Real-time Multitasking System Research Articles

Power Consumption Prediction in Real-Time Multitasking Systems

The paper presents a practical methodology for the prediction of power consumption of a multitask real-time system. The authors briefly recall the structure of the original multitasking time-predictable system. The system has a regular and scalable architecture. It consists of many cores based on pipeline processing with threads’ interleaving mechanism. In previous works, the authors have presented a number of issues related to the methodology of designing a time-predictable system and the scheduling of hardware threads with different design goals and constraints. The current article presents an accurate method for measuring the dynamic power dissipated in a system for various scenarios and the system configuration. The proposed approach is based on continuous monitoring of the power consumed by the FPGA, transmitting the measurements to the computer from the measuring device, and online analysis of the obtained results. The authors based their power estimation method on the original task frequency factor (TF). A theoretical analysis was made, and a series of practical experiments were carried out. The results obtained enable accurate estimation of the power requirements for the tasks performed in the real-time system. The presented technique can be useful during the design stage of multitasking real-time systems.

A Novel Multidimensional Tensile, Shear, and Buckling Sensor for the Measurement of Flexible Fibrous Materials.

To meet the complex and diverse demands for low-stress mechanical measurements of fabrics and other flexible materials, two integrated multidimensional force sensors with the same structure but different ranges were explored. They can support both rapid and precise low-noise, high-precision, low-cost, easy-to-use, reliable, and intelligent solutions for the complex measurement of fabric mechanics. Having analysed the mechanical relationship of the parallel beam theory, and considering the specific requirements of fabric measurement, a novel multi-dimensional force sensor is designed, capable of measuring tensile, shear, and buckling properties. Finite element analysis is used to simulate the mechanical performance of this sensor for fabric-loading/unloading measurement, and the sensitivity of the mechanical quantity transfer, the amount of sensor deformation, the stress distribution, and the degree of inter-dimensional coupling have been investigated and verified. The basis for subsequent digital processing is achieved by a low-offset, low-temperature-drift, low-power-consumption analogue front end, 24-bit ADC circuit, and signal conditioning electronics, suitable for the measurement of fabric mechanics under low stress, which is like the end-user requirements. The sensor information channel is supported by a host microcontroller with a DSP and a floating-point processing instruction set. Information processing is performed in time-sharing with the support of a multitasking real-time operating system. The purpose of designing this sensor is to facilitate the development of a new testing instrument, which will adopt the advances of current instruments whilst eliminating their shortcomings.

Specification and Verification of Multitask Real-Time Systems Using the OTS/CafeOBJ Method

Specification and Verification of Multitask Real-Time Systems Using the OTS/CafeOBJ Method

IJARCCE - Computer and Communication Engineering

Embedded system application is a hot topic in today's date & Linux gradually becomes the most important operating system for embedded applications. Embedded real-time system must be able to response and deal with system events within the pre-defined time limitation. In real-time multi-tasking system, a lot of events and multiple concurrent tasks are running at the same time. Therefore, to meet the system response time requirement, we must ensure that each mission can be achieved within the required time frame. Current Operating Systems includes a graphical user interface that is widely used. Due to the absence of Real-Time ability, current Operating Systems has not been suitable for all industrial applications. On the other hand normal operating system has the advantage of having both widespread applications and broad user acceptance. Moreover lot many low priced user programs are available. This is an attempt to create a way to make operating system useful for industrial real-time applications eliminating its disadvantages without giving up its advantages of popular user applications.

Explicit reservation of cache memory in a predictable, preemptive multitasking real-time system

We describe and evaluate explicit reservation of cache memory to reduce the cache-related preemption delay (CRPD) observed when tasks share a cache in a preemptive multitasking hard real-time system. We demonstrate the approach using measurements obtained from a hardware prototype, and present schedulability analyses for systems that share a cache by explicit reservation. These analyses form the basis for a series of experiments to further evaluate the approach. We find that explicit reservation is most useful for larger task sets with high utilization. Some task sets cannot be scheduled with a conventional cache, but are schedulable with explicit reservation.

실시간 운영체제에서 관절 공간 궤적 생성

This paper presents an implementation of a smooth path planning method considering physical limits on a real time operating system for a two-wheel mobile robot. A Bezier curve is utilized to make a smooth path considering a robot`s position and direction angle through the defined path. A convolution operator is used to generate the center velocity trajectory to travel the distance of the planned path while satisfying the physical limits. The joint space velocity is computed to drive the two-wheel mobile robot from the center velocity. Trajectory planning, velocity command according to the planned trajectory, and monitoring of encoder data are implemented with a multi-tasking system. And the synchronization of tasks is performed with a real-time mechanism of Event Flag. A real time system with multi-tasks is implemented and the result is compared with a non-real-time system in terms of path tracking to the designed path. The result shows the usefulness of a real-time multi-tasking system to the control system which requires real-time features.

Optimizing a combined WCET-WCEC problem in instruction fetching for real-time systems

In real-time systems, time is usually so critical that other parameters such as energy consumption are often not even considered. However, optimizing the worst energy consumption case can be a key factor in systems with severe power-supply limitations. In this paper we study several memory architectures using combined time and energy optimization models for real-time multitasking systems. Each task is modeled using Lock-MS, a method to optimize the WCET of a task, with an added set of constraints to model in the same way the WCEC (worst case energy consumption). Our tested hardware components focus on instruction fetching, including a lockable cache, a line buffer and a sequential prefetch buffer. We test a variety of instruction fetch alternatives optimizing time and energy consumption. Our results show that the accuracy of the estimation of the number of context switches in the worst case may affect very much the resulting WCEC (up to 8 times in our experiments) and that optimizing the WCEC may provide similar execution times than optimizing the WCET, with up to 5 times less energy consumption Additionally optimization functions combining WCET and WCEC with different weights show very interesting WCET-WCEC trade-offs. This confirms that methodologies testing such optimizations at design time could be very helpful to provide a precise system set-up.

A Thread Pool Scheduling Optimization Method of Real-time System

To deal with concurrent requests, thread pool technology is wildly used in multi-task real-time systems, which chief demand is timeout avoidance. In order to reduce request timeout ratio, least square support vector machine(LS-SVM) algorithm which parame- ters optimization based on hybrid quantum-behaved particle swarm optimization(HQPSO) was applied to estimate the execution time of requests. Also, a scheduling priority algorithm of thread pool was designed based on the estimation results. In performance test, a node of wireless sensor network is implemented to test the request timeout ratios of HQPSO LS-SVM based thread pool and other ones in different states. Test result indicates that HQPSO LS-SVM based thread pool has remarkable superiority of timeout avoidance while the thread amount of thread pool is set properly.

TCEC: Temperature and Energy-Constrained Scheduling in Real-Time Multitasking Systems

The ongoing scaling of semiconductor technology is causing severe increase of on-chip power density and temperature in microprocessors. This urgently requires both power and thermal management during system design. In this paper, we propose a model checking-based technique using extended timed automata to solve the processor frequency assignment problem in a temperature and energy-constrained multitasking system. We also develop a polynomial time-approximation algorithm to address the state-space explosion problem caused by symbolic model checker. Our approximation scheme is guaranteed to not generate any false-positive answer, while it may return false-negative answer in rare cases. Our method is universally applicable since it is independent of any system and task characteristics. Experimental results demonstrate the usefulness of our approach.

Dynamic Cache Reconfiguration for Soft Real-Time Systems

In recent years, efficient dynamic reconfiguration techniques have been widely employed for system optimization. Dynamic cache reconfiguration is a promising approach for reducing energy consumption as well as for improving overall system performance. It is a major challenge to introduce cache reconfiguration into real-time multitasking systems, since dynamic analysis may adversely affect tasks with timing constraints. This article presents a novel approach for implementing cache reconfiguration in soft real-time systems by efficiently leveraging static analysis during runtime to minimize energy while maintaining the same service level. To the best of our knowledge, this is the first attempt to integrate dynamic cache reconfiguration in real-time scheduling techniques. Our experimental results using a wide variety of applications have demonstrated that our approach can significantly reduce the cache energy consumption in soft real-time systems (up to 74%).

Energy-aware dynamic slack allocation for real-time multitasking systems

Dynamic voltage scaling (DVS) has been a very effective technique for processor energy reduction. It adjusts processor voltage and frequency level during runtime. In this article, we propose a general and flexible processor voltage scaling algorithm for real-time multitasking systems. Our approach focuses on exploiting dynamic slack that is created when a task finishes earlier than its estimated worst-case execution time (WCET). Our algorithm is efficient enough to execute at runtime and can be configured flexibly to make tradeoffs between running time and energy savings. By rescheduling tasks effectively, we can achieve almost as much energy savings as if there is no arrival time constraints. Furthermore, our approach can effectively incorporate both leakage power consumption as well as variable scaling overhead. Also, it is relatively independent of task characteristics and scheduling policy. Experimental results show that our technique can achieve significant energy savings at runtime over statically generated schedules and up to 12% more savings compared to the state-of-art techniques.

Design of Hybrid Kernel and the Performance Improvement of the Operating System

Embedded system application is a hot topic in today's date & Linux gradually becomes the most important operating system for embedded applications. Embedded real- time system must be able to response and deal with system events within the pre-defined time limitation. In real-time multi-tasking system, a lot of events and multiple concurrent tasks are running at the same time. Therefore, to meet the system response time requirement, we must ensure that each mission can be achieved within the required time frame. Current Operating Systems includes a graphical user interface that is widely used. Due to the absence of Real-Time ability, current Operating Systems has not been suitable for all industrial applications. On the other hand normal operating system has the advantage of having both widespread applications and broad user acceptance. Moreover lot many low priced user programs are available. This is an attempt to create a way to make operating system useful for industrial real-time applications eliminating its disadvantages without giving up its advantages of popular user applications.

Energy-aware dynamic reconfiguration algorithms for real-time multitasking systems

System optimization techniques based on dynamic reconfiguration are widely adopted for energy conservation. While dynamic voltage scaling (DVS) techniques have been extensively studied for processor energy conservation, dynamic cache reconfiguration (DCR) for reducing cache energy consumption in multitasking systems is still in its infancy. In this paper, we propose a general and flexible algorithm for energy optimization based on dynamic reconfiguration in multitasking systems. Our algorithm is flexibly parameterized and can be used to provide tradeoffs between running time and solution quality. Furthermore, it can easily incorporate variable reconfiguration overhead. Experimental results show that our technique can generate near-optimal solutions with significantly low running time and memory requirements.

Timing analysis for preemptive multitasking real-time systems with caches

In this paper, we propose an approach to estimate the worst-case response time (WCRT) of each task in a preemptive multitasking single-processor real-time system utilizing an L1 cache. The approach combines intertask cache-eviction analysis and intratask cache-access analysis to estimate the number of cache lines that can possibly be evicted by the preempting task and also be accessed again by the preempted task after preemptions (thus requiring the preempted task to reload the cache line(s)). This cache-reload delay caused by preempting task(s) is then incorporated into WCRT analysis. Three sets of applications with up to six concurrent tasks running are used to test our approach. The experimental results show that our approach can tighten the WCRT estimate by up to 32% (1.4X) over prior state-of-the-art.

A Domain-Specific Language for Multitask Systems, Applying Discrete Controller Synthesis

We propose a simple programming language, called Nemo, specific to the domain of multitask real-time control systems, such as in robotic, automotive, or avionics systems. It can be used to specify a set of resources with usage constraints, a set of tasks that consume them according to various modes, and applications sequencing the tasks. We automatically obtain an application-specific task handler that correctly manages the constraints (if there exists one), through a compilation-like process including a phase of discrete controller synthesis. This way, this formal technique contributes to the safety of the designed systems, while being encapsulated in a tool that makes it usable by application experts. Our approach is based on the synchronous modelling techniques, languages, and tools.

WCRT analysis for a uniprocessor with a unified prioritized cache

In this paper, we investigate the problem of inter-task cache interference in preemptive multi-tasking real-time systems. A prioritized cache is used to reduce cache conflicts among tasks by partitioning the cache. Cache partitions are assigned to tasks according to their priorities. We extend a known tool, SYMTA, in order to estimate the Worst Case Execution Time of tasks executing on a uniprocessor with a unified prioritized L1 cache. Furthermore, we apply a formal timing analysis approach to estimate the Worst Case Response Time of tasks using the prioritized cache. The prioritized cache is compared to a conventional set associative cache of the same size. Our experiments show that the WCRT estimate can be reduced up to 50% when a prioritized cache is used.

Regression testing of multi-tasking real-time systems

Regression testing is one of the most intricate parts of software development and maintenance. In complex multi-tasking real-time systems, task interleaving issues, deadlines and other factors further complicate this activity. In all software, however, the process of regression testing comes down to two basic activities: (1) selecting which test cases to re-execute and (2) actually performing the re-tests.The twofold contribution of this paper is the definition of the following problems: The regression test selection problem and the reproducibility problem for multi-tasking real-time system regression testing.

A PROBABILISTIC APPROACH TO THE STABILITY ANALYSIS OF REAL-TIME CONTROL SYSTEMS

In real-time multitasking systems, feasible periodic tasks execute within their periods. However, the exact time at which each task executes vary due to other task interferences. For control tasks, this produces irregular sampling and varying time delays, which may degrade system performance and bring the system to instability. In this paper we present stability conditions that allow us to evaluate if a closed-loop system designed to work at a nominal sampling period hd with a nominal time delay τd will remain stable if the run-time sampling is not strictly periodic and time delays vary randomly. In the closed-loop system model, we consider the irregular sampling and the varying time delays as random variables with known expectation. With this model, the system evolution can be seen as a sequence of random state vectors generated by the system closed-loop matrix. Then, we derive stability conditions for the system in terms of convergence of a sequence of random variables.

Specification and analysis of power-managed systems

Dynamic power management encompasses several techniques for reducing energy dissipation in electronic systems by selective slowdown or shutdown of components. We present a theoretical framework for explaining and classifying different approaches to power management. Within this framework, we model power-manageable components, workloads, and controllers as discrete-event systems (DESs). The structure of these DESs is specified in terms of physical states (representing operation modes) and events (triggering state transitions), while system behavior is specified in terms of next-event and next-state functions. In particular, nondeterministic next-event and next-state functions are modeled by conditional probability distributions, according to generalized semi-Markov processes (GSMPs). The modeling framework provides a general denotational model for system specification and a rigorous execution semantics that enables event-driven simulation. We introduce a modeling framework, built on top of MathWork's Simulink, supporting the specification and execution of our model. In particular, we present templates for the Simulink simulator to execute GSMP models, and we describe how to use such templates for specifying, analyzing, and optimizing dynamic power-managed systems. Finally, we demonstrate the expressive power and versatility of the proposed approach by using the modeling framework and the simulator for the analysis of representative real-life case studies, including the Intel Xscale processor architecture, a multitasking real-time system, and a sensor network.

From Mobile Mapping to Telegeoinformatics

Technological advances in positioning and imaging sensors, combined with the explosion in wireless mobile communication systems that occurred during the last decade of the twentieth century, practically redefined and substantially extended the concept of mobile mapping. The advent of the first mobile mapping systems (MMS) in the early 1990s initiated the process of establishing modern, virtually ground-control-free photogrammetry and digital mapping. By the end of the last decade, mobile mapping technology had made remarkable progress, evolving from rather simple land-based systems to more sophisticated, real-time multitasking and multisensor systems, operational in land and airborne environments. New specialized systems, based on modern imaging sensors, such as CCD (charge-coupled device) cameras, lidar (Light Detection and Ranging) and hyperspectral/multispectral scanners, are being developed, aimed at automatic data acquisition for geoinformatics, thematic mapping, land classification, terrain modeling, emergency response, homeland security, etc. This paper provides an overview of the mobile mapping concept, with a special emphasis on the MMS paradigm shift from the post-mission to near-real-time systems that occurred in the past few years. A short review of the direct georeferencing concept is given, and the major techniques (sensors) used for platform georegistration, as well as the primary radiolocation techniques based on wireless networks, are presented. An overview of the major imaging sensors and the importance of multisensor system calibration are also provided. Future perspectives of mobile mapping and its extension towards telegeoinformatics are also discussed. Some examples of mobile geospatial technology used in automatic object recognition, real-time highway centerline mapping, thematic mapping, and city modeling with lidar and multispectral imagery are included.