ZXHawk: implemented +2a/+3 floating bus (confirmed working with 2017 release of 'A Yankee in Iraq')

BizHawk.Emulation.Cores/Computers/SinclairSpectrum/Machine/CPUMonitor.cs

@@ -62,6 +62,11 @@ namespace BizHawk.Emulation.Cores.Computers.SinclairSpectrum
         /// </summary>
         public ushort lastPortAddr;
 
+        /// <summary>
+        /// If true, the next read memory operation has been contended
+        /// </summary>
+        public bool NextMemReadContended;
+
         #endregion
 
         #region Methods
@@ -87,6 +92,7 @@ namespace BizHawk.Emulation.Cores.Computers.SinclairSpectrum
                         if (cont > 0)
                         {
                             _cpu.TotalExecutedCycles += cont;
+                            NextMemReadContended = true;
                         }
                     }
                 }
@@ -393,7 +399,8 @@ namespace BizHawk.Emulation.Cores.Computers.SinclairSpectrum
         public void SyncState(Serializer ser)
         {
             ser.BeginSection("CPUMonitor");
-            ser.Sync("", ref lastPortAddr);
+            ser.Sync("lastPortAddr", ref lastPortAddr);
+            ser.Sync("NextMemReadContended", ref NextMemReadContended);
             ser.EndSection();
         }
 

BizHawk.Emulation.Cores/Computers/SinclairSpectrum/Machine/SpectrumBase.Memory.cs

@@ -50,7 +50,7 @@ namespace BizHawk.Emulation.Cores.Computers.SinclairSpectrum
         /// Signs that all paging is disabled
         /// If this is TRUE, then 128k and above machines need a hard reset before paging is allowed again
         /// </summary>
-        protected bool PagingDisabled;
+        public bool PagingDisabled;
 
         /// <summary>
         /// Index of the currently paged ROM
@@ -87,6 +87,11 @@ namespace BizHawk.Emulation.Cores.Computers.SinclairSpectrum
         /// </summary>
         protected int PagingConfiguration;
 
+        /// <summary>
+        /// The last byte that was read after contended cycles
+        /// </summary>
+        public byte LastContendedReadByte;
+
         #endregion
 
         #region Memory Related Methods

BizHawk.Emulation.Cores/Computers/SinclairSpectrum/Machine/SpectrumBase.cs

@@ -357,11 +357,13 @@ namespace BizHawk.Emulation.Cores.Computers.SinclairSpectrum
             ser.Sync("PagingConfiguration", ref PagingConfiguration);
             ser.Sync("ROMhigh", ref ROMhigh);
             ser.Sync("ROMlow", ref ROMlow);
+            ser.Sync("LastContendedReadByte", ref LastContendedReadByte);
 
             KeyboardDevice.SyncState(ser);
             BuzzerDevice.SyncState(ser);
             TapeBuzzer.SyncState(ser);
             ULADevice.SyncState(ser);
+            CPUMon.SyncState(ser);
 
             if (AYDevice != null)
             {

BizHawk.Emulation.Cores/Computers/SinclairSpectrum/Machine/ULA.cs

@@ -667,12 +667,31 @@ namespace BizHawk.Emulation.Cores.Computers.SinclairSpectrum
             }
         }
 
+        /// <summary>
+        /// Generates the port lookup table for +2a/+3 allowed floating bus ports
+        /// </summary>
+        public void GenerateP3PortTable()
+        {
+            List<ushort> table = new List<ushort>();
+            for (int i = 0; i < 0x1000; i++)
+            {
+                ushort r = (ushort)(1 + (4 * i));
+                if (r > 4093)
+                    break;
+                table.Add(r);
+            }
+
+            Plus3FBPortTable = table.ToArray();
+        }
+
+        private ushort[] Plus3FBPortTable = new ushort[1];
+
         /// <summary>
         /// Returns floating bus value (if available)
         /// </summary>
         /// <param name="tstate"></param>
         /// <returns></returns>
-        public void ReadFloatingBus(int tstate, ref int result)
+        public void ReadFloatingBus(int tstate, ref int result, ushort port)
         {
             tstate += FloatingBusOffset;
             if (tstate >= RenderingTable.Renderer.Length)
@@ -688,13 +707,7 @@ namespace BizHawk.Emulation.Cores.Computers.SinclairSpectrum
                 case MachineType.ZXSpectrum48:
                 case MachineType.ZXSpectrum128:
                 case MachineType.ZXSpectrum128Plus2:
-                    /*
+
-                    if (item.FloatingBusAddress > 0)
-                    {
-                        result = _machine.FetchScreenMemory(item.FloatingBusAddress);
-                        //result = 0x00;
-                    }
-                    */
                     switch (item.RAction)
                     {
                         case RenderTable.RenderAction.BorderAndFetchByte1:
@@ -708,15 +721,46 @@ namespace BizHawk.Emulation.Cores.Computers.SinclairSpectrum
                             result = _machine.FetchScreenMemory(item.AttributeAddress);
                             break;
                         default:
-                            //result = _machine.FetchScreenMemory(fetchA2);
                             break;
                     }
-                    
-
                     break;
 
                 case MachineType.ZXSpectrum128Plus2a:
                 case MachineType.ZXSpectrum128Plus3:
+                    
+                    // http://sky.relative-path.com/zx/floating_bus.html
+                    if (_machine.PagingDisabled)
+                    {
+                        result = 0xff;
+                        break;
+                    }
+
+                    // check whether fb is found on this port
+                    ushort pLook = Array.Find(Plus3FBPortTable, s => s == port);
+                    if (pLook == 0)
+                    {
+                        result = 0xff;
+                        break;
+                    }  
+
+                    // floating bus on +2a/+3 always returns a byte with Bit0 set
+                    switch (item.RAction)
+                    {
+                        case RenderTable.RenderAction.BorderAndFetchByte1:
+                        case RenderTable.RenderAction.Shift1AndFetchByte2:
+                        case RenderTable.RenderAction.Shift2AndFetchByte1:
+                            result = (byte)(_machine.FetchScreenMemory(item.ByteAddress) | 0x01);
+                            break;
+                        case RenderTable.RenderAction.BorderAndFetchAttribute1:
+                        case RenderTable.RenderAction.Shift1AndFetchAttribute2:
+                        case RenderTable.RenderAction.Shift2AndFetchAttribute1:
+                            result = (byte)(_machine.FetchScreenMemory(item.AttributeAddress) | 0x01);
+                            break;
+                        default:
+                            result = (byte)(_machine.LastContendedReadByte | 0x01);
+                            break;
+                    }
+
                     break;
             }
         }

BizHawk.Emulation.Cores/Computers/SinclairSpectrum/Machine/ZXSpectrum128K/ZX128.Port.cs

@@ -32,7 +32,7 @@ namespace BizHawk.Emulation.Cores.Computers.SinclairSpectrum
                 // -asni (2018-06-08) - need this to pass the final portread tests from fusetest.tap
 
                 // get the floating bus value
-                ULADevice.ReadFloatingBus((int)CurrentFrameCycle, ref result);
+                ULADevice.ReadFloatingBus((int)CurrentFrameCycle, ref result, port);
                 // use this to set the paging registers
                 WritePort(port, (byte)result);
                 // return the floating bus value
@@ -71,7 +71,7 @@ namespace BizHawk.Emulation.Cores.Computers.SinclairSpectrum
             if (!deviceAddressed)
             {
                 // If this is an unused port the floating memory bus should be returned
-                ULADevice.ReadFloatingBus((int)CurrentFrameCycle, ref result);
+                ULADevice.ReadFloatingBus((int)CurrentFrameCycle, ref result, port);
             }
 
             return (byte)result;

BizHawk.Emulation.Cores/Computers/SinclairSpectrum/Machine/ZXSpectrum128KPlus2a/ZX128Plus2a.Memory.cs

@@ -358,6 +358,12 @@ namespace BizHawk.Emulation.Cores.Computers.SinclairSpectrum
         public override byte ReadMemory(ushort addr)
         {
             var data = ReadBus(addr);
+            if (CPUMon.NextMemReadContended)
+            {
+                LastContendedReadByte = data;
+                CPUMon.NextMemReadContended = false;
+            }
+                
             return data;
         }
 

BizHawk.Emulation.Cores/Computers/SinclairSpectrum/Machine/ZXSpectrum128KPlus2a/ZX128Plus2a.Port.cs

@@ -52,7 +52,7 @@ namespace BizHawk.Emulation.Cores.Computers.SinclairSpectrum
             if (!deviceAddressed)
             {
                 // If this is an unused port the floating memory bus should be returned
-                ULADevice.ReadFloatingBus((int)CurrentFrameCycle, ref result);                
+                ULADevice.ReadFloatingBus((int)CurrentFrameCycle, ref result, port);                
             }
 
             return (byte)result;

BizHawk.Emulation.Cores/Computers/SinclairSpectrum/Machine/ZXSpectrum128KPlus2a/ZX128Plus2a.Screen.cs

@@ -19,7 +19,7 @@ namespace BizHawk.Emulation.Cores.Computers.SinclairSpectrum
             // offsets
             RenderTableOffset = 58;
             ContentionOffset = 9;
-            FloatingBusOffset = 1;
+            FloatingBusOffset = 0;
             // timing
             ClockSpeed = 3546900;
             FrameCycleLength = 70908;
@@ -43,6 +43,8 @@ namespace BizHawk.Emulation.Cores.Computers.SinclairSpectrum
                 MachineType.ZXSpectrum128Plus2a);
 
             SetupScreenSize();
+
+            GenerateP3PortTable();
         }
 
         #endregion

BizHawk.Emulation.Cores/Computers/SinclairSpectrum/Machine/ZXSpectrum128KPlus3/ZX128Plus3.Memory.cs

@@ -358,6 +358,8 @@ namespace BizHawk.Emulation.Cores.Computers.SinclairSpectrum
         public override byte ReadMemory(ushort addr)
         {
             var data = ReadBus(addr);
+            if (CPUMon.NextMemReadContended)
+                LastContendedReadByte = data;
             return data;
         }
 

BizHawk.Emulation.Cores/Computers/SinclairSpectrum/Machine/ZXSpectrum128KPlus3/ZX128Plus3.Port.cs

@@ -56,7 +56,7 @@ namespace BizHawk.Emulation.Cores.Computers.SinclairSpectrum
             if (!deviceAddressed)
             {
                 // If this is an unused port the floating memory bus should be returned
-                ULADevice.ReadFloatingBus((int)CurrentFrameCycle, ref result);              
+                ULADevice.ReadFloatingBus((int)CurrentFrameCycle, ref result, port);              
             }
 
             return (byte)result;

BizHawk.Emulation.Cores/Computers/SinclairSpectrum/Machine/ZXSpectrum48K/ZX48.Port.cs

@@ -55,7 +55,7 @@ namespace BizHawk.Emulation.Cores.Computers.SinclairSpectrum
 
 
                 // If this is an unused port the floating memory bus should be returned
-                ULADevice.ReadFloatingBus((int)CurrentFrameCycle, ref result);                
+                ULADevice.ReadFloatingBus((int)CurrentFrameCycle, ref result, port);                
             }
 
             return (byte)result;