86 lines
2.0 KiB
C#
86 lines
2.0 KiB
C#
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using System;
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using System.Collections.Generic;
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using System.Linq;
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using System.Text;
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namespace BizHawk.Emulation.Consoles.Nintendo
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{
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// rewires pins to use internal CIRAM as both nametable and pattern data, so
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// the entire cart is just a single PRGROM chip (plus CIC)
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public class Mapper218 : NES.NESBoardBase
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{
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//configuration
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int prg_byte_mask;
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int chr_addr_mask;
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public override bool Configure(NES.EDetectionOrigin origin)
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{
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switch (Cart.board_type)
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{
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case "MAPPER218":
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// the cart actually has 0k vram, but due to massive abuse of the ines format, is labeled as 8k
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// supposed vram is (correctly) not used in our implementation
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AssertPrg(8, 16, 32); AssertChr(0); /*AssertVram(0);*/ AssertWram(0);
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break;
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default:
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return false;
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}
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// due to massive abuse of the ines format, the mirroring and 4 screen bits have slightly different meanings
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switch (Cart.inesmirroring)
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{
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case 1: // VA10 to PA10
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chr_addr_mask = 1 << 10;
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break;
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case 0: // VA10 to PA11
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chr_addr_mask = 1 << 11;
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break;
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case 2: // VA10 to PA12
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chr_addr_mask = 1 << 12;
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break;
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case 3: // VA10 to PA13
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chr_addr_mask = 1 << 13;
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break;
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default:
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// we need an ines identification for correct mirroring
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return false;
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}
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prg_byte_mask = (Cart.prg_size*1024) - 1;
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return true;
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}
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int TransformPPU(int addr)
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{
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if ((addr & chr_addr_mask) != 0)
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addr = addr & 0x3ff | 0x400;
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else
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addr = addr & 0x3ff;
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return addr;
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}
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public override byte ReadPPU(int addr)
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{
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if (addr < 0x3f00)
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return NES.CIRAM[TransformPPU(addr)];
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else
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// palettes only
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return base.ReadPPU(addr);
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}
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public override void WritePPU(int addr, byte value)
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{
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if (addr < 0x3f00)
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NES.CIRAM[TransformPPU(addr)] = value;
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else
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// palettes only
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base.WritePPU(addr, value);
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}
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public override byte ReadPRG(int addr)
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{
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addr &= prg_byte_mask;
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return ROM[addr];
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}
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}
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}
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