Research On Real-Time Measurement And Control System Based On Linux And RTAI

It is evident that the real-time performance of the system is very important in the field of real-time measurement and control system.Both periodic tasks such as information acquisition, control, data communication and aperiodic tasks such as arising from arbitrary critical events must be completed within their deadlines.RTOS at the core of the real-time system, which is the cornerstone of all functions can be achieved Although today's mainstream RTOS have good performance, they are very expensive and keep secret their source codes from public, which causes many inconveniences to the development. The emergence of Linux gives us a chance to change this situation. However, Linux is originally designed as a divided-time OS in general use and the inherent characteristics of it make it is not suitable for direct use in real-time systems.So many schems have been designed to make it a hared real-time OS, and RTAI is a typical representative. But most of the current research on RTAI limited to theoretical studies and practical real-time system based on it is very rare.This thesis expands my research, and a real-time measurement and control system based on Linux and RTAI is implemented. After the through analysis of the scheme of RTAI , a new program aimed at improving the accuracy of response time of Linux is proposed.The methods to improve the real-time performance of Linux are introduced first. The scheduling system,interrupt system and clock system are analysed. The improvement and deficiency of Linux2.6 are studied and the main factors affecting the real-time performance of Linux were pointed out. After the analysis of the principle of RTAI, which is a hard real-time Linux most suitable for industrial measurement and control system, the defects in the organization of tasks of RTAI is pointed out and the way to improve it is discussed too. After all of the work above, a real-time measurement and control system is developed based on RTAI and Linux. And two set control and display systems are designed in kernel space module and user space independently. In the implementation of kernel mode, Control tasks are implemented with kernel modules supplied by RTAI and display tasks are completed with SVGAlib LXRT, the extension of RTAI, and QT are applied to build the control tasks and display tasks in order to accomplish the system in user mode.Finally, after the thorough study the principles of ADEOS, based on which RTAI is implemented, a method is put forward in order to improve the accuracy of response time of Linux. This method creates a real-time domain with a higher priority than Linux first. And then a real-time dynamic timer system is implemented which adopt a shot clock mode, and of the response time of Linux is greatly enhanced without significant increasing system load.