Updated Z80 CPU to fix interrupts etc...

Core/Cpu/Z80.cs

@@ -30,7 +30,8 @@ namespace Core.Cpu
         public bool IFF1 { get; private set; } = false;
         public bool IFF2 { get; private set; } = false;
         public bool InterruptRequested { get; private set; } = false;
-        private bool _eiPending = false;
+        private int _eiDelay = 0;
+        public bool IsHalted { get; private set; } = false;
 
         // Main Register Set
         public RegisterPair AF;
@@ -50,7 +51,7 @@ namespace Core.Cpu
 
         // Special Purpose Registers
         public ushort PC; // Program Counter
-        public ushort SP; // Stack Pointer
+        public ushort SP;
         public byte I;    // Interrupt Vector
         public byte R;    // Memory Refresh
 
@@ -98,6 +99,10 @@ namespace Core.Cpu
             IFF2 = false;
             InterruptMode = 0;
             TotalTStates = 0;
+
+            _eiDelay = 0;
+            IsHalted = false;
+            InterruptRequested = false;
         }
 
         public void SaveState(BinaryWriter bw)
@@ -137,6 +142,7 @@ namespace Core.Cpu
 
         public int RequestInterrupt()
         {
+            IsHalted = false;
             InterruptRequested = true;
             // 1. If the ROM has disabled interrupts (DI), ignore the request
             if (!IFF1) return 0;
@@ -145,6 +151,8 @@ namespace Core.Cpu
             IFF1 = false;
             IFF2 = false;
 
+            _eiDelay = 0;
+
             // 3. Push the current Program Counter to the stack so we can return later
             Push(PC);
 
@@ -216,26 +224,40 @@ namespace Core.Cpu
 
         public int Step()
         {
-            bool triggerEi = _eiPending;
+            int tStates;
 
-            // Fetch the next opcode and increment the Program Counter
+            R = (byte)((R & 0x80) | ((R + 1) & 0x7F));
-            byte opcode = ReadMemory(PC++);
-            R = (byte)((R + 1) & 0x7F);
-            int tStates = ExecuteOpcode(opcode);
-            TotalTStates += tStates;
 
-            if (triggerEi)
+            if (IsHalted)
             {
-                IFF1 = true;
+                // The CPU is asleep! Do not fetch instructions, just pass the time.
-                IFF2 = true;
+                tStates = 4;
-                _eiPending = false;
+                TotalTStates += tStates;
+            }
+            else
+            {
+                // Normal execution
+                byte opcode = ReadMemory(PC++);
+                tStates = ExecuteOpcode(opcode);
+                TotalTStates += tStates;
+            }
+
+            // The interrupt enablement perfectly mimics the physical hardware delay.
+            // This MUST tick down even if the CPU is halted!
+            if (_eiDelay > 0)
+            {
+                _eiDelay--;
+                if (_eiDelay == 0)
+                {
+                    IFF1 = true;
+                    IFF2 = true;
+                }
             }
 
-            // Decode and execute
             return tStates;
         }
 
-        
+
 
         public string GetFlagsString()
         {
@@ -931,17 +953,21 @@ namespace Core.Cpu
                 case 0x73: WriteMemory(HL.Word, DE.Low); return 7;
                 case 0x74: WriteMemory(HL.Word, HL.High); return 7;
                 case 0x75: WriteMemory(HL.Word, HL.Low); return 7;
-                case 0x76: //HALT
+                case 0x76: // HALT
-                    if (!InterruptRequested)
+                    IsHalted = true;
-                    {
+                    return 4;
-                        PC--;
+
-                        return 4;
+                //case 0x76: //HALT
-                    }
+                //    if (!InterruptRequested)
-                    else
+                //    {
-                    {
+                //        PC--;
-                        InterruptRequested = false;
+                //        return 4;
-                        return 4;
+                //    }
-                    }
+                //    else
+                //    {
+                //        InterruptRequested = false;
+                //        return 4;
+                //    }
                 case 0x77: WriteMemory(HL.Word, AF.High); return 7;
 
                 // --- LD A, r ---
@@ -1279,7 +1305,11 @@ namespace Core.Cpu
                 case 0xF3: // DI 
                     IFF1 = false;
                     IFF2 = false;
-                    _eiPending = false;
+                    _eiDelay = 0; // Hard cancel any pending EI delays
+                    return 4;
+
+                case 0xFB: // EI
+                    _eiDelay = 2; // Ticks down across the current and subsequent instruction
                     return 4;
                 case 0xf5: //push af
                     Push(AF.Word);
@@ -1290,9 +1320,7 @@ namespace Core.Cpu
                 case 0xF9: // LD SP, HL
                     SP = HL.Word;
                     return 6;
-                case 0xFB: // EI
+                
-                    _eiPending = true;
-                    return 4;
                 case 0xFD:
                     return ExecuteFDPrefix();
                 case 0xFE: // CP n

Core/Memory/SmsMemoryBus.cs

@@ -64,7 +64,7 @@ namespace Core.Memory
             if (address < 0xC000)
             {
                 // Slot 2 (Or SRAM)
-                if (SramUsed && (_mapperControl & 0x08) != 0)
+                if ((_mapperControl & 0x08) != 0)
                     return _cartridgeRam[address - 0x8000];
                 else
                     return _cartridgeRom[(_romBank2 * 0x4000) + (address - 0x8000)];
@@ -80,7 +80,7 @@ namespace Core.Memory
 
             if (address < 0xC000)
             {
-                if (SramUsed && (_mapperControl & 0x08) != 0)
+                if ((_mapperControl & 0x08) != 0)
                     _cartridgeRam[address - 0x8000] = value;
                 return;
             }

Core/SmsMachine.cs

@@ -17,6 +17,7 @@ namespace Core
         public SmsVdp VideoProcessor { get; private set; }
         public SmsApu AudioProcessor { get; private set; }
         public ushort? Breakpoint { get; set; } = null;
+        private int _tStateCarryover = 0;
 
         // NTSC SMS T-States per frame
         public const int TStatesPerFrame = 59736; //NTSC
@@ -40,13 +41,15 @@ namespace Core
         public void Reset()
         {
             MemoryBus.CleanRAMData();
+            VideoProcessor.Reset();
             Cpu.Reset();
+            _tStateCarryover = 0;
         }
 
-        
+
         public void RunFrame()
         {
-            int tStatesThisFrame = 0;
+            int tStatesThisFrame = _tStateCarryover;
             while (tStatesThisFrame < TStatesPerFrame) // Standard NTSC frame time
             {
                 // 1. Run one CPU instruction
@@ -58,12 +61,16 @@ namespace Core
                 AudioProcessor.Update(cycles);
 
                 // 3. Check if the VDP is begging for attention!
-                if (VideoProcessor.InterruptPending && Cpu.IFF1)
+                //if (VideoProcessor.InterruptPending && Cpu.IFF1)
+                if (VideoProcessor.InterruptPending)
                 {
                     int intCycles = Cpu.RequestInterrupt();
-                    tStatesThisFrame += intCycles;
+                    if (intCycles > 0)
-                    VideoProcessor.Update(intCycles);
+                    {
-                    AudioProcessor.Update(intCycles);
+                        tStatesThisFrame += intCycles;
+                        VideoProcessor.Update(intCycles);
+                        AudioProcessor.Update(intCycles);
+                    }
                 }
 
                 // 4. THE RESTORED BREAKPOINT TRAP

Core/Video/SmsVdp.cs

@@ -376,6 +376,17 @@ namespace Core.Video
 
             return (255 << 24) | (r << 16) | (g << 8) | b;
         }
+
+        public void Reset()
+        {
+            _tStateCounter = 0;
+            _currentScanline = 0;
+            _lineCounter = 0;
+            _statusRegister = 0x00;
+            _controlWord = 0;
+            _isSecondControlByte = false;
+            _readBuffer = 0;
+        }
         public void SaveState(BinaryWriter bw)
         {
             bw.Write(VRAM);

Desktop/DebuggerForm.Designer.cs

@@ -63,6 +63,8 @@
             lblTone2 = new Label();
             lblNoise = new Label();
             lblTone0 = new Label();
+            lblHalt = new Label();
+            lblR = new Label();
             groupBox1.SuspendLayout();
             SuspendLayout();
             // 
@@ -243,7 +245,7 @@
             // lblIff1
             // 
             lblIff1.AutoSize = true;
-            lblIff1.Location = new Point(9, 426);
+            lblIff1.Location = new Point(10, 472);
             lblIff1.Name = "lblIff1";
             lblIff1.Size = new Size(35, 20);
             lblIff1.TabIndex = 24;
@@ -252,7 +254,7 @@
             // lblIff2
             // 
             lblIff2.AutoSize = true;
-            lblIff2.Location = new Point(9, 469);
+            lblIff2.Location = new Point(10, 515);
             lblIff2.Name = "lblIff2";
             lblIff2.Size = new Size(35, 20);
             lblIff2.TabIndex = 25;
@@ -261,7 +263,7 @@
             // lblIE
             // 
             lblIE.AutoSize = true;
-            lblIE.Location = new Point(9, 389);
+            lblIE.Location = new Point(10, 435);
             lblIE.Name = "lblIE";
             lblIE.Size = new Size(26, 20);
             lblIE.TabIndex = 26;
@@ -287,7 +289,7 @@
             // lblFrames
             // 
             lblFrames.AutoSize = true;
-            lblFrames.Location = new Point(11, 528);
+            lblFrames.Location = new Point(10, 605);
             lblFrames.Margin = new Padding(2, 0, 2, 0);
             lblFrames.Name = "lblFrames";
             lblFrames.Size = new Size(124, 20);
@@ -297,7 +299,7 @@
             // lblFPS
             // 
             lblFPS.AutoSize = true;
-            lblFPS.Location = new Point(103, 606);
+            lblFPS.Location = new Point(102, 683);
             lblFPS.Margin = new Padding(2, 0, 2, 0);
             lblFPS.Name = "lblFPS";
             lblFPS.Size = new Size(32, 20);
@@ -307,7 +309,7 @@
             // lblFrameTime
             // 
             lblFrameTime.AutoSize = true;
-            lblFrameTime.Location = new Point(48, 565);
+            lblFrameTime.Location = new Point(47, 642);
             lblFrameTime.Margin = new Padding(2, 0, 2, 0);
             lblFrameTime.Name = "lblFrameTime";
             lblFrameTime.Size = new Size(87, 20);
@@ -351,9 +353,9 @@
             groupBox1.Controls.Add(lblNoise);
             groupBox1.Controls.Add(lblTone0);
             groupBox1.Location = new Point(213, 526);
-            groupBox1.Margin = new Padding(2, 2, 2, 2);
+            groupBox1.Margin = new Padding(2);
             groupBox1.Name = "groupBox1";
-            groupBox1.Padding = new Padding(2, 2, 2, 2);
+            groupBox1.Padding = new Padding(2);
             groupBox1.Size = new Size(318, 178);
             groupBox1.TabIndex = 35;
             groupBox1.TabStop = false;
@@ -399,11 +401,31 @@
             lblTone0.TabIndex = 0;
             lblTone0.Text = "Tone0";
             // 
+            // lblHalt
+            // 
+            lblHalt.AutoSize = true;
+            lblHalt.Location = new Point(9, 564);
+            lblHalt.Name = "lblHalt";
+            lblHalt.Size = new Size(37, 20);
+            lblHalt.TabIndex = 36;
+            lblHalt.Text = "Halt";
+            // 
+            // lblR
+            // 
+            lblR.AutoSize = true;
+            lblR.Location = new Point(9, 392);
+            lblR.Name = "lblR";
+            lblR.Size = new Size(18, 20);
+            lblR.TabIndex = 37;
+            lblR.Text = "R";
+            // 
             // DebuggerForm
             // 
             AutoScaleDimensions = new SizeF(8F, 20F);
             AutoScaleMode = AutoScaleMode.Font;
             ClientSize = new Size(965, 714);
+            Controls.Add(lblR);
+            Controls.Add(lblHalt);
             Controls.Add(groupBox1);
             Controls.Add(CpuRun);
             Controls.Add(btnCpuStep);
@@ -478,6 +500,8 @@
         private Label lblTone2;
         private Label lblNoise;
         private Label lblTone0;
+        private Label lblHalt;
+        private Label lblR;
         //private TextBox textBox4;
     }
 }

Desktop/DebuggerForm.cs

@@ -110,11 +110,12 @@ namespace Desktop
             lblFrames.Text = $"Frames Rendered: {_mainForm.TotalFrameCount}";
             lblFrameTime.Text = $"Frame Time: {((float)_mainForm.FrameTime):F1}ms";
             lblFPS.Text = $"FPS: {_mainForm.FramesPerSecond:F2}";
+            lblHalt.Text = $"CPU Halted: {_cpu.IsHalted}";
+            lblR.Text = $"R: {_cpu.R:X2}";
             UpdateMemoryView();
             UpdateStackView();
             UpdateDisassemblyView();
-            // --- AUDIO REGISTERS ---
+            // --- AUDIO REGISTERS ---//
-            // Use _mainForm to access the Machine, and then grab the AudioProcessor!
             if (_mainForm._machine != null && _mainForm._machine.AudioProcessor != null)
             {
                 ushort[] apuRegs = _mainForm._machine.AudioProcessor.Registers;
@@ -668,6 +669,9 @@ namespace Desktop
                     case 0xC9:
                         mnemonic = "RET";
                         break;
+                    case 0x76:
+                        mnemonic = "HALT!";
+                        break;
                     case 0xCB:
                         cbOp = _memoryBus.Read((ushort)(currentPc + 1));