Synchronise the controller status more spread out inside a rendered frame:

* before rendering a background;
* before rendering sprites;
* while rendering more than 128 samples of audio at once ("Prefer fluid video");
* after every 16 scanlines of CPU execution instead of every 1;
* while waiting for an audio buffer to become available;
* while killing time between frames with fast-forward disabled.

Controller presses and releases are now combined in a DS button bitfield using a shorter 32-bit algorithm. See entry.cpp:NDSSFCAccumulateJoypad and #define ACCUMULATE_JOYPAD in the source.

This is still not suitable for playing platformers frame-perfectly, but it's much better than half a second of latency to press or release a button, and one still needs to press buttons a bit more than just light taps. I'd say 50 milliseconds is the latency now. Platformers requiring more precision can be played with frameskip 0.

DMA does not require double-buffered displaying, so synchronise the controller more often by disabling double-buffered displaying again.

Makefile

@@ -71,7 +71,7 @@ DEFS   := -DSPC700_C -DEXECUTE_SUPERFX_PER_LINE -DSDD1_DECOMP \
           -DNO_INLINE_SET_GET -DNOASM -DHAVE_MKSTEMP '-DACCEPT_SIZE_T=size_t' \
           -DUNZIP_SUPPORT -DFOREVER_16_BIT_SOUND -DFOREVER_STEREO \
           -DFOREVER_FORWARD_STEREO -DNO_VOLATILE_SOUND \
-          -DSYNC_JOYPAD_AT_HBLANK -DDS2_DMA
+          -DACCUMULATE_JOYPAD -DDS2_DMA
 
 .PHONY: clean makedirs
 .SUFFIXES: .elf .dat .plg

source/cpuexec.cpp

@@ -105,7 +105,7 @@
 #include "sa1.h"
 #include "spc7110.h"
 
-#ifdef SYNC_JOYPAD_AT_HBLANK
+#ifdef ACCUMULATE_JOYPAD
 #include "display.h"
 #endif
 
@@ -473,15 +473,14 @@ void S9xDoHBlankProcessing_SFX ()
     switch (CPU.WhichEvent)
     {
 		case HBLANK_START_EVENT:
-#ifdef SYNC_JOYPAD_AT_HBLANK
-		// Re-get the controls every hblank. A resolution algorithm in
-		// ppu.cpp will determine with greater accuracy whether a key was
-		// pressed or released during the frame.
-		uint32 i;
-		for (i = 0; i < 5; i++)
-		{
-			IPPU.JoypadsAtHBlanks [i][CPU.V_Counter] = S9xReadJoypad (i);
-		}
+#ifdef ACCUMULATE_JOYPAD
+/*
+ * This call allows NDSSFC to synchronise the DS controller more often.
+ * If porting a later version of Snes9x into NDSSFC, it is essential to
+ * preserve it.
+ */
+		if ((CPU.V_Counter & 0xF) == 0)
+			NDSSFCAccumulateJoypad ();
 #endif
 		if (IPPU.HDMA && CPU.V_Counter <= PPU.ScreenHeight)
 			IPPU.HDMA = S9xDoHDMA (IPPU.HDMA);
@@ -663,15 +662,13 @@ void S9xDoHBlankProcessing_NoSFX ()
     switch (CPU.WhichEvent)
     {
 		case HBLANK_START_EVENT:
-#ifdef SYNC_JOYPAD_AT_HBLANK
-		// Re-get the controls every hblank. A resolution algorithm in
-		// ppu.cpp will determine with greater accuracy whether a key was
-		// pressed or released during the frame.
-		uint32 i;
-		for (i = 0; i < 5; i++)
-		{
-			IPPU.JoypadsAtHBlanks [i][CPU.V_Counter] = S9xReadJoypad (i);
-		}
+#ifdef ACCUMULATE_JOYPAD
+/*
+ * This call allows NDSSFC to synchronise the DS controller more often.
+ * If porting a later version of Snes9x into NDSSFC, it is essential to
+ * preserve it.
+ */
+		NDSSFCAccumulateJoypad ();
 #endif
 		if (IPPU.HDMA && CPU.V_Counter <= PPU.ScreenHeight)
 			IPPU.HDMA = S9xDoHDMA (IPPU.HDMA);

source/display.h

@@ -97,6 +97,9 @@ void S9xGraphicsMode ();
 char *S9xParseArgs (char **argv, int argc);
 void S9xParseArg (char **argv, int &index, int argc);
 void S9xExtraUsage ();
+#ifdef ACCUMULATE_JOYPAD
+void NDSSFCAccumulateJoypad ();
+#endif
 uint32 S9xReadJoypad (int which1_0_to_4);
 bool8 S9xReadMousePosition (int which1_0_to_1, int &x, int &y, uint32 &buttons);
 bool8 S9xReadSuperScopePosition (int &x, int &y, uint32 &buttons);

source/gfx.cpp

@@ -1169,6 +1169,14 @@ void S9xSetupOBJ ()
 
 static void DrawOBJS (bool8 OnMain = FALSE, uint8 D = 0)
 {
+#ifdef ACCUMULATE_JOYPAD
+/*
+ * This call allows NDSSFC to synchronise the DS controller more often.
+ * If porting a later version of Snes9x into NDSSFC, it is essential to
+ * preserve it.
+ */
+	NDSSFCAccumulateJoypad ();
+#endif
 #ifdef MK_DEBUG_RTO
 	if(Settings.BGLayering) fprintf(stderr, "Entering DrawOBJS() for %d-%d\n", GFX.StartY, GFX.EndY);
 #endif
@@ -2314,6 +2322,14 @@ static void DrawBackgroundMode5 (uint32 /* BGMODE */, uint32 bg, uint8 Z1, uint8
 
 static void DrawBackground (uint32 BGMode, uint32 bg, uint8 Z1, uint8 Z2)
 {
+#ifdef ACCUMULATE_JOYPAD
+/*
+ * This call allows NDSSFC to synchronise the DS controller more often.
+ * If porting a later version of Snes9x into NDSSFC, it is essential to
+ * preserve it.
+ */
+	NDSSFCAccumulateJoypad ();
+#endif
     GFX.PixSize = 1;
 	
     BG.TileSize = BGSizes [PPU.BG[bg].BGSize];

source/nds/entry.cpp

@@ -734,6 +734,14 @@ void S9xSyncSpeed ()
 			{
 				do {
 					S9xProcessSound (0);
+#ifdef ACCUMULATE_JOYPAD
+/*
+ * This call allows NDSSFC to synchronise the DS controller more often.
+ * If porting a later version of Snes9x into NDSSFC, it is essential to
+ * preserve it.
+ */
+					NDSSFCAccumulateJoypad ();
+#endif
 					syncdif = sync_next - getSysTime();
 				} while (syncdif > 0);
 			}
@@ -767,6 +775,14 @@ void S9xSyncSpeed ()
 			{
 				do {
 					S9xProcessSound (0);
+#ifdef ACCUMULATE_JOYPAD
+/*
+ * This call allows NDSSFC to synchronise the DS controller more often.
+ * If porting a later version of Snes9x into NDSSFC, it is essential to
+ * preserve it.
+ */
+					NDSSFCAccumulateJoypad ();
+#endif
 					syncdif = sync_next - getSysTime();
 				} while (syncdif > 0);
 				// After that little delay, what time is it?
@@ -968,17 +984,17 @@ void S9xProcessSound (unsigned int)
 	if (!game_enable_audio)
 		return;
 
-	if(ds2_checkAudiobuff() > AUDIO_BUFFER_COUNT * 3/4)
-	{
-		LastSoundEmissionTime++;
-		return;
-	}
-
-	unsigned short *audiobuff;
-
 	unsigned int Now = getSysTime();
 	if (Now - LastSoundEmissionTime >= SOUND_EMISSION_INTERVAL)
 	{
+		if(ds2_checkAudiobuff() > AUDIO_BUFFER_COUNT * 3/4)
+		{
+			LastSoundEmissionTime++;
+			return;
+		}
+
+		unsigned short *audiobuff;
+
 		if (Now - LastSoundEmissionTime >= 11719 /* 500 milliseconds */)
 		{
 			LastSoundEmissionTime = Now;
@@ -1003,9 +1019,14 @@ void S9xProcessSound (unsigned int)
 		}
 #endif
 
-		do {
+		audiobuff = (unsigned short*)ds2_getAudiobuff();
+		while (audiobuff == NULL) //There are audio queue in sending or wait to send
+		{
+#ifdef ACCUMULATE_JOYPAD
+			NDSSFCAccumulateJoypad ();
+#endif
 			audiobuff = (unsigned short*)ds2_getAudiobuff();
-		} while (audiobuff == NULL); //There are audio queue in sending or wait to send
+		}
 
 		/* If we need more audio samples */
 		if (so.samples_mixed_so_far < sample_count)
@@ -1141,72 +1162,99 @@ const unsigned int keymap[12] = {
 
 static bool8 SoundToggleWasHeld = FALSE;
 
-unsigned int S9xReadJoypad (int which1)
-{
-    struct key_buf inputdata;
+#ifdef ACCUMULATE_JOYPAD
+// These are kept as DS key bitfields until it's time to send them to Snes9x.
+static uint32 PreviousControls = 0x00000000;
+static uint32 ControlsPressed  = 0x00000000;
+static uint32 ControlsReleased = 0x00000000;
 
+void NDSSFCAccumulateJoypad ()
+{
+	struct key_buf inputdata;
 	ds2_getrawInput(&inputdata);
 
-	if (inputdata.key & KEY_LID)
-	{
-		LowFrequencyCPU();
-		ds2_setSupend();
-		do {
-			ds2_getrawInput(&inputdata);
-			mdelay(1);
-		} while (inputdata.key & KEY_LID);
-		ds2_wakeup();
-		// Before starting to emulate again, turn off the lower
-		// screen's backlight.
-		mdelay(100); // needed to avoid ds2_setBacklight crashing
-		ds2_setBacklight(2);
-		GameFrequencyCPU();
-	}
-
-	u32 HotkeyReturnToMenu = game_config.HotkeyReturnToMenu != 0 ? game_config.HotkeyReturnToMenu : emu_config.HotkeyReturnToMenu;
-	u32 HotkeyTemporaryFastForward = game_config.HotkeyTemporaryFastForward != 0 ? game_config.HotkeyTemporaryFastForward : emu_config.HotkeyTemporaryFastForward;
-	u32 HotkeyToggleSound = game_config.HotkeyToggleSound != 0 ? game_config.HotkeyToggleSound : emu_config.HotkeyToggleSound;
-
-	if(inputdata.key & KEY_TOUCH ||
-		(HotkeyReturnToMenu && ((inputdata.key & HotkeyReturnToMenu) == HotkeyReturnToMenu))
-	)	//Active menu
-		Settings.Paused = 1;
-
-	temporary_fast_forward =
-		(HotkeyTemporaryFastForward && ((inputdata.key & HotkeyTemporaryFastForward) == HotkeyTemporaryFastForward))
-	;
-
-	bool8 SoundToggleIsHeld = 
-		(HotkeyToggleSound && ((inputdata.key & HotkeyToggleSound) == HotkeyToggleSound))
-	;
-
-	if (SoundToggleIsHeld && !SoundToggleWasHeld)
-	{
-		game_enable_audio = !game_enable_audio;
-		game_disableAudio();
-	}
-
-	SoundToggleWasHeld = SoundToggleIsHeld;
+	ControlsPressed |= inputdata.key & ~PreviousControls;
+	ControlsReleased |= PreviousControls & ~inputdata.key;
+}
+#endif // ACCUMULATE_JOYPAD
 
+uint32 S9xReadJoypad (int which1)
+{
 	if(which1 < 1)
 	{
-		unsigned int key;
+		uint32 Controls;
+#ifdef ACCUMULATE_JOYPAD
+		Controls = (PreviousControls | ControlsPressed) & ~ControlsReleased;
+		PreviousControls = Controls;
+		ControlsPressed = ControlsReleased = 0x00000000;
+#else
+		{
+			struct key_buf inputdata;
+			ds2_getrawInput(&inputdata);
+
+			Controls = inputdata.key;
+		}
+#endif
+
+		if (Controls & KEY_LID)
+		{
+			LowFrequencyCPU();
+			ds2_setSupend();
+			struct key_buf inputdata;
+			do {
+				ds2_getrawInput(&inputdata);
+				mdelay(1);
+			} while (inputdata.key & KEY_LID);
+			ds2_wakeup();
+			// Before starting to emulate again, turn off the lower
+			// screen's backlight.
+			mdelay(100); // needed to avoid ds2_setBacklight crashing
+			ds2_setBacklight(2);
+			GameFrequencyCPU();
+		}
+
+		u32 HotkeyReturnToMenu = game_config.HotkeyReturnToMenu != 0 ? game_config.HotkeyReturnToMenu : emu_config.HotkeyReturnToMenu;
+		u32 HotkeyTemporaryFastForward = game_config.HotkeyTemporaryFastForward != 0 ? game_config.HotkeyTemporaryFastForward : emu_config.HotkeyTemporaryFastForward;
+		u32 HotkeyToggleSound = game_config.HotkeyToggleSound != 0 ? game_config.HotkeyToggleSound : emu_config.HotkeyToggleSound;
+
+		if(Controls & KEY_TOUCH ||
+			(HotkeyReturnToMenu && ((Controls & HotkeyReturnToMenu) == HotkeyReturnToMenu))
+		)	//Active menu
+			Settings.Paused = 1;
+
+		temporary_fast_forward =
+			(HotkeyTemporaryFastForward && ((Controls & HotkeyTemporaryFastForward) == HotkeyTemporaryFastForward))
+		;
+
+		bool8 SoundToggleIsHeld = 
+			(HotkeyToggleSound && ((Controls & HotkeyToggleSound) == HotkeyToggleSound))
+		;
+
+		if (SoundToggleIsHeld && !SoundToggleWasHeld)
+		{
+			game_enable_audio = !game_enable_audio;
+			game_disableAudio();
+		}
+
+		SoundToggleWasHeld = SoundToggleIsHeld;
+
+		uint32 key = 0x80000000;  // Required by Snes9x
 
 		                                           //   DS   ->  SNES
-		key  = (inputdata.key & KEY_A     ) <<  7; // 0x0001 -> 0x0080
-		key |= (inputdata.key & KEY_B     ) << 14; // 0x0002 -> 0x8000
-		key |= (inputdata.key & KEY_SELECT) << 11; // 0x0004 -> 0x2000
-		key |= (inputdata.key & KEY_START ) <<  9; // 0x0008 -> 0x1000
-		key |= (inputdata.key & KEY_UP    ) <<  5; // 0x0040 -> 0x0800
+		key |= (Controls & KEY_A     ) <<  7;      // 0x0001 -> 0x0080
+		key |= (Controls & KEY_B     ) << 14;      // 0x0002 -> 0x8000
+		key |= (Controls & KEY_SELECT) << 11;      // 0x0004 -> 0x2000
+		key |= (Controls & KEY_START ) <<  9;      // 0x0008 -> 0x1000
+		key |= (Controls & KEY_UP    ) <<  5;      // 0x0040 -> 0x0800
 		// 0x0010 -> 0x0100; 0x0020 -> 0x0200
 		// 0x0030 -> 0x0300
-		key |= (inputdata.key & (KEY_RIGHT | KEY_LEFT))  <<  4;
+		key |= (Controls & (KEY_RIGHT | KEY_LEFT))  <<  4;
 		// 0x0100 -> 0x0010; 0x0200 -> 0x0020; 0x0400 -> 0x0040
 		// 0x0700 -> 0x0070
-		key |= (inputdata.key & (KEY_R | KEY_L | KEY_X)) >>  4;
+		key |= (Controls & (KEY_R | KEY_L | KEY_X)) >>  4;
 		// 0x0080 -> 0x0400; 0x0800 -> 0x4000
 		// 0x0880 -> 0x4400
-		key |= (inputdata.key & (KEY_DOWN | KEY_Y))      <<  3;
+		key |= (Controls & (KEY_DOWN | KEY_Y))      <<  3;
 /*
 		for(i= 0; i < 12; i++)	//remap key
 		{
@@ -1214,7 +1262,7 @@ unsigned int S9xReadJoypad (int which1)
 		}
 */
 
-		return (key | 0x80000000);
+		return key;
 	}
 	else
 		return 0;

source/nds/gui.h

@@ -24,11 +24,7 @@
 #include "fs_api.h"
 #include "gcheat.h"
 
-#ifdef DS2_DMA
-#define UP_SCREEN_UPDATE_METHOD   1
-#else
 #define UP_SCREEN_UPDATE_METHOD   0
-#endif
 #define DOWN_SCREEN_UPDATE_METHOD 2
 
 #define MAX_GAMEPAD_MAP 16

source/ppu.cpp

@@ -2853,43 +2853,10 @@ void S9xUpdateJoypads ()
 {
     uint32 i;
 
-#ifdef SYNC_JOYPAD_AT_HBLANK
-	uint32 j, k, KeyValue;
-	bool8 StartedPressed;
-
-	// For each joypad
-	for (i = 0; i < 5; i++)
-	{
-		IPPU.Joypads [i] = 0;
-		// Sync each key
-		for (k = 1; k != 0; k <<= 1)
-		{
-			KeyValue = IPPU.JoypadsAtHBlanks[i][0] & k;
-			StartedPressed = KeyValue != 0;
-			// from each line.
-			// If, initially, the key is NOT pressed, one line of it being
-			// pressed means that the key MUST be pressed.
-			// Otherwise, the key MUST be depressed if it starts pressed.
-			for (j = 1; j < (Settings.PAL ? SNES_MAX_PAL_VCOUNTER : SNES_MAX_NTSC_VCOUNTER); j++)
-			{
-				if ((StartedPressed) && ((IPPU.JoypadsAtHBlanks[i][j] & k) == 0)) {
-					KeyValue = 0;
-					break;
-				}
-				else if ((!StartedPressed) && ((IPPU.JoypadsAtHBlanks[i][j] & k) != 0)) {
-					KeyValue = k;
-					break;
-				}
-			}
-			IPPU.Joypads [i] |= KeyValue;
-		}
-	}
-#else
 	for (i = 0; i < 5; i++)
 	{
 		IPPU.Joypads [i] = S9xReadJoypad (i);
 	}
-#endif
 
 //	S9xMovieUpdate();
 

source/ppu.h

@@ -152,9 +152,6 @@ struct InternalPPU {
     int	   CurrentLine;
     int	   Controller;
     uint32 Joypads[5];
-#ifdef SYNC_JOYPAD_AT_HBLANK
-	uint32 JoypadsAtHBlanks[5][SNES_MAX_PAL_VCOUNTER];
-#endif
     uint32 SuperScope;
     uint32 Mouse[2];
     int    PrevMouseX[2];

source/soundux.cpp

@@ -1233,6 +1233,15 @@ static inline void MixMono (int sample_count)
 		
 		for (uint32 I = 0; I < (uint32) sample_count; I++)
 		{
+#ifdef ACCUMULATE_JOYPAD
+/*
+ * This call allows NDSSFC to synchronise the DS controller more often.
+ * If porting a later version of Snes9x into NDSSFC, it is essential to
+ * preserve it.
+ */
+			if ((I & 0x7F) == 0x7F)
+				NDSSFCAccumulateJoypad ();
+#endif
 			unsigned long freq = freq0;
 			
 			if (mod)