implement cpu

1 files changed, 61 insertions, 0 deletions

diff --git a/src/nes/mapper.cc b/src/nes/mapper.cc
new file mode 100644
index 0000000..a540dbf
--- /dev/null
+++ b/src/nes/mapper.cc
@@ -0,0 +1,61 @@
+#include "nes/mapper.hh"
+#include "nes/cartridge.hh"
+#include <iostream>
+
+namespace nes
+{
+	mapper::mapper(cartridge& cartridge, read_func const read, write_func const write)
+		: cartridge_{ cartridge }
+		, read_{ read }
+		, write_{ write }
+	{
+	}
+
+	auto mapper::select(cartridge& cartridge) -> mapper
+	{
+		switch (cartridge.get_mapper_number())
+		{
+			case 0x00:
+				return mapper{ cartridge, &mapper::nrom_read, &mapper::nrom_write };
+			default:
+				std::cerr << "Mapper not implemented: " << std::hex << cartridge.get_mapper_number() << std::endl;
+				std::abort();
+		}
+	}
+
+	// NROM
+
+	auto mapper::nrom_read(address const addr) -> std::uint8_t
+	{
+		if (addr <= address{ 0x7FFF })
+		{
+			return cartridge_.get_ram()[addr.get_absolute() % 0x2000];
+		}
+		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(address const addr, std::uint8_t const value) -> void
+	{
+		if (addr <= address{ 0x7FFF })
+		{
+			cartridge_.get_ram_mut()[addr.get_absolute() % 0x2000] = value;
+		}
+	}
+
+} // namespace nes
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