Time-triggered Controller Area Network Research Articles

High Accuracy Software-Based Clock Synchronization Over CAN

In distributed real-time communication systems, common knowledge of the global time is crucial. It prevents message violations on the bus and allows independent components to collaborate within a real-time system on a timely basis. Systems with hard real-time requirements need to have high precision and accuracy of time. This is achieved by hardware-supported frame time-stamping mechanisms as found in dedicated protocols, such as time-triggered CAN (TTCAN), Flexray, and time-sensitive networking (TSN)-enabled Ethernet. However, many microcontroller units are not specifically designed to provide such a hardware-based solution at the communication interface. Therefore, a software-based implementation of the time synchronization algorithm is needed. Nevertheless, some commercial off-the-shelf (COTS) microcontroller units already provide an IEEE 1588-enabled Ethernet interface, including a high-precision timer module with rate correction. This module can be used for time synchronization purposes to align a set of distributed clocks via various communication interfaces. This article investigates the accuracy of software-based and hardware-supported time synchronization algorithm over the controller area network (CAN) protocol using a COTS microcontroller. As a result, we present identified jitter and delay sources as well as the achieved time accuracy. We show that using an advanced timer module combined with additional system knowledge allows submicrosecond precision and accuracies.

DCW

Real-time systems continuously interact with the physical environment and often have to satisfy stringent timing constraints imposed by their interactions. Those systems involve two main properties: reactivity and predictability. Reactivity allows the system to continuously react to a non-deterministic external environment, while predictability guarantees the deterministic execution of safety-critical parts of applications. However, with the increase in software complexity, traditional approaches to develop real-time systems make temporal behaviors difficult to infer, especially when the system is required to address non-deterministic aperiodic events from the physical environment. In this article, we propose a reactive and predictable programming framework, Distributed Clockwerk (DCW), for distributed real-time systems. DCW introduces the Servant, which is a non-preemptible execution entity, to implement periodic tasks based on the Logical Execution Time (LET) model. Furthermore, a joint schedule policy, based on the slack stealing algorithm, is proposed to efficiently address aperiodic events with no violated hard-time constraints. To further support predictable communication among distributed nodes, DCW implements the Time-Triggered Controller Area Network (TTCAN) to avoid collisions while accessing the shared communication medium. Moreover, a programming framework implements to provide a set of programming APIs for defining timing and functional behaviors of concurrent tasks. An example is further implemented to illustrate the DCW design flow. The evaluation results demonstrate that our proposal can improve both periodic and aperiodic reactivity compared with existing work, and the implemented DCW can also ensure the system predictability by achieving extremely low overheads.

Error Recovery in the Time-Triggered Paradigm with FTT-CAN.

Data networks are naturally prone to interferences that can corrupt messages, leading to performance degradation or even to critical failure of the corresponding distributed system. To improve resilience of critical systems, time-triggered networks are frequently used, based on communication schedules defined at design-time. These networks offer prompt error detection, but slow error recovery that can only be compensated with bandwidth overprovisioning. On the contrary, the Flexible Time-Triggered (FTT) paradigm uses online traffic scheduling, which enables a compromise between error detection and recovery that can achieve timely recovery with a fraction of the needed bandwidth. This article presents a new method to recover transmission errors in a time-triggered Controller Area Network (CAN) network, based on the Flexible Time-Triggered paradigm, namely FTT-CAN. The method is based on using a server (traffic shaper) to regulate the retransmission of corrupted or omitted messages. We show how to design the server to simultaneously: (1) meet a predefined reliability goal, when considering worst case error recovery scenarios bounded probabilistically by a Poisson process that models the fault arrival rate; and, (2) limit the direct and indirect interference in the message set, preserving overall system schedulability. Extensive simulations with multiple scenarios, based on practical and randomly generated systems, show a reduction of two orders of magnitude in the average bandwidth taken by the proposed error recovery mechanism, when compared with traditional approaches available in the literature based on adding extra pre-defined transmission slots.

Holistic Scheduling of Real-Time Applications in Time-Triggered In-Vehicle Networks

As time-triggered communication protocols [e.g., time-triggered controller area network (TTCAN), time-triggered protocol (TTP), and FlexRay] are widely used on vehicles, the scheduling of tasks and messages on in-vehicle networks becomes a critical issue for offering quality-of-service (QoS) guarantees to time-critical applications on vehicles. This paper studies a holistic scheduling problem for handling real-time applications in time-triggered in-vehicle networks where practical aspects in system design and integration are captured. The contributions of this paper are multifold. First, it designs a novel scheduling algorithm, referred to as <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Unfixed Start Time</i> (UST) algorithm, which schedules tasks and messages in a flexible way to enhance schedulability. In addition, to tolerate assignment conflicts and further improve schedulability, it proposes two rescheduling and backtracking methods, namely, <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Rescheduling with Offset Modification</i> (ROM) and <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Backtracking and Priority Promotion</i> (BPP) procedures. Extensive performance evaluation studies are conducted to quantify the performance of the proposed algorithm under a variety of scenarios.

Real-time and reliability analysis of time-triggered CAN-bus

Real-time performance and reliability are two most important issues in applications of time-triggered controller area network (CAN) bus systems at present. A scheduling matrix of time-triggered CAN-bus system is established using average-loading algorithm. Periodic messages are guaranteed to transmit without delay by distributing independent transmission windows within the system matrix. Considering the traditional CAN-bus transmission mechanism and the time-triggered feature, an algorithm is improved to calculate the worst-case delay of event-triggered messages in time-triggered CAN-bus systems. The failure probability is calculated for event-triggered messages whose worst-case delay exceeds their deadlines. Different levels of redundant structures of CAN-bus circuits are analyzed and the maintenance management is proposed to improve the system reliability. Finally, the reliabilities of different structures are calculated and the influences of maintenance on the system reliability are analyzed.

Experimental Study on Communication Delay of Powertrain System of Plug-In Hybrid Electric Vehicles

In order to contrast and analyze the real-time performance of the powertrain system of a plug-in hybrid electric vehicle, a mathematical model of the system delay is established under the circumstances that the transmission adopts the CAN (controller area network) protocol and the TTCAN (time-triggered CAN) protocol, respectively, and the interior of the controller adopts the foreground-background mode and the OSEK mode respectively. In addition, an experimental platform is developed to test communication delays of messages under 4 different implementation models. The 4 models are testing under the CAN protocol while the controller interior adopts the foreground-background mode; testing under the CAN protocol while the controller interior adopts the OSEK mode; testing under the TTCAN protocol while the controller interior adopts the foreground-background mode, and testing under the TTCAN protocol while the controller interior adopts the OSEK mode. The theoretical and testing results indicate that the communication delay of the OSEK mode is a little longer than the one of the foreground-background mode. Moreover, compared with the CAN protocol, the periodic message has a better real-time performance under the TTCAN protocol, while the nonperiodic message has a worse one.

PEMFC Optimization Strategy with Auxiliary Power Source in Fuel Cell Hybrid Vehicle

one of the present-day implementation of fuel cell is acting as main power source in Fuel Cell Hybrid Vehicle (FCHV). This paper proposes some strategies to optimize the performance of Polymer Electrolyte Membrane Fuel Cell (PEMFC) implanted with auxiliary power source to construct a proper FCHV hybridization. The strategies consist of the most updated optimization method determined from three point of view i.e. Energy Storage System (ESS), hybridization topology and control system analysis. The goal of these strategies is to achieve an optimum hybridization with long lifetime, low cost, high efficiency, and hydrogen consumption rate improvement. The energy storage system strategy considers battery, supercapacitor, and high-speed flywheel as the most promising alternative auxiliary power source. The hybridization topology strategy analyzes the using of multiple storage devices injected with electronic components to bear a higher fuel economy and cost saving. The control system strategy employs nonlinear control system to optimize the ripple factor of the voltage and the current and using the AOC-EMS system to improve the hydrogen consumption rate. ECMS and BERS strategy based on Time-Triggered Controller Area Network (TTCAN) also promoted to optimize hydrogen consumption rate from recovered kinetic energy while in braking regeneration mode.

Message scheduling with reduced matrix cycle and evenly distributed sparse allocation for time-triggered CAN

Controller Area Network (CAN) was initially developed as an in-vehicle real-time communication bus. Due to its low cost and high reliability, it has also become a widely accepted standard in industrial distributed control applications. The CAN protocol has an event-triggered architecture. Although its priority based medium access mechanism provides guaranteed immediate access for the highest priority messages, it may cause unpredictability in communication media for the lower priority messages. In order to address the problems caused by the event-triggered architecture, different time-triggered network architectures, such as TTP, Byteflight, and Flexray, have been introduced. This paper focuses on time-triggered CAN (TTCAN), which is built on the existing CAN standard with the addition of time division multiple access (TDMA). In order to combine the advantages of the event-triggered and time-triggered communication to meet the requirements of the distributed real-time systems, it is crucial to construct feasible message schedules. In this study, a schedule construction method, based on the reduced matrix cycle and evenly distributed sparse allocation, is introduced to produce the best optimum message schedules possible in terms of the message delay performance. The simulation results show that the method introduced in this study provides significant performance improvement not only for the time-triggered messages but also for the event-triggered messages.

Evaluating a new communication protocol for real-time distributed control

The recent trend in distributed automation and control systems has been towards event-triggered system architectures such as UML and IEC 61499. Although existing communication protocols (e.g., Ethernet) can support high-level communication within these systems, there is contention as to which low-level protocol to use, or if any exist that meet the requirements of being event-triggered and hard real-time. This paper proposes a new way to measure communication performance. The goal of the new measurement method is to stress the necessity that a real-time communication protocol needs to be both efficient and fair. This is illustrated by comparing three communication strategies: Controller Area Network (CAN), Time-Triggered CAN (TTCAN) and Escalating Priority CAN (EPCAN). The first two represent the extremes between event-triggered and time-triggered communication strategies; the third is introduced to illustrate the benefits of a new event-based communication protocol proposed by the authors.

Researches on Fault Diagnosis of Time Master in TTCAN on Hybrid

Determinant factors of time interval for sending reference message in Time Triggered Controller Area Network, called TTCAN below, was analyzed. A software method for fault diagnosis and tolerance of time master was also proposed and the method was validated in a network of hybrid electric vehicle topology. The results indicate that it does work to monitor local time counter in each potential time master and to compare it with basic cycle to diagnose the fault of current time master and that it does make sense to set multi-potential time masters to get tolerance of current time master’s fault and to guarantee proper operation and reliability of TTCAN system.

Online management of lithium-ion battery based on time-triggered controller area network for fuel-cell hybrid vehicle applications

This paper introduces a state of charge (SOC) estimation algorithm that was implemented for an automotive lithium-ion battery system used in fuel-cell hybrid vehicles (FCHVs). The proposed online control strategy for the lithium-ion battery, based on the Ah current integration method and time-triggered controller area network (TTCAN), incorporates a signal filter and adaptive modifying concepts to estimate the Li 2MnO 4 battery SOC in a timely manner. To verify the effectiveness of the proposed control algorithm, road test experimentation was conducted with an FCHV using the proposed SOC estimation algorithm. It was confirmed that the control technique can be used to effectively manage the lithium-ion battery and conveniently estimate the SOC.

Optimal vehicle control strategy of a fuel cell/battery hybrid city bus

In this article, an optimal vehicle control strategy based on a time-triggered controller area network (TTCAN) system for a polymer electrolyte membrane (PEM) fuel cell/nickel-metal hydride (Ni-MH) battery powered city bus is presented. Aiming at improving the fuel economy of the city bus, the control strategy comprises an equivalent consumption minimization strategy (ECMS) and a braking energy regeneration strategy (BERS). On the basis of the introduction of a battery equivalent hydrogen consumption model incorporating a charge-sustaining coefficient, an analytical solution to the equivalent consumption minimization problem is given. The proposed strategy has been applied in several city buses for the Beijing Olympic Games of 2008. Results of the “China city bus typical cycle” testing show that, the ECMS and the BERS lowered hydrogen consumption by 2.5% and 15.3% respectively, compared with a rule-based strategy. The BERS contributes much more than the ECMS to the fuel economy, because the fuel cell system does not leave much room for the optimal algorithm in improving the efficiency.

A Scheduling Algorithm for Minimizing Exclusive Window Durations in Time-Triggered Controller Area Network

Time-Triggered Controller Area Network is widely accepted as a viable solution for real-time communication systems such as in-vehicle communications. However, although TTCAN has been designed to support both periodic and sporadic real-time messages, previous studies mostly focused on providing deterministic real-time guarantees for periodic messages while barely addressing the performance issue of sporadic messages. In this paper, we present an O(n2) scheduling algorithm that can minimize the maximum duration of exclusive windows occupied by periodic messages, thereby minimizing the worst-case scheduling delays experienced by sporadic messages.

Application and Performance Analysis of Dynamic-planning-based Flexible Time Triggered Controller Area Network

To meet the requirement of automotive intelligentizing,the next step in the direction of automotive bus is to support both time-and event-triggered communication services and to attain more flexible of design and scheduling.But controller area network (CAN) protocol is inefficient for time-triggered messages,while time-triggered controller area network (TTCAN) can efficiently fulfill joint support for both event- and time-triggered traffic but lacks flexibility in message scheduling.To these questions,a new dynamic planning-based protocol that is flexible in time-triggered controller area network (FTTCAN) is analyzed.And the elemen- tary cycle comprising of two phases and real-time analysis method for communications of messages in the two phases are explained. Then an FTTCAN-bus system of electric vehicle based on FTTCAN protocol is designed,and the scheduling strategy of signals based on dynamic planning is adopted.And performance analysis of the new system is carried out by comparing with CAN system. Finally,operation test of FTTCAN protocol is carried out on CAN bus development system.The comparison and test results verify that FTrCAN is a good way to design automotive bus system,which can meet the requirements of supporting both time-and event-triggered communication services and being flexible in design and scheduling.

Systematic Message Schedule Construction for Time-Triggered CAN

The most widely used standard for in-vehicle communication networks that interconnect electronic control units is the controller area network (CAN). However, the event-triggered architecture of CAN introduces several issues, such as predictability, signal jitter, and reliability. Different time-triggered networks are being developed to address these issues. In this paper, we focus on time-triggered CAN (TTCAN), which achieves time-triggered behavior by implementing time-division multiple access on the existing CAN network standard. The main task is thus to construct a message schedule for a given set of messages while fulfilling certain performance criteria. To this end, we provide a formal framework for the construction of feasible message schedules in TTCAN networks by considering several performance metrics, such as bandwidth utilization and jitter, as well as the hardware constraints of the TTCAN controller specification.

A new measurement technique for communications in IEC 61499 systems

Distributed systems are relying more heavily on event-triggered system architectures such as UML and IEC 61499. Existing communication protocols can support the high-level communication within these systems, but there is contention as to which low-level protocol to use, or if any exist that meet the requirements of being event-triggered and hard real-time. This paper presents a new way to measure communication performance. The goal of the new measurement method is to stress the necessity that a system be both efficient and fair. This is illustrated by comparing three communication strategies; Controller Area Network (CAN), Time-Triggered CAN (TTCAN) and Alternating Priority CAN. The first two represent the extremes between event-triggered and time-triggered communication strategies. The third is introduced to illustrate the benefits of the new measurement technique.

Timing Analysis of Real-Time Communication Under Electromagnetic Interference

This paper discusses aspects of dependability of real-time communication. In particular, we consider timing behaviour under fault conditions for Controller Area Network (CAN) and the extension Time-triggered CAN (TTCAN) based on a time-driven schedule. We discuss the differences between these buses and their behaviour under electromagnetic interference. We present response timing analyses for CAN and TTCAN in the presence of transient network faults using a probabilistic fault model where random faults from electromagnetic interference occur. The CAN analysis provides a probability distribution of worst case response times for message frames. The results indicate that CAN may generally provide a higher probability of delivering messages on time than TTCAN. The CAN analysis result is used to discuss an approach to implementing a bus guardian for event-triggered systems.

Clock synchronisation on multiple TTCAN network channels

The Controller Area Network (CAN) is a well established control network for automotive and automation control applications. Time-Triggered Controller Area Network (TTCAN) is a recent development which introduces a session layer, for message scheduling, to the existing CAN standard, which is a two layer standard comprising of a physical layer and a data link layer. TTCAN facilitates network communication in a time-triggered fashion, by introducing a Time Division Multiple Access style communication scheme. This allows deterministic network behaviour, where maximum message latency times can be quantified and guaranteed. However, for safety-critical applications the market requires fault-tolerant control networks, which support spatial redundancy. The TTCAN standard does not support such built-in redundancy. This paper proposes a prototype design implementation for a synchronisation layer between two or more independent TTCAN network channels. This synchronisation layer can be used as a building block for network redundancy leading to a fault-tolerant network architecture by introducing related and comparable message transmissions on multiple network channels. This leads to improved error tolerance and also facilitates increased bandwidth by running multiple synchronised TTCAN network channels in parallel.

A time-triggered transducer network based on an enhanced IEEE 1451 model

The IEEE 1451 set of standards defines an architectural model for interfacing multiple ‘smart transducers’ in a distributed environment, which can gate to a fieldbus or local area network. However, the IEEE 1451 standards do not support strict real-time message scheduling within the transducer cluster environment. This work proposes that a time-triggered control network, TTCAN (time-triggered controller area network), be employed as the multiplexed interface for smart transducers. Such a development would allow a deterministic control message scheduling matrix to be defined so that all transducer message scheduling can be guaranteed. The proposal effectively changes the IEEE 1451 architecture from an event-driven system to a true time-driven system. The existing set of IEEE 1451 standards are briefly reviewed and the new TTCAN control network is described. A complete prototype design implementation of the proposed system is presented. The prototype system demonstrates that the concept is feasible and workable. Time-triggered networks are synchronous control networks where the scheduling of control messages is progressed, based strictly on the passage of time, based on the network's sense of global time. Such time-triggered networks are being developed primarily for the automotive industry to support reliable scheduling for safety-critical control systems such as brake-by-wire and steer-by-wire systems. This work shows that it is now possible to apply such time-triggered paradigms to general transducer interfacing environments.

TTCAN: a new time-triggered controller area network

The controller area network (CAN) communications protocol is used extensively in the automotive and industrial control sectors. Much work has been done to establish the bounded response time of transmissions in an event-triggered CAN. However, a new time-triggered architecture for CAN is being developed and will soon be available on the market. This new control network, referred to as time-triggered controller area network, defines a session layer protocol for CAN, which is based on a static schedule time-triggered paradigm and provides intrinsic deterministic behaviour. This paper describes the new protocol and provides some practical performance equations to calculate utilisation limits for this control network.