Embedded Real-time Linux System

Among main open source softwares, Linux is quickly entering the real-time control field with open kernel source codes, stable performance, UNIX compatibility, multiple processes applicability, great network capabilities, high security and pruned kernel. In the beginning, Linux is designed as all-purpose operation system on the basis of fundamentals that the average response time is as possible as short and the throughput is as possible as high. Although Linux also supports the real-time process with POSIX compliant real-time function, multithread, multitasks, its real-time capability is very poor. Up to now, many ways are applied to improve real-time performance of Linux kernel,some of them are relatively successful. These ways focused on the following fieilds: add rescheduling points, improve its preempt ability; add another kernel to take over the standard Linux kernel, make the added kernel taking care of real-time interrupts; modify the standard Linux interrupts, makeInterrupt handled as a task.Our work is part of the project the network monitoring system based on Linux. Based on some rearch we know that the Linux has gain great improvement in real-time capability. So we focus on how to improve the real-time capability for application from the Linux kernel inside.Firstly we analyse the interrupt mechanism in standard Linux 2.6 and the Linux 2.6 patched by Ingo Molar, and find how to realize the interrupt thread mechanism.Secondly we give a method to improve the interrupt mechanism, make a thread for each interrupt. The interrupt threads are in the same level with current tasks' threads, and can be scheduled just by the value of the thread's real-time priority. Furthur more, we add a comparison mechanism to compare the priority of the current real-time task and the interrupt thread, if the current thread is not a real-time one or its priority is lower than the interrupt thread's, it will directly call the user's interrupt service routine, instead of waking up the interrupt thread. In this way, the interrupt's response time will be decreased.Thirdly we analyse and test the improved method, from the tests we conclude that our method could meet the needs of a soft real-time system, for it greatly decreases the task response time and could applied widely.Last we port the real-time Linux system to a platform based on Samsang s3c2410 microprocessor. The task is contained of the followed jobs: developing the bootloader for the platform; making the real-time kernel image; developing the root file system.