Linux Operating System Real-time Technology

Real-time system is a hot spot in computer application and RTOS(real-timeoperating system) is the core of real-time system. As the improvement of hardwareperformance and in order to meet the requirement of real-time application, RTOSneeds not only better performance, but also to provide more functions or services,such as GUI, network etc. The commercial RTOSs that exist today is either too simplein funtionalty or too expensive. There is no such a RTOS that is open enough,standard, widely supporting, efficient and also cheap, so many institutes beginresearch on turning the non-real-time universal operating systems which arefunctional strong into RTOS. Linux is natualy a good candidate, because it is capableof providing many services, supporting varied hardware, open source, modularizeddevelopment, compatible with many international and industry standard..Linux is originally designed as an time share operating system. Due to it'snon-preemptive kernel, coarse time granularity, frequently interrupt disable, virtualmemory and other buffer mechanism, Linux is not so "real-time"as an RTOS.There are two ways to improve Linux's real-time performance. One way, you canmodify Linux kernel directly and this way you make it so-called soft real-time. Theother way, you can adopt the so called sub-kernel idea, that is to implement an extrareal-time kernel besides Linux kernel. The real-time kernel is in charge of managingand scheduling all the real-time tasks's and Linux kernel is treated as a real-timekernel's task with the lowest priority. This way, Linux can gain hard real-timeperformance.RTAI is a typical example of sub-kernel way. RTAI's theory and implementationis analysed and it's deficiency is pointed out. In order to improve RTAI,an so-calledtwo-step scheduling mechanism is created and implemented in RTAI in this paper.With this mechanism, RTAI's real-time scheduler is extended and can support bothRM and EDF scheduling algorithms. Application developers can flexibly choosebetween these algorithms according to specific situations, so RTAI's application areahas been extended too.