DC-PTP: Drift Correction-Based Precision Time Protocol for CAN in Automotive Embedded Systems

The Controller Area Network (CAN) is widely used in safety-critical systems, such as powertrain and chassis control systems in automotive embedded systems. Because the functions in safety-critical systems are highly time-sensitive, any slight time deviation (i.e., offset) among the Electronic Control Units (ECUs) of these systems may cause functions to run abnormally. The offset is mainly caused by clock drift. The clock frequency of ECU driven by a crystal oscillator may have different deviations (known as clock drift) due to differences in hardware manufacturers’ engineering and process or external environmental factors such as temperature and vibration. The clock drift will affect clock accuracy and eventually be reflected in the timestamps of CAN controller when sending or receiving CAN frames, meaning that the generation of offset occurs in ECU. Reducing the offset using time synchronization techniques is of utmost importance. In order to further lower the offset, we propose a clock drift correction-based Precision Time Protocol (DC-PTP) for CAN to solve this problem. For clock drift correction, we first measure the clock drift of master ECU and slave ECU, and then calculate the relative clock drift between the master and slave on the basis of the measured clock drift. The relative clock drift is used to correct the acquired timestamps during Precision Time Protocol time synchronization to reduce the effect of clock drift. Furthermore, a synchronization convergence approach is presented to continuously converge the offset until the offset is within the given range. We implement DC-PTP on a prototype built with heterogeneous microcontrollers. Experimental results show that the offset using DC-PTP is within 1 μ s along with low memory overheads of 2% for the master. The memory overhead of the slave is slightly higher than that of the master, and the bus load of DC-PTP is only 17%.