copy reference implementation

1 files changed, 134 insertions, 0 deletions

diff --git a/lib/nes/ref/mapper.cc b/lib/nes/ref/mapper.cc
new file mode 100644
index 0000000..7e4cffe
--- /dev/null
+++ b/lib/nes/ref/mapper.cc
@@ -0,0 +1,134 @@
+#include "nes/ref/mapper.hh"
+#include "nes/ref/cartridge.hh"
+#include <iostream>
+
+namespace nes::ref
+{
+	mapper::mapper(
+		cartridge& cartridge,
+		read_cpu_func const read_cpu, write_cpu_func const write_cpu,
+		read_ppu_func const read_ppu, write_ppu_func const write_ppu)
+		: cartridge_{ cartridge }
+		, read_cpu_{ read_cpu }
+		, write_cpu_{ write_cpu }
+		, read_ppu_{ read_ppu }
+		, write_ppu_{ write_ppu }
+	{
+	}
+
+	auto mapper::select(cartridge& cartridge) -> mapper
+	{
+		switch (cartridge.get_mapper_number())
+		{
+			case 0x00:
+				return mapper{
+					cartridge,
+					&mapper::nrom_read_cpu, &mapper::nrom_write_cpu,
+					&mapper::nrom_read_ppu, &mapper::nrom_write_ppu };
+			default:
+				std::cerr << "Mapper not implemented: " << std::hex << cartridge.get_mapper_number() << std::endl;
+				std::abort();
+		}
+	}
+
+	// -----------------------------------------------------------------------------------------------------------------
+	// NROM
+	// -----------------------------------------------------------------------------------------------------------------
+
+	auto mapper::nrom_read_cpu(address const addr) -> std::uint8_t
+	{
+		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() - 0x8000;
+			if (rel >= cartridge_.get_prg_rom_length()) { return 0x0; }
+
+			return cartridge_.get_prg_rom()[rel];
+		}
+		if (addr <= address{ 0xFFFF })
+		{
+			auto rel = addr.get_absolute() - 0xC000;
+			if (cartridge_.get_prg_rom_length() > 0x4000) { rel += 0x4000; }
+			if (rel >= cartridge_.get_prg_rom_length()) { return 0x0; }
+
+			return cartridge_.get_prg_rom()[rel];
+		}
+
+		return 0x0;
+	}
+
+	auto mapper::nrom_write_cpu(address const addr, std::uint8_t const value) -> void
+	{
+		if (addr <= address{ 0x5FFF })
+		{
+			return;
+		}
+		if (addr <= address{ 0x7FFF })
+		{
+			cartridge_.get_ram_mut()[addr.get_absolute() - 0x6000] = value;
+			return;
+		}
+	}
+
+	auto mapper::nrom_read_ppu(address const addr, std::uint8_t const* vram) -> std::uint8_t
+	{
+		if (addr <= address{ 0x1FFF })
+		{
+			auto const rel = addr.get_absolute();
+			if (rel >= cartridge_.get_chr_rom_length()) { return 0x0; }
+
+			return cartridge_.get_chr_rom()[rel];
+		}
+		if (addr <= address{ 0x3EFF })
+		{
+			return vram[nrom_mirrored_vram_address(addr)];
+		}
+
+		return 0x0;
+	}
+
+	auto mapper::nrom_write_ppu(address const addr, std::uint8_t* vram, std::uint8_t const value) -> void
+	{
+		if (addr <= address{ 0x1FFF })
+		{
+			return;
+		}
+		if (addr <= address{ 0x3EFF })
+		{
+			vram[nrom_mirrored_vram_address(addr)] = value;
+			return;
+		}
+	}
+
+	auto mapper::nrom_mirrored_vram_address(address const addr) const -> unsigned
+	{
+		auto const rel = addr.get_absolute() % 0x1000;
+
+		switch (cartridge_.get_name_table_arrangement())
+		{
+			case name_table_arrangement::horizontal:
+				// $2000 = $2400, $2800 = $2c00
+				if (rel <= 0x3FF) { return 0x000 + (rel % 0x400); }
+				if (rel <= 0x7FF) { return 0x000 + (rel % 0x400); }
+				if (rel <= 0xBFF) { return 0x400 + (rel % 0x400); }
+				if (rel <= 0xFFF) { return 0x400 + (rel % 0x400); }
+				break;
+			case name_table_arrangement::vertical:
+				// $2000 = $2800, $2400 = $2c00
+				if (rel <= 0x3FF) { return 0x000 + (rel % 0x400); }
+				if (rel <= 0x7FF) { return 0x400 + (rel % 0x400); }
+				if (rel <= 0xBFF) { return 0x000 + (rel % 0x400); }
+				if (rel <= 0xFFF) { return 0x400 + (rel % 0x400); }
+				break;
+		}
+
+		return 0;
+	}
+} // namespace nes::ref
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