230. 验证微小 ROM 写入 PPU 寄存器

验证测试:微小的 iNES ROM 写入 PPU 寄存器。

第 230 / 356 · tests/chapter_03_ppu_memory_and_graphics_data/test_230_VALIDATION_tiny_rom_writes_ppu_registers.py

该文件不是一个学生实现步骤。

这个测试没有新的内容需要实现。它的存在只是为了验证目前构建的各个部分能否通过它们真实的边界协同工作:

iNES bytes
    -> Cartridge.from_ines_bytes(data)
    -> CpuBus(cartridge=cartridge, ppu=ppu)
    -> CPU.reset()
    -> CPU.step()
    -> STA $2000 / STA $2001
    -> CpuBus.write(...)
    -> PPU.write_register(...)

该验证存在的原因

之前的测试分别独立验证了 PPU 寄存器和 CpuBus 路由。这个测试证明了从 cartridge PRG ROM 中取出的实际 CPU 指令,能够通过总线写入 PPU 寄存器。

放置在 CPU 地址 $8000 处的微小程序:

A9 80       LDA #$80
8D 00 20    STA $2000
A9 1E       LDA #$1E
8D 01 20    STA $2001
EA          NOP

预期结果

ppu.ctrl == $80
ppu.mask == $1E

范围之外

渲染
VBlank 时序
NMI 行为
OAMDMA
真实的 PPUSCROLL/PPUADDR 锁存行为

运行本课

uv run pytest tests/chapter_03_ppu_memory_and_graphics_data/test_230_VALIDATION_tiny_rom_writes_ppu_registers.py -v

示例实现

iNES bytes
    -> Cartridge.from_ines_bytes(data)
    -> CpuBus(cartridge=cartridge, ppu=ppu)
    -> CPU.reset()
    -> CPU.step()
    -> STA $2000 / STA $2001
    -> CpuBus.write(...)
    -> PPU.write_register(...)

该验证存在的原因

A9 80       LDA #$80
8D 00 20    STA $2000
A9 1E       LDA #$1E
8D 01 20    STA $2001
EA          NOP

预期结果

ppu.ctrl == $80
ppu.mask == $1E

查看测试代码test_230_VALIDATION_tiny_rom_writes_ppu_registers.py

from emulator.bus.cpu_bus import CpuBus
from emulator.cartridge.cartridge import Cartridge
from emulator.cartridge.ines import CHR_ROM_BANK_SIZE, PRG_ROM_BANK_SIZE
from emulator.cpu.cpu import CPU
from emulator.ppu.ppu import PPU


def make_tiny_ines_rom_that_writes_ppu_registers() -> bytes:
    """Build a minimal Mapper000 iNES ROM that writes PPUCTRL and PPUMASK."""
    header = bytearray(16)
    header[0:4] = b"NES\x1A"
    header[4] = 1  # one 16KB PRG ROM bank
    header[5] = 1  # one 8KB CHR ROM bank
    header[6] = 0x00  # mapper 0, no trainer
    header[7] = 0x00  # mapper 0

    prg_rom = bytearray(PRG_ROM_BANK_SIZE)

    program = [
        0xA9, 0x80,        # LDA #$80
        0x8D, 0x00, 0x20,  # STA $2000
        0xA9, 0x1E,        # LDA #$1E
        0x8D, 0x01, 0x20,  # STA $2001
        0xEA,              # NOP
    ]
    prg_rom[0 : len(program)] = bytes(program)

    # Reset vector: CPU $FFFC-$FFFD -> PRG offsets $3FFC-$3FFD for 16KB NROM.
    prg_rom[0x3FFC] = 0x00
    prg_rom[0x3FFD] = 0x80

    chr_rom = bytes([0x00]) * CHR_ROM_BANK_SIZE

    return bytes(header) + bytes(prg_rom) + chr_rom


def test_tiny_ines_rom_writes_ppu_registers_through_cpu_bus():
    """
    Validation objective:
    Prove that CPU instructions fetched from cartridge PRG ROM can update PPU
    registers through CpuBus.write routing.
    """
    cartridge = Cartridge.from_ines_bytes(make_tiny_ines_rom_that_writes_ppu_registers())
    ppu = PPU()
    bus = CpuBus(cartridge=cartridge, ppu=ppu)
    cpu = CPU(bus=bus)

    cpu.reset()

    cpu.step()  # LDA #$80
    cpu.step()  # STA $2000
    cpu.step()  # LDA #$1E
    cpu.step()  # STA $2001

    assert ppu.ctrl == 0x80
    assert ppu.mask == 0x1E

测试函数 (1)

test_tiny_ines_rom_writes_ppu_registers_through_cpu_bus