From 0a354c2748bd80f41445e5b067ff3d8cd5964706 Mon Sep 17 00:00:00 2001
From: beirich <beirich@4bbf4f03-6f44-549e-7e59-35d4b0962838>
Date: Sat, 19 Mar 2011 06:00:33 +0000
Subject: [PATCH] PCE: Fix a bug in the timer; fix glitch in VBlank interrupt
 handling (fixing intro in Dungeon Explorer)

---
 BizHawk.Emulation/CPUs/HuC6280/Execute.cs          |  4 ++--
 BizHawk.Emulation/Consoles/PC Engine/VDC.Render.cs | 11 ++++++-----
 CpuCoreGenerator/HuC6280/CoreGenerator.cs          |  4 ++--
 3 files changed, 10 insertions(+), 9 deletions(-)

diff --git a/BizHawk.Emulation/CPUs/HuC6280/Execute.cs b/BizHawk.Emulation/CPUs/HuC6280/Execute.cs
index 84a911b428..a314c04818 100644
--- a/BizHawk.Emulation/CPUs/HuC6280/Execute.cs
+++ b/BizHawk.Emulation/CPUs/HuC6280/Execute.cs
@@ -2125,10 +2125,10 @@ throw new Exception("break");
                 if (TimerEnabled)
                 {
                     TimerTickCounter += delta;
-                    if (TimerTickCounter >= 1024)
+                    while (TimerTickCounter >= 1024)
                     {
                         TimerValue--;
-                        TimerTickCounter &= 1023;
+                        TimerTickCounter -= 1024;
                         if (TimerValue == 0xFF)
                         {
                             TimerValue = TimerReloadValue;
diff --git a/BizHawk.Emulation/Consoles/PC Engine/VDC.Render.cs b/BizHawk.Emulation/Consoles/PC Engine/VDC.Render.cs
index 53a19df6c7..c81870f4ba 100644
--- a/BizHawk.Emulation/Consoles/PC Engine/VDC.Render.cs	
+++ b/BizHawk.Emulation/Consoles/PC Engine/VDC.Render.cs	
@@ -74,13 +74,14 @@ namespace BizHawk.Emulation.Consoles.TurboGrafx
                     RenderScanLine();
 
                 if (ScanLine == VBlankScanline && VBlankInterruptEnabled)
-                {
-                    Log.Note("VDC", "Firing VBlank interrupt at {0}", ScanLine);
                     StatusByte |= StatusVerticalBlanking;
-                    cpu.IRQ1Assert = true;
-                }
+                
+                cpu.Execute(2);
 
-                cpu.Execute(455-hblankCycles);
+                if ((StatusByte & StatusVerticalBlanking) > 0)
+                    cpu.IRQ1Assert = true;
+
+                cpu.Execute(455-hblankCycles-2);
 
                 if (ScanLine == VBlankScanline)
                     UpdateSpriteAttributeTable();
diff --git a/CpuCoreGenerator/HuC6280/CoreGenerator.cs b/CpuCoreGenerator/HuC6280/CoreGenerator.cs
index f2e11df9b0..de65607d53 100644
--- a/CpuCoreGenerator/HuC6280/CoreGenerator.cs
+++ b/CpuCoreGenerator/HuC6280/CoreGenerator.cs
@@ -510,10 +510,10 @@ namespace HuC6280
             w.WriteLine("                if (TimerEnabled)");
             w.WriteLine("                {");
             w.WriteLine("                    TimerTickCounter += delta;");
-            w.WriteLine("                    if (TimerTickCounter >= 1024)");
+            w.WriteLine("                    while (TimerTickCounter >= 1024)");
             w.WriteLine("                    {");
             w.WriteLine("                        TimerValue--;");
-            w.WriteLine("                        TimerTickCounter &= 1023;");
+            w.WriteLine("                        TimerTickCounter -= 1024;");
             w.WriteLine("                        if (TimerValue == 0xFF)");
             w.WriteLine("                        {");
             w.WriteLine("                            TimerValue = TimerReloadValue;");