Research And Implementation Of Clock Synchronization And Trigger For Distributed Test System

The distributed test system is usually composed of a large number of test units distributed in each test area.Each test unit completes the test task according to a specific time sequence.In order to ensure that each test unit can complete the synchronous test task,it is necessary to ensure the clock synchronization characteristics of each test unit.With the development of high-speed transient test of the distributed test system,the test system puts forward higher requirements for the clock synchronization accuracy of the test unit.The PTP(precise time protocol)proposed by IEEE in 2002 is a good solution to this problem.Therefore,in order to meet the needs of high-precision clock synchronization for all test equipment in the distributed test system,this paper designs a distributed test clock synchronization and trigger system based on PTP protocol.By networking the distributed clock synchronization and trigger nodes in the system,the sub microsecond and upper clock synchronization accuracy are realized,so as to provide high-precision time base signal and trigger signal for the test unit.Firstly,this paper analyzes and compares several clock synchronization technologies commonly used,and selects PTP protocol to realize clock synchronization based on the characteristics of network test of distributed test system.Then according to the requirements of the distributed test clock synchronization and trigger system design,determine the design and development of the distributed clock synchronization and trigger node as the main research content of this paper.In this paper,the key technology of realizing clock synchronization and trigger of distributed test system is analyzed,including the implementation of PTP protocol,the analysis of PTP synchronization trigger technology and the analysis of factors affecting synchronization accuracy.In order to achieve high-precision clock synchronization accuracy,the hardware implementation scheme of STM32 + DP83640 distributed clock synchronization and trigger node is determined.The synchronization accuracy can be effectively improved by obtaining timestamps in the physical layer.The hardware circuit design of the distributed clock synchronization and trigger node includes the main control module(main controller,USB serial port,power module,etc.),clock synchronization and trigger module(DP83640,RMII interface circuit,synchronous trigger interface circuit,etc.).In order to realize clock synchronization and trigger function,PTP software is designed for distributed clock synchronization and trigger node,including bottom driver software,transplantation of lwip protocol stack,PTP clock synchronization software(PTP state machine,BMC algorithm,local clock adjustment algorithm,etc.),synchronous trigger software design and upper computer management software to ensure the normal operation of PTP protocol.By building a test platform to test the synchronization accuracy of distributed clock synchronization and trigger nodes,and explore the impact of different synchronization interval T,the introduction of network intermediate nodes and the increase of the number of nodes on the synchronization accuracy.And running the upper computer management software,real-time monitoring the operation status of distributed network nodes and providing the relevant trigger function settings.And the PTP trigger test is carried out under the built test platform.The experimental results show that the synchronization accuracy of distributed network nodes is within one hundred nanoseconds,and the highest synchronization accuracy is 37 ns in point-to-point measurement.And the PTP synchronous trigger function is realized,which meets the design requirements of distributed test clock synchronization and trigger system.