A Real-Time Linux Research And Design Based On Intel XScale PXA255 Processor

Real time OS is an operation system that can provide QOS in a deadline limit. The tasks running on the system is predictable. The Two classes of real time system are: soft real-time and hard real-time. Soft real-time is a statistical real time, means high throughput and fast response speed, but it can't ensure the task deadline. On the other hand, the timing limitation is very strict in hard real-time systems. It must be capable of working in harsh environments, rich in electromagnetic noise and elementary-particle radiation, and in the face of rapidly changing computation loads. The field of real-time computing is especially rich in research problems because all problems in computer architecture, fault-tolerant computing and operating systems are also problems in real-time computing, with the added complexity that real-time constrains must be met. UNIX (or Linux) is a soft real-time system, not hard real-time. A few efforts are necessary to make Linux support hard real time features.Firstly, this paper introduces the differences between Real-Time system and general purpose system and the principles and structures of real time system. In Real-Time system, task schedule and real-time communication are two key techs during real time system design procedure: task schedule does its best to make tasks surely not exceeding deadlines, real-time communication provides efficient and reliable data switch tunnel between each nodes of the distributed real-time system. Then, we reveal a few limitations of standard Linux operation system focusing on real time computing such as no high resolution timer, doesn't support deadline based schedule algorithms and the Linux kernel can't be preempted under some special conditions. After consulting some solutions by other researching departments which solve individual problems smartly, we integrate these solutions such as RT-Linux, RTAI, RED-Linux, KURT and gives out a real time OS implementations based on Intel Xscale PXA255 processor and Linux kernel version 2.4.18.At last we analyze the real time timing model and measures the timing parameters of the enhanced system.