DVS scheduled real-time system. Simulations show that an effective distributed DVS scheduling is capable of saving as much as 89% of energy that would be consumed without using DVS scheduling. It is also shown that task assignment and deadline assignment affect the energy- conserving performance of DVS scheduling algorithms. For some aggressive DVS scheduling algorithms, however, the effect of task assignment is negligible. The ad- mission test accept over 80% of tasks that can be accepted by a non-DVS scheduler to a DVS scheduled real-time system.

A distributed real-time database (DRTDB) is a database distributed over a network on several nodes and where the transactions are associated with deadlines. The issues of concern in this kind of database are data consistency and the ability to meet deadlines. In addition, there is the possibility that the nodes, on which the database is distributed, are heterogeneous. This means that the nodes may be built on different platforms and written in different languages. This makes the integration of these nodes difficult, since data types may be represented differently on different nodes. The common object request broker architecture (CORBA), defined by the Object Management Group (OMG), is a distributed object computing (DOC) middleware created to overcome problems with heterogeneous sites. The project described in this paper aims to investigate the suitability of CORBA as a middleware in a DRTDB. Two extensions to CORBA, Fault-Tolerance CORBA (FT-CORBA) and Real-Time CORBA (RT-CORBA) is of particular interest since the combination of these extensions provides the features for object replication and end-to-end predictability, respectively. The project focuses on the ability of RT-CORBA meeting hard deadlines and FT-CORBA maintaining replica consistency by using replication with eventual consistency. The investigation of the combination of RT-CORBA and FT-CORBA results in two proposed architectures that meet real-time requirements and provides replica consistency with CORBA as the middleware in a DRTDB.

Software testing is an important phase the of software development cycle which reveals faults and ensures correctness of the developed software. Distributed real-time systems are mostly safety critical systems for which the correctness and quality of the software is much more significant. However, majority of the current testing techniques have been developed for sequential (non real-time) software and there is a limited amount of research on testing distributed real-time systems. In this thesis, a proposed approach in the academic literature testing distributed real-time systems using a distributed test architecture is implemented and compared to existing software testing practices in a software development company on a case study. Evaluation of the results show the benefits of using the considered distributed test approach on distributed real-time systems in terms of software correctness.

<p>Simulation is a good way to gain insight into a system, for example during development, without having to run or build the actual system. This is especially true for real-time systems, which often operate in hazardous environments or control critical entities in the 'real' world, making testing of these systems in their real environment unsafe during development.</p><p>When building simulations, one simulator is not likely to fit every type of simulation project. Therefore, different simulators, which focus on different aspects of simulation, are built. The High Level Architecture (HLA) from the Defense Modeling and Simulation Office (DMSO) is an architecture for distributed simulations providing a means to communicate between different simulations.</p><p>However, the HLA standard has limitations if viewed from a real-time perspective. For example, there is no built-in support for fault tolerance. In this thesis some of the limitations in HLA are identified and an extended architecture that uses a distributed active real-time database as a way to overcome these limitations is presented. One of the major advantages with this new extended HLA architecture is that it is still compliant with HLA, i.e., no modifications have been made to the HLA interfaces.</p>

<p>A distributed real-time database (DRTDB) is a database distributed over a network on several nodes and where the transactions are associated with deadlines. The issues of concern in this kind of database are data consistency and the ability to meet deadlines. In addition, there is the possibility that the nodes, on which the database is distributed, are heterogeneous. This means that the nodes may be built on different platforms and written in different languages. This makes the integration of these nodes difficult, since data types may be represented differently on different nodes. The common object request broker architecture (CORBA), defined by the Object Management Group (OMG), is a distributed object computing (DOC) middleware created to overcome problems with heterogeneous sites.</p><p>The project described in this paper aims to investigate the suitability of CORBA as a middleware in a DRTDB. Two extensions to CORBA, Fault-Tolerance CORBA (FT-CORBA) and Real-Time CORBA (RT-CORBA) is of particular interest since the combination of these extensions provides the features for object replication and end-to-end predictability, respectively. The project focuses on the ability of RT-CORBA meeting hard deadlines and FT-CORBA maintaining replica consistency by using replication with eventual consistency. The investigation of the combination of RT-CORBA and FT-CORBA results in two proposed architectures that meet real-time requirements and provides replica consistency with CORBA as the middleware in a DRTDB.</p>

<p>In a distributed real-time environment where it is imperative to make correct decisions it is important to have all facts available to make the most accurate decision in a certain situation. An example of such an environment is an Unmanned Aerial Vehicle (UAV) system where several UAVs cooperate to carry out a certain task and the data recorded is analyzed after the completion of the mission. This project aims to define and implement a time series architecture for use together with a distributed real-time database for the ability to store temporal data. The result from this project is a time series (TS) architecture that uses DeeDS, a distributed real-time database, for storage. The TS architecture is used by an application modelled from a UAV scenario for storing temporal data. The temporal data is produced by a simulator. The TS architecture solves the problem of storing temporal data for applications using DeeDS. The TS architecture is also useful as a foundation for integrating time series in DeeDS since it is designed for space efficiency and real-time requirements.</p>

The model- and component-based development approach has emerged as an attractive option for the development of Distributed Real-time Embedded (DRE) systems. In this thesis we target several issues such as modeling of legacy communication, extraction of end-to-end timing models and support for holistic response-time analysis of industrial component-based DRE systems. We introduce a new approach for modeling legacy network communication in component-based DRE systems. By introducing special-purpose components to encapsulate and abstract the communication protocols in DRE systems, we allow the use of legacy nodes and legacy protocols in a component- and model-based software engineering environment. The proposed approach also supports the state-of-the-practice development of component-based DRE systems. The Controller Area Network (CAN) is one of the widely used real-time networks in DRE systems especially in automotive domain. We identify that the existing analysis of CAN does not support common message transmission patterns which are implemented by some high-level protocols used in the industry. Consequently, we extend the existing analysis to facilitate the worst-case response-time computation of these transmission patterns. The extended analysis is generally applicable to any high-level protocol for CAN that uses periodic, sporadic, or both periodic and sporadic transmission of messages. Because an end-to-end timing model should be available to perform the holistic response-time analysis, we present a method to extract the end-to-end timing models from component-based DRE systems. In order to show the applicability of our modeling techniques and extended analysis, we provide a proof of concept by extending the existing industrial component model (Rubus Component Model), implementing the holistic response-time analysis along with the extended analysis of CAN in the industrial tool suite (Rubus-ICE), and conducting an automotive case study. / EEMDEF