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assembler.py
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assembler.py
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# Instruction encoding
#
# __________________________________________________________________
# | opcode | r_dest | r_a | r_b | immediate val |
# ------------------------------------------------------------------
# 4-bit 4-bit 4-bit 4-bit 16-bit
# <------------------ 32-bit --------------------------------->
#
import sys
import struct
def decode_register(reg, line_num):
# reg = R0 or R1 or .... R15
# input: R5 should give output: 0101
num = int(reg[1:])
if num > 15 or num < 0:
raise Exception(f"line: {line_num} unknown register")
num = bin(num)[2:] # 5 becomes 0b101
while len(num) != 4:
num = '0' + num
return num
def int_to_16bit_signed(value, line_num):
if not -32768 <= value <= 32767:
raise ValueError(
f"line: {line_num} value out of range for 16-bit signed integer")
# h = short datatype of c i.e 16-bits. In big-endian
return struct.pack('>h', value)
def decode_immediate(number, line_num):
number = int_to_16bit_signed(int(number), line_num)
return ''.join(format(byte, '08b') for byte in number)
def decode_instruction(text, line_num, instruction_num, labels_map):
text = text.split('//')[0].strip()
codes = text.split()
codes = [item.split(',')[0] for item in codes]
takes_0_operand = ['HLT']
takes_1_operand = ['JMP']
takes_2_operands = ['MOV', 'MVI', 'NOT', 'JEZ', 'JNZ']
takes_3_operands = ['LOD', 'STR', 'ADD',
'SUB', 'MUL', 'AND', 'ORR', 'LES', 'GTR']
if codes[0] in takes_0_operand and len(codes) != 1:
raise Exception(f"line: {line_num} {
codes[0]} doesn't take any operand")
if codes[0] in takes_1_operand and len(codes) != 2:
raise Exception(f"line: {line_num} {
codes[0]} takes one operand")
if codes[0] in takes_2_operands and len(codes) != 3:
raise Exception(f"line: {line_num} {
codes[0]} takes two operands")
if codes[0] in takes_3_operands and len(codes) != 4:
raise Exception(f"line: {line_num} {
codes[0]} takes three operands")
opcode = '0000'
r_dest = '0000'
r_a = '0000'
r_b = '0000'
immediate = '0000' * 4
unresolved = False
match codes[0].upper():
case "HLT":
opcode = '0000'
case "MOV":
opcode = '0001'
r_dest = decode_register(codes[1], line_num)
r_a = decode_register(codes[2], line_num)
case "MVI":
opcode = '0010'
r_dest = decode_register(codes[1], line_num)
immediate = decode_immediate(codes[2], line_num)
case "LOD":
opcode = '0011'
r_dest = decode_register(codes[1], line_num)
r_a = decode_register(codes[2], line_num)
immediate = decode_immediate(codes[3], line_num)
case "STR":
opcode = '0100'
r_dest = decode_register(codes[1], line_num)
r_a = decode_register(codes[2], line_num)
immediate = decode_immediate(codes[3], line_num)
case "ADD":
opcode = '0101'
r_dest = decode_register(codes[1], line_num)
r_a = decode_register(codes[2], line_num)
r_b = decode_register(codes[3], line_num)
case "SUB":
opcode = '0110'
r_dest = decode_register(codes[1], line_num)
r_a = decode_register(codes[2], line_num)
r_b = decode_register(codes[3], line_num)
case "MUL":
opcode = '0111'
r_dest = decode_register(codes[1], line_num)
r_a = decode_register(codes[2], line_num)
r_b = decode_register(codes[3], line_num)
case "AND":
opcode = '1000'
r_dest = decode_register(codes[1], line_num)
r_a = decode_register(codes[2], line_num)
r_b = decode_register(codes[3], line_num)
case "ORR":
opcode = '1001'
r_dest = decode_register(codes[1], line_num)
r_a = decode_register(codes[2], line_num)
r_b = decode_register(codes[3], line_num)
case "NOT":
opcode = '1010'
r_dest = decode_register(codes[1], line_num)
r_a = decode_register(codes[2], line_num)
case "LES":
opcode = '1011'
r_dest = decode_register(codes[1], line_num)
r_a = decode_register(codes[2], line_num)
r_b = decode_register(codes[3], line_num)
case "GTR":
opcode = '1100'
r_dest = decode_register(codes[1], line_num)
r_a = decode_register(codes[2], line_num)
r_b = decode_register(codes[3], line_num)
case "JEZ":
opcode = '1101'
r_dest = decode_register(codes[1], line_num)
if codes[2] not in labels_map:
unresolved = True
else:
instr_to_jump = labels_map[codes[2]]
offset = instr_to_jump - instruction_num
immediate = decode_immediate(offset, line_num)
case "JNZ":
opcode = '1110'
r_dest = decode_register(codes[1], line_num)
if codes[2] not in labels_map:
unresolved = True
else:
instr_to_jump = labels_map[codes[2]]
offset = instr_to_jump - instruction_num
immediate = decode_immediate(offset, line_num)
case "JMP":
opcode = '1111'
if codes[1] not in labels_map:
unresolved = True
else:
instr_to_jump = labels_map[codes[1]]
offset = instr_to_jump - instruction_num
immediate = decode_immediate(offset, line_num)
case _:
raise Exception(f"line: {line_num} unknown opcode")
binary_debug = f"{opcode} {r_dest} {r_a} {r_b} {immediate}"
instruction = int(opcode + r_dest + r_a + r_b + immediate, 2)
return {
'complete': not unresolved,
'instruction': instruction,
'binary_debug': binary_debug,
'source': text,
'line_num': line_num,
'instruction_num': instruction_num
}
def assembler(assembly_file):
instructions = []
labels_map = {}
labels_reverse_map = {}
with open(assembly_file, 'r') as file:
for line_num, line in enumerate(file, start=1):
line = line.strip()
if len(line) == 0:
continue
elif len(line) > 0 and line[0] == '/':
continue
elif len(line) > 0 and line[0] == ':':
label_name = line.split()[0][1:]
instr_num = len(instructions)
labels_map[label_name] = instr_num
labels_reverse_map[instr_num] = label_name
else:
instructions.append(decode_instruction(
line, line_num, len(instructions), labels_map))
instructions = [
decode_instruction(item['source'], item['line_num'],
item['instruction_num'], labels_map)
if not item['complete']
else item
for item in instructions
]
print("\n" + "-"*27 + " debug info " + "-"*27)
for i, inst in enumerate(instructions):
line_num = f"#{i}"
label = ""
if i in labels_reverse_map:
label = ":" + labels_reverse_map[i]
src = inst['source']
binary_debug = inst['binary_debug']
LINE_NUM_LEN = 5
LABEL_LEN = 10
SRC_LEN = 18
if len(line_num) < LINE_NUM_LEN:
line_num = ' ' * (LINE_NUM_LEN - len(line_num)) + line_num
if len(label) < LABEL_LEN:
label = ' ' * (LABEL_LEN - len(label)) + label
if len(src) < SRC_LEN:
src = src + ' ' * (SRC_LEN - len(src))
print(f"{line_num} {label} {src} {binary_debug}")
print("\n----- assembled instructions -------")
for inst in instructions:
print(inst['instruction'])
print("\n----- generated code -------")
for i, inst in enumerate(instructions):
print(f"computer.instruction_memory[{i}]={inst['instruction']};")
if __name__ == "__main__":
if len(sys.argv) != 2:
print("Usage: python3 assembler assembly_src.s")
exit(1)
print(f"Assembling {sys.argv[1]} ---")
assembler(sys.argv[1])