BizHawk/BizHawk.Emulation/Consoles/Intellivision/Intellicart.cs

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;

namespace BizHawk.Emulation.Consoles.Intellivision
{
	public sealed class Intellicart : ICart
	{
		private ushort[] Data = new ushort[65536];
		private bool[][] MemoryAttributes = new bool[32][];
		private ushort[][] FineAddresses = new ushort[32][];

		private ushort[] CRC16_table =
		{
			0x0000, 0x1021, 0x2042, 0x3063, 0x4084, 0x50A5, 0x60C6, 0x70E7,
			0x8108, 0x9129, 0xA14A, 0xB16B, 0xC18C, 0xD1AD, 0xE1CE, 0xF1EF,
			0x1231, 0x0210, 0x3273, 0x2252, 0x52B5, 0x4294, 0x72F7, 0x62D6,
			0x9339, 0x8318, 0xB37B, 0xA35A, 0xD3BD, 0xC39C, 0xF3FF, 0xE3DE,
			0x2462, 0x3443, 0x0420, 0x1401, 0x64E6, 0x74C7, 0x44A4, 0x5485,
			0xA56A, 0xB54B, 0x8528, 0x9509, 0xE5EE, 0xF5CF, 0xC5AC, 0xD58D,
			0x3653, 0x2672, 0x1611, 0x0630, 0x76D7, 0x66F6, 0x5695, 0x46B4,
			0xB75B, 0xA77A, 0x9719, 0x8738, 0xF7DF, 0xE7FE, 0xD79D, 0xC7BC,
			0x48C4, 0x58E5, 0x6886, 0x78A7, 0x0840, 0x1861, 0x2802, 0x3823,
			0xC9CC, 0xD9ED, 0xE98E, 0xF9AF, 0x8948, 0x9969, 0xA90A, 0xB92B,
			0x5AF5, 0x4AD4, 0x7AB7, 0x6A96, 0x1A71, 0x0A50, 0x3A33, 0x2A12,
			0xDBFD, 0xCBDC, 0xFBBF, 0xEB9E, 0x9B79, 0x8B58, 0xBB3B, 0xAB1A,
			0x6CA6, 0x7C87, 0x4CE4, 0x5CC5, 0x2C22, 0x3C03, 0x0C60, 0x1C41,
			0xEDAE, 0xFD8F, 0xCDEC, 0xDDCD, 0xAD2A, 0xBD0B, 0x8D68, 0x9D49,
			0x7E97, 0x6EB6, 0x5ED5, 0x4EF4, 0x3E13, 0x2E32, 0x1E51, 0x0E70,
			0xFF9F, 0xEFBE, 0xDFDD, 0xCFFC, 0xBF1B, 0xAF3A, 0x9F59, 0x8F78,
			0x9188, 0x81A9, 0xB1CA, 0xA1EB, 0xD10C, 0xC12D, 0xF14E, 0xE16F,
			0x1080, 0x00A1, 0x30C2, 0x20E3, 0x5004, 0x4025, 0x7046, 0x6067,
			0x83B9, 0x9398, 0xA3FB, 0xB3DA, 0xC33D, 0xD31C, 0xE37F, 0xF35E,
			0x02B1, 0x1290, 0x22F3, 0x32D2, 0x4235, 0x5214, 0x6277, 0x7256,
			0xB5EA, 0xA5CB, 0x95A8, 0x8589, 0xF56E, 0xE54F, 0xD52C, 0xC50D,
			0x34E2, 0x24C3, 0x14A0, 0x0481, 0x7466, 0x6447, 0x5424, 0x4405,
			0xA7DB, 0xB7FA, 0x8799, 0x97B8, 0xE75F, 0xF77E, 0xC71D, 0xD73C,
			0x26D3, 0x36F2, 0x0691, 0x16B0, 0x6657, 0x7676, 0x4615, 0x5634,
			0xD94C, 0xC96D, 0xF90E, 0xE92F, 0x99C8, 0x89E9, 0xB98A, 0xA9AB,
			0x5844, 0x4865, 0x7806, 0x6827, 0x18C0, 0x08E1, 0x3882, 0x28A3,
			0xCB7D, 0xDB5C, 0xEB3F, 0xFB1E, 0x8BF9, 0x9BD8, 0xABBB, 0xBB9A,
			0x4A75, 0x5A54, 0x6A37, 0x7A16, 0x0AF1, 0x1AD0, 0x2AB3, 0x3A92,
			0xFD2E, 0xED0F, 0xDD6C, 0xCD4D, 0xBDAA, 0xAD8B, 0x9DE8, 0x8DC9,
			0x7C26, 0x6C07, 0x5C64, 0x4C45, 0x3CA2, 0x2C83, 0x1CE0, 0x0CC1,
			0xEF1F, 0xFF3E, 0xCF5D, 0xDF7C, 0xAF9B, 0xBFBA, 0x8FD9, 0x9FF8,
			0x6E17, 0x7E36, 0x4E55, 0x5E74, 0x2E93, 0x3EB2, 0x0ED1, 0x1EF0
		};

		private ushort UpdateCRC16(ushort crc, byte data)
		{
			return (ushort)((crc << 8) ^ CRC16_table[(crc >> 8) ^ data]);
		}

		public int Parse(byte[] Rom)
		{
			int offset = 0;
			// Check to see if the header is valid.
			if (Rom[offset++] != 0xA8 || Rom[offset++] != (0xFF ^ Rom[offset++]))
			{
				return -1;
			}
			ushort crc, expected;
			// Parse for data segments.
			for (int segment = 0; segment < Rom[1]; segment++)
			{
				crc = 0xFFFF;
				byte upper_start = Rom[offset++];
				byte upper_end = Rom[offset++];
				crc = UpdateCRC16(crc, upper_start);
				crc = UpdateCRC16(crc, upper_end);
				ushort start = (ushort)(upper_start << 8);
				ushort end = (ushort)((upper_end << 8) | 0xFF);
				if (end < start)
				{
					throw new ArgumentException("Ranges can't start higher than they end.");
				}
				for (int addr = start; addr <= end; addr++)
				{
					ushort data;
					byte high = Rom[offset++];
					byte low = Rom[offset++];
					crc = UpdateCRC16(crc, high);
					crc = UpdateCRC16(crc, low);
					data = (ushort)((high << 8) | low);
					Data[addr] = data;
				}
				expected = (ushort)((Rom[offset++] << 8) | Rom[offset++]);
				if (expected != crc)
				{
					throw new ArgumentException("Invalid CRC.");
				}
			}
			// Parse for memory attributes.
			for (int range = 0; range < 32; range++)
			{
				byte attributes = Rom[offset + (range >> 1)];
				// Every second 2K block is stored in the upper 4 bits.
				if ((range & 0x1) != 0)
				{
					attributes = (byte)(attributes >> 4);
				}
				attributes &= 0xF;
				MemoryAttributes[range] = new bool[4];
				// Readable.
				MemoryAttributes[range][0] = ((range & 0x1) != 0);
				// Writeable.
				MemoryAttributes[range][1] = ((range & 0x2) != 0);
				// Narrow.
				MemoryAttributes[range][2] = ((range & 0x4) != 0);
				// Bank-switched.
				MemoryAttributes[range][3] = ((range & 0x8) != 0);
			}
			// Parse for fine addresses (Trimmed 2K ranges).
			for (int range = 0; range < 32; range++)
			{
				int index;
				// The lower and upper 2K in a 4K range are 16 addresses away from each other.
				if ((range & 0x1) != 0)
				{
					index = offset + 16 + (range >> 1);
				}
				else
				{
					index = offset + 32 + (range >> 1);
				}
				int range_start = range * 2048;
				ushort start = (ushort)((((Rom[index] >> 4) & 0x07) << 8) + range_start);
				ushort end = (ushort)((((Rom[index]) & 0x07) << 8) + 0xFF + range_start);
				if (end < start)
				{
					throw new ArgumentException("Ranges can't start higher than they end.");
				}
				FineAddresses[range] = new ushort[2];
				FineAddresses[range][0] = start;
				FineAddresses[range][1] = end;
			}
			crc = 0xFFFF;
			for (int index = 0; index < 48; index++)
			{
				crc = UpdateCRC16(crc, Rom[offset++]);
			}
			expected = (ushort)((Rom[offset++] << 8) | (Rom[offset++] & 0xFF));
			// Check if there is an invalid CRC for the memory attributes / fine addresses.
			if (expected != crc)
			{
				throw new ArgumentException("Invalid CRC.");
			}
			return offset;
		}

		public ushort? ReadCart(ushort addr)
		{
			int range = addr / 2048;
			bool[] attributes = MemoryAttributes[range];
			if (attributes[0] && addr >= FineAddresses[range][0] && addr <= FineAddresses[range][1])
			{
				return Data[addr];
			}
			return null;
		}

		public bool WriteCart(ushort addr, ushort value)
		{
			int range = addr / 2048;
			bool[] attributes = MemoryAttributes[range];
			if (attributes[1] && addr >= FineAddresses[range][0] && addr <= FineAddresses[range][1])
			{
				// Only write lower 8 bits if the Narrow attribute is set.
				if (attributes[2])
				{
					value &= 0xFF;
				}
				if (attributes[3])
				{
					throw new NotImplementedException("Bank-switched memory attribute not implemented.");
				}
				Data[addr] = value;
				return true;
			}
			return false;
		}
	}
}