Fix GA20 mute

src/engine/platform/ga20.cpp

@@ -121,8 +121,12 @@ void DivPlatformGA20::tick(bool sysTick) {
       }
     }
     if (chan[i].volumeChanged) {
-      chan[i].resVol=(chan[i].active && isMuted[i])?0:chan[i].outVol&0xff;
-      chWrite(i,0x5,chan[i].resVol);
+      if (isMuted[i]) {
+        chWrite(i,0x5,0);
+      } else {
+        chan[i].resVol=(isMuted[i])?0:chan[i].outVol&0xff;
+        chWrite(i,0x5,chan[i].resVol);
+      }
       chan[i].volumeChanged=false;
     }
     if (chan[i].setPos) {
@@ -320,6 +324,7 @@ int DivPlatformGA20::dispatch(DivCommand c) {
 
 void DivPlatformGA20::muteChannel(int ch, bool mute) {
   isMuted[ch]=mute;
+  ga20.set_mute(ch,mute);
   chan[ch].volumeChanged=true;
 }
 

src/engine/platform/sound/ga20/iremga20.cpp

@@ -104,7 +104,7 @@ void iremga20_device::sound_stream_update(short** outputs, int len)
 					ch.play = false;
 				else
 				{
-					sampleout = (sample - 0x80) * (s32)ch.volume;
+					sampleout = ch.mute ? 0 : (sample - 0x80) * (s32)ch.volume;
 					ch.counter--;
 					if (ch.counter <= ch.rate)
 					{

src/engine/platform/sound/ga20/iremga20.h

@@ -38,6 +38,8 @@ public:
 	void write(u32 offset, u8 data);
 	u8 read(u32 offset);
 
+	inline void set_mute(const int ch, const bool mute) { m_channel[ch & 3].mute = mute; }
+
 	// device-level overrides
 	void device_reset();
 
@@ -53,7 +55,8 @@ private:
 			counter(0),
 			end(0),
 			volume(0),
-			play(0)
+			play(0),
+			mute(false)
 		{
 		}
 
@@ -63,6 +66,7 @@ private:
 		u32 end;
 		u32 volume;
 		bool play;
+		bool mute;
 	};
 
 	u8 m_regs[0x20];