Distributed IO System Based On Real-time Ethernet

In control systems of Shanghai Synchrotron Radiation Facility (SSRF), Shanghai AdvancedProton Therapy facility (SAPT) and other large-scale accelerators, there are high-speed andreal-time distributed control systems which consist of multiple controllers. For example, therequirement of response time is less than1millisecond in the fast interlock protection system ofSSRF, whose IO signals distribute in20units around the432m circumference storage ring.In order to achieve the goal of the subject, a solution based on real-time Ethernet is adopted.Within1millisecond, the real-time communication between100stations is completed. Thedesign transmits the real-time data according to the principle of time slicing, and it points out thattime synchronization is the key to implement real-time Ethernet. After analyzing and comparingthe existing time synchronization protocol, the subject adopts IEEE1588precise timesynchronization protocol to realize the time synchronization of all the stations.Firstly, the paper introduces the related knowledge of IEEE1588precise timesynchronization protocol including the basic principle of IEEE1588time synchronization and theclock types of IEEE1588protocol, and analyzes the mark of IEEE1588hardware timestamp,various factors influencing the time synchronization and various solutions to realize IEEE1588.Secondly, FPGA(Field Programmable Gate Array) and gigabit Ethernet technology was adopted toimplement IEEE1588time synchronization and real-time Ethernet, and we customized the IOboard according to the requirement and finished the hardware framework of the distributed IOsystem. Finally, the VHDL(Very High Speed Integrated Circuit Hardware Description Language)hardware language program written on FPGA development platform implemented the IEEE1588time synchronization module and real-time Ethernet. For the problem of low precision of timesynchronization caused by the frequency deviation of ordinary crystal, the paper proposeddynamic frequency compensation algorithm, and realized higher precision of time synchronizationof the master clock and the slave clock.Two methods was used to test IEEE1588time synchronization. The first method verified thefeasibility of dynamic frequency compensation algorithm，which greatly improved the precision oftime synchronization; The second method tested the precision of IEEE1588time synchronizationin different synchronizing cycle and in the given synchronizing cycle with different connectionways，and the impact of the switch delay jitter and synchronous cycle on the precision of timesynchronization was analyzed. As a result of the large delay jitter, the time synchronization testingresult of current control network of SSRF can’t meet the requirement of the design, the real-timeEthernet designed in the paper can’t be realized in the current control network system of SSRF.Nevertheless, the tests of the real-time Ethernet designed in the paper obtained relativelysatisfactory results under laboratory conditions.At the end of the paper, the problem of unable to realize high precision time synchronizationcaused by the large delay jitter of the current control network system of SSRF was analyzed, newnetwork topology system was proposed to realize the real-time Ethernet.