Abstract
Modern cars are characterized by a growing number of sensors, actuators, and advanced driver assistance systems that require a synchronized view of the time. These devices are typically interconnected by CAN, which is still the most important in-vehicle network. Precise clock synchronization over CAN is difficult due to the properties of the bus, and current approaches often use dedicated hardware or proprietary software solutions. A few years ago, however, the AUTomotive Open System ARchitecture (AUTOSAR) development alliance published a standardized synchronization method. In this article, we investigate what synchronization precision can be realistically achieved in a real-world automotive hardware and software environment. This involves pure software timestamping, standard CAN controllers without hardware modifications, and a typical automotive real-time operating system. We evaluate several approaches to reduce the synchronization jitter using filtering and optimizing the timestamping procedure. Experiments show that, ultimately, a precision better than 50 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\mu$</tex-math></inline-formula> s can be achieved with a fully AUTOSAR-compliant software implementation.
Highlights
O VER the years, many in-vehicle networks have been developed to meet the needs of the increasing number of devices and data volume to be processed
The communication controller for the CAN bus is implemented in the Field Programmable Gate Array (FPGA) uses the MCAN IP core from Bosch [27]. This controller would offer an integrated function for recording both transmission and reception timestamps in the data link layer. These timestamps are drawn at the beginning of a frame, which is incompatible with the AUTOSAR specification mandating timestamping at the end of the frame
Time series and histogram of the clock offsets are similar to Figs. 6 and and not explicitly shown, but the aggregated results are depicted in Fig. and included in Tab
Summary
O VER the years, many in-vehicle networks have been developed to meet the needs of the increasing number of devices and data volume to be processed. Autonomous driving and in general driver assistance systems require sensors like cameras, RADAR, or LIDAR and accentuate the need for high communication bandwidth [2], [3]. There are classical safety-relevant applications that do not require large amounts of data, such as ABS, braking systems, or traction control. In this domain, the CAN bus is still, more than 30 years after its introduction, the predominant networking solution to connect electronic control units (ECUs), sensors, and actuators. Automotive applications, like all distributed systems, require a proper alignment of processes and, the synchronization of local clocks at the network nodes to achieve a common view on time.
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