Some fixes and code refactoring

Core/Cpu/Z80.cs

@@ -25,10 +25,12 @@ namespace Core.Cpu
 
         public int InterruptMode { get; private set; } = 0;
 
+
         // Interrupt Flip-Flops
         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;
 
         // Main Register Set
         public RegisterPair AF;
@@ -213,7 +215,8 @@ namespace Core.Cpu
         }
 
         public int Step()
-        {           
+        {
+            bool triggerEi = _eiPending;
 
             // Fetch the next opcode and increment the Program Counter
             byte opcode = ReadMemory(PC++);
@@ -221,6 +224,13 @@ namespace Core.Cpu
             int tStates = ExecuteOpcode(opcode);
             TotalTStates += tStates;
 
+            if (triggerEi)
+            {
+                IFF1 = true;
+                IFF2 = true;
+                _eiPending = false;
+            }
+
             // Decode and execute
             return tStates;
         }
@@ -240,9 +250,6 @@ namespace Core.Cpu
                    $"C:{f & 1}";
         }
 
-        // =========================================================================
-        // MATH AND LOGIC HELPERS
-        // =========================================================================
 
         private void SubA(byte value, bool isCompare)
         {
@@ -1272,6 +1279,7 @@ namespace Core.Cpu
                 case 0xF3: // DI 
                     IFF1 = false;
                     IFF2 = false;
+                    _eiPending = false;
                     return 4;
                 case 0xf5: //push af
                     Push(AF.Word);
@@ -1283,8 +1291,7 @@ namespace Core.Cpu
                     SP = HL.Word;
                     return 6;
                 case 0xFB: // EI
-                    IFF1 = true;
-                    IFF2 = true;
+                    _eiPending = true;
                     return 4;
                 case 0xFD:
                     return ExecuteFDPrefix();