Controller Area Network (CAN) is used extensively in automotive applications, with in excess of 400 million CAN enabled microcontrollers manufactured each year. In 1994 schedulability analysis was developed for CAN, showing how worst-case response times of CAN messages could be calculated and hence guarantees provided that message response times would not exceed their deadlines. This seminal research has been cited in over 200 subsequent papers and transferred to industry in the form of commercial CAN schedulability analysis tools. These tools have been used by a large number of major automotive manufacturers in the design of in-vehicle networks for a wide range of cars, millions of which have been manufactured during the last decade.

This paper shows that the original schedulability analysis given for CAN messages is flawed. It may provide guarantees for messages that will in fact miss their deadlines in the worst-case. This paper provides revised analysis resolving the problems with the original approach. Further, it highlights that the priority assignment policy, previously claimed to be optimal for CAN, is not in fact optimal and cites a method of obtaining an optimal priority ordering that is applicable to CAN. The paper discusses the possible impact on commercial CAN systems designed and developed using flawed schedulability analysis and makes recommendations for the revision of CAN schedulability analysis tools.

/pdf/controller-area-network-can-schedulability-analysis-refuted-3vkjnart12.pdf

Controller Area Network (CAN) schedulability analysis: Refuted, revisited and revised

The distributed systems architect assembles pieces of hardware that are at least as large as a computer or a network router, and assigns pieces of software that are self-contained - such as Java applets - to those hardware components. As system complexity, size and diversity grow, the probability of inconsistency, unreliability, non-responsiveness and insecurity, increases. It is absolutely necessary for distributed systems architects to understand the management of such complex systems. Distributed Systems for System Architects addresses these issues.

Distributed Systems for System Architects

Controller Area Network (CAN) is widely used in automotive applications. Existing schedulability analysis for CAN is based on the assumption that the highest priority message ready for transmission at each node on the network will be entered into arbitration on the bus. However, in practice, some CAN device drivers implement FIFO rather than priority-based queues invalidating this assumption. In this paper, we introduce response time analysis and optimal priority assignment policies for CAN messages in networks where some nodes use FIFO queues while other nodes use priority queues. We show, via a case study and experimental evaluation, the detrimental impact that FIFO queues have on the real-time performance of CAN.

/pdf/controller-area-network-can-schedulability-analysis-with-4r9osotsvc.pdf

Controller Area Network (CAN) Schedulability Analysis with FIFO Queues

Designing distributed real-time systems as being composed of communicating objects offers many advantages with respect to modularity and extensibility of these systems. However, distributed real-time applications exhibit communication patterns that significantly differ from the traditional object invocation style. The publisher/subscriber model for inter-object communication matches well with these patterns. Any implementation of that model must address the problems of binding subscribers to publishers, of routing and filtering of messages, as well as reliability, efficiency and latency of message delivery. In the context of real-time applications, all these issues must be subject to a rigid inspection with respect to meeting real-time requirements. We argue that for embedded control systems built around smart microcontroller-powered devices these requirements can only be met when exploiting the properties of the underlying network. The CAN-Bus (CAN: Controller Area Network) which is an emerging standard in the field of real-time embedded systems is particularly suited to implement a publisher/subscriber model of communication. We present an implementation of the real-time publisher/subscriber model that exploits the underlying facilities of the CAN-Bus. In particular, we introduce a novel addressing scheme for publisher/subscriber communication that makes efficient use of the CAN-Bus addressing method. We provide a detailed design and implementation details along with some preliminary performance estimations.

Implementing the real-time publisher/subscriber model on the controller area network (CAN)

We present a guardian-based approach to detecting 'babbling idiots', faulty nodes which erroneously consume extra resource in an event triggered system. In general, one cannot detect all babbling idiots, but the maximum effect of undetected faults is bounded and small, and therefore can be taken into account in worst case response time analysis to guarantee that a babbling idiot cannot cause a timing failure elsewhere in the system. The approach is applied specifically to the CAN protocol to protect against faulty nodes transmitting message frames too often. We show that the overhead of including the effect of undetected frames into the worst case response time analysis is small enough to be of practical value.

An analysable bus-guardian for event-triggered communication

Fault-tolerant distributed systems based on field-buses may take advantage from reliable and atomic broadcast. There is a current belief that CAN native mechanisms provide atomic broadcast. In this paper, we dismiss this misconception, explaining how network errors may lead to: inconsistent message delivery; generation of message duplicates. These errors may occur when faults hit the last two bits of the end of frame delimiter. Although rare, its influence cannot be ignored, for highly fault-tolerant systems. Finally, we give a protocol suite that handles the problem effectively.

Fault-tolerant broadcasts in CAN

Network media redundancy is a clean and effective way of achieving high levels of reliability against temporary medium faults and availability in the presence of permanent faults. This is specially true of critical control applications such as those supported by the Controller Area Network (CAN). In our endeavor to provide CAN with media redundancy we ended-up devising a scheme which is extraordinarily simpler than previous approaches known for CAN or other LANs and field-buses.

A Columbus' egg idea for CAN media redundancy

Fault-tolerant distributed systems based on fieldbuses may benefit to a great extent from the availability of semantically rich communication services, such as those provided by group communication, clock synchronization, membership and failure detection. This is specially true of distributed critical control applications. However, the migration of those services to the realm of simple fieldbuses, such as the native Controller Area Network (CAN) protocol family, presents non-negligible problems, since it lacks most of the functionality required of a fault-tolerant distributed system, such as reliable message broadcast guarantees, distributed node failure detection, and site membership services. As part of our endeavor to design a CAN-based infrastructure support for extremely reliable distributed computer control, dubbed CAN Enhanced Layer (CANELy), we have been addressing the problem of fault-tolerant communications on fieldbuses in a comprehensive way. In this paper, we show that node failure detection and site membership services can be efficiently supported by a simple software layer built on top of an exposed CAN controller interface.

Node failure detection and membership in CANELy

Standard fieldbuses, such as the Controller Area Network (CAN), are today a cost-effective solution for distributed computer control systems. However, the standard CAN protocol exhibits a set of severe shortcomings in respect to the provision of strict dependability and timeliness guarantees. This paper identifies those shortcomings and discusses the main design challenges we have been tackling in a comprehensive way to provide a CAN-based infrastructure support for extremely reliable hard real-time communications, dubbed CAN Enhanced Layer (CANELv).

/pdf/enforcing-dependability-and-timeliness-in-controller-area-od6juoy1u5.pdf

Enforcing Dependability and Timeliness in Controller Area Networks

Object oriented techniques have been along the last decade one of the most useful programming paradigms. However, for distributed embedded systems, the semantic gap between the object orientation layer and the underlying infrastructure is extremely large. This gap can be narrowed, should the embedded system platform provide semantically rich communication and management services. The paper outlines our research effort in the provision of such services by CAN based (Controller Area Network) systems.

/pdf/embedded-platforms-for-distributed-real-time-computing-176pp0yg81.pdf

Embedded platforms for distributed real-time computing: challenges and results

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