64 lines
2.2 KiB
C#
64 lines
2.2 KiB
C#
using Core.Audio;
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using Core.Interfaces;
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using Core.Video;
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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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public SmsVdp VideoProcessor { get; set; }
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public SmsApu 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 Joypad1Keyboard = 0xFF;
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public byte Joypad1Gamepad = 0xFF;
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public byte Joypad2State = 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 == 0x7E)
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{
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// VDP V-Counter (Vertical Scanline Position)
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return VideoProcessor.ReadVCounter();
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}
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if (lowerPort >= 0x80 && lowerPort <= 0xBF)
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{
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// Even ports (like 0xBE) are Data. Odd ports (like 0xBF) are Control.
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if ((lowerPort & 0x01) == 0) return VideoProcessor.ReadDataPort();
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else return VideoProcessor.ReadControlPort();
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}
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if (lowerPort == 0xDC) return (byte)(Joypad1Keyboard & Joypad1Gamepad);
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if (lowerPort == 0xDD) return Joypad2State;
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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 == 0x7E || lowerPort == 0x7F)
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{
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AudioProcessor.WritePort7F(value);
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}
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// THE FIX: Video Ports are mirrored across the entire 0x80 to 0xBF range!
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else if (lowerPort >= 0x80 && lowerPort <= 0xBF)
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{
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// Even ports are Data, Odd ports are Control
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if ((lowerPort & 0x01) == 0) VideoProcessor.WriteDataPort(value);
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else VideoProcessor.WriteControlPort(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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} |