Bounds on Worst-Case Deadline Failure Probabilities in Controller Area Networks

Industrial communication networks like the Controller Area Network (CAN) are often required to operate reliably in harsh environments which expose the communication network to random errors. Probabilistic schedulability analysis can employ rich stochastic error models to capture random error behaviors, but this is most often at the expense of increased analysis complexity. In this paper, an efficient method (of time complexity O(n log n)) to bound the message deadline failure probabilities for an industrial CAN network consisting of n periodic/sporadic message transmissions is proposed. The paper develops bounds for Deadline Minus Jitter Monotonic (DMJM) and Earliest Deadline First (EDF) message scheduling techniques. Both random errors and random bursts of errors can be included in the model. Stochastic simulations and a case study considering DMJM and EDF scheduling of an automotive benchmark message set provide validation of the technique and highlight its application

Software Fault Tolerance in Real-Time Systems: Identifying the Future Research Questions

Tolerating hardware faults in modern architectures is becoming a prominent problem due to the miniaturization of the hardware components, their increasing complexity, and the necessity to reduce the costs. Software-Implemented Hardware Fault Tolerance approaches have been developed to improve the system dependability to hardware faults without resorting to custom hardware solutions. However, these come at the expense of making the satisfaction of the timing constraints of the applications/activities harder from a scheduling standpoint. This paper surveys the current state of the art of fault tolerance approaches when used in the context real-time systems, identifying the main challenges and the cross-links between these two topics. We propose a joint scheduling-failure analysis model that highlights the formal interactions among software fault tolerance mechanisms and timing properties. This model allows us to present and discuss many open research questions with the final aim to spur the future research activities

Analysis of Embedded Controllers Subject to Computational Overruns

Microcontrollers have become an integral part of modern everyday embedded systems, such as smart bikes, cars, and drones. Typically, microcontrollers operate under real-time constraints, which require the timely execution of programs on the resource-constrained hardware. As embedded systems are becoming increasingly more complex, microcontrollers run the risk of violating their timing constraints, i.e., overrunning the program deadlines. Breaking these constraints can cause severe damage to both the embedded system and the humans interacting with the device. Therefore, it is crucial to analyse embedded systems properly to ensure that they do not pose any significant danger if the microcontroller overruns a few deadlines.However, there are very few tools available for assessing the safety and performance of embedded control systems when considering the implementation of the microcontroller. This thesis aims to fill this gap in the literature by presenting five papers on the analysis of embedded controllers subject to computational overruns. Details about the real-time operating system's implementation are included into the analysis, such as what happens to the controller's internal state representation when the timing constraints are violated. The contribution includes theoretical and computational tools for analysing the embedded system's stability, performance, and real-time properties.The embedded controller is analysed under three different types of timing violations: blackout events (when no control computation is completed during long periods), weakly-hard constraints (when the number of deadline overruns is constrained over a window), and stochastic overruns (when violations of timing constraints are governed by a probabilistic process). These scenarios are combined with different implementation policies to reduce the gap between the analysis and its practical applicability. The analyses are further validated with a comprehensive experimental campaign performed on both a set of physical processes and multiple simulations.In conclusion, the findings of this thesis reveal that the effect deadline overruns have on the embedded system heavily depends the implementation details and the system's dynamics. Additionally, the stability analysis of embedded controllers subject to deadline overruns is typically conservative, implying that additional insights can be gained by also analysing the system's performance

Real-Time Guarantees For Wireless Networked Sensing And Control

Wireless networks are increasingly being explored for mission-critical sensing and control in emerging domains such as connected and automated vehicles, Industrial 4.0, and smart city. In wireless networked sensing and control (WSC) systems, reliable and real- time delivery of sensed data plays a crucial role for the control decision since out-of-date information will often be irrelevant and even leads to negative effects to the system. Since WSC differs dramatically from the traditional real-time (RT) systems due to its wireless nature, new design objective and perspective are necessary to achieve real-time guarantees. First, we proposed Optimal Node Activation Multiple Access (ONAMA) scheduling protocol that activates as many nodes as possible while ensuring transmission reliability (in terms of packets delivery ratio). We implemented and tested ONAMA on two testbeds both with 120+ sensor nodes. Second, we proposed algorithms to address the problem of clustering heterogeneous reliability requirements into a limit set of service levels. Our solutions are optimal, and they also provide guaranteed reliability, which is critical for wireless sensing and control. Third, we proposed a probabilistic real-time wireless communication framework that effectively integrates real-time scheduling theory with wireless communication. The per- packet probabilistic real-time QoS was formally modeled. By R3 mapping, the upper-layer requirement and the lower-layer link reliability are translated into the number of trans- mission opportunities needed. By optimal real-time communication scheduling as well as admission test and traffic period optimization, the system utilization is maximized while the schedulability is maintained. Finally, we further investigated the problem of how to minimize delay variation (i.e., jitter) while ensuring that packets are delivered by their deadlines

Error handling and controller design for controller area network-based networked control system

Networked Control System (NCS) is a feedback control system which dynamic process is running via the communication channel. Surrounded by many choices of network types that can be used to establish an NCS, Controller Area Network (CAN) is a popular choice widely used in most real-time applications. Under harsh environment, fault at transmission line for CAN-based NCS is more prominent compared to fault in network nodes. Fault in bus line of CAN will induce data error which will result in data dropout or/and time delay which consequently lead to performance degradation or system instability. In this thesis, strategies to handle fault occurrence in CAN bus are proposed in order to properly analyse the effect of fault to CAN-based NCS performance. To implement the strategies, first, fault occurrences are modelled based on fault inter-arrival time, fault bursts duration and Poisson law. By using fault and message attributes, Response Time Analysis (RTA) is performed and the probability of NCS message that misses its deadline is calculated based on Homogeneous Poisson Process (HPP). A new error handling algorithm per-sample-error-counter (PSeC) is introduced to replace native error handling of CAN. PSeC mechanism is designed based on online monitoring and counting of erroneous sensor and control signal data at every sampling instance and it gives a bound parameters known as Maximum Allowable Number of Data Retransmission (MADR). If the number of retransmission for NCS message violates the value of MADR, the data will be discarded. With the utilization of PSeC mechanism to replace the Native Error Handling (NEH) of CAN, the probability of NCS message that misses its deadline can be translated to the probability of data dropout of NCS message. Despite the PSeC has prevented network from congestion which can lead to prolonged loop delay, it also introduces one-step loop delay and data dropout. Therefore, the controller that is able to compensate the effect of delay and data dropout should be introduced. Thus, a control algorithm is designed based on Lyapunov stability theory formulated in Linear Matrix Inequality (LMI) form by taking into account network delay and data dropout probability. In order to proof the efficacy of the strategies, Steer-by-Wire (SbW) system is used and simulated in TrueTime MATLAB R /Simulink environment. Simulation results show that the strategies of introducing PSeC mechanism and the designed controller in this work have superior performance than NEH mechanism for CAN-based NCS environment in terms of integral of the absolute error (IAE) and energy consumption

A measurement-based approach to service modeling and bandwidth estimation in IEEE 802.11 wireless networks

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