From 41e0605f17a784e8f125b3ad10ddfe5ef63337d9 Mon Sep 17 00:00:00 2001
From: jacqueline <me@jacqueline.id.au>
Date: Mon, 8 Jul 2024 15:06:43 +1000
Subject: Give PcmBuffer pairs a name, and wire them up in the audio stack

---
 src/drivers/include/drivers/bluetooth.hpp  |  6 +++---
 src/drivers/include/drivers/i2s_dac.hpp    |  8 ++++----
 src/drivers/include/drivers/pcm_buffer.hpp | 12 ++++++++++++
 3 files changed, 19 insertions(+), 7 deletions(-)

(limited to 'src/drivers/include')

diff --git a/src/drivers/include/drivers/bluetooth.hpp b/src/drivers/include/drivers/bluetooth.hpp
index b3b12ffc..eaecfb2b 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 SetSources(PcmBuffer*, PcmBuffer*) -> void;
+  auto SetSources(OutputBuffers*) -> void;
   auto SetVolumeFactor(float) -> void;
 
   auto SetEventHandler(std::function<void(bluetooth::Event)> cb) -> void;
@@ -118,8 +118,8 @@ class BluetoothState : public tinyfsm::Fsm<BluetoothState> {
   static auto discovery() -> bool;
   static auto discovery(bool) -> void;
 
-  static auto sources() -> std::pair<PcmBuffer*, PcmBuffer*>;
-  static auto sources(PcmBuffer*, PcmBuffer*) -> void;
+  static auto sources() -> OutputBuffers*;
+  static auto sources(OutputBuffers*) -> void;
 
   static auto event_handler(std::function<void(Event)>) -> void;
 
diff --git a/src/drivers/include/drivers/i2s_dac.hpp b/src/drivers/include/drivers/i2s_dac.hpp
index 0fe462b4..891acb56 100644
--- a/src/drivers/include/drivers/i2s_dac.hpp
+++ b/src/drivers/include/drivers/i2s_dac.hpp
@@ -40,9 +40,10 @@ constexpr size_t kI2SBufferLengthFrames = 1024;
  */
 class I2SDac {
  public:
-  static auto create(IGpios& expander, PcmBuffer&, PcmBuffer&) -> std::optional<I2SDac*>;
+  static auto create(IGpios& expander, OutputBuffers&)
+      -> std::optional<I2SDac*>;
 
-  I2SDac(IGpios& gpio, PcmBuffer&, i2s_chan_handle_t i2s_handle);
+  I2SDac(IGpios& gpio, OutputBuffers&, i2s_chan_handle_t i2s_handle);
   ~I2SDac();
 
   auto SetPaused(bool) -> void;
@@ -77,8 +78,7 @@ class I2SDac {
   auto set_channel(bool) -> void;
 
   IGpios& gpio_;
-  PcmBuffer& buffer1_;
-  PcmBuffer& buffer2_;
+  OutputBuffers& buffers_;
   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 27e9eec6..968c3398 100644
--- a/src/drivers/include/drivers/pcm_buffer.hpp
+++ b/src/drivers/include/drivers/pcm_buffer.hpp
@@ -74,4 +74,16 @@ class PcmBuffer {
   RingbufHandle_t ringbuf_;
 };
 
+/*
+ * Convenience type for a pair of PcmBuffers. Each audio output handles mixing
+ * streams together to ensure that low-latency sounds in one channel (e.g. a
+ * system notification bleep) aren't delayed by a large audio buffer in the
+ * other channel (e.g. a long-running track).
+ *
+ * By convention, the first buffer of this pair is used for tracks, whilst the
+ * second is reserved for 'system sounds'; usually TTS, but potentially maybe
+ * other informative noises.
+ */
+using OutputBuffers = std::pair<PcmBuffer, PcmBuffer>;
+
 }  // namespace drivers
-- 
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