Real-time Guarantees Research Articles

Fog computing support scheme based on fusion of location service and privacy preservation for QoS enhancement

In the case of large-scale concurrent multimedia services, the resource utilization, QoS guarantee ability and system execution efficiency of distributed multimedia systems are facing many challenges. In order to further solve the above problems, this paper introduces fog computing into distributed multimedia systems and large-scale concurrent multimedia services, and considers the privacy protection of location services. Firstly, in order to solve the limitations of computing, storage, energy continuity, network access and other aspects of the fog node mobile devices, the framework of the fog computing multimedia information service system is constructed to obtain accurate location service data of the mobile terminal. At the same time, collaborative control of fog nodes, fog computing support nodes, public networks and other devices, to achieve the various functions of multimedia services. Secondly, to further improve the efficiency and security of fog computing, this section studies the time slice, bandwidth, hardware and other network resource allocation and management algorithms. Finally, the superiority and feasibility of the proposed algorithm in enhancing QoS performance are validated from different aspects of mathematical analysis and simulation experiments. For example, the resource utilization of multimedia system is increased by 1.34 times, and the load balancing capability and real-time guarantee are improved.

Real-time control architecture based on Xenomai using ROS packages for a service robot

This paper proposes a real-time (RT) control architecture based on Xenomai, an RT embedded Linux, to control a service robot along with non-real-time (NRT) robot operating system (ROS) packages. Most software, including device drivers and ROS, are developed to operate under the standard Linux kernel that does not provide RT guarantees. Standard Linux system calls in an RT context stimulates mode switching, resulting in non-deterministic responses and stability problems such as priority inversion and kernel panic. This paper overcomes such issues through a communication interface between RT and NRT tasks, termed cross-domain datagram protocol. The proposed architecture supports priority-based scheduling of multiple tasks while exposing an interface compatible with the original ROS packages. Moreover, it enables standard device driver operation inside RT tasks without developing RT device drivers that requires significant amount of development time. Feasibility is proven by implementation on a Raspberry Pi 3, a low-cost open embedded hardware platform, and conducted various experiments to analyze its performance and applied it to a service robot using ROS navigation packages. The results indicate that the proposed architecture can effectively provide an RT environment without stability issues when utilizing ROS packages and standard device drivers.

Multibody dynamical modeling of the FPSO soft yoke mooring system and prototype validation

The Soft Yoke Mooring System (SYMS) is a single point mooring system for shallow water. It is composed of a mooring framework, mooring legs, yoke, and single point, and is located at the Floating Production Storage and Offloading (FPSO) through 13 hinge joints, such as universal joints and thrust bearings. Mooring restoring force, motions and postures of mooring components, and mechanical behaviors of hinge joints are major criteria for the structural design of the SYMS. Aiming at the difficulties of the multibody dynamics in traditional design of the SYMS, a multi-body dynamic mathematical modeling with seven independent degrees of freedom (DOFs) which is applicable to prototype field engineering was developed in this study. The proposed mathematical modeling of the SYMS multibody dynamic system has several advantages: 1. Internal tribological behaviors in hinge joints are considered within the presented multibody dynamics model to illustrate the good dynamic effects of the SYMS. 2. The multibody dynamic model can be applied in field service. Correctness and feasibility of the proposed multibody dynamic simulation method for describing motions and postures of hinges and single-body were validated by the prototype monitoring data. 3. The horizontal restoring force of the SYMS was calculated according to field measurement data. The motion state of each single body and internal stress distributions at each hinge joint in the SYMS are given. 4. The multibody dynamics calculation program can be directly used for the real-time monitoring of mechanical behaviors of the SYMS under the service state. The simulated results can provide real-time guarantee for safety alarming of the system. The vulnerability of the mooring system in service was evaluated based on long-term monitoring data analysis.

A Design-Time/Run-Time Application Mapping Methodology for Predictable Execution Time in MPSoCs

Executing multiple applications on a single MPSoC brings the major challenge of satisfying multiple quality requirements regarding real-time, energy, and so on. Hybrid application mapping denotes the combination of design-time analysis with run-time application mapping. In this article, we present such a methodology, which comprises a design space exploration coupled with a formal performance analysis. This results in several resource reservation configurations, optimized for multiple objectives, with verified real-time guarantees for each individual application. The Pareto-optimal configurations are handed over to run-time management, which searches for a suitable mapping according to this information. To provide any real-time guarantees, the performance analysis needs to be composable and the influence of the applications on each other has to be bounded. We achieve this either by spatial or a novel temporal isolation for tasks and by exploiting composable networks-on-chip (NoCs). With the proposed temporal isolation, tasks of different applications can be mapped to the same resource, while, with spatial isolation, one computing resource can be exclusively used by only one application. The experiments reveal that the success rate in finding feasible application mappings can be increased by the proposed temporal isolation by up to 30% and energy consumption can be reduced compared to spatial isolation.

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.

Real-time analysis of priority-preemptive NoCs with arbitrary buffer sizes and router delays

Nowadays available multiprocessor platforms predominantly use a network-on-chip (NoC) architecture as an interconnect medium, due to its good scalability and performance. During the last decade, NoCs received a significant amount of attention from the real-time community. One promising category of approaches suggests to employ already existing hardware features called virtual channels, and dedicate them, exclusively, to individual communication traffic flows. In this way, NoCs become more amenable to the real-time analysis, which is an essential requirement for providing both safe and tight worst-case analysis methods, and consequently deriving real-time guarantees. In this manuscript, we present the approach which falls in the aforementioned category. Specifically, we propose a novel method for the worst-case analysis of the NoC traffic, assuming the existence of per-flow dedicated virtual channels. Compared to the state-of-the-art techniques, our approach yields substantially tighter upper-bounds on the worst-case traversal times (WCTTs) of communication traffic flows. By employing the proposed method, resource over-provisioning can be mitigated to a large extent, and significant design-cost reductions can be achieved. Moreover, we implemented a cycle-accurate simulator of the assumed NoC architecture, and used it to assess the tightness of derived WCTT bounds. Finally, we reached an interesting conclusion that bigger virtual channel buffers do not necessarily lead to better results, and in many cases can be counter-productive, which is a very important finding for system designers.

Probabilistic Per-Packet Real-Time Guarantees for Wireless Networked Sensing and Control

The mission-critical nature of wireless networked sensing and control (WSC) systems, such as the control of industrial plants, requires stringent real-time delivery of packets. Due to inherent dynamics and uncertainties in wireless communication, real-time communication guarantees are probabilistic in nature. In this paper, a probabilistic framework is therefore proposed for per-packet real-time delivery guarantee. The notion of real-time in this paper differs from the existing work in the sense that it ensures, in an execution history of arbitrary length, every packet is successfully delivered before its deadline with a probability no less than a user-specified threshold (e.g., 99%). The framework has several novel building blocks: First, “R3 (requirement-reliability-resource) mapping” translates the upper layer probabilistic real-time communication requirement , and the lower layer links reliability into the resource (i.e., optimal number of transmission opportunities) reserved for each packet. Second, “EDF (earliest deadline first) based real-time scheduling” as well as the “admission test” and “traffic load optimization” maximize system utility while satisfying per-packet real-time communication requirements. The proposed admission test is proved to be both sufficient and necessary, and the simulation results show that the proposed framework ensures probabilistic per-packet real-time communication.

Incremental Flow Scheduling and Routing in Time-Sensitive Software-Defined Networks

Several networking architectures have been developed atop IEEE 802.3 networks to provide real-time communication guarantees for time-sensitive applications in industrial automation systems. The basic principle underlying these technologies is the precise transmission scheduling of time-triggered traffic through the network for providing deterministic and bounded latency and jitter. These transmission schedules are typically synthesized offline (computational time in the order of hours) and remain fixed thereafter, making it difficult to dynamically add or remove network applications. This paper presents algorithms for incrementally adding time-triggered flows in a time-sensitive software-defined network (TSSDN). The TSSDN is a network architecture based on software-defined networking, which provides real-time guarantees for time-triggered flows by scheduling their transmissions on the hosts (network edge) only. These algorithms exploit the global view of the control plane on the data plane to schedule and route time-triggered flows needed for the dynamic applications in the Industrial Internet of Things (Industry 4.0). The evaluations show that these algorithms can compute incremental schedules for time-triggered flows in subseconds with an average relative optimality of 68%.

Multi-Hop Real-Time Communications Over Bluetooth Low Energy Industrial Wireless Mesh Networks

Industrial wireless sensor networks (IWSNs) are used to acquire sensor data that need real-time processing, therefore they require predictable behavior and real-time guarantees. To be cost effective, IWSNs are also expected to be low cost and low power. In this context, Bluetooth low energy (BLE) is a promising technology, as it allows implementing low-cost industrial networks. As BLE is a short-range technology, a multihop mesh network is needed to cover a large area. Nevertheless, the recently published Bluetooth mesh networking specifications do not provide support for real-time communications over multihop mesh networks. To overcome this limitation, this paper proposes the multihop real-time BLE (MRT-BLE) protocol, a real-time protocol developed on top of BLE, that allows for bounded packet delays over mesh networks. MRT-BLE also provides priority support. This paper describes in detail the MRT-BLE protocol and how to implement it on commercial-off-the-shelf devices. Two kinds of performance evaluation for the MRT-BLE protocol are provided. The first one is a worst case end-to-end delay analysis, while the second one is based on the experimental results obtained through measurements on a real testbed.

DetServ: Network Models for Real-Time QoS Provisioning in SDN-Based Industrial Environments

Industrial networks require real-time guarantees for the flows they carry. That is, flows have hard end-to-end delay requirements that have to be deterministically guaranteed. While proprietary extensions of Ethernet have provided solutions, these often require expensive forwarding devices. The rise of software-defined networking (SDN) opens the door to the design of centralized traffic engineering frameworks for providing such real-time guarantees. As part of such a framework, a network model is needed for the computation of worst-case delays and for access control. In this paper, we propose two network models based on network calculus theory for providing deterministic services (DetServ). While our first model, the multi-hop model (MHM), assigns a rate and a buffer budget to each queue in the network, our second model, the threshold-based model (TBM), simply fixes a maximum delay for each queue. Via a packet-level simulation, we confirm that the delay bounds guaranteed by both models are never exceeded and that no packet loss occurs. We further show that the TBM provides more flexibility with respect to the characteristics of the flows to be embedded and that it has the potential of accepting more flows in a given network. Finally, we show that the runtime cost for this increase in flexibility stays reasonable for online request processing in industrial scenarios.

Tackling the Bus Turnaround Overhead in Real-Time SDRAM Controllers

Synchronous dynamic random access memories (SDRAMs) are widely employed in multi- and many-core platforms due to their high-density and low-cost. Nevertheless, their benefits come at the price of a complex two-stage access protocol, which reflects their bank-based structure and an internal level of explicitly managed caching. In scenarios in which requestors demand real-time guarantees, these features pose a predictability challenge and, in order to tackle it, several SDRAM controllers have been proposed. In this context, recent research shows that a combination of bank privatization and open-row policy (exploiting the caching over the boundary of a single request) represents an effective way to tackle the problem. However, such approach uncovered a new challenge: the data bus turnaround overhead. In SDRAMs, a single data bus is shared by read and write operations. Alternating read and write operations is, consequently, highly undesirable, as the data bus must remain idle during a turnaround. Therefore, in this article, we propose a SDRAM controller that reorders read and write commands, which minimizes data bus turnarounds. Moreover, we compare our approach analytically and experimentally with existing real-time SDRAM controllers both from the worst-case latency and power consumption perspectives.

OR.NET RT: how service-oriented medical device architecture meets real-time communication.

Today's landscape of medical devices is dominated by stand-alone systems and proprietary interfaces lacking cross-vendor interoperability. This complicates or even impedes the innovation of novel, intelligent assistance systems relying on the collaboration of medical devices. Emerging approaches use the service-oriented architecture (SOA) paradigm based on Internet protocol (IP) to enable communication between medical devices. While this works well for scenarios with no or only soft timing constraints, the underlying best-effort communication scheme is insufficient for time critical data. Real-time (RT) networks are able to reliably guarantee fixed latency boundaries, for example, by using time division multiple access (TDMA) communication patterns. However, deterministic RT networks come with their own limitations such as tedious, inflexible configuration and a more restricted bandwidth allocation. In this contribution we overcome the drawbacks of both approaches by describing and implementing mechanisms that allow the two networks to interact. We introduce the first implementation of a medical device network that offers hard RT guarantees for control and sensor data and integrates into SOA networks. Based on two application examples we show how the flexibility of SOA networks and the reliability of RT networks can be combined to achieve an open network infrastructure for medical devices in the operating room (OR).

Age Aware Pre-emptive Garbage Collection for SSD RAID

Flash-based storage systems offer high performance, robustness, and reliability for embedded applications; however the physical nature of flash memory means that there are limitations to its usage in high reliability applications. In previous work, we have developed RAID architectures and associated controller hardware that increase the reliability and lifespan of these storage systems. However, flash memory needs regular garbage collection and this presents two issues in a high reliability context. The first issue concerns response times as when a garbage collector is active, the flash memory cannot be used by the application layer. This non-determinism in terms of response is problematic in high reliability systems that require real-time guarantees. The second issue concerns lifespan of flash chips. If the garbage collector is allowed free rein over erase operations while garbage collecting, this affects management of the lifespan of each SSD in the array.In this paper we present an enhanced, dynamic, real-time garbage collection method for SSD RAID that does not ignore the strict age distribution management, while offering deterministic response times for access. Real-time efficiency is further improved by dynamically coordinating garbage collection across each device in the array. Our simulation results indicate that the dynamic garbage collection technique maintains the age distribution at a level that does not affect reliability of individual devices. This is evidences using various synthetic and realistic traces dominated by random I/O loads.

DYNASCORE

In real-time mixed-critical systems, Worst-Case Execution Time (WCET) analysis is required to guarantee that timing constraints are respected—at least for high-criticality tasks. However, the WCET is pessimistic compared to the real execution time, especially for multicore platforms. As WCET computation considers the worst-case scenario, it means that whenever a high-criticality task accesses a shared resource in multicore platforms, it is considered that all cores use the same resource concurrently. This pessimism in WCET computation leads to a dramatic underutilization of the platform resources, or even failing to meet the timing constraints. In order to increase resource utilization while guaranteeing real-time guarantees for high-criticality tasks, previous works proposed a runtime control system to monitor and decide when the interferences from low-criticality tasks cannot be further tolerated. However, in the initial approaches, the points where the controller is executed were statically predefined. In this work, we propose a dynamic runtime control which adapts its observations to online temporal properties, further increasing the dynamism of the approach, and mitigating the unnecessary overhead implied by existing static approaches. Our dynamic adaptive approach allows one to control the ongoing execution of tasks based on runtime information, and further increases the gains in terms of resource utilization compared with static approaches.

Phasing of Periodic Tasks Distributed over Real-time Fieldbus

In designing a distributed hard real-time system, it is important to reduce the end-to-end delay of each real-time message in order to ensure quick responses to external inputs and a high degree of synchronization among cooperating actuators. In order to provide a real-time guarantee for each message, the related literature has focused on the analysis of end-to-end delays based on worst-case task phasing. However, such analyses are too pessimistic because they do not assume a global clock. With the assumption that task phases can be managed by using a global clock provided by emerging real-time fieldbuses, such as EtherCAT, we can try to calculate the optimal task phasing that yields the minimal worst-case end-to-end delay. In this study, we propose a heuristic to manage the phase offsets in the distributed tasks to reduce the theoretical end-to-end delay bound. The proposed heuristic reduces the search time for a solution by identifying time intervals where actual communication occurs among inter-dependent tasks. Furthermore, to analyze the distribution of endto- end delays in different phases, we implemented a simulation tool. The simulation results showed that the proposed heuristic can reduce worst-case end-to-end delay as well as jitter in end-to-end delays.

DSERR: Delay Sensitive Energy Efficient Reliable Routing Algorithm

Routing strategies need to strike a balance between responsiveness and energy efficiency. Achieving this balance poses new challenges that do not coalesce either with infrastructure or ad hoc wireless networks performance requirements. Multiple strategies have emerged as a workable solution to the routing problem. Either of these solutions however cater to but one of the many constraints posed by the networks. To address this issue we propose a delay sensitive energy efficient reliable routing (DSERR) algorithm which achieves application specified soft delays with energy scavenging being the foremost concern. We try to provide soft end-to-end (e2e) delay guarantee that is proportional to the distance between the source and destination. Our algorithm uses the per hop greedy selection for soft real-time guarantees as it is impossible to provide hard guarantees in a dynamic network. DSERR presents a stateless architecture providing hop by hop reliability of data delivery to support desired delivery reliability across the sensor network.

Rt-muse: measuring real-time characteristics of execution platforms

Operating systems code is often developed according to principles like simplicity, low overhead, and low memory footprint. Schedulers are no exceptions. A scheduler is usually developed with flexibility in mind, and this restricts the ability to provide real-time guarantees. Moreover, even when schedulers can provide real-time guarantees, it is unlikely that these guarantees are properly quantified using theoretical analysis that carries on to the implementation. To be able to analyze the guarantees offered by operating systems’ schedulers, we developed a publicly available tool that analyzes timing properties extracted from the execution of a set of threads and computes the lower and upper bounds to the supply function offered by the execution platform, together with information about migrations and statistics on execution times. rt-muse evaluates the impact of many application and platform characteristics including the scheduling algorithm, the amount of available resources, the usage of shared resources, and the memory access overhead. Using rt-muse, we show the impact of Linux scheduling classes, shared data and application parallelism, on the delivered computing capacity. The tool provides useful insights on the runtime behavior of the applications and scheduler. In the reported experiments, rt-muse detected some issues arising with the real-time Linux scheduler: despite having available cores, Linux does not migrate SCHED_RR threads which are enqueued behind SCHED_FIFO threads with the same priority.

A software stack for next-generation automotive systems on many-core heterogeneous platforms

The next-generation of partially and fully autonomous cars will be powered by embedded many-core platforms. Technologies for Advanced Driver Assistance Systems (ADAS) need to process an unprecedented amount of data within tight power budgets, making those platform the ideal candidate architecture. Integrating tens-to-hundreds of computing elements that run at lower frequencies allows obtaining impressive performance capabilities at a reduced power consumption, that meets the size, weight and power (SWaP) budget of automotive systems. Unfortunately, the inherent architectural complexity of many-core platforms makes it almost impossible to derive real-time guarantees using “traditional” state-of-the-art techniques, ultimately preventing their adoption in real industrial settings. Having impressive average performances with no guaranteed bounds on the response times of the critical computing activities is of little if no use in safety-critical applications. Project Hercules will address this issue, and provide the required technological infrastructure to exploit the tremendous potential of embedded many-cores for the next generation of automotive systems. This work gives an overview of the integrated Hercules software framework, which allows achieving an order-of-magnitude of predictable performance on top of cutting-edge Commercial-Off-The-Shelf components (COTS). The proposed software stack will let both real-time and non real-time application coexist on next-generation, power-efficient embedded platforms, with preserved timing guarantees.

IT Assembly Process Gripper Real-Time Embedded System Design

In this paper we propose the gripper handle real-time based embedded system for operating robot manipulator. The general gripper has only a simple function and has also I/O module. Thus general gripper and position based robot controller combination is not suitable for precision process operation, IT assembly process. In order to give various functions and intelligence to the gripper, it is necessary to have an embedded controller that real-time guarantees. The proposed embedded system have five component that handle the pose of the gripper, measure the pose and translation of gripper, motoring the gripping tip, operate the stiffness of the gripper and communicate with Ethernet interface to the external robot controller. The external robot interface parts are supported to communicate with various external robot maker, KUKA, DENSO, ROBOSTAR etc. The validation and functional ability is tested on the LAB environment.

Optimal minimal routing and priority assignment for priority-preemptive real-time NoCs

The Network-on-Chip (NoC) architecture is an interconnect network with a good performance and scalability potential. Thus, it comes as no surprise that NoCs are among the most popular interconnect mediums in nowadays available many-core platforms. Over the years, the real-time community has been attempting to make NoCs amenable to the real-time analysis. One such approach advocates to employ virtual channels. Virtual channels are hardware resources that can be used as an infrastructure to facilitate flit-level preemptions between communication traffic flows. This gives the possibility to implement priority-preemptive arbitration policies in routers, which is a promising step towards deriving real-time guarantees for NoC traffic. So far, various aspects of priority-preemptive NoCs were studied, such as arbitration, priority assignment, routing, and workload mapping. Due to a potentially large solution space, the majority of available techniques are heuristic-centric, that is, either pure heuristics, or heuristic-based search strategies are used. Such approaches may lead to an inefficient use of hardware resources, and may cause a resource over-provisioning as well as unnecessarily high design-cost expenses. Motivated by this reality, we take a different approach, and propose an integer linear program to solve the problems of priority assignment and routing of NoC traffic. The proposed method finds optimal routes and priorities, but also allows to reduce the search space (and the computation time) by fixing either priorities or routes, and derive optimal values for remaining parameters. This framework is used to experimentally evaluate both the scalability of the proposed method, as well as the efficiency of existing priority assignment and routing techniques.