244. 验证:微型 ROM 写入 PPU 内存

验证测试:微型 iNES ROM 通过 PPUADDR/PPUDATA 写入 PPU 内存。

第 244 / 356 · tests/chapter_03_ppu_memory_and_graphics_data/test_244_VALIDATION_tiny_rom_writes_ppu_memory.py

本文件并不是供学生实现的步骤。

这个测试没有任何需要新实现的内容。它的存在只是为了验证目前已构建的各个部分能够通过其真实边界协同工作:

iNES bytes
    -> Cartridge.from_ines_bytes(data)
    -> CpuBus(cartridge=cartridge, ppu=ppu)
    -> CPU.reset()
    -> CPU.step()
    -> STA $2006 / STA $2007
    -> CpuBus.write(...)
    -> PPU.write_register(...)
    -> PPUADDR sets vram_addr
    -> PPUDATA writes through PpuBus
    -> VRAM stores the byte

为什么需要这个验证

之前的测试各自隔离地验证了 PPUADDR、PPUDATA、PPUCTRL 递增行为、PpuBus 以及 CpuBus 路由。本测试证明,一个从微型卡带式 iNES ROM 中取出的真实 CPU 程序能够写入 PPU 侧内存。

放置在 CPU 地址 $8000 处的微型程序:

A9 20       LDA #$20
8D 06 20    STA $2006    ; PPUADDR high byte
A9 00       LDA #$00
8D 06 20    STA $2006    ; PPUADDR low byte
A9 AA       LDA #$AA
8D 07 20    STA $2007    ; PPUDATA write to PPU memory at $2000
EA          NOP

预期结果

ppu.ppu_bus.read($2000) == $AA
ppu.vram_addr == $2001

超出范围

渲染
命名表镜像精度
调色板 RAM 精度
CHR RAM 写入
PPUDATA 读取/读取缓冲
VBlank/NMI 时序

运行本课

uv run pytest tests/chapter_03_ppu_memory_and_graphics_data/test_244_VALIDATION_tiny_rom_writes_ppu_memory.py -v

示例实现

iNES bytes
    -> Cartridge.from_ines_bytes(data)
    -> CpuBus(cartridge=cartridge, ppu=ppu)
    -> CPU.reset()
    -> CPU.step()
    -> STA $2006 / STA $2007
    -> CpuBus.write(...)
    -> PPU.write_register(...)
    -> PPUADDR sets vram_addr
    -> PPUDATA writes through PpuBus
    -> VRAM stores the byte

为什么需要这个验证

A9 20       LDA #$20
8D 06 20    STA $2006    ; PPUADDR high byte
A9 00       LDA #$00
8D 06 20    STA $2006    ; PPUADDR low byte
A9 AA       LDA #$AA
8D 07 20    STA $2007    ; PPUDATA write to PPU memory at $2000
EA          NOP

预期结果

ppu.ppu_bus.read($2000) == $AA
ppu.vram_addr == $2001

查看测试代码test_244_VALIDATION_tiny_rom_writes_ppu_memory.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_memory() -> bytes:
    """Build a minimal Mapper000 iNES ROM that writes one byte to PPU memory."""
    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, 0x20,        # LDA #$20
        0x8D, 0x06, 0x20,  # STA $2006
        0xA9, 0x00,        # LDA #$00
        0x8D, 0x06, 0x20,  # STA $2006
        0xA9, 0xAA,        # LDA #$AA
        0x8D, 0x07, 0x20,  # STA $2007
        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_memory_through_ppuaddr_and_ppudata():
    """
    Validation objective:
    Prove that CPU instructions can set PPUADDR and write PPUDATA into PPU-side
    memory through CpuBus, PPU, PpuBus, and VRAM.
    """
    cartridge = Cartridge.from_ines_bytes(make_tiny_ines_rom_that_writes_ppu_memory())
    ppu = PPU()
    bus = CpuBus(cartridge=cartridge, ppu=ppu)
    cpu = CPU(bus=bus)

    cpu.reset()

    cpu.step()  # LDA #$20
    cpu.step()  # STA $2006
    cpu.step()  # LDA #$00
    cpu.step()  # STA $2006
    cpu.step()  # LDA #$AA
    cpu.step()  # STA $2007

    assert ppu.ppu_bus.read(0x2000) == 0xAA
    assert ppu.vram_addr == 0x2001

测试函数 (1)

test_tiny_ines_rom_writes_ppu_memory_through_ppuaddr_and_ppudata