From 9ce63952fbc0f8c940207f1f8a191989505da0b8 Mon Sep 17 00:00:00 2001
From: Connor McLaughlin <stenzek@gmail.com>
Date: Tue, 24 Mar 2020 00:20:45 +1000
Subject: [PATCH] TimingEvent: Fix events losing time when rescheduling outside
 handler

---
 src/core/cdrom.cpp        |  2 +-
 src/core/timing_event.cpp | 35 ++++++++++-------------------------
 src/core/timing_event.h   |  3 ---
 3 files changed, 11 insertions(+), 29 deletions(-)

diff --git a/src/core/cdrom.cpp b/src/core/cdrom.cpp
index 4c0f0284f..d05eb1a03 100644
--- a/src/core/cdrom.cpp
+++ b/src/core/cdrom.cpp
@@ -523,7 +523,7 @@ TickCount CDROM::GetTicksForSeek() const
 void CDROM::BeginCommand(Command command)
 {
   m_command = command;
-  m_command_event->SetDowncount(GetAckDelayForCommand());
+  m_command_event->Schedule(GetAckDelayForCommand());
   UpdateCommandEvent();
   UpdateStatusRegister();
 }
diff --git a/src/core/timing_event.cpp b/src/core/timing_event.cpp
index a45c443c4..ed3000b3b 100644
--- a/src/core/timing_event.cpp
+++ b/src/core/timing_event.cpp
@@ -28,26 +28,21 @@ TickCount TimingEvent::GetTicksUntilNextExecution() const
 
 void TimingEvent::Schedule(TickCount ticks)
 {
-  m_downcount = ticks;
-  m_time_since_last_run = 0;
+  const TickCount pending_ticks = m_system->m_cpu->GetPendingTicks();
+  m_downcount = pending_ticks + ticks;
 
-  // Factor in partial time if this was rescheduled outside of an event handler. Say, an MMIO write.
-  if (!m_system->m_running_events)
+  if (!m_active)
   {
-    const TickCount pending_ticks = m_system->m_cpu->GetPendingTicks();
-    m_downcount += pending_ticks;
-    m_time_since_last_run -= pending_ticks;
-  }
-
-  if (m_active)
-  {
-    // If this is a call from an IO handler for example, re-sort the event queue.
-    m_system->SortEvents();
+    // Event is going active, so we want it to only execute ticks from the current timestamp.
+    m_time_since_last_run = -pending_ticks;
+    m_active = true;
+    m_system->AddActiveEvent(this);
   }
   else
   {
-    m_active = true;
-    m_system->AddActiveEvent(this);
+    // Event is already active, so we leave the time since last run alone, and just modify the downcount.
+    // If this is a call from an IO handler for example, re-sort the event queue.
+    m_system->SortEvents();
   }
 }
 
@@ -118,13 +113,3 @@ void TimingEvent::Deactivate()
   m_active = false;
   m_system->RemoveActiveEvent(this);
 }
-
-void TimingEvent::SetDowncount(TickCount downcount)
-{
-  const TickCount pending_ticks = m_system->m_running_events ? 0 : m_system->m_cpu->GetPendingTicks();
-  m_downcount = downcount + pending_ticks;
-  m_time_since_last_run = -pending_ticks;
-
-  if (m_active)
-    m_system->SortEvents();
-}
diff --git a/src/core/timing_event.h b/src/core/timing_event.h
index 252753c0d..b7070c77b 100644
--- a/src/core/timing_event.h
+++ b/src/core/timing_event.h
@@ -57,9 +57,6 @@ public:
       Deactivate();
   }
 
-  // Directly alters the downcount of the event.
-  void SetDowncount(TickCount downcount);
-
   // Directly alters the interval of the event.
   void SetInterval(TickCount interval) { m_interval = interval; }
   void SetPeriod(TickCount period) { m_period = period; }