Pad: Fix timing issues w/ BIOS

src/pse/digital_controller.cpp

@@ -25,7 +25,7 @@ bool DigitalController::Transfer(const u8 data_in, u8* data_out)
       Log_DebugPrintf("Access");
 
       // response is hi-z
-      *data_out = data_in;
+      *data_out = 0xFF;
       ack = true;
     }
     break;

src/pse/pad.cpp

@@ -3,14 +3,16 @@
 #include "common/state_wrapper.h"
 #include "interrupt_controller.h"
 #include "pad_device.h"
+#include "system.h"
 Log_SetChannel(Pad);
 
 Pad::Pad() = default;
 
 Pad::~Pad() = default;
 
-bool Pad::Initialize(InterruptController* interrupt_controller)
+bool Pad::Initialize(System* system, InterruptController* interrupt_controller)
 {
+  m_system = system;
   m_interrupt_controller = interrupt_controller;
   return true;
 }
@@ -22,6 +24,8 @@ void Pad::Reset()
 
 bool Pad::DoState(StateWrapper& sw)
 {
+  sw.Do(&m_state);
+  sw.Do(&m_ticks_remaining);
   sw.Do(&m_JOY_CTRL.bits);
   sw.Do(&m_JOY_STAT.bits);
   sw.Do(&m_JOY_MODE.bits);
@@ -49,7 +53,11 @@ u32 Pad::ReadRegister(u32 offset)
     }
 
     case 0x04: // JOY_STAT
-      return m_JOY_STAT.bits;
+    {
+      const u32 bits = m_JOY_STAT.bits;
+      m_JOY_STAT.ACKINPUT = false;
+      return bits;
+    }
 
     case 0x08: // JOY_MODE
       return ZeroExtend32(m_JOY_MODE.bits);
@@ -78,8 +86,8 @@ void Pad::WriteRegister(u32 offset, u32 value)
 
       m_TX_FIFO.Push(Truncate8(value));
 
-      if (m_JOY_CTRL.SELECT)
-        DoTransfer();
+      if (!IsTransmitting() && CanTransfer())
+        BeginTransfer();
 
       return;
     }
@@ -96,13 +104,19 @@ void Pad::WriteRegister(u32 offset, u32 value)
       if (m_JOY_CTRL.ACK)
       {
         // reset stat bits
-        m_JOY_STAT.ACKINPUTLEVEL = false;
         m_JOY_STAT.INTR = false;
-        m_JOY_CTRL.ACK = true;
       }
 
-      if (!old_select && m_JOY_CTRL.SELECT && !m_TX_FIFO.IsEmpty())
-        DoTransfer();
+      if (!m_JOY_CTRL.SELECT || !m_JOY_CTRL.TXEN)
+      {
+        if (IsTransmitting())
+          EndTransfer();
+      }
+      else
+      {
+        if (!IsTransmitting() && CanTransfer())
+          BeginTransfer();
+      }
 
       return;
     }
@@ -126,8 +140,28 @@ void Pad::WriteRegister(u32 offset, u32 value)
   }
 }
 
+void Pad::Execute(TickCount ticks)
+{
+  switch (m_state)
+  {
+    case State::Idle:
+      break;
+
+    case State::Transmitting:
+    {
+      m_ticks_remaining -= ticks;
+      if (m_ticks_remaining <= 0)
+        DoTransfer();
+    }
+    break;
+  }
+}
+
 void Pad::SoftReset()
 {
+  if (IsTransmitting())
+    EndTransfer();
+
   m_JOY_CTRL.bits = 0;
   m_JOY_STAT.bits = 0;
   m_JOY_MODE.bits = 0;
@@ -143,35 +177,84 @@ void Pad::UpdateJoyStat()
   m_JOY_STAT.TXRDY = !m_TX_FIFO.IsFull();
 }
 
+void Pad::BeginTransfer()
+{
+  DebugAssert(m_state == State::Idle && CanTransfer());
+  Log_DebugPrintf("Starting transfer");
+
+  m_JOY_CTRL.RXEN = true;
+
+  // The transfer or the interrupt must be delayed, otherwise the BIOS thinks there's no device detected.
+  // It seems to do something resembling the following:
+  //  1) Sets the control register up for transmitting, interrupt on ACK.
+  //  2) Writes 0x01 to the TX FIFO.
+  //  3) Delays for a bit.
+  //  4) Writes ACK to the control register, clearing the interrupt flag.
+  //  5) Clears IRQ7 in the interrupt controller.
+  //  6) Waits until the RX FIFO is not empty, reads the first byte to $zero.
+  //  7) Checks if the interrupt status register had IRQ7 set. If not, no device connected.
+  //
+  // Performing the transfer immediately will result in both the INTR bit and the bit in the interrupt
+  // controller being discarded in (4)/(5), but this bit was set by the *new* transfer. Therefore, the
+  // test in (7) will fail, and it won't send any more data. So, the transfer/interrupt must be delayed
+  // until after (4) and (5) have been completed.
+
+  m_system->Synchronize();
+  m_state = State::Transmitting;
+  m_ticks_remaining = TRANSFER_TICKS;
+  m_system->SetDowncount(m_ticks_remaining);
+}
+
 void Pad::DoTransfer()
 {
   Log_DebugPrintf("Transferring slot %d", m_JOY_CTRL.SLOT.GetValue());
 
   const std::shared_ptr<PadDevice>& dev = m_devices[m_JOY_CTRL.SLOT];
-  if (!dev)
+  if (!dev || !CanTransfer())
   {
     // no device present, don't set ACK and read hi-z
     m_TX_FIFO.Clear();
     m_RX_FIFO.Clear();
     m_RX_FIFO.Push(0xFF);
     UpdateJoyStat();
+    EndTransfer();
     return;
   }
 
-  while (!m_TX_FIFO.IsEmpty())
-  {
-    const u8 data_out = m_TX_FIFO.Pop();
-    u8 data_in;
-    m_JOY_STAT.ACKINPUTLEVEL |= dev->Transfer(data_out, &data_in);
-    m_RX_FIFO.Push(data_in);
-    m_JOY_CTRL.RXEN = true;
-  }
+  // set rx?
+  m_JOY_CTRL.RXEN = true;
 
-  if (m_JOY_STAT.ACKINPUTLEVEL && m_JOY_CTRL.ACKINTEN)
+  const u8 data_out = m_TX_FIFO.Pop();
+  u8 data_in;
+  m_JOY_STAT.ACKINPUT |= dev->Transfer(data_out, &data_in);
+  m_RX_FIFO.Push(data_in);
+
+  if (m_JOY_STAT.ACKINPUT && m_JOY_CTRL.ACKINTEN)
   {
+    Log_DebugPrintf("Triggering interrupt");
     m_JOY_STAT.INTR = true;
     m_interrupt_controller->InterruptRequest(InterruptController::IRQ::IRQ7);
   }
 
+  if (m_TX_FIFO.IsEmpty())
+  {
+    EndTransfer();
+  }
+  else
+  {
+    // queue the next byte
+    m_ticks_remaining += TRANSFER_TICKS;
+    m_system->SetDowncount(m_ticks_remaining);
+  }
+
   UpdateJoyStat();
 }
+
+void Pad::EndTransfer()
+{
+  DebugAssert(m_state == State::Transmitting);
+  Log_DebugPrintf("Ending transfer");
+
+  m_state = State::Idle;
+  m_ticks_remaining = 0;
+}

src/pse/pad.h

@@ -7,6 +7,7 @@
 
 class StateWrapper;
 
+class System;
 class InterruptController;
 class PadDevice;
 
@@ -16,7 +17,7 @@ public:
   Pad();
   ~Pad();
 
-  bool Initialize(InterruptController* interrupt_controller);
+  bool Initialize(System* system, InterruptController* interrupt_controller);
   void Reset();
   bool DoState(StateWrapper& sw);
 
@@ -26,8 +27,17 @@ public:
   u32 ReadRegister(u32 offset);
   void WriteRegister(u32 offset, u32 value);
 
+  void Execute(TickCount ticks);
+
 private:
   static constexpr u32 NUM_SLOTS = 2;
+  static constexpr u32 TRANSFER_TICKS = 500;
+
+  enum class State : u32
+  {
+    Idle,
+    Transmitting
+  };
 
   union JOY_CTRL
   {
@@ -52,7 +62,6 @@ private:
     BitField<u32, bool, 0, 1> TXRDY;
     BitField<u32, bool, 1, 1> RXFIFONEMPTY;
     BitField<u32, bool, 2, 1> TXDONE;
-    BitField<u32, bool, 3, 1> ACKINPUTLEVEL;
     BitField<u32, bool, 7, 1> ACKINPUT;
     BitField<u32, bool, 9, 1> INTR;
     BitField<u32, u32, 11, 21> TMR;
@@ -69,12 +78,24 @@ private:
     BitField<u16, u8, 8, 1> clk_polarity;
   };
 
+  bool IsTransmitting() const { return m_state == State::Transmitting; }
+  bool CanTransfer() const
+  {
+    return !m_TX_FIFO.IsEmpty() && !m_RX_FIFO.IsFull() && m_JOY_CTRL.SELECT && m_JOY_CTRL.TXEN;
+  }
+
   void SoftReset();
   void UpdateJoyStat();
+  void BeginTransfer();
   void DoTransfer();
+  void EndTransfer();
 
+  System* m_system = nullptr;
   InterruptController* m_interrupt_controller = nullptr;
 
+  State m_state = State::Idle;
+  TickCount m_ticks_remaining = 0;
+
   JOY_CTRL m_JOY_CTRL = {};
   JOY_STAT m_JOY_STAT = {};
   JOY_MODE m_JOY_MODE = {};

src/pse/system.cpp

@@ -49,7 +49,7 @@ bool System::Initialize()
   if (!m_cdrom->Initialize(this, m_dma.get(), m_interrupt_controller.get()))
     return false;
 
-  if (!m_pad->Initialize(m_interrupt_controller.get()))
+  if (!m_pad->Initialize(this, m_interrupt_controller.get()))
     return false;
 
   if (!m_timers->Initialize(this, m_interrupt_controller.get()))
@@ -219,6 +219,7 @@ void System::Synchronize()
   m_gpu->Execute(pending_ticks);
   m_timers->AddSystemTicks(pending_ticks);
   m_cdrom->Execute(pending_ticks);
+  m_pad->Execute(pending_ticks);
 }
 
 void System::SetDowncount(TickCount downcount)