Timestamp Accuracy of 10BASE-T1L for TSN Applications

Time Sensitive Networking (TSN) is a technology for deterministic networking that constantly gains momentum. Precise time synchronization is a prerequisite for TSN systems. This paper presents results of research on timestamping accuracy with 10BASE-T1L PHYs on their MII and RMII interfaces. Various sources for constant and dynamic time error superimpose in real systems, resulting in time stamp inaccuracies of several hundred nanoseconds in the worst case. Asymmetry and measured link delay may vary between successive link establishments. Measurements with existing 10BASE-T1L PHY components from two different vendors show that timestamping on the MAC-PHY interface with components available today is not sufficient to meet the requirements of IEEE 802.1AS-2020 (gPTP). 10BASE-T1L is a very useful technology, but system designers should be aware of shown limitations in this paper.