Flesh out basic bluetooth support

No ui yet, and performance isn't great. It kinda works though!!

15 files changed, 534 insertions, 31 deletions

diff --git a/src/app_console/app_console.cpp b/src/app_console/app_console.cpp
index 30b7d2dc..7804fd34 100644
--- a/src/app_console/app_console.cpp
+++ b/src/app_console/app_console.cpp
@@ -37,6 +37,7 @@ namespace console {
 
 std::weak_ptr<database::Database> AppConsole::sDatabase;
 audio::TrackQueue* AppConsole::sTrackQueue;
+drivers::Bluetooth* AppConsole::sBluetooth;
 
 int CmdListDir(int argc, char** argv) {
   auto lock = AppConsole::sDatabase.lock();
@@ -439,6 +440,47 @@ void RegisterTaskStates() {
   esp_console_cmd_register(&cmd);
 }
 
+int CmdBtList(int argc, char** argv) {
+  static const std::string usage = "usage: bt_list <index>";
+  if (argc > 2) {
+    std::cout << usage << std::endl;
+    return 1;
+  }
+
+  auto devices = AppConsole::sBluetooth->KnownDevices();
+  if (argc == 2) {
+    int index = std::atoi(argv[1]);
+    if (index < 0 || index >= devices.size()) {
+      std::cout << "index out of range" << std::endl;
+      return -1;
+    }
+    AppConsole::sBluetooth->SetPreferredDevice(devices[index].address);
+  } else {
+    std::cout << "mac\t\trssi\tname" << std::endl;
+    for (const auto& device : devices) {
+      for (size_t i = 0; i < device.address.size(); i++) {
+        std::cout << std::hex << std::setfill('0') << std::setw(2)
+                  << static_cast<int>(device.address[i]);
+      }
+      float perc =
+          (static_cast<double>(device.signal_strength) + 127.0) / 256.0 * 100;
+      std::cout << "\t" << std::fixed << std::setprecision(0) << perc << "%";
+      std::cout << "\t" << device.name << std::endl;
+    }
+  }
+
+  return 0;
+}
+
+void RegisterBtList() {
+  esp_console_cmd_t cmd{.command = "bt_list",
+                        .help = "lists and connects to bluetooth devices",
+                        .hint = NULL,
+                        .func = &CmdBtList,
+                        .argtable = NULL};
+  esp_console_cmd_register(&cmd);
+}
+
 auto AppConsole::RegisterExtraComponents() -> void {
   RegisterListDir();
   RegisterPlayFile();
@@ -452,6 +494,7 @@ auto AppConsole::RegisterExtraComponents() -> void {
   RegisterDbIndex();
   RegisterDbDump();
   RegisterTaskStates();
+  RegisterBtList();
 }
 
 }  // namespace console
diff --git a/src/app_console/include/app_console.hpp b/src/app_console/include/app_console.hpp
index 3cb62b21..667e452f 100644
--- a/src/app_console/include/app_console.hpp
+++ b/src/app_console/include/app_console.hpp
@@ -8,6 +8,7 @@
 
 #include <memory>
 
+#include "bluetooth.hpp"
 #include "console.hpp"
 #include "database.hpp"
 #include "track_queue.hpp"
@@ -18,6 +19,7 @@ class AppConsole : public Console {
  public:
   static std::weak_ptr<database::Database> sDatabase;
   static audio::TrackQueue* sTrackQueue;
+  static drivers::Bluetooth* sBluetooth;
 
  protected:
   virtual auto RegisterExtraComponents() -> void;
diff --git a/src/audio/CMakeLists.txt b/src/audio/CMakeLists.txt
index 2d332a1e..a7dda8fd 100644
--- a/src/audio/CMakeLists.txt
+++ b/src/audio/CMakeLists.txt
@@ -6,7 +6,7 @@ idf_component_register(
   SRCS "audio_task.cpp" "chunk.cpp" "fatfs_audio_input.cpp"
   "stream_message.cpp" "i2s_audio_output.cpp" "stream_buffer.cpp" "track_queue.cpp"
   "stream_event.cpp" "stream_info.cpp" "audio_fsm.cpp" "sink_mixer.cpp" "resample.cpp"
-  "fatfs_source.cpp"
+  "fatfs_source.cpp" "bt_audio_output.cpp"
   INCLUDE_DIRS "include"
   REQUIRES "codecs" "drivers" "cbor" "result" "tasks" "span" "memory" "tinyfsm"
   "database" "system_fsm" "playlist" "speexdsp")
diff --git a/src/audio/audio_fsm.cpp b/src/audio/audio_fsm.cpp
index 617272b3..8791b9c4 100644
--- a/src/audio/audio_fsm.cpp
+++ b/src/audio/audio_fsm.cpp
@@ -11,6 +11,8 @@
 #include "audio_decoder.hpp"
 #include "audio_events.hpp"
 #include "audio_task.hpp"
+#include "bluetooth.hpp"
+#include "bt_audio_output.hpp"
 #include "esp_log.h"
 #include "event_queue.hpp"
 #include "fatfs_audio_input.hpp"
@@ -35,6 +37,7 @@ std::weak_ptr<database::Database> AudioState::sDatabase;
 std::unique_ptr<AudioTask> AudioState::sTask;
 std::unique_ptr<FatfsAudioInput> AudioState::sFileSource;
 std::unique_ptr<I2SAudioOutput> AudioState::sI2SOutput;
+std::unique_ptr<BluetoothAudioOutput> AudioState::sBtOutput;
 
 TrackQueue* AudioState::sTrackQueue;
 std::optional<database::TrackId> AudioState::sCurrentTrack;
@@ -42,6 +45,7 @@ std::optional<database::TrackId> AudioState::sCurrentTrack;
 auto AudioState::Init(drivers::IGpios* gpio_expander,
                       std::weak_ptr<database::Database> database,
                       std::shared_ptr<database::ITagParser> tag_parser,
+                      drivers::Bluetooth* bluetooth,
                       TrackQueue* queue) -> bool {
   sIGpios = gpio_expander;
   sTrackQueue = queue;
@@ -55,8 +59,10 @@ auto AudioState::Init(drivers::IGpios* gpio_expander,
 
   sFileSource.reset(new FatfsAudioInput(tag_parser));
   sI2SOutput.reset(new I2SAudioOutput(sIGpios, sDac));
+  // sBtOutput.reset(new BluetoothAudioOutput(bluetooth));
 
   AudioTask::Start(sFileSource.get(), sI2SOutput.get());
+  // AudioTask::Start(sFileSource.get(), sBtOutput.get());
 
   return true;
 }
@@ -125,6 +131,7 @@ void Standby::react(const QueueUpdate& ev) {
 void Playback::entry() {
   ESP_LOGI(kTag, "beginning playback");
   sI2SOutput->SetInUse(true);
+  // sBtOutput->SetInUse(true);
 }
 
 void Playback::exit() {
@@ -133,6 +140,7 @@ void Playback::exit() {
   // to drain.
   vTaskDelay(pdMS_TO_TICKS(250));
   sI2SOutput->SetInUse(false);
+  // sBtOutput->SetInUse(false);
 }
 
 void Playback::react(const QueueUpdate& ev) {
diff --git a/src/audio/bt_audio_output.cpp b/src/audio/bt_audio_output.cpp
new file mode 100644
index 00000000..71e40d02
--- /dev/null
+++ b/src/audio/bt_audio_output.cpp
@@ -0,0 +1,79 @@
+/*
+ * Copyright 2023 jacqueline <me@jacqueline.id.au>
+ *
+ * SPDX-License-Identifier: GPL-3.0-only
+ */
+
+#include "bt_audio_output.hpp"
+#include <stdint.h>
+#include <sys/_stdint.h>
+
+#include <algorithm>
+#include <cstddef>
+#include <cstdint>
+#include <memory>
+#include <variant>
+
+#include "esp_err.h"
+#include "esp_heap_caps.h"
+#include "freertos/portmacro.h"
+
+#include "audio_element.hpp"
+#include "freertos/projdefs.h"
+#include "gpios.hpp"
+#include "i2c.hpp"
+#include "i2s_dac.hpp"
+#include "result.hpp"
+#include "stream_info.hpp"
+#include "wm8523.hpp"
+
+static const char* kTag = "BTOUT";
+
+namespace audio {
+
+static constexpr size_t kDrainBufferSize = 48 * 1024;
+
+BluetoothAudioOutput::BluetoothAudioOutput(drivers::Bluetooth* bt)
+    : IAudioSink(kDrainBufferSize, MALLOC_CAP_SPIRAM), bluetooth_(bt) {}
+
+BluetoothAudioOutput::~BluetoothAudioOutput() {}
+
+auto BluetoothAudioOutput::SetInUse(bool in_use) -> void {
+  if (in_use) {
+    bluetooth_->SetSource(stream());
+  } else {
+    bluetooth_->SetSource(nullptr);
+  }
+}
+
+auto BluetoothAudioOutput::SetVolumeImbalance(int_fast8_t balance) -> void {}
+
+auto BluetoothAudioOutput::SetVolume(uint_fast8_t percent) -> void {}
+
+auto BluetoothAudioOutput::GetVolume() -> uint_fast8_t {
+  return 50;
+}
+
+auto BluetoothAudioOutput::AdjustVolumeUp() -> bool {
+  return false;
+}
+
+auto BluetoothAudioOutput::AdjustVolumeDown() -> bool {
+  return false;
+}
+
+auto BluetoothAudioOutput::PrepareFormat(const Format& orig) -> Format {
+  // ESP-IDF's current Bluetooth implementation currently handles SBC encoding,
+  // but requires a fixed input format.
+  return Format{
+      .sample_rate = 44100,
+      .num_channels = 2,
+      .bits_per_sample = 16,
+  };
+}
+
+auto BluetoothAudioOutput::Configure(const Format& fmt) -> void {
+  // No configuration necessary; the output format is fixed.
+}
+
+}  // namespace audio
diff --git a/src/audio/i2s_audio_output.cpp b/src/audio/i2s_audio_output.cpp
index b7fcf104..8b7d130f 100644
--- a/src/audio/i2s_audio_output.cpp
+++ b/src/audio/i2s_audio_output.cpp
@@ -14,7 +14,9 @@
 #include <memory>
 #include <variant>
 
+#include "audio_sink.hpp"
 #include "esp_err.h"
+#include "esp_heap_caps.h"
 #include "freertos/portmacro.h"
 
 #include "audio_element.hpp"
@@ -41,9 +43,12 @@ static constexpr uint16_t kMaxVolumeBeforeClipping = 0x185;
 static constexpr uint16_t kLineLevelVolume = 0x13d;
 static constexpr uint16_t kDefaultVolume = 0x128;
 
+static constexpr size_t kDrainBufferSize = 8 * 1024;
+
 I2SAudioOutput::I2SAudioOutput(drivers::IGpios* expander,
                                std::weak_ptr<drivers::I2SDac> dac)
-    : expander_(expander),
+    : IAudioSink(kDrainBufferSize, MALLOC_CAP_INTERNAL | MALLOC_CAP_8BIT),
+      expander_(expander),
       dac_(dac.lock()),
       current_config_(),
       left_difference_(0),
diff --git a/src/audio/include/audio_fsm.hpp b/src/audio/include/audio_fsm.hpp
index d10f31e1..5d44fcda 100644
--- a/src/audio/include/audio_fsm.hpp
+++ b/src/audio/include/audio_fsm.hpp
@@ -12,6 +12,7 @@
 
 #include "audio_events.hpp"
 #include "audio_task.hpp"
+#include "bt_audio_output.hpp"
 #include "database.hpp"
 #include "display.hpp"
 #include "fatfs_audio_input.hpp"
@@ -33,6 +34,7 @@ class AudioState : public tinyfsm::Fsm<AudioState> {
   static auto Init(drivers::IGpios* gpio_expander,
                    std::weak_ptr<database::Database>,
                    std::shared_ptr<database::ITagParser>,
+                   drivers::Bluetooth* bluetooth,
                    TrackQueue* queue) -> bool;
 
   virtual ~AudioState() {}
@@ -68,6 +70,7 @@ class AudioState : public tinyfsm::Fsm<AudioState> {
   static std::unique_ptr<AudioTask> sTask;
   static std::unique_ptr<FatfsAudioInput> sFileSource;
   static std::unique_ptr<I2SAudioOutput> sI2SOutput;
+  static std::unique_ptr<BluetoothAudioOutput> sBtOutput;
 
   static TrackQueue* sTrackQueue;
   static std::optional<database::TrackId> sCurrentTrack;
diff --git a/src/audio/include/audio_sink.hpp b/src/audio/include/audio_sink.hpp
index 2fb4bf63..b5d6ef57 100644
--- a/src/audio/include/audio_sink.hpp
+++ b/src/audio/include/audio_sink.hpp
@@ -18,15 +18,11 @@ namespace audio {
 
 class IAudioSink {
  private:
-  static const std::size_t kDrainBufferSize = 24 * 1024;
   StreamBufferHandle_t stream_;
 
  public:
-  IAudioSink()
-      : stream_(xStreamBufferCreateWithCaps(
-            kDrainBufferSize,
-            1,
-            MALLOC_CAP_INTERNAL | MALLOC_CAP_8BIT)) {}
+  IAudioSink(size_t buffer_size, uint32_t caps)
+      : stream_(xStreamBufferCreateWithCaps(buffer_size, 1, caps)) {}
 
   virtual ~IAudioSink() { vStreamBufferDeleteWithCaps(stream_); }
 
diff --git a/src/audio/include/bt_audio_output.hpp b/src/audio/include/bt_audio_output.hpp
new file mode 100644
index 00000000..e11a5d44
--- /dev/null
+++ b/src/audio/include/bt_audio_output.hpp
@@ -0,0 +1,49 @@
+/*
+ * Copyright 2023 jacqueline <me@jacqueline.id.au>
+ *
+ * SPDX-License-Identifier: GPL-3.0-only
+ */
+
+#pragma once
+
+#include <sys/_stdint.h>
+#include <cstdint>
+#include <memory>
+#include <vector>
+
+#include "audio_element.hpp"
+#include "audio_sink.hpp"
+#include "bluetooth.hpp"
+#include "chunk.hpp"
+#include "result.hpp"
+
+#include "gpios.hpp"
+#include "i2s_dac.hpp"
+#include "stream_info.hpp"
+
+namespace audio {
+
+class BluetoothAudioOutput : public IAudioSink {
+ public:
+  BluetoothAudioOutput(drivers::Bluetooth* bt);
+  ~BluetoothAudioOutput();
+
+  auto SetInUse(bool) -> void override;
+
+  auto SetVolumeImbalance(int_fast8_t balance) -> void override;
+  auto SetVolume(uint_fast8_t percent) -> void override;
+  auto GetVolume() -> uint_fast8_t override;
+  auto AdjustVolumeUp() -> bool override;
+  auto AdjustVolumeDown() -> bool override;
+
+  auto PrepareFormat(const Format&) -> Format override;
+  auto Configure(const Format& format) -> void override;
+
+  BluetoothAudioOutput(const BluetoothAudioOutput&) = delete;
+  BluetoothAudioOutput& operator=(const BluetoothAudioOutput&) = delete;
+
+ private:
+  drivers::Bluetooth* bluetooth_;
+};
+
+}  // namespace audio
diff --git a/src/drivers/bluetooth.cpp b/src/drivers/bluetooth.cpp
index f9ab4e95..79999b2c 100644
--- a/src/drivers/bluetooth.cpp
+++ b/src/drivers/bluetooth.cpp
@@ -2,25 +2,31 @@
 
 #include <stdint.h>
 
+#include <algorithm>
 #include <atomic>
+#include <mutex>
 #include <ostream>
 #include <sstream>
 
 #include "esp_a2dp_api.h"
 #include "esp_avrc_api.h"
 #include "esp_bt.h"
+#include "esp_bt_defs.h"
 #include "esp_bt_device.h"
 #include "esp_bt_main.h"
 #include "esp_gap_bt_api.h"
 #include "esp_log.h"
 #include "esp_mac.h"
+#include "esp_wifi.h"
+#include "esp_wifi_types.h"
+#include "freertos/portmacro.h"
 #include "tinyfsm/include/tinyfsm.hpp"
 
 namespace drivers {
 
 static constexpr char kTag[] = "bluetooth";
 
-static std::atomic<StreamBufferHandle_t> sStream;
+static StreamBufferHandle_t sStream = nullptr;
 
 auto gap_cb(esp_bt_gap_cb_event_t event, esp_bt_gap_cb_param_t* param) -> void {
   tinyfsm::FsmList<bluetooth::BluetoothState>::dispatch(
@@ -42,7 +48,7 @@ auto a2dp_data_cb(uint8_t* buf, int32_t buf_size) -> int32_t {
   if (buf == nullptr || buf_size <= 0) {
     return 0;
   }
-  StreamBufferHandle_t stream = sStream.load();
+  StreamBufferHandle_t stream = sStream;
   if (stream == nullptr) {
     return 0;
   }
@@ -65,6 +71,32 @@ auto Bluetooth::Disable() -> void {
       bluetooth::events::Disable{});
 }
 
+auto Bluetooth::KnownDevices() -> std::vector<bluetooth::Device> {
+  std::vector<bluetooth::Device> out = bluetooth::BluetoothState::devices();
+  std::sort(out.begin(), out.end(), [](const auto& a, const auto& b) -> bool {
+    return a.signal_strength < b.signal_strength;
+  });
+  return out;
+}
+
+auto Bluetooth::SetPreferredDevice(const bluetooth::mac_addr_t& mac) -> void {
+  if (mac == bluetooth::BluetoothState::preferred_device()) {
+    return;
+  }
+  bluetooth::BluetoothState::preferred_device(mac);
+  tinyfsm::FsmList<bluetooth::BluetoothState>::dispatch(
+      bluetooth::events::PreferredDeviceChanged{});
+}
+
+auto Bluetooth::SetSource(StreamBufferHandle_t src) -> void {
+  if (src == bluetooth::BluetoothState::source()) {
+    return;
+  }
+  bluetooth::BluetoothState::source(src);
+  tinyfsm::FsmList<bluetooth::BluetoothState>::dispatch(
+      bluetooth::events::SourceChanged{});
+}
+
 auto DeviceName() -> std::string {
   uint8_t mac[8]{0};
   esp_efuse_mac_get_default(mac);
@@ -75,6 +107,42 @@ auto DeviceName() -> std::string {
 
 namespace bluetooth {
 
+std::mutex BluetoothState::sDevicesMutex_;
+std::map<mac_addr_t, Device> BluetoothState::sDevices_;
+std::optional<mac_addr_t> BluetoothState::sPreferredDevice_;
+mac_addr_t BluetoothState::sCurrentDevice_;
+
+std::atomic<StreamBufferHandle_t> BluetoothState::sSource_;
+
+auto BluetoothState::devices() -> std::vector<Device> {
+  std::lock_guard lock{sDevicesMutex_};
+  std::vector<Device> out;
+  for (const auto& device : sDevices_) {
+    out.push_back(device.second);
+  }
+  return out;
+}
+
+auto BluetoothState::preferred_device() -> std::optional<mac_addr_t> {
+  std::lock_guard lock{sDevicesMutex_};
+  return sPreferredDevice_;
+}
+
+auto BluetoothState::preferred_device(const mac_addr_t& addr) -> void {
+  std::lock_guard lock{sDevicesMutex_};
+  sPreferredDevice_ = addr;
+}
+
+auto BluetoothState::source() -> StreamBufferHandle_t {
+  std::lock_guard lock{sDevicesMutex_};
+  return sSource_.load();
+}
+
+auto BluetoothState::source(StreamBufferHandle_t src) -> void {
+  std::lock_guard lock{sDevicesMutex_};
+  sSource_.store(src);
+}
+
 static bool sIsFirstEntry = true;
 
 void Disabled::entry() {
@@ -126,8 +194,8 @@ void Disabled::react(const events::Enable&) {
   esp_bt_gap_register_callback(gap_cb);
 
   // Initialise AVRCP. This handles playback controls; play/pause/volume/etc.
-  // esp_avrc_ct_init();
-  // esp_avrc_ct_register_callback(avrcp_cb);
+  esp_avrc_ct_init();
+  esp_avrc_ct_register_callback(avrcp_cb);
 
   // Initialise A2DP. This handles streaming audio. Currently ESP-IDF's SBC
   // encoder only supports 2 channels of interleaved 16 bit samples, at
@@ -156,8 +224,93 @@ void Scanning::exit() {
   esp_bt_gap_cancel_discovery();
 }
 
-auto OnDeviceDiscovered(esp_bt_gap_cb_param_t* param) -> void {
-  ESP_LOGI(kTag, "device discovered");
+void Scanning::react(const events::Disable& ev) {
+  transit<Disabled>();
+}
+
+auto Scanning::OnDeviceDiscovered(esp_bt_gap_cb_param_t* param) -> void {
+  Device device{};
+  std::copy(std::begin(param->disc_res.bda), std::end(param->disc_res.bda),
+            device.address.begin());
+
+  // Discovery results come back to us as a grab-bag of different key/value
+  // pairs. Parse these into a more structured format first so that they're
+  // easier to work with.
+  uint8_t* eir = nullptr;
+  for (size_t i = 0; i < param->disc_res.num_prop; i++) {
+    esp_bt_gap_dev_prop_t& property = param->disc_res.prop[i];
+    switch (property.type) {
+      case ESP_BT_GAP_DEV_PROP_BDNAME:
+        // Ignored -- we get the device name from the EIR field instead.
+        break;
+      case ESP_BT_GAP_DEV_PROP_COD:
+        device.class_of_device = *reinterpret_cast<uint32_t*>(property.val);
+        break;
+      case ESP_BT_GAP_DEV_PROP_RSSI:
+        device.signal_strength = *reinterpret_cast<int8_t*>(property.val);
+        break;
+      case ESP_BT_GAP_DEV_PROP_EIR:
+        eir = reinterpret_cast<uint8_t*>(property.val);
+        break;
+      default:
+        ESP_LOGW(kTag, "unknown GAP param %u", property.type);
+    }
+  }
+
+  // Ignore devices with missing or malformed data.
+  if (!esp_bt_gap_is_valid_cod(device.class_of_device) || eir == nullptr) {
+    return;
+  }
+
+  // Note: ESP-IDF example code does additional filterering by class of device
+  // at this point. We don't! Per the Bluetooth spec; "No assumptions should be
+  // made about specific functionality or characteristics of any application
+  // based solely on the assignment of the Major or Minor device class."
+
+  // Resolve the name of the device.
+  uint8_t* name;
+  uint8_t length;
+  name = esp_bt_gap_resolve_eir_data(eir, ESP_BT_EIR_TYPE_CMPL_LOCAL_NAME,
+                                     &length);
+  if (!name) {
+    name = esp_bt_gap_resolve_eir_data(eir, ESP_BT_EIR_TYPE_SHORT_LOCAL_NAME,
+                                       &length);
+  }
+
+  if (!name) {
+    return;
+  }
+
+  device.name =
+      std::string{reinterpret_cast<char*>(name), static_cast<size_t>(length)};
+
+  bool is_preferred = false;
+  {
+    std::lock_guard<std::mutex> lock{sDevicesMutex_};
+    sDevices_[device.address] = device;
+
+    if (device.address == sPreferredDevice_) {
+      sCurrentDevice_ = device.address;
+      is_preferred = true;
+    }
+  }
+
+  if (is_preferred) {
+    transit<Connecting>();
+  }
+}
+
+void Scanning::react(const events::PreferredDeviceChanged& ev) {
+  bool is_discovered = false;
+  {
+    std::lock_guard<std::mutex> lock{sDevicesMutex_};
+    if (sPreferredDevice_ && sDevices_.contains(sPreferredDevice_.value())) {
+      is_discovered = true;
+    }
+  }
+  if (is_discovered) {
+    transit<Connecting>();
+  }
 }
 
 void Scanning::react(const events::internal::Gap& ev) {
@@ -167,7 +320,6 @@ void Scanning::react(const events::internal::Gap& ev) {
       break;
     case ESP_BT_GAP_DISC_STATE_CHANGED_EVT:
       if (ev.param->disc_st_chg.state == ESP_BT_GAP_DISCOVERY_STOPPED) {
-        ESP_LOGI(kTag, "still scanning");
         esp_bt_gap_start_discovery(ESP_BT_INQ_MODE_GENERAL_INQUIRY,
                                    kDiscoveryTimeSeconds, kDiscoveryMaxResults);
       }
@@ -183,30 +335,63 @@ void Scanning::react(const events::internal::Gap& ev) {
 
 void Connecting::entry() {
   ESP_LOGI(kTag, "connecting to device");
-  esp_a2d_source_connect(nullptr);
+  esp_a2d_source_connect(sPreferredDevice_.value().data());
 }
 
 void Connecting::exit() {}
 
+void Connecting::react(const events::Disable& ev) {
+  // TODO: disconnect gracefully
+}
+
+void Connecting::react(const events::PreferredDeviceChanged& ev) {
+  // TODO. Cancel out and start again.
+}
+
 void Connecting::react(const events::internal::Gap& ev) {
   switch (ev.type) {
     case ESP_BT_GAP_AUTH_CMPL_EVT:
-      // todo: auth completed. check if we succeeded.
+      if (ev.param->auth_cmpl.stat != ESP_BT_STATUS_SUCCESS) {
+        ESP_LOGE(kTag, "auth failed");
+        sPreferredDevice_ = {};
+        transit<Scanning>();
+      }
+      break;
+    case ESP_BT_GAP_ACL_CONN_CMPL_STAT_EVT:
+      // ACL connection complete. We're now ready to send data to this
+      // device(?)
       break;
     case ESP_BT_GAP_PIN_REQ_EVT:
-      // todo: device needs a pin to connect.
+      ESP_LOGW(kTag, "device needs a pin to connect");
+      sPreferredDevice_ = {};
+      transit<Scanning>();
       break;
     case ESP_BT_GAP_CFM_REQ_EVT:
-      // todo: device needs user to click okay.
+      ESP_LOGW(kTag, "user needs to do cfm. idk man.");
+      sPreferredDevice_ = {};
+      transit<Scanning>();
       break;
     case ESP_BT_GAP_KEY_NOTIF_EVT:
-      // todo: device is telling us a password?
+      ESP_LOGW(kTag, "the device is telling us a password??");
+      sPreferredDevice_ = {};
+      transit<Scanning>();
       break;
     case ESP_BT_GAP_KEY_REQ_EVT:
-      // todo: device needs a password
+      ESP_LOGW(kTag, "the device wants a password!");
+      sPreferredDevice_ = {};
+      transit<Scanning>();
       break;
     case ESP_BT_GAP_MODE_CHG_EVT:
-      // todo: mode change. is this important?
+      ESP_LOGI(kTag, "GAP mode changed");
+      break;
+    case ESP_BT_GAP_DISC_STATE_CHANGED_EVT:
+      // Discovery state changed. Probably because we stopped scanning, but
+      // either way this isn't actionable or useful.
+      break;
+    case ESP_BT_GAP_DISC_RES_EVT:
+      // New device discovered. We could actually process this so that the
+      // device list remains fresh whilst we're connecting, but for now just
+      // ignore it.
       break;
     default:
       ESP_LOGW(kTag, "unhandled GAP event: %u", ev.type);
@@ -216,21 +401,78 @@ void Connecting::react(const events::internal::Gap& ev) {
 void Connecting::react(const events::internal::A2dp& ev) {
   switch (ev.type) {
     case ESP_A2D_CONNECTION_STATE_EVT:
-      // todo: connection state changed. we might be connected!
+      if (ev.param->conn_stat.state == ESP_A2D_CONNECTION_STATE_CONNECTED) {
+        ESP_LOGI(kTag, "connected okay!");
+        transit<Connected>();
+      }
+      break;
+    case ESP_A2D_REPORT_SNK_DELAY_VALUE_EVT:
+      // The sink is telling us how much of a delay to expect with playback.
+      // We don't care about this yet.
       break;
     default:
       ESP_LOGW(kTag, "unhandled A2DP event: %u", ev.type);
   }
 }
 
+void Connected::entry() {
+  ESP_LOGI(kTag, "entering connected state");
+  // TODO: if we already have a source, immediately start playing
+}
+
+void Connected::exit() {
+  ESP_LOGI(kTag, "exiting connected state");
+}
+
+void Connected::react(const events::Disable& ev) {
+  // TODO: disconnect gracefully
+}
+
+void Connected::react(const events::PreferredDeviceChanged& ev) {
+  // TODO: disconnect, move to connecting? or scanning?
+}
+
+void Connected::react(const events::SourceChanged& ev) {
+  sStream = sSource_;
+  if (sStream != nullptr) {
+    ESP_LOGI(kTag, "checking source is ready");
+    esp_a2d_media_ctrl(ESP_A2D_MEDIA_CTRL_CHECK_SRC_RDY);
+  } else {
+    esp_a2d_media_ctrl(ESP_A2D_MEDIA_CTRL_STOP);
+  }
+}
+
+void Connected::react(const events::internal::Gap& ev) {
+  switch (ev.type) {
+    case ESP_BT_GAP_MODE_CHG_EVT:
+      // todo: is this important?
+      ESP_LOGI(kTag, "GAP mode changed");
+      break;
+    default:
+      ESP_LOGW(kTag, "unhandled GAP event: %u", ev.type);
+  }
+}
+
 void Connected::react(const events::internal::A2dp& ev) {
   switch (ev.type) {
     case ESP_A2D_CONNECTION_STATE_EVT:
-      // todo: connection state changed. we might have dropped
+      if (ev.param->conn_stat.state != ESP_A2D_CONNECTION_STATE_CONNECTED &&
+          ev.param->conn_stat.state != ESP_A2D_CONNECTION_STATE_DISCONNECTING) {
+        ESP_LOGE(kTag, "a2dp connection dropped :(");
+        transit<Connecting>();
+      }
       break;
     case ESP_A2D_AUDIO_STATE_EVT:
       // todo: audio state changed. who knows, dude.
       break;
+    case ESP_A2D_MEDIA_CTRL_ACK_EVT:
+      // Sink is responding to our media control request.
+      if (ev.param->media_ctrl_stat.cmd == ESP_A2D_MEDIA_CTRL_CHECK_SRC_RDY) {
+        // TODO: check if success
+        ESP_LOGI(kTag, "starting playback");
+        esp_a2d_media_ctrl(ESP_A2D_MEDIA_CTRL_START);
+      }
+      break;
     default:
       ESP_LOGW(kTag, "unhandled A2DP event: %u", ev.type);
   }
@@ -239,7 +481,17 @@ void Connected::react(const events::internal::A2dp& ev) {
 void Connected::react(const events::internal::Avrc& ev) {
   switch (ev.type) {
     case ESP_AVRC_CT_CONNECTION_STATE_EVT:
-      // todo: avrc connected. send our capabilities.
+      if (ev.param->conn_stat.connected) {
+        // TODO: tell the target about our capabilities
+      }
+      // Don't worry about disconnect events; if there's a serious problem then
+      // the entire bluetooth connection will drop out, which is handled
+      // elsewhere.
+      break;
+    case ESP_AVRC_CT_REMOTE_FEATURES_EVT:
+      // The remote device is telling us about its capabilities! We don't
+      // currently care about any of them.
+      break;
     default:
       ESP_LOGW(kTag, "unhandled AVRC event: %u", ev.type);
   }
diff --git a/src/drivers/include/bluetooth.hpp b/src/drivers/include/bluetooth.hpp
index 2b5e6a8d..bdc45910 100644
--- a/src/drivers/include/bluetooth.hpp
+++ b/src/drivers/include/bluetooth.hpp
@@ -1,6 +1,11 @@
 
 #pragma once
 
+#include <array>
+#include <atomic>
+#include <map>
+#include <mutex>
+#include <optional>
 #include <string>
 #include <vector>
 
@@ -14,6 +19,18 @@
 
 namespace drivers {
 
+namespace bluetooth {
+
+typedef std::array<uint8_t, 6> mac_addr_t;
+
+struct Device {
+  mac_addr_t address;
+  std::string name;
+  uint32_t class_of_device;
+  int8_t signal_strength;
+};
+}  // namespace bluetooth
+
 /*
  * A handle used to interact with the bluetooth state machine.
  */
@@ -24,6 +41,9 @@ class Bluetooth {
   auto Enable() -> bool;
   auto Disable() -> void;
 
+  auto KnownDevices() -> std::vector<bluetooth::Device>;
+  auto SetPreferredDevice(const bluetooth::mac_addr_t& mac) -> void;
+
   auto SetSource(StreamBufferHandle_t) -> void;
 };
 
@@ -33,6 +53,9 @@ namespace events {
 struct Enable : public tinyfsm::Event {};
 struct Disable : public tinyfsm::Event {};
 
+struct PreferredDeviceChanged : public tinyfsm::Event {};
+struct SourceChanged : public tinyfsm::Event {};
+
 namespace internal {
 struct Gap : public tinyfsm::Event {
   esp_bt_gap_cb_event_t type;
@@ -51,6 +74,13 @@ struct Avrc : public tinyfsm::Event {
 
 class BluetoothState : public tinyfsm::Fsm<BluetoothState> {
  public:
+  static auto devices() -> std::vector<Device>;
+  static auto preferred_device() -> std::optional<mac_addr_t>;
+  static auto preferred_device(const mac_addr_t&) -> void;
+
+  static auto source() -> StreamBufferHandle_t;
+  static auto source(StreamBufferHandle_t) -> void;
+
   virtual ~BluetoothState(){};
 
   virtual void entry() {}
@@ -58,13 +88,24 @@ class BluetoothState : public tinyfsm::Fsm<BluetoothState> {
 
   virtual void react(const events::Enable& ev){};
   virtual void react(const events::Disable& ev) = 0;
+  virtual void react(const events::PreferredDeviceChanged& ev){};
+  virtual void react(const events::SourceChanged& ev){};
 
   virtual void react(const events::internal::Gap& ev) = 0;
-  virtual void react(const events::internal::A2dp& ev) = 0;
+  virtual void react(const events::internal::A2dp& ev){};
   virtual void react(const events::internal::Avrc& ev){};
+
+ protected:
+  static std::mutex sDevicesMutex_;
+  static std::map<mac_addr_t, Device> sDevices_;
+  static std::optional<mac_addr_t> sPreferredDevice_;
+  static mac_addr_t sCurrentDevice_;
+
+  static std::atomic<StreamBufferHandle_t> sSource_;
 };
 
 class Disabled : public BluetoothState {
+ public:
   void entry() override;
 
   void react(const events::Enable& ev) override;
@@ -72,35 +113,53 @@ class Disabled : public BluetoothState {
 
   void react(const events::internal::Gap& ev) override {}
   void react(const events::internal::A2dp& ev) override {}
+  using BluetoothState::react;
 };
 
 class Scanning : public BluetoothState {
+ public:
   void entry() override;
   void exit() override;
 
   void react(const events::Disable& ev) override;
+  void react(const events::PreferredDeviceChanged& ev) override;
 
   void react(const events::internal::Gap& ev) override;
-  void react(const events::internal::A2dp& ev) override;
+
+  using BluetoothState::react;
+
+ private:
+  auto OnDeviceDiscovered(esp_bt_gap_cb_param_t*) -> void;
 };
 
 class Connecting : public BluetoothState {
+ public:
   void entry() override;
   void exit() override;
 
+  void react(const events::PreferredDeviceChanged& ev) override;
+
   void react(const events::Disable& ev) override;
   void react(const events::internal::Gap& ev) override;
   void react(const events::internal::A2dp& ev) override;
+
+  using BluetoothState::react;
 };
 
 class Connected : public BluetoothState {
+ public:
   void entry() override;
   void exit() override;
 
+  void react(const events::PreferredDeviceChanged& ev) override;
+  void react(const events::SourceChanged& ev) override;
+
   void react(const events::Disable& ev) override;
   void react(const events::internal::Gap& ev) override;
   void react(const events::internal::A2dp& ev) override;
   void react(const events::internal::Avrc& ev) override;
+
+  using BluetoothState::react;
 };
 
 }  // namespace bluetooth
diff --git a/src/system_fsm/booting.cpp b/src/system_fsm/booting.cpp
index 3d6c6a46..7bd5f890 100644
--- a/src/system_fsm/booting.cpp
+++ b/src/system_fsm/booting.cpp
@@ -6,6 +6,7 @@
 
 #include "assert.h"
 #include "audio_fsm.hpp"
+#include "bluetooth.hpp"
 #include "core/lv_obj.h"
 #include "display_init.hpp"
 #include "esp_err.h"
@@ -60,12 +61,15 @@ auto Booting::entry() -> void {
     return;
   }
 
+  ESP_LOGI(kTag, "starting bluetooth");
+  sBluetooth.reset(new drivers::Bluetooth());
+
   // At this point we've done all of the essential boot tasks. Start remaining
   // state machines and inform them that the system is ready.
 
   ESP_LOGI(kTag, "starting audio");
   if (!audio::AudioState::Init(sGpios.get(), sDatabase, sTagParser,
-                               sTrackQueue.get())) {
+                               sBluetooth.get(), sTrackQueue.get())) {
     events::System().Dispatch(FatalError{});
     events::Ui().Dispatch(FatalError{});
     return;
@@ -80,6 +84,7 @@ auto Booting::exit() -> void {
   // TODO(jacqueline): Gate this on something. Debug flag? Flashing mode?
   sAppConsole = new console::AppConsole();
   sAppConsole->sTrackQueue = sTrackQueue.get();
+  sAppConsole->sBluetooth = sBluetooth.get();
   sAppConsole->Launch();
 }
 
diff --git a/src/system_fsm/include/system_fsm.hpp b/src/system_fsm/include/system_fsm.hpp
index d30a712c..3d513666 100644
--- a/src/system_fsm/include/system_fsm.hpp
+++ b/src/system_fsm/include/system_fsm.hpp
@@ -10,6 +10,7 @@
 
 #include "app_console.hpp"
 #include "battery.hpp"
+#include "bluetooth.hpp"
 #include "database.hpp"
 #include "display.hpp"
 #include "gpios.hpp"
@@ -62,6 +63,7 @@ class SystemState : public tinyfsm::Fsm<SystemState> {
   static std::shared_ptr<drivers::Battery> sBattery;
   static std::shared_ptr<drivers::SdStorage> sStorage;
   static std::shared_ptr<drivers::Display> sDisplay;
+  static std::shared_ptr<drivers::Bluetooth> sBluetooth;
 
   static std::shared_ptr<database::Database> sDatabase;
   static std::shared_ptr<database::TagParserImpl> sTagParser;
diff --git a/src/system_fsm/system_fsm.cpp b/src/system_fsm/system_fsm.cpp
index 527a8770..96e806f4 100644
--- a/src/system_fsm/system_fsm.cpp
+++ b/src/system_fsm/system_fsm.cpp
@@ -24,6 +24,7 @@ std::shared_ptr<drivers::RelativeWheel> SystemState::sRelativeTouch;
 std::shared_ptr<drivers::Battery> SystemState::sBattery;
 std::shared_ptr<drivers::SdStorage> SystemState::sStorage;
 std::shared_ptr<drivers::Display> SystemState::sDisplay;
+std::shared_ptr<drivers::Bluetooth> SystemState::sBluetooth;
 
 std::shared_ptr<database::Database> SystemState::sDatabase;
 std::shared_ptr<database::TagParserImpl> SystemState::sTagParser;
diff --git a/src/tasks/tasks.cpp b/src/tasks/tasks.cpp
index ce5f17dc..493d6ba9 100644
--- a/src/tasks/tasks.cpp
+++ b/src/tasks/tasks.cpp
@@ -62,7 +62,7 @@ auto AllocateStack<Type::kAudio>() -> cpp::span<StackType_t> {
 template <>
 auto AllocateStack<Type::kUi>() -> cpp::span<StackType_t> {
   std::size_t size = 32 * 1024;
-  return {static_cast<StackType_t*>(heap_caps_malloc(size, MALLOC_CAP_DEFAULT)),
+  return {static_cast<StackType_t*>(heap_caps_malloc(size, MALLOC_CAP_SPIRAM)),
           size};
 }
 // UI flushes *must* be done from internal RAM. Thankfully, there is very little
@@ -84,8 +84,7 @@ auto AllocateStack<Type::kFileStreamer>() -> cpp::span<StackType_t> {
 template <>
 auto AllocateStack<Type::kMixer>() -> cpp::span<StackType_t> {
   std::size_t size = 4 * 1024;
-  return {static_cast<StackType_t*>(
-              heap_caps_malloc(size, MALLOC_CAP_INTERNAL | MALLOC_CAP_8BIT)),
+  return {static_cast<StackType_t*>(heap_caps_malloc(size, MALLOC_CAP_SPIRAM)),
           size};
 }