The Research And Implementation Of Industrial Ethernet Real-time Scheduling Technology

With the development of computer network, communication and control technology, the application of Ethernet in the industrial control field becomes a research hotspot. However, the inherent uncertainty caused by communication delay of Ethernet highly prevents its step into the industrial control area.EPA (Ethernet for plant automation) is a device-layer solution for the real-time Ethernet. It enhances the real-time performance of Ethernet by expanding the data link layer set in ISO/IEC 8802-3 protocol with a CSME (communication scheduling management entity) which consequently schedules the sending of packets to avoid data collision in the network.This paper provides a comprehensive study on the principle of IEEE1588 precise time protocol and gives out analysis of the factors influencing the synchronization precision. An approach is proposed to improve the precision of clock synchronization among distributed devices by modifying Linux kernel, which includes: 1) enhancing the precision of the kernel's default clock management timer, 2) capturing time stamps in the link layer by modifying the ISR of NIC driver and 3) compensating the offset by iterated filtering. The test result indicates that a precision of 10μs is achieved.Based upon the precise clock synchronization, the architecture of the network protocol stack and the implementation of data link layer in the Linux kernel are studied and then give an implementation of EPA's data link scheduling algorithm, by modifying the QoS interface and NIC driver is given..The test platform is established based on DUT5000 Ethernet control module and Linux OS and the test programs are developed separately on PC and in the embedded device. The PC test program, developed in VC++6.0, is used for the visual configuration of bandwidth and for the display of graphic test result. The embedded test program is developed with Linux C. A final analysis of EPA's real-time performance is given through the tests of clock synchronization accuracy, delivery time and scheduling.