def branch(cpu, oper, mode):
"""
See
:data:`~mach8.operations.BCS`,
:data:`~mach8.operations.BCC`,
:data:`~mach8.operations.BEQ`,
:data:`~mach8.operations.BMI`,
:data:`~mach8.operations.BNE`,
:data:`~mach8.operations.BPL`,
:data:`~mach8.operations.BRA`,
:data:`~mach8.operations.BVC`,
:data:`~mach8.operations.BVS`.
"""
displacement = cpu.fetch()
branch = False
if oper == op.BCS: branch = cpu.c
elif oper == op.BCC: branch = not cpu.c
elif oper == op.BEQ: branch = cpu.z
elif oper == op.BMI: branch = cpu.n
elif oper == op.BNE: branch = not cpu.z
elif oper == op.BPL: branch = not cpu.n
elif oper == op.BRA: branch = True
elif oper == op.BVC: branch = not cpu.v
elif oper == op.BVS: branch = cpu.v
else: assert False
if branch:
cpu.pc += vm.twos_inverse(displacement)
def add(cpu, oper, mode):
"""
See :data:`~mach8.operations.ADC`.
"""
operand = _load_am(cpu, mode)
carry = 1 if cpu.c else 0
if cpu.d:
b1 = vm.bcd_inverse(cpu.a)
b2 = vm.bcd_inverse(operand)
bcd = b1 + b2 + carry
cpu.c = bcd > vm.DIGITS2
if bcd > vm.DIGITS2:
bcd -= vm.DIGITS2 + 1
result = vm.bcd_forward(bcd) & vm.BITS8
else:
value = cpu.a + operand + carry
cpu.c = value > vm.BITS8
result = value & vm.BITS8
signed = vm.twos_inverse(cpu.a) + vm.twos_inverse(operand)
cpu.v = signed > vm.SBYTE_MAX or signed < vm.SBYTE_MIN
_flags(cpu, result)
cpu.a = result
def sub(cpu, oper, mode):
"""
See :data:`~mach8.operations.SBC`,
"""
operand = _load_am(cpu, mode)
carry = 0 if cpu.c else 1
if cpu.d:
b1 = vm.bcd_inverse(cpu.a)
b2 = vm.bcd_inverse(operand)
value = b1 - b2 - carry
cpu.c = not value < 0
if value < 0:
value += 100
result = vm.bcd_forward(value) & vm.BITS8
else:
value = cpu.a - operand - carry
cpu.c = not value < 0
result = value & vm.BITS8
signed = vm.twos_inverse(cpu.a) - vm.twos_inverse(operand)
cpu.v = signed > vm.SBYTE_MAX or signed < vm.SBYTE_MIN
_flags(cpu, result)
cpu.a = result
def next(self):
"""
Description
"""
d = Disassembled()
d.address = vm.size16(self.position)
d.labels = self.meta.get_labels(d.address)
d.remarks = self.meta.get_remarks(d.address)
d.argument = self.meta.get_argument(d.address)
d.data = self.meta.get_data(d.address)
if d.data is not None:
self.position = d.data.address + d.data.length
return d
opcode = self.pc.load()
if opcode in self._opcodes:
i = self._opcodes[opcode]
else:
op = '?{:02X}'.format(opcode)
i = x6502.Instruction(opcode, op, am.IMP, None)
d.instruction = i
if i.addressing_mode in AM_ADDRESS_16:
arg = self.pc.load2()
d.bytes = [opcode, vm.lb(arg), vm.hb(arg)]
elif (i.addressing_mode in AM_ADDRESS_8 or
i.addressing_mode in (am.REL, am.IMM)):
arg = self.pc.load()
if i.addressing_mode == am.REL and d.argument is None:
# Branch is displacement after consuming bytes, therefore
# add two.
d.argument = vm.hex16(d.address + vm.twos_inverse(arg) + 2)
d.bytes = [opcode, arg]
elif i.addressing_mode in AM_NO_ARGUMENT:
d.bytes = [opcode]
else:
assert False
return d
def test_twos_inverse_max(self):
self.assertEquals(127, vm.twos_inverse(0x7f))
def test_twos_inverse_min(self):
self.assertEquals(-128, vm.twos_inverse(0x80))
def test_twos_inverse_negative(self):
self.assertEquals(-1, vm.twos_inverse(0xff))
def test_twos_inverse(self):
self.assertEquals(2, vm.twos_inverse(0x02))