Free the i2s dma channel when it's not in use

It turns out this is why bluetooth playback keeps running out of memory
/facepalm

src/audio/audio_fsm.cpp

@@ -98,13 +98,6 @@ namespace states {
 void Uninitialised::react(const system_fsm::BootComplete& ev) {
   sServices = ev.services;
 
-  auto dac = drivers::I2SDac::create(sServices->gpios());
-  if (!dac) {
-    events::System().Dispatch(system_fsm::FatalError{});
-    events::Ui().Dispatch(system_fsm::FatalError{});
-    return;
-  }
-
   constexpr size_t kDrainBufferSize =
       drivers::kI2SBufferLengthFrames * sizeof(sample::Sample) * 2 * 8;
   ESP_LOGI(kTag, "allocating drain buffer, size %u KiB",
@@ -113,8 +106,7 @@ void Uninitialised::react(const system_fsm::BootComplete& ev) {
       kDrainBufferSize, sizeof(sample::Sample) * 2, MALLOC_CAP_DMA);
 
   sFileSource.reset(new FatfsAudioInput(sServices->tag_parser()));
-  sI2SOutput.reset(new I2SAudioOutput(stream, sServices->gpios(),
+  sI2SOutput.reset(new I2SAudioOutput(stream, sServices->gpios()));
-                                      std::unique_ptr<drivers::I2SDac>{*dac}));
   sBtOutput.reset(new BluetoothAudioOutput(stream, sServices->bluetooth()));
 
   auto& nvs = sServices->nvs();

src/audio/i2s_audio_output.cpp

@@ -43,18 +43,15 @@ static constexpr uint16_t kDefaultVolume = 0x100;
 static constexpr size_t kDrainBufferSize = 8 * 1024;
 
 I2SAudioOutput::I2SAudioOutput(StreamBufferHandle_t s,
-                               drivers::IGpios& expander,
+                               drivers::IGpios& expander)
-                               std::unique_ptr<drivers::I2SDac> dac)
     : IAudioOutput(s),
       expander_(expander),
-      dac_(std::move(dac)),
+      dac_(),
       current_mode_(Modes::kOff),
       current_config_(),
       left_difference_(0),
       current_volume_(0),
-      max_volume_(0) {
+      max_volume_(0) {}
-  dac_->SetSource(stream());
-}
 
 I2SAudioOutput::~I2SAudioOutput() {
   dac_->Stop();
@@ -67,8 +64,15 @@ auto I2SAudioOutput::SetMode(Modes mode) -> void {
   }
   if (mode == Modes::kOff) {
     dac_->Stop();
+    dac_.reset();
     return;
   } else if (current_mode_ == Modes::kOff) {
+    auto instance = drivers::I2SDac::create(expander_);
+    if (!instance) {
+      return;
+    }
+    dac_.reset(*instance);
+    dac_->SetSource(stream());
     dac_->Start();
   }
   current_mode_ = mode;

src/audio/include/i2s_audio_output.hpp

@@ -21,8 +21,7 @@ namespace audio {
 class I2SAudioOutput : public IAudioOutput {
  public:
   I2SAudioOutput(StreamBufferHandle_t,
-                 drivers::IGpios& expander,
+                 drivers::IGpios& expander);
-                 std::unique_ptr<drivers::I2SDac> dac);
   ~I2SAudioOutput();
 
   auto SetMode(Modes) -> void override;

src/drivers/i2s_dac.cpp

@@ -91,15 +91,12 @@ I2SDac::I2SDac(IGpios& gpio, i2s_chan_handle_t i2s_handle)
                                                        I2S_SLOT_MODE_STEREO)) {
   clock_config_.clk_src = I2S_CLK_SRC_APLL;
 
-  // Keep the 5V circuity off until it's needed.
+  gpio_.WriteSync(IGpios::Pin::kAmplifierEnable, true);
-  gpio_.WriteSync(IGpios::Pin::kAmplifierEnable, false);
 
   // Reset all registers back to their default values.
   wm8523::WriteRegister(wm8523::Register::kReset, 1);
   vTaskDelay(pdMS_TO_TICKS(10));
   wm8523::WriteRegister(wm8523::Register::kPsCtrl, 0b0);
-
-  gpio_.WriteSync(IGpios::Pin::kAmplifierEnable, true);
 }
 
 I2SDac::~I2SDac() {