From 58040d478aad749ffae87b0097c26614bf820a4f Mon Sep 17 00:00:00 2001
From: Eladash <elad3356p@gmail.com>
Date: Thu, 28 Oct 2021 21:53:34 +0300
Subject: [PATCH] rsx: Implement NTSC fixup mode, improve VBLANK accuracy

---
 rpcs3/Emu/RSX/RSXThread.cpp | 31 ++++++++++++++++++++++++++++---
 rpcs3/Emu/system_config.h   |  1 +
 2 files changed, 29 insertions(+), 3 deletions(-)

diff --git a/rpcs3/Emu/RSX/RSXThread.cpp b/rpcs3/Emu/RSX/RSXThread.cpp
index ff71fc757c..3d0bcd2902 100644
--- a/rpcs3/Emu/RSX/RSXThread.cpp
+++ b/rpcs3/Emu/RSX/RSXThread.cpp
@@ -641,20 +641,45 @@ namespace rsx
 #endif
 			u64 start_time = get_system_time();
 
+			u64 vblank_rate = g_cfg.video.vblank_rate;
+			u64 vblank_period = 1'000'000 + u64{g_cfg.video.vblank_ntsc.get()} * 1000;
+
+			u64 local_vblank_count = 0;
+
 			// TODO: exit condition
 			while (!is_stopped())
 			{
+				// Get current time
 				const u64 current = get_system_time();
-				const u64 period_time = 1000000 / g_cfg.video.vblank_rate;
-				const u64 wait_for = period_time - std::min<u64>(current - start_time, period_time);
+
+				// Calculate the time at which we need to send a new VBLANK signal
+				const u64 post_event_time = start_time + (local_vblank_count + 1) * vblank_period / vblank_rate;
+
+				// Calculate time remaining to that time (0 if we passed it)
+				const u64 wait_for = current >= post_event_time ? 0 : post_event_time - current;
+
+				// Substract host operating system min sleep quantom to get sleep time
 				const u64 wait_sleep = wait_for - u64{wait_for >= host_min_quantum} * host_min_quantum;
 
 				if (!wait_for)
 				{
 					{
-						start_time += period_time;
+						local_vblank_count++;
 						vblank_count++;
 
+						if (local_vblank_count == vblank_rate)
+						{
+							// Advance start_time to the moment of the current VBLANK
+							// Which is the last VBLANK event in this period
+							// This is in order for multiplication by ratio above to use only small numbers
+							start_time += vblank_period;
+							local_vblank_count = 0;
+
+							// We have a rare chance to update settings without losing precision whenever local_vblank_count is 0
+							vblank_rate = g_cfg.video.vblank_rate;
+							vblank_period = 1'000'000 + u64{g_cfg.video.vblank_ntsc.get()} * 1000;
+						}
+	
 						if (isHLE)
 						{
 							if (vblank_handler)
diff --git a/rpcs3/Emu/system_config.h b/rpcs3/Emu/system_config.h
index 099baa1f21..da0b170b76 100644
--- a/rpcs3/Emu/system_config.h
+++ b/rpcs3/Emu/system_config.h
@@ -142,6 +142,7 @@ struct cfg_root : cfg::node
 		cfg::_int<0, 30000000> driver_recovery_timeout{ this, "Driver Recovery Timeout", 1000000, true };
 		cfg::_int<0, 16667> driver_wakeup_delay{ this, "Driver Wake-Up Delay", 1, true };
 		cfg::_int<1, 1800> vblank_rate{ this, "Vblank Rate", 60, true }; // Changing this from 60 may affect game speed in unexpected ways
+		cfg::_bool vblank_ntsc{ this, "Vblank NTSC Fixup", false, true };
 		cfg::_bool decr_memory_layout{ this, "DECR memory layout", false}; // Force enable increased allowed main memory range as DECR console
 
 		struct node_vk : cfg::node