This project was conducted in collaboration with Zurich Instruments AG (ZI) and the Commission for Technology and Innovation. The aim was to implement a Ethernet based time synchronization between multiple Etzel, which are advanced digital lock-in amplifiers from ZI, and validate and verify the performance. The requested time synchronization accuracy is in the order of 10 ns.
PTP was determined to be the most suitable time synchronization protocol because of the precision, the independence of other devices and the availability of an in-house PTP stack implementation of the protocol. The feasibility of a time synchronization solution using PTP was proven by evaluating multiple simulations and implementing the available stack on two Apalis evaluation hardware boards. A concept was devised for integrating the time synchronization functionality into existing Etzel devices and implemented with the help of ZI. Testing was conducted on the underlying implementation on Apalis boards as well as on the final system with multiple Etzels in order to verify the performance requirements.
During the implementation of the PTP stack, adjustments had to be made to the Ethernet controller driver. The PTP stack was adapted to work on a Linux with 3.1 kernel and the integrated interfaces for the PTP clock as well as the hardware timestamping. Hardware limitations (routing of pins) led to two variants for pin assignment. The accuracy of the time synchronization is dependent on environmental conditions and configuration of the PTP application. Time synchronization measurements between two Etzels show a standard deviation between the timestamp registers under best measurement conditions of 12.1 ns and a mean value of -1.7 ns.
The performance of the system was found to satisfy the needs of Zurich Instruments under the condition that the Ethernet connection is realized in a direct (Peer-to-Peer) manner or via a PTP-capable switch.