Research Of Real-Time Capability Of Embedded Linux System

Real-time Operating System (RTOS) is now becoming a research hot spot. RTOS can be wildly used in various real-time application fields, such as defense, industrial automation control and communication. Nowadays, real-time applications need more strict timing request, and response time of the system need to be reduced from milliseconds to microseconds or even nanosecond, thus stronger real-time perfermance of RTOS that support hard real time application are needed. Linux is originally designed as a time-sharing OS for general purpose and mainly stick to fairness and system throughput; it is quite different from rapid response demand of real-time OS. This article focus on Linux clock system, discovered factors of affecting its real-time capability through analysis of Linux kernel code and proposed the thought of increasing parallel and precision clock system with fine grain and gives method of design and realization so as to improve real-time performance of Linux operating system.Common methods of modifying Linux time clock system are based on software level by rewrite kernel clock module, which have insufficiencies such as increasing system burden, larger changes in the kernel and so on. The rapid development of hardware nowadays can provide a great convenience for promotion real-time system performance. Therefore, through hardware programming, realizing a precision clock system coexisted with original clock system to supported applications with stronger real-time requirements can be a new approach to promote Linux real-time capability. Technical route to realize a new fine clock system ai as follow: resetting interrupt vectors; designing a new queue structure of real-time timer; carrying on programming on high-level programmable interrupt controller APIC. Firstly, Linux original timer queue uses "calendar structure", and response time is only a millisecond level, thus, another real-time timer queue specialized for real-time processes in the kernel is established. Secondly, APIC interruption function code is modified to complete the interrupt control of the new clock system. Finally, coexistence problem of old and new clock is resolved by the way of closing interrupt.Testing verification scheme has been designed and performed. Experiments result show that the reformed kernel can meet real-time demands in microsecond level during its long time running on PC . The response time is only 1/12 of Linux 2.6 and excellent result has been achieved. As can be seen through analysis and comparison that double clock system can effectively meet real-time applications' respond requests in time, met need of hard real-time missions' deadline, and having advantage of small modification for the kerne. This method orient to hardware, and will have certain reference significance for promotion systemreal-time performance.