| Summary: | 碩士 === 國立成功大學 === 電腦與通信工程研究所 === 95 === This thesis presents the design and implementation of a dynamic code loading mechanism with overlay functionality on an embedded system platform of heterogeneous multiprocessor. The heterogeneous multiprocessor platform is composed of an ARM7 general purpose processor and a DSP special purpose processor. The ARM processor handles the general operations of the platform while the DSP processor runs digital signal processing software and plays the role of programmable external device. Because the available memory space at DSP side is limited, the development of application program faces big challenge. This thesis takes the policy of trading time for space to design and implement the code overlay mechanism to address the issue of limited memory space.
The code overlay mechanism designed in this thesis has three characteristics: programmers don’t need to modify source code; without the restriction of compiler; there is just little overhead imposed on programmers and the mechanism is built on platform of heterogeneous multiprocessor. The implementation of the code overlay mechanism is composed of a preprocessing tool, dynamic code loading service on the ARM side and overlay manager on the DSP side. While the later two components implement the dynamic code overlay at run time, the preprocessing tool divides the application into segments, from the object program, in units of function modules to reduce the overhead incurred from loading overlays.
Code structure affects the effect of overlay mechanism in general. For application programs using the dynamic code overlay mechanism there is no need for programmers to modify source program structure because the target of preprocessing is object file and the performance impact is acceptable as observed from the result of testing. Therefore, the memory space used by application program can be reduced effectively.
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