| Topic backgroundAt present, PC-based CNC system is one of the important developing directions of CNC system. As universal operation systems on PC, DOS and Windows are applied as the main software platforms of PC-based CNC system.Since either DOS or Windows is only a general and non real-time operation system, we must try to implement the real-time multitask environment in them before using them as the software platforms of PC-based CNC system.It is easy to reach this goal in DOS, so, nowadays the majority of PC-based CNC system software are developed on DOS. But, because the functions of DOS are very limited, especially being contrasted with the higher and higher requirements of modem CNC systems, DOS has become backward and outdated.Windows has very strong capabilities. But because Windows only permits applications construct wanted functions through the interfaces provided by operation system, and none of these means can implement high-resolution timing tasks, so, the real-time quality of timing tasks cannot be guaranteed in Windows. On the other hand, the designing of task scheduler in Windows did not consider the needs of real-time applications and its scheduling efficiency is very low as to the real-time controlling. Then the real-time quality of task scheduling in Windows cannot be guaranteed also. So, it is impossible to develop high quality CNC system software only on Windows.Varying from DOS and Windows, RTLinux is a genuine hard real-time multitask operation system. Its real-time quality is only limited by hardware conditions. While hardware conditions are promoted, its real-time performance is promoted accordingly. In addition, it is of very excellent stability. All these factors ensure the performances of RTLinux-based CNC system software. RTLinux is a open-resource software, then its costs is very low.U Researching contentThe running mechanism of real-time operation system has strong effects on real-time applications based on it. This paper has conducted thoroughly researching on some aspects in RTLinux that have close relation with the real-time programming, such as performance parameters, real-time principle, and the real-time programming methods, etc.In RTLinux, Linux runs as a lowest priority thread, so none of the functions in it (such as graphics, networks, etc.) has real-time quality. Although the real-time tasks in RTLinux can make use of all of the functions in Linux, but they can only realize these in indirect means. It is right this mechanism that results in the speciality in RlLinux real-time programming. This paper has focused on the effects of RTLinux s implementing mechanism on the CNC system software developing.In RTLinux, the application tasks have to be split into two fields: real-time field and non real-time field. The real-time kemel of RTLinux can ensure the real-time quality of real-time tasks, but these tasks cannot use any Linux functions that can introduce resources contention; theillnon real-time tasks can use all the Linux functions, but they cannot have any real-timerequirements. According this programming mechanism of RTLinux, this paper has put fOrwardthe RTLinux-based CNC system software's architecture and structure.RTLinux suPpofts SMP (Symmetric Multi-Processing), and can be used as multi-CPUmachine's operation system. The SMP operation system can equally share the loads among a1lthe CPUs in computer. RTLinux-based CNC system software can make use of SMP function toimplement high-performance CNC system. This paPer introduced the methods in this aspect.Using multi-threads techniques can make CNC system's tasks running reasonably andefficiently. Threads in RTLinux can be divided tWo levels: one is the threads scheduled byRTLinux real-time kernel, such as intemipt handlers, real-time tasks, Linux kernel, etc., the otheris the thIeads scheduled by Linux kemel. This paper has thoroughly researched the aPplyingmethods of multi-threads techniques in these tWo levels, and discussed the concreteimp... |
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