Soheil Samii

Integrated scheduling and synthesis of control applications on distributed embedded systems

Many embedded control systems comprise several control loops that are closed over a network of computation nodes. In such systems, complex timing behavior and communication lead to delay and jitter, which both degrade the performance of each control loop and must be considered during the controller synthesis. Also, the control performance should be taken into account during system scheduling. The contribution of this paper is a control-scheduling co-design method that integrates controller design with both static and priority-based scheduling of the tasks and messages, and in which the overall control performance is optimized.

A simulation methodology for worst-case response time estimation of distributed real-time systems

In this paper, we propose a simulation-based methodology for worst-case response time estimation of distributed real-time systems. Schedulability analysis produces pessimistic upper bounds on process response times. Consequently, such an analysis can lead to overdesigned systems resulting in unnecessarily increased costs. Simulations, if well conducted, can lead to tight lower bounds on worst-case response times, which can be an essential input at design time. Moreover, such a simulation methodology is very important in situations when the running application or the underlying platform is such that no formal timing analysis is available. Another important application of the proposed simulation environment is the validation of formal analysis approaches, by estimating their degree of pessimism. We have performed such an estimation of pessimism for two response-time analysis approaches for distributed embedded systems based on two of the most important automotive communication protocols: CAN and FlexRay.

Quality-driven synthesis of embedded multi-mode control systems

At runtime, an embedded control system can switch between alternative functional modes. In each mode, the system operates by using a schedule and controllers that exploit the available computation and communication resources to optimize the control performance in the running mode. The number of modes is usually exponential in the number of control loops, which means that all controllers and schedules cannot be produced in affordable design-time and stored in memory. This paper addresses synthesis of multi-mode embedded control systems. Our contribution is a method that trades control quality with optimization time, and that efficiently selects the schedules and controllers to be synthesized and stored in memory.

Dynamic Scheduling and Control-Quality Optimization of Self-Triggered Control Applications

Time-triggered periodic control implementations are over provisioned for many execution scenarios in which the states of the controlled plants are close to equilibrium. To address this inefficient use of computation resources, researchers have proposed self-triggered control approaches in which the control task computes its execution deadline at runtime based on the state and dynamical properties of the controlled plant. The potential advantages of this control approach cannot, however, be achieved without adequate online resource-management policies. This paper addresses scheduling of multiple self-triggered control tasks that execute on a uniprocessor platform, where the optimization objective is to find trade-offs between the control performance and CPU usage of all control tasks. Our experimental results show that efficiency in terms of control performance and reduced CPU usage can be achieved with the heuristic proposed in this paper.

Designing High-Quality Embedded Control Systems with Guaranteed Stability

Many embedded systems comprise several controllers sharing available resources. It is well known that such resource sharing leads to complex timing behavior that degrades the quality of control, and more importantly, can jeopardize stability in the worst-case, if not properly taken into account during design. Although stability of the control applications is absolutely essential, a design flow driven by the worst-case scenario often leads to poor control quality due to the significant amount of pessimism involved and the fact that the worst-case scenario occurs very rarely. On the other hand, designing the system merely based on control quality, determined by the expected (average-case) behavior, does not guarantee the stability of control applications in the worst-case. Therefore, both control quality and worst-case stability have to be considered during the design process, i.e., period assignment, task scheduling, and control-synthesis. In this paper, we present an integrated approach for designing high-quality embedded control systems, while guaranteeing their stability.

Immune Genetic Algorithms for Optimization of Task Priorities and FlexRay Frame Identifiers

FlexRay is an automotive communication protocol that combines the comprehensive time-triggered paradigm with an adaptive phase that is more suitable for event-based communication. We study optimization of average response times by assigning priorities and frame identifiers to tasks and messages. Our optimization approach is based on immune genetic algorithms, where in addition to the crossover and mutation operators, we use a vaccination operator that results in considerable improvements in optimization time and quality.

Design Optimization and Synthesis of FlexRay Parameters for Embedded Control Applications

FlexRay is a popular communication protocol in modern automotive systems with several computation nodes and communication units. The complex temporal behavior of such systems depends highly on the FlexRay configuration and influences the performance of running control applications. In our previous work, we presented a design framework for integrated scheduling and design of embedded control applications, where control quality is the optimization objective. This paper presents our extension to the design framework to handle FlexRay-based embedded control systems. Our contribution is a method for the decision of FlexRay parameters and optimization of control quality.

The Frame Packing Problem for CAN-FD

CAN with flexible data rate (CAN-FD) allows transmission of larger payloads compared to standard CAN. However, efficient utilization of CAN-FD bandwidth space calls for a systematic strategy. The challenge arises from the nature of the frame sizes stipulated by CAN-FD as well as the heterogeneity of the periods of the messages and the signals. In this paper, we formulate a frame packing problem for CAN-FD with the optimization objective of bandwidth utilization while meeting temporal constraints. As part of the solution, first, we propose a formula to compute the best-case and the worst-case transmission times of the CAN-FD frames. Thereafter, we propose a framework that solves the optimization problem in pseudo-polynomial time. Experiments show the gains achieved by our framework. The results also show that, when applied to standard CAN, our heuristic provides improved results over existing techniques.

Urgency-Based Scheduler for Time-Sensitive Switched Ethernet Networks

Due to increasing bandwidth requirements, Ethernet technology is emerging in embedded systems application areas such as automotive, avionics, and industrial control. In the automotive domain, Ethernet enables integration of cameras, radars, and fusion to build active safety and automated driving systems. While Ethernet provides the necessary communication bandwidth, solutions are needed to satisfy stringent dependability and temporal requirements of such safety-critical systems. This paper introduces an asynchronous traffic scheduling algorithm, which gives low delay guarantees in a switched Ethernet network, while maintaining a low implementation complexity. We present a timing analysis and demonstrate the tightness of the delay bounds by extensive simulation experiments.

Control-Quality Driven Task Mapping for Distributed Embedded Control Systems

Many embedded control systems are implemented on execution platforms with several computation nodes and communication components. Distributed embedded control systems typically comprise multiple control loops that share the available computation and communication resources of the platform. It is well known that such resource sharing leads to complex delay characteristics that degrade the control quality if not properly taken into account at design time. Scheduling in computation nodes and communication infrastructure, as well as execution periods of the controllers impact the delay characteristics and, consequently, the control quality. In addition, mapping of tasks on computation nodes affect both scheduling of tasks and messages, and the assignment of periods of the control applications. Therefore, control synthesis must be considered during mapping, scheduling, and period assignment in order to achieve high control quality. This paper presents a control-quality optimization approach for integrated mapping, scheduling, period selection, and control synthesis for distributed embedded control systems.