swan: Implement headphone/internal speaker output toggle

src/engine/platform/sound/swan.c

@@ -127,7 +127,9 @@ void swan_sound_out(swan_sound_t *snd, uint16_t port, uint8_t value) {
 }
 
 static void swan_sound_subtick(swan_sound_t *snd, uint32_t cycles) {
+    // TODO: Do period counters update when a channel is inactive?
     for (int ch = 0; ch < 4; ch++) {
+        if (snd->ch_ctrl & (1 << ch)) {
             snd->period_counter[ch] += cycles;
             uint32_t step = 2048 - snd->frequency[ch];
             while (snd->period_counter[ch] >= step) {
@@ -135,6 +137,7 @@ static void swan_sound_subtick(swan_sound_t *snd, uint32_t cycles) {
                 snd->period_counter[ch] -= step;
             }
         }
+    }
 
     if (snd->ch_ctrl & SND_CH3_SWEEP) {
         snd->sweep_counter += cycles;

src/engine/platform/swan.cpp

@@ -107,8 +107,12 @@ void DivPlatformSwan::acquire(short** buf, size_t len) {
       }
     }
 
+    if (stereo) {
       buf[0][h] = ws.output_left;
       buf[1][h] = ws.output_right;  
+    } else {
+      buf[0][h] = ((int)ws.output_speaker - 0x80) << 8;  
+    }
   }
 
   for (int i=0; i<4; i++) {
@@ -597,7 +601,7 @@ void DivPlatformSwan::reset() {
 }
 
 int DivPlatformSwan::getOutputCount() {
-  return 2;
+  return stereo?2:1;
 }
 
 void DivPlatformSwan::notifyWaveChange(int wave) {
@@ -627,6 +631,7 @@ void DivPlatformSwan::setFlags(const DivConfig& flags) {
   chipClock=3072000;
   CHECK_CUSTOM_CLOCK;
   rate=chipClock/128;
+  stereo=flags.getBool("stereo",false);
   for (int i=0; i<4; i++) {
     oscBuf[i]->setRate(rate);
   }

src/engine/platform/swan.h

@@ -38,6 +38,7 @@ class DivPlatformSwan: public DivDispatch {
   Channel chan[4];
   DivDispatchOscBuffer* oscBuf[4];
   bool isMuted[4];
+  bool stereo=true;
   bool pcm, sweep, furnaceDac, setPos;
   unsigned char sampleBank, noise;
   int dacPeriod, dacRate;

src/gui/sysConf.cpp

@@ -2664,7 +2664,19 @@ bool FurnaceGUI::drawSysConf(int chan, int sysPos, DivSystem type, DivConfig& fl
       }
       break;
     }
-    case DIV_SYSTEM_SWAN:
+    case DIV_SYSTEM_SWAN: {
+      bool stereo=flags.getBool("stereo",true);
+      if (ImGui::Checkbox(_("Headphone output##_SWAN_STEREO"),&stereo)) {
+        altered=true;
+      }
+
+      if (altered) {
+        e->lockSave([&]() {
+          flags.set("stereo",stereo);
+        });
+      }
+      break;
+    }
     case DIV_SYSTEM_BUBSYS_WSG:
     case DIV_SYSTEM_PET:
     case DIV_SYSTEM_GA20: