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Merge pull request #15 from LIV2/master

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Correct BRK/IRQ behavior
This commit is contained in:
Seth Morabito 2016-03-20 11:43:42 -07:00
commit da88aadda2
3 changed files with 115 additions and 20 deletions
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29
src/main/java/com/loomcom/symon/Cpu.java
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@ -258,9 +258,7 @@ public class Cpu implements InstructionTable {
/** Single Byte Instructions; Implied and Relative **/
case 0x00: // BRK - Force Interrupt - Implied
if (!getIrqDisableFlag()) {
handleIrq(state.pc + 1);
}
handleBrk(state.pc + 1);
break;
case 0x08: // PHP - Push Processor Status - Implied
// Break flag is always set in the stack value.
@ -744,13 +742,18 @@ public class Cpu implements InstructionTable {
}
}
private void handleBrk(int returnPc) throws MemoryAccessException {
handleInterrupt(returnPc, IRQ_VECTOR_L, IRQ_VECTOR_H, true);
clearIrq();
}
private void handleIrq(int returnPc) throws MemoryAccessException {
handleInterrupt(returnPc, IRQ_VECTOR_L, IRQ_VECTOR_H);
handleInterrupt(returnPc, IRQ_VECTOR_L, IRQ_VECTOR_H, false);
clearIrq();
}
private void handleNmi() throws MemoryAccessException {
handleInterrupt(state.pc, NMI_VECTOR_L, NMI_VECTOR_H);
handleInterrupt(state.pc, NMI_VECTOR_L, NMI_VECTOR_H, false);
clearNmi();
}
@ -759,9 +762,19 @@ public class Cpu implements InstructionTable {
*
* @throws MemoryAccessException
*/
private void handleInterrupt(int returnPc, int vectorLow, int vectorHigh) throws MemoryAccessException {
// Set the break flag before pushing.
setBreakFlag();
private void handleInterrupt(int returnPc, int vectorLow, int vectorHigh, boolean isBreak) throws MemoryAccessException {
if (isBreak)
{
// Set the break flag before pushing.
setBreakFlag();
}
else
{
// IRQ & NMI clear break flag
clearBreakFlag();
}
// Push program counter + 1 onto the stack
stackPush((returnPc >> 8) & 0xff); // PC high byte
stackPush(returnPc & 0xff); // PC low byte

40
src/test/java/com/loomcom/symon/CpuImpliedModeTest.java
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@ -117,9 +117,22 @@ public class CpuImpliedModeTest {
}
@Test
public void test_BRK_HonorsIrqDisableFlag() throws MemoryAccessException {
public void test_BRK_IgnoresIrqDisableFlag() throws MemoryAccessException {
cpu.setIrqDisableFlag();
cpu.setCarryFlag();
cpu.setOverflowFlag();
assertEquals(0x20 | Cpu.P_CARRY | Cpu.P_OVERFLOW | Cpu.P_IRQ_DISABLE,
cpu.getProcessorStatus());
assertEquals(0x00, cpu.stackPeek());
assertFalse(cpu.getBreakFlag());
assertEquals(0x0200, cpu.getProgramCounter());
assertEquals(0xff, cpu.getStackPointer());
// Set the IRQ vector
bus.write(0xffff, 0x12);
bus.write(0xfffe, 0x34);
bus.loadProgram(0xea,
0xea,
0xea,
@ -131,23 +144,26 @@ public class CpuImpliedModeTest {
assertEquals(0x203, cpu.getProgramCounter());
// Triggers the BRK, which should do nothing because
// of the Interrupt Disable flag
// Triggers the BRK
cpu.step();
// Reset to original contents of PC
assertEquals(0x0204, cpu.getProgramCounter());
// Empty stack
assertEquals(0xff, cpu.getStackPointer());
cpu.step(2); // Two more NOPs
// Was at PC = 0x204. PC+1 should now be on the stack
assertEquals(0x02, bus.read(0x1ff)); // PC high byte
assertEquals(0x05, bus.read(0x1fe)); // PC low byte
assertEquals(0x20 | Cpu.P_CARRY | Cpu.P_OVERFLOW | Cpu.P_BREAK | Cpu.P_IRQ_DISABLE,
bus.read(0x1fd)); // Processor Status, with B set
// Reset to original contents of PC
assertEquals(0x0206, cpu.getProgramCounter());
// Empty stack
assertEquals(0xff, cpu.getStackPointer());
// Interrupt vector held 0x1234, so we should be there.
assertEquals(0x1234, cpu.getProgramCounter());
assertEquals(0xfc, cpu.getStackPointer());
// B and I flags should have been set on P
assertEquals(0x20 | Cpu.P_CARRY | Cpu.P_OVERFLOW | Cpu.P_BREAK | Cpu.P_IRQ_DISABLE,
cpu.getProcessorStatus());
}
/* CLC - Clear Carry Flag - $18 */
@Test
public void test_CLC() throws MemoryAccessException {

66
src/test/java/com/loomcom/symon/CpuTest.java
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@ -384,6 +384,41 @@ public class CpuTest extends TestCase {
assertFalse(cpu.getCpuState().irqAsserted);
}
public void testIrqDoesNotSetBRK() throws Exception {
// Ensure the IRQ disable flag is cleared
cpu.clearIrqDisableFlag();
// Set the IRQ vector
bus.write(0xffff, 0x12);
bus.write(0xfffe, 0x34);
// Create an IRQ handler at 0x1234
cpu.setProgramCounter(0x1234);
bus.loadProgram(0xa9, 0x33, // LDA #$33
0x69, 0x01); // ADC #$01
cpu.setProgramCounter(0x0200);
// Create a little program at 0x0200
bus.loadProgram(0x18, // CLC
0xa9, 0x01, // LDA #$00
0x69, 0x01); // ADC #$01
cpu.step();
assertEquals(0x0201, cpu.getProgramCounter()); // First instruction executed.
assertEquals(0x00, cpu.getAccumulator());
cpu.step();
assertEquals(0x0203, cpu.getProgramCounter());
assertEquals(0x01, cpu.getAccumulator());
cpu.assertIrq();
cpu.step();
assertTrue(cpu.getIrqDisableFlag()); // Should have been set by the IRQ
assertFalse(cpu.getBreakFlag());
}
public void testIrqHonorsIrqDisabledFlag() throws Exception {
// Ensure the IRQ disable flag is set
cpu.setIrqDisableFlag();
@ -498,6 +533,37 @@ public class CpuTest extends TestCase {
assertFalse(cpu.getCpuState().nmiAsserted);
}
public void testNmiDoesNotSetBRK() throws Exception {
// Set the NMI vector to 0x1000
bus.write(0xfffb, 0x10);
bus.write(0xfffa, 0x00);
// Create an NMI handler at 0x1000
cpu.setProgramCounter(0x1000);
bus.loadProgram(0xa9, 0x33, // LDA #$33
0x69, 0x01); // ADC #$01
// Create a little program at 0x0200
cpu.setProgramCounter(0x0200);
bus.loadProgram(0x18, // CLC
0xa9, 0x01, // LDA #$00
0x69, 0x01); // ADC #$01
cpu.step();
assertEquals(0x0201, cpu.getProgramCounter()); // First instruction executed.
assertEquals(0x00, cpu.getAccumulator());
cpu.step();
assertEquals(0x0203, cpu.getProgramCounter());
assertEquals(0x01, cpu.getAccumulator());
cpu.assertNmi();
cpu.step();
assertFalse(cpu.getBreakFlag());
}
public void testNmiIgnoresIrqDisableFlag() throws Exception {
// Set the IRQ disable flag, which should be ignored by the NMI
cpu.setIrqDisableFlag();