White Rabbit: Sub-Nanosecond Synchronization for Embedded Systems

Grzegorz Daniluk and Tomasz Wlostowski

Abstract:	The article describes the design of the White Rabbit PTP Core (WRPC) – an easy-to-use HDL module implementing an IEEE1588-v2 synchronization model extended with the White Rabbit (WR) protocol. The WRPC can provide sub-nanosecond timing in standard FPGA-based designs or enhance the accuracy of existing systems through OEM modules. WRPC delivers the time and frequency reference via a common timing interface (1-PPS, timecode and reference frequency) to simplify the integration with existing modules. It also features a Gigabit Ethernet fiber optic link (1000Base-X) to communicate with other WR-compliant devices. We also describe the details of the synchronization algorithm of White Rabbit which is implemented in the WRPC. WR combines IEEE1588-v2 timestamping with a synchronous physical layer based on Synchronous Ethernet. Sub-nanosecond accuracy is achieved by actively compensating the link delay using phase measurements done with Digital Dual Mixer Time Difference (DDMTD) phase detectors and on-line calibration of the gigabit transceivers' latencies. The measurements presented in the article show a long-term master-to-slave offset below 1 ns, while the precision is better than 20 ps rms for a 5 km single mode fiber connection. The protocol is being developed by CERN, Elproma Elektronika, GSI and other institutes and companies. In addition to fine synchronization, it also provides deterministic frame delivery and extended link redundancy features, developed for critical controls applications, such as the control networks of the particle accelerators at CERN.
Published in:	Proceedings of the 43rd Annual Precise Time and Time Interval Systems and Applications Meeting November 14 - 17, 2011 Hyatt Regency Long Beach Long Beach, California
Pages:	45 - 60
Cite this article:	Daniluk, Grzegorz, Wlostowski, Tomasz, "White Rabbit: Sub-Nanosecond Synchronization for Embedded Systems," Proceedings of the 43rd Annual Precise Time and Time Interval Systems and Applications Meeting, Long Beach, California, November 2011, pp. 45-60.
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