Core\APU: emulate PSG DAC enable/disable (fixes #64).

source/emulator/core/hw/apu/channel/channel_noise.cpp

@@ -24,6 +24,8 @@ void NoiseChannel::Reset() {
   frequency_ratio = 0;
   width = 0;
   length_enable = false;
+  dac_enable = false;
+  enabled = false;
 
   lfsr = 0;
   sample = 0;
@@ -34,6 +36,9 @@ void NoiseChannel::Reset() {
 
 void NoiseChannel::Generate(int cycles_late) {
   if (length_enable && sequencer.length <= 0) {
+    // TODO: enabled should be unset immediately when length becomes zero.
+    // Updating it here is too late.
+    enabled = false;
     sample = 0;
     scheduler.Add(GetSynthesisInterval(7, 15) - cycles_late, event_cb);
     return;
@@ -53,6 +58,8 @@ void NoiseChannel::Generate(int cycles_late) {
 
   sample *= sequencer.envelope.current_volume;
 
+  if (!dac_enable) sample = 0;
+
   /* Skip samples that will never be sampled by the audio mixer. */
   for (int i = 0; i < skip_count; i++) {
     carry = lfsr & 1;
@@ -122,6 +129,10 @@ void NoiseChannel::Write(int offset, std::uint8_t value) {
       envelope.divider = value & 7;
       envelope.direction = Envelope::Direction((value >> 3) & 1);
       envelope.initial_volume = value >> 4;
+      dac_enable = (value >> 3) != 0;
+      if (!dac_enable) {
+        enabled = false;
+      }
       break;
     }
 
@@ -136,9 +147,10 @@ void NoiseChannel::Write(int offset, std::uint8_t value) {
       length_enable = value & 0x40;
 
       if (value & 0x80) {
-        /* TODO: are these the correct initialization values? */
-        const std::uint16_t lfsr_init[] = { 0x4000, 0x0040 };
-
+        constexpr std::uint16_t lfsr_init[] = { 0x4000, 0x0040 };
+        if (dac_enable) {
+          enabled = true;
+        }
         sequencer.Restart();
         lfsr = lfsr_init[width];
       }

source/emulator/core/hw/apu/channel/channel_noise.hpp

@@ -20,6 +20,7 @@ class NoiseChannel {
   NoiseChannel(Scheduler& scheduler, BIAS& bias);
 
   void Reset();
+  bool IsEnabled() { return enabled; }
 
   void Generate(int cycles_late);
   auto Read (int offset) -> std::uint8_t;
@@ -53,6 +54,8 @@ class NoiseChannel {
   int  frequency_ratio;
   int  width;
   bool length_enable;
+  bool dac_enable;
+  bool enabled;
 
   BIAS& bias;
   int skip_count;

source/emulator/core/hw/apu/channel/channel_quad.cpp

@@ -22,11 +22,17 @@ void QuadChannel::Reset() {
   sample = 0;
   wave_duty = 0;
   length_enable = false;
+  dac_enable = false;
+  enabled = false;
+
   scheduler.Add(GetSynthesisIntervalFromFrequency(0), event_cb);
 }
 
 void QuadChannel::Generate(int cycles_late) {
   if ((length_enable && sequencer.length <= 0) || sequencer.sweep.channel_disabled) {
+    // TODO: enabled should be unset immediately when length becomes zero.
+    // Updating it here is too late.
+    enabled = false;
     sample = 0;
     scheduler.Add(GetSynthesisIntervalFromFrequency(0) - cycles_late, event_cb);
     return;
@@ -39,7 +45,11 @@ void QuadChannel::Generate(int cycles_late) {
     { +8, +8, +8, +8, +8, +8, -8, -8 }
   };
 
-  sample = std::int8_t(pattern[wave_duty][phase] * sequencer.envelope.current_volume);
+  if (dac_enable) {
+    sample = std::int8_t(pattern[wave_duty][phase] * sequencer.envelope.current_volume);
+  } else {
+    sample = 0;
+  }
   phase = (phase + 1) % 8;
 
   scheduler.Add(GetSynthesisIntervalFromFrequency(sequencer.sweep.current_freq) - cycles_late, event_cb);
@@ -102,6 +112,10 @@ void QuadChannel::Write(int offset, std::uint8_t value) {
       envelope.divider = value & 7;
       envelope.direction = Envelope::Direction((value >> 3) & 1);
       envelope.initial_volume = value >> 4;
+      dac_enable = (value >> 3) != 0;
+      if (!dac_enable) {
+        enabled = false;
+      }
       break;
     }
 
@@ -117,6 +131,9 @@ void QuadChannel::Write(int offset, std::uint8_t value) {
       length_enable = value & 0x40;
 
       if (value & 0x80) {
+        if (dac_enable) {
+          enabled = true;
+        }
         phase = 0;
         sequencer.Restart();
       }

source/emulator/core/hw/apu/channel/channel_quad.hpp

@@ -19,6 +19,7 @@ class QuadChannel {
   QuadChannel(Scheduler& scheduler);
 
   void Reset();
+  bool IsEnabled() { return enabled; }
 
   void Generate(int cycles_late);
   auto Read (int offset) -> std::uint8_t;
@@ -37,12 +38,15 @@ class QuadChannel {
   }
 
   Scheduler& scheduler;
-  int phase;
-  int wave_duty;
-  bool length_enable;
   std::function<void(int)> event_cb = [this](int cycles_late) {
     this->Generate(cycles_late);
   };
+
+  int phase;
+  int wave_duty;
+  bool length_enable;
+  bool dac_enable;
+  bool enabled;
 };
 
 } // namespace nba::core

source/emulator/core/hw/apu/channel/channel_wave.hpp

@@ -19,6 +19,7 @@ class WaveChannel {
   WaveChannel(Scheduler& scheduler);
 
   void Reset();
+  bool IsEnabled() { return enabled; }
 
   void Generate(int cycles_late);
   auto Read (int offset) -> std::uint8_t;
@@ -42,12 +43,11 @@ class WaveChannel {
     return 8 * (2048 - frequency);
   }
 
+  Scheduler& scheduler;
   std::function<void(int)> event_cb = [this](int cycles_late) {
     this->Generate(cycles_late);
   };
 
-  Scheduler& scheduler;
-
   bool enabled;
   bool force_volume;
   int  volume;

source/emulator/core/hw/apu/registers.cpp

@@ -58,7 +58,7 @@ auto SoundControl::Read(int address) -> std::uint8_t {
              (dma[DMA_B].enable[SIDE_LEFT ] ? 32 : 0) |
              (dma[DMA_B].timer_id       ? 64 : 0);
     case 4:
-      /* FIXME: emulate bits 0-3 PSG ON/OFF state. */
+      // FIXME: emulate bits 0-3 PSG ON/OFF state.
       return 0b1111 | (master_enable ? 128 : 0);
 
     default: return 0;
@@ -99,6 +99,7 @@ void SoundControl::Write(int address, std::uint8_t value) {
 
       break;
     case 4:
+      // TODO: reset PSG registers to zero on disable.
       master_enable = value & 128;
       break;
   }