3 files changed, 16 insertions, 11 deletions

diff --git a/src/drivers/include/drivers/bluetooth.hpp b/src/drivers/include/drivers/bluetooth.hpp
index 94a85263..b3b12ffc 100644
--- a/src/drivers/include/drivers/bluetooth.hpp
+++ b/src/drivers/include/drivers/bluetooth.hpp
@@ -43,7 +43,7 @@ class Bluetooth {
   auto SetPreferredDevice(std::optional<bluetooth::MacAndName> dev) -> void;
   auto PreferredDevice() -> std::optional<bluetooth::MacAndName>;
 
-  auto SetSource(PcmBuffer*) -> void;
+  auto SetSources(PcmBuffer*, PcmBuffer*) -> void;
   auto SetVolumeFactor(float) -> void;
 
   auto SetEventHandler(std::function<void(bluetooth::Event)> cb) -> void;
@@ -57,7 +57,7 @@ struct Disable : public tinyfsm::Event {};
 
 struct ConnectTimedOut : public tinyfsm::Event {};
 struct PreferredDeviceChanged : public tinyfsm::Event {};
-struct SourceChanged : public tinyfsm::Event {};
+struct SourcesChanged : public tinyfsm::Event {};
 struct DeviceDiscovered : public tinyfsm::Event {
   const Device& device;
 };
@@ -118,8 +118,8 @@ class BluetoothState : public tinyfsm::Fsm<BluetoothState> {
   static auto discovery() -> bool;
   static auto discovery(bool) -> void;
 
-  static auto source() -> PcmBuffer*;
-  static auto source(PcmBuffer*) -> void;
+  static auto sources() -> std::pair<PcmBuffer*, PcmBuffer*>;
+  static auto sources(PcmBuffer*, PcmBuffer*) -> void;
 
   static auto event_handler(std::function<void(Event)>) -> void;
 
@@ -132,7 +132,7 @@ class BluetoothState : public tinyfsm::Fsm<BluetoothState> {
   virtual void react(const events::Disable& ev) = 0;
   virtual void react(const events::ConnectTimedOut& ev){};
   virtual void react(const events::PreferredDeviceChanged& ev){};
-  virtual void react(const events::SourceChanged& ev){};
+  virtual void react(const events::SourcesChanged& ev){};
 
   virtual void react(const events::DeviceDiscovered&);
 
@@ -152,7 +152,6 @@ class BluetoothState : public tinyfsm::Fsm<BluetoothState> {
   static std::optional<bluetooth::MacAndName> sConnectingDevice_;
   static int sConnectAttemptsRemaining_;
 
-  static std::atomic<PcmBuffer*> sSource_;
   static std::function<void(Event)> sEventHandler_;
 
   auto connect(const bluetooth::MacAndName&) -> bool;
@@ -205,7 +204,7 @@ class Connected : public BluetoothState {
   void exit() override;
 
   void react(const events::PreferredDeviceChanged& ev) override;
-  void react(const events::SourceChanged& ev) override;
+  void react(const events::SourcesChanged& ev) override;
 
   void react(const events::Disable& ev) override;
   void react(events::internal::Gap ev) override;
diff --git a/src/drivers/include/drivers/i2s_dac.hpp b/src/drivers/include/drivers/i2s_dac.hpp
index cf9258c0..0fe462b4 100644
--- a/src/drivers/include/drivers/i2s_dac.hpp
+++ b/src/drivers/include/drivers/i2s_dac.hpp
@@ -40,7 +40,7 @@ constexpr size_t kI2SBufferLengthFrames = 1024;
  */
 class I2SDac {
  public:
-  static auto create(IGpios& expander, PcmBuffer&) -> std::optional<I2SDac*>;
+  static auto create(IGpios& expander, PcmBuffer&, PcmBuffer&) -> std::optional<I2SDac*>;
 
   I2SDac(IGpios& gpio, PcmBuffer&, i2s_chan_handle_t i2s_handle);
   ~I2SDac();
@@ -77,7 +77,8 @@ class I2SDac {
   auto set_channel(bool) -> void;
 
   IGpios& gpio_;
-  PcmBuffer& buffer_;
+  PcmBuffer& buffer1_;
+  PcmBuffer& buffer2_;
   i2s_chan_handle_t i2s_handle_;
 
   bool i2s_active_;
diff --git a/src/drivers/include/drivers/pcm_buffer.hpp b/src/drivers/include/drivers/pcm_buffer.hpp
index 6630f720..27e9eec6 100644
--- a/src/drivers/include/drivers/pcm_buffer.hpp
+++ b/src/drivers/include/drivers/pcm_buffer.hpp
@@ -35,8 +35,13 @@ class PcmBuffer {
    * Fills the given span with samples. If enough samples are available in
    * the buffer, then the span will be filled with samples from the buffer. Any
    * shortfall is made up by padding the given span with zeroes.
+   *
+   * If `mix` is set to true then, instead of overwriting the destination span,
+   * the retrieved samples will be mixed into any existing samples contained
+   * within the destination. This mixing uses a naive sum approach, and so may
+   * introduce clipping.
    */
-  auto receive(std::span<int16_t>, bool isr) -> BaseType_t;
+  auto receive(std::span<int16_t>, bool mix, bool isr) -> BaseType_t;
 
   auto clear() -> void;
   auto isEmpty() -> bool;
@@ -58,7 +63,7 @@ class PcmBuffer {
   PcmBuffer& operator=(const PcmBuffer&) = delete;
 
  private:
-  auto readSingle(std::span<int16_t>, bool isr)
+  auto readSingle(std::span<int16_t>, bool mix, bool isr)
       -> std::pair<size_t, BaseType_t>;
 
   StaticRingbuffer_t meta_;