Add a few comments to cartridge stuff (#473)

* Add a few comments to cartridge stuff

* Fix comment to clarify cartridge detection logic

---------

Co-authored-by: ejaquay <[email protected]>

Author: ejaquay

libcommon/src/cartridges/capi_adapter_cartridge.cpp

@@ -18,6 +18,7 @@
 #include <vcc/cartridges/capi_adapter_cartridge.h>
 #include <stdexcept>
 
+// C API hardware cartridge interface
 
 namespace vcc::cartridges
 {

libcommon/src/cartridges/empty_cartridge.cpp

@@ -17,6 +17,7 @@
 ////////////////////////////////////////////////////////////////////////////////
 #include <vcc/cartridges/empty_cartridge.h>
 
+// Interface for empty cartridge
 
 namespace vcc::cartridges
 {

libcommon/src/cartridges/rom_cartridge.cpp

@@ -17,6 +17,7 @@
 ////////////////////////////////////////////////////////////////////////////////
 #include <vcc/cartridges/rom_cartridge.h>
 
+// Interface for ROM cartridge
 
 namespace vcc::cartridges
 {
@@ -63,6 +64,7 @@ namespace vcc::cartridges
 		bank_offset_ = 0;
 	}
 
+	// A write to port 0x40 of a bank switching cart (eg RoboCop) will set the bank offset
 	void rom_cartridge::write_port(unsigned char port_id, unsigned char value)
 	{
 		if (enable_bank_switching_ && port_id == 0x40)
@@ -73,7 +75,7 @@ namespace vcc::cartridges
 
 	unsigned char rom_cartridge::read_memory_byte(unsigned short memory_address)
 	{
-		return buffer_[((memory_address & 32767) + bank_offset_) % buffer_.size()];
+		return buffer_[((memory_address & 0x7fff) + bank_offset_) % buffer_.size()];
 	}
 
 

libcommon/src/utils/cartridge_loader.cpp

@@ -44,7 +44,7 @@ namespace vcc::utils
 
 	}
 
-
+	// Look for magic "MZ" to detect DLL.  Assume rom if not.
 	cartridge_file_type determine_cartridge_type(const std::string& filename)
 	{
 		std::ifstream input(filename, std::ios::binary);
@@ -61,11 +61,12 @@ namespace vcc::utils
 		return cartridge_file_type::rom_image;
 	}
 
+	// Load rom cartridge
 	cartridge_loader_result load_rom_cartridge(
 		const std::string& filename,
 		std::unique_ptr<::vcc::core::cartridge_context> context)
 	{
-		constexpr size_t PAK_MAX_MEM = 0x40000;
+		constexpr size_t PAK_MAX_MEM = 0x40000;   // 256KB
 
 		std::vector<uint8_t> romImage;
 
@@ -91,7 +92,7 @@ namespace vcc::utils
 		}
 
 		// Force enable bank switching since we don't have a way to detect if
-		// it should be enabled.
+		// it should be enabled.   (CCC file > 16KB?)
 		constexpr bool enable_bank_switching = true;
 
 		return {
@@ -106,6 +107,7 @@ namespace vcc::utils
 		};
 	}
 
+	// Load C API hardware cart
 	cartridge_loader_result load_capi_cartridge(
 		const std::string& filename,
 		std::unique_ptr<::vcc::core::cartridge_context> cartridge_context,