Implementation Of CNC System Real-Time Communication By DMA Method Based On IEEE1394 Bus

With the rapid development of Numerical Control technology, a high-grade CNC machine tool can meet the reqirements such as high-speed and high-precision machining, as well as multi-channal and multi-axis control. It is important to build a data transmission channal between NC and PC, in order to realize the excellent performance of a high-grade CNC machine tool.The aim of the CNC system designed in this thesis is to ensure that the comunication between computer and servo unit can meet the requirements of real-time and reliability. The following schemes are adopted in order to meet the requirements mentioned above:Firstly, IEEE 1394 bus is selected to connect the computer and servo unit, because the application of the high-speed and high-performance numerical servo bus technology has become a major characteristic and trend in the development of the advanced CNC system. IEEE 1394 bus which has a flexible framework and supports synchronous and asynchronous data transmission with the speed up to 400Mbps, hot-pluggable has become the best choice of high-speed servo bus. Secondly, Windows+RTX (Real Time Extension) which is selected as the operation system of host computer provides the platform for the software of data transmission. Finally, asynchronous data transmission by DMA method is implemented based on Open Host Controller Interface (OHCI) protocol in order to improve the transmission speed further. Thus, the process of data transmission becomes as clear as possible, and it is beneficial to trace the status of data transmission.The thesis firstly makes a deep study of IEEE 1394 standards, including the system architecture of IEEE 1394, the hierarchical structure of the IEEE 1394 protocol and communication modal of IEEE 1394. This is the theoretical basis of our system. Then the RTX real time enviroment is analyzed in terms of principle, characteristics and application. RTX, as a subsystem for the Windows system, provides a kernel-mode execution environment for Win32 compatible tasks and threads that have hard real-time performance characteristics. In addition, the 1394 interface of the CNC system is explicated. The PCI-1394 interface card is used to act as the interface of host computer, and the 1394 front-end module designed specially is used to act as the interface of servo units. Then, the main research in this thesis focuses on 1394 OHCI protocol, especially the registers related to DMA in the protocol and the principles of communication by DMA methods applied in CNC system,that is,the registers on 1394 chips are operated directly to implement the data transmission via API (Application Program Interface) functions provided by RTX. Then according to the"transmission—receive"model, the software of data transmission by DMA methods is designed. The whole process of communication is explicated, and the usage of API functions provided by RTX is given. During the process of the software design, the program is modularized according to the requirement of software engineering, and in consequence it improves the efficiency of program and makes the structure of program clearer. Finally, the software which implements the data transmission between host computer and 1394 front-end module is tested. Large numbers of experimental data are analyzed to verify that the system is enough reliable and real-time to meet the requirements of a high-grade CNC system.