Dynamic Loading Mechanism Design And Implementation On Embedded System

The wide application of the embedded system needs good software system to support .the systematic expansile ability become one basic demand already with embedded system deep to develop, system needs urgently one mechanism that can dispose system at runtime , that is to say system at runtime may add dynamically the module, this kind of mechanism is dynamic loading mechanism that this thesis will study. Dynamic loading mechanism in this thesis is that application starts from scratch . So system only need a dynamic loading mechanism , which can load dynamically the module and dispose the embedded systems which suit different uses.We have analyzed several kinds of loading mode existing at present in this thesis: the java_based dynamic loading mode, the dynamic loading mode of embedded Linux and the principle of the dynamic linking library in windows. On this basis we have put forward the principle and the process of dynamic loading mechanism under the general meaning. The principle of dynamic loading mechanism requires the ability of dynamic loading and dynamic analyzing. Dynamic loading mechanism use dynamic linking principle and the module is linked to system only while be called and carried out. Dynamic loading can be divided into three operation : download, load and unload. Download finishes download module from long-distance to native. Load operation is to finish to read module into memory, then to analyze unresolved reference outside module. Unload the module from memory when it is no longer used.There are a lot of problems that need considering in dynamic loading mechanism. Some key problems must be solved while designing the dynamic loading mechanism, some problems can be solved in the course of operating. These key problems are the choice of module format, the organization way of module, module communication mechanism, stack space management, namespace management and symbol resolve and indirection. To these key problems we provide the solution suitable for little memory requirement. Besides these key problems, there are some questions for example module dependency, type safety, load ISR(Interrupt Service Routine)and so on that can be considered or not temporarily in the course of operating. Finally, for dynamic loading mechanism under the little memory environment, we proved some elements of dynamic loading mechanism with the simulation operation of one general meaning embedded operating system. In this simulation experiment we select the OBJ file that Turbo C 2.0 produce and after limiting as loadable object module, introduce the system structure of dynamic loading mechanism, state two key elements of dynamic loading emphatically : symbol resolve and indirection .This thesis provides the principle and process of dynamic loading mechanism under general meaning, and the key problem and solution that must be solved, and there is more important reference value to the study and design of dynamic loading mechanism afterwards.