Linux Operating System Real-time Technology Research And Applications

With the improvement of hardware performance,RTOS needs better performance and more functions or services to meet the requirement of real-time application. The commercial RTOSs that exist today are either too simple in funtionality or too expensive in price. There is no such a RTOS that is open enough, standard, widely supporting, efficient and cheap. So many institutes begin researching on turning the non-real-time universal operating systems into RTOS.Linux is naturally a good candidate, because it is capable of providing many services, supporting various hardware and modularized development. Besides, it is open-source and compatible with many international and industry standards. Linux has got the favor of many IT magnates, such as IBM, HP and Sun. Moreover, many governments support the research of Linux. Linux is originally designed as a time-sharing operating system. Due to its non-preemptive kernel, coarse time granularity, frequent disabled interrupt, virtual memory and other buffer mechanism, Linux is not so"real-time"as RTOS.There are two ways to improve the real-time performances of Linux. One way, Linux kernel can be modified directly to reduce the schedule latency and this is so-called soft real-time. The other way, the so called sub-kernel idea can be adopted, which adds an extra real-time kernel besides Linux kernel. The real-time kernel is in charge of managing and scheduling all the real-time tasks and Linux kernel is treated as a real-time kernel's task with the lowest priority. This way, Linux can gain hard real-time performance.RTAI is a typical example of sub-kernel way. Theory and implementation of the RTAI are analysed and the deficiencies of RTAI are pointed out. Because of the lack of many schedule algorithms supportment, RTAI was limited in application scope. So, two classic scheduling algorithms are added to RTAI. Then, RTAI can choose the corresponding scheduling algorithms according to the real tasks's attribute, so RTAI's application area has been extended too.