85 lines
1.7 KiB
C#
85 lines
1.7 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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FA (RAM Plus)
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-----
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CBS Thought they'd throw a few tricks of their own at the 2600 with It's got
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12K of ROM and 256 bytes of RAM.
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This works similar to F8, except there's only 3 4K ROM banks. The banks are selected by
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accessing 1FF8, 1FF9, and 1FFA. There's also 256 bytes of RAM mapped into 1000-11FF.
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The write port is at 1000-10FF, and the read port is 1100-11FF.
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*/
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internal class mFA : MapperBase
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{
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private int _toggle;
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private ByteBuffer _auxRam = new ByteBuffer(256);
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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 _auxRam[addr & 0xFF];
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}
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return core.rom[(_toggle << 12) + (addr & 0xFFF)];
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}
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public override byte ReadMemory(ushort addr)
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{
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return ReadMem(addr, false);
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}
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public override byte PeekMemory(ushort addr)
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{
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return ReadMem(addr, true);
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}
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public override void WriteMemory(ushort addr, byte value)
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{
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Address(addr);
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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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_auxRam[addr & 0xFF] = value;
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}
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}
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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("toggle", ref _toggle);
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ser.Sync("ram", ref _auxRam);
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}
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private void Address(ushort addr)
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{
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if (addr == 0x1FF8) _toggle = 0;
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if (addr == 0x1FF9) _toggle = 1;
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if (addr == 0x1FFA) _toggle = 2;
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}
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}
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}
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