57 lines
1.5 KiB
C#
57 lines
1.5 KiB
C#
using System;
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using System.Collections.Generic;
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using System.IO;
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using BizHawk.Emulation.CPUs.M6502;
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using BizHawk.Emulation.Consoles.Atari;
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namespace BizHawk
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{
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partial class Atari2600
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{
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/*
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F8 (Atari style 8K)
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-----
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This is the fairly standard way 8K of cartridge ROM was implemented. There are two
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4K ROM banks, which get mapped into the 4K of cartridge space. Accessing 1FF8 or
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1FF9 selects one of the two 4K banks. When one of these two addresses are accessed,
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the banks switch spontaniously.
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ANY kind of access will trigger the switching- reading or writing. Usually games use
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LDA or BIT on 1FF8/1FF9 to perform the switch.
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When the switch occurs, the entire 4K ROM bank switches, including the code that is
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reading the 1FF8/1FF9 location. Usually, games put a small stub of code in BOTH banks
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so when the switch occurs, the code won't crash.
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*/
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class mF8 : MapperBase
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{
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int toggle = 0;
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public override byte ReadMemory(ushort addr)
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{
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Address(addr);
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if (addr < 0x1000) return base.ReadMemory(addr);
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return core.rom[toggle*4*1024 + (addr&0xFFF)];
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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) base.WriteMemory(addr, value);
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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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}
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void Address(ushort addr)
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{
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if (addr == 0x1FF8) toggle = 0;
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else if (addr == 0x1FF9) toggle = 1;
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}
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}
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}
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} |