Technique Of Improving The Real-time Capability Of UClinux

The more development of embedded system brings forward the higher requirement to EOS(Embedded Operating System). Usually, the EOS is reqirement to be ERTOS(Embedded Real-Time Operating System). But uClinux, which is the most excellent EOS and inherits the most advantages of Linux, has poor real-time capability for response to real-time task. Fortunately we have gotten RTLinux to resovle this problem. RTLinux supports hard real-time perfomance by inserting a tiny and preemptive real-time kernel between the hardware level and the Linux kernel. After a deep analysis and research on the theory of realizing the hard real-time capability, we finished the repotting of RTLinux into uClinux and made the repotten ERTOS, RT_uClinux have faster response to real-time task.The repotting work must integrate the characteristic of embedded hardware. So we chose the platform which bases on Intel Xscale PXA255 microprocessor. To obtain less interrupt latency which results from the disabling interrupt operation by uClinux kernel, an interrupt simulator was used to take over the interrupt handling instead of uClinux, which was made by the simulator never close the interrupt. On the other hand, the system clock was improved with more refined granularity by setting one-shot mode timer to make the clock interrupt happens on needed time. So more accurate timing on the kernel was achieved. Furthermore, for the sake of resolving the problem that uClinux can not satisfy the requirement of real-time memory management, we made use of the memory management supported by PXA255 and realized a dynamic memory management module, so that the memory requirement of real-time kernel could be satisfied by dynamic allotion and callback. Such a memory management mechanism is real-time, efficient and reliable. Besides, the native scheduler was used to sched real-time task, which made the running task was always the most urgent and important. And that the communication between the real-time and non-real-time was achieved by RT_FIFO.After that, a real-time ability test was carried through based on the embedded system. Interrupt latency, task switch time and clock granularity were chosen to measure the real-time reponse capability of uClinux and RT_uClinux. The test result shows that RT_uClinux has gotten better performance as compared with common uClinux kernel.