quicknes: support Bite Off

quicknes/nes_emu/Nes_Mapper.h

@@ -121,7 +121,7 @@ protected:
 	
 	// Map 'size' bytes from 'CHR + bank * size' to PPU address space starting at 'addr'
 	void set_chr_bank( nes_addr_t addr, bank_size_t size, int bank );
-	void set_chr_bank_ex( nes_addr_t addr, bank_size_t size, int bank );
+	void set_chr_bank_ex( nes_addr_t addr, bank_size_t size, int bank ); // mmc24 only
 	
 	// Set PPU mirroring. All mappings implemented using mirror_manual().
 	void mirror_manual( int page0, int page1, int page2, int page3 );

quicknes/nes_emu/Nes_Ppu_Impl.h

@@ -44,7 +44,7 @@ public:
 	enum { vaddr_clock_mask = 0x1000 };
 	void set_nt_banks( int bank0, int bank1, int bank2, int bank3 );
 	void set_chr_bank( int addr, int size, long data );
-	void set_chr_bank_ex( int addr, int size, long data );
+	void set_chr_bank_ex( int addr, int size, long data ); // mmc24 only
 	
 	// Nametable and CHR RAM
 	enum { nt_ram_size = 0x1000 };
@@ -103,13 +103,16 @@ private:
 	// Mapping
 	enum { chr_page_size = 0x400 };
 	long chr_pages [chr_addr_size / chr_page_size];
-	long chr_pages_ex [chr_addr_size / chr_page_size];
+	long chr_pages_ex [chr_addr_size / chr_page_size]; // mmc24 only
 	long map_chr_addr( unsigned a ) /*const*/
 	{
 		if (!mmc24_enabled)
 			return chr_pages [a / chr_page_size] + a;
 
+		// mmc24 calculations
+
 		int page = a >> 12 & 1;
+		// can't check against bit 3 of address, because quicknes never actually fetches those
 		int newval0 = (a & 0xff0) != 0xfd0;
 		int newval1 = (a & 0xff0) == 0xfe0;
 
@@ -126,8 +129,8 @@ private:
 	}
 	byte* nt_banks [4];
 	
-	bool mmc24_enabled;
+	bool mmc24_enabled; // true if mmc24 regs need to be latched and checked
-	byte mmc24_latched [2];
+	byte mmc24_latched [2]; // current latch value for the first\second 4k of memory
 
 	// CHR data
 	byte const* chr_data; // points to chr ram when there is no read-only data

quicknes/nes_emu/Nes_Ppu_Rendering.cpp

@@ -176,7 +176,16 @@ void Nes_Ppu_Rendering::draw_background_( int remain )
 		byte const* nametable2 = get_nametable( addr ^ 0x400 );
 		int count2 = addr & 31;
 		int count = 32 - count2 - left_clip;
-		if ( pixel_x )
+
+		// this conditional is commented out because of mmc2\4
+		// normally, the extra row of pixels is only fetched when pixel_ x is not 0, which makes sense
+		// but here, we need a correct fetch pattern to pick up 0xfd\0xfe tiles off the edge of the display
+		
+		// this doesn't cause any problems with buffer overflow because the framebuffer we're rendering to is
+		// already guarded (width = 272)
+		// this doesn't give us a fully correct ppu fetch pattern, but it's close enough for punch out
+
+		//if ( pixel_x )
 			count2++;
 		
 		byte const* attr_table = &nametable [0x3c0 | (addr >> 4 & 0x38)];