Implemented Zero Page,X, Zero Page,Y, and Indirect addressing mode instructions, along with unit tests.

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

@@ -0,0 +1,101 @@
+package com.loomcom.symon;
+
+import com.loomcom.symon.devices.Memory;
+import com.loomcom.symon.exceptions.MemoryRangeException;
+import junit.framework.TestCase;
+
+public class CpuZeroPageYModeTest extends TestCase {
+
+  protected Cpu cpu;
+  protected Bus bus;
+  protected Memory mem;
+
+  protected void setUp() throws Exception {
+    this.cpu = new Cpu();
+    this.bus = new Bus(0x0000, 0xffff);
+    this.mem = new Memory(0x0000, 0x10000);
+    bus.addCpu(cpu);
+    bus.addDevice(mem);
+
+    // Load the reset vector.
+    bus.write(0xfffc, Cpu.DEFAULT_BASE_ADDRESS & 0x00ff);
+    bus.write(0xfffd, (Cpu.DEFAULT_BASE_ADDRESS & 0xff00)>>>8);
+
+    cpu.reset();
+    // Assert initial state
+    assertEquals(0, cpu.getAccumulator());
+    assertEquals(0, cpu.getXRegister());
+    assertEquals(0, cpu.getYRegister());
+    assertEquals(0x200, cpu.getProgramCounter());
+    assertEquals(0xff, cpu.getStackPointer());
+    assertEquals(0x20, cpu.getProcessorStatus());
+  }
+
+  /*
+   * The following opcodes are tested for correctness in this file:
+   *
+   * STX - $96
+   * LDX - $b6
+   *
+   */
+
+  /* STX - Store X Register - $96 */
+
+  public void test_STX() {
+    cpu.setYRegister(0x30);
+    cpu.setXRegister(0x00);
+    bus.loadProgram(0x96, 0x10);  // STX $10,Y
+    cpu.step();
+    assertEquals(0x00, bus.read(0x40));
+    assertTrue(cpu.getZeroFlag());
+    assertFalse(cpu.getNegativeFlag());
+
+    cpu.reset();
+    cpu.setYRegister(0x30);
+    cpu.setXRegister(0x0f);
+    bus.loadProgram(0x96, 0x10);  // STX $10,Y
+    cpu.step();
+    assertEquals(0x0f, bus.read(0x40));
+    assertFalse(cpu.getZeroFlag());
+    assertFalse(cpu.getNegativeFlag());
+
+    cpu.reset();
+    cpu.setYRegister(0x30);
+    cpu.setXRegister(0x80);
+    bus.loadProgram(0x96, 0x10);  // STX $10,Y
+    cpu.step();
+    assertEquals(0x80, bus.read(0x40));
+    assertFalse(cpu.getZeroFlag());
+    assertTrue(cpu.getNegativeFlag());
+  }
+
+  /* LDX - Load X Register - $b6 */
+
+  public void test_LDX() {
+    bus.write(0x40, 0x00);
+    bus.write(0x41, 0x0f);
+    bus.write(0x42, 0x80);
+
+    bus.loadProgram(0xb6, 0x10,
+                    0xb6, 0x11,
+                    0xb6, 0x12);
+
+    cpu.setYRegister(0x30);
+
+    cpu.step();
+    assertEquals(0x00, cpu.getXRegister());
+    assertTrue(cpu.getZeroFlag());
+    assertFalse(cpu.getNegativeFlag());
+
+    cpu.step();
+    assertEquals(0x0f, cpu.getXRegister());
+    assertFalse(cpu.getZeroFlag());
+    assertFalse(cpu.getNegativeFlag());
+
+    cpu.step();
+    assertEquals(0x80, cpu.getXRegister());
+    assertFalse(cpu.getZeroFlag());
+    assertTrue(cpu.getNegativeFlag());
+  }
+
+}