This paper proposes weak TDMA (WTDMA) as a new method for slotted medium access on the controller area network (CAN). Different from TDMA, WTDMA does not require guard times for the temporal isolation of different time slots. Instead, a certain degree of overlap of time slots can be tolerated due to the usage of Carrier Sense Multiple Access/Collision Resolution (CSMA/CR) and the non-preemptive message transmission on CAN. WTDMA can be realized in software with a moderate accuracy of the synchronized clocks of different CAN nodes and without any modifications to the CAN standard. The paper provides sufficient conditions for the correct operation of WTDMA and performs a comprehensive experimental evaluation. We show that bus loads above 90% can be achieved, whereby the message latencies are mostly determined by the message transmission times in the order of hundreds of microseconds. In addition, WTDMA is robust to disturbances such as bit errors. These properties are vital for contemporary mission-critical real-time vehicle applications.

Accurate timestamps are important for clock synchronization (CS) and cyber-security on the controller area network (CAN). This article proposes a new predictable timestamping (TS) method on CAN. Different from existing TS methods, our method reduces the effect of uncertainties that are caused by the CAN bit timing, oscillator drifts, and different cable lengths. Accordingly, our TS method provides an improved TS quality, which is confirmed in comprehensive hardware experiments. We further show the positive impact of our TS method on CS for CAN with clock accuracies below 100 ns.

Modern vehicles, that have to be considered as safety-critical cyber-physical systems, require highly accurateclock synchronization(CS) among their distributed computing devices. Since Controller Area Network (CAN) is the predominant in-vehicle communication bus, it is highly relevant to support CS for CAN. This article proposes an original CS method for distributed in-vehicle networks based on CAN with bothoffsetanddrift correction. While offset correction is performed based on timestamps in periodic reference messages (RMs), our new method benefits from the re-synchronization mechanism of the CAN bit timing to apply highly accurate drift correction. Our algorithm does not make any modifications to the CAN protocol but requires the measurement of the phase error from the CAN controller. We derive analytical bounds for the expected clock differences and further validate the practicability of the proposed method by comprehensive experiments. As the main result, our method achieves a clock accuracy below$2\;\mu$s independent of important parameters such as the bit rate, RM period, bus utilization and time-varying clock drifts.

Synchronizing clocks is crucial for distributed safety-critical in-vehicle applications. Since Controller Area Network (CAN) is the predominant in-vehicle communication bus, it is highly relevant to realize clock synchronization (CS) on CAN. This paper proposes a new software-based CS (SW-CS) algorithm based on the periodic transmission of reference messages (RMs) by a Master node and discrete-time feedback control. Different from existing algorithms, that only update clocks after receiving a RM, our algorithm corrects the clock drift between RMs. Measurements on a hardware setup show a decrease of the clock differences by more than one order of magnitude.

Safety-critical in-vehicle applications require an accurate global time in order to coordinate their actions. Although Controller Area Network (CAN) is the most widely used in-vehicle communication bus, it does not support synchronized clocks. Hence, the realization of clock synchronization on CAN is highly relevant. This paper develops two new ideas for the clock synchronization on CAN. The first contribution is a new software-based algorithm based on periodic reference messages. Different from existing algorithms, the proposed algorithm enables the use of timestamps that are taken close to the reference message transmission hence improves the clock accuracy. The second contribution of the paper is an original method for correcting clocks between reference messages. In particular, the proposed algorithm updates local clocks based on the bit timing on the CAN bus. Results from simulation experiments show an improvement of about 60% in the clock precision.