Real-time System Of Memory Management Technology And Implementation

Due to the function enhancement of real-time system and the decrease of its cost, the real-time system has been more and more widely used in many fields. Conventionally, the use of virtual memory has been avoided in the real-time systems, because virtual memory leads to the I/O operation that will make the timing analysis very difficult. However, within safety-critical systems, there is move towards implementations where tasks of differing integrity levels are allocated to the same processor. Thus in the same system, we hope to offer virtual address space for soft real-time tasks to raise their flexibility, meanwhile offering the predictable and effective address translation for hard real-time systems. In addition, in order to enable tasks with differing integrity levels to safely coexist in the same system, real-time system must offer adequate partitioning to ensure the safe availability of the resources. Through the usage of virtual memory and space domain protection technology, we can effectively support the separation partitioning mechanism.This paper is focused on the research of virtual memory technology and space domain protection mechanism in real-time systems. Through the comparison of the advantages and disadvantages of three different addressing space (the equal single address space, the single address space and the multiple address space), we present a combined memory model which can offer virtual memory mechanism, meanwhile supporting the real-time address space, optimizing the performance of real-time environment. In real-time systems, the time overhead cause by TLB failure will significantly affect the overall performance of the system, thus we studied the strategy of TLB software management to solve this problem. In addition, as one of the important mechanisms of system safety, space domain protection has been part of the design theory for safety-critical real-time system, this paper researched the implementation of this technology in real-time systems. Last, based on the real-time system CRTOSII, we have finished the detailed design and implementation of a memory management system, the test result shows that this system can simultaneously support real-time environment and virtual memory.