269. Validación de la ruta NMI de VBlank en la consola

VALIDACIÓN: Console.step ejecuta la ruta completa de NMI de VBlank.

Lección 269 de 356 · tests/chapter_04_ppu_timing_and_vblank/test_269_VALIDATION_console_vblank_nmi_path.py

No debería ser necesaria ninguna implementación nueva para esta prueba si los pasos 259-268 están completos.

Referencias

https://www.nesdev.org/wiki/PPU_registers#PPUCTRL
https://www.nesdev.org/wiki/PPU_registers#Vblank_NMI
https://www.nesdev.org/wiki/CPU_interrupts

Por qué existe esta validación

Las pruebas anteriores verificaron cada mecanismo por separado

PPU.step() advances timing
PPU enters VBlank and sets VBLANK_STARTED
PPUCTRL bit 7 enables NMI requests
CPU.step() returns CPU cycles
Console.step() advances PPU by cpu_cycles * 3
Console consumes ppu.nmi_requested
CPU.interrupt_nmi() jumps through $FFFA/$FFFB

Esta prueba valida que esas piezas funcionan juntas en un pequeño escenario a nivel de máquina.

Ruta de extremo a extremo que se valida

CPU executes LDA #$80
    -> A = $80

CPU executes STA $2000
    -> CpuBus routes $2000 to PPUCTRL
    -> PPUCTRL bit 7 enables NMI

Console.step() keeps advancing CPU and PPU together
    -> CPU cycles advance PPU by cycles * 3
    -> PPU enters VBlank
    -> PPU sets nmi_requested = True
    -> Console consumes the request
    -> CPU.interrupt_nmi() reads $FFFA/$FFFB
    -> CPU jumps to the NMI handler address

Pequeño programa usado en esta validación

$8000: A9 80       LDA #$80       ; set PPUCTRL NMI-enable bit
$8002: 8D 00 20    STA $2000      ; write A to PPUCTRL
$8005: EA          NOP            ; wait while PPU reaches VBlank
$8006: EA          NOP
...

Configuración del vector NMI

$FFFA = $00
$FFFB = $90

Resultado esperado

CPU PC becomes $9000 after Console consumes the VBlank NMI request.

Importante

Esta es todavía una temporización simplificada. La prueba coloca intencionalmente la PPU cerca del VBlank para que la validación sea rápida y determinista. Esto no es una prueba de latencia NMI precisa a nivel de punto.

Fuera de alcance

renderizado de píxeles
comportamiento de sprites de la PPU
OAM DMA
entrada de controlador
latencia exacta de NMI
penalizaciones dinámicas de ciclo de la CPU

Ejecutar esta lección

uv run pytest tests/chapter_04_ppu_timing_and_vblank/test_269_VALIDATION_console_vblank_nmi_path.py -v

Implementación de ejemplo

Referencias

https://www.nesdev.org/wiki/PPU_registers#PPUCTRL
https://www.nesdev.org/wiki/PPU_registers#Vblank_NMI
https://www.nesdev.org/wiki/CPU_interrupts

Las pruebas anteriores verificaron cada mecanismo por separado

PPU.step() advances timing
PPU enters VBlank and sets VBLANK_STARTED
PPUCTRL bit 7 enables NMI requests
CPU.step() returns CPU cycles
Console.step() advances PPU by cpu_cycles * 3
Console consumes ppu.nmi_requested
CPU.interrupt_nmi() jumps through $FFFA/$FFFB

Ruta de extremo a extremo que se valida

CPU executes LDA #$80
    -> A = $80

CPU executes STA $2000
    -> CpuBus routes $2000 to PPUCTRL
    -> PPUCTRL bit 7 enables NMI

Console.step() keeps advancing CPU and PPU together
    -> CPU cycles advance PPU by cycles * 3
    -> PPU enters VBlank
    -> PPU sets nmi_requested = True
    -> Console consumes the request
    -> CPU.interrupt_nmi() reads $FFFA/$FFFB
    -> CPU jumps to the NMI handler address

Pequeño programa usado en esta validación

$8000: A9 80       LDA #$80       ; set PPUCTRL NMI-enable bit
$8002: 8D 00 20    STA $2000      ; write A to PPUCTRL
$8005: EA          NOP            ; wait while PPU reaches VBlank
$8006: EA          NOP
...

Configuración del vector NMI

$FFFA = $00
$FFFB = $90

Ver código del testtest_269_VALIDATION_console_vblank_nmi_path.py

from emulator.console import Console
from emulator.ppu.ppu import (
    CTRL_NMI_ENABLE,
    PPU_CYCLES_PER_SCANLINE,
    PPU_VBLANK_START_SCANLINE,
    VBLANK_STARTED,
)
from tests.helpers import load_program, make_cpu_with_rom


def write_nmi_vector(rom, addr: int) -> None:
    """Install the NMI vector in FakeROM."""
    rom.write(0x7FFA, addr & 0xFF)
    rom.write(0x7FFB, (addr >> 8) & 0xFF)


def make_console_with_fake_rom():
    """Build a small Console using the same PPU instance attached to CpuBus."""
    cpu, bus, rom = make_cpu_with_rom()
    return Console(cpu=cpu, ppu=bus.ppu), cpu, bus.ppu, rom


def test_VALIDATION_tiny_program_enables_ppu_nmi_and_reaches_nmi_handler():
    """
    VALIDATION:
    A tiny CPU program can enable PPU NMI, then Console.step() can drive the PPU
    into VBlank and route the NMI request back into CPU.interrupt_nmi().

    No new implementation is required by this test. If it fails, inspect the
    earlier mechanisms: CpuBus PPU register routing, PPU timing, PPU NMI request,
    CPU.step cycles, Console.step, or CPU.interrupt_nmi().
    """
    console, cpu, ppu, rom = make_console_with_fake_rom()
    write_nmi_vector(rom, 0x9000)

    # Program:
    #   LDA #$80
    #   STA $2000
    #   NOP
    program = [
        0xA9, CTRL_NMI_ENABLE,
        0x8D, 0x00, 0x20,
        0xEA,
    ]
    load_program(rom, 0x8000, program)

    cpu.pc = 0x8000
    cpu.s = 0xFD

    # Put the PPU close to VBlank so this validation stays small and deterministic.
    # The first two CPU instructions enable NMI before VBlank is reached.
    ppu.scanline = PPU_VBLANK_START_SCANLINE - 1
    # The next three instructions advance the PPU by:
    #   LDA #imm: 2 CPU cycles * 3 = 6 PPU cycles
    #   STA abs:  4 CPU cycles * 3 = 12 PPU cycles
    #   NOP:      2 CPU cycles * 3 = 6 PPU cycles
    # Total: 24 PPU cycles, exactly enough to enter VBlank here.
    ppu.cycle = PPU_CYCLES_PER_SCANLINE - 24

    # Step 1: LDA #$80. This prepares the value for PPUCTRL.
    cycles = console.step()
    assert cycles == 2
    assert cpu.a == CTRL_NMI_ENABLE
    assert cpu.pc == 0x8002
    assert ppu.ctrl == 0x00

    # Step 2: STA $2000. CpuBus routes this write to PPUCTRL.
    cycles = console.step()
    assert cycles == 4
    assert cpu.pc == 0x8005
    assert ppu.ctrl & CTRL_NMI_ENABLE

    # Step 3: NOP. PPU crosses into VBlank during this Console.step(), requests
    # NMI, and Console consumes it by calling CPU.interrupt_nmi().
    cycles = console.step()

    assert cycles == 2
    assert ppu.scanline == PPU_VBLANK_START_SCANLINE
    assert ppu.cycle == 0
    assert ppu.status & VBLANK_STARTED
    assert ppu.nmi_requested is False
    assert cpu.pc == 0x9000
    assert cpu.s == 0xFA

Funciones de test (1)

test_VALIDATION_tiny_program_enables_ppu_nmi_and_reaches_nmi_handler