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Refactoring CPU cycles handling #12

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Merged
mjbohn merged 4 commits into from
Jul 13, 2025
Merged

Refactoring CPU cycles handling #12

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24273cb
add /docs
Jun 29, 2025
94c628a
refactor class member 'cycles'
Jul 13, 2025
5d1176a
introduce IncrementCpuCycle(ulong count)
Jul 13, 2025
9f61fb7
visualize cycles in GUI staus panel
Jul 13, 2025
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20 changes: 10 additions & 10 deletions CPU_emu/CPU_emu.CMD_Methods.cs
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Original file line number Diff line number Diff line change
Expand Up @@ -18,21 +18,21 @@ public void Cmd_00()
// Load Accumulator immidiate A9
public void Cmd_A9()
{
SetRegister("A", FetchByte(ref cycles));
SetRegister("A", FetchByte(ref _CpuCycle));
SetZeroAndNegativeFlags(A);
}

// Load Accumulator zeropage A5
public void Cmd_A5()
{
SetRegister("A", ReadByteFromMemory(FetchByte(ref cycles)));
SetRegister("A", ReadByteFromMemory(FetchByte(ref _CpuCycle)));
SetZeroAndNegativeFlags(A);
}

// Load Accumulator zeropage X B5
public void Cmd_B5()
{
byte b_tmp = FetchByte(ref cycles);
byte b_tmp = FetchByte(ref _CpuCycle);
b_tmp += X; // add regX to address
SetRegister("A", ReadByteFromMemory(b_tmp));
SetZeroAndNegativeFlags(A);
Expand All @@ -43,23 +43,23 @@ public void Cmd_B5()
// Load X immidiate A2
public void Cmd_A2()
{
byte b_tmp = FetchByte(ref cycles);
byte b_tmp = FetchByte(ref _CpuCycle);
SetRegister("X", b_tmp);
SetZeroAndNegativeFlags(X);
}

// Load X zeropage A6
public void Cmd_A6()
{
byte b_tmp = FetchByte(ref cycles);
byte b_tmp = FetchByte(ref _CpuCycle);
SetRegister("X", ReadByteFromMemory(b_tmp));
SetZeroAndNegativeFlags(X);
}

// Load X zeropage Y B6
public void Cmd_B6()
{
byte b_tmp = FetchByte(ref cycles); // Get ZP address
byte b_tmp = FetchByte(ref _CpuCycle); // Get ZP address
b_tmp += Y; // add regY to address
SetRegister("X", ReadByteFromMemory(b_tmp));
SetZeroAndNegativeFlags(X);
Expand All @@ -71,23 +71,23 @@ public void Cmd_B6()
// Load Y immidiate A0
public void Cmd_A0()
{
byte b_tmp = FetchByte(ref cycles);
byte b_tmp = FetchByte(ref _CpuCycle);
SetRegister("Y", b_tmp);
SetZeroAndNegativeFlags(Y);
}

// Load Y zeropage A4
public void Cmd_A4()
{
byte b_tmp = FetchByte(ref cycles);
byte b_tmp = FetchByte(ref _CpuCycle);
SetRegister("Y", ReadByteFromMemory(b_tmp));
SetZeroAndNegativeFlags(Y);
}

// Load Y zeropage X B4
public void Cmd_B4()
{
byte b_tmp = FetchByte(ref cycles); // Get ZP address
byte b_tmp = FetchByte(ref _CpuCycle); // Get ZP address
b_tmp += X; // add regX to address
SetRegister("Y", ReadByteFromMemory(b_tmp));
SetZeroAndNegativeFlags(Y);
Expand All @@ -100,7 +100,7 @@ public void Cmd_B4()
// Push Accumulator on Stack
public void Cmd_48()
{
PushByteToStack(A,ref cycles);
PushByteToStack(A,ref _CpuCycle);
}

#endregion
Expand Down
53 changes: 35 additions & 18 deletions CPU_emu/Class_CPU.cs
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Original file line number Diff line number Diff line change
Expand Up @@ -27,7 +27,7 @@ public partial class CPU
private ulong _InterruptPeriod;
private bool _ExitRequested;
private bool _SteppingMode;
private ulong cycles;
internal ulong _CpuCycle;
private const uint MAX_MEM = 1024 * 64;
private byte[] Data = new byte[MAX_MEM];

Expand Down Expand Up @@ -62,6 +62,7 @@ public byte[] Memory
public event EventHandler<CPUEventArgs> OnFlagsUpdate;
public event EventHandler<CPUEventArgs> OnMemoryUpdate;
public event EventHandler<CPUEventArgs> OnRegisterUpdate;
public event EventHandler<CPUEventArgs> OnCpuCycleIncrement;
public event EventHandler<CPUEventArgs> OnProgramCounterUpdate;
public event EventHandler<CPUEventArgs> OnStackPointerUpdate;
public event EventHandler<CPUEventArgs> OnPCoverflow;
Expand Down Expand Up @@ -100,6 +101,7 @@ public void Reset()

OnFlagsUpdate?.Invoke(this, new CPUEventArgs(this));
OnProgramCounterUpdate?.Invoke(this, new CPUEventArgs(this));
ResetCpuCycle();

}

Expand Down Expand Up @@ -161,14 +163,14 @@ public void Start()

private void CpuRunner_DoWork(object sender, DoWorkEventArgs e)
{
cycles = InterruptPeriod;
//_CpuCycle = InterruptPeriod;

Type thisType = this.GetType();


while (CpuIsRunning)
{
byte instruction = FetchByte(ref cycles);
byte instruction = FetchByte(ref _CpuCycle);

// Build method name from 'Cmd' + opcode
string cmd = "Cmd_" + instruction.ToString("X2").ToUpper();
Expand Down Expand Up @@ -198,10 +200,11 @@ private void CpuRunner_DoWork(object sender, DoWorkEventArgs e)
break;
}

if (cycles <= 0)
{
cycles = InterruptPeriod;
}
//ToDo remove
//if (_CpuCycle <= 0)
//{
// _CpuCycle = InterruptPeriod;
//}

if (SlowDown && !_SteppingMode)
{
Expand All @@ -214,24 +217,24 @@ private void CpuRunner_DoWork(object sender, DoWorkEventArgs e)

private uint AddrAbsolute()
{
return FetchWord(ref cycles);
return FetchWord(ref _CpuCycle);
}

private byte PullByteFromStack(ref ulong cycles)
private byte PullByteFromStack(ref ulong CpuCycle)
{
IncrementSP();
cycles--;
IncrementCpuCycle(1);
byte b = ReadByteFromMemory(SP);
cycles--;
IncrementCpuCycle(1);
return b;
}

private void PushByteToStack(byte b,ref ulong cycles)
private void PushByteToStack(byte b,ref ulong CpuCycle)
{
WriteByteToMemory(b, SP);
cycles--;
IncrementCpuCycle(1);
DecrementSP();
cycles--;
IncrementCpuCycle(1);

}

Expand All @@ -248,21 +251,21 @@ private void SetZeroAndNegativeFlags(byte register)
OnFlagsUpdate?.Invoke(this, new CPUEventArgs(this));
}

private byte FetchByte(ref ulong cycles)
private byte FetchByte(ref ulong CpuCycle)
{
byte data = Data[PC];
IncrementPC();
cycles--;
IncrementCpuCycle(1);
return data;
}

private ushort FetchWord(ref ulong cycles)
private ushort FetchWord(ref ulong CpuCycle)
{
ushort LoByte = ReadByteFromMemory((ushort)PC);
PC++;
ushort HiByte = (ushort)(ReadByteFromMemory((ushort)PC) << 8);

cycles -= 2;
IncrementCpuCycle(2);

return LoByte |= HiByte;
}
Expand Down Expand Up @@ -310,6 +313,18 @@ private void DecrementSP()
OnStackPointerUpdate?.Invoke(this, new CPUEventArgs(this));
}

private void IncrementCpuCycle(ulong count)
{
_CpuCycle += count;
OnCpuCycleIncrement?.Invoke(this, new CPUEventArgs(this));
}

private void ResetCpuCycle()
{
_CpuCycle =0;
OnCpuCycleIncrement?.Invoke(this, new CPUEventArgs(this));
}

// Programcounter PC
//UT
public void SetPC(uint value)
Expand Down Expand Up @@ -386,6 +401,7 @@ public class CPUEventArgs : EventArgs
public byte A { get; set; }
public byte X { get; set; }
public byte Y { get; set; }
public ulong Cycles { get; set; }
public IDictionary<string, bool> Flags { get; set; }

public CPUEventArgs(CPU cpu)
Expand All @@ -404,6 +420,7 @@ private void SetProperties()
X = cpu.X;
Y = cpu.Y;
Flags = cpu.flags;
Cycles = cpu._CpuCycle;
}


Expand Down
26 changes: 17 additions & 9 deletions CPU_emu/Forms/CPU_emu.Designer.cs
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16 changes: 16 additions & 0 deletions CPU_emu/Forms/CPU_emu.cs
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Original file line number Diff line number Diff line change
Expand Up @@ -40,13 +40,16 @@ public CPU_emu()
Cpu.OnProgramCounterUpdate += Cpu_OnProgramCounterUpdate;
Cpu.OnPCoverflow += Cpu_OnPCgtThenMaxMem;
Cpu.OnBreak += Cpu_OnBreak;
Cpu.OnCpuCycleIncrement += Cpu_OnCpuCycleIncrement;

Cpu.Reset();

// config.OnPropertyChanged gets initialized @ CPU_emu_Load() due to race conditions

}



private void Config_OnPropertyChanged(object sender, PropertyChangedEventArgs e)
{
if (InvokeRequired)
Expand Down Expand Up @@ -190,6 +193,19 @@ private void Cpu_onFlagsUpdate(object sender, CPUEventArgs e)

}

private void Cpu_OnCpuCycleIncrement(object? sender, CPUEventArgs e)
{
if (InvokeRequired)
{
CpuEventCallback cb = new CpuEventCallback(Cpu_OnCpuCycleIncrement);
this.Invoke(cb, new object[] { sender, e });
}
else
{
toolStripStatusLabel3.Text = $"Cycles: {e.Cycles}";
}
}

#endregion


Expand Down
8 changes: 8 additions & 0 deletions docs/index.html
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Original file line number Diff line number Diff line change
@@ -0,0 +1,8 @@
<html>
<head>
<title>sim6502</title>
</head>
<body>
<strong>sim6502</strong>
</body>
</html>