[esp32_ble] Reduce GATT event latency from 8ms to 12μs with notification socket (#11663)

esphome/components/esp32_ble/ble.cpp

@@ -27,6 +27,10 @@ extern "C" {
 #include <esp32-hal-bt.h>
 #endif
 
+#ifdef USE_SOCKET_SELECT_SUPPORT
+#include <lwip/sockets.h>
+#endif
+
 namespace esphome::esp32_ble {
 
 static const char *const TAG = "esp32_ble";
@@ -293,10 +297,21 @@ bool ESP32BLE::ble_setup_() {
   // BLE takes some time to be fully set up, 200ms should be more than enough
   delay(200);  // NOLINT
 
+  // Set up notification socket to wake main loop for BLE events
+  // This enables low-latency (~12μs) event processing instead of waiting for select() timeout
+#ifdef USE_SOCKET_SELECT_SUPPORT
+  this->setup_event_notification_();
+#endif
+
   return true;
 }
 
 bool ESP32BLE::ble_dismantle_() {
+  // Clean up notification socket first before dismantling BLE stack
+#ifdef USE_SOCKET_SELECT_SUPPORT
+  this->cleanup_event_notification_();
+#endif
+
   esp_err_t err = esp_bluedroid_disable();
   if (err != ESP_OK) {
     ESP_LOGE(TAG, "esp_bluedroid_disable failed: %d", err);
@@ -394,6 +409,12 @@ void ESP32BLE::loop() {
       break;
   }
 
+#ifdef USE_SOCKET_SELECT_SUPPORT
+  // Drain any notification socket events first
+  // This clears the socket so it doesn't stay "ready" in subsequent select() calls
+  this->drain_event_notifications_();
+#endif
+
   BLEEvent *ble_event = this->ble_events_.pop();
   while (ble_event != nullptr) {
     switch (ble_event->type_) {
@@ -582,6 +603,10 @@ void ESP32BLE::gap_event_handler(esp_gap_ble_cb_event_t event, esp_ble_gap_cb_pa
 void ESP32BLE::gatts_event_handler(esp_gatts_cb_event_t event, esp_gatt_if_t gatts_if,
                                    esp_ble_gatts_cb_param_t *param) {
   enqueue_ble_event(event, gatts_if, param);
+  // Wake up main loop to process GATT event immediately
+#ifdef USE_SOCKET_SELECT_SUPPORT
+  global_ble->notify_main_loop_();
+#endif
 }
 #endif
 
@@ -589,6 +614,10 @@ void ESP32BLE::gatts_event_handler(esp_gatts_cb_event_t event, esp_gatt_if_t gat
 void ESP32BLE::gattc_event_handler(esp_gattc_cb_event_t event, esp_gatt_if_t gattc_if,
                                    esp_ble_gattc_cb_param_t *param) {
   enqueue_ble_event(event, gattc_if, param);
+  // Wake up main loop to process GATT event immediately
+#ifdef USE_SOCKET_SELECT_SUPPORT
+  global_ble->notify_main_loop_();
+#endif
 }
 #endif
 
@@ -628,6 +657,89 @@ void ESP32BLE::dump_config() {
   }
 }
 
+#ifdef USE_SOCKET_SELECT_SUPPORT
+void ESP32BLE::setup_event_notification_() {
+  // Create UDP socket for event notifications
+  this->notify_fd_ = lwip_socket(AF_INET, SOCK_DGRAM, IPPROTO_UDP);
+  if (this->notify_fd_ < 0) {
+    ESP_LOGW(TAG, "Event socket create failed: %d", errno);
+    return;
+  }
+
+  // Bind to loopback with auto-assigned port
+  struct sockaddr_in addr = {};
+  addr.sin_family = AF_INET;
+  addr.sin_addr.s_addr = lwip_htonl(INADDR_LOOPBACK);
+  addr.sin_port = 0;  // Auto-assign port
+
+  if (lwip_bind(this->notify_fd_, (struct sockaddr *) &addr, sizeof(addr)) < 0) {
+    ESP_LOGW(TAG, "Event socket bind failed: %d", errno);
+    lwip_close(this->notify_fd_);
+    this->notify_fd_ = -1;
+    return;
+  }
+
+  // Get the assigned address and connect to it
+  // Connecting a UDP socket allows using send() instead of sendto() for better performance
+  struct sockaddr_in notify_addr;
+  socklen_t len = sizeof(notify_addr);
+  if (lwip_getsockname(this->notify_fd_, (struct sockaddr *) &notify_addr, &len) < 0) {
+    ESP_LOGW(TAG, "Event socket address failed: %d", errno);
+    lwip_close(this->notify_fd_);
+    this->notify_fd_ = -1;
+    return;
+  }
+
+  // Connect to self (loopback) - allows using send() instead of sendto()
+  // After connect(), no need to store notify_addr - the socket remembers it
+  if (lwip_connect(this->notify_fd_, (struct sockaddr *) &notify_addr, sizeof(notify_addr)) < 0) {
+    ESP_LOGW(TAG, "Event socket connect failed: %d", errno);
+    lwip_close(this->notify_fd_);
+    this->notify_fd_ = -1;
+    return;
+  }
+
+  // Set non-blocking mode
+  int flags = lwip_fcntl(this->notify_fd_, F_GETFL, 0);
+  lwip_fcntl(this->notify_fd_, F_SETFL, flags | O_NONBLOCK);
+
+  // Register with application's select() loop
+  if (!App.register_socket_fd(this->notify_fd_)) {
+    ESP_LOGW(TAG, "Event socket register failed");
+    lwip_close(this->notify_fd_);
+    this->notify_fd_ = -1;
+    return;
+  }
+
+  ESP_LOGD(TAG, "Event socket ready");
+}
+
+void ESP32BLE::cleanup_event_notification_() {
+  if (this->notify_fd_ >= 0) {
+    App.unregister_socket_fd(this->notify_fd_);
+    lwip_close(this->notify_fd_);
+    this->notify_fd_ = -1;
+    ESP_LOGD(TAG, "Event socket closed");
+  }
+}
+
+void ESP32BLE::drain_event_notifications_() {
+  // Called from main loop to drain any pending notifications
+  // Must check is_socket_ready() to avoid blocking on empty socket
+  if (this->notify_fd_ >= 0 && App.is_socket_ready(this->notify_fd_)) {
+    char buffer[BLE_EVENT_NOTIFY_DRAIN_BUFFER_SIZE];
+    // Drain all pending notifications with non-blocking reads
+    // Multiple BLE events may have triggered multiple writes, so drain until EWOULDBLOCK
+    // We control both ends of this loopback socket (always write 1 byte per event),
+    // so no error checking needed - any errors indicate catastrophic system failure
+    while (lwip_recvfrom(this->notify_fd_, buffer, sizeof(buffer), 0, nullptr, nullptr) > 0) {
+      // Just draining, no action needed - actual BLE events are already queued
+    }
+  }
+}
+
+#endif  // USE_SOCKET_SELECT_SUPPORT
+
 uint64_t ble_addr_to_uint64(const esp_bd_addr_t address) {
   uint64_t u = 0;
   u |= uint64_t(address[0] & 0xFF) << 40;