110 lines
3.4 KiB
Python
110 lines
3.4 KiB
Python
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# Assignment A1 - Pass 1 and pass 2 assembler
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# Example Opcode Table (OPTAB)
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OPTAB = {
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"LOAD": "01",
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"STORE": "02",
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"ADD": "03",
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"SUB": "04",
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"JMP": "05"
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}
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# Example Assembler Directives
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DIRECTIVES = ["START", "END", "WORD", "RESW", "RESB"]
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# Symbol Table (SYMTAB) and Intermediate Code
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SYMTAB = {}
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intermediate_code = []
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# Pass-I: Generates the symbol table and intermediate code
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def pass1(input_lines):
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locctr = 0
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start_address = 0
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for line in input_lines:
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label, opcode, operand = parse_line(line.strip())
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if opcode == "START":
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start_address = int(operand)
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locctr = start_address
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intermediate_code.append((locctr, label, opcode, operand))
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continue
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# Process label
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if label:
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if label in SYMTAB:
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print(f"Error: Duplicate symbol {label}")
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SYMTAB[label] = locctr
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# Process opcode
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if opcode in OPTAB:
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intermediate_code.append((locctr, label, opcode, operand))
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locctr += 3 # Assume all instructions are 3 bytes
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elif opcode in DIRECTIVES:
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if opcode == "WORD":
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locctr += 3
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elif opcode == "RESW":
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locctr += 3 * int(operand)
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elif opcode == "RESB":
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locctr += int(operand)
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elif opcode == "END":
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intermediate_code.append((locctr, label, opcode, operand))
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break
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else:
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print(f"Error: Invalid opcode {opcode}")
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return start_address, intermediate_code
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# Parse a line of input (splits line into label, opcode, operand)
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def parse_line(line):
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parts = line.split()
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label = parts[0] if len(parts) == 3 else None
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opcode = parts[1] if len(parts) == 3 else parts[0]
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operand = parts[2] if len(parts) == 3 else parts[1] if len(parts) == 2 else None
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return label, opcode, operand
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# Pass-II: Generates the final machine code
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def pass2(start_address, intermediate_code):
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final_code = []
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for locctr, label, opcode, operand in intermediate_code:
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if opcode in OPTAB:
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machine_code = OPTAB[opcode]
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if operand in SYMTAB:
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address = format(SYMTAB[operand], '04X') # 4-digit hex address
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else:
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address = '0000' # Default if symbol not found
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final_code.append(f"{locctr:04X} {machine_code} {address}")
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elif opcode == "WORD":
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final_code.append(f"{locctr:04X} {int(operand):06X}")
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elif opcode == "RESW" or opcode == "RESB":
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final_code.append(f"{locctr:04X} ----")
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elif opcode == "END":
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final_code.append(f"{locctr:04X} END")
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return final_code
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# Main function to read the input file and run both passes
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def main():
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# Read the assembly code from input.txt
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with open("assemblerIP.txt", "r") as file:
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input_lines = file.readlines()
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# Run Pass-I
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start_address, intermediate_code = pass1(input_lines)
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# Display Symbol Table and Intermediate Code
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print("\nPass-I Output:")
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print("Symbol Table (SYMTAB):", SYMTAB)
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print("\nIntermediate Code:")
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for entry in intermediate_code:
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print(entry)
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# Run Pass-II
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final_code = pass2(start_address, intermediate_code)
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# Display Final Machine Code
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print("\nPass-II Output (Final Machine Code):")
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for code in final_code:
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print(code)
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# Run the main function
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if __name__ == "__main__":
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main()
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