Sub-nanosecond Synchronization over 1G ethernet data links using white rabbit technologies on the WR-ZEN board

The White Rabbit (WR) technology has been introduced as an enhancement and next generation of the Precision Time Protocol (PTP, IEEE 1588), providing a boost in synchronization accuracy from the usual sub-microsecond range commonly found in PTPv2-based applications, down to the much more precise sub-nanosecond range. A number of White Rabbit-capable network nodes have been developed with the goal of allowing simultaneous deterministic time transfer and regular Ethernet data traffic to coexist on the same link without significant performance degradation over fiber links spanning tens of kilometers. The first SoC-based platform amongst these nodes is the WR-ZEN board, which implements a real-time White Rabbit stack in the Programmable Logic (PL) of the Zynq-7000 SoC; and features a hardened, ARM dual-core Processing System (PS) for running an embedded Linux environment. This paper presents the work carried out to upgrade the WR-ZEN board implementation, whose peak data throughput is limited just below 70 Mbps, so that a 1 Gbps data rate can be attained without impacting the performance of the White Rabbit synchronization. This goal is fulfilled by designing additional custom logic based on the Xilinx AXI DMA core, as well as an updated Linux network driver. This enhancement allows the widespread deployment of the WR-ZEN for major scientific infrastructure projects that require high-speed data transmission and deterministic timing transfer, as is the case of telescope arrays. Lastly, experimental results are presented comparing the synchronization performance of a baseline PTP-based setup to that achieved on the enhanced WR-ZEN board in the presence of high throughput data traffic. Conclusions are drawn and potential scientific and industrial applications that tap this increased bandwidth with deterministic timing transfer are discussed.