Check if we use LFXO and guard with 2 second timeout for broken crystals

src/helpers/nrf52/SerialBLEInterface.cpp

@@ -134,9 +134,18 @@ void SerialBLEInterface::begin(const char* prefix, char* name, uint32_t pin_code
   // On fast boots (filesystem already formatted), Bluefruit.begin() can
   // be called before the crystal is stable, hanging sd_softdevice_enable().
   // See: https://github.com/meshcore-dev/MeshCore/issues/1780
-  while (!NRF_CLOCK->EVENTS_LFCLKSTARTED) {
-    delay(1);
+#ifdef USE_LFXO
+  {
+    uint32_t lfclk_start = millis();
+    while (!NRF_CLOCK->EVENTS_LFCLKSTARTED) {
+      if (millis() - lfclk_start >= 2000) {
+        Serial.println("WARNING: LFXO crystal did not start within 2s — check 32.768kHz crystal");
+        break;
+      }
+      delay(1);
+    }
   }
+#endif
 
   // If we want to control BLE LED ourselves, uncomment this:
   // Bluefruit.autoConnLed(false);