The Research And Implementation Of Embedded Network Node Based On IEEE1588 Protocol

With the development of Ethernet technology, Ethernet has entered into industrial control application. However, as media access control protocol CSMA/CD exists unforeseen delay characteristics, it is difficult to guarantee the real-time characteristics for Ethernet. This has brought difficulties in the application of Ethernet for industrial control especially in field device level. IEEE1588 Precision Time Protocol is proposed to solve this problem effectively. It executes clock correction for the nodes in the network through a periodic synchronization signal and make distributed control system based on Ethernet to achieve accurate clock synchronization to obtain real-time behavior in a certain extend.IEEE1588 synchronizes messages via UDP/IP protocol for transmission. The accuracy of the timestamp when synchronization messages are sent and received will directly affect the synchronization accuracy. Pure software clock synchronization strategy can get accuracy in microseconds, which can meet the requirement of the majority of the industrial control field. However, this synchronization accuracy is not sufficient for some time critical applications such as motion control etc. To further improve the synchronization accuracy to sub-microsecond or even nanosecond, it must be hardware assisted and stamp the time as closely as possible near the location of the physical transmission medium. This paper aims to establish an embedded network node that supports IEEE1588 protocol and timestamps the synchronization messages through hardware.This paper has studied the implementation scheme based on DP83640 PHYTER, and established a node with hardware composed of ARM9, AX88780 and DP83640. ARM9 adopts Samsung's microcontroller S3C2440, and is responsible for running the operating system and the PTP protocol stack. AX88780 is Asix's Fast Ethernet controller and is responsible for sending and receiving clock synchronization messages. DP83640 is National Semiconductor's high precision Ethernet transceiver and is responsible for timestamping synchronization messages in physical layer. This scheme can achieve high precision clock synchronization between embedded network nodes, and avoid the time uncertainty of Ethernet.This paper has realized the software design based on real-time operating system Windows CE, including system kernel customization, NIC driver development and clock synchronization verification between two nodes. The experiment indicated that the clock offset between master and slave nodes is within the range of±10 nanoseconds, which can meet the requirements of distributed control system.