Add README.md

README.md

+# Implementing a MIPS Assembler
+
+## 개요
+이 프로젝트는 MIPS ISA assembler를 구현하는 것이다. assembler는 assembly code를 binary 파일로 변환하는 도구이다.
+이 프로젝트의 목표는 MIPS ISA instruction set을 이해하고 assembler의 원리를 숙지하기 위한 것이다.
+
+
+## 사용된 환경 & version
+- Ubuntu 18.04.1 LTS (64bit)
+- gcc (Ubuntu 7.4.0-1ubuntu1~18.04.1) 7.4.0
+
+
+## 사용 시 주의사항
+
+**object파일 생성 및 assembler 테스트**
+
+```bash
+make
+make test
+```
+
+**생성 된 object파일 삭제**
+
+```bash
+make clean
+```
+
+
+## 기능 설명
+### Instruction Set
+
+- 상세한 instruction 정보는 /handout/MIPS_Green_Sheet.pdf 를 참고한다
+    - **Only instructions for unsigned operations need to be implemented.** (addu, addiu, subu, sltiu, sltu, sll, srl)
+    - **However, the immediate fields for certain instructions are sign extended to allow negative numbers** (addui, beq, bne, lw, sw, sltui)
+    - **Only loads and stores with 4B word need to be implemented.**
+    - **The assembler must support decimal and hexadecimal numbers (0x) for the immediate field, and** *.data* **section.**
+    - **The register name is always** *“$n”* **n is from 0 to 31.**
+    - la **(load address) is a pseudo instruction; it should be converted to one or two assembly instructions.**
+    
+    
+    la $2, VAR1: VAR1 is a label in the data section
+    - It should be converted to lui and ori instructions.
+    - lui $register, upper 16bit address
+    - ori $register, lower 16bit address
+    - If the lower 16bit address is 0x0000, the ori instruction is useless.
+        - Case1) load address is 0x1000 0000
+            - lui $2, 0x1000
+        - Case2) load address is 0x1000 0004
+            - lui $2, 0x1000
+            - ori $2, $2, 0x0004
+            
+###Directives
+- .text
+    - indicates that following items are stored in the user text segment, typically instructions
+    - It always starts from 0x400000
+- .data
+    - indicates that following data items are stored in the data segment
+    - It always starts from 0x10000000
+- .word
+    - store n 32-bit quantities in successive memory words
+    
+- You can assume that the .data and .text directives appear only once, and the .data must appear
+  before .text directive. Assume that each word in the data section is initialized (Each word has an
+  initial value). In the following figure, we illustrate the memory map used in our projects.
+  
+
+
+### 입력예시
+
+
+
+### 출력예시
+
+The output of the assembler is an object file. We use a simplified custom format.
+- The first two words (32bits) are the size of text section, and data section.
+- The next bytes are the instructions in binary. The length must be equal to the specified text section
+length.
+- After the text section, the rest of bytes are the initial values of the data section.
+
+The following must be the final binary format:
+
+<text section size>
+<data section size>
+<instruction 1>
+…
+<instruction n>
\ No newline at end of file