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disassembler.py
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49 lines (41 loc) · 2.04 KB
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"""Simple 6502 disassembler."""
from __future__ import annotations
from pyatari.memory import MemoryBus
from pyatari.opcodes import AddressMode, OPCODES
def disassemble(memory: MemoryBus, addr: int) -> tuple[str, int]:
opcode_byte = memory.read_byte(addr)
opcode = OPCODES.get(opcode_byte)
if opcode is None:
return (f".DB ${opcode_byte:02X}", 1)
if opcode.mode == AddressMode.IMPLIED:
return (opcode.mnemonic, opcode.bytes)
if opcode.mode == AddressMode.ACCUMULATOR:
return (f"{opcode.mnemonic} A", opcode.bytes)
op1 = memory.read_byte((addr + 1) & 0xFFFF)
if opcode.mode == AddressMode.IMMEDIATE:
return (f"{opcode.mnemonic} #${op1:02X}", opcode.bytes)
if opcode.mode == AddressMode.ZERO_PAGE:
return (f"{opcode.mnemonic} ${op1:02X}", opcode.bytes)
if opcode.mode == AddressMode.ZERO_PAGE_X:
return (f"{opcode.mnemonic} ${op1:02X},X", opcode.bytes)
if opcode.mode == AddressMode.ZERO_PAGE_Y:
return (f"{opcode.mnemonic} ${op1:02X},Y", opcode.bytes)
if opcode.mode == AddressMode.INDEXED_INDIRECT:
return (f"{opcode.mnemonic} (${op1:02X},X)", opcode.bytes)
if opcode.mode == AddressMode.INDIRECT_INDEXED:
return (f"{opcode.mnemonic} (${op1:02X}),Y", opcode.bytes)
if opcode.mode == AddressMode.RELATIVE:
offset = op1 - 0x100 if op1 & 0x80 else op1
target = (addr + opcode.bytes + offset) & 0xFFFF
return (f"{opcode.mnemonic} ${target:04X}", opcode.bytes)
op2 = memory.read_byte((addr + 2) & 0xFFFF)
operand = op1 | (op2 << 8)
if opcode.mode == AddressMode.ABSOLUTE:
return (f"{opcode.mnemonic} ${operand:04X}", opcode.bytes)
if opcode.mode == AddressMode.ABSOLUTE_X:
return (f"{opcode.mnemonic} ${operand:04X},X", opcode.bytes)
if opcode.mode == AddressMode.ABSOLUTE_Y:
return (f"{opcode.mnemonic} ${operand:04X},Y", opcode.bytes)
if opcode.mode == AddressMode.INDIRECT:
return (f"{opcode.mnemonic} (${operand:04X})", opcode.bytes)
return (f".DB ${opcode_byte:02X}", 1)