Study And Design For The LXI Precision Clock Synchronization Technology And Interface

Since21^st century, along with the rapid development of electronic technology,computer technology and network technology, the industry of the measuring instrumentshas also made an encouraging progress. As we all know, the system testing bus is the mainsymbol of the development of the industry of the measuring instruments, LXI-a newgeneration of instrument testing bus based on Ethernet-focus a number of advantages of theinstruments bus.Thus, it has a broad development prospect and competitive potential, andwill become a new direction of the fields of the measuring instruments. The clocksynchronization technology is a key technology of the LXI bus. Especially with theextensive application of distributed systems, the demand of high-precision clocksynchronization system is increasing. In the fields of measurements and communicationsand so on, it has delivered a microsecond level requirements for the clock synchronization.In order to meet the high-precision clock synchronization requirements, this paper firstintroduces the basic concept of clock synchronization and the status of development, andthen introduces the IEEE1588clock synchronization protocol. IEEE1588precision clocksynchronization protocol is the hot topical of the present distributed test system, becausethis protocal has advantage of simple, taking up small network bandwidth,low requirementsfor the system resources and so on. After detailed introduces the basic principle ofIEEE1588clock synchronization protocol, this paper puts forward pure software designand hardware assisted design for the clock synchronization. Then this paper set up a testplatform based on the ARM11microprocessor S3C6410, using the μC/OS-II real timeoperating system, meanwhile detailed design clock circuit, Ethernet interface circuit, thememory interface circuit, the serial interface circuit, power supply and reset circuit, theJTAG interface circuit and so on. Under this platform, clock synchronization using thedesign of pure software can only achieve sub-millisecond. The main reason is that in theprocess of IEEE1588synchronous clock message transmit packets from master clock toslave clock, it exsits delay and jitter of the operating system and communication protocolstack. So this paper mainly clarifies hardware assisted design based on the semiconductorchip DP83640. Hardware assisted design detects the IEEE1588synchronization message inthe MII（Media Independent Interface） between the Ethernet physical layer and the MAClayer, and then mark the precise time. It can eliminate the delay and jitter of the operating system and communication protocol stack. After test, hardware assisted design based on thesemiconductor chip DP83640can achieve sub-microsecond level, completely meet therequirements of clock synchronization of measurement and communication field.Finally, this paper analysis the impact factor of the IEEE1588clock synchronization,and take measures to improve it, meanwhile present the summary and future for theIEEE1588clock synchronization.