Flexible Time-Triggered Communication Research Articles

The FTT-CAN protocol: why and how

The requirement for flexible operation is becoming increasingly important in modern industrial systems. This requirement has to be supported at all system levels, including the field level in process industry, as well as the cell and machine control levels in manufacturing industry, where fieldbus-based communication systems are commonly found. Furthermore, typical applications at these levels require both time- and event-triggered communication services, in most cases under stringent timing constraints, to convey state data in the former case and alarms and management data in the latter. However, neither the requirement for flexible operation under guaranteed timeliness nor for joint support of time and event-triggered traffic are efficiently fulfilled by most of existing fieldbus systems. This paper presents a new protocol, flexible time-triggered communication on controller area network, which fulfills both requirements: it supports time-triggered communication in a flexible way as well as being an efficient combination of both time- and event-triggered traffic with temporal isolation. These types of traffic are handled by two complementary subsystems, the synchronous and the asynchronous messaging systems, respectively. The paper includes a justification for the new protocol as well as its description and worst case temporal analysis for both subsystems. This analysis shows the capability of the protocol to convey real-time traffic of either type.

EDF message scheduling on controller area network

The controller area network (CAN) has a maximum transmission rate of 1 Mbit/s and its fixed priorities-based medium access control (MAC) limits the maximum bus utilisation when timeliness guarantees are required. An implementation of earliest deadline first (EDF) message scheduling on the CAN, based on the FTT-CAN (flexible time-triggered communication on CAN) protocol, is presented, which allows higher utilisation factors with timeliness guarantees. The advantages of using EDF instead of rate-monotonic scheduling on the FTT-CAN are highlighted, and a comparison with other implementations of EDF scheduling on the CAN is presented.

FTT-CAN: A Network-Centric Approach for CAN-Based Distributed Systems

The requirement for flexible operation is becoming increasingly important in many distributed computer control systems. This paper briefly presents the FTT-CAN protocol (Flexible Time-Triggered communication on Controller Area Network) which allows for flexible operation, i.e. dynamic communication requirements, under timeliness guarantees. Then, the paper discusses a particular approach to the global management of such distributed systems named network-centric. This is based on the synchronisation of the distributed tasks in remote nodes with the network traffic. Thus, on-line changes in the rates and/or relative phasing of the network traffic can be automatically applied to the tasks that use it, in all the remote nodes in the distributed system. This approach is fully supported by the FTT-CAN protocol.