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Implemented a load more Z80 OpCodes. Added a breakpoint to the debugger

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This commit is contained in:
Marc Parsons
2026-04-09 17:31:56 +01:00
parent f22da937b5
commit 0ef8b9f3eb
4 changed files with 154 additions and 16 deletions
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66
Core/Cpu/Z80.cs
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@@ -160,6 +160,37 @@ namespace Core.Cpu
if (result < 0) AF.Low |= 0x01;
}
private byte Dec8(byte value)
{
byte result = (byte)(value - 1);
// Store the existing Carry flag so we can preserve it
byte carry = (byte)(AF.Low & 0x01);
// Clear all flags
AF.Low = 0;
// Sign Flag (Bit 7)
if ((result & 0x80) != 0) AF.Low |= 0x80;
// Zero Flag (Bit 6)
if (result == 0) AF.Low |= 0x40;
// Half-Carry Flag (Bit 4) - Set if borrow from bit 4 (happens if the lower nibble was 0)
if ((value & 0x0F) == 0) AF.Low |= 0x10;
// Parity/Overflow Flag (Bit 2) - Set if the original value was 0x80 (maximum negative)
if (value == 0x80) AF.Low |= 0x04;
// Subtract Flag (Bit 1) - ALWAYS SET for decrements
AF.Low |= 0x02;
// Restore the original Carry Flag (Bit 0)
AF.Low |= carry;
return result;
}
private void Cp(byte value)
{
byte a = AF.High;
@@ -263,6 +294,16 @@ namespace Core.Cpu
case 0x23: // INC HL
HL.Word++;
return 6;
case 0x28: // JR Z, e
offset = (sbyte)FetchByte();
// Check if the Zero Flag (Bit 6) IS set
if ((AF.Low & 0x40) != 0)
{
PC = (ushort)(PC + offset);
return 12; // Jump taken
}
return 7; // Jump not taken
case 0x2B: // DEC HL
HL.Word--;
return 6;
@@ -276,6 +317,17 @@ namespace Core.Cpu
return 12; // Jump taken
}
return 7; // Jump not taken
case 0x35: // DEC (HL)
// Read the current byte from memory
byte memValue = _memory.Read(HL.Word);
// Decrement it and update flags
byte decremented = Dec8(memValue);
// Write the new value back to memory
_memory.Write(HL.Word, decremented);
return 11; // Takes 11 T-States
case 0x36: // LD (HL), n
byte nValue = FetchByte();
_memory.Write(HL.Word, nValue);
@@ -310,6 +362,20 @@ namespace Core.Cpu
_ioBus.Write(portAddress, AF.High);
return 11; // Takes 11 T-States
case 0xD9: // EXX
ushort tempBC = BC.Word;
BC.Word = BC_Prime.Word;
BC_Prime.Word = tempBC;
ushort tempDE = DE.Word;
DE.Word = DE_Prime.Word;
DE_Prime.Word = tempDE;
ushort tempHL = HL.Word;
HL.Word = HL_Prime.Word;
HL_Prime.Word = tempHL;
return 4; // Takes 4 T-States
case 0xDE: // SBC A, n
Sbc(FetchByte());
return 7;

40
Desktop/DebuggerForm.Designer.cs generated
View File

@@ -44,6 +44,10 @@
lstDisassembly = new ListBox();
lstStack = new ListBox();
btnExit = new Button();
saveFileDialog1 = new SaveFileDialog();
label1 = new Label();
txtBreakpoint = new TextBox();
label2 = new Label();
SuspendLayout();
//
// lblAF
@@ -128,7 +132,7 @@
//
// txtMemoryStart
//
txtMemoryStart.Location = new Point(238, 10);
txtMemoryStart.Location = new Point(300, 21);
txtMemoryStart.Margin = new Padding(2);
txtMemoryStart.Name = "txtMemoryStart";
txtMemoryStart.Size = new Size(121, 27);
@@ -161,7 +165,7 @@
//
// btnRefreshMemory
//
btnRefreshMemory.Location = new Point(376, 7);
btnRefreshMemory.Location = new Point(425, 21);
btnRefreshMemory.Margin = new Padding(2);
btnRefreshMemory.Name = "btnRefreshMemory";
btnRefreshMemory.Size = new Size(90, 27);
@@ -208,11 +212,39 @@
btnExit.UseVisualStyleBackColor = true;
btnExit.Click += btnExit_Click;
//
// label1
//
label1.AutoSize = true;
label1.Location = new Point(289, 288);
label1.Name = "label1";
label1.Size = new Size(81, 20);
label1.TabIndex = 19;
label1.Text = "Breakpoint";
//
// txtBreakpoint
//
txtBreakpoint.Location = new Point(376, 281);
txtBreakpoint.Name = "txtBreakpoint";
txtBreakpoint.Size = new Size(125, 27);
txtBreakpoint.TabIndex = 20;
//
// label2
//
label2.AutoSize = true;
label2.Location = new Point(233, 21);
label2.Name = "label2";
label2.Size = new Size(62, 20);
label2.TabIndex = 21;
label2.Text = "Address";
//
// DebuggerForm
//
AutoScaleDimensions = new SizeF(8F, 20F);
AutoScaleMode = AutoScaleMode.Font;
ClientSize = new Size(928, 350);
Controls.Add(label2);
Controls.Add(txtBreakpoint);
Controls.Add(label1);
Controls.Add(btnExit);
Controls.Add(lstStack);
Controls.Add(lstDisassembly);
@@ -254,6 +286,10 @@
private ListBox lstStack;
private Button btnExit;
public ListBox lstDisassembly;
private SaveFileDialog saveFileDialog1;
private Label label1;
private TextBox txtBreakpoint;
private Label label2;
//private TextBox textBox4;
}
}

57
Desktop/DebuggerForm.cs
View File

@@ -11,6 +11,7 @@ namespace Desktop
private readonly Z80 _cpu;
private readonly MemoryBus _memoryBus;
private bool _isRunning = false;
private ushort? _breakpoint = null;
public DebuggerForm(Z80 cpu, MemoryBus memoryBus)
{
@@ -57,18 +58,45 @@ namespace Desktop
return;
}
// --- NEW: Parse the Breakpoint ---
if (!string.IsNullOrWhiteSpace(txtBreakpoint.Text))
{
if (ushort.TryParse(txtBreakpoint.Text, System.Globalization.NumberStyles.HexNumber, null, out ushort parsedBp))
{
_breakpoint = parsedBp;
}
else
{
MessageBox.Show("Invalid hex address in breakpoint!", "Error", MessageBoxButtons.OK, MessageBoxIcon.Warning);
return;
}
}
else
{
_breakpoint = null; // No text means no breakpoint
}
// ---------------------------------
// Start the run state
_isRunning = true;
btnRun.Text = "Stop";
// Fire up a background thread so the Windows UI doesn't freeze
// Fire up a background thread
await Task.Run(() =>
{
try
{
// Free-run the CPU until the flag is flipped or it crashes!
while (_isRunning)
{
// --- NEW: Breakpoint Check ---
// We check BEFORE stepping so it stops exactly on the instruction
if (_breakpoint.HasValue && _cpu.PC == _breakpoint.Value)
{
_isRunning = false;
break; // Cleanly exit the while loop
}
// -----------------------------
_cpu.Step();
}
}
@@ -76,23 +104,18 @@ namespace Desktop
{
_isRunning = false;
// We are on a background thread. We MUST use Invoke to tell the
// main UI thread to update the labels and show the message box!
this.Invoke((MethodInvoker)delegate
{
btnRun.Text = "Run";
UpdateDisplay();
MessageBox.Show(ex.Message, "CPU Break", MessageBoxButtons.OK, MessageBoxIcon.Information);
});
}
});
// If the user clicked Stop manually (no exception thrown), we still want to update the UI
if (!_isRunning)
{
// Whether it stopped because of a breakpoint, a crash, or the user clicking "Stop",
// we MUST update the UI when the background thread finishes!
btnRun.Text = "Run";
UpdateDisplay();
}
}
private void btnExit_Click(object sender, EventArgs e)
{
@@ -186,8 +209,6 @@ namespace Desktop
{
lstDisassembly.Items.Clear();
// THIS is the critical link! It forces the top of the list
// to always be exactly where the CPU currently is.
ushort currentPc = _cpu.PC;
int instructionsToShow = 8;
@@ -220,6 +241,12 @@ namespace Desktop
case 0x23:
mnemonic = "INC HL";
break;
case 0x28:
sbyte jrZOffset = (sbyte)_memoryBus.Read((ushort)(currentPc + 1));
ushort jrZDest = (ushort)(currentPc + 2 + jrZOffset);
mnemonic = $"JR Z, 0x{jrZDest:X4}";
instructionLength = 2;
break;
case 0x2B:
mnemonic = "DEC HL";
break;
@@ -229,6 +256,9 @@ namespace Desktop
mnemonic = $"JR NC, 0x{dest:X4}";
instructionLength = 2;
break;
case 0x35:
mnemonic = "DEC (HL)";
break;
case 0x36:
byte memValue = _memoryBus.Read((ushort)(currentPc + 1));
mnemonic = $"LD (HL), 0x{memValue:X2}";
@@ -268,6 +298,9 @@ namespace Desktop
mnemonic = $"OUT (0x{outPort:X2}), A";
instructionLength = 2;
break;
case 0xD9:
mnemonic = "EXX";
break;
case 0xDE:
byte sbcValue = _memoryBus.Read((ushort)(currentPc + 1));
mnemonic = $"SBC A, 0x{sbcValue:X2}";

3
Desktop/DebuggerForm.resx
View File

@@ -117,4 +117,7 @@
<resheader name="writer">
<value>System.Resources.ResXResourceWriter, System.Windows.Forms, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089</value>
</resheader>
<metadata name="saveFileDialog1.TrayLocation" type="System.Drawing.Point, System.Drawing, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a">
<value>17, 17</value>
</metadata>
</root>