gb: fix cart RAM writes on MBC5

Fixed an issue whereby only the first bank on MBC5 RAM was being written
to. This fixes LSDJ.

Fixed an issue whereby the upper nibble of data stored in MBC2 RAM was
set to LOW instead of HIGH.

Signed-off-by: Mahyar Koshkouei <[email protected]>

peanut_gb.h

@@ -966,6 +966,7 @@ void __gb_write(struct gb_s *gb, uint_fast16_t addr, uint8_t val)
 		if(gb->mbc == 3 && val && gb->cart_mode_select == 0)
 			memcpy(&gb->rtc_latched.bytes, &gb->rtc_real.bytes, sizeof(gb->rtc_latched.bytes));
 
+		/* Set banking mode select. */
 		gb->cart_mode_select = val;
 		return;
 
@@ -995,13 +996,18 @@ void __gb_write(struct gb_s *gb, uint_fast16_t addr, uint8_t val)
 				addr &= 0x1FF;
 				/* Data is only 4 bits wide in MBC2 RAM. */
 				val &= 0x0F;
+				/* Upper nibble is set to high. */
+				val |= 0xF0;
 				gb->gb_cart_ram_write(gb, addr, val);
 			}
-			else if(gb->cart_mode_select &&
+			/* If cart has RAM, use this. If MBC1, only the first
+			 * RAM bank can be written to if the advanced banking
+			 * mode is selected. */
+			else if(((gb->mbc == 1 && gb->cart_mode_select) || gb->mbc != 1) &&
 					gb->cart_ram_bank < gb->num_ram_banks)
 			{
 				gb->gb_cart_ram_write(gb,
-						      addr - CART_RAM_ADDR + (gb->cart_ram_bank * CRAM_BANK_SIZE), val);
+					addr - CART_RAM_ADDR + (gb->cart_ram_bank * CRAM_BANK_SIZE), val);
 			}
 			else if(gb->num_ram_banks)
 				gb->gb_cart_ram_write(gb, addr - CART_RAM_ADDR, val);
@@ -3639,15 +3645,19 @@ enum gb_init_error_e gb_init(struct gb_s *gb,
 		0, 1, 1, 1, -1, 2, 2, -1, 0, 0, -1, 0, 0, 0, -1, 3,
 		3, 3, 3, 3, -1, -1, -1, -1, -1, 5, 5, 5, 5, 5, 5, -1
 	};
+	/* Whether cart has RAM. */
 	const uint8_t cart_ram[] =
 	{
 		0, 0, 1, 1, 0, 1, 1, 0, 1, 1, 0, 0, 0, 0, 0, 0,
 		1, 0, 1, 1, 0, 0, 0, 0, 0, 0, 1, 1, 0, 0, 0, 0
 	};
+	/* How large the ROM is in banks of 16 KiB. */
 	const uint16_t num_rom_banks_mask[] =
 	{
 		2, 4, 8, 16, 32, 64, 128, 256, 512
 	};
+	/* How large the cart RAM is in banks of 8 KiB. Code $01 is unused, but
+	 * some early homebrew ROMs supposedly may use this value. */
 	const uint8_t num_ram_banks[] = { 0, 1, 1, 4, 16, 8 };
 
 	gb->gb_rom_read = gb_rom_read;