Feature/base memory interface

illNES/illNES.CPU/BaseMemoryInterface.cs

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+namespace illNES.CPU
+{
+    public class BaseMemoryInterface : IMemoryInterface
+    {
+        /// <summary>
+        /// Always provide 64k of RAM, allow AccessMemory() to handle mapping and what is actually used.
+        /// This represents what the CPU is capable of accessing (64k) while AccessMemory() can choose to only use
+        /// for example, the range 0x0 - 0x7ff, which would provide 2k of RAM like in the NES.
+        /// </summary>
+        protected byte[] ram = new byte[0xffff];
+
+        /// <summary>
+        /// Accesses memory at a given address, and writes a value if provided.
+        /// Overriding this method allows for changing the way in which RAM is accessed.
+        /// </summary>
+        /// <param name="address">The address to access</param>
+        /// <param name="value">An optional value to write</param>
+        /// <returns>The value at the memory address when the method returns</returns>
+        protected virtual byte AccessMemory(ushort address, byte? value = null)
+        {
+            //This provides direct access to the full 64k of RAM
+            if (value.HasValue) ram[address] = value.Value;
+            return ram[address];
+        }
+
+        public string DumpRam(ushort start, byte offset)
+        {
+            throw new System.NotImplementedException();
+        }
+
+        public void FileDump(string filePath, ushort address)
+        {
+            throw new System.NotImplementedException();
+        }
+
+        public byte Read(ushort address)
+            => AccessMemory(address);
+
+        public ushort ReadWord(ushort address)
+            => (ushort)(AccessMemory((ushort)(address + 1)) << 8 | AccessMemory(address));
+
+        public void Write(ushort address, byte value)
+            => AccessMemory(address, value);
+    }
+}

illNES/illNES.CPU/IMemoryInterface.cs

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+namespace illNES.CPU {
+
+    /// <summary>
+    /// The public API for the CPU to interface with RAM, 64k at a time ;)
+    /// </summary>
+    public interface IMemoryInterface {
+
+        /// <summary>
+        /// Read a byte value at a 16bit memory address
+        /// </summary>
+        /// <param name="address">The memory address to read from</param>
+        /// <returns>The byte stored at the requested address</returns>
+        byte Read(ushort address);
+
+        /// <summary>
+        /// Read a 16 bit value comprised of the byte at the specified 16-bit address,
+        /// and the next consecutive address.
+        /// Note that memory wraps within the 16-bit address range,
+        /// so the word read from `0xffff` will be the byte from `0xffff` and the byte from `0x0000`.
+        /// 
+        /// MOS6502 is little endian.
+        /// </summary>
+        /// <param name="address">The memory address to start reading at</param>
+        /// <returns>
+        /// The 16 bit value comprised of the byte stored at `address`,
+        /// and the byte stored at `address+1`
+        /// </returns>
+        ushort ReadWord(ushort address);
+
+        /// <summary>
+        /// Write a byte value to the specified 16bit memory address.
+        /// </summary>
+        /// <param name="address">The memory address to write to</param>
+        /// <param name="value">The byte value to write</param>
+        void Write(ushort address, byte value);
+
+        /// <summary>
+        /// Dump up to 256 contiguous values from memory, starting at a given address.
+        /// </summary>
+        /// <param name="start">The memory address to start from</param>
+        /// <param name="offset">The offset relative to `start` to cease dumping at</param>
+        /// <returns></returns>
+        string DumpRam(ushort start, byte offset);
+
+        /// <summary>
+        /// Dump the contents of a binary file into memory, starting at the specified address.
+        /// </summary>
+        /// <param name="filePath">Path to the file</param>
+        /// <param name="address">The memory address to start the dump at</param>
+        void FileDump(string filePath, ushort address);
+    }
+}