Keep ESP32 USB startup responsive during optional GPS discovery

src/helpers/sensors/EnvironmentSensorManager.cpp

@@ -1112,7 +1112,16 @@ const char* EnvironmentSensorManager::getSettingValue(int i) const {
 
 bool EnvironmentSensorManager::setSettingValue(const char* name, const char* value) {
   #if ENV_INCLUDE_GPS
-  if (gps_detected && strcmp(name, "gps") == 0) {
+  bool gps_setting_available = gps_detected;
+#if defined(ESP32_PLATFORM) && !defined(RAK_WISBLOCK_GPS)
+  gps_setting_available = gps_setting_available || gps_discovery_pending;
+#endif
+  if (gps_setting_available && strcmp(name, "gps") == 0) {
+#if defined(ESP32_PLATFORM) && !defined(RAK_WISBLOCK_GPS)
+    // Preferences load before a cold receiver finishes its bounded probe.
+    // Retain intent so late discovery cannot replace a saved off/on choice.
+    gps_discovery_preference_known = true;
+#endif
     bool enabled = strcmp(value, "0") != 0;
 #if defined(RAK_WISBLOCK_GPS) && defined(FORCE_GPS_ALIVE)
     // A UART L76K cannot remove power from the shared 3V3_S rail. "Off" stops
@@ -1172,6 +1181,51 @@ void EnvironmentSensorManager::setPowerSavingEnabled(bool enabled) {
 }
 
 #if ENV_INCLUDE_GPS
+#if defined(ESP32_PLATFORM) && !defined(RAK_WISBLOCK_GPS)
+void EnvironmentSensorManager::finishBasicGpsDiscovery(bool found) {
+  gps_discovery_pending = false;
+  gps_detected = found;
+  gps_serial_transport = found;
+  if (found) {
+    MESH_DEBUG_PRINTLN("GPS detected");
+#ifdef PERSISTANT_GPS
+    // Keep the established always-on default only when no loaded preference
+    // has superseded it. The receiver is already awake from the probe.
+    if (!gps_discovery_preference_known || isGpsTelemetryUserEnabled()) {
+      gps_active = true;
+      if (!gps_discovery_preference_known) setGpsTelemetryUserEnabled(true);
+      _location->setGPSPowerSaving(powersaving_enabled);
+      armGpsPowerSavingCycle();
+      return;
+    }
+#endif
+  } else {
+    MESH_DEBUG_PRINTLN("No GPS detected");
+  }
+  _location->stop();
+  gps_active = false;
+  if (found && isGpsTelemetryUserEnabled()) {
+    _location->setGPSPowerSaving(powersaving_enabled);
+    start_gps();
+  }
+}
+
+void EnvironmentSensorManager::serviceBasicGpsDiscovery() {
+  // A bridge may own Serial1 until it explicitly releases the receiver. Keep
+  // its pending probe reserved, but never poll or power it while blocked.
+  if (!gps_discovery_pending || gps_serial_transport_blocked) return;
+#ifdef ENV_SKIP_GPS_DETECT
+  const bool found = true;
+#else
+  const bool found = Serial1.available() > 0;
+#endif
+  // Unsigned elapsed time keeps the same five-second cold-start window even
+  // when the millisecond clock wraps. No startup or command loop waits here.
+  if (!found && static_cast<uint32_t>(millis() - gps_discovery_started_at) < 5000UL) return;
+  finishBasicGpsDiscovery(found);
+}
+#endif
+
 void EnvironmentSensorManager::initBasicGPS() {
 
   // A repeated discovery pass must not steal a UART which an active bridge
@@ -1184,6 +1238,10 @@ void EnvironmentSensorManager::initBasicGPS() {
   resetGpsTelemetryTransportState();
   gps_serial_transport = false;
   gps_serial_transport_blocked = false;
+#if defined(ESP32_PLATFORM) && !defined(RAK_WISBLOCK_GPS)
+  gps_detected = false;
+  gps_active = false;
+#endif
 
   Serial1.setPins(PIN_GPS_TX, PIN_GPS_RX);
 
@@ -1201,6 +1259,15 @@ void EnvironmentSensorManager::initBasicGPS() {
     MESH_DEBUG_PRINTLN("No GPS wake/reset pin found for this board. Continuing on...");
   #endif
 
+#if defined(ESP32_PLATFORM) && !defined(RAK_WISBLOCK_GPS)
+  // Reserve the configured UART immediately, including while presence is
+  // still unknown. Continue discovery from loop() so an absent optional GPS
+  // cannot consume the website's entire five-second USB bootstrap deadline.
+  gps_serial_transport = true;
+  gps_discovery_pending = true;
+  gps_discovery_started_at = millis();
+  serviceBasicGpsDiscovery();
+#else
   // Cold-start receivers can take several seconds to emit their first NMEA
   // data. Check immediately, then wait at most five seconds; an already awake
   // receiver and the explicit bypass need no extra startup delay.
@@ -1227,6 +1294,7 @@ void EnvironmentSensorManager::initBasicGPS() {
   }
   _location->stop();
   gps_active = false; //Set GPS visibility off until setting is changed
+#endif
 }
 
 // gps code for rak might be moved to MicroNMEALoactionProvider
@@ -1472,7 +1540,12 @@ void EnvironmentSensorManager::stop_gps() {
 
 bool EnvironmentSensorManager::gpsUsesSerialUart(uint8_t uart) const {
 #if ENV_INCLUDE_GPS
+#if defined(ESP32_PLATFORM) && !defined(RAK_WISBLOCK_GPS)
+  // The pending probe owns this UART before presence has been established.
+  return uart == 1 && gps_serial_transport;
+#else
   return uart == 1 && gps_detected && gps_serial_transport;
+#endif
 #else
   (void)uart;
   return false;
@@ -1530,10 +1603,21 @@ bool EnvironmentSensorManager::setGpsSerialTransportBlocked(uint8_t uart,
     // Cancel remote-query acquisition/hold state before releasing the UART.
     setGpsTelemetryTransportAvailable(false);
     gps_serial_transport_blocked = true;
+#if defined(ESP32_PLATFORM) && !defined(RAK_WISBLOCK_GPS)
+    if (gps_discovery_pending) _location->stop();
+#endif
     if (gps_active) stop_gps();
     Serial1.end();
   } else {
     gps_serial_transport_blocked = false;
+#if defined(ESP32_PLATFORM) && !defined(RAK_WISBLOCK_GPS)
+    if (gps_discovery_pending) {
+      // The bridge's time cannot count as a GPS absence timeout. Reclaim only
+      // after release and give the newly awakened receiver its full window.
+      initBasicGPS();
+      return true;
+    }
+#endif
     // Restoring availability restarts the receiver only when the user's GPS
     // preference is on. Otherwise a future authorized location query may
     // acquire it on demand.
@@ -1553,6 +1637,9 @@ void EnvironmentSensorManager::loop() {
   #if ENV_INCLUDE_GPS
   static unsigned long next_gps_update = 0;
   unsigned long now = millis();
+#if defined(ESP32_PLATFORM) && !defined(RAK_WISBLOCK_GPS)
+  serviceBasicGpsDiscovery();
+#endif
   loopGpsTelemetry(now);
 
   if (powersaving_enabled && gps_detected && _location->getGPSPowerSaving()) {

src/helpers/sensors/EnvironmentSensorManager.h

@@ -26,6 +26,13 @@ protected:
   bool     gps_serial_transport_blocked = false;
 
   #if ENV_INCLUDE_GPS
+  #if defined(ESP32_PLATFORM) && !defined(RAK_WISBLOCK_GPS)
+  bool gps_discovery_pending = false;
+  bool gps_discovery_preference_known = false;
+  uint32_t gps_discovery_started_at = 0;
+  void finishBasicGpsDiscovery(bool found);
+  void serviceBasicGpsDiscovery();
+  #endif
   LocationProvider* _location;
   LocationProvider* _configured_location;
   void armGpsPowerSavingCycle();