refactor: move emulation logic into sys

1 files changed, 172 insertions, 0 deletions

diff --git a/lib/nes/sys/mapper.cc b/lib/nes/sys/mapper.cc
new file mode 100644
index 0000000..4951966
--- /dev/null
+++ b/lib/nes/sys/mapper.cc
@@ -0,0 +1,172 @@
+#include "nes/sys/mapper.hh"
+#include "nes/sys/cartridge.hh"
+
+namespace nes
+{
+	namespace
+	{
+		// -------------------------------------------------------------------------------------------------------------
+		// NROM
+		// -------------------------------------------------------------------------------------------------------------
+
+		class mapper_nrom final : public mapper
+		{
+		public:
+			explicit mapper_nrom() = default;
+
+			auto validate(cartridge& cartridge) -> status override
+			{
+				if (cartridge.get_ram_length() != 0x2000)
+				{
+					return status::error_invalid_ines_data;
+				}
+
+				if (cartridge.get_prg_rom_length() != 0x4000 && cartridge.get_prg_rom_length() != 0x8000)
+				{
+					return status::error_invalid_ines_data;
+				}
+
+				if (cartridge.get_chr_rom_length() != 0x2000)
+				{
+					return status::error_invalid_ines_data;
+				}
+
+				return status::success;
+			}
+
+			auto read_cpu(address const addr, cartridge& cartridge) -> std::uint8_t override
+			{
+				if (addr <= address{ 0x5FFF })
+				{
+					return 0x0;
+				}
+				if (addr <= address{ 0x7FFF })
+				{
+					return cartridge.get_ram()[addr.get_absolute() - 0x6000];
+				}
+				if (addr <= address{ 0xBFFF })
+				{
+					auto const rel = addr.get_absolute() - 0x8000u;
+					return cartridge.get_prg_rom()[rel];
+				}
+				if (addr <= address{ 0xFFFF })
+				{
+					auto rel = addr.get_absolute() - 0xC000u;
+					if (cartridge.get_prg_rom_length() > 0x4000) { rel += 0x4000; }
+					return cartridge.get_prg_rom()[rel];
+				}
+
+				return 0x0;
+			}
+
+			auto write_cpu(address const addr, std::uint8_t const value, cartridge& cartridge) -> void override
+			{
+				if (addr <= address{ 0x5FFF })
+				{
+					return;
+				}
+				if (addr <= address{ 0x7FFF })
+				{
+					cartridge.get_ram_mut()[addr.get_absolute() - 0x6000] = value;
+					return;
+				}
+			}
+
+			auto read_ppu(address const addr, cartridge& cartridge, std::uint8_t const* vram) -> std::uint8_t override
+			{
+				if (addr <= address{ 0x1FFF })
+				{
+					auto const rel = addr.get_absolute();
+					return cartridge.get_chr_rom()[rel];
+				}
+				if (addr <= address{ 0x3EFF })
+				{
+					return vram[mirrored_vram_address(addr, cartridge)];
+				}
+
+				return 0x0;
+			}
+
+			auto write_ppu(address const addr, std::uint8_t const value, cartridge& cartridge, std::uint8_t* vram) -> void override
+			{
+				if (addr <= address{ 0x1FFF })
+				{
+					return;
+				}
+				if (addr <= address{ 0x3EFF })
+				{
+					vram[mirrored_vram_address(addr, cartridge)] = value;
+					return;
+				}
+			}
+
+		private:
+			static auto mirrored_vram_address(address const addr, cartridge const& cartridge) -> unsigned
+			{
+				auto const rel = addr.get_absolute() % 0x1000u;
+
+				switch (cartridge.get_name_table_arrangement())
+				{
+					case name_table_arrangement::horizontal:
+						// $2000 = $2400, $2800 = $2c00
+						if (rel <= 0x3FF) { return 0x000u + (rel % 0x400u); }
+						if (rel <= 0x7FF) { return 0x000u + (rel % 0x400u); }
+						if (rel <= 0xBFF) { return 0x400u + (rel % 0x400u); }
+						if (rel <= 0xFFF) { return 0x400u + (rel % 0x400u); }
+						break;
+					case name_table_arrangement::vertical:
+						// $2000 = $2800, $2400 = $2c00
+						if (rel <= 0x3FF) { return 0x000u + (rel % 0x400u); }
+						if (rel <= 0x7FF) { return 0x400u + (rel % 0x400u); }
+						if (rel <= 0xBFF) { return 0x000u + (rel % 0x400u); }
+						if (rel <= 0xFFF) { return 0x400u + (rel % 0x400u); }
+						break;
+				}
+
+				return 0;
+			}
+		};
+
+		// -------------------------------------------------------------------------------------------------------------
+		// Invalid
+		// -------------------------------------------------------------------------------------------------------------
+
+		class mapper_invalid final : public mapper
+		{
+		public:
+			explicit mapper_invalid() = default;
+
+			auto validate(cartridge&) -> status override { return status::error_unsupported_mapper; }
+			auto read_cpu(address, cartridge&) -> std::uint8_t override { return 0; }
+			auto write_cpu(address, std::uint8_t, cartridge&) -> void override {}
+			auto read_ppu(address, cartridge&, std::uint8_t const*) -> std::uint8_t override { return 0; }
+			auto write_ppu(address, std::uint8_t, cartridge&, std::uint8_t*) -> void override {}
+		};
+	} // namespace
+
+	// -----------------------------------------------------------------------------------------------------------------
+	// Instances
+	// -----------------------------------------------------------------------------------------------------------------
+
+	auto mapper::invalid() -> mapper&
+	{
+		static auto instance = mapper_invalid{};
+		return instance;
+	}
+
+	auto mapper::get(std::uint8_t const number) -> mapper&
+	{
+		switch (number)
+		{
+			case 0x00:
+			{
+				static auto instance = mapper_nrom{};
+				return instance;
+			}
+			default:
+			{
+				return invalid();
+			}
+		}
+	}
+} // namespace nes
\ No newline at end of file