284. 验证：CPU 写入 PPU 内存后进行渲染

验证：CPU 写入 PPU 内存，然后 Console 渲染背景帧缓冲。

第 284 / 356 · tests/chapter_05_rendering_pipeline/test_284_VALIDATION_cpu_writes_ppu_memory_then_render.py

如果前面的 CPU、PPU、总线和渲染步骤都已完成，本测试不需要新的实现。

为什么需要这项验证

模拟器现在有两条重要的路径

CPU/PPU write path:
    CPU program writes PPUADDR/PPUDATA
    -> PPU memory changes

Rendering path:
    Console.render_background_framebuffer()
    -> reads current PPU memory
    -> returns Framebuffer

这个测试验证这两条路径观察到的是同一个 PPU 状态。

端到端路径

CPU executes STA $2006/$2007
    -> CpuBus routes $2000-$2007 to PPU registers
    -> PPUADDR selects PPU memory address
    -> PPUDATA writes through PpuBus

Console.render_background_framebuffer()
    -> reads nametable/palette/pattern memory from console.ppu
    -> renders pure Framebuffer data

微型 CPU 程序的行为

write $01 to PPU $2000
    nametable[0] = tile ID 1

write $0F,$01,$02,$03 to PPU $3F00-$3F03
    background palette 0 maps color index 3 to NES color $03

合成的 CHR 设置

为了这项验证，CHR 数据直接在 PPU 内存中准备好。这样可以让测试专注于 CPU 对名称表/调色板 RAM 的写入以及渲染路径。对于 Mapper000/CHR ROM，CHR 图形通常来自卡带。

预期结果

top-left framebuffer pixel uses get_nes_rgb_color($03)

重要的不变量

CPU 写入和 Console 渲染必须使用同一个 PPU 实例。

范围之外

pygame 显示
真实的 ROM 测试夹具
通过卡带加载 CHR ROM
精灵
滚动
OAMDMA

运行本课

uv run pytest tests/chapter_05_rendering_pipeline/test_284_VALIDATION_cpu_writes_ppu_memory_then_render.py -v

示例实现

微型 CPU 程序的行为

write $01 to PPU $2000
    nametable[0] = tile ID 1

write $0F,$01,$02,$03 to PPU $3F00-$3F03
    background palette 0 maps color index 3 to NES color $03

查看测试代码test_284_VALIDATION_cpu_writes_ppu_memory_then_render.py

from emulator.bus.cpu_bus import CpuBus
from emulator.console import Console
from emulator.cpu.cpu import CPU
from emulator.memory.fake_rom import FakeROM
from emulator.rendering.nes_palette import get_nes_rgb_color
from emulator.rendering.ppu_background_renderer import PATTERN_TABLE_0_ADDR
from tests.helpers import load_program


def make_console_with_fake_rom():
    """Build a Console whose CPU bus and rendering path share the same PPU."""
    rom = FakeROM()
    bus = CpuBus(program_rom=rom)
    cpu = CPU(bus)
    return Console(cpu=cpu, ppu=bus.ppu), cpu, bus.ppu, rom


def set_tile_row_to_color_index_in_ppu(
    ppu,
    tile_id: int,
    row: int,
    color_index: int,
) -> None:
    """Write one synthetic CHR tile row into pattern table 0."""
    tile_offset = tile_id * 16
    low_bit = color_index & 0b01
    high_bit = (color_index >> 1) & 0b01

    ppu.ppu_bus.write(PATTERN_TABLE_0_ADDR + tile_offset + row, 0xFF if low_bit else 0x00)
    ppu.ppu_bus.write(PATTERN_TABLE_0_ADDR + tile_offset + 8 + row, 0xFF if high_bit else 0x00)


def test_VALIDATION_cpu_writes_nametable_and_palette_then_console_renders_expected_pixel():
    """
    VALIDATION:
    A CPU program writes nametable and palette RAM through PPU registers, then
    Console renders a framebuffer from the same PPU memory.

    If this fails, inspect earlier systems:
        CpuBus PPU register routing
        PPUADDR/PPUDATA behavior
        PpuBus nametable/palette mapping
        ppu_background_to_framebuffer()
        Console.render_background_framebuffer()
    """
    console, cpu, ppu, rom = make_console_with_fake_rom()

    # Synthetic CHR setup: tile #1 row 0 emits color index 3.
    set_tile_row_to_color_index_in_ppu(
        ppu,
        tile_id=1,
        row=0,
        color_index=3,
    )

    program = [
        # PPUADDR = $2000
        0xA9, 0x20,        # LDA #$20
        0x8D, 0x06, 0x20,  # STA $2006
        0xA9, 0x00,        # LDA #$00
        0x8D, 0x06, 0x20,  # STA $2006

        # PPUDATA = $01, so nametable[0] = tile ID 1
        0xA9, 0x01,        # LDA #$01
        0x8D, 0x07, 0x20,  # STA $2007

        # PPUADDR = $3F00
        0xA9, 0x3F,        # LDA #$3F
        0x8D, 0x06, 0x20,  # STA $2006
        0xA9, 0x00,        # LDA #$00
        0x8D, 0x06, 0x20,  # STA $2006

        # PPUDATA writes background palette 0: $0F,$01,$02,$03
        0xA9, 0x0F,        # LDA #$0F
        0x8D, 0x07, 0x20,  # STA $2007
        0xA9, 0x01,        # LDA #$01
        0x8D, 0x07, 0x20,  # STA $2007
        0xA9, 0x02,        # LDA #$02
        0x8D, 0x07, 0x20,  # STA $2007
        0xA9, 0x03,        # LDA #$03
        0x8D, 0x07, 0x20,  # STA $2007
    ]
    load_program(rom, 0x8000, program)
    cpu.pc = 0x8000

    instruction_count = 18
    for _ in range(instruction_count):
        console.step()

    framebuffer = console.render_background_framebuffer()

    assert framebuffer.get_pixel(0, 0) == get_nes_rgb_color(0x03)

测试函数 (1)

test_VALIDATION_cpu_writes_nametable_and_palette_then_console_renders_expected_pixel