103 lines
1.9 KiB
C#
103 lines
1.9 KiB
C#
using BizHawk.Common;
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namespace BizHawk.Emulation.Cores.Atari.Atari2600
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{
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/*
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This is an extended version of the CBS RAM Plus bankswitching scheme
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supported by the Harmony cartridge.
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There are six (or seven) 4K banks and 256 bytes of RAM.
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*/
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internal sealed class mFA2 : MapperBase
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{
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private int _bank4K;
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private byte[] _ram = new byte[256];
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public mFA2(Atari2600 core) : base(core)
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{
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}
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public override byte[] CartRam => _ram;
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public override void SyncState(Serializer ser)
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{
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base.SyncState(ser);
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ser.Sync("bank4k", ref _bank4K);
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ser.Sync("auxRam", ref _ram, false);
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}
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public override void HardReset()
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{
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_bank4K = 0;
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_ram = new byte[256];
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}
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public override byte ReadMemory(ushort addr) => ReadMem(addr, false);
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public override byte PeekMemory(ushort addr) => ReadMem(addr, true);
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public override void WriteMemory(ushort addr, byte value)
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=> WriteMem(addr, value, false);
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public override void PokeMemory(ushort addr, byte value)
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=> WriteMem(addr, value, true);
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private byte ReadMem(ushort addr, bool peek)
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{
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if (!peek)
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{
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Address(addr);
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}
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if (addr < 0x1000)
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{
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return base.ReadMemory(addr);
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}
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if (addr < 0x1100)
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{
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return 0xFF;
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}
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if (addr < 0x1200)
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{
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return _ram[addr & 0xFF];
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}
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return Core.Rom[(_bank4K << 12) + (addr & 0xFFF)];
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}
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private void WriteMem(ushort addr, byte value, bool poke)
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{
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if (!poke)
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{
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Address(addr);
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}
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if (addr < 0x1000)
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{
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base.WriteMemory(addr, value);
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}
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else if (addr < 0x1100)
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{
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_ram[addr & 0xFF] = value;
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}
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}
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private void Address(ushort addr)
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{
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_bank4K = addr switch
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{
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0x1FF5 => 0,
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0x1FF6 => 1,
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0x1FF7 => 2,
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0x1FF8 => 3,
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0x1FF9 => 4,
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0x1FFA => 5,
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0x1FFB when Core.Rom.Length == 28 * 1024 => 6,
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_ => _bank4K
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};
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}
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}
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}
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