Make the 6581 waveform offset adjustable (#13)

src/SID.cpp

@@ -142,6 +142,7 @@ SID::SID() :
     filter6581(new Filter6581()),
     filter8580(new Filter8580()),
     resampler(nullptr),
+    offset_6581(OFFSET_6581),
     cws(AVERAGE),
     dacLeakage(1.0),
     p(new Params)
@@ -269,8 +270,7 @@ void SID::setChipModel(ChipModel new_model)
         Dac dacBuilder(OSC_DAC_BITS);
         dacBuilder.kinkedDac(model, dacLeakage);
 
-        //const double offset = dacBuilder.getOutput(is6581 ? OFFSET_6581 : OFFSET_8580);
-        const double offset = dacBuilder.getOutput(is6581 ? OFFSET_6581 : 0x7ff, is6581);
+        const double offset = dacBuilder.getOutput(is6581 ? offset_6581 : 0x800, is6581);
 
         for (unsigned int i = 0; i < (1 << OSC_DAC_BITS); i++)
         {
@@ -616,7 +616,6 @@ void SID::setPaddle(uint8_t x, uint8_t y)
     paddleY = y;
 }
 
-
 void SID::setDacLeakage(double level)
 {
 #ifdef HAVE_CXX17
@@ -627,4 +626,11 @@ void SID::setDacLeakage(double level)
     setChipModel(model);
 }
 
+void SID::setOffset6581(double offset)
+{
+    // TODO determine a reasonable range
+    offset_6581 = 0x380 + static_cast<unsigned int>((1. - offset) * 0x200);
+    setChipModel(model);
+}
+
 } // namespace reSIDfp

src/SID.h

@@ -98,6 +98,8 @@ class SID
     /// Time until #voiceSync must be run.
     unsigned int nextVoiceSync;
 
+    unsigned int offset_6581;
+
     /// Currently active chip model.
     ChipModel model;
 
@@ -366,6 +368,11 @@ class SID
      * Set the DAC leakage level.
      */
     void setDacLeakage(double level);
+
+    /*
+     * Set the 6581 wave offset.
+     */
+    void setOffset6581(double offset);
 };
 
 } // namespace reSIDfp

src/State.cpp

@@ -88,6 +88,7 @@ int State::saveState(SID &s, char* buffer, int size)
     state.bus_value = s.busValue;
     state.bus_value_ttl = s.busValueTtl;
     state.nextVoiceSync = s.nextVoiceSync;
+    state.offset_6581 = s.offset_6581;
     state.paddle_x = s.paddleX;
     state.paddle_y = s.paddleY;
     state.model = s.model;
@@ -199,6 +200,7 @@ void State::restoreState(SID &s, char* buffer, int size)
     s.busValue = state.bus_value;
     s.busValueTtl = state.bus_value_ttl;
     s.nextVoiceSync = state.nextVoiceSync;
+    s.offset_6581 = state.offset_6581;
     s.paddleX = state.paddle_x;
     s.paddleY = state.paddle_y;
     s.model = state.model;

src/State.h

@@ -63,6 +63,7 @@ struct State
     // SID
     int bus_value_ttl;
     unsigned int nextVoiceSync;
+    unsigned int offset_6581;
     ChipModel model;
     CombinedWaveforms cws;
     double dacLeakage;

src/residfp/residfp.cpp

@@ -155,6 +155,11 @@ void residfp::enableOld6581caps(bool enable)
     sid.enableOld6581caps(enable);
 }
 
+void residfp::setOffset6581(double offset)
+{
+    sid.setOffset6581(offset);
+}
+
 void residfp::setPaddle(unsigned char x, unsigned char y)
 {
     sid.setPaddle(x, y);

src/residfp/residfp.h

@@ -290,6 +290,16 @@ class RESIDFP_EXTERN residfp
      * @since 1.2
      */
     void setDacLeakage(double level);
+
+    /**
+     * Set the 6581 wave offset.
+     * Affects the volume of digi samples.
+     *
+     * @param offset the waveform offset, between 0 (faint digis) and 1 (loud digis)
+     *
+     * @since 1.2
+     */
+    void setOffset6581(double offset);
 };
 
 }