090. Asl 累加器

接入 ASL 累加器操作码。

第 90 / 356 · tests/chapter_01_cpu/test_090_ASL_accumulator.py

在这一步中，使用测试 089 中的 asl_a，仅添加累加器分发。测试 091-094 会添加内存形式。

生产代码位置与符号

emulator/cpu/opcodes.py: imported `asl_a` and `OPCODE_TABLE[0x0A]`

本步骤存在的原因

操作码 0x0A 选中的是累加器本身，因此分发可以直接调用 asl_a(cpu)，而无需解析内存地址。

本步骤的实现建议

# emulator/cpu/opcodes.py
from emulator.cpu.instructions import asl_a  # alongside existing imports

OPCODE_TABLE = {
    # ... existing entries ...
    0x0A: asl_a,
}

重要不变量

操作码 0x0A 映射到精确的 asl_a(cpu) 函数
不发生任何寻址辅助或内存读写
这条单字节指令恰好将 PC 推进一位
测试 089 的函数负责 A 的掩码处理以及 C/Z/N 更新

常见误解

ASL A 并不是省略了操作数的零页 ASL；它是一种独立的累加器形式，因此不需要 asl_* 寻址包装器。

不在本步骤范围内

asl_zero_page、asl_zero_page_x、asl_absolute 以及 asl_absolute_x
测试 091-094 中的映射 0x06、0x16、0x0E 以及 0x1E
周期计时以及总线精确的读-改-写行为

运行本课

uv run pytest tests/chapter_01_cpu/test_090_ASL_accumulator.py -v

示例实现

本步骤的实现建议

# emulator/cpu/opcodes.py
from emulator.cpu.instructions import asl_a  # alongside existing imports

OPCODE_TABLE = {
    # ... existing entries ...
    0x0A: asl_a,
}

查看测试代码test_090_ASL_accumulator.py

import inspect

from emulator.bus.cpu_bus import CpuBus
from emulator.cpu import opcodes
from emulator.cpu.cpu import CPU
from emulator.memory.fake_rom import FakeROM
from tests.helpers import NEGATIVE_FLAG, ZERO_FLAG


CARRY_FLAG = 1 << 0


def make_cpu_with_rom():
    rom = FakeROM()
    rom.write(0x7FFC, 0x00)
    rom.write(0x7FFD, 0x80)
    bus = CpuBus(program_rom=rom)
    return CPU(bus), bus, rom


def test_asl_accumulator_opcode_exists_and_is_in_opcode_table():
    """Objective: import asl_a and add 0x0A to OPCODE_TABLE."""
    assert hasattr(opcodes, "asl_a")
    assert callable(opcodes.asl_a)
    assert list(inspect.signature(opcodes.asl_a).parameters) == ["cpu"]
    assert opcodes.OPCODE_TABLE[0x0A] is opcodes.asl_a


def test_opcode_0A_asl_accumulator_shifts_a_and_advances_pc_by_one():
    """Objective: 0A means ASL A, so only A is shifted and PC advances by 1."""
    cpu, bus, rom = make_cpu_with_rom()
    rom.write(0x0000, 0x0A)

    cpu.reset()
    cpu.a = 0b0000_0011
    cpu.step()

    assert cpu.a == 0b0000_0110
    assert cpu.pc == 0x8001


def test_opcode_0A_asl_accumulator_sets_carry_from_old_a_bit_7():
    """Objective: old A bit 7 is copied into Carry before the result wraps."""
    cpu, bus, rom = make_cpu_with_rom()
    rom.write(0x0000, 0x0A)

    cpu.reset()
    cpu.a = 0b1000_0001
    cpu.step()

    assert cpu.a == 0b0000_0010
    assert (cpu.p & CARRY_FLAG) != 0


def test_opcode_0A_asl_accumulator_updates_zero_flag():
    """Objective: A=0x80 shifts to 0x00 and sets Zero flag."""
    cpu, bus, rom = make_cpu_with_rom()
    rom.write(0x0000, 0x0A)

    cpu.reset()
    cpu.a = 0x80
    cpu.step()

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


def test_opcode_0A_asl_accumulator_updates_negative_flag():
    """Objective: A=0x40 shifts to 0x80 and sets Negative flag."""
    cpu, bus, rom = make_cpu_with_rom()
    rom.write(0x0000, 0x0A)

    cpu.reset()
    cpu.a = 0x40
    cpu.step()

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

测试函数 (5)

test_asl_accumulator_opcode_exists_and_is_in_opcode_table
test_opcode_0A_asl_accumulator_shifts_a_and_advances_pc_by_one
test_opcode_0A_asl_accumulator_sets_carry_from_old_a_bit_7
test_opcode_0A_asl_accumulator_updates_zero_flag
test_opcode_0A_asl_accumulator_updates_negative_flag