Real-time Extension Research Articles

A formal framework capturing real-time and stochastic behavior in connectors

• We propose an extension for Reo, including both new primitive channels and semantics as stochastic timed automata. • We adapt PTCTL to describe the properties of stochastic and timed connectors. • We develop a Python framework to model and verify stochastic and timed connectors. Modern distributed systems are often coupled with flexible architectures, composed of heterogeneous components, and deployed on different execution nodes. In such architectures, connectors (or middlewares) are widely used to orchestrate the separated components and make them functioning. Apparently, correctness of such systems highly depends on the behavior of connectors. Reo is a channel-based coordination language where complex connectors are compositionally constructed from simpler ones. In this paper, we propose a stochastic and real-time extension of Reo, including a set of new primitive channels and an expressive semantics as Stochastic Timed Automata for Reo ( STA r ). Furthermore, a logical formalization of STA r for property analysis has been proposed and the transformation from STA r to PRISM and JANI has been implemented. Several case studies are presented to demonstrate how STA r and its corresponding logic can be used to capture coordination scenarios in the real world.

A Method for Measuring the Constraint Complexity of Components in Automotive Embedded Software Systems

The rapid growth of software-based functionalities has made automotive Electronic Control Units (ECUs) significantly complex. Factors affecting the software complexity of components embedded in an ECU depend not only on their interface and interaction properties, but also on the structural constraints characterized by a component’s functional semantics and timing constraints described by AUTomotive Open System ARchitecture (AUTOSAR) languages. Traditional constraint complexity measures are not adequate for the components in embedded software systems as they do not yet sufficiently provide a measure of the complexity due to timing constraints which are important for quantifying the dynamic behavior of components at run-time. This paper presents a method for measuring the constraint complexity of components in automotive embedded software systems at the specification level. It first enables system designers to define non-deterministic constraints on the event chains associated with components using the AUTOSAR-based Modeling and Analysis of Real-Time and Embedded systems (MARTE)-UML and Timing Augmented Description Language (TADL). Then, system analysts use Unified Modeling Language (UML)-compliant Object Constraint Language (OCL) and its Real-time extension (RT-OCL) to specify the structural and timing constraints on events and event chains and estimate the constraint complexity of components using a measure we have developed. A preliminary version of the method was presented in M. Garg and R. Lai, Measuring the constraint complexity of automotive embedded software systems, in Proc. Int. Conf. Data and Software Engineering, 2014, pp. 1–6. To demonstrate the usefulness of our method, we have applied it to an automotive Anti-lock Brake System (ABS).

Application validation on RTDroid

Android is becoming used more frequently in domains that expect some real-time guarantees. To facilitate the adoption of Android for programming real-time systems, this work presents a first effort to apply real-time scheduling theories to a real-time extension on Android, RTDroid. We integrate real-time properties specified in RT-Droid's application manifest with an existing real-time scheduling framework, Cheddar. We leverage Cheddar to perform schedulability analysis and feasibility tests, based on the properties of RTDroid application components specified in the application manifest. This paper details our integration process and reports our experience of validating real-time properties in a real-time application developed on RTDroid.

A compositional approach for modeling and timing analysis of wireless sensor and actuator networks

Wireless sensor and actuator networks (WSAN) are created through the integration of multiple nodes which acquire data and perform reaction based on them. In a general overview, sensor nodes of WSANs are responsible for data acquisition and sending them to a central node. The central node stores all the received data and performs reactions. Timing verification of WSAN applications to ensure schedulability of tasks is a challenge, and is generally performed by worst-case analysis. This process is error-prone and inherently conservative. On the other hand, using model checking for analyzing WSAN applications results in state space explosion even for middle-sized configurations. The reason is the necessity of considering the interleaving of the large number of sensors in WSANs. In this paper, we show how to build an actor-based model of WSAN applications, starting from sensor node-level and moving towards the full system, and we show how this compositional modeling improves analysability and modifiability. Realtime extension of actor model is appropriate for modeling WSAN applications where we have many concurrent and asynchronous processes, and interdependent realtime deadlines. We demonstrate the approach using a case study of a distributed realtime data acquisition system for high-frequency sensing, where Timed Rebeca is used for modeling. We use model checking to check the intra/inter-sensor node schedulability.

공개 임베디드 하드웨어의 실시간 메커니즘 성능 분석

Open hardware platforms are gaining wide popularity in various fields of technology for their accessibility and inexpensiveness. Although availability of these platforms is undeniable, the performance of these machines in handling tasks which require execution within critical time constraints is still in question. Moreover, technical documentation and support for open hardware are scarce in comparison to expensive commercially distributed platforms. In this paper, we present a detailed process to implement embedded Linux and the real-time extension of Xenomai to two popular open embedded hardware, BeagleBone Black and i.MX6Q SABRELite. Also, we analyze the response time of real-time mechanisms and its performance for inter-task communication (ITC) between real-time tasks. Response time of real-time mechanisms is an important measure to predict the realtime performance of each platform. The performance evaluation is performed both in kernel space and user space using the metrics of jitter, to estimate the periodicity of the cyclic task, and execution time of three real-time mechanisms including semaphore, message queue, and message pipe. The results of this study would serve as a guideline in developing real-time systems on low cost open embedded hardware platforms using the real-time Linux extension of Xenomai.

P.1.g.059 - Acute dose-response effects of LSD in healthy humans

EtherCAT has been widely applied in the motion control domain due to its advantages of the fast response speed, low CPU usage and good synchronization performance. Although the built-in distributed clock (DC) synchronization mechanism exhibits strong performance between slaves, the method of clock synchronization between the master and the reference clock is left open for selection by users and there are very few studies in this area. This paper introduces three synchronization modes for EtherCAT and analyzes the reasons for packet loss in free run mode and DC mode. This paper presents a novel method to realize the master clock synchronization with the reference clock. The proposed method can eliminate the settling time which is unusual in other synchronization mechanisms. The method is implemented on Windows with real-time extension and experimental results prove its feasibility.

The design and experimental research of an open architecture soft-CNC system based on RTX and an IPC

The concept of open architectures has been discussed extensively for many years. Software-oriented Computer Numerical Control (soft-CNC) is considered as one of the ideal solutions for open architecture CNC (OACNC). In recent years, this has become the mainstream direction for open CNC systems by employing a personal computer (PC) as the hardware platform and a real-time operating system as the software platform. However, existing CNC systems are limited in expansibility, portability, modularity, networking, and openness. In order to overcome these problems and in accordance with the characteristics and requirements of an OACNC system, a novel numerical control kernel (NCK) based on the real-time extension (RTX) and an industrial personal computer (IPC) is proposed. The implementation of the NCK is a difficult task, especially when real-time performance is desired. To compensate for the lack of real-time features in Windows NT, RTX provides a real-time software environment to implement the time-critical operations of a CNC system on an IPC by modifying the hardware abstraction layer (HAL). The proposed soft-CNC system consists of four components: the human machine interface (HMI), shared memory, the real-time subsystem (RTSS), and the device layer. This work first presents the hierarchical system architecture for developing an open architecture soft-CNC system and then describes the choices for the hardware and software platform of the soft-CNC system. Furthermore, this paper focuses on the software design and implementation of the soft-CNC system; thus, the software tasks, data flow, and the communication mechanisms are studied in detail. Finally, experiments are conducted to validate the real-time performance, the schedulability and the functions of the proposed soft-CNC system, thus verifying its feasibility.

A clock synchronization method for EtherCAT master

EtherCAT has been widely applied in the motion control domain due to its advantages of the fast response speed, low CPU usage and good synchronization performance. Although the built-in distributed clock (DC) synchronization mechanism exhibits strong performance between slaves, the method of clock synchronization between the master and the reference clock is left open for selection by users and there are very few studies in this area. This paper introduces three synchronization modes for EtherCAT and analyzes the reasons for packet loss in free run mode and DC mode. This paper presents a novel method to realize the master clock synchronization with the reference clock. The proposed method can eliminate the settling time which is unusual in other synchronization mechanisms. The method is implemented on Windows with real-time extension and experimental results prove its feasibility.

Estimation of Link Speed Distribution from Probe Vehicle Data

Probes with GPS devices reveal useful information for traffic conditions, but the high level of noise and the sparsity of observations make it challenging to estimate speed distribution from the data collected. This paper proposes a Bayesian approach for estimating link speed distribution from GPS-equipped probe data. The key contribution of the study is a generic hierarchical Monte Carlo Markov chain algorithm for sampling from probe speed distribution, with Gaussian mixture models for probe speed clustering. The algorithm combines Gibbs sampling and Metropolis–Hastings sampling to improve convergence speed. A rigorous mathematical discussion is provided for the simulation approach. The algorithm is evaluated with synthetic data and real-world probe data and shows the feasibility of the approach. Results also confirm the computational advantages of the proposed algorithm and suggest its potential for real-time extension.

Real-time capabilities of Linux RTAI

Abstract: This article deals with the Linux real-time extension RTAI. This extension provides soft real-time capabilities in the user space and hard real-time capabilities in the kernel space. In this work, some key parameters of the RTOS are measured such as switching context time, periodic thread jitter, interrupt latency response, execution time of synchronization primitives and heap allocation time. This measurements create a test bench of real-time system capabilities which should help the developer to create truly real-time application on the specific hardware based on measured real-time capabilities. RTAI functions can be called from the user space using LXRT and also from the kernel space. These two spaces are compared from the point of view of the developer and real-time capabilities. All measurements have been done on the LinuxCNC 2.7 based on Debian 3.4 distribution running on AMD Athlon XP 3000+ uniprocessor. To accomplish these measurements, new benchmark application has been developed.

Real-time motion control on Android platform

Recently, it is increasingly important to provide good real-time performance with the Android platform, since it has been used in industrial devices. The Android platform, however, does not provide a tight real-time guarantee that is required by such industrial devices as robots. Until a real-time extension of the Android platform becomes publicly available, application developers need a lightweight application-centric approach to achieve good real-time performance on the existing platform. This paper proposes an application-centric approach requiring no real-time extensions of the Android platform, which centers around multi-core partitioning and partition-aware application design. Following the proposed approach, we present an implementation study of motion control applications where the real-time tasks of the target application run on dedicated processor cores as a native Linux process while the non-real-time tasks run on other cores as an Android process. In the paper, we prove that the proposed approach is enough effective to deal with motion control applications on the existing Android platform with no real-time extensions. Our experiments show that on a quad-core Android board we can achieve such a good real-time performance as 99 % task activation jitters less than 5 µs for a motion control application with four real-time tasks and a period of 500 µs.

Abstraction in Fixpoint Logic

We present a theory of abstraction for the framework of parameterised Boolean equation systems, a first-order fixpoint logic. Parameterised Boolean equation systems can be used to solve a variety of problems in verification. We study the capabilities of the abstraction theory by comparing it to an abstraction theory for Generalised Kripke modal Transition Systems (GTSs). We show that for model checking the modal μ-calculus, our abstractions can be exponentially more succinct than GTSs and our theory is as complete as the GTS framework for abstraction. Furthermore, we investigate the completeness of our theory irrespective of the encoded decision problem. We illustrate the potential of our theory through case studies using the first-order modal μ-calculus and a real-time extension thereof, conducted using a prototype implementation of a new syntactic transformation for parameterised Boolean equation systems.

3D culture model of fibroblast-mediated collagen creep to identify abnormal cell behaviour.

Native collagen gels are important biomimetic cell support scaffolds, and a plastic compression process can now be used to rapidly remove fluid to any required collagen density, producing strong 3D tissue-like models. This study aimed to measure the mechanical creep properties of such scaffolds and to quantify any enhanced creep occurring in the presence of cells (cell-mediated creep). The test rig developed applies constant creep tension during culture and measures real-time extension due to cell action. This was used to model extracellular matrix creep, implicated in the transversalis fascia (TF) in inguinal hernia. Experiments showed that at an applied tension equivalent to 15% break strength, cell-mediated creep over 24-h culture periods was identified at creep rates of 0.46 and 0.38%/h for normal TF and human dermal fibroblasts, respectively. However, hernia TF fibroblasts produced negligible cell-mediated creep levels under the same conditions. Raising the cell culture temperature from 4 to 37 °C was used to demonstrate live cell dependence of this creep. This represents the first in vitro demonstration of TF cell-mediated collagen creep and to our knowledge the first demonstration of a functional, hernia-related cell abnormality.

Embedded Real-Time HTTP Server

This paper presents the architecture of embedded real-time web server. Unlike existing web servers, in our approach, requests are processed not in the “first in first out” order but according to their deadlines and the expected server load. For this purpose the Least Laxity First scheduling method is used. First, requests with imposed hard real-time constraints are served. Then requests enclosed by soft deadlines are processed. Finally, request without time requirements are served in the order they arrived. We also present real-time extensions to the Hypertext Transfer Protocol. We propose headers that enable defining hard and soft deadlines, as well as responses containing time information, that are being sent to the client application. The experimental results showed that in case of real-time applications our server misses significantly fewer requests, due to time out, then existing solutions. The presented server may be very useful for implementing real-time services supported by embedded systems, e.g. in future real-time “Internet of things” applications.

Study on Real-time Extension Fault Detection for a XXY Stage by using Chaos Synchronization

This paper proposes the chaos synchronization-based XXY stage real-time extension fault detection; the main characteristic signal is extracted by filtering from the microvibration of stage. The chaos synchronization systems are used to extract the dynamical map of chaotic synchronization error. The Eigen value is extracted from the centroid value of phase plane plot, and the value is analyzed by extension theory, so as to determine the state of XXY stage. The stage states can be detected by the PC based real-time analysis; there are four fault statuses, including normal, X1 motor fault, X2 motor fault and Y motor fault. The dSPACE is used for signal acquisition and monitoring interface making. The real-time fault monitoring and diagnosis can be implemented at the computer side. All Rights Reserved © 2015 Universidad Nacional Autonoma de Mexico, Centro de Ciencias Aplicadas y Desarrollo Tecnologico. This is an open access item distributed under the Creative Commons CC License BY-NC-ND 4.0.

Real-Time Communication Subsystem for CAN Bus

Networked control systems (NCS) are focused on a real-time control over the several bus types. Real-time extensions for the operating systems, which are popular in industrial applications, were developed to ensure precise timing. Aim of this paper is to present a communication platform for real-time process control. Platform communicates with CNC laboratory model of industrial plasma cutter via CAN bus. Real-time extension RTAI with communication driver modification was used to develop such platform. Console application was programmed to interact with the laboratory model in manual operation mode.

An executable formal semantics for UML-RT

We propose a formal semantics for UML-RT, a UML profile for real-time and embedded systems. The formal semantics is given by mapping UML-RT models into a language called kiltera, a real-time extension of the $$\pi $$ -calculus. Previous attempts to formalize the semantics of UML-RT have fallen short by considering only a very small subset of the language and providing fundamentally incomplete semantics based on incorrect assumptions, such as a one-to-one correspondence between “capsules” and threads. Our semantics is novel in several ways: (1) it deals with both state machine diagrams and capsule diagrams; (2) it deals with aspects of UML-RT that have not been formalized before, such as thread allocation, service provision points, and service access points; (3) it supports an action language; and (4) the translation has been implemented in the form of a transformation from UML-RT models created with IBM’s RSA-RTE tool, into kiltera code. To our knowledge, this is the most comprehensive formal semantics for UML-RT to date.

Scalable and Robust Demand Response With Mixed-Integer Constraints

A demand response (DR) problem is considered entailing a set of devices/subscribers, whose operating conditions are modeled using mixed-integer constraints. Device operational periods and power consumption levels are optimized in response to dynamic pricing information to balance user satisfaction and energy cost. Renewable energy resources and energy storage systems are also incorporated. Since DR becomes more effective as the number of participants grows, scalability is ensured through a parallel distributed algorithm, in which a DR coordinator and DR subscribers solve individual subproblems, guided by certain coordination signals. As the problem scales, the recovered solution becomes near-optimal. Robustness to random variations in electricity price and renewable generation is effected through robust optimization techniques. Real-time extension is also discussed. Numerical tests validate the proposed approach.

Research for the Control Software of Six-Freedom Simulation Platform Based on RTX

This paper proposes a kind of design and realization method of real time control system that based on the Windows real time extension module RTX, which can meet the requirement of six-freedom Stewart platform control system to the real time. The design of the control system was divided into real-time layer and non-real-time layer according to the requirements of various functions to the real-time, and the data communication was realized by means of inter-process communication mechanism. The analysis conclusion to experiments data indicates that the control system is stable in operation and good in real-time performance.

1553B Bus Interface Driver Software Design and Implement Based on RTX

In order to solve the application problem of 1553B bus under RTX, we design 1553B bus interface driver software based on RXT, system operating environment are Windows XP and RTX real-time extension module, it can solve the issues of 1553B bus real-time drive under RXT and ensure the real-time and fault-tolerant character of bus interface drive software.