96 lines
2.2 KiB
C#
96 lines
2.2 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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3F (Tigervision)
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-----
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Traditionally, this method was used on the Tigervision games. The ROMs were all 8K, and
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there's two 2K pages in the 4K of address space. The upper bank is fixed to the last 2K
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of the ROM.
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The first 2K is selectable by writing to any location between 0000 and 003F. Yes, this
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overlaps the TIA, but this is not a big deal. You simply use the mirrors of the TIA at
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40-7F instead! To select a bank, the games write to 3Fh, because it's not implemented
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on the TIA.
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The homebrew community has decided that if 8K is good, more ROM is better! This mapper
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can support up to 512K bytes of ROM just by implementing all 8 bits on the mapper
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register, and this has been done... however I do not think 512K ROMs have been made just
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yet.
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*/
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internal class m3F : MapperBase
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{
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private int _lowbank2K;
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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("lowbank_2k", ref _lowbank2K);
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}
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public override void HardReset()
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{
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_lowbank2K = 0;
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base.HardReset();
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}
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public override byte ReadMemory(ushort 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 < 0x1800) // Low 2k Bank
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{
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return Core.Rom[(_lowbank2K << 11) + (addr & 0x07FF)];
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}
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if (addr < 0x2000) // High bank fixed to last 2k of ROM
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{
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return Core.Rom[(Core.Rom.Length - 2048) + (addr & 0x07FF)];
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}
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return base.ReadMemory(addr);
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}
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public override byte PeekMemory(ushort addr)
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{
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return ReadMemory(addr);
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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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if (addr < 0x0040)
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{
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if ((value << 11) < Core.Rom.Length)
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{
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_lowbank2K = value;
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}
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else
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{
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_lowbank2K = value & (Core.Rom.Length >> 11);
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}
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}
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}
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base.WriteMemory(addr, value);
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}
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public override void WriteMemory(ushort addr, byte value)
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{
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WriteMem(addr, value, poke: false);
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}
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public override void PokeMemory(ushort addr, byte value)
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{
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WriteMem(addr, value, poke: true);
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}
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}
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}
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