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chip8.py
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import random
import struct
import winsound
from font import Font
from opcode import OpcodeData, OpcodeDesc
from bit_buffer import BitBuffer
# Memory layout
# ----------0x1000------------
# | Frame buffer |
# ----------0xf00-------------
# | Stack |
# ..........0xea0.............
# | Code |
# ----------0x200-------------
# | Reserved |
# ----------0x052-------------
# | Keyboard |
# ----------0x050-------------
# | Font |
# ----------0x000-------------
class HardFaultError(BaseException):
def __init__(self, msg):
self.msg = msg
class _Handler:
def __init__(self, handler, get_desc):
self.handler = handler
self.get_desc = get_desc
class Chip8Emulator:
def __init__(self, code):
self.screen_width = 64
self.screen_height = 32
self.pending_clear_screren_buffer = bytearray(
self.screen_width * self.screen_height)
self.needs_to_redraw = True
# Registers
self.registers = bytearray(16)
self.I = 0
self.pc = 0x200
self.sp = 0xea0
# RAM
self.ram = bytearray(0x1000)
self.screen_buffer = BitBuffer(self.ram, 0xf00)
self.key_buffer = BitBuffer(self.ram, 0x50)
# Timer
self.delay_count = 0
self.sound_count = 0
self.ram[self.pc:self.pc + len(code)] = code
self.opcode_handler = {
0x0: _Handler(self._clear_or_return, OpcodeDesc.clear_or_return),
0x1: _Handler(self._jump, OpcodeDesc.jump),
0x2: _Handler(self._call_subroutine, OpcodeDesc.call_subroutine),
0x3: _Handler(self._skip_if_x_equal, OpcodeDesc.skip_if_x_equal),
0x4: _Handler(self._skip_if_x_not_equal, OpcodeDesc.skip_if_x_not_equal),
0x5: _Handler(self._skip_if_x_equal_to_y, OpcodeDesc.skip_if_x_equal_to_y),
0x6: _Handler(self._set_x, OpcodeDesc.set_x),
0x7: _Handler(self._add_x, OpcodeDesc.add_x),
0x8: _Handler(self._arithmetic, OpcodeDesc.arithmetic),
0x9: _Handler(self._skip_if_x_not_equal_to_y, OpcodeDesc.skip_if_x_not_equal_to_y),
0xa: _Handler(self._set_I, OpcodeDesc.set_I),
0xb: _Handler(self._jump_with_offset, OpcodeDesc.jump_with_offset),
0xc: _Handler(self._rnd, OpcodeDesc.rnd),
0xd: _Handler(self._draw_sprite, OpcodeDesc.draw_sprite),
0xe: _Handler(self._skip_on_key, OpcodeDesc.skip_on_key),
0xf: _Handler(self._misc, OpcodeDesc.misc),
}
self.misc_opcode_handler = {
0x07: self._set_x_to_delay,
0x0a: self._wait_for_key,
0x15: self._set_delay,
0x18: self._set_sound,
0x1e: self._add_to_I,
0x29: self._set_I_for_char,
0x33: self._binary_coded_decimal,
0x55: self._save_x,
0x65: self._load_x,
}
self._init_font()
def reset(self):
print('Reset')
def key_down(self, key):
self.key_buffer[key] = 1
def key_up(self, key):
self.key_buffer[key] = 0
def get_key_status(self):
buffer = []
for i in range(16):
buffer.append(self.key_buffer[i])
return buffer
def run_loop(self):
opcode = struct.unpack_from('>H', self.ram, self.pc)[0]
self.pc += 2
data = OpcodeData(opcode)
something = opcode >> 12
if something in self.opcode_handler:
return self.opcode_handler[something].handler(data)
else:
raise HardFaultError(f'Unknown opcode : {opcode}')
def get_description(self, opcode):
data = OpcodeData(opcode)
something = opcode >> 12
return self.opcode_handler[something].get_desc(data)
def tick60Hz(self):
if self.delay_count > 0:
self.delay_count -= 1
if self.sound_count > 0:
self.sound_count -= 1
if self.sound_count == 0:
winsound.Beep(32000, 100)
def _init_font(self):
ptr = 0
arr = [
Font.D0, Font.D1, Font.D2, Font.D3,
Font.D4, Font.D5, Font.D6, Font.D7,
Font.D8, Font.D9, Font.DA, Font.DB,
Font.DC, Font.DD, Font.DE, Font.DF,
]
for font in arr:
self.ram[ptr + 0] = (font & 0xF000000000) >> (8 * 4)
self.ram[ptr + 1] = (font & 0x00F0000000) >> (8 * 3)
self.ram[ptr + 2] = (font & 0x0000F00000) >> (8 * 2)
self.ram[ptr + 3] = (font & 0x000000F000) >> (8 * 1)
self.ram[ptr + 4] = (font & 0x00000000F0) >> (8 * 0)
ptr += 5
def _push(self, value):
struct.pack_into('>H', self.ram, self.sp, value)
self.sp += 2
def _pop(self):
self.sp -= 2
return struct.unpack_from('>H', self.ram, self.sp)[0]
def _clear_or_return(self, data):
if data.NN == 0xe0:
for i in range(self.screen_width * self.screen_height):
self.screen_buffer[i] = 0
elif data.NN == 0xee:
self.pc = self._pop()
else:
raise HardFaultError(f'Unknown opcode, data.NN = {data.NN:X}')
def _jump(self, data):
self.pc = data.NNN
def _call_subroutine(self, data):
self._push(self.pc)
self.pc = data.NNN
def _skip_if_x_equal(self, data):
if self.registers[data.X] == data.NN:
self.pc += 2
def _skip_if_x_not_equal(self, data):
if self.registers[data.X] != data.NN:
self.pc += 2
def _skip_if_x_equal_to_y(self, data):
if self.registers[data.X] == self.registers[data.Y]:
self.pc += 2
def _set_x(self, data):
self.registers[data.X] = data.NN
def _add_x(self, data):
if self.registers[data.X] + data.NN > 0xff:
self.registers[data.X] = self.registers[data.X] + data.NN - 0x100
else:
self.registers[data.X] += data.NN
def _arithmetic(self, data):
reg = self.registers
if data.N == 0x00:
reg[data.X] = reg[data.Y]
elif data.N == 0x01:
reg[data.X] |= reg[data.Y]
elif data.N == 0x02:
reg[data.X] &= reg[data.Y]
elif data.N == 0x03:
reg[data.X] ^= reg[data.Y]
elif data.N == 0x04:
if reg[data.X] + reg[data.Y] > 0xff:
reg[0xf] = 1
else:
reg[0xf] = 0
reg[data.X] = (reg[data.X] + reg[data.Y]) & 0xff
elif data.N == 0x05:
reg[0xf] = 1 if reg[data.X] > reg[data.Y] else 0
reg[data.X] = (reg[data.X] - reg[data.Y]) & 0xff
elif data.N == 0x06:
reg[0xf] = 1 if ((reg[data.X] & 0x01) != 0) else 0
reg[data.Y] >>= 1
elif data.N == 0x07:
reg[0xf] = 1 if reg[data.Y] > reg[data.X] else 0
reg[data.Y] = (reg[data.Y] - reg[data.X]) & 0xff
elif data.N == 0x0e:
reg[0xf] = 1 if (reg[data.X] & 0xf) != 0 else 0
reg[data.X] = (reg[data.X] << 1) & 0xff
else:
raise HardFaultError(f'Invalid data.N({data.N} in arithmetic')
def _skip_if_x_not_equal_to_y(self, data):
if self.registers[data.X] != self.registers[data.Y]:
self.pc += 2
def _set_I(self, data):
self.I = data.NNN
def _jump_with_offset(self, data):
self.pc = data.NNN + self.registers[0]
def _rnd(self, data):
self.registers[data.X] = random.randint(0, 0xff) & data.NN
def _draw_sprite(self, data):
start_x = self.registers[data.X]
start_y = self.registers[data.Y]
self.registers[0xf] = 0
for i in range(data.N):
sprite_line = self.ram[self.I + i]
for bit in range(8):
x = (start_x + bit) % self.screen_width
y = (start_y + i) % self.screen_height
index = y * self.screen_width + x
sprite_bit = (sprite_line >> (7 - bit)) & 1
old_bit = self.screen_buffer[index]
if old_bit != sprite_bit:
self.needs_to_redraw = True
new_bit = old_bit ^ sprite_bit
if new_bit != 0:
self.screen_buffer[index] = 1
else:
self.screen_buffer[index] = 0
if old_bit != 0 and new_bit == 0:
self.registers[0xf] = 1
def _skip_on_key(self, data):
x = self.registers[data.X]
if data.NN == 0x9e and self.key_buffer[x]:
self.pc += 2
elif data.NN == 0xa1 and not self.key_buffer[x]:
self.pc += 2
def _misc(self, data):
if data.NN in self.misc_opcode_handler:
self.misc_opcode_handler[data.NN](data)
else:
raise HardFaultError(f'Unknow misc opcode, data.NN = {data.NN}')
def _set_x_to_delay(self, data):
self.registers[data.X] = self.delay_count
def _wait_for_key(self, data):
find = False
for i in range(16):
if self.key_buffer[i]:
self.registers[data.X] = i
find = True
break
if not find:
self.pc -= 2
def _set_delay(self, data):
self.delay_count = self.registers[data.X]
def _set_sound(self, data):
self.sound_count = self.registers[data.X]
def _add_to_I(self, data):
self.I += self.registers[data.X]
def _set_I_for_char(self, data):
self.I = self.registers[data.X] * 5
def _binary_coded_decimal(self, data):
self.ram[self.I + 0] = (self.registers[data.X] // 100) % 10
self.ram[self.I + 1] = (self.registers[data.X] // 10) % 10
self.ram[self.I + 2] = (self.registers[data.X] // 1) % 10
def _save_x(self, data):
for i in range(data.X + 1):
self.ram[self.I + i] = self.registers[i]
def _load_x(self, data):
for i in range(data.X + 1):
self.registers[i] = self.ram[self.I + i]