z80: implement data bus

-needed for ZXspectrum mode 2 interrupts
-use with FetchDB function

BizHawk.Emulation.Cores/CPUs/Z80A/Interrupts.cs

@@ -89,22 +89,22 @@ namespace BizHawk.Emulation.Cores.Components.Z80A
 			cur_instr = new ushort[]
 						{IDLE,
 						IDLE,
+						FTCH_DB,
+						TR, Z, DB,
+						TR, W, I,						
+						IDLE,
 						DEC16, SPl, SPh,
 						WR, SPl, SPh, PCh,
 						IDLE,
 						DEC16, SPl, SPh,
-						WR, SPl, SPh, PCl,
-						IDLE,					
-						ASGN, PCl, 0,
-						TR, PCh, I,
-						IDLE,					
+						WR, SPl, SPh, PCl,										
 						IDLE,
-						RD, Z, PCl, PCh,
-						INC16, PCl, PCh,
+						RD, PCl, Z, W,
+						INC16, Z, W,
+						IDLE,
+						RD, PCh, Z, W,
 						IDLE,
-						RD, W, PCl, PCh,
 						IDLE,
-						TR16, PCl, PCh, Z, W,
 						OP };
 		}
 

BizHawk.Emulation.Cores/CPUs/Z80A/Operations.cs

@@ -8,31 +8,37 @@ namespace BizHawk.Emulation.Cores.Components.Z80A
 		public void Read_Func(ushort dest, ushort src_l, ushort src_h)
 		{
 			Regs[dest] = ReadMemory((ushort)(Regs[src_l] | (Regs[src_h]) << 8));
+			Regs[DB] = Regs[dest];
 		}
 
 		public void I_Read_Func(ushort dest, ushort src_l, ushort src_h, ushort inc)
 		{
 			Regs[dest] = ReadMemory((ushort)((Regs[src_l] | (Regs[src_h] << 8)) + inc));
+			Regs[DB] = Regs[dest];
 		}
 
 		public void Write_Func(ushort dest_l, ushort dest_h, ushort src)
 		{
+			Regs[DB] = Regs[src];
 			WriteMemory((ushort)(Regs[dest_l] | (Regs[dest_h] << 8)), (byte)Regs[src]);
 		}
 
 		public void I_Write_Func(ushort dest_l, ushort dest_h, ushort inc,  ushort src)
 		{
+			Regs[DB] = Regs[src];
 			WriteMemory((ushort)((Regs[dest_l] | (Regs[dest_h] << 8)) + inc), (byte)Regs[src]);
 		}
 
 		public void OUT_Func(ushort dest, ushort src)
 		{
+			Regs[DB] = Regs[src];
 			WriteHardware(Regs[dest], (byte)(Regs[src]));
 		}
 
 		public void IN_Func(ushort dest, ushort src)
 		{
 			Regs[dest] = ReadHardware(Regs[src]);
+			Regs[DB] = Regs[dest];
 		}
 
 		public void TR_Func(ushort dest, ushort src)
@@ -738,5 +744,10 @@ namespace BizHawk.Emulation.Cores.Components.Z80A
 				Flag3 = (Regs[A] & 0x08) != 0;
 			}
 		}
+
+		public void FTCH_DB_Func()
+		{
+			Regs[DB] = FetchDB();
+		}
 	}
 }

BizHawk.Emulation.Cores/CPUs/Z80A/Registers.cs

@@ -6,7 +6,6 @@ namespace BizHawk.Emulation.Cores.Components.Z80A
 	public partial class Z80A
 	{
 		// registers
-		// note these are not constants. When shadows are used, they will be changed accordingly
 		public ushort PCl = 0;
 		public ushort PCh = 1;
 		public ushort SPl = 2;
@@ -40,6 +39,7 @@ namespace BizHawk.Emulation.Cores.Components.Z80A
 		public ushort E_s = 29;
 		public ushort H_s = 30;
 		public ushort L_s = 31;
+		public ushort DB = 32;
 
 		public ushort[] Regs = new ushort[36];
 

BizHawk.Emulation.Cores/CPUs/Z80A/Z80A.cs

@@ -74,6 +74,7 @@ namespace BizHawk.Emulation.Cores.Components.Z80A
 		public const ushort SET_FL_IR = 59;
 		public const ushort I_BIT = 60;
 		public const ushort HL_BIT = 61;
+		public const ushort FTCH_DB = 62;
 
 		public byte temp_R;
 
@@ -106,6 +107,11 @@ namespace BizHawk.Emulation.Cores.Components.Z80A
 		public Func<ushort, byte> ReadHardware;
 		public Action<ushort, byte> WriteHardware;
 
+		// Data BUs
+		// Interrupting Devices are responsible for putting a value onto the data bus
+		// for as long as the interrupt is valid
+		public Func<byte> FetchDB;
+
 		//this only calls when the first byte of an instruction is fetched.
 		public Action<ushort> OnExecFetch;
 
@@ -339,6 +345,9 @@ namespace BizHawk.Emulation.Cores.Components.Z80A
 
 				case HALT:
 					halted = true;
+					// NOTE: Check how halt state effects the DB
+					Regs[DB] = 0xFF;
+
 					if (EI_pending > 0)
 					{
 						EI_pending--;
@@ -595,6 +604,9 @@ namespace BizHawk.Emulation.Cores.Components.Z80A
 				case SET_FL_IR:
 					SET_FL_IR_Func(cur_instr[instr_pntr++]);
 					break;
+				case FTCH_DB:
+					FTCH_DB_Func();
+					break;
 			}
 			totalExecutedCycles++;
 		}