Improve bt scanning responsiveness

src/drivers/bluetooth.cpp

@@ -97,6 +97,15 @@ auto Bluetooth::SetPreferredDevice(const bluetooth::mac_addr_t& mac) -> void {
       bluetooth::events::PreferredDeviceChanged{});
 }
 
+auto Bluetooth::SetDeviceDiscovery(bool allowed) -> void {
+  if (allowed == bluetooth::BluetoothState::discovery()) {
+    return;
+  }
+  bluetooth::BluetoothState::discovery(allowed);
+  tinyfsm::FsmList<bluetooth::BluetoothState>::dispatch(
+      bluetooth::events::DiscoveryChanged{});
+}
+
 auto Bluetooth::SetSource(StreamBufferHandle_t src) -> void {
   if (src == bluetooth::BluetoothState::source()) {
     return;
@@ -122,12 +131,144 @@ auto DeviceName() -> std::pmr::string {
 
 namespace bluetooth {
 
+static constexpr uint8_t kDiscoveryTimeSeconds = 5;
+static constexpr uint8_t kDiscoveryMaxResults = 0;
+
+Scanner::Scanner() : enabled_(false), is_discovering_(false) {}
+
+auto Scanner::ScanContinuously() -> void {
+  if (enabled_) {
+    return;
+  }
+  ESP_LOGI(kTag, "beginning continuous scan");
+  enabled_ = true;
+  if (enabled_ && !is_discovering_) {
+    ScanOnce();
+  }
+}
+
+auto Scanner::ScanOnce() -> void {
+  if (is_discovering_) {
+    return;
+  }
+  is_discovering_ = true;
+  ESP_LOGI(kTag, "scanning...");
+  esp_bt_gap_start_discovery(ESP_BT_INQ_MODE_GENERAL_INQUIRY,
+                             kDiscoveryTimeSeconds, kDiscoveryMaxResults);
+}
+
+auto Scanner::StopScanning() -> void {
+  ESP_LOGI(kTag, "stopping scan");
+  enabled_ = false;
+}
+
+auto Scanner::StopScanningNow() -> void {
+  StopScanning();
+  if (is_discovering_) {
+    ESP_LOGI(kTag, "cancelling scan");
+    is_discovering_ = false;
+    esp_bt_gap_cancel_discovery();
+  }
+}
+
+auto Scanner::HandleGapEvent(const events::internal::Gap& ev) -> void {
+  switch (ev.type) {
+    case ESP_BT_GAP_DISC_RES_EVT:
+      if (ev.param != nullptr) {
+        // Handle device discovery even if we've been told to stop discovering.
+        HandleDeviceDiscovery(*ev.param);
+      }
+      break;
+    case ESP_BT_GAP_DISC_STATE_CHANGED_EVT:
+      if (ev.param->disc_st_chg.state == ESP_BT_GAP_DISCOVERY_STOPPED) {
+        ESP_LOGI(kTag, "discovery finished");
+        if (enabled_) {
+          ESP_LOGI(kTag, "restarting discovery");
+          esp_bt_gap_start_discovery(ESP_BT_INQ_MODE_GENERAL_INQUIRY,
+                                     kDiscoveryTimeSeconds,
+                                     kDiscoveryMaxResults);
+        } else {
+          is_discovering_ = false;
+        }
+      }
+      break;
+    case ESP_BT_GAP_MODE_CHG_EVT:
+      // todo: mode change. is this important?
+      ESP_LOGI(kTag, "GAP mode changed");
+      break;
+    default:
+      ESP_LOGW(kTag, "unhandled GAP event: %u", ev.type);
+  }
+}
+
+auto Scanner::HandleDeviceDiscovery(const 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::pmr::string{reinterpret_cast<char*>(name),
+                                 static_cast<size_t>(length)};
+  events::DeviceDiscovered ev{.device = device};
+  tinyfsm::FsmList<bluetooth::BluetoothState>::dispatch(ev);
+}
+
 NvsStorage* BluetoothState::sStorage_;
+Scanner* BluetoothState::sScanner_;
 
 std::mutex BluetoothState::sDevicesMutex_{};
 std::map<mac_addr_t, Device> BluetoothState::sDevices_{};
 std::optional<mac_addr_t> BluetoothState::sPreferredDevice_{};
-mac_addr_t BluetoothState::sCurrentDevice_;
+mac_addr_t BluetoothState::sCurrentDevice_{0};
+bool BluetoothState::sIsDiscoveryAllowed_{false};
 
 std::atomic<StreamBufferHandle_t> BluetoothState::sSource_;
 std::function<void(Event)> BluetoothState::sEventHandler_;
@@ -152,11 +293,21 @@ auto BluetoothState::preferred_device() -> std::optional<mac_addr_t> {
   return sPreferredDevice_;
 }
 
-auto BluetoothState::preferred_device(const mac_addr_t& addr) -> void {
+auto BluetoothState::preferred_device(std::optional<mac_addr_t> addr) -> void {
   std::lock_guard lock{sDevicesMutex_};
   sPreferredDevice_ = addr;
 }
 
+auto BluetoothState::discovery() -> bool {
+  std::lock_guard lock{sDevicesMutex_};
+  return sIsDiscoveryAllowed_;
+}
+
+auto BluetoothState::discovery(bool en) -> void {
+  std::lock_guard lock{sDevicesMutex_};
+  sIsDiscoveryAllowed_ = en;
+}
+
 auto BluetoothState::source() -> StreamBufferHandle_t {
   std::lock_guard lock{sDevicesMutex_};
   return sSource_.load();
@@ -172,21 +323,67 @@ auto BluetoothState::event_handler(std::function<void(Event)> cb) -> void {
   sEventHandler_ = cb;
 }
 
+auto BluetoothState::react(const events::DeviceDiscovered& ev) -> void {
+  ESP_LOGI(kTag, "discovered device %s", ev.device.name.c_str());
+  bool is_preferred = false;
+  {
+    std::lock_guard<std::mutex> lock{sDevicesMutex_};
+    sDevices_[ev.device.address] = ev.device;
+
+    if (ev.device.address == sPreferredDevice_) {
+      sCurrentDevice_ = ev.device.address;
+      is_preferred = true;
+    }
+
+    if (sEventHandler_) {
+      std::invoke(sEventHandler_, Event::kKnownDevicesChanged);
+    }
+  }
+
+  if (is_preferred && is_in_state<Idle>()) {
+    ESP_LOGI(kTag, "new device is preferred. connecting.");
+    transit<Connecting>();
+  }
+}
+
+auto BluetoothState::react(const events::DiscoveryChanged& ev) -> void {
+  if (sIsDiscoveryAllowed_) {
+    sScanner_->ScanContinuously();
+  } else {
+    sScanner_->StopScanning();
+  }
+}
+
 static bool sIsFirstEntry = true;
 
 void Disabled::entry() {
   if (sIsFirstEntry) {
     // We only use BT Classic, to claw back ~60KiB from the BLE firmware.
     esp_bt_controller_mem_release(ESP_BT_MODE_BLE);
+    sScanner_ = new Scanner();
     sIsFirstEntry = false;
     return;
   }
 
+  sScanner_->StopScanningNow();
+
   esp_bluedroid_disable();
   esp_bluedroid_deinit();
   esp_bt_controller_disable();
 }
 
+void Disabled::exit() {
+  if (sIsDiscoveryAllowed_) {
+    ESP_LOGI(kTag, "bt enabled, beginning discovery");
+    sScanner_->ScanContinuously();
+  } else if (sPreferredDevice_) {
+    ESP_LOGI(kTag, "bt enabled, checking for preferred device");
+    sScanner_->ScanOnce();
+  } else {
+    ESP_LOGI(kTag, "bt enabled, but not scanning");
+  }
+}
+
 void Disabled::react(const events::Enable&) {
   esp_bt_controller_config_t config = BT_CONTROLLER_INIT_CONFIG_DEFAULT();
   if (esp_bt_controller_init(&config) != ESP_OK) {
@@ -237,103 +434,18 @@ void Disabled::react(const events::Enable&) {
   // Don't let anyone interact with us before we're ready.
   esp_bt_gap_set_scan_mode(ESP_BT_NON_CONNECTABLE, ESP_BT_NON_DISCOVERABLE);
 
-  transit<Scanning>();
+  transit<Idle>();
 }
 
-static constexpr uint8_t kDiscoveryTimeSeconds = 10;
+void Idle::entry() {
-static constexpr uint8_t kDiscoveryMaxResults = 0;
+  ESP_LOGI(kTag, "bt is idle");
-
-void Scanning::entry() {
-  ESP_LOGI(kTag, "scanning for devices");
-  esp_bt_gap_start_discovery(ESP_BT_INQ_MODE_GENERAL_INQUIRY,
-                             kDiscoveryTimeSeconds, kDiscoveryMaxResults);
-}
-
-void Scanning::exit() {
-  esp_bt_gap_cancel_discovery();
 }
 
-void Scanning::react(const events::Disable& ev) {
+void Idle::react(const events::Disable& ev) {
   transit<Disabled>();
 }
 
-auto Scanning::OnDeviceDiscovered(esp_bt_gap_cb_param_t* param) -> void {
+void Idle::react(const events::PreferredDeviceChanged& ev) {
-  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::pmr::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 (sEventHandler_) {
-      std::invoke(sEventHandler_, Event::kKnownDevicesChanged);
-    }
-  }
-
-  if (is_preferred) {
-    transit<Connecting>();
-  }
-}
-
-void Scanning::react(const events::PreferredDeviceChanged& ev) {
   bool is_discovered = false;
   {
     std::lock_guard<std::mutex> lock{sDevicesMutex_};
@@ -342,28 +454,13 @@ void Scanning::react(const events::PreferredDeviceChanged& ev) {
     }
   }
   if (is_discovered) {
+    ESP_LOGI(kTag, "selected known device");
     transit<Connecting>();
   }
 }
 
-void Scanning::react(const events::internal::Gap& ev) {
+void Idle::react(const events::internal::Gap& ev) {
-  switch (ev.type) {
+  sScanner_->HandleGapEvent(ev);
-    case ESP_BT_GAP_DISC_RES_EVT:
-      OnDeviceDiscovered(ev.param);
-      break;
-    case ESP_BT_GAP_DISC_STATE_CHANGED_EVT:
-      if (ev.param->disc_st_chg.state == ESP_BT_GAP_DISCOVERY_STOPPED) {
-        esp_bt_gap_start_discovery(ESP_BT_INQ_MODE_GENERAL_INQUIRY,
-                                   kDiscoveryTimeSeconds, kDiscoveryMaxResults);
-      }
-      break;
-    case ESP_BT_GAP_MODE_CHG_EVT:
-      // todo: mode change. is this important?
-      ESP_LOGI(kTag, "GAP mode changed");
-      break;
-    default:
-      ESP_LOGW(kTag, "unhandled GAP event: %u", ev.type);
-  }
 }
 
 void Connecting::entry() {
@@ -375,6 +472,7 @@ void Connecting::exit() {}
 
 void Connecting::react(const events::Disable& ev) {
   // TODO: disconnect gracefully
+  transit<Disabled>();
 }
 
 void Connecting::react(const events::PreferredDeviceChanged& ev) {
@@ -382,12 +480,13 @@ void Connecting::react(const events::PreferredDeviceChanged& ev) {
 }
 
 void Connecting::react(const events::internal::Gap& ev) {
+  sScanner_->HandleGapEvent(ev);
   switch (ev.type) {
     case ESP_BT_GAP_AUTH_CMPL_EVT:
       if (ev.param->auth_cmpl.stat != ESP_BT_STATUS_SUCCESS) {
         ESP_LOGE(kTag, "auth failed");
         sPreferredDevice_ = {};
-        transit<Scanning>();
+        transit<Idle>();
       }
       break;
     case ESP_BT_GAP_ACL_CONN_CMPL_STAT_EVT:
@@ -397,22 +496,22 @@ void Connecting::react(const events::internal::Gap& ev) {
     case ESP_BT_GAP_PIN_REQ_EVT:
       ESP_LOGW(kTag, "device needs a pin to connect");
       sPreferredDevice_ = {};
-      transit<Scanning>();
+      transit<Idle>();
       break;
     case ESP_BT_GAP_CFM_REQ_EVT:
       ESP_LOGW(kTag, "user needs to do cfm. idk man.");
       sPreferredDevice_ = {};
-      transit<Scanning>();
+      transit<Idle>();
       break;
     case ESP_BT_GAP_KEY_NOTIF_EVT:
       ESP_LOGW(kTag, "the device is telling us a password??");
       sPreferredDevice_ = {};
-      transit<Scanning>();
+      transit<Idle>();
       break;
     case ESP_BT_GAP_KEY_REQ_EVT:
       ESP_LOGW(kTag, "the device wants a password!");
       sPreferredDevice_ = {};
-      transit<Scanning>();
+      transit<Idle>();
       break;
     case ESP_BT_GAP_MODE_CHG_EVT:
       ESP_LOGI(kTag, "GAP mode changed");
@@ -464,6 +563,7 @@ void Connected::exit() {
 
 void Connected::react(const events::Disable& ev) {
   // TODO: disconnect gracefully
+  transit<Disabled>();
 }
 
 void Connected::react(const events::PreferredDeviceChanged& ev) {
@@ -481,6 +581,7 @@ void Connected::react(const events::SourceChanged& ev) {
 }
 
 void Connected::react(const events::internal::Gap& ev) {
+  sScanner_->HandleGapEvent(ev);
   switch (ev.type) {
     case ESP_BT_GAP_MODE_CHG_EVT:
       // todo: is this important?

src/drivers/include/bluetooth.hpp

@@ -32,6 +32,12 @@ class Bluetooth {
   auto Disable() -> void;
   auto IsEnabled() -> bool;
 
+  /*
+   * Sets whether or not the bluetooth stack is allowed to actively scan for
+   * new devices.
+   */
+  auto SetDeviceDiscovery(bool) -> void;
+
   auto KnownDevices() -> std::vector<bluetooth::Device>;
   auto SetPreferredDevice(const bluetooth::mac_addr_t& mac) -> void;
 
@@ -47,6 +53,10 @@ struct Disable : public tinyfsm::Event {};
 
 struct PreferredDeviceChanged : public tinyfsm::Event {};
 struct SourceChanged : public tinyfsm::Event {};
+struct DiscoveryChanged : public tinyfsm::Event {};
+struct DeviceDiscovered : public tinyfsm::Event {
+  const Device& device;
+};
 
 namespace internal {
 struct Gap : public tinyfsm::Event {
@@ -64,13 +74,37 @@ struct Avrc : public tinyfsm::Event {
 }  // namespace internal
 }  // namespace events
 
+/*
+ * Utility for managing scanning, independent of the current connection state.
+ */
+class Scanner {
+ public:
+  Scanner();
+
+  auto ScanContinuously() -> void;
+  auto ScanOnce() -> void;
+  auto StopScanning() -> void;
+  auto StopScanningNow() -> void;
+
+  auto HandleGapEvent(const events::internal::Gap&) -> void;
+
+ private:
+  bool enabled_;
+  bool is_discovering_;
+
+  auto HandleDeviceDiscovery(const esp_bt_gap_cb_param_t& param) -> void;
+};
+
 class BluetoothState : public tinyfsm::Fsm<BluetoothState> {
  public:
   static auto Init(NvsStorage& storage) -> void;
 
   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 preferred_device(std::optional<mac_addr_t>) -> void;
+
+  static auto discovery() -> bool;
+  static auto discovery(bool) -> void;
 
   static auto source() -> StreamBufferHandle_t;
   static auto source(StreamBufferHandle_t) -> void;
@@ -86,6 +120,9 @@ class BluetoothState : public tinyfsm::Fsm<BluetoothState> {
   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::DiscoveryChanged&);
+
+  virtual void react(const events::DeviceDiscovered&);
 
   virtual void react(const events::internal::Gap& ev) = 0;
   virtual void react(const events::internal::A2dp& ev){};
@@ -93,11 +130,13 @@ class BluetoothState : public tinyfsm::Fsm<BluetoothState> {
 
  protected:
   static NvsStorage* sStorage_;
+  static Scanner* sScanner_;
 
   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 bool sIsDiscoveryAllowed_;
 
   static std::atomic<StreamBufferHandle_t> sSource_;
   static std::function<void(Event)> sEventHandler_;
@@ -106,19 +145,21 @@ class BluetoothState : public tinyfsm::Fsm<BluetoothState> {
 class Disabled : public BluetoothState {
  public:
   void entry() override;
+  void exit() override;
 
   void react(const events::Enable& 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::DiscoveryChanged& ev) override{};
+
   using BluetoothState::react;
 };
 
-class Scanning : public BluetoothState {
+class Idle : public BluetoothState {
  public:
   void entry() override;
-  void exit() override;
 
   void react(const events::Disable& ev) override;
   void react(const events::PreferredDeviceChanged& ev) override;
@@ -126,9 +167,6 @@ class Scanning : public BluetoothState {
   void react(const events::internal::Gap& ev) override;
 
   using BluetoothState::react;
-
- private:
-  auto OnDeviceDiscovered(esp_bt_gap_cb_param_t*) -> void;
 };
 
 class Connecting : public BluetoothState {

src/ui/include/screen_settings.hpp

@@ -33,10 +33,11 @@ class Settings : public MenuScreen {
 class Bluetooth : public MenuScreen {
  public:
   Bluetooth(models::TopBar&, drivers::Bluetooth& bt, drivers::NvsStorage& nvs);
+  ~Bluetooth();
 
   auto ChangeEnabledState(bool enabled) -> void;
   auto RefreshDevicesList() -> void;
-  auto OnDeviceSelected(size_t index) -> void;
+  auto OnDeviceSelected(ssize_t index) -> void;
 
  private:
   auto RemoveAllDevices() -> void;

src/ui/screen_settings.cpp

@@ -119,6 +119,11 @@ static auto select_device_cb(lv_event_t* ev) {
   instance->OnDeviceSelected(lv_obj_get_index(ev->target));
 }
 
+static auto remove_preferred_cb(lv_event_t* ev) {
+  Bluetooth* instance = reinterpret_cast<Bluetooth*>(ev->user_data);
+  instance->OnDeviceSelected(-1);
+}
+
 Bluetooth::Bluetooth(models::TopBar& bar,
                      drivers::Bluetooth& bt,
                      drivers::NvsStorage& nvs)
@@ -141,6 +146,11 @@ Bluetooth::Bluetooth(models::TopBar& bar,
 
   devices_list_ = lv_list_create(content_);
   RefreshDevicesList();
+  bt_.SetDeviceDiscovery(true);
+}
+
+Bluetooth::~Bluetooth() {
+  bt_.SetDeviceDiscovery(false);
 }
 
 auto Bluetooth::ChangeEnabledState(bool enabled) -> void {
@@ -228,6 +238,11 @@ auto Bluetooth::RemoveAllDevices() -> void {
 auto Bluetooth::AddPreferredDevice(const drivers::bluetooth::Device& dev)
     -> void {
   preferred_device_ = lv_list_add_btn(devices_list_, NULL, dev.name.c_str());
+  lv_obj_t* remove = lv_btn_create(preferred_device_);
+  lv_obj_t* remove_icon = lv_label_create(remove);
+  lv_label_set_text(remove_icon, "x");
+  lv_group_add_obj(group_, remove);
+
   macs_in_list_.push_back(dev.address);
 }
 
@@ -238,7 +253,16 @@ auto Bluetooth::AddDevice(const drivers::bluetooth::Device& dev) -> void {
   macs_in_list_.push_back(dev.address);
 }
 
-auto Bluetooth::OnDeviceSelected(size_t index) -> void {
+auto Bluetooth::OnDeviceSelected(ssize_t index) -> void {
+  if (index == -1) {
+    events::System().RunOnTask([=]() {
+      nvs_.PreferredBluetoothDevice({});
+      bt_.SetPreferredDevice({});
+    });
+    RefreshDevicesList();
+    return;
+  }
+
   // Tell the bluetooth driver that our preference changed.
   auto it = macs_in_list_.begin();
   std::advance(it, index);