From 5103774f6de1cd757dcff2fbfe9a2ac845143dd7 Mon Sep 17 00:00:00 2001
From: notaz <notasas@gmail.com>
Date: Sat, 30 Sep 2017 18:14:20 +0300
Subject: [PATCH] sn76496: simplify writes

---
 pico/sound/sn76496.c | 122 ++++++++++++++-----------------------------
 1 file changed, 40 insertions(+), 82 deletions(-)

diff --git a/pico/sound/sn76496.c b/pico/sound/sn76496.c
index 8474c70..b212759 100644
--- a/pico/sound/sn76496.c
+++ b/pico/sound/sn76496.c
@@ -73,96 +73,54 @@ int *sn76496_regs;
 void SN76496Write(int data)
 {
 	struct SN76496 *R = &ono_sn;
-	int n;
-
+	int n, r, c;
 
 	/* update the output buffer before changing the registers */
 	//stream_update(R->Channel,0);
 
+	r = R->LastRegister;
 	if (data & 0x80)
-	{
-		int r = (data & 0x70) >> 4;
-		int c = r/2;
+		r = R->LastRegister = (data & 0x70) >> 4;
+	c = r / 2;
 
-		R->LastRegister = r;
-		R->Register[r] = (R->Register[r] & 0x3f0) | (data & 0x0f);
-		switch (r)
-		{
-			case 0:	/* tone 0 : frequency */
-			case 2:	/* tone 1 : frequency */
-			case 4:	/* tone 2 : frequency */
-				R->Period[c] = R->UpdateStep * R->Register[r];
-				if (R->Period[c] == 0) R->Period[c] = R->UpdateStep;
-				if (r == 4)
-				{
-					/* update noise shift frequency */
-					if ((R->Register[6] & 0x03) == 0x03)
-						R->Period[3] = 2 * R->Period[2];
-				}
-				break;
-			case 1:	/* tone 0 : volume */
-			case 3:	/* tone 1 : volume */
-			case 5:	/* tone 2 : volume */
-			case 7:	/* noise  : volume */
-				R->Volume[c] = R->VolTable[data & 0x0f];
-				break;
-			case 6:	/* noise  : frequency, mode */
-				{
-					int n = R->Register[6];
-					R->NoiseFB = (n & 4) ? FB_WNOISE : FB_PNOISE;
-					n &= 3;
-					/* N/512,N/1024,N/2048,Tone #3 output */
-					R->Period[3] = ((n&3) == 3) ? 2 * R->Period[2] : (R->UpdateStep << (5+(n&3)));
-
-					/* reset noise shifter */
-					R->RNG = NG_PRESET;
-					R->Output[3] = R->RNG & 1;
-				}
-				break;
-		}
-	}
+	if (!(data & 0x80) && (r == 0 || r == 2 || r == 4))
+		// data byte (tone only)
+		R->Register[r] = (R->Register[r] & 0x0f) | ((data & 0x3f) << 4);
 	else
-	{
-		int r = R->LastRegister;
-		int c = r/2;
+		R->Register[r] = (R->Register[r] & 0x3f0) | (data & 0x0f);
 
-		switch (r)
-		{
-			case 0:	/* tone 0 : frequency */
-			case 2:	/* tone 1 : frequency */
-			case 4:	/* tone 2 : frequency */
-				R->Register[r] = (R->Register[r] & 0x0f) | ((data & 0x3f) << 4);
-				R->Period[c] = R->UpdateStep * R->Register[r];
-				if (R->Period[c] == 0) R->Period[c] = R->UpdateStep;
-				if (r == 4)
-				{
-					/* update noise shift frequency */
-					if ((R->Register[6] & 0x03) == 0x03)
-						R->Period[3] = 2 * R->Period[2];
-				}
-				break;
-			case 1:	/* tone 0 : volume */
-			case 3:	/* tone 1 : volume */
-			case 5:	/* tone 2 : volume */
-			case 7:	/* noise  : volume */
-				R->Volume[c] = R->VolTable[data & 0x0f];
-				R->Register[r] = (R->Register[r] & 0x3f0) | (data & 0x0f);
-				break;
-			case 6:	/* noise  : frequency, mode */
-				{
-					R->Register[r] = (R->Register[r] & 0x3f0) | (data & 0x0f);
-					n = R->Register[6];
-					R->NoiseFB = (n & 4) ? FB_WNOISE : FB_PNOISE;
-					n &= 3;
-					/* N/512,N/1024,N/2048,Tone #3 output */
-					R->Period[3] = ((n&3) == 3) ? 2 * R->Period[2] : (R->UpdateStep << (5+(n&3)));
-
-					/* reset noise shifter */
-					R->RNG = NG_PRESET;
-					R->Output[3] = R->RNG & 1;
-				}
-				break;
-		}
+	data = R->Register[r];
+	switch (r)
+	{
+		case 0:	/* tone 0 : frequency */
+		case 2:	/* tone 1 : frequency */
+		case 4:	/* tone 2 : frequency */
+			R->Period[c] = R->UpdateStep * data;
+			if (R->Period[c] == 0) R->Period[c] = R->UpdateStep;
+			if (r == 4)
+			{
+				/* update noise shift frequency */
+				if ((R->Register[6] & 0x03) == 0x03)
+					R->Period[3] = 2 * R->Period[2];
+			}
+			break;
+		case 1:	/* tone 0 : volume */
+		case 3:	/* tone 1 : volume */
+		case 5:	/* tone 2 : volume */
+		case 7:	/* noise  : volume */
+			R->Volume[c] = R->VolTable[data & 0x0f];
+			break;
+		case 6:	/* noise  : frequency, mode */
+			n = data;
+			R->NoiseFB = (n & 4) ? FB_WNOISE : FB_PNOISE;
+			n &= 3;
+			/* N/512,N/1024,N/2048,Tone #3 output */
+			R->Period[3] = (n == 3) ? 2 * R->Period[2] : (R->UpdateStep << (5 + n));
+
+			/* reset noise shifter */
+			R->RNG = NG_PRESET;
+			R->Output[3] = R->RNG & 1;
+			break;
 	}
 }
 
-- 
2.39.2