121 lines
2.4 KiB
C#
121 lines
2.4 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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X07 (Atariage)
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-----
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Apparently, this was only used on one cart: Stella's Stocking.
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Similar to EF, there are 16 4K banks, for a total of up to 64K of ROM.
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The addresses to select banks is below the ROM area, however.
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The following TWO masks are used:
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A13 A0
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----------------
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0 1xxx nnnn 1101
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This means the address 80B selects bank 0, 81B selects bank 1, etc.
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In addition to this, there is another way:
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A13 A0
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----------------
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0 0xxx 0nxx xxxx
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This is somewhat special purpose: Accessing here does nothing, unless one of the
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last two banks are selected (banks 14 or 15). In that case, the new bank is:
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111n i.e. accessing 0000 will select bank 14 (Eh, 1110b) while accessing 0040
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will select bank 15 (Fh, 1111b). This allows for bankswitching by accessing
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TIA registers at 00-3F or 40-7F without incurring any overhead.
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*/
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internal class mX07 : MapperBase
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{
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private int _rombank2K;
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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("rombank_2k", ref _rombank2K);
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}
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public override void HardReset()
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{
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_rombank2K = 0;
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base.HardReset();
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}
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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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return Core.Rom[(_rombank2K << 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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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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}
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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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private void Address(ushort addr)
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{
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if ((addr & 0x180F) == 0x080D)
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{
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Bank((addr & 0xF0) >> 4);
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}
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else if ((addr & 0x1880) == 0)
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{
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if ((_rombank2K & 0xE) == 0xE)
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{
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Bank(((addr & 0x40) >> 6) | (_rombank2K & 0xE));
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}
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}
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}
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private void Bank(int bank)
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{
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_rombank2K = bank & 0x0F;
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}
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}
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}
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