From fdc5a0620031e3f049b121479d62d69005e3c1ab Mon Sep 17 00:00:00 2001
From: Peter Veenstra <qbix79@users.sourceforge.net>
Date: Mon, 11 Jun 2018 14:51:22 +0000
Subject: [PATCH] No irq generating when masking the IRQ channel. Fixes later
 sci games and bug #482.

Imported-from: https://svn.code.sf.net/p/dosbox/code-0/dosbox/trunk@4113
---
 src/hardware/sblaster.cpp | 25 ++++++++++++++++++++++---
 1 file changed, 22 insertions(+), 3 deletions(-)

diff --git a/src/hardware/sblaster.cpp b/src/hardware/sblaster.cpp
index d6d2a9da..9058df08 100644
--- a/src/hardware/sblaster.cpp
+++ b/src/hardware/sblaster.cpp
@@ -273,11 +273,27 @@ static INLINE void DSP_FlushData(void) {
 	sb.dsp.out.pos=0;
 }
 
+static double last_dma_callback = 0.0f;
+
 static void DSP_DMA_CallBack(DmaChannel * chan, DMAEvent event) {
 	if (chan!=sb.dma.chan || event==DMA_REACHED_TC) return;
 	else if (event==DMA_MASKED) {
 		if (sb.mode==MODE_DMA) {
-			GenerateDMASound(sb.dma.min);
+			//Catch up to current time, but don't generate an IRQ!
+			//Fixes problems with later sci games.
+			double t = PIC_FullIndex() - last_dma_callback;
+			Bitu s = static_cast<Bitu>(sb.dma.rate * t / 1000.0f);
+			if (s > sb.dma.min) {
+				LOG(LOG_SB,LOG_NORMAL)("limiting amount masked to sb.dma.min");
+				s = sb.dma.min;
+			}
+			Bitu min_size = sb.dma.mul >> SB_SH;
+			if (!min_size) min_size = 1;
+			min_size *= 2;
+			if (sb.dma.left > min_size) {
+				if (s > (sb.dma.left-min_size)) s = sb.dma.left - min_size;
+				GenerateDMASound(s);
+			}
 			sb.mode=MODE_DMA_MASKED;
 //			DSP_ChangeMode(MODE_DMA_MASKED);
 			LOG(LOG_SB,LOG_NORMAL)("DMA masked,stopping output, left %d",chan->currcnt);
@@ -394,12 +410,15 @@ INLINE Bit8u decode_ADPCM_3_sample(Bit8u sample,Bit8u & reference,Bits& scale) {
 
 static void GenerateDMASound(Bitu size) {
 	Bitu read=0;Bitu done=0;Bitu i=0;
+	last_dma_callback = PIC_FullIndex();
 
 	if(sb.dma.autoinit) {
 		if (sb.dma.left <= size) 
 			size = sb.dma.left;
-	} else if (sb.dma.left <= sb.dma.min) 
-		size = sb.dma.left;
+	} else {
+		if (sb.dma.left <= sb.dma.min) 
+			size = sb.dma.left;
+	}
 
 	switch (sb.dma.mode) {
 	case DSP_DMA_2: