126. ORA 立即数

将 ORA immediate 暴露为操作码 ``0x09``。

第 126 / 356 · tests/chapter_01_cpu/test_126_ORA_immediate.py

此步骤存在的原因

immediate 操作码以字面字节的形式将 ORA 暴露给 CPU 执行,并验证解码过程会将结果与标志位处理委托给共享基元。

在此步骤中,在第 125 课创建 `or_a 之后,请在 emulator/cpu/opcodes.py` 中进行以下添加:

from emulator.cpu.instructions import (..., and_a, or_a)

def ora_immediate(cpu: CPU):
    or_a(cpu, immediate(cpu))

OPCODE_TABLE = {
    ...
    0x09: ora_immediate,
}

`emulator/cpu/addressing_modes.py::immediate 直接返回由 CPU.fetch_byte 获取的字节。instructions.or_a` 存储 A | value 的结果,并仅改变 Z/N;Carry/Overflow 及内存保持不变,操作码加操作数使 PC 前进两个字节。

常见误解:立即数字节本身就是值,若再通过 `cpu.bus` 读取一次,就会错误地将其当作地址处理。不在本步骤范围内:基于内存的 ORA 处理程序(第 127-133 课)以及第 134-145 课中的 EOR/BIT 导入与处理程序。

运行本课

uv run pytest tests/chapter_01_cpu/test_126_ORA_immediate.py -v

示例实现

此步骤存在的原因

from emulator.cpu.instructions import (..., and_a, or_a)

def ora_immediate(cpu: CPU):
    or_a(cpu, immediate(cpu))

OPCODE_TABLE = {
    ...
    0x09: ora_immediate,
}

查看测试代码test_126_ORA_immediate.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


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_ora_immediate_handler_exists_and_is_in_opcode_table():
    """Objective: create ora_immediate(cpu) and add 0x09 to OPCODE_TABLE."""
    assert hasattr(opcodes, "ora_immediate")
    assert callable(opcodes.ora_immediate)
    assert list(inspect.signature(opcodes.ora_immediate).parameters) == ["cpu"]
    assert opcodes.OPCODE_TABLE[0x09] is opcodes.ora_immediate


def test_opcode_09_ora_immediate_updates_accumulator():
    """Objective: 09 0F means ORA #$0F, so A becomes A | 0x0F."""
    cpu, bus, rom = make_cpu_with_rom()
    rom.write(0x0000, 0x09)
    rom.write(0x0001, 0x0F)

    cpu.reset()
    cpu.a = 0xF0
    cpu.step()

    assert cpu.a == 0xFF
    assert cpu.pc == 0x8002


def test_opcode_09_ora_immediate_updates_zero_flag():
    """Objective: result 0 sets Zero flag."""
    cpu, bus, rom = make_cpu_with_rom()
    rom.write(0x0000, 0x09)
    rom.write(0x0001, 0x00)

    cpu.reset()
    cpu.a = 0x00
    cpu.step()

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


def test_opcode_09_ora_immediate_updates_negative_flag():
    """Objective: result bit 7 sets Negative flag."""
    cpu, bus, rom = make_cpu_with_rom()
    rom.write(0x0000, 0x09)
    rom.write(0x0001, 0x80)

    cpu.reset()
    cpu.a = 0x01
    cpu.step()

    assert cpu.a == 0x81
    assert (cpu.p & NEGATIVE_FLAG) != 0
    assert (cpu.p & ZERO_FLAG) == 0

测试函数 (4)

test_ora_immediate_handler_exists_and_is_in_opcode_table
test_opcode_09_ora_immediate_updates_accumulator
test_opcode_09_ora_immediate_updates_zero_flag
test_opcode_09_ora_immediate_updates_negative_flag