fix broken DAC mode

adds new compat flag

papers/format.md

@@ -29,6 +29,7 @@ furthermore, an `or reserved` indicates this field is always present, but is res
 
 the format versions are:
 
+- 64: Furnace dev64
 - 63: Furnace dev63
 - 62: Furnace dev62
 - 61: Furnace dev61
@@ -203,7 +204,8 @@ size | description
   1  | ignore duplicate slides (>=50) or reserved
   1  | stop portamento on note off (>=62) or reserved
   1  | continuous vibrato (>=62) or reserved
-  4  | reserved
+  1  | broken DAC mode (>=64) or reserved
+  3  | reserved
  4?? | pointers to instruments
  4?? | pointers to wavetables
  4?? | pointers to samples

src/engine/engine.h

@@ -37,8 +37,8 @@
     warnings+=(String("\n")+x); \
   }
 
-#define DIV_VERSION "dev63"
-#define DIV_ENGINE_VERSION 63
+#define DIV_VERSION "dev64"
+#define DIV_ENGINE_VERSION 64
 
 enum DivStatusView {
   DIV_STATUS_NOTHING=0,

src/engine/fileOps.cpp

@@ -140,6 +140,7 @@ bool DivEngine::loadDMF(unsigned char* file, size_t len) {
     ds.algMacroBehavior=false;
     ds.brokenShortcutSlides=false;
     ds.ignoreDuplicateSlides=true;
+    ds.brokenDACMode=true;
 
     // 1.1 compat flags
     if (ds.version>24) {
@@ -799,6 +800,9 @@ bool DivEngine::loadFur(unsigned char* file, size_t len) {
     if (ds.version<62) {
       ds.stopPortaOnNoteOff=true;
     }
+    if (ds.version<64) {
+      ds.brokenDACMode=false;
+    }
     ds.isDMF=false;
 
     reader.readS(); // reserved
@@ -975,7 +979,12 @@ bool DivEngine::loadFur(unsigned char* file, size_t len) {
         reader.readC();
         reader.readC();
       }
-      for (int i=0; i<4; i++) reader.readC();
+      if (ds.version>=64) {
+        ds.brokenDACMode=reader.readC();
+      } else {
+        reader.readC();
+      }
+      for (int i=0; i<3; i++) reader.readC();
     } else {
       for (int i=0; i<20; i++) reader.readC();
     }
@@ -1417,7 +1426,8 @@ SafeWriter* DivEngine::saveFur() {
   w->writeC(song.ignoreDuplicateSlides);
   w->writeC(song.stopPortaOnNoteOff);
   w->writeC(song.continuousVibrato);
-  for (int i=0; i<4; i++) {
+  w->writeC(song.brokenDACMode);
+  for (int i=0; i<3; i++) {
     w->writeC(0);
   }
 

src/engine/platform/genesis.cpp

@@ -99,6 +99,9 @@ void DivPlatformGenesis::acquire_nuked(short* bufL, short* bufR, size_t start, s
               dacPos=s->loopStart;
             } else {
               dacSample=-1;
+              if (parent->song.brokenDACMode) {
+                rWrite(0x2b,0);
+              }
             }
           }
           dacPeriod+=MAX(40,dacRate);
@@ -163,6 +166,9 @@ void DivPlatformGenesis::acquire_ymfm(short* bufL, short* bufR, size_t start, si
               dacPos=s->loopStart;
             } else {
               dacSample=-1;
+              if (parent->song.brokenDACMode) {
+                rWrite(0x2b,0);
+              }
             }
           }
           dacPeriod+=MAX(40,dacRate);
@@ -460,6 +466,7 @@ int DivPlatformGenesis::dispatch(DivCommand c) {
             if (dumpWrites) addWrite(0xffff0002,0);
             break;
           } else {
+            rWrite(0x2b,1<<7);
             if (dumpWrites) addWrite(0xffff0000,dacSample);
           }
           dacPos=0;
@@ -477,6 +484,7 @@ int DivPlatformGenesis::dispatch(DivCommand c) {
             if (dumpWrites) addWrite(0xffff0002,0);
             break;
           } else {
+            rWrite(0x2b,1<<7);
             if (dumpWrites) addWrite(0xffff0000,dacSample);
           }
           dacPos=0;
@@ -541,6 +549,10 @@ int DivPlatformGenesis::dispatch(DivCommand c) {
       if (c.chan==5) {
         dacSample=-1;
         if (dumpWrites) addWrite(0xffff0002,0);
+        if (parent->song.brokenDACMode) {
+          rWrite(0x2b,0);
+          break;
+        }
       }
       chan[c.chan].keyOff=true;
       chan[c.chan].keyOn=false;

src/engine/song.h

@@ -295,6 +295,7 @@ struct DivSong {
   bool ignoreDuplicateSlides;
   bool stopPortaOnNoteOff;
   bool continuousVibrato;
+  bool brokenDACMode;
 
   DivOrders orders;
   std::vector<DivInstrument*> ins;
@@ -359,7 +360,8 @@ struct DivSong {
     brokenShortcutSlides(false),
     ignoreDuplicateSlides(false),
     stopPortaOnNoteOff(false),
-    continuousVibrato(false) {
+    continuousVibrato(false),
+    brokenDACMode(false) {
     for (int i=0; i<32; i++) {
       system[i]=DIV_SYSTEM_NULL;
       systemVol[i]=64;

src/gui/gui.cpp

@@ -2115,6 +2115,10 @@ void FurnaceGUI::drawCompatFlags() {
     if (ImGui::IsItemHovered()) {
       ImGui::SetTooltip("when enabled, vibrato will not be reset on a new note.");
     }
+    ImGui::Checkbox("Broken DAC mode",&e->song.brokenDACMode);
+    if (ImGui::IsItemHovered()) {
+      ImGui::SetTooltip("when enabled, the DAC in YM2612 will be disabled if there isn't any sample playing.");
+    }
 
     ImGui::Text("Loop modality:");
     if (ImGui::RadioButton("Reset channels",e->song.loopModality==0)) {