PTP-Synchronized Tri-Level Sync Generation for Networked Multi-Sensor Systems

Synchronization of sensor devices is crucial for concurrent data acquisition. Numerous protocols have emerged for this task, and for some multi-sensor setups to operate synchronized, a conversion between deployed protocols is needed. This paper presents a bare-metal implementation of a Tri- Level Sync signal generator on a microcontroller unit (MCU) synchronized to a master clock via the IEEE 1588 Precision Time Protocol (PTP). Cameras can be synchronized by locking their frame generators to the Tri-Level Sync signal. As this synchronization depends on a stable analog signal, a careful design of the signal generation based on a PTP-managed clock is required. The limited tolerance of a camera to clock frequency adjustments for continuous operations imposes rate-limits on the PTP-controller. Simulations using a software model demonstrate the resulting controller instabilities from rate-limiting. This problem is addressed by introducing a linear prediction mode to the controller, which estimates the realizable offset change during rate-limited frequency alignment. By adjusting the frequency in a timely manner, a large overshoot of the controller can be avoided. Additionally, a cascading controller design that decouples the PTP from the clock update rate proved to be advantageous to increase the camera’s tolerable frequency change. This paper demonstrates that a MCU is a viable platform to perform PTP-synchronized Tri-Level Sync generation. Our open source implementation is available for use by the research community at https://github.com/IMS-AS-LUH/t41-tri-sync-ptp.