Checkpoint of my Swing UI refactoring. Usable for output-only programs, but only barely.

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

@@ -1,124 +1,132 @@
 package com.loomcom.symon.devices;
 
 import com.loomcom.symon.exceptions.*;
-import com.loomcom.symon.util.*;
+
 
 /**
  * This is a simulation of the MOS 6551 ACIA, with limited
  * functionality.  Interrupts are not supported.
- *
+ * <p/>
  * Unlike a 16550 UART, the 6551 ACIA has only one-byte transmit and
  * receive buffers. It is the programmer's responsibility to check the
  * status (full or empty) for transmit and receive buffers before
- * writing / reading.  However, in the simulation we maintain two
- * small buffers of 256 characters, since we only wake up to check for
- * keyboard input and do output every 500 instructions.
+ * writing / reading.
  */
 public class Acia extends Device {
 
-  public static final int ACIA_SIZE = 4;
-  public static final int BUF_LEN = 256;
+    public static final int ACIA_SIZE = 4;
 
-  static final int DATA_REG = 0;
-  static final int STAT_REG = 1;
-  static final int CMND_REG = 2;
-  static final int CTRL_REG = 3;
+    static final int DATA_REG = 0;
+    static final int STAT_REG = 1;
+    static final int CMND_REG = 2;
+    static final int CTRL_REG = 3;
 
-  /** Register addresses */
-  private int baseAddress;
+    /**
+     * Register addresses
+     */
+    private int baseAddress;
 
-  /** Registers. These are ignored in the current implementation. */
-  private int commandRegister;
-  private int controlRegister;
+    /**
+     * Registers. These are ignored in the current implementation.
+     */
+    private int commandRegister;
+    private int controlRegister;
 
-  /** Read/Write buffers */
-  private FifoRingBuffer rxBuffer = new FifoRingBuffer(BUF_LEN);
-  private FifoRingBuffer txBuffer = new FifoRingBuffer(BUF_LEN);
+    /**
+     * Read/Write buffers
+     */
+    private int rxChar = 0;
+    private int txChar = 0;
 
-  public Acia(int address) throws MemoryRangeException {
-    super(address, ACIA_SIZE, "ACIA");
-    this.baseAddress = address;
-  }
+    private boolean rxFull = false;
+    private boolean txFull = false;
 
-  @Override
-  public int read(int address) throws MemoryAccessException {
-    switch (address) {
-    case DATA_REG:
-      try {
-        return rxRead();
-      } catch (FifoUnderrunException ex) {
-        throw new MemoryAccessException("Buffer underrun");
-      }
-    case STAT_REG:
-      return ((rxBuffer.isEmpty() ? 0x00 : 0x08) |
-              (txBuffer.isEmpty() ? 0x10 : 0x00));
-    case CMND_REG:
-      return commandRegister;
-    case CTRL_REG:
-      return controlRegister;
-    default:
-      throw new MemoryAccessException("No register.");
+    public Acia(int address) throws MemoryRangeException {
+        super(address, ACIA_SIZE, "ACIA");
+        this.baseAddress = address;
     }
-  }
 
-  @Override
-  public void write(int address, int data) throws MemoryAccessException {
-    switch (address) {
-    case 0:
-      txWrite(data);
-      break;
-    case 1:
-      reset();
-      break;
-    case 2:
-      commandRegister = data;
-      break;
-    case 3:
-      controlRegister = data;
-      break;
-    default:
-      throw new MemoryAccessException("No register.");
+    @Override
+    public int read(int address) throws MemoryAccessException {
+        switch (address) {
+            case DATA_REG:
+                return rxRead();
+            case STAT_REG:
+                return ((rxFull ? 0x08 : 0x00) |
+                        (txFull ? 0x00 : 0x10));
+            case CMND_REG:
+                return commandRegister;
+            case CTRL_REG:
+                return controlRegister;
+            default:
+                throw new MemoryAccessException("No register.");
+        }
     }
-  }
 
-  @Override
-  public String toString() {
-    return "ACIA@" + String.format("%04X", baseAddress);
-  }
+    @Override
+    public void write(int address, int data) throws MemoryAccessException {
+        switch (address) {
+            case 0:
+                txWrite(data);
+                break;
+            case 1:
+                reset();
+                break;
+            case 2:
+                commandRegister = data;
+                break;
+            case 3:
+                controlRegister = data;
+                break;
+            default:
+                throw new MemoryAccessException("No register.");
+        }
+    }
 
-  public int rxRead() throws FifoUnderrunException {
-    return rxBuffer.pop();
-  }
+    @Override
+    public String toString() {
+        return "ACIA@" + String.format("%04X", baseAddress);
+    }
 
-  public void rxWrite(int data) {
-    rxBuffer.push(data);
-  }
+    public synchronized int rxRead() {
+        rxFull = false;
+        return rxChar;
+    }
 
-  public int txRead() throws FifoUnderrunException {
-    return txBuffer.pop();
-  }
+    public synchronized void rxWrite(int data) {
+        rxFull = true;
+        rxChar = data;
+    }
 
-  public void txWrite(int data) {
-    txBuffer.push(data);
-  }
+    public synchronized int txRead() {
+        txFull = false;
+        return txChar;
+    }
 
-  /**
-   * @return true if there is character data in the TX register.
-   */
-  public boolean hasTxChar() {
-    return !txBuffer.isEmpty();
-  }
+    public synchronized void txWrite(int data) {
+        txFull = true;
+        txChar = data;
+    }
 
-  /**
-   * @return true if there is character data in the RX register.
-   */
-  public boolean hasRxChar() {
-    return !rxBuffer.isEmpty();
-  }
+    /**
+     * @return true if there is character data in the TX register.
+     */
+    public boolean hasTxChar() {
+        return txFull;
+    }
 
-  private void reset() {
-    txBuffer.reset();
-    rxBuffer.reset();
-  }
+    /**
+     * @return true if there is character data in the RX register.
+     */
+    public boolean hasRxChar() {
+        return rxFull;
+    }
+
+    private synchronized void reset() {
+        txChar = 0;
+        txFull = false;
+        rxChar = 0;
+        rxFull = false;
+    }
 
 }