Archive | 2021
AUTOSAR-compliant precision clock synchronization over CAN
Abstract
The automotive sector is subject to constant change. Meanwhile, a single vehicle is a highly distributed system. For such systems, a common concept of time is particularly important for proper functioning. For Ethernet based communication there is PTP for such tasks. This is the quasi-standard for high precision synchronization of clocks. In the automotive sector, however, the CAN bus plays a decisive role. However, there is still no standardized approach for clock synchronization. Existing solutions such as TTCAN require special hardware and change the communication scheme on the bus. The biggest problem with known solutions, however, is the precision achieved. While PTP can synchronize in the subnanosecond range, the best current solution for the CAN bus reaches 2 microseconds. This problem is addressed here. The focus of this work is to develop a strategy for clock synchronization over the CAN bus that does not limit the choice of controller or communication scheme. The implementation is based on the AUTOSAR standard for clock synchronization over CAN. Only the message format is adopted, which means that the findings of this work can also be applied to other synchronization protocols. It has been shown that the way the timestamp is generated has the greatest influence on precision. However, even software-based timestamps could be improved by understanding the sources of error. The evaluation of the at the end of the work has shown that a precision in the two-digit nanosecond range is possible with the CAN bus.