id_sd_sdl: Make register write delays configurable

Currently, we delay a few samples after every register write. This can
be confusing, particularly with Nuked_OPL3, which also delays a couple
of samples when OPL3_WriteRegBuffered() is used. It's also ugly to have
to track all of the extra samples queued here and there.

Make the number of delayed samples configurable with:
sd_oplWriteDelay = <num>

It's still based of the sample rate by default, otherwise put the number
of samples you want, or 0 to disable it entirely.

You can also disable/enable the OPL3_WriteRegBuffered() function with
sd_nukedBufferWrites. By default, it's only enabled when
sd_oplWriteDelay is nonzero.

A PR to make NukedOPL3's buffering configurable exists here:
nukeykt/Nuked-OPL3#27

Note that NukedOPL3's buffering is based in the 49716Hz samples, not the
resampled values, like our sd_oplWriteDelay.

src/id_sd_sdl.c

@@ -58,6 +58,9 @@ static bool sd_sdl_queueAudio = false;
 #endif
 static int sd_sdl_queueAudioMinBufSize = 0;
 
+static int sd_oplDelaySamples;
+static bool sd_nukedBufferWrites;
+
 #define PC_PIT_RATE 1193182
 #define SD_SFX_PART_RATE 140
 /* In the original exe, upon setting a rate of 140Hz or 560Hz for some
@@ -141,9 +144,16 @@ static inline bool YM3812Init(int numChips, int clock, int rate)
 static inline void YM3812Write(Chip *which, Bit32u reg, Bit8u val)
 {
 	if (sd_oplEmulator == SD_OPL_EMULATOR_DBOPL)
+	{
 		Chip__WriteReg(which, reg, val);
+	}
 	else if (sd_oplEmulator == SD_OPL_EMULATOR_NUKED)
-		OPL3_WriteRegBuffered(&nuked_oplChip, reg, val);
+	{
+		if (sd_nukedBufferWrites)
+			OPL3_WriteRegBuffered(&nuked_oplChip, reg, val);
+		else
+			OPL3_WriteReg(&nuked_oplChip, reg, val);
+	}
 }
 
 static inline void YM3812UpdateOne(Chip *which, int16_t *stream, int length)
@@ -278,7 +288,7 @@ void SD_SDL_alOut(uint8_t reg, uint8_t val)
 	// at the least. For now a hack is implied.
 	YM3812Write(&oplChip, reg, val);
 	// Hack comes with a "magic number" that appears to make it work better
-	int length = SD_SDL_AudioSpec.freq / 10000;
+	int length = sd_oplDelaySamples;
 	if (length)
 	{
 #ifdef SD_SDL_WITH_QUEUEAUDIO
@@ -506,6 +516,9 @@ void SD_SDL_Startup(void)
 #endif
 	sd_sdl_queueAudioMinBufSize = CFG_GetConfigInt("sd_sdl_queueAudioMinBufSize", 0);
 
+	sd_oplDelaySamples = CFG_GetConfigInt("sd_oplDelaySamples", SD_SDL_AudioSpec.freq / 10000);
+	sd_nukedBufferWrites = CFG_GetConfigBool("sd_nukedBufferWrites", sd_oplDelaySamples == 0);
+
 	// Setup a condition variable to signal threads waiting for timer updates.
 	SD_SDL_WaitTicksSpin = CFG_GetConfigBool("sd_sdl_waitTicksSpin", false);
 	if (!SD_SDL_WaitTicksSpin)