Safety-Critical Communication in Avionics

The aircraft of today use electrical fly-by-wire systems for manoeuvring. These safety-critical distributed systems are called flight control systems and put high requirements on the communication networks that interconnect the parts of the systems. Reliability, predictability, flexibility, low weight and cost are important factors that all need to be taken in to consideration when designing a safety-critical communication system. In this thesis certification issues, requirements in avionics, fault management, protocols and topologies for safety-critical communication systems in avionics are discussed and investigated. The protocols that are investigated in this thesis are: TTP/C, FlexRay and AFDX, as a reference protocol MIL-STD-1553 is used. As reference architecture analogue point-to-point is used. The protocols are described and evaluated regarding features such as services, maturity, supported physical layers and topologies.Pros and cons with each protocol are then illustrated by a theoretical implementation of a flight control system that uses each protocol for the highly critical communication between sensors, actuators and flight computers.The results show that from a theoretical point of view TTP/C could be used as a replacement for a point-to-point flight control system. However, there are a number of issues regarding the physical layer that needs to be examined. Finally a TTP/C cluster has been implemented and basic functionality tests have been conducted. The plan was to perform tests on delays, start-up time and reintegration time but the time to acquire the proper hardware for these tests exceeded the time for the thesis work. More advanced testing will be continued here at Saab beyond the time frame of this thesis

Services for safety-critical applications on dual-scheduled TDMA networks

Tese de doutoramento. Engenharia Electrotécnica e de Computadores. Faculdade de Engenharia. Universidade do Porto. 200

Towards Efficient Transient Fault Handling in Time-Triggered Systems

DETITransient communication faults in distributed control systems (DCS) are unavoidable but must be handled adequately in order to enforce correct system behaviour. A typical way of handling transient faults is temporal redundancy by means of retransmissions. However, DCS are frequently designed with time-triggered architectures, being scheduled offline and not coping efficiently with retransmissions as these require the pre-allocation of bandwidth that, in the absence of errors, is wasted. In this paper we propose using the Flexible Time-Triggered paradigm to reconcile the Time-Triggered model with on-line scheduling of retransmissions when needed, only, leading to an efficient bandwidth usage. This is confirmed with preliminary experimental results obtained on an FTT-CAN network

In-vehicle communication networks : a literature survey

The increasing use of electronic systems in automobiles instead of mechanical and hydraulic parts brings about advantages by decreasing their weight and cost and providing more safety and comfort. There are many electronic systems in modern automobiles like antilock braking system (ABS) and electronic brakeforce distribution (EBD), electronic stability program (ESP) and adaptive cruise control (ACC). Such systems assist the driver by providing better control, more comfort and safety. In addition, future x-by-wire applications aim to replace existing braking, steering and driving systems. The developments in automotive electronics reveal the need for dependable, efficient, high-speed and low cost in-vehicle communication. This report presents the summary of a literature survey on in-vehicle communication networks. Different in-vehicle system domains and their requirements are described and main invehicle communication networks that have been used in automobiles or are likely to be used in the near future are discussed and compared with key references

Synthesis of Fault-Tolerant Embedded Systems

This work addresses the issue of design optimization for faulttolerant hard real-time systems. In particular, our focus is on the handling of transient faults using both checkpointing with rollback recovery and active replication. Fault tolerant schedules are generated based on a conditional process graph representation. The formulated system synthesis approaches decide 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, transparency requirements are considered, and the timing constraints of the application are satisfied. 1

Estudo do impacto de transientes elétricos em protocolos de comunicação em sistemas embarcados

O aumento da complexidade e responsabilidade dos dispositivos embarcados nos veículos hoje, tem orientado os esforços no desenvolvimento de sistemas de controle para que estes sejam mais rápidos, precisos, robustos e principamente seguros. Com isso, estes dispositivos estão levando os protocolos de comunicação a um patamar inédito de exigência, tanto no quesito de capacidade como confiabilidade. Protocolos como CAN, CAN-FD e FlexRay entre outros, tem sido utilizados devido às suas características de segurança e a capacidade de atender aos requisitos temporais dos diversos circuitos embarcados. O desenvolvimento e utilização cada vez mais frequente de dispositivos focados em segurança, fazem com que a comunicação entre os diversos componentes destes dispositivos seja exigida ao máximo, levando à necessidade de respostas confiáveis ao extremo. Sistemas como freios ABS, suspensão ativa, frenagem autonoma de emergência, controle de velocidade e distância adaptativo, entre outros, que envolvem várias ECUs distribuídas ao longo do veículo, dispões de frações de segundo para a reação do sistema, entre o sinal de entrada e a atuação correspondente, demandando uma comunicação segura e tolerante à falhas. Os veículos hoje estão passando por grandes mudanças conceituais, trazendo cada vez mais elementos onde o funcionamento demanda mais energia das fontes de alimentação. Diversos sistemas existentes nos veículos geram ruídos como os Transientes Elétricos Rápidos, ou "Electric Fast Transient" (EFT), que estão presentes nas mais simples operações cotidianas do veículo, como ligar e desligar o farol, o ar condicionado, o limpador de para brisas, ou mesmo o acionamento de iluminação diurna (DRL), etc. Neste trabalho foram realizados diversos ensaios, utilizando ECUs com diferentes funções e protocolos, para identificar a susceptibilidade dos referidos sistemas e os protocolos à presença destes ruídos. Visando atender às normas IEC 62228 e a ISO26262, este trabalho demandou o projeto e construção de dois circuitos eletrônicos diferentes, um circuito observando os dados de tempos de subida e de descida (rise and fall time) dos pulsos de EFT, e outro observando a arquitetura do layout da placa de circuito impresso (PCB), as suas entradas, saídas, componentes, etc. Estes ensaios visaram identificar o quanto estes protocolos são suscetíveis à estes tipos de ruídos, utilizando métricas de análise baseadas nos tempos de latência e variação de jitter dos pacotes de comunicação.The increasing complexity and accountability of embedded devices in vehicles today has driven efforts to develop control systems to make them faster, accuratest, safest, robustest. Thus, these devices are taking communication protocols to an unprecedented level of demand, both in terms of capacity and reliability. Protocols such as CAN, CANFD and FlexRay among others have been used due to their safety characteristics and the ability to meet the time requirements of various embedded circuits. The increasing development and use of safety-focused devices, means that communication between the various components of these devices is required to the utmost, leading to the need for extremely reliable responses. Systems such as ABS brakes, active suspension, autonomous emergency braking, adaptative cruise control, among others, which involve various ECUs distributed throughout the vehicle, have milliseconds for system reaction, between input signal and concrete actuation, requiring safe and failure tolerant communication. Vehicles today are undergoing major conceptual changes, bringing more and more elements whose operation require more energy from power supplies. These systems generate noise such as "Electric Fast Transient" (EFT), which are present in the simplest daily operations of the vehicle, such as turning the headlight on, the air conditioner, the windscreen wiper, or even the daytime running light (DRL), etc. In this work several tests were carried out, using different ECUs with different functions and different protocols to identify the susceptibility of these systems and the protocols to these noises. In order to comply with IEC 62228 and ISO 26262 standards, this work required the design and construction of two different electronic circuits, one circuit observing the rise and fall time data of the EFT pulses, and the other observing the architecture of the printed circuit board (PCB) layout, its inputs and outputs, components, etc. These tests aimed to identify how susceptible these protocols are to these types of noise, using analysis metrics based on latency time and jitter variation of communication packets

Arquitecturas de hardware para um veículo eléctrico

Tese de mestrado integrado. Engenharia Electrotécnica e de Computadores. Faculdade de Engenharia. Universidade do Porto. 201