copy reference implementation

1 files changed, 737 insertions, 0 deletions

diff --git a/lib/nes/ref/ppu.cc b/lib/nes/ref/ppu.cc
new file mode 100644
index 0000000..0856093
--- /dev/null
+++ b/lib/nes/ref/ppu.cc
@@ -0,0 +1,737 @@
+#include "nes/ref/ppu.hh"
+#include "nes/ref/cpu.hh"
+#include "nes/ref/mapper.hh"
+#include "nes/util/address.hh"
+#include "nes/util/display.hh"
+#include "nes/util/rgb.hh"
+#include "nes/util/snapshot.hh"
+#include "nes/util/debug.hh"
+
+namespace nes::ref
+{
+	ppu::ppu(cpu& cpu, mapper& mapper, display& display)
+		: cpu_{ cpu }
+		, mapper_{ mapper }
+		, display_{ display }
+	{
+	}
+
+	auto ppu::build_snapshot(snapshot& snapshot) -> void
+	{
+		snapshot.vram = std::vector(std::begin(vram_), std::end(vram_));
+		snapshot.oam = std::vector(std::begin(oam_), std::end(oam_));
+	}
+
+	auto ppu::step() -> void
+	{
+		// See https://www.nesdev.org/wiki/PPU_rendering
+		// Based on: https://github.com/fogleman/nes/blob/master/nes/ppu.go
+
+		auto const enable_rendering = mask_.enable_background || mask_.enable_sprites;
+
+		current_cycles_ += cycle_count::from_ppu(1);
+		scanline_cycle_ += 1;
+		if (enable_rendering && !even_frame_ && scanline_ == 261 && scanline_cycle_ == 340)
+		{
+			current_cycles_ += cycle_count::from_ppu(1);
+			scanline_cycle_ += 1;
+		}
+		if (scanline_cycle_ == 341)
+		{
+			scanline_cycle_ = 0;
+			scanline_ += 1;
+
+			if (scanline_ == 262)
+			{
+				scanline_ = 0;
+				even_frame_ = !even_frame_;
+			}
+		}
+
+		auto const pre_line = scanline_ == 261;
+		auto const visible_line = scanline_ < 240;
+		auto const render_line = pre_line || visible_line;
+		auto const pre_fetch_cycle = scanline_cycle_ >= 321 && scanline_cycle_ <= 336;
+		auto const visible_cycle = scanline_cycle_ >= 1 && scanline_cycle_ <= 256;
+		auto const fetch_cycle = pre_fetch_cycle || visible_cycle;
+
+		// Background Logic
+		if (enable_rendering)
+		{
+			if (visible_line && visible_cycle)
+			{
+				render_pixel();
+			}
+
+			if (render_line && fetch_cycle)
+			{
+				tile_data_ <<= 4;
+				switch (scanline_cycle_ % 8)
+				{
+					case 1:
+						fetch_name_table_byte();
+						break;
+					case 3:
+						fetch_attribute_table_byte();
+						break;
+					case 5:
+						fetch_low_tile_byte();
+						break;
+					case 7:
+						fetch_high_tile_byte();
+						break;
+					case 0:
+						store_tile_data();
+						break;
+					default:
+						break;
+				}
+			}
+
+			if (pre_line && scanline_cycle_ >= 280 && scanline_cycle_ <= 304)
+			{
+				copy_y();
+			}
+
+			if (render_line)
+			{
+				if (fetch_cycle && scanline_cycle_ % 8 == 0)
+				{
+					increment_x();
+				}
+				if (scanline_cycle_ == 256)
+				{
+					increment_y();
+				}
+				if (scanline_cycle_ == 257)
+				{
+					copy_x();
+				}
+			}
+		}
+
+		// Sprite Logic
+		if (enable_rendering)
+		{
+			if (scanline_cycle_ == 257)
+			{
+				if (visible_line)
+				{
+					evaluate_sprites();
+				}
+				else
+				{
+					sprite_count_ = 0;
+				}
+			}
+		}
+
+		// Vblank Logic
+		if (scanline_ == 241 && scanline_cycle_ == 1)
+		{
+			display_.switch_buffers();
+			status_.vblank = true;
+			nmi_change();
+		}
+		if (pre_line && scanline_cycle_ == 1)
+		{
+			status_.vblank = false;
+			status_.sprite_zero_hit = false;
+			status_.sprite_overflow = false;
+		}
+	}
+
+	auto ppu::render_pixel() -> void
+	{
+		auto const x = scanline_cycle_ - 1;
+		auto const y = scanline_;
+
+		auto background_color = color_index{ 0 };
+		if (mask_.enable_background)
+		{
+			auto const tile_data = static_cast<std::uint32_t>(tile_data_ >> 32);
+			background_color = color_index{ static_cast<std::uint8_t>((tile_data >> ((7 - internal_.x) * 4)) & 0xF) };
+			background_color.role = role::background;
+		}
+
+		auto foreground = sprite{};
+		auto foreground_color = color_index{ 0 };
+		if (mask_.enable_sprites)
+		{
+			for (auto i = unsigned{ 0 }; i < sprite_count_; ++i)
+			{
+				auto const s = sprites_[i];
+				auto const offset = static_cast<int>(x) - static_cast<int>(s.position);
+				if (offset < 0 || offset > 7) { continue; }
+				auto const color = color_index{ static_cast<std::uint8_t>((s.pattern >> ((7 - offset) * 4)) & 0xF) };
+				if (color.color == 0) { continue; }
+
+				foreground = s;
+				foreground_color = color;
+				foreground_color.role = role::sprite;
+				break;
+			}
+		}
+
+		auto has_background = background_color.color != 0;
+		auto has_foreground = foreground_color.color != 0;
+
+		if (x < 8 && !mask_.show_background_start) { has_background = false; }
+		if (x < 8 && !mask_.show_sprites_start) { has_foreground = false; }
+
+		auto color = color_index{ 0 };
+		if (!has_background && has_foreground)
+		{
+			color = foreground_color;
+		}
+		if (has_background && !has_foreground)
+		{
+			color = background_color;
+		}
+		if (has_background && has_foreground)
+		{
+			if (foreground.is_sprite_zero && x < 255)
+			{
+				status_.sprite_zero_hit = true;
+			}
+
+			color = foreground.is_in_front ? foreground_color : background_color;
+		}
+
+		display_.set(x, y, resolve_color(get_color(color)));
+	}
+
+	auto ppu::fetch_name_table_byte() -> void
+	{
+		auto const addr = static_cast<std::uint16_t>(0x2000 | (internal_.v & 0x0FFF));
+		name_table_byte_ = read8(address{ addr });
+	}
+
+	auto ppu::fetch_attribute_table_byte() -> void
+	{
+		auto const v = internal_.v;
+		auto const addr = static_cast<std::uint16_t>(0x23C0 | (v & 0x0C00) | ((v >> 4) & 0x38) | ((v >> 2) & 0x07));
+		auto const shift = ((v >> 4) & 4) | (v & 2);
+		attribute_table_byte_ = static_cast<std::uint8_t>(((read8(address{ addr }) >> shift) & 3) << 2);
+	}
+
+	auto ppu::fetch_low_tile_byte() -> void
+	{
+		auto const fine_y = (internal_.v >> 12) & 7;
+		auto const table = control_.background_pattern_table;
+		auto const tile = name_table_byte_;
+		auto const addr = static_cast<std::uint16_t>(0x1000 * table + 16 * tile + fine_y);
+		low_tile_byte_ = read8(address{ addr });
+	}
+
+	auto ppu::fetch_high_tile_byte() -> void
+	{
+		auto const fine_y = (internal_.v >> 12) & 7;
+		auto const table = control_.background_pattern_table;
+		auto const tile = name_table_byte_;
+		auto const addr = static_cast<std::uint16_t>(0x1000 * table + 16 * tile + fine_y);
+		high_tile_byte_ = read8(address{ addr } + 8);
+	}
+
+	auto ppu::store_tile_data() -> void
+	{
+		auto data = std::uint32_t{ 0 };
+		for (auto i = unsigned{ 0 }; i < 8; ++i)
+		{
+			auto const p1 = (low_tile_byte_ & 0x80) >> 7;
+			auto const p2 = (high_tile_byte_ & 0x80) >> 6;
+			low_tile_byte_ <<= 1;
+			high_tile_byte_ <<= 1;
+			data <<= 4;
+			data |= attribute_table_byte_ | p1 | p2;
+		}
+		tile_data_ |= data;
+	}
+
+	auto ppu::increment_x() -> void
+	{
+		// If coarse X == 31
+		if ((internal_.v & 0x1F) == 0x1F)
+		{
+			// Coarse X = 0
+			// TODO: Check
+			// internal_.v &= ~0x1F;
+			   internal_.v &= 0xFFE0;
+			// Switch horizontal nametable
+			internal_.v ^= 0x400;
+		}
+		else
+		{
+			// Increment coarse X
+			internal_.v += 1;
+		}
+	}
+
+	auto ppu::increment_y() -> void
+	{
+		// If fine Y == 7
+		if ((internal_.v & 0x7000) == 0x7000)
+		{
+			// Fine Y = 0
+			internal_.v &= 0x8FFF;
+			// Let y = coarse Y
+			auto y = (internal_.v & 0x03E0) >> 5;
+			if (y == 29)
+			{
+				// Coarse Y = 0
+				y = 0;
+				// Switch vertical nametable
+				internal_.v ^= 0x0800;
+			}
+			else if (y == 31)
+			{
+				// Coarse Y = 0, nametable not switched
+				y = 0;
+			}
+			else
+			{
+				// Increment coarse Y
+				y += 1;
+			}
+			// Put coarse Y back into v
+			// TODO: Check
+			// internal_.v &= ~0x03E0;
+			   internal_.v &= 0xFC1F;
+			internal_.v |= y << 5;
+		}
+		else
+		{
+			// Increment fine Y
+			internal_.v += 0x1000;
+		}
+	}
+
+	auto ppu::copy_x() -> void
+	{
+		internal_.v = (internal_.v & 0xFBE0) | (internal_.t & 0x041F);
+	}
+
+	auto ppu::copy_y() -> void
+	{
+		internal_.v = (internal_.v & 0x841F) | (internal_.t & 0x7BE0);
+	}
+
+	auto ppu::evaluate_sprites() -> void
+	{
+		auto const height = sprite_height();
+		sprite_count_ = 0;
+		for (auto i = unsigned{ 0 }; i < 64; ++i)
+		{
+			auto const y = oam_[i * 4 + 0];
+			auto const a = oam_[i * 4 + 2];
+			auto const x = oam_[i * 4 + 3];
+			auto const row = static_cast<int>(scanline_) - static_cast<int>(y);
+			if (row < 0 || row >= height) { continue; }
+
+			if (sprite_count_ < 8)
+			{
+				sprites_[sprite_count_].pattern = fetch_sprite_pattern(i, row);
+				sprites_[sprite_count_].position = x;
+				// TODO: Check
+				// sprites_[sprite_count_].is_in_front = a & 0b00100000;
+				   sprites_[sprite_count_].is_in_front = ((a >> 5) & 1) == 0;
+				sprites_[sprite_count_].is_sprite_zero = i == 0;
+				sprite_count_ += 1;
+			}
+			else
+			{
+				status_.sprite_overflow = true;
+				break;
+			}
+		}
+	}
+
+	auto ppu::fetch_sprite_pattern(unsigned const i, unsigned row) -> std::uint32_t
+	{
+		auto tile = oam_[i * 4 + 1];
+		auto const attributes = oam_[i * 4 + 2];
+		auto const flip_vertical = (attributes & 0x80) == 0x80;
+		if (flip_vertical) { row = sprite_height() - 1 - row; }
+		auto addr = address{};
+		switch (control_.sprite_size)
+		{
+			case sprite_size::_8x8:
+			{
+				auto const table = control_.sprite_pattern_table;
+				addr = address{ static_cast<std::uint16_t>(0x1000 * table + 16 * tile + row) };
+				break;
+			}
+			case sprite_size::_8x16:
+			{
+				auto const table = tile & 1;
+				tile &= 0xFE;
+				if (row > 7)
+				{
+					tile += 1;
+					row -= 8;
+				}
+				addr = address{ static_cast<std::uint16_t>(0x1000 * table + 16 * tile + row) };
+				break;
+			}
+		}
+
+		auto const a = (attributes & 3) << 2;
+		auto low_tile_byte = read8(addr);
+		auto high_tile_byte = read8(addr + 8);
+		auto data = std::uint32_t{ 0 };
+		for (auto j = unsigned{ 0 }; j < 8; ++j)
+		{
+			auto const flip_horizontal = (attributes & 0x40) == 0x40;
+			std::uint8_t p1, p2;
+			if (flip_horizontal)
+			{
+				p1 = (low_tile_byte & 1) << 0;
+				p2 = (high_tile_byte & 1) << 1;
+				low_tile_byte >>= 1;
+				high_tile_byte >>= 1;
+			}
+			else
+			{
+				p1 = (low_tile_byte & 0x80) >> 7;
+				p2 = (high_tile_byte & 0x80) >> 6;
+				low_tile_byte <<= 1;
+				high_tile_byte <<= 1;
+			}
+			data <<= 4;
+			data |= a | p1 | p2;
+		}
+
+		return data;
+	}
+
+	// -----------------------------------------------------------------------------------------------------------------
+	// Memory Access
+	// -----------------------------------------------------------------------------------------------------------------
+
+	//
+	// See: https://www.nesdev.org/wiki/PPU_memory_map
+	//
+
+	auto ppu::read8(address addr) -> std::uint8_t
+	{
+		addr = addr % 0x4000; // PPU only has 16 KiB addresses.
+		if (addr <= address{ 0x3EFF }) { return mapper_.read_ppu(addr, vram_); }
+		if (addr <= address{ 0x3FFF })
+		{
+			auto const index = color_index{ static_cast<std::uint8_t>(addr.get_absolute() % 0x20) };
+			auto const color = get_color(index);
+			return static_cast<std::uint8_t>(color);
+		}
+
+		return 0x0;
+	}
+
+	auto ppu::write8(address addr, std::uint8_t const value) -> void
+	{
+		addr = addr % 0x4000; // PPU only has 16 KiB addresses.
+		if (addr <= address{ 0x3EFF })
+		{
+			mapper_.write_ppu(addr, vram_, value);
+			return;
+		}
+		if (addr <= address{ 0x3FFF })
+		{
+			auto const index = color_index{ static_cast<std::uint8_t>(addr.get_absolute() % 0x20) };
+			get_color(index) = color{ value };
+			return;
+		}
+	}
+
+	// -----------------------------------------------------------------------------------------------------------------
+	// IO Registers
+	// -----------------------------------------------------------------------------------------------------------------
+
+	//
+	// See: https://www.nesdev.org/wiki/PPU_registers
+	//
+
+	auto ppu::read_latch() -> std::uint8_t
+	{
+		return latch_;
+	}
+
+	auto ppu::read_ppustatus() -> std::uint8_t
+	{
+		auto const base = latch_ & ~status_mask;
+		auto const res = base | (status_.value & status_mask);
+		NES_DEBUG_LOG(ppu, "PPUSTATUS -> {:#2x}", res);
+
+		status_.vblank = false;
+		internal_.w = false;
+
+		write_latch(res);
+		return res;
+	}
+
+	auto ppu::read_oamdata() -> std::uint8_t
+	{
+		auto res = oam_[oamaddr_];
+		if ((oamaddr_ & 0x3) == 0x2)
+		{
+			res &= 0xE3;
+		}
+		NES_DEBUG_LOG(ppu, "OAMDATA -> {:#2x}", res);
+		write_latch(res);
+		return res;
+	}
+
+	auto ppu::read_ppudata() -> std::uint8_t
+	{
+		auto const addr = address{ internal_.v };
+		auto res = read8(addr);
+		write_latch(ppudata_read_buffer_);
+
+		if (addr % 0x4000 <= address{ 0x3EFF })
+		{
+			std::swap(res, ppudata_read_buffer_);
+		}
+		else
+		{
+			// For palette buffers: buffer the mirrored nametable instead.
+			ppudata_read_buffer_ = read8(addr - 0x1000);
+		}
+
+		NES_DEBUG_LOG(ppu, "PPUDATA -> {:#2x}", res);
+		increment_vram();
+		return res;
+	}
+
+	auto ppu::write_latch(std::uint8_t const value) -> void
+	{
+		latch_ = value;
+	}
+
+	auto ppu::write_ppuctrl(std::uint8_t const value) -> void
+	{
+		write_latch(value);
+		if (current_cycles_ > boot_up_cycles)
+		{
+			NES_DEBUG_LOG(ppu, "PPUCTRL <- {:#2x}", value);
+			control_.value = value;
+			internal_.t = (internal_.t & 0xF3FF) | ((value & 0x03) << 10);
+			nmi_change();
+		}
+	}
+
+	auto ppu::write_ppuscroll(std::uint8_t const value) -> void
+	{
+		write_latch(value);
+		if (current_cycles_ > boot_up_cycles)
+		{
+			NES_DEBUG_LOG(ppu, "PPUSCROLL <- {:#2x}", value);
+			if (!internal_.w)
+			{
+				// First write -> x value.
+				internal_.t = (internal_.t & 0b1111111111100000) | (value >> 3);
+				internal_.x = value & 0b00000111;
+			}
+			else
+			{
+				// Second write -> y value.
+				internal_.t = (internal_.t & 0b1000111111111111) | ((value & 0b00000111) << 12);
+				internal_.t = (internal_.t & 0b1111110000011111) | ((value & 0b11111000) << 2);
+			}
+
+			internal_.w = !internal_.w;
+		}
+	}
+
+	auto ppu::write_ppumask(std::uint8_t const value) -> void
+	{
+		write_latch(value);
+		if (current_cycles_ > boot_up_cycles)
+		{
+			NES_DEBUG_LOG(ppu, "PPUMASK <- {:#2x}", value);
+			mask_.value = value;
+		}
+	}
+
+	auto ppu::write_ppuaddr(std::uint8_t const value) -> void
+	{
+		write_latch(value);
+		if (current_cycles_ > boot_up_cycles)
+		{
+			NES_DEBUG_LOG(ppu, "PPUADDR <- {:#2x}", value);
+			if (!internal_.w)
+			{
+				// First write.
+				internal_.t = (internal_.t & 0b1000000011111111) | ((value & 0b00111111) << 8);
+			}
+			else
+			{
+				// Second write.
+				internal_.t = (internal_.t & 0b1111111100000000) | ((value & 0b11111111) << 0);
+				internal_.v = internal_.t;
+			}
+
+			internal_.w = !internal_.w;
+		}
+	}
+
+	auto ppu::write_ppudata(std::uint8_t const value) -> void
+	{
+		NES_DEBUG_LOG(ppu, "PPUDATA <- {:#2x} (address: {:#4x})", value, internal_.v);
+		write_latch(value);
+		write8(address{ internal_.v }, value);
+		increment_vram();
+	}
+
+	auto ppu::write_oamaddr(std::uint8_t const value) -> void
+	{
+		NES_DEBUG_LOG(ppu, "OAMADDR <- {:#2x}", value);
+		write_latch(value);
+		oamaddr_ = value;
+	}
+
+	auto ppu::write_oamdata(std::uint8_t const value) -> void
+	{
+		NES_DEBUG_LOG(ppu, "OAMDATA <- {:#2x}", value);
+		write_latch(value);
+		oam_[oamaddr_] = value;
+		oamaddr_ += 1;
+	}
+
+	auto ppu::write_oamdma(std::uint8_t const value) -> void
+	{
+		// TODO: Do this in CPU::step instead in case there's an NMI?
+		NES_DEBUG_LOG(ppu, "OAMDMA <- {:#2x}", value);
+		auto addr = address{ value, 0x00 };
+		for (auto i = unsigned{ 0 }; i < 256; ++i)
+		{
+			oam_[oamaddr_] = cpu_.read8(addr);
+			oamaddr_ += 1;
+			addr = addr + 1;
+		}
+
+		auto const stalled_cycles = cycle_count::from_cpu((cpu_.get_cycles().to_cpu() % 2 == 0) ? 513 : 514);
+		cpu_.stall_cycles(stalled_cycles);
+	}
+
+	// -----------------------------------------------------------------------------------------------------------------
+	// Helpers
+	// -----------------------------------------------------------------------------------------------------------------
+
+	auto ppu::nmi_change() -> void
+	{
+		if (control_.vblank_nmi && status_.vblank)
+		{
+			cpu_.trigger_nmi();
+		}
+	}
+
+	auto ppu::sprite_height() -> unsigned
+	{
+		switch (control_.sprite_size)
+		{
+			case sprite_size::_8x8:
+				return 8;
+			case sprite_size::_8x16:
+				return 16;
+		}
+
+		return 8;
+	}
+
+	auto ppu::increment_vram() -> void
+	{
+		switch (control_.vram_increment)
+		{
+			case vram_increment::add_1_across:
+				internal_.v += 1;
+				break;
+			case vram_increment::add_32_down:
+				internal_.v += 32;
+				break;
+		}
+	}
+
+	auto ppu::get_color(color_index index) -> color&
+	{
+		// See https://www.nesdev.org/wiki/PPU_palettes
+		index.value = index.value % 0x20;
+		if (index.color == 0)
+		{
+			// The first color is mirrored between background and foreground palettes.
+			index.role = role::background;
+		}
+		return palette_buffer_[index.value];
+	}
+
+	auto ppu::resolve_color(color const color) -> rgb
+	{
+		auto const index = static_cast<std::uint8_t>(color);
+		switch (index & 0x3F)
+		{
+			case 0x00: return rgb::from_hex(0x666666);
+			case 0x01: return rgb::from_hex(0x002A88);
+			case 0x02: return rgb::from_hex(0x1412A7);
+			case 0x03: return rgb::from_hex(0x3B00A4);
+			case 0x04: return rgb::from_hex(0x5C007E);
+			case 0x05: return rgb::from_hex(0x6E0040);
+			case 0x06: return rgb::from_hex(0x6C0600);
+			case 0x07: return rgb::from_hex(0x561D00);
+			case 0x08: return rgb::from_hex(0x333500);
+			case 0x09: return rgb::from_hex(0x0B4800);
+			case 0x0A: return rgb::from_hex(0x005200);
+			case 0x0B: return rgb::from_hex(0x004F08);
+			case 0x0C: return rgb::from_hex(0x00404D);
+			case 0x0D: return rgb::from_hex(0x000000);
+			case 0x0E: return rgb::from_hex(0x000000);
+			case 0x0F: return rgb::from_hex(0x000000);
+			case 0x10: return rgb::from_hex(0xADADAD);
+			case 0x11: return rgb::from_hex(0x155FD9);
+			case 0x12: return rgb::from_hex(0x4240FF);
+			case 0x13: return rgb::from_hex(0x7527FE);
+			case 0x14: return rgb::from_hex(0xA01ACC);
+			case 0x15: return rgb::from_hex(0xB71E7B);
+			case 0x16: return rgb::from_hex(0xB53120);
+			case 0x17: return rgb::from_hex(0x994E00);
+			case 0x18: return rgb::from_hex(0x6B6D00);
+			case 0x19: return rgb::from_hex(0x388700);
+			case 0x1A: return rgb::from_hex(0x0C9300);
+			case 0x1B: return rgb::from_hex(0x008F32);
+			case 0x1C: return rgb::from_hex(0x007C8D);
+			case 0x1D: return rgb::from_hex(0x000000);
+			case 0x1E: return rgb::from_hex(0x000000);
+			case 0x1F: return rgb::from_hex(0x000000);
+			case 0x20: return rgb::from_hex(0xFFFEFF);
+			case 0x21: return rgb::from_hex(0x64B0FF);
+			case 0x22: return rgb::from_hex(0x9290FF);
+			case 0x23: return rgb::from_hex(0xC676FF);
+			case 0x24: return rgb::from_hex(0xF36AFF);
+			case 0x25: return rgb::from_hex(0xFE6ECC);
+			case 0x26: return rgb::from_hex(0xFE8170);
+			case 0x27: return rgb::from_hex(0xEA9E22);
+			case 0x28: return rgb::from_hex(0xBCBE00);
+			case 0x29: return rgb::from_hex(0x88D800);
+			case 0x2A: return rgb::from_hex(0x5CE430);
+			case 0x2B: return rgb::from_hex(0x45E082);
+			case 0x2C: return rgb::from_hex(0x48CDDE);
+			case 0x2D: return rgb::from_hex(0x4F4F4F);
+			case 0x2E: return rgb::from_hex(0x000000);
+			case 0x2F: return rgb::from_hex(0x000000);
+			case 0x30: return rgb::from_hex(0xFFFEFF);
+			case 0x31: return rgb::from_hex(0xC0DFFF);
+			case 0x32: return rgb::from_hex(0xD3D2FF);
+			case 0x33: return rgb::from_hex(0xE8C8FF);
+			case 0x34: return rgb::from_hex(0xFBC2FF);
+			case 0x35: return rgb::from_hex(0xFEC4EA);
+			case 0x36: return rgb::from_hex(0xFECCC5);
+			case 0x37: return rgb::from_hex(0xF7D8A5);
+			case 0x38: return rgb::from_hex(0xE4E594);
+			case 0x39: return rgb::from_hex(0xCFEF96);
+			case 0x3A: return rgb::from_hex(0xBDF4AB);
+			case 0x3B: return rgb::from_hex(0xB3F3CC);
+			case 0x3C: return rgb::from_hex(0xB5EBF2);
+			case 0x3D: return rgb::from_hex(0xB8B8B8);
+			case 0x3E: return rgb::from_hex(0x000000);
+			case 0x3F: return rgb::from_hex(0x000000);
+			default: return rgb::from_hex(0x000000);
+		}
+	}
+} // namespace nes::ref
\ No newline at end of file