gba: add under-the-hood support for direct MMIO reading, to be used for something at some point, maybe

BizHawk.Emulation/Consoles/Nintendo/GBA/LibMeteor.cs

@@ -116,13 +116,38 @@ namespace BizHawk.Emulation.Consoles.Nintendo.GBA
 		/// </summary>
 		public enum MemoryArea : int
 		{
+			/// <summary>
+			/// BIOS, may be invalid if bios not loaded. valid size: 16K.  system bus: @00000000h
+			/// </summary>
 			bios = 0,
+			/// <summary>
+			/// external workram.  valid size: 256K.  system bus: @02000000h
+			/// </summary>
 			ewram = 1,
+			/// <summary>
+			/// internal workram.  valid size: 32K.  system bus: @03000000h
+			/// </summary>
 			iwram = 2,
+			/// <summary>
+			/// palettes.  valid size: 1K.  system bus: @05000000h
+			/// </summary>
 			palram = 3,
+			/// <summary>
+			/// video ram.  valid size: 96K.  system bus: @06000000h
+			/// </summary>
 			vram = 4,
+			/// <summary>
+			/// sprite attribute ram.  valid size: 1K.  system bus: @07000000h
+			/// </summary>
 			oam = 5,
-			rom = 6
+			/// <summary>
+			/// rom.  always valid to full size, even if no rom or small rom loaded.  valid size: 32M.  system bus: @08000000h, others
+			/// </summary>
+			rom = 6,
+			/// <summary>
+			/// direct access to cached io port values.  this should NEVER be modified!  valid size: 4K.  system bus: @04000000h (sort of)
+			/// </summary>
+			io = 7
 		}
 
 		/// <summary>

libmeteor/cinterface.cpp

@@ -144,7 +144,12 @@ EXPORT void libmeteor_loadbios(const void *data, unsigned size)
 
 EXPORT uint8_t *libmeteor_getmemoryarea(int which)
 {
-	return AMeteor::_memory.GetMemoryArea(which);
+	if (which < 7)
+		return AMeteor::_memory.GetMemoryArea(which);
+	else if (which == 7)
+		return AMeteor::_io.GetIoPointer();
+	else
+		return NULL;
 }
 
 EXPORT int libmeteor_loadsaveram(const void *data, unsigned size)

libmeteor/include/ameteor/io.hpp

@@ -208,6 +208,9 @@ namespace AMeteor
 			bool SaveState (std::ostream& stream);
 			bool LoadState (std::istream& stream);
 
+			// this should be considered very dangerous to use
+			uint8_t* GetIoPointer() {return m_iomem;}
+
 		private :
 			uint8_t* m_iomem;
 	};