Correct INT handling. Should continually fire until INT is raised.

Z80/Z80.UnitTests/IffTests.cs

@@ -68,19 +68,21 @@ namespace Z80.UnitTests
             this.cpu.IFF1 = false;
             this.cpu.IM = 1;
 
-            this.cpu.LowerINT(); // pending=true, but IFF1=false
-            this.cpu.Step();     // pending cleared (IFF1=false), EI runs → IFF1=true
+            this.cpu.LowerINT(); // but IFF1=false
+            this.cpu.Step();     // IFF1=false, no interrupt, EI runs → IFF1=true
             Assert.IsTrue(this.cpu.IFF1, "IFF1 must be true after EI");
-            Assert.AreEqual(0x0001, this.cpu.PC.Joined, "No interrupt must fire during EI step");
+            Assert.AreEqual(0x0001, this.cpu.PC.Joined, "Normal execution, no interrupt");
 
-            this.cpu.Step();     // NOP at 0x0001 — still no interrupt (pending was cleared)
-            Assert.AreEqual(0x0002, this.cpu.PC.Joined, "No interrupt must fire on instruction after EI");
+            this.cpu.Step();     // IFF1 true, INT still low
+            Assert.AreEqual(0x0038, this.cpu.PC.Joined, "INT fires if INT is low");
 
             // Produce a new falling edge on INT (raise then lower) to retrigger
             this.cpu.RaiseINT();
             this.cpu.LowerINT();
+
+            Assert.IsFalse(this.cpu.IFF1, "IFF1 has been disabled by the INT handler");
             this.cpu.Step();
-            Assert.AreEqual(0x0038, this.cpu.PC.Joined, "INT must fire after new falling edge post-EI");
+            Assert.AreEqual(0x0038, this.cpu.PC.Joined - 1, "Inside INT handled at 0x38");
         }
 
         [TestMethod]

Z80/Z80.cs

@@ -17,12 +17,8 @@ namespace Z80
             this.UpdateRegisterBank();
             this.UpdateAFBank();
             this.RaisedPOWER += this.Z80_RaisedPOWER;
-            this.LoweredNMI += this.Z80_LoweredNMI;
-            this.LoweredINT += this.Z80_LoweredINT;
         }
 
-        private bool _interruptPending;
-        private bool _nonMaskableInterruptPending;
 
         private readonly InputOutput _ports;
 
@@ -185,15 +181,14 @@ namespace Z80
                 this.HandleRESET();
                 return;
             }
-            else if (this._nonMaskableInterruptPending)
+            else if (this._nonMaskableInterruptTriggered)
             {
-                this._nonMaskableInterruptPending = false;
+                this._nonMaskableInterruptTriggered = false;
                 this.HandleNMI();
                 return;
             }
-            else if (this._interruptPending)
+            else if (this.INT.Lowered())
             {
-                this._interruptPending = false;
                 if (this.IFF1)
                 {
                     this.HandleINT();
@@ -247,14 +242,16 @@ namespace Z80
             this.ResetRegisterSet();
         }
 
-        private void Z80_LoweredINT(object? sender, EventArgs e) => this._interruptPending = true;
+        //private void Z80_LoweredINT(object? sender, EventArgs e) => this._interruptPending = true;
 
-        private void Z80_LoweredNMI(object? sender, EventArgs e) => this._nonMaskableInterruptPending = true;
+        //private void Z80_LoweredNMI(object? sender, EventArgs e) => this._nonMaskableInterruptPending = true;
 
         #region Z80 specific pins
 
         #region NMI pin
 
+        private bool _nonMaskableInterruptTriggered;
+
         public event EventHandler<EventArgs>? RaisingNMI;
 
         public event EventHandler<EventArgs>? RaisedNMI;
@@ -284,6 +281,7 @@ namespace Z80
             {
                 LoweringNMI?.Invoke(this, EventArgs.Empty);
                 this.NMI.Lower();
+                this._nonMaskableInterruptTriggered = true;
                 LoweredNMI?.Invoke(this, EventArgs.Empty);
             }
         }