Decouple play/pause from output on/off

I think this was the cause of toggling play/pause making audio go away.
Or at least I can't repro that bug anymore, anyway.

src/audio/audio_fsm.cpp

@@ -81,6 +81,7 @@ void AudioState::react(const OutputModeChanged& ev) {
   // TODO: handle SetInUse
   ESP_LOGI(kTag, "output mode changed");
   auto new_mode = sServices->nvs().OutputMode();
+  sOutput->SetMode(IAudioOutput::Modes::kOff);
   switch (new_mode) {
     case drivers::NvsStorage::Output::kBluetooth:
       sOutput = sBtOutput;
@@ -89,6 +90,7 @@ void AudioState::react(const OutputModeChanged& ev) {
       sOutput = sI2SOutput;
       break;
   }
+  sOutput->SetMode(IAudioOutput::Modes::kOnPaused);
 }
 
 namespace states {
@@ -125,6 +127,7 @@ void Uninitialised::react(const system_fsm::BootComplete& ev) {
   } else {
     sOutput = sBtOutput;
   }
+  sOutput->SetMode(IAudioOutput::Modes::kOnPaused);
 
   sSampleConverter.reset(new SampleConverter());
   sSampleConverter->SetOutput(sOutput);
@@ -170,7 +173,7 @@ void Standby::react(const TogglePlayPause& ev) {
 
 void Playback::entry() {
   ESP_LOGI(kTag, "beginning playback");
-  sOutput->SetInUse(true);
+  sOutput->SetMode(IAudioOutput::Modes::kOnPlaying);
 
   events::System().Dispatch(PlaybackStarted{});
   events::Ui().Dispatch(PlaybackStarted{});
@@ -181,7 +184,7 @@ void Playback::exit() {
   // TODO(jacqueline): Second case where it's useful to wait for the i2s buffer
   // to drain.
   vTaskDelay(pdMS_TO_TICKS(10));
-  sOutput->SetInUse(false);
+  sOutput->SetMode(IAudioOutput::Modes::kOnPaused);
 
   events::System().Dispatch(PlaybackFinished{});
   events::Ui().Dispatch(PlaybackFinished{});

src/audio/bt_audio_output.cpp

@@ -33,8 +33,8 @@ BluetoothAudioOutput::BluetoothAudioOutput(StreamBufferHandle_t s,
 
 BluetoothAudioOutput::~BluetoothAudioOutput() {}
 
-auto BluetoothAudioOutput::SetInUse(bool in_use) -> void {
-  if (in_use) {
+auto BluetoothAudioOutput::SetMode(Modes mode) -> void {
+  if (mode == Modes::kOnPlaying) {
     bluetooth_.SetSource(stream());
   } else {
     bluetooth_.SetSource(nullptr);

src/audio/i2s_audio_output.cpp

@@ -48,6 +48,7 @@ I2SAudioOutput::I2SAudioOutput(StreamBufferHandle_t s,
     : IAudioOutput(s),
       expander_(expander),
       dac_(std::move(dac)),
+      current_mode_(Modes::kOff),
       current_config_(),
       left_difference_(0),
       current_volume_(0),
@@ -60,12 +61,18 @@ I2SAudioOutput::~I2SAudioOutput() {
   dac_->SetSource(nullptr);
 }
 
-auto I2SAudioOutput::SetInUse(bool in_use) -> void {
-  if (in_use) {
-    dac_->Start();
-  } else {
-    dac_->Stop();
+auto I2SAudioOutput::SetMode(Modes mode) -> void {
+  if (mode == current_mode_) {
+    return;
   }
+  if (mode == Modes::kOff) {
+    dac_->Stop();
+    return;
+  } else if (current_mode_ == Modes::kOff) {
+    dac_->Start();
+  }
+  current_mode_ = mode;
+  dac_->SetPaused(mode == Modes::kOnPaused);
 }
 
 auto I2SAudioOutput::SetVolumeImbalance(int_fast8_t balance) -> void {

src/audio/include/audio_sink.hpp

@@ -31,11 +31,17 @@ class IAudioOutput {
 
   virtual ~IAudioOutput() {}
 
+  enum class Modes {
+    kOff,
+    kOnPaused,
+    kOnPlaying,
+  };
+
   /*
    * Indicates whether this output is currently being sent samples. If this is
    * false, the output should place itself into a low power state.
    */
-  virtual auto SetInUse(bool) -> void = 0;
+  virtual auto SetMode(Modes) -> void = 0;
 
   virtual auto SetVolumeImbalance(int_fast8_t balance) -> void = 0;
   virtual auto SetVolume(uint_fast8_t percent) -> void = 0;

src/audio/include/bt_audio_output.hpp

@@ -24,7 +24,7 @@ class BluetoothAudioOutput : public IAudioOutput {
   BluetoothAudioOutput(StreamBufferHandle_t, drivers::Bluetooth& bt);
   ~BluetoothAudioOutput();
 
-  auto SetInUse(bool) -> void override;
+  auto SetMode(Modes) -> void override;
 
   auto SetVolumeImbalance(int_fast8_t balance) -> void override;
   auto SetVolume(uint_fast8_t percent) -> void override;

src/audio/include/i2s_audio_output.hpp

@@ -25,7 +25,7 @@ class I2SAudioOutput : public IAudioOutput {
                  std::unique_ptr<drivers::I2SDac> dac);
   ~I2SAudioOutput();
 
-  auto SetInUse(bool) -> void override;
+  auto SetMode(Modes) -> void override;
 
   auto SetMaxVolume(uint16_t) -> void;
   auto SetVolumeDb(uint16_t) -> void;
@@ -46,6 +46,7 @@ class I2SAudioOutput : public IAudioOutput {
   drivers::IGpios& expander_;
   std::unique_ptr<drivers::I2SDac> dac_;
 
+  Modes current_mode_;
   std::optional<Format> current_config_;
   int_fast8_t left_difference_;
   uint16_t current_volume_;

src/drivers/i2s_dac.cpp

@@ -111,38 +111,23 @@ I2SDac::~I2SDac() {
 
 auto I2SDac::Start() -> void {
   std::lock_guard<std::mutex> lock(configure_mutex_);
-
-  gpio_.WriteSync(IGpios::Pin::kAmplifierUnmute, false);
-
-  // Ensure the DAC powers up to a muted state.
-  wm8523::WriteRegister(wm8523::Register::kPsCtrl, 0b10);
-
-  // Enable MCLK; this has the side effect of triggering the DAC's startup
-  // sequence.
-  i2s_channel_enable(i2s_handle_);
-  i2s_active_ = true;
-
   wm8523::WriteRegister(wm8523::Register::kPsCtrl, 0b11);
-  gpio_.WriteSync(IGpios::Pin::kAmplifierUnmute, true);
 }
 
 auto I2SDac::Stop() -> void {
   std::lock_guard<std::mutex> lock(configure_mutex_);
-
-  // Mute the DAC.
-  wm8523::WriteRegister(wm8523::Register::kPsCtrl, 0b10);
-  vTaskDelay(pdMS_TO_TICKS(5));
-  // Silence the output.
-  gpio_.WriteSync(IGpios::Pin::kAmplifierUnmute, false);
-
-  vTaskDelay(pdMS_TO_TICKS(5));
-
-  // Turn everything off.
+  set_channel(false);
   wm8523::WriteRegister(wm8523::Register::kPsCtrl, 0b0);
-  i2s_channel_disable(i2s_handle_);
-  i2s_active_ = false;
+}
 
-  gpio_.WriteSync(IGpios::Pin::kAmplifierEnable, false);
+auto I2SDac::SetPaused(bool paused) -> void {
+  if (paused) {
+    gpio_.WriteSync(IGpios::Pin::kAmplifierUnmute, false);
+    set_channel(false);
+  } else {
+    set_channel(true);
+    gpio_.WriteSync(IGpios::Pin::kAmplifierUnmute, true);
+  }
 }
 
 auto I2SDac::Reconfigure(Channels ch, BitsPerSample bps, SampleRate rate)
@@ -261,4 +246,16 @@ auto I2SDac::SetSource(StreamBufferHandle_t buffer) -> void {
   }
 }
 
+auto I2SDac::set_channel(bool enabled) -> void {
+  if (i2s_active_ == enabled) {
+    return;
+  }
+  i2s_active_ = enabled;
+  if (enabled) {
+    i2s_channel_enable(i2s_handle_);
+  } else {
+    i2s_channel_disable(i2s_handle_);
+  }
+}
+
 }  // namespace drivers

src/drivers/include/i2s_dac.hpp

@@ -46,6 +46,7 @@ class I2SDac {
 
   auto Start() -> void;
   auto Stop() -> void;
+  auto SetPaused(bool) -> void;
 
   enum Channels {
     CHANNELS_MONO,
@@ -75,6 +76,8 @@ class I2SDac {
   I2SDac& operator=(const I2SDac&) = delete;
 
  private:
+  auto set_channel(bool) -> void;
+
   IGpios& gpio_;
   i2s_chan_handle_t i2s_handle_;
   bool i2s_active_;