-Ming Huang

Cyber-physical systems for real-time hybrid structural testing: a case study

Real-time hybrid testing of civil structures, in which computational models and physical components must be integrated with high fidelity at run-time, represents a grand challenge in the emerging area of cyber-physical systems. Actuator dynamics, complex interactions among computers and physical components, and computation and communication delays all must be managed carefully to achieve accurate tests. In this paper we present a case study of several fundamental interlocking challenges in developing and evaluating cyber-physical systems for real-time hybrid structural testing: (1) how physical and simulated components can be integrated flexibly and efficiently within a common reusable middleware architecture; (2) how predictable timing can be achieved atop commonly available hardware and software platforms; and (3) how physical vs. simulated versions of different components within a system can be interchanged with high fidelity between comparable configurations. Experimental results obtained through this case study give evidence of the feasibility and efficacy of these steps towards our overall goal: to develop a Cyber-physical Instrument for Real-time hybrid Structural Testing (CIRST).

Towards Configurable Real-Time Hybrid Structural Testing: A Cyber-Physical System Approach

Real-time hybrid testing of civil structures represents agrand challenge in the emerging area of cyber-physical systems. Hybrid testing improves significantly on either purely numerical or purely empirical approaches by integrating physical structural components and computational models. Actuator dynamics, complex interactions among computers and physical components, and computation and communication delays all hamper the ability to conduct accurate tests. To address these challenges, this paper presents initial work towards a Cyber-physical Instrument for Real-time hybrid Structural Testing (CIRST). CIRST aims to provide two salient features: a highly configurable architecture for integrating computers and physical components; and system support for real-time operations in distributed hybrid testing. This paper presents the motivation of the CIRST architectureand preliminary test results from a proof-of-concept implementation that integrates a simple structural element and simulation model. CIRST will have broad impacts on thefields of both civil engineering and real-time computing.It will enable high-fidelity real-time hybrid testing of awide range of civil infrastructures, and will also providea high-impact cyber-physical application for the study andevaluation of real-time middleware.

ORB middleware evolution for networked embedded systems

Standards-based COTS (common-off-the-shelf) middleware has been shown to be effective in meeting a range of functional and QoS (quality of service) requirements for distributed real-time and embedded (DRE) systems. Each standard makes limiting assumptions, often implicit, about the fundamental set of system capabilities and constraints typical of the domain to which the standard applies. When the characteristics of a particular class of systems violates a standards assumptions, it may be appropriate to modify or extent the standard and its conforming implementations to better match the actual characteristics of that class of systems while still exploiting the capabilities of the standard. In this paper, we argue that key assumptions upon which even the more advanced middleware standards are based, e.g., Real-Time CORBA (RT-CORBA), are violated by an important class of DRE systems characterized by the following properties: (1) highly connected networks of (2) numerous memory-constrained endsystems, with (3) stringent timeliness requirements, and (4) support for adaptive reconfiguration of computation and communication elements and their associated timeliness requirements. We describe our recent work on nORB, a small footprint ORB middleware framework for the Boeing Open Experimental Platform (OEP) under the DARPA Nest program, to meet this entire set of requirements by adapting, unifying, and extending patterns and techniques from earlier related research on COTS middleware frameworks, such as UBI-core, ACE, Kokyu, and TAO.

Priority Scheduling in TinyOS : A Case Study

In recent years, networked sensors are finding use in a variety of different applications ranging from temperature monitoring to battlefield strategy planning. Advances in fabrication techniques have led to the development of sensor-actuator devices called MEMS. It has now become possible to move software closer to where the “action” is, i.e. the sensors themselves. These sensor devices typically have a micro-controller, instruction and data memory, a radio module for wireless communication and an operating system. These devices are severely resource constrained in terms of memory, processing power and energy, since most of these devices are battery driven. A sensor network consists of a number of sensors spread across a geographical area. Each sensor has wireless communication capability and sufficient intelligence for signal processing and networking of the data. In this paper, we discuss a mechanism to achieve prioritized task scheduling in TinyOS. We investigate into the details of how the task scheduling is currently done in TinyOS and the adverse effects that this could cause. We show use-cases where certain ”important” tasks could be given less preference when compared to other ”notso-important” tasks. We propose a new mechanism at the programming model level to introduce the concept of priority for a task and explain how the scheduling module has to be changed to enforce this priority scheme. Finally, we show empirical results to justify our solution.

CAMRIT: control-based adaptive middleware for real-time image transmission

Real-time image transmission is crucial to an emerging class of distributed embedded systems operating in open network environments. Examples include avionics mission re-planning over Link-16, security systems based on wireless camera networks, and online collaboration using camera phones. Meeting image transmission deadlines is a key challenge in such systems due to unpredictable network conditions. In this paper, we present CAMRIT, a control-based adaptive middleware framework for real-time image transmission in distributed real-time embedded systems. CAMRIT features a distributed feedback control loop that meets image transmission deadlines by dynamically adjusting the quality of image tiles. We derive an analytic model that captures the dynamics of a distributed middleware architecture. A control theoretic methodology is applied to systematically design a control algorithm with analytic assurance of system stability and performance, despite uncertainties in network bandwidth. Experimental results demonstrate that CAMRIT can provide robust real-time guarantees for a representative application scenario.

Control-Based Adaptive Middleware for Real-Time Image Transmission over Bandwidth-Constrained Networks

Real-time image transmission is crucial to an emerging class of distributed embedded systems operating in open network environments. Examples include avionics mission replanning over Link-16, security systems based on wireless camera networks, and online collaboration using camera phones. Meeting image transmission deadlines is a key challenge in such systems due to unpredictable network conditions. In this paper, we present CAMRIT, a Control-based Adaptive Middleware framework for Real-time Image Transmission in distributed real-time embedded systems. CAMRIT features a distributed feedback control loop that meets image transmission deadlines by dynamically adjusting the quality of image tiles. We derive an analytic model that captures the dynamics of a distributed middleware architecture. A control-theoretic methodology is applied to systematically design a control algorithm with analytic assurance of system stability and performance, despite uncertainties in network bandwidth. Experimental results demonstrate that CAMRIT can provide robust real-time guarantees for a representative application scenario.

Design and performance of a fault-tolerant real-time CORBA event service

Developing distributed real-time and embedded (DRE) systems in which multiple quality-of-service (QoS) dimensions must be managed is an important and challenging problem. This paper makes three contributions to research on multi-dimensional QoS for DRE systems. First, it describes the design and implementation of a fault-tolerant real-time CORBA event service for the ACE ORB (TAO). Second, it describes our enhancements and extensions to features in TAO, to integrate real-time and fault tolerance properties. Third, it presents an empirical evaluation of our approach. Our results show that with some refinements, real-time and fault-tolerance features can be integrated effectively and efficiently in a CORBA event service

MCFlow: A Real-Time Multi-core Aware Middleware for Dependent Task Graphs

Driven by the evolution of modern computer architectures from uni-processor to multi-core platforms, there is an increasing need to provide light-weight, efficient, and predictable support for fine-grained parallel and distributed execution of soft real-time tasks with end-to-end timing constraints, modeled as directed a cyclic graphs whose edges capture dependences among their subtasks. At the same time, there is a need to support state of the art programming models such as distributed components, whose ability to encapsulate functionality and allow context-specific optimizations is essential to manage the increasing complexity of modern distributed real-time and embedded systems and systems-of-systems. Real-time distributed middleware such as RT-CORBA has not kept pace with these developments, and a new generation of middleware is needed that can map these dependent subtask graphs onto distributed hosts with multi-core architectures, efficiently and within a simple, lightweight, and intuitive component programming model. To overcome these limitations, we have designed and implemented MC Flow, a novel distributed real-time component middleware for dependent subtask graphs running on multi-core platforms. MC Flow provides three new contributions to the state of the art in real-time component middleware: (1) a very lightweight component model that facilitates system integration and deployment through automatic code generation at compile time from a deployment plan specification, (2) transparent optimization of inter-component communication, and (3) the use of interface polymorphism to separate functional correctness from data copying and other performance constraints so that they can be configured and enforced independently but in a type-safe manner. Empirical evaluations of our approach in comparison to the widely used TAO real-time middleware show that MC Flow performs comparably to TAO when only one core is used and outperforms TAO when multiple cores are involved.

Modeling Timed Component-Based Real-time Systems

Component based middleware helps to facilitate software reuse by separating application-specific concerns into modular components that are shielded from the concerns of other components and from the common concerns addressed by underlying middleware services. In real-time systems, concerns such as invocation rates, execution latencies, deadlines, and concurrency semantics cross-cut multiple component and middleware abstractions. Thus, the verification of these systems must consider features of the application components (e.g., their execution latencies and relative invocation rates) and of the supporting middleware (e.g., concurrency and scheduling) together. However, existing approaches only address a sub-set of the features that must be modeled in component based real-time systems, and a new more comprehensive approach is needed. To address that need, this paper offers three main contributions to the state of the art in the verification of component based real-time systems: (1) it introduces a formal model called component automata that combines new input/output rate specifications with input/output actions and timed internal actions from the existing interface automata and timed automata models respectively; (2) it presents new component composition operations for single-threaded and cooperative Notes: This research was supported in part by NSF grant CCF-0448562 titled CAREER: Time and Event Based System Software Construction. Type of Report: Other Department of Computer Science & Engineering Washington University in St. Louis Campus Box 1045 St. Louis, MO 63130 ph: (314) 935-6160 Modeling Timed Component-Based Real-time Systems∗ Huang-Ming Huang and Christopher Gill Department of Computer Science and Engineering Washington University, St.Louis, MO, USA {hh1, cdgill}@cse.wustl.edu

Corrections to and Discussion of “Implementation and Evaluation of Mixed-criticality Scheduling Approaches for Sporadic Tasks”

The AMC-IA mixed-criticality scheduling analysis was proposed as an improvement to the AMC-MAX adaptive mixed-criticality scheduling analysis. However, we have identified several necessary corrections to the AMC-IA analysis. In this article, we motivate and describe those corrections, and discuss and illustrate why the corrected AMC-IA analysis cannot be shown to outperform AMC-MAX.