62 lines
2.1 KiB
C#
62 lines
2.1 KiB
C#
using Core.Interfaces;
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namespace Core.Io
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{
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public class SmsIoBus : IIoBus
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{
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// We will wire these up in the next phases!
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// public Vdp VideoProcessor { get; set; }
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// public Psg AudioProcessor { get; set; }
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// Joypad State (0xFF means no buttons pressed - the SMS uses Active-Low logic!)
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public byte Joypad1State { get; set; } = 0xFF;
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public byte Joypad2State { get; set; } = 0xFF;
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public byte ReadPort(ushort port)
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{
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// The Z80 can output 16-bit port addresses, but the Master System
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// hardware only physically wires up the bottom 8 bits.
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byte lowerPort = (byte)(port & 0xFF);
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if (lowerPort >= 0x80 && lowerPort <= 0xBF)
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{
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// VDP Read (Usually 0xBE for VRAM Data, 0xBF for Status Flags)
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// return VideoProcessor.ReadPort(lowerPort);
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return 0x00;
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}
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if (lowerPort == 0xDC)
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{
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// Port 0xDC: Player 1 (Up, Down, Left, Right, 1, 2) + Player 2 (Up, Down)
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return Joypad1State;
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}
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if (lowerPort == 0xDD)
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{
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// Port 0xDD: Player 2 (Left, Right, 1, 2) + Reset Button
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return Joypad2State;
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}
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return 0xFF; // Floating bus
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}
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public void WritePort(ushort port, byte value)
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{
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byte lowerPort = (byte)(port & 0xFF);
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if (lowerPort >= 0x40 && lowerPort <= 0x7F)
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{
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// PSG Audio Write (Usually written exactly to 0x7F)
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// AudioProcessor.WriteData(value);
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}
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else if (lowerPort >= 0x80 && lowerPort <= 0xBF)
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{
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// VDP Write (Usually 0xBE for VRAM Data, 0xBF for Control Registers)
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// VideoProcessor.WritePort(lowerPort, value);
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}
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else if (lowerPort <= 0x3F)
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{
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// Port 0x3E is used by the BIOS to enable/disable the cartridge slot
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// We can usually ignore this if we are just directly booting game ROMs!
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}
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}
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}
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} |