ZXSpectrum48K/Core/Memory/MemoryBus.cs

using System;
using Core.Interfaces;

namespace Core.Memory
{
    public class MemoryBus : IMemory
    {
        // The flat 64KB memory space
        private readonly byte[] _memory = new byte[0x10000];

        public byte Read(ushort address)
        {
            return _memory[address];
        }

        public void Write(ushort address, byte value)
        {
            /* ZX Spectrum 48K Memory Map:
             * 0x0000 - 0x3FFF: ROM (16KB) -> Cannot write here!
             * 0x4000 - 0x57FF: Display File (Screen Pixels)
             * 0x5800 - 0x5AFF: Color Attributes
             * 0x5B00 - 0xFFFF: General Purpose RAM
             */

            if (address < 0x4000)
            {
                // Cannot write to ROM - Do nothing - maybe throw an exception
                return;
            }

            _memory[address] = value;
        }

        //Put some initial random data into RAM for authenticity
        public void CrapRAMData()
        {
            Random random = new Random();
            for (int i = 0x4000; i < 0xFFFF; i++)
            {
                _memory[i] = (byte)random.Next(0x00, 0xFF);
            }
        }

        public void CleanRAMData()
        {            
            for (int i = 0x4000; i < 0xFFFF; i++)
            {
                _memory[i] = 0x00;
            }
        }

        // Load the ROM file
        public void LoadRom(byte[] romData)
        {
            if (romData.Length > 0x4000)
            {
                throw new ArgumentException("ROM file exceeds the 16KB capacity of Bank 0.");
            }

            // Copy the ROM
            Array.Copy(romData, 0, _memory, 0, romData.Length);
        }
        
    }
}