Integrating real-time inter-task communication channels into hardware–software codesign

Summary form only given. We address the design of pipelined systems able to sustain the throughput of a given periodic task and, at the same time, to serve aperiodic requests associated with hard real-time constraints. The proposed method is based on the allocation of the global graph (periodic and aperiodic tasks), over-dimensioning the design of the system devoted to process the periodic task, deserving the unused parts of the resources to the management of aperiodic requests. A formal definition of such a mapping problem, together with the formalization of the searching space, is given. The searching space is structured in a way such as the minimization process moves toward a solution, which satisfies, if possible, all the real-time constraints and has minimal HW requirements. Once formulated as a minimization problem, the pipelined architecture and the corresponding scheduling are determined by means of a simulated annealing algorithm. A theorem is given to ensure that all the feasible mappings are reachable in the optimization process.

Real-time wireless sensor networking platform should satisfy requirements of sensor networking features - efficient exploitation of limited resources and energy efficiency, real-time characteristics and scalability. Existing studies on sensor networking platforms, such as TinyOS and DCOS, have been focused on solving the maximization problem of exploitation of limited resources and the energy efficiency. Envisioned application scenarios applied in sensor networking platforms need to perform real-time sensing activity as well as provide good response time with task communication, and support the scalability to improve productivity. The proposed method is able to support task scheduling which meets deadlines of all the periodic tasks and provides aperiodic tasks with good average response time. It also supports the scalability by dividing the functionalities in sensor node into periodic and aperiodic tasks. Experimental results show that our method improves real-time characteristics of sensor networking platforms by means of guaranteeing to complete the execution of all the periodic tasks within their deadlines and having a good response time for aperiodic tasks.

In a real-time system with both hard deadline periodic tasks and soft deadline aperiodic tasks, hard deadline tasks must be guaranteed to meet their deadlines and soft deadline tasks are serviced in a best-effort manner. To schedule soft deadline aperiodic tasks in dynamic priority systems, one can assign a virtual deadline like the TBS algorithm or use capacity servers like the DPE algorithm. Both approaches have their own advantages, and we cannot say which one is better in terms of response time. In some cases, TBS provides shorter response time than DPE server. In other cases, the reverse may happen. In this paper, we propose a combined approach to improve the response time of soft deadline aperiodic tasks. The proposed method combines the deadline assignment and the capacity server approach. When there is enough capacity available for aperiodic tasks, the aperiodic tasks are served by capacity servers. Otherwise, our method assigns a deadline and schedule aperiodic task together with periodic tasks by EDF algorithm. In the worst case, the proposed method provides response time no later than TBS. Experimental results show that the proposed approach improves the responsiveness of soft deadline aperiodic tasks.

A data chain is a sequence of periodic realtime communicating tasks that are processing the data from sensors up to actuators. It determines an order in which the tasks propagate data but not in which they are executed: inter-task communication and scheduling are independent. In this paper, we focus on the latency computation, considered as the time elapsed from getting the data from an input and processing it to an output of a data chain. We propose a method for the worst-case latency calculation of periodic tasks' data chains executed by a partitioned fixed-priority preemptive scheduler upon a multiprocessor platform. As far as we know, there is no such formal approach based on closed-form expression for communicating real-time tasks.

OEA-scheduler is a scheduler that generates a schedule of aperiodic tasks and periodic tasks by the principle of eliminating unnecessary context switches under the rate monotonic algorithm. This new scheduler will minimize the average response time of aperiodic tasks and also guarantee the hard deadlines of an arbitrary number of periodic tasks in hard real-time environments. In previous research, the OE-scheduler was developed to schedule periodic tasks only, and later improved to use object-oriented methods. Due to the object-oriented approach, the authors have been able to reuse the OE-scheduler algorithm and extend it to work with both periodic tasks and aperiodic tasks. An object oriented design of the scheduler will be presented, along with an implementation result

Real-time communication (RTC) is a new standard and industry-wide effort that expand the web browsing model, allowing access to information in areas like social media, chat, video conferencing, and television over the internet, and unified communication. These systems users can view, record, remark, or edit video and audio content flows using time-critical cloud infrastructures that enforce the quality of services. However, there are many proprietary protocols and codecs available that are not easily interoperable and scalable to implement multipoint video-conference systems. WebRTC (Web Real-Time Communication) is a State-of-the-Art open technology that makes real-time communication capabilities in audio, video, and data transmission possible in real-time communication through web browsers using JavaScript APIs (Application Programming Interfaces) without plug-ins. This paper aims to introduce the P2P video conferencing system based on Web Real-Time Communication (WebRTC). In this paper, we have proposed a web-based peer-to-peer real-time communication system using the Mozilla Firefox together with the ScaleDrone service that enables users to communicate with high-speed data transmission over the communication channel using WebRTC technology, HTML5 and use Node.js server address. Our experiments show that WebRTC is a capable building block for scalable live video conferencing within a web browser.We also study a thermal camera for the videoconference system to identify the temperature body results regarding the COVID 19 crisis.

In hard real-time task systems where periodic and aperiodic tasks coexist, the object of task scheduling is to reduce the response time of the aperiodic tasks while meeting the deadline of periodic tasks. Total bandwidth server (TBS) and advanced TBS (ATBS) are used in dynamic priority systems. However, these methods are not optimal solutions because they use the worst-case execution time (WCET) or the estimation value of the actual execution time of the aperiodic tasks. This paper presents an online slack-stealing algorithm called SSML that can make significant response time reducing by modification of look-ahead earliest deadline first (laEDF) algorithm as the slack computation method. While the conventional slack-stealing method has a disadvantage that the slack amount of each frame must be calculated in advance, SSML calculates the slack when aperiodic tasks arrive. Our simulation results show that SSML outperforms the existing TBS based algorithms when the periodic task utilization is higher than 60%. Compared to ATBS with virtual release advancing (VRA), the proposed algorithm can reduce the response time up to about 75%. The performance advantage becomes much larger as the utilization increases. Moreover, it shows a small performance variation of response time for various task environments.

A real-time system is considered in which a set of periodic tasks are scheduled on an earliest-deadline-first basis and exclusively access critical sections through a dynamic priority ceiling protocol. An optimal online acceptance test is described for hard deadline aperiodic tasks. Aperiodic tasks are accepted only if all deadlines can be met. Here, optimality means that the algorithm is able to answer ‘yes’ to the question of the acceptance of a newly occurring task each time it is possible. The time complexity of the test is O(⌈R/p⌉.n+m) where n is the number of periodic tasks, R is the longest deadline, p is the shortest period and m is the number of aperiodic tasks that have previously been accepted but not completed.

Real-time communication with performance guarantees is becoming very important to many applications, like computer integrated manufacturing, multimedia, and many embedded systems. Though several real-time protocols have been proposed for the multiple access bus networks, there is no guarantee based protocol which addresses the problem of integrated scheduling of dynamically arriving periodic and aperiodic messages. In this paper, we propose two guarantee based protocols, EDF and BUS protocols, which address this problem. In the simulation studies, the performance metrics, success ratio (measure of schedulability) and channel utilization are used to study the performance of the two protocols. It is observed that the EDF protocol offers higher schedulability as compared to the BUS protocol for periodic messages, while the BUS protocol offers better channel utilization for aperiodic messages as compared to the EDF protocol.

In IEEE 802.12 network, a repeater arbitrates among transmission requests on a round robin basis. A node can transmit a packet only when it is granted by the repeater. Recently, the IEEE 802.12 Committee approved a burst mode in which a node can transmit multiple packets per grant. In burst mode a bandwidth, or the number of packets per grant should be allocated taking into account the timing constraints of real-time messages. This paper proposes bandwidth allocation algorithms based on the burst mode to guarantee the deadlines of periodic real-time messages. Once the bandwidth of each node is derived from the lengths and deadlines of periodic messages, a node is allowed to transmit packets up to the allocated bandwidth per grant. Experimental results show that the proposed algorithms providemuch higher guarantee ratio and graceful degradation for heavy network load, compared with the existing approaches.

The Hierarchical Real-Time Scheduling (HiRTS) technique helps improve overall resource utilization in real-time embedded systems. With HiRTS, a computation resource is divided into a group of temporal resource partitions, each of which accommodates multiple real-time tasks. Besides the computation resource partitioning problem, real-time task scheduling on resource partitions is also a major problem of HiRTS. The existing scheduling techniques for dedicated resources, like schedulability tests and utilization bounds, are unable to work without changes on temporal resource partitions in most cases. In this paper, we show how to achieve maximal transparency for task scheduling on Regular Partitions, a type of resource partition introduced by the Regularity-based Resource Partition (RRP) Model. We show that several classes of real-time scheduling problems on a regular partition can be transformed into equivalent problems on a dedicated single resource, such that comprehensive single-resource scheduling techniques provide optimal solutions. Furthermore, this transformation method could be applied to different types of real-time tasks such as periodic tasks, sporadic tasks and aperiodic tasks.

As for the aperiodic tasks of node in network control systems, the FC-ABS (Feedback Controlled Adaptive Bandwidth Server) scheduling algorithm is designed. The different scheduling methods are used according to time characteristics of aperiodic tasks, and feedback scheduling is used to mitigate the effect of aperiodic tasks on periodic tasks. The simulation results show that the method is effective. Keyword: Network Control Systems; Server Scheduling; Feedback Scheduling; FC-ABS.

본 논문에서는 단일 처리기를 가지는 임베디드 시스템에서 실시간성과 결함 허용을 고려한 태스크 스케줄러를 설계하고 구현한다. RMS(Rate Monotonic Scheduling) 기법을 이용하여 주기적 태스크를 실행하고 태스크의 실행 마감 시간을 보장하며 잉여 시간을 관리함으로써 비주기적 태스크의 실행 및 완료 방법을 제시한다. 또한 백업 시간을 관리함으로써 일시적인 태스크의 단일 결함을 허용하기 위한 결함 허용 기법을 제공한다. 주기적 태스크와 비주기적 태스크의 응답시간을 조절할 수 있는 주기적 태스크의 중요도를 제시한다. 마지막으로 시뮬레이션을 통해 제시한 방법의 결과를 분석하고 평가한다. In this paper, we design and implement a task scheduler that considers real-time and fault tolerance in embedded system with a single processor. We propose a method how it can meet the deadlines of periodic tasks using RMS and complete the execution of aperiodic tasks by calculating surplus times from a periodic task set. And we describe a method how to recover of a transient fault task by managing backup time. We propose an important level of periodic tasks that can control the response time of periodic and aperiodic tasks. Finally, we analyse and evaluate the proposed methods by simulation.

The Rate Monotonic Scheduling (RMS) policy is a widely accepted scheduling strategy for real-time systems due to strong theoretical foundations and features attractive to practical uses. For a periodic task set of n tasks with deadlines at the end of task periods, it guarantees a feasible schedule on a single processor as long as the utilization factor of the task set is below n(2/sup 1/n/-1) which converges to 0.69 for large n. We analyze the schedulability of a set of periodic tasks that is scheduled by the RMS policy and is susceptible to a single fault. The recovery action is the reexecution of all uncompleted tasks. The priority of the RMS policy is maintained even during recovery. Under these conditions, we guarantee that no task will miss a single deadline, even in the presence of a fault, if the utilization factor on the processor does not exceed 0.5. Thus, 0.5 is the minimum achievable utilization that permits recovery from faults before the expiration of the deadlines of the tasks. This bound is better than the trivial bound of 0.6912=0.345 that would be obtained if computation times were doubled to provide for reexecutions in the RMS analysis. Our result provides scheduling guarantees for tolerating a variety of intermittent and transient hardware and software faults that can be handled simply by reexecution. In addition, we demonstrate how permanent faults can be tolerated efficiently by maintaining common spares among a set of processors that are independently executing periodic tasks.

Within the context of hard real-time systems, the schedulability analysis of a task set is a major issue. The problem consists in proving that the tasks always satisfy their temporal constraints for a given scheduling policy and a given platform. Extensive work has been done in the last decades for defining sufficient criteria and exact algorithms. Sufficient criteria usually have an excellent complexity but often lead to an over-dimension of the system. On the opposite, exact algorithms, especially in the case of multiprocessor platform, suffer from an exponential complexity. In this paper, we study an exact technique: we apply a brute force search combined with a model checker (Uppaal) that determines whether the exploration is complete. We consider periodic tasks which execute on parallel platforms composed of homogeneous processors. Under these hypotheses, we have encoded four policies: fixed task priority, gEDF, gLLF and LLREF. The analyser is user friendly and provides promising performances.