- Continued refactoring of address decoding.

- Device read and write may now throw MemoryAccessException, and appropriate
  throws clauses have been added throughout the code.

src/main/java/com/loomcom/symon/devices/Device.java

@@ -29,13 +29,17 @@ public abstract class Device implements Comparable<Device> {
   }
 
   /* Methods required to be implemented by inheriting classes. */
-  public abstract void write(int address, int data);
-  public abstract int read(int address);
+  public abstract void write(int address, int data) throws MemoryAccessException;
+  public abstract int read(int address) throws MemoryAccessException;
   public abstract String toString();
 
   public void setBus(Bus bus) {
     this.bus = bus;
   }
+  
+  public Bus getBus() {
+    return this.bus;
+  }
 
   public MemoryRange getMemoryRange() {
     return memoryRange;

src/main/java/com/loomcom/symon/devices/Memory.java

@@ -2,7 +2,6 @@ package com.loomcom.symon.devices;
 
 import java.util.*;
 
-import com.loomcom.symon.*;
 import com.loomcom.symon.exceptions.*;
 
 public class Memory extends Device {
@@ -24,11 +23,15 @@ public class Memory extends Device {
     this(address, size, false);
   }
 
-  public void write(int address, int data) {
-    this.mem[address] = data;
+  public void write(int address, int data) throws MemoryAccessException {
+    if (readOnly) {
+      throw new MemoryAccessException("Cannot write to read-only memory at address " + address);
+    } else {
+      this.mem[address] = data;
+    }
   }
 
-  public int read(int address) {
+  public int read(int address) throws MemoryAccessException {
     return this.mem[address];
   }