Class R2C02

Defined in File 2C02.h

Nested Relationships

Nested Types

Inheritance Relationships

Base Type

public Component (Class Component)

Class Documentation

class R2C02 : public Component 

NES PPU emulation. Both foreground and background cycle-accurate rendering implemented, sprite 0 bug and other quirks are also emulated.

Ports: data “ppuBus” to control a communication on the PPU’s own bus; signal “INT” to send interrupts to the CPU (normally connected to the NMI). Connectors: data “cpuBus” to connect to the CPU, signal “CLK” to clock the PPU (standard rate is 21.477272 MHz ÷ 4).

Public Functions

R2C02(): Default constructor. Reset PPU status and rendering.

~R2C02() = default: Default destructor.

virtual void init(): Reset the PPU.

void clock(): Proceed one clock further in emulation. Works as a physical CLK input. 1 PPU cycle = 186 ns

void OAMDMA(uint8_t addr, uint8_t data)

PPU OAM DMA. Used to write to the OAM during DMA proccess.

Parameters

addr – OAM address.
data – Data to write.

std::vector<RGBPixel> getPalette(uint8_t paletteId)

uint8_t *getPaletteRAM()

std::vector<std::vector<RGBPixel>> getPatternTable(uint8_t colorType, uint8_t paletteId, uint8_t index, bool applyEffects = false): Get a pattern table.

std::vector<RGBPixel> getScreen(): Get a NES screen.

bool scanlineFinished() const

Is a scanline finished?

Returns: true if clock index >= 341

bool frameFinished() const

Is a frame finished?

Returns: true if scanline index >= 261

virtual std::vector<EmulatorWindow> getGUIs() override

Get GUI windows: metadata and rendering functions.

Note

For Component developer: If the component have a debugger or other GUI, return an arbitrary count of windows, they will be rendered on a load of a system which contains the component.

Returns: A vector of windows to be rendered.

Public Members

uint8_t primaryOAM[256]

uint8_t secondaryOAM[32]

uint8_t attrLatch[8]

uint8_t x[8]

uint8_t shiftLo[8]: 8 pairs of 8 bit shifters Pattern table data for up to 8 sprites to be rendered on the current scanline.

uint8_t shiftHi[8]

uint8_t allowShift[8]

uint8_t secondarySpriteId

uint8_t feedY

uint16_t feedTileAddress

uint8_t feedIndex

uint8_t ntByte

uint8_t atByte

uint16_t tileData

uint16_t shiftTileLo

uint16_t shiftTileHi

uint16_t shiftAttrLo

uint16_t shiftAttrHi

Protected Functions

void verticalIncrement()

void horizontalIncrement()

void verticalTransfer()

void horizontalTransfer()

void fetchNT()

void fetchAT()

void fetchTileLo()

void fetchTileHi()

void feedShifters()

void shiftShifters()

void evaluateSprites()

void fetchSprite(uint8_t offset)

uint8_t ppuBusRead(uint16_t addr)

Read from the internal bus.

Parameters: addr – Address to read from.
Returns: Data.

void ppuBusWrite(uint16_t addr, uint8_t data)

Write to the internal bus.

Parameters

addr – Address to write to.
data – Data to write.

RGBPixel getPixelColor(uint8_t paletteId, uint8_t pixel)

RGBPixel getColorFromPalette(uint8_t bgFg, uint8_t paletteNumber, uint8_t pixelValue)

RGBPixel applyPixelEffects(RGBPixel pixel) const

Protected Attributes

uint8_t m_dataBuffer = 0x00: Data lines sometimes act as a buffer because of their capacitance.

struct R2C02::internalRegisters_t m_internalRegisters

struct R2C02::[anonymous] m_spriteData

struct R2C02::[anonymous] m_backgroundData

struct R2C02::registers_t m_registers

bool m_scanlineReady = false

bool m_frameReady = false

bool m_oddScan = false: True if the odd field of the frame is being rendered (see interlaced video).

bool m_settingsEnableForeground = true: Foreground pixel placement enabled.

bool m_settingsEnableBackground = true: Background pixel placement enabled.

bool m_blockNMI = false: Suppress NMI generation and NMI flag setting. Used by a special case during reading NMI flag near the clock 1 of the scanline 241, which is when the NMI is supposed to generate. See read method for more information.

const RGBPixel m_colors2C02[64]: Default 2C02 color pallete.

const RGBPixel *m_colors = m_colors2C02 

uint8_t m_palettes[32]: 2C02 bus components: 0x0000 - 0x1FFF Pattern memory (CHR ROM) - on cartridge (sprites) 0x2000 - 0x3EFF Nametable memory (VRAM) - on cartridge or built-in (sprite locations) 0x3F00 - 0x3FFF Palette memory - built-in (colors)

int m_clock

int m_scanline

std::vector<std::vector<RGBPixel>> m_screen = {OUTPUT_BITMAP_HEIGHT, {OUTPUT_BITMAP_WIDTH, {0, 0, 0}}}

DataPort m_ppuBus

SignalPort m_INT

Protected Static Functions

static uint8_t saturate(uint8_t x, uint8_t y)

static uint8_t desaturate(uint8_t x, uint8_t y)

Protected Static Attributes

static constexpr AddressRange ADDR_PATTERN_TABLES = {0x0000, 0x1FFF}: Frame rendering: 256 341 xxxxxxxxxxxxxxx <- scanline -1 @@@@@@@— @@@@@@@— @@@@@@@—

static constexpr AddressRange ADDR_NAMETABLES = {0x2000, 0x2FFF}

static constexpr AddressRange ADDR_PALETTE_RAM = {0x3F00, 0x3FFF}

static const uint16_t OUTPUT_BITMAP_WIDTH = 256

static const uint16_t OUTPUT_BITMAP_HEIGHT = 240

static const uint16_t PATTERN_TABLE_TILE_ROW_COUNT = 16

static const uint16_t PATTERN_TABLE_TILE_COLUMN_COUNT = 16

static const uint16_t PATTERN_TABLE_PLANE_SIZE = 8

struct internalRegisters_t

Internal registers of the PPU for the rendering purposes. These are not exposed.

Public Members

uint16_t coarseX

uint16_t coarseY

uint16_t nameX

uint16_t nameY

uint16_t fineY

uint16_t padding

struct R2C02::internalRegisters_t::[anonymous]::STR bits

uint16_t data

union R2C02::internalRegisters_t::[anonymous] v: v = current VRAM address t = temporary VRAM address

union R2C02::internalRegisters_t::[anonymous] t

uint8_t x: Fine X scroll. 3 bits.

bool w: First or second write toggle. Shared by 0x2005 and 0x2006 register. 1 bit.

struct registers_t

“Public” registers accessible by the CPU.

Public Members

uint8_t nameX: Base nametable address, scroll X coordinate MSB. (1 = add 256)

uint8_t nameY: Base nametable address, scroll Y coordinate MSB. (1 = add 240)

uint8_t incMode: VRAM address increment per CPU R/W of PPUDATA. (0 = add 1, 1 = add 32).

uint8_t spriteAddress: Sprite pattern table address for 8x8 sprites.

uint8_t backgroundAddress: Background pattern table address.

uint8_t spriteSize: Sprite size (8x8, 8x16).

uint8_t masterSlave: PPU master/slave.

uint8_t nmi: Generate NMI on vblank.

struct R2C02::registers_t::[anonymous]::[anonymous] bits

uint8_t data

union R2C02::registers_t::[anonymous] ppuctrl: Controller (0x2000) - PPUCTRL Access: write Controls PPU operation.

uint8_t grayscale: Enable grayscale.

uint8_t showBackgroundLeft: Show background in leftmost 8 pixels.

uint8_t showSpritesLeft: Show sprites in leftmost 8 pixels.

uint8_t showBackground: Show bg.

uint8_t showSprites: Show sprites.

uint8_t eRed: Enhance red. (Green on PAL/Dendy.)

uint8_t eGreen: Enhance green. (Red on PAL/Dendy.)

uint8_t eBlue: Enhance blue.

struct R2C02::registers_t::[anonymous]::[anonymous] bits

union R2C02::registers_t::[anonymous] ppumask: Mask register (0x2001) - PPUMASK Access: write Controls the rendering of sprites and backgrounds and color effects.

uint8_t padding: Least sig. bits of previous value written to PPU register. Some Vs. systems return a constant that game checks.

uint8_t spriteOverflow: Buggy detection of the existence of more than 8 sprites on a scanline.

uint8_t spriteZeroHit: Nonzero pixel of sprite 0 overlaps nonzero background.

uint8_t vBlank: True if vblank started, cleared after reading this register.

struct R2C02::registers_t::[anonymous]::[anonymous] bits

union R2C02::registers_t::[anonymous] ppustatus: Status register (0x2002) - PPUSTATUS Access: read Reflects the state of the PPU.

uint8_t byte

uint8_t index

struct R2C02::registers_t::[anonymous]::[anonymous] bits

union R2C02::registers_t::[anonymous] oamAddress