implement ppu io registers

1 files changed, 143 insertions, 0 deletions

diff --git a/src/nes/ppu.hh b/src/nes/ppu.hh
index 8f116c7..1d08614 100644
--- a/src/nes/ppu.hh
+++ b/src/nes/ppu.hh
@@ -4,17 +4,129 @@
 
 namespace nes
 {
+	class address;
 	class cpu;
 	class mapper;
+	class rgb;
 
 	class ppu
 	{
 		static constexpr auto vram_size = std::size_t{ 0x800 };
+		static constexpr auto oam_size = std::size_t{ 0x100 };
+		static constexpr auto palette_buffer_size = std::size_t{ 0x20 };
+		static constexpr auto status_mask = std::uint8_t{ 0b11100000 };
+		// Writes to some registers are ignored until this clock cycle.
+		static constexpr auto boot_up_cycles = cycle_count::from_ppu(29658);
+
+		enum class vram_increment
+		{
+			add_1_across = 0,
+			add_32_down = 1,
+		};
+
+		enum class sprite_size
+		{
+			_8x8 = 0,
+			_8x16 = 1,
+		};
+
+		enum class role
+		{
+			background = 0,
+			sprite = 1,
+		};
+
+		enum class color : std::uint8_t
+		{
+		};
+
+		union color_index
+		{
+			struct
+			{
+				unsigned color   : 2;
+				unsigned palette : 2;
+				role     role    : 1;
+			};
+			unsigned value;
+
+			explicit color_index(unsigned const value)
+				: value{ value }
+			{
+			}
+		};
 
 		cycle_count current_cycles_;
 		cpu& cpu_;
 		mapper& mapper_;
 		std::uint8_t vram_[vram_size]{};
+		std::uint8_t oam_[oam_size]{};
+		color palette_buffer_[palette_buffer_size]
+		{
+			color{ 0x09 }, color{ 0x01 }, color{ 0x00 }, color{ 0x01 },
+			color{ 0x00 }, color{ 0x02 }, color{ 0x02 }, color{ 0x0D },
+			color{ 0x08 }, color{ 0x10 }, color{ 0x08 }, color{ 0x24 },
+			color{ 0x00 }, color{ 0x00 }, color{ 0x04 }, color{ 0x2C },
+			color{ 0x09 }, color{ 0x01 }, color{ 0x34 }, color{ 0x03 },
+			color{ 0x00 }, color{ 0x04 }, color{ 0x00 }, color{ 0x14 },
+			color{ 0x08 }, color{ 0x3A }, color{ 0x00 }, color{ 0x02 },
+			color{ 0x00 }, color{ 0x20 }, color{ 0x2C }, color{ 0x08 },
+		};
+		std::uint8_t latch_{}; // The last read/written IO register value, returned when reading write-only registers.
+		union
+		{
+			struct
+			{
+				bool                 : 1;
+				bool                 : 1;
+				bool                 : 1;
+				bool                 : 1;
+				bool                 : 1;
+				bool sprite_overflow : 1;
+				bool sprite_0_hit    : 1;
+				bool vblank          : 1;
+			};
+			std::uint8_t value{ 0b00000000 };
+		} status_{};
+		union
+		{
+			struct
+			{
+				std::uint8_t   base_name_table          : 2; // Base nametable address.
+				vram_increment vram_increment           : 1; // VRAM increment per CPU read/write of PPUDATA.
+				std::uint8_t   sprite_pattern_table     : 1; // Sprite pattern table address for 8x8 sprites.
+				std::uint8_t   background_pattern_table : 1; // Background pattern table address.
+				sprite_size    sprite_size              : 1; // Sprite size.
+				bool           enable_ext_pin           : 1; // PPU master/slave select.
+				bool           vblank_nmi               : 1; // Enable/disable Vblank NMI
+			};
+			std::uint8_t value{ 0b00000000 };
+		} control_{};
+		union
+		{
+			struct
+			{
+				bool grayscale             : 1; // Enable/disable grayscale.
+				bool show_background_start : 1; // Show background in leftmost 8 pixels of screen.
+				bool show_sprites_start    : 1; // Show sprites in leftmost 8 pixels of screen.
+				bool enable_background     : 1; // Enable background rendering.
+				bool enable_sprites        : 1; // Enable sprite rendering.
+				bool emphasize_red         : 1; // Emphasize red.
+				bool emphasize_green       : 1; // Emphasize green.
+				bool emphasize_blue        : 1; // Emphasize blue.
+			};
+			std::uint8_t value{ 0b00000000 };
+		} mask_{};
+		struct
+		{
+			// See https://www.nesdev.org/wiki/PPU_scrolling#PPU_internal_registers
+			std::uint16_t v{}; // Current VRAM address (15 bits)
+			std::uint16_t t{}; // Temporary VRAM address (15 bits)
+			std::uint8_t  x{}; // Fine X scroll (3 bits)
+			bool          w{}; // Second write toggle (1 bit)
+		} internal_{};
+		std::uint8_t oamaddr_{}; // Address accessed by IO registers
+		std::uint8_t ppudata_read_buffer_{}; // Delays PPUDATA reads by one.
 
 	public:
 		explicit ppu(cpu& cpu, mapper& mapper);
@@ -25,5 +137,36 @@ namespace nes
 		auto operator=(ppu&&) -> ppu& = delete;
 
 		auto step_to(cycle_count) -> void;
+
+		// Memory access
+
+		auto read8(address) -> std::uint8_t;
+		auto write8(address, std::uint8_t) -> void;
+
+		// IO registers
+
+		auto read_latch() -> std::uint8_t;
+		auto read_ppustatus() -> std::uint8_t;
+		auto read_oamdata() -> std::uint8_t;
+		auto read_ppudata() -> std::uint8_t;
+
+		auto write_latch(std::uint8_t) -> void;
+		auto write_ppuctrl(std::uint8_t) -> void;
+		auto write_ppuscroll(std::uint8_t) -> void;
+		auto write_ppumask(std::uint8_t) -> void;
+		auto write_ppuaddr(std::uint8_t) -> void;
+		auto write_ppudata(std::uint8_t) -> void;
+		auto write_oamaddr(std::uint8_t) -> void;
+		auto write_oamdata(std::uint8_t) -> void;
+		auto write_oamdma(std::uint8_t) -> void;
+
+	private:
+		auto step() -> void;
+
+		// Helpers
+
+		auto increment_vram() -> void;
+		auto get_color(color_index) -> color&;
+		auto resolve_color(color) -> rgb;
 	};
 } // namespace nes
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