Abstract-We present an approach to the synthesis of fault-tolerant hard real-time systems for safety-critical applications. We use checkpointing with rollback recovery and active replication for tolerating transient faults. Processes and communications are statically scheduled. Our synthesis approach decides the assignment of fault-tolerance policies to processes, the optimal placement of checkpoints and the mapping of processes to processors such that multiple transient faults are tolerated and the timing constraints of the application are satisfied. We present several design optimization approaches which are able to find fault-tolerant implementations given a limited amount of resources. The developed algorithms are evaluated using extensive experiments, including a real-life example.

FlexRay will very likely become the de- IntroductionMany safety-critical applications, following physical, modularity or safety constraints, are implemented using distributed architectures composed of several different types of hardware units (called nodes), interconnected in a network. For such systems, the communication between functions implemented on different nodes has an important impact on the overall system properties, such as performance, cost and maintainability.There are several communication protocols for realtime networks. Among the protocols that have been proposed for in-vehicle communication, only the Controller Area Network (CAN) [4], the Local Interconnection Network (LIN) [17], and SAE's J1850 [30] are currently in use on a large scale [20]. Moreover, only a few of the proposed protocols are suitable for safety-critical applications where predictability is mandatory [29].Communication activities can be triggered either dynamically, in response to an event (event-driven), or statically, at predetermined moments in time (time-driven). Therefore, on one hand, there are protocols that schedule the messages statically based on the progression of time, such as the SAFEbus A large consortium of automotive manufacturers and suppliers has recently proposed a hybrid type of protocol, namely the FlexRay communication protocol [11]. FlexRay allows the sharing of the bus among event-driven (ET) and time-driven (TT) messages, thus offering the advantages of both worlds. FlexRay will very likely become the de-facto standard for in-vehicle communications. 1 However, before it can be successfully deployed in applications that require predictability, timing analysis techniques are necessary to provide bounds for the message communication times [20].FlexRay is composed of static (ST) and dynamic (DYN) segments, which are arranged to form a bus cycle that is repeated periodically. The ST segment is similar to TTP, and employs a generalized time-division multiple-access (GTDMA) scheme. The DYN segment of the FlexRay protocol is similar to Byteflight and uses a flexible TDMA (FTDMA) bus access scheme.Although [24], none of these analyses is applicable to the DYN segment in FlexRay. In [7], the authors consider the case of a hard real-time application implemented on a FlexRay bus. However, in their discussion they restrict themselves exclusively to the static segment, which means that, in fact, only the classical problem of communication scheduling over a TDMA bus [24,12] is considered. The performance analysis of the Byteflight protocol, which is similar to the DYN segment of FlexRay, is analyzed in [5]. The authors assume a very restrictive "quasi-TDMA" transmission scheme for time-critical messages, which basically means that the DYN segment would behave as an ST (TDMA) segment in order to guarantee timeliness.In this paper we present the first approach to timing analysis of applications communicating over a FlexRay bus, taking into consideration the specific aspects of this protocol, including the DYN ...

Abstract-We present an approach to the synthesis of fault-tolerant hard real-time systems for safety-critical applications. We use checkpointing with rollback recovery and active replication for tolerating transient faults. Processes and communications are statically scheduled. Our synthesis approach decides the assignment of fault-tolerance policies to processes, the optimal placement of checkpoints and the mapping of processes to processors such that multiple transient faults are tolerated and the timing constraints of the application are satisfied. We present several design optimization approaches which are able to find fault-tolerant implementations given a limited amount of resources. The developed algorithms are evaluated using extensive experiments, including a real-life example.

Abstract-In this paper, we concentrate on aspects related to the synthesis of distributed embedded systems consisting of programmable processors and application-specific hardware components. The approach is based on an abstract graph representation that captures, at process level, both dataflow and the flow of control. Our goal is to derive a worst case delay by which the system completes execution, such that this delay is as small as possible; to generate a logically and temporally deterministic schedule; and to optimize parameters of the communication protocol such that this delay is guaranteed. We have further investigated the impact of particular communication infrastructures and protocols on the overall performance and, specially, how the requirements of such an infrastructure have to be considered for process and communication scheduling. Not only do particularities of the underlying architecture have to be considered during scheduling but also the parameters of the communication protocol should be adapted to fit the particular embedded application. The optimization algorithm, which implies both process scheduling and optimization of the parameters related to the communication protocol, generates an efficient bus access scheme as well as the schedule tables for activation of processes and communications.

Abstract

Dynamic voltage scaling and adaptive body biasing have been shown to reduce dynamic and leakage power consumption effectively. In this paper, we optimally solve the combined supply voltage and body bias selection problem for multi-processor systems with imposed time constraints, explicitly taking into account the transition overheads implied by changing voltage levels. Both energy and time overheads are considered. We investigate the continuous voltage scaling as well as its discrete counterpart, and we prove NP-hardness in the discrete case. Furthermore, the continuous voltage scaling problem is formulated and solved using nonlinear programming with polynomial time complexity, while for the discrete problem we use mixed integer linear programming. Extensive experiments, conducted on several benchmarks and a real-life example, are used to validate the approaches.

ABSTRACT

Abstract-Time-redundancy techniques are commonly used in real-time systems to achieve fault tolerance without incurring high energy overhead. However, reliability requirements of hard real-time systems that are used in safety-critical applications are so stringent that time-redundancy techniques are sometimes unable to achieve them. Standby sparing as a hardwareredundancy technique can be used to meet high reliability requirements of safety-critical applications. However, conventional standby-sparing techniques are not suitable for lowenergy hard real-time systems as they either impose considerable energy overheads or are not proper for hard timing constraints. In this paper we provide a technique to use standby sparing for hard real-time systems with limited energy budgets. The principal contribution of this work is an online energymanagement technique which is specifically developed for standby-sparing systems that are used in hard real-time applications. This technique operates at runtime and exploits dynamic slacks to reduce the energy consumption while guaranteeing hard deadlines. We compared the low-energy standby-sparing (LESS) system with a low-energy timeredundancy system (from a previous work). The results show that for relaxed time constraints, the LESS system is more reliable and provides about 26% energy saving as compared to the time-redundancy system. For tight deadlines when the timeredundancy system is not sufficiently reliable (for safety-critical application), the LESS system preserves its reliability but with about 49% more energy consumption.