turn Acia into an abstract class so that the 6551 and 6850 ACIAs can reuse code and an unified interface.

src/main/java/com/loomcom/symon/Simulator.java

@@ -24,6 +24,7 @@
 package com.loomcom.symon;
 
 import com.loomcom.symon.devices.Acia;
+import com.loomcom.symon.devices.Acia6551;
 import com.loomcom.symon.devices.Crtc;
 import com.loomcom.symon.devices.Memory;
 import com.loomcom.symon.devices.Via;
@@ -157,7 +158,7 @@ public class Simulator {
         this.cpu = new Cpu();
         this.ram = new Memory(MEMORY_BASE, MEMORY_BASE + MEMORY_SIZE - 1, false);
         this.via = new Via(VIA_BASE);
-        this.acia = new Acia(ACIA_BASE);
+        this.acia = new Acia6551(ACIA_BASE);
         this.crtc = new Crtc(CRTC_BASE, ram);
 
         bus.addCpu(cpu);

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

@@ -23,179 +23,47 @@
 
 package com.loomcom.symon.devices;
 
-import com.loomcom.symon.exceptions.MemoryAccessException;
 import com.loomcom.symon.exceptions.MemoryRangeException;
 
 
 /**
- * This is a simulation of the MOS 6551 ACIA, with limited
+ * Abstract base class for ACIAS such as the 6551 and 6580
- * 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.
  */
-public class Acia extends Device {
 
-    public static final int ACIA_SIZE = 4;
+public abstract class Acia extends Device {
 
-    static final int DATA_REG = 0;
+    private String name;
-    static final int STAT_REG = 1;
-    static final int CMND_REG = 2;
-    static final int CTRL_REG = 3;
     
     /**
      * Register addresses
      */
-    private int baseAddress;
+    int baseAddress;
 
-    /**
+    boolean receiveIrqEnabled = false;
-     * Registers. These are ignored in the current implementation.
+    boolean transmitIrqEnabled = false;
-     */
+    boolean overrun = false;
-    private int commandRegister;
-    private int controlRegister;
     
-    private boolean receiveIrqEnabled = false;
+	long lastTxWrite   = 0;
-    private boolean transmitIrqEnabled = false;
+    long lastRxRead    = 0;
-    private boolean overrun = false;
+    int  baudRate      = 0;
+    long baudRateDelay = 0;
 	
-    private long lastTxWrite   = 0;
+	/**
-    private long lastRxRead    = 0;
-    private int  baudRate      = 0;
-    private long baudRateDelay = 0;
-
-    /**
      * Read/Write buffers
      */
-    private int rxChar = 0;
+    int rxChar = 0;
-    private int txChar = 0;
+    int txChar = 0;
 
-    private boolean rxFull  = false;
+    boolean rxFull  = false;
-    private boolean txEmpty = true;
+    boolean txEmpty = true;
 	
-    public Acia(int address) throws MemoryRangeException {
+	
-        super(address, address + ACIA_SIZE - 1, "ACIA");
+    public Acia(int address, int size, String name) throws MemoryRangeException {
+        super(address, address + size - 1, name);
+        this.name = name;
         this.baseAddress = address;
     }
 
-    @Override
-    public int read(int address) throws MemoryAccessException {
-        switch (address) {
-            case DATA_REG:
-                return rxRead();
-            case STAT_REG:
-                return statusReg();
-            case CMND_REG:
-                return commandRegister;
-            case CTRL_REG:
-                return controlRegister;
-            default:
-                throw new MemoryAccessException("No register.");
-        }
-    }
-
-    @Override
-    public void write(int address, int data) throws MemoryAccessException {
-        switch (address) {
-            case 0:
-                txWrite(data);
-                break;
-            case 1:
-                reset();
-                break;
-            case 2:
-                setCommandRegister(data);
-                break;
-            case 3:
-                setControlRegister(data);
-                break;
-            default:
-                throw new MemoryAccessException("No register.");
-        }
-    }
-
-
-    private void setCommandRegister(int data) {
-        commandRegister = data;
-
-        // Bit 1 controls receiver IRQ behavior
-        receiveIrqEnabled = (commandRegister & 0x02) == 0;
-        // Bits 2 & 3 controls transmit IRQ behavior
-        transmitIrqEnabled = (commandRegister & 0x08) == 0 && (commandRegister & 0x04) != 0;
-    }
-
-    /**
-     * Set the control register and associated state.
-     *
-     * @param data
-     */
-    private void setControlRegister(int data) {
-        controlRegister = data;
-
-        // If the value of the data is 0, this is a request to reset,
-        // otherwise it's a control update.
-
-        if (data == 0) {
-            reset();
-        } else {
-            // Mask the lower three bits to get the baud rate.
-            int baudSelector = data & 0x0f;
-            switch (baudSelector) {
-                case 0:
-                    baudRate = 0;
-                    break;
-                case 1:
-                    baudRate = 50;
-                    break;
-                case 2:
-                    baudRate = 75;
-                    break;
-                case 3:
-                    baudRate = 110; // Real rate is actually 109.92
-                    break;
-                case 4:
-                    baudRate = 135; // Real rate is actually 134.58
-                    break;
-                case 5:
-                    baudRate = 150;
-                    break;
-                case 6:
-                    baudRate = 300;
-                    break;
-                case 7:
-                    baudRate = 600;
-                    break;
-                case 8:
-                    baudRate = 1200;
-                    break;
-                case 9:
-                    baudRate = 1800;
-                    break;
-                case 10:
-                    baudRate = 2400;
-                    break;
-                case 11:
-                    baudRate = 3600;
-                    break;
-                case 12:
-                    baudRate = 4800;
-                    break;
-                case 13:
-                    baudRate = 7200;
-                    break;
-                case 14:
-                    baudRate = 9600;
-                    break;
-                case 15:
-                    baudRate = 19200;
-                    break;
-            }
-
-            // Recalculate the baud rate delay.
-            baudRateDelay = calculateBaudRateDelay();
-        }
-    }
 
     /*
      * Calculate the delay in nanoseconds between successive read/write operations, based on the
@@ -225,26 +93,17 @@ public class Acia extends Device {
      */
     public void setBaudRate(int rate) {
         this.baudRate = rate;
+		this.baudRateDelay = calculateBaudRateDelay();
     }
 
     /**
      * @return The contents of the status register.
      */
-    public int statusReg() {
+    public abstract int statusReg();
-        // TODO: Overrun, Parity Error, Framing Error, DTR, DSR, and Interrupt flags.
-        int stat = 0;
-        if (rxFull && System.nanoTime() >= (lastRxRead + baudRateDelay)) {
-            stat |= 0x08;
-        }
-        if (txEmpty && System.nanoTime() >= (lastTxWrite + baudRateDelay)) {
-            stat |= 0x10;
-        }
-        return stat;
-    }
 
     @Override
     public String toString() {
-        return "ACIA@" + String.format("%04X", baseAddress);
+        return name + "@" + String.format("%04X", baseAddress);
     }
 
     public synchronized int rxRead() {
@@ -293,13 +152,4 @@ public class Acia extends Device {
         return rxFull;
     }
 
-    private synchronized void reset() {
-        txChar = 0;
-        txEmpty = true;
-        rxChar = 0;
-        rxFull = false;
-        receiveIrqEnabled = false;
-        transmitIrqEnabled = false;
-    }
-
 }

src/main/java/com/loomcom/symon/devices/Acia6551.java

@@ -0,0 +1,205 @@
+/*
+ * Copyright (c) 2008-2013 Seth J. Morabito <sethm@loomcom.com>
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining
+ * a copy of this software and associated documentation files (the
+ * "Software"), to deal in the Software without restriction, including
+ * without limitation the rights to use, copy, modify, merge, publish,
+ * distribute, sublicense, and/or sell copies of the Software, and to
+ * permit persons to whom the Software is furnished to do so, subject to
+ * the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be
+ * included in all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
+ * EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
+ * MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
+ * NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE
+ * LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION
+ * OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION
+ * WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
+ */
+
+package com.loomcom.symon.devices;
+
+import com.loomcom.symon.exceptions.MemoryAccessException;
+import com.loomcom.symon.exceptions.MemoryRangeException;
+
+
+/**
+ * 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.
+ */
+public class Acia6551 extends Acia {
+
+    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;
+
+
+    /**
+     * Registers. These are ignored in the current implementation.
+     */
+    private int commandRegister;
+    private int controlRegister;
+
+
+    public Acia6551(int address) throws MemoryRangeException {
+        super(address, ACIA_SIZE, "ACIA");
+    }
+
+    @Override
+    public int read(int address) throws MemoryAccessException {
+        switch (address) {
+            case DATA_REG:
+                return rxRead();
+            case STAT_REG:
+                return statusReg();
+            case CMND_REG:
+                return commandRegister;
+            case CTRL_REG:
+                return controlRegister;
+            default:
+                throw new MemoryAccessException("No register.");
+        }
+    }
+
+    @Override
+    public void write(int address, int data) throws MemoryAccessException {
+        switch (address) {
+            case 0:
+                txWrite(data);
+                break;
+            case 1:
+                reset();
+                break;
+            case 2:
+                setCommandRegister(data);
+                break;
+            case 3:
+                setControlRegister(data);
+                break;
+            default:
+                throw new MemoryAccessException("No register.");
+        }
+    }
+
+
+    private void setCommandRegister(int data) {
+        commandRegister = data;
+
+        // Bit 1 controls receiver IRQ behavior
+        receiveIrqEnabled = (commandRegister & 0x02) == 0;
+        // Bits 2 & 3 controls transmit IRQ behavior
+        transmitIrqEnabled = (commandRegister & 0x08) == 0 && (commandRegister & 0x04) != 0;
+    }
+
+    /**
+     * Set the control register and associated state.
+     *
+     * @param data
+     */
+    private void setControlRegister(int data) {
+        controlRegister = data;
+        int rate = 0;
+
+        // If the value of the data is 0, this is a request to reset,
+        // otherwise it's a control update.
+
+        if (data == 0) {
+            reset();
+        } else {
+            // Mask the lower three bits to get the baud rate.
+            int baudSelector = data & 0x0f;
+            switch (baudSelector) {
+                case 0:
+                    rate = 0;
+                    break;
+                case 1:
+                    rate = 50;
+                    break;
+                case 2:
+                    rate = 75;
+                    break;
+                case 3:
+                    rate = 110; // Real rate is actually 109.92
+                    break;
+                case 4:
+                    rate = 135; // Real rate is actually 134.58
+                    break;
+                case 5:
+                    rate = 150;
+                    break;
+                case 6:
+                    rate = 300;
+                    break;
+                case 7:
+                    rate = 600;
+                    break;
+                case 8:
+                    rate = 1200;
+                    break;
+                case 9:
+                    rate = 1800;
+                    break;
+                case 10:
+                    rate = 2400;
+                    break;
+                case 11:
+                    rate = 3600;
+                    break;
+                case 12:
+                    rate = 4800;
+                    break;
+                case 13:
+                    rate = 7200;
+                    break;
+                case 14:
+                    rate = 9600;
+                    break;
+                case 15:
+                    rate = 19200;
+                    break;
+            }
+
+            setBaudRate(rate);
+        }
+    }
+
+
+    /**
+     * @return The contents of the status register.
+     */
+    @Override
+    public int statusReg() {
+        // TODO: Overrun, Parity Error, Framing Error, DTR, DSR, and Interrupt flags.
+        int stat = 0;
+        if (rxFull && System.nanoTime() >= (lastRxRead + baudRateDelay)) {
+            stat |= 0x08;
+        }
+        if (txEmpty && System.nanoTime() >= (lastTxWrite + baudRateDelay)) {
+            stat |= 0x10;
+        }
+        return stat;
+    }
+
+
+    private synchronized void reset() {
+        txChar = 0;
+        txEmpty = true;
+        rxChar = 0;
+        rxFull = false;
+        receiveIrqEnabled = false;
+        transmitIrqEnabled = false;
+    }
+
+}

src/main/java/com/loomcom/symon/devices/Acia6850.java

@@ -37,7 +37,7 @@ import com.loomcom.symon.exceptions.MemoryRangeException;
  * status (full or empty) for transmit and receive buffers before
  * writing / reading.
  */
-public class Acia6850 extends Device {
+public class Acia6850 extends Acia {
 
     public static final int ACIA_SIZE = 2;
 
@@ -49,37 +49,14 @@ public class Acia6850 extends Device {
     static final int TX_REG = 1;	// write-only
 
     
-    /**
-     * Register addresses
-     */
-    private int baseAddress;
-
     /**
      * Registers. These are ignored in the current implementation.
      */
     private int commandRegister;
 
-    private boolean receiveIrqEnabled = false;
-    private boolean transmitIrqEnabled = false;
-    private boolean overrun = false;
-
-    private long lastTxWrite   = 0;
-    private long lastRxRead    = 0;
-    private int  baudRate      = 0;
-    private long baudRateDelay = 0;
-
-    /**
-     * Read/Write buffers
-     */
-    private int rxChar = 0;
-    private int txChar = 0;
-
-    private boolean rxFull  = false;
-    private boolean txEmpty = true;
 
     public Acia6850(int address) throws MemoryRangeException {
-        super(address, address + ACIA_SIZE - 1, "ACIA");
+        super(address, ACIA_SIZE, "ACIA6850");
-        this.baseAddress = address;
 		setBaudRate(2400);
     }
 
@@ -126,40 +103,11 @@ public class Acia6850 extends Device {
     }
 
 
-    /*
-     * Calculate the delay in nanoseconds between successive read/write operations, based on the
-     * configured baud rate.
-     */
-    private long calculateBaudRateDelay() {
-        if (baudRate > 0) {
-            // TODO: This is a pretty rough approximation based on 8 bits per character,
-            // and 1/baudRate per bit. It could certainly be improved
-            return (long)((1.0 / baudRate) * 1000000000 * 8);
-        } else {
-            return 0;
-        }
-    }
-
-    /**
-     * @return The simulated baud rate in bps.
-     */
-    public int getBaudRate() {
-        return baudRate;
-    }
-
-    /**
-     * Set the baud rate of the simulated ACIA.
-     *
-     * @param rate The baud rate in bps. 0 means no simulated baud rate delay.
-     */
-    public void setBaudRate(int rate) {
-        this.baudRate = rate;
-		this.baudRateDelay = calculateBaudRateDelay();
-    }
 
     /**
      * @return The contents of the status register.
      */
+    @Override
     public int statusReg() {
         // TODO: Parity Error, Framing Error, DTR, DSR, and Interrupt flags.
         int stat = 0;
@@ -176,62 +124,6 @@ public class Acia6850 extends Device {
         return stat;
     }
 
-    @Override
-    public String toString() {
-        return "ACIA6850@" + String.format("%04X", baseAddress);
-    }
-
-    public synchronized int rxRead() {
-        lastRxRead = System.nanoTime();
-        rxFull = false;
-		overrun = false;
-        return rxChar;
-    }
-
-    public synchronized void rxWrite(int data) {
-		// when receiving while full: overrun
-		if(rxFull) {
-			overrun = true;
-		}
-		
-        rxFull = true;
-
-        if (receiveIrqEnabled) {
-            getBus().assertIrq();
-        }
-
-        rxChar = data;
-    }
-
-    public synchronized int txRead() {
-        txEmpty = true;
-
-        if (transmitIrqEnabled) {
-            getBus().assertIrq();
-        }
-
-        return txChar;
-    }
-
-    public synchronized void txWrite(int data) {
-        lastTxWrite = System.nanoTime();
-        txChar = data;
-        txEmpty = false;
-    }
-
-    /**
-     * @return true if there is character data in the TX register.
-     */
-    public boolean hasTxChar() {
-        return !txEmpty;
-    }
-
-    /**
-     * @return true if there is character data in the RX register.
-     */
-    public boolean hasRxChar() {
-        return rxFull;
-    }
 
     private synchronized void reset() {
 		overrun = false;

src/test/java/com/loomcom/symon/AciaTest.java

@@ -1,6 +1,7 @@
 package com.loomcom.symon;
 
 import com.loomcom.symon.devices.Acia;
+import com.loomcom.symon.devices.Acia6551;
 import org.junit.Test;
 
 import static org.junit.Assert.assertEquals;
@@ -12,7 +13,7 @@ public class AciaTest {
     public void shouldTriggerInterruptOnRxFullIfRxIrqEnabled() throws Exception {
         Bus mockBus = mock(Bus.class);
 
-        Acia acia = new Acia(0x000);
+        Acia acia = new Acia6551(0x000);
         acia.setBus(mockBus);
 
         // Disable TX IRQ, Enable RX IRQ
@@ -27,7 +28,7 @@ public class AciaTest {
     public void shouldNotTriggerInterruptOnRxFullIfRxIrqNotEnabled() throws Exception {
         Bus mockBus = mock(Bus.class);
 
-        Acia acia = new Acia(0x000);
+        Acia acia = new Acia6551(0x000);
         acia.setBus(mockBus);
 
         // Disable TX IRQ, Disable RX IRQ
@@ -42,7 +43,7 @@ public class AciaTest {
     public void shouldTriggerInterruptOnTxEmptyIfTxIrqEnabled() throws Exception {
         Bus mockBus = mock(Bus.class);
 
-        Acia acia = new Acia(0x000);
+        Acia acia = new Acia6551(0x000);
         acia.setBus(mockBus);
 
         // Enable TX IRQ, Disable RX IRQ
@@ -63,7 +64,7 @@ public class AciaTest {
     public void shouldNotTriggerInterruptOnTxEmptyIfTxIrqNotEnabled() throws Exception {
         Bus mockBus = mock(Bus.class);
 
-        Acia acia = new Acia(0x000);
+        Acia acia = new Acia6551(0x000);
         acia.setBus(mockBus);
 
         // Disable TX IRQ, Disable RX IRQ
@@ -80,14 +81,14 @@ public class AciaTest {
 
     @Test
     public void newAciaShouldHaveTxEmptyStatus() throws Exception {
-        Acia acia = new Acia(0x000);
+        Acia acia = new Acia6551(0x000);
 
         assertEquals(0x10, acia.read(0x0001));
     }
 
     @Test
     public void aciaShouldHaveTxEmptyStatusOffIfTxHasData() throws Exception {
-        Acia acia = new Acia(0x000);
+        Acia acia = new Acia6551(0x000);
 
         acia.txWrite('a');
         assertEquals(0x00, acia.read(0x0001));
@@ -95,7 +96,7 @@ public class AciaTest {
 
     @Test
     public void aciaShouldHaveRxFullStatusOffIfRxHasData() throws Exception {
-        Acia acia = new Acia(0x000);
+        Acia acia = new Acia6551(0x000);
 
         acia.rxWrite('a');
         assertEquals(0x18, acia.read(0x0001));
@@ -104,7 +105,7 @@ public class AciaTest {
     @Test
     public void aciaShouldHaveTxEmptyAndRxFullStatusOffIfRxAndTxHaveData()
             throws Exception {
-        Acia acia = new Acia(0x000);
+        Acia acia = new Acia6551(0x000);
 
         acia.rxWrite('a');
         acia.txWrite('b');
@@ -115,7 +116,7 @@ public class AciaTest {
     @Test
     public void readingBuffersShouldResetStatus()
             throws Exception {
-        Acia acia = new Acia(0x0000);
+        Acia acia = new Acia6551(0x0000);
 
         acia.rxWrite('a');
         acia.txWrite('b');