Improving the performance and reliability of systems which employ the ’CONTROLLER AREA NETWORK’ protocol through low-level changes to the controller implementation

摘要

The CAN (Controller Area Network) protocol provides one of the cost-effective methods to network current generations of distributed embedded systems. Although it is a robust protocol with short messages and simple priorities, it is largely thought of as only being suitable for soft real-time, event-triggered systems. Safety critical applications require highly predictable behaviour with strict bounds on worst-case message transmission times; the next-generation mechatronic systems also requires a high level of information throughput. In its current form, CAN lacks most of these requirements principally due to its medium access scheme and physical-layer design.\udThis thesis presents a frame work which aims to enhance the capabilities of CAN, in order to push the boundaries of the protocol’s current operation. In particular, the main research question to be addressed is the exploration of the extent to which low-level modifications can enhance CAN suitability for use in the next generation of critical systems. In order to answer this question, it is first necessary to develop a flexible and robust platform to implement these modifications using a novel facility made up from custom soft-core CAN controllers. This novel facility was then employed to implement and experimentally investigate three small but conceptually significant protocol modifications as follows:\udIncreasing the effective data rate from 1 to 10 Mbps whilst doubling the effective payload from 8 to 16 bytes; Reduction of unwanted transmission jitter by compensating for bit stuffing; Enabling a windowed transmission scheme to provide optimal trade-off’s between transmission reliability and real-time behaviour in noisy environments.\udThe thesis describes the results obtained from these experiments and summarizes the main pros and cons that appear. The thesis then concludes with observation that the modified CAN protocol may be suitable for use with certain classes, of the next generation time-critical distributed embedded systems.