| Summary: | 碩士 === 國立交通大學 === 資訊工程系 === 88 === For most embedded systems, program memory occupies a significant portion of the circuit. A larger die size or wider bus causes more cost and power consumption. Compressing program code will not only reduce the cost of embedded systems by reducing instruction memory requirement, but also reduce the demand of external instruction fetch bandwidth. In this thesis, we use a code compression approach that establishes partitioned dictionaries according to the opcode and operand sequences rather than a single dictionary with full 32-bit instruction sequences. We also propose five advanced compression techniques — factorizing condition field in ARM instructions, using operand remapping and operand majority, compressing across branch instructions, and redirecting the index of sub-dictionary entry — to reduce the dictionary size in advance and include more dictionary entries to make the programs smaller. For example, operand remapping and operand majority use less bits to record the dependencies and the most frequent operands in the operand sequences, respectively. Experimental results show that on average 38% compression ratio can be achieved. Compared with 70% compression ratio of the traditional dictionary-based compression method or the Thumb instruction set proposed by ARM, the partitioned dictionary-based code compression with the operand remapping techniques presented in this thesis contributes a great deal.
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