gen: fix dumb tile priority bug (primarily affects Ghouls n Ghosts, which use the layers backwards from normal)

BizHawk.Emulation/CPUs/Native68000/Musashi.cs

@@ -48,6 +48,9 @@ namespace Native68000
         [DllImport("MusashiDLL.dll", CallingConvention = CallingConvention.Cdecl)]
         public static extern int QueryCpuState(int regcode);
 
+        [DllImport("MusashiDLL.dll", CallingConvention = CallingConvention.Cdecl)]
+        public static extern int GetCyclesRemaining();
+
         public static int D0 { get { return QueryCpuState(0); } }
         public static int D1 { get { return QueryCpuState(1); } }
         public static int D2 { get { return QueryCpuState(2); } }

BizHawk.Emulation/Consoles/Sega/Genesis/Compat.txt

@@ -6,3 +6,26 @@ Timings:
  - How many cycles does TRAP take to execute?
  - How many cycles does it take to accept an interrupt?
  - AND has some funky timings when it comes to immediates?
+
+ GAMES:
+
+ Monster World 4 - Music is messed up now. Timing is all off. It used to work.
+ Quackshot doesn't boot.
+ Moonwalker doesn't boot.
+ Altered Beast: start with 0 health, 0 lives???
+  Contra Hard Corps: Scrolling is messed up in level 1... used to work.
+ After Burner 2: No music
+ MUSHA: Intro music starts too soon
+ MUSHA: uses unimplemented VRAM copy
+ MUSHA: Some sprites have messed up left/right symmetry
+ Landstalker: freezes during new game sequence, very early
+ 
+ Things that read from VRAM work like 50%-90%, but not 100%. It's frustrating. Kid Chameleon and Eternal Champions are examples.
+
+ Some games flicker in the rightmost columns. Is this caused by mid-frame mode shifting(32/40 col modes?) Alisia Dragoon is one example.
+
+
+ TODO: non-instant DMA emulation
+ TODO: Add 68000/VDP interrupt enable delay (one instruction, similar to After Burner/PCE)
+ TODO: freaking H-interrupts
+ TODO: Test DMA/ VDP command words.... I'm not at all convinced that VRAM is always correct

BizHawk.Emulation/Consoles/Sega/Genesis/GenVDP.Render.cs

@@ -64,7 +64,7 @@ namespace BizHawk.Emulation.Consoles.Sega
                 int palette = (nameTableEntry >> 13) & 3;
 
                 if (priority && PriorityBuffer[x] >= highPriority) continue;
-                if (PriorityBuffer[x] >= lowPriority) continue;
+                if (!priority && PriorityBuffer[x] >= lowPriority) continue;
 
                 if (vFlip) yOfs = 7 - yOfs;
                 if (hFlip) xOfs = 7 - xOfs;

BizHawk.Emulation/Consoles/Sega/Genesis/GenVDP.cs

@@ -18,6 +18,7 @@ namespace BizHawk.Emulation.Consoles.Sega
         public int FrameWidth = 256;
 
         public int ScanLine;
+        public int HIntLineCounter;
 
         public bool HInterruptsEnabled   { get { return (Registers[0] & 0x10) != 0; } }
         public bool DisplayEnabled       { get { return (Registers[1] & 0x40) != 0; } }
@@ -26,6 +27,8 @@ namespace BizHawk.Emulation.Consoles.Sega
         public bool CellBasedVertScroll  { get { return (Registers[11] & 0x08) != 0; } }
         public bool Display40Mode        { get { return (Registers[12] & 0x81) != 0; } }
 
+        public bool InDisplayPeriod      { get { return ScanLine < 224 && DisplayEnabled; } }
+
         ushort NameTableAddrA;
         ushort NameTableAddrB;
         ushort NameTableAddrWindow;
@@ -46,12 +49,12 @@ namespace BizHawk.Emulation.Consoles.Sega
         const int CommandCramRead   = 7;
 
         public ushort VdpStatusWord = 0x3400;
-        public const int StatusVerticalInterruptPending = 0x80;
-        public const int StatusSpriteOverflow           = 0x40;
-        public const int StatusSpriteCollision          = 0x20;
-        public const int StatusOddFrame                 = 0x10;
-        public const int StatusVerticalBlanking         = 0x08;
         public const int StatusHorizBlanking            = 0x04;
+        public const int StatusVerticalBlanking         = 0x08;
+        public const int StatusOddFrame                 = 0x10;
+        public const int StatusSpriteCollision          = 0x20;
+        public const int StatusSpriteOverflow           = 0x40;
+        public const int StatusVerticalInterruptPending = 0x80;
 
         public ushort ReadVdp(int addr)
         {
@@ -64,8 +67,7 @@ namespace BizHawk.Emulation.Consoles.Sega
                 case 6:
                     return ReadVdpControl();
                 default:
-                    //throw new Exception("HV Counter read....");
+                    return ReadHVCounter();
-                    return 0;
             }
         }
 
@@ -142,7 +144,11 @@ namespace BizHawk.Emulation.Consoles.Sega
 
         public ushort ReadVdpControl()
         {
-            VdpStatusWord |= 0x0200; // Fifo empty
+            VdpStatusWord |= 0x0200; // Fifo empty // TODO kill this, emulating the damn FIFO.
+
+            // sprite overflow flag should clear.
+            // sprite collision flag should clear.
+
             return VdpStatusWord;
         }
 
@@ -151,9 +157,11 @@ namespace BizHawk.Emulation.Consoles.Sega
             ControlWordPending = false; 
 
             // byte-swap incoming data when A0 is set
-            // TODO what is the reason for thinking that this happens?
+            if ((VdpDataAddr & 1) != 0)
-            //if ((VdpDataAddr & 1) != 0) 
+            {
-            //    data = (ushort) ((data >> 8) | (data << 8));
+                data = (ushort)((data >> 8) | (data << 8));
+                Console.WriteLine("VRAM byte-swap is happening because A0 is not 0");
+            }
 
             if (DmaFillModePending)
             {
@@ -182,7 +190,7 @@ namespace BizHawk.Emulation.Consoles.Sega
                     VdpDataAddr += Registers[0x0F];
                     break;
                 default: 
-                    //Console.WriteLine("VDP DATA WRITE WITH UNHANDLED CODE!!!");
+                    Console.WriteLine("VDP DATA WRITE WITH UNHANDLED CODE!!!");
                     break;
             }
         }
@@ -203,11 +211,30 @@ namespace BizHawk.Emulation.Consoles.Sega
                     throw new Exception("VSRAM read");
                 case CommandCramRead:
                     throw new Exception("CRAM read");
+                default:
+                    throw new Exception("VRAM read with unexpected code!!!");
             }
 
             return retval;
         }
 
+        ushort ReadHVCounter()
+        {
+            int vcounter = ScanLine;
+            if (vcounter > 0xEA)
+                vcounter -= 7; 
+            // TODO generalize this across multiple video modes and stuff.
+
+            // TODO dont tie this to musashi cycle count.
+            // Figure out a "clean" way to get cycle counter information available to VDP.
+            int hcounter = (487 - Native68000.Musashi.GetCyclesRemaining()) * 255 / 487;
+
+            ushort res = (ushort) ((vcounter << 8) | (hcounter & 0xFF));
+            Console.WriteLine("READ HVC: V={0:X2} H={1:X2}  ret={2:X4}", vcounter, hcounter, res);
+
+            return res;
+        }
+
         public void WriteVdpRegister(int register, byte data)
         {
             Log.Note("VDP", "Register {0}: {1:X2}", register, data);
@@ -317,13 +344,13 @@ namespace BizHawk.Emulation.Consoles.Sega
                 case 0x11: // Window H Position
                     int whp = data & 31;
                     bool fromright = (data & 0x80) != 0;
-                    Log.Error("VDP", "Window H is {0} units from {1}", whp, fromright ? "right" : "left");
+                    //Log.Error("VDP", "Window H is {0} units from {1}", whp, fromright ? "right" : "left");
                     break;
 
                 case 0x12: // Window V
                     whp = data & 31;
                     fromright = (data & 0x80) != 0;
-                    Log.Error("VDP", "Window V is {0} units from {1}", whp, fromright ? "lower" : "upper");
+                    //Log.Error("VDP", "Window V is {0} units from {1}", whp, fromright ? "lower" : "upper");
                     break;
 
                 case 0x13: // DMA Length Low

BizHawk.Emulation/Consoles/Sega/Genesis/Genesis.cs

@@ -137,6 +137,12 @@ namespace BizHawk.Emulation.Consoles.Sega
             Controller.UpdateControls(Frame++);
 			PSG.BeginFrame(SoundCPU.TotalExecutedCycles);
             YM2612.BeginFrame(SoundCPU.TotalExecutedCycles);
+
+            // Do start-of-frame events
+            VDP.HIntLineCounter = VDP.Registers[10];
+            //VDP.VdpStatusWord &= 
+            unchecked { VDP.VdpStatusWord &= (ushort)~GenVDP.StatusVerticalBlanking; }
+
 			for (VDP.ScanLine = 0; VDP.ScanLine < 262; VDP.ScanLine++)
 			{
 				//Log.Error("VDP","FRAME {0}, SCANLINE {1}", Frame, VDP.ScanLine);
@@ -164,12 +170,13 @@ namespace BizHawk.Emulation.Consoles.Sega
 
 					if (Z80Runnable)
 						SoundCPU.Interrupt = true;
+                    //The INT output is asserted every frame for exactly one scanline, and it can't be disabled. A very short Z80 interrupt routine would be triggered multiple times if it finishes within 228 Z80 clock cycles. I think (but cannot recall the specifics) that some games have delay loops in the interrupt handler for this very reason. 
 				}
 			}
 			PSG.EndFrame(SoundCPU.TotalExecutedCycles);
             YM2612.EndFrame(SoundCPU.TotalExecutedCycles);
 
-            unchecked { VDP.VdpStatusWord &= (ushort)~GenVDP.StatusVerticalBlanking; }
+            
 
 			if (lagged)
 			{

BizHawk.Emulation/Consoles/Sega/Genesis/MemoryMap.68000.cs

@@ -28,7 +28,7 @@ namespace BizHawk.Emulation.Consoles.Sega
 
             if (address >= 0xC00000 && address < 0xC00010)
             {
-                Console.WriteLine("byte-reading the VDP. someone is probably stupid.");
+                //Console.WriteLine("byte-reading the VDP. someone is probably stupid.");
                 ushort value = VDP.ReadVdp(address & 0x0E);
                 if ((address & 1) == 0) // read MSB
                     return (sbyte) (value >> 8);