050. 转移指令

添加核心 TAX、TXA、TAY 和 TYA 指令。

第 50 / 356 · tests/chapter_01_cpu/test_050_transfer_instructions.py

要更新的文件

emulator/cpu/instructions.py

位置

instructions.tax
instructions.txa
instructions.tay
instructions.tya

为什么需要这一步

这些隐含寻址的操作在 A、X 和 Y 之间进行复制，且不需要取操作数。每个目的寄存器随后都会使用加载指令已经用过的相同 Zero/Negative 更新逻辑。

完整示例实现

# emulator/cpu/instructions.py
def tax(cpu: CPU):
    cpu.x = cpu.a
    cpu._update_zero_and_negative_flags(cpu.x)


def txa(cpu: CPU):
    cpu.a = cpu.x
    cpu._update_zero_and_negative_flags(cpu.a)


def tay(cpu: CPU):
    cpu.y = cpu.a
    cpu._update_zero_and_negative_flags(cpu.y)


def tya(cpu: CPU):
    cpu.a = cpu.y
    cpu._update_zero_and_negative_flags(cpu.a)

重要不变量

TAX 把 A 复制到 X，TXA 把 X 复制到 A，TAY 把 A 复制到 Y，TYA 把 Y 复制到 A
源寄存器保持不变
当结果恰为 $00 时设置 Zero，Negative 则镜像目的寄存器的第 7 位
当复制得到的值不再满足这两个标志位的条件时，它们也会被清除
这些函数不取任何字节，也不进行总线访问

常见误区

只更新会被置位的标志位会遗留过期状态。每次复制之后都应对目的寄存器复用 cpu._update_zero_and_negative_flags。

范围之外

转移指令操作码的导入及 OPCODE_TABLE 条目，将在 Test 051 中引入
栈指针相关的转移操作
周期时序

运行本课

uv run pytest tests/chapter_01_cpu/test_050_transfer_instructions.py -v

示例实现

完整示例实现

# emulator/cpu/instructions.py
def tax(cpu: CPU):
    cpu.x = cpu.a
    cpu._update_zero_and_negative_flags(cpu.x)


def txa(cpu: CPU):
    cpu.a = cpu.x
    cpu._update_zero_and_negative_flags(cpu.a)


def tay(cpu: CPU):
    cpu.y = cpu.a
    cpu._update_zero_and_negative_flags(cpu.y)


def tya(cpu: CPU):
    cpu.a = cpu.y
    cpu._update_zero_and_negative_flags(cpu.a)

查看测试代码test_050_transfer_instructions.py

import inspect

from emulator.cpu import instructions
from tests.helpers import NEGATIVE_FLAG, ZERO_FLAG, make_cpu


def test_tax_instruction_exists():
    """
    Objective:
    Create in instructions.py:
        def tax(cpu):
            ...

    TAX means:
        X = A
    """
    assert hasattr(instructions, "tax")
    assert callable(instructions.tax)
    assert list(inspect.signature(instructions.tax).parameters) == ["cpu"]


def test_txa_instruction_exists():
    """
    Objective:
    Create in instructions.py:
        def txa(cpu):
            ...

    TXA means:
        A = X
    """
    assert hasattr(instructions, "txa")
    assert callable(instructions.txa)
    assert list(inspect.signature(instructions.txa).parameters) == ["cpu"]


def test_tay_instruction_exists():
    """
    Objective:
    Create in instructions.py:
        def tay(cpu):
            ...

    TAY means:
        Y = A
    """
    assert hasattr(instructions, "tay")
    assert callable(instructions.tay)
    assert list(inspect.signature(instructions.tay).parameters) == ["cpu"]


def test_tya_instruction_exists():
    """
    Objective:
    Create in instructions.py:
        def tya(cpu):
            ...

    TYA means:
        A = Y
    """
    assert hasattr(instructions, "tya")
    assert callable(instructions.tya)
    assert list(inspect.signature(instructions.tya).parameters) == ["cpu"]


def test_tax_transfers_a_to_x_and_updates_flags():
    """Objective: TAX copies A into X and updates Zero/Negative flags."""
    cpu = make_cpu()
    cpu.a = 0x80

    instructions.tax(cpu)

    assert cpu.x == 0x80
    assert (cpu.p & ZERO_FLAG) == 0
    assert (cpu.p & NEGATIVE_FLAG) != 0


def test_txa_transfers_x_to_a_and_updates_flags():
    """Objective: TXA copies X into A and updates Zero/Negative flags."""
    cpu = make_cpu()
    cpu.x = 0x00

    instructions.txa(cpu)

    assert cpu.a == 0x00
    assert (cpu.p & ZERO_FLAG) != 0
    assert (cpu.p & NEGATIVE_FLAG) == 0


def test_tay_transfers_a_to_y_and_updates_flags():
    """Objective: TAY copies A into Y and updates Zero/Negative flags."""
    cpu = make_cpu()
    cpu.a = 0x42
    cpu.p |= ZERO_FLAG | NEGATIVE_FLAG

    instructions.tay(cpu)

    assert cpu.y == 0x42
    assert (cpu.p & ZERO_FLAG) == 0
    assert (cpu.p & NEGATIVE_FLAG) == 0


def test_tya_transfers_y_to_a_and_updates_flags():
    """Objective: TYA copies Y into A and updates Zero/Negative flags."""
    cpu = make_cpu()
    cpu.y = 0x80

    instructions.tya(cpu)

    assert cpu.a == 0x80
    assert (cpu.p & ZERO_FLAG) == 0
    assert (cpu.p & NEGATIVE_FLAG) != 0

测试函数 (8)

test_tax_instruction_exists
test_txa_instruction_exists
test_tay_instruction_exists
test_tya_instruction_exists
test_tax_transfers_a_to_x_and_updates_flags
test_txa_transfers_x_to_a_and_updates_flags
test_tay_transfers_a_to_y_and_updates_flags
test_tya_transfers_y_to_a_and_updates_flags