fix: power brownout and dirty write flush on restart or shutdown

examples/companion_radio/AbstractUITask.h

@@ -22,17 +22,24 @@ enum class UIEventType {
     ack
 };
 
+class ShutdownHandler {
+public:
+  virtual void onBeforeShutdown() = 0;
+};
+
 class AbstractUITask {
 protected:
   mesh::MainBoard* _board;
   BaseSerialInterface* _serial;
   bool _connected;
+  ShutdownHandler* _shutdown_handler = nullptr;
 
   AbstractUITask(mesh::MainBoard* board, BaseSerialInterface* serial) : _board(board), _serial(serial) {
     _connected = false;
   }
 
 public:
+  void setShutdownHandler(ShutdownHandler* h) { _shutdown_handler = h; }
   void setHasConnection(bool connected) { _connected = connected; }
   bool hasConnection() const { return _connected; }
   uint16_t getBattMilliVolts() const { return _board->getBattMilliVolts(); }

examples/companion_radio/MyMesh.h

@@ -84,7 +84,7 @@ struct AdvertPath {
   uint8_t path[MAX_PATH_SIZE];
 };
 
-class MyMesh : public BaseChatMesh, public DataStoreHost {
+class MyMesh : public BaseChatMesh, public DataStoreHost, public ShutdownHandler {
 public:
   MyMesh(mesh::Radio &radio, mesh::RNG &rng, mesh::RTCClock &rtc, SimpleMeshTables &tables, DataStore& store, AbstractUITask* ui=NULL);
 
@@ -166,6 +166,14 @@ class MyMesh : public BaseChatMesh, public DataStoreHost {
 public:
   void savePrefs() { _store->savePrefs(_prefs, sensors.node_lat, sensors.node_lon); }
 
+  void onBeforeShutdown() override {
+    if (dirty_contacts_expiry) {
+      saveContacts();
+      dirty_contacts_expiry = 0;
+    }
+    savePrefs();
+  }
+
 #if ENV_INCLUDE_GPS == 1
   void applyGpsPrefs() {
     sensors.setSettingValue("gps", _prefs.gps_enabled ? "1" : "0");

examples/companion_radio/main.cpp

@@ -237,6 +237,7 @@ void setup() {
 
 #ifdef DISPLAY_CLASS
   ui_task.begin(disp, &sensors, the_mesh.getNodePrefs());  // still want to pass this in as dependency, as prefs might be moved
+  ui_task.setShutdownHandler(&the_mesh);
 #endif
 
   board.onBootComplete();

examples/companion_radio/ui-new/UITask.cpp

@@ -694,6 +694,8 @@ void UITask::shutdown(bool restart){
 
   #endif // PIN_BUZZER
 
+  if (_shutdown_handler) _shutdown_handler->onBeforeShutdown();
+
   if (restart) {
     _board->reboot();
   } else {
@@ -821,26 +823,31 @@ void UITask::loop() {
 
 #ifdef AUTO_SHUTDOWN_MILLIVOLTS
   if (millis() > next_batt_chck) {
-    uint16_t milliVolts = getBattMilliVolts();
-    if (milliVolts > 0 && milliVolts < AUTO_SHUTDOWN_MILLIVOLTS) {
-
-      // show low battery shutdown alert
-      // we should only do this for eink displays, which will persist after power loss
-      #if defined(THINKNODE_M1) || defined(LILYGO_TECHO)
-      if (_display != NULL) {
-        _display->startFrame();
-        _display->setTextSize(2);
-        _display->setColor(DisplayDriver::RED);
-        _display->drawTextCentered(_display->width() / 2, 20, "Low Battery.");
-        _display->drawTextCentered(_display->width() / 2, 40, "Shutting Down!");
-        _display->endFrame();
-      }
-      #endif
+    uint32_t now = millis();
+    if (!_board->isBattReadSafe(now)) {
+      // TX just completed — voltage hasn't recovered yet; retry after settle window.
+      next_batt_chck = now + POST_TX_BATT_SETTLE_MS + 50;
+    } else {
+      uint16_t milliVolts = getBattMilliVolts();
+      if (milliVolts > 0 && milliVolts < AUTO_SHUTDOWN_MILLIVOLTS) {
+
+        // show low battery shutdown alert
+        // we should only do this for eink displays, which will persist after power loss
+        #if defined(THINKNODE_M1) || defined(LILYGO_TECHO)
+        if (_display != NULL) {
+          _display->startFrame();
+          _display->setTextSize(2);
+          _display->setColor(DisplayDriver::RED);
+          _display->drawTextCentered(_display->width() / 2, 20, "Low Battery.");
+          _display->drawTextCentered(_display->width() / 2, 40, "Shutting Down!");
+          _display->endFrame();
+        }
+        #endif
 
-      shutdown();
+        shutdown();
 
-    }
-    next_batt_chck = millis() + 8000;
+      }
+      next_batt_chck = millis() + 8000;
   }
 #endif
 }

examples/simple_repeater/MyMesh.h

@@ -192,6 +192,14 @@ class MyMesh : public mesh::Mesh, public CommonCLICallbacks {
     _cli.savePrefs(_fs);
   }
 
+  void flushPending() {
+    if (dirty_contacts_expiry) {
+      acl.save(_fs);
+      dirty_contacts_expiry = 0;
+    }
+    savePrefs();
+  }
+
   void sendFloodScoped(const TransportKey& scope, mesh::Packet* pkt, uint32_t delay_millis, uint8_t path_hash_size);
 
   // CommonCLICallbacks

examples/simple_repeater/main.cpp

@@ -142,6 +142,7 @@ void loop() {
       userBtnDownAt = millis();
     } else if ((unsigned long)(millis() - userBtnDownAt) >= USER_BTN_HOLD_OFF_MILLIS) {
       Serial.println("Powering off...");
+      the_mesh.flushPending();
       board.powerOff();  // does not return
     }
   } else {

examples/simple_sensor/SensorMesh.cpp

@@ -920,6 +920,10 @@ void SensorMesh::loop() {
 
   uint32_t curr = getRTCClock()->getCurrentTime();
   if (curr >= last_read_time + SENSOR_READ_INTERVAL_SECS) {
+    // Skip this cycle if TX just completed — the current spike sags battery
+    // voltage enough to falsely trigger low-battery alerts on weaker cells.
+    // The loop runs again in milliseconds, so the read is only deferred briefly.
+    if (!board.isBattReadSafe(millis())) return;
     telemetry.reset();
     telemetry.addVoltage(TELEM_CHANNEL_SELF, (float)board.getBattMilliVolts() / 1000.0f);
     // query other sensors -- target specific

src/MeshCore.h

@@ -41,8 +41,29 @@ namespace mesh {
 #define  BD_STARTUP_NORMAL     0  // getStartupReason() codes
 #define  BD_STARTUP_RX_PACKET  1
 
+// Milliseconds to wait after TX completes before trusting battery ADC readings.
+// LoRa TX causes a current spike that sags battery terminal voltage; on LiPo
+// cells below ~50% SoC the sag is large enough to cross shutdown/alert thresholds.
+#ifndef POST_TX_BATT_SETTLE_MS
+#define POST_TX_BATT_SETTLE_MS 250
+#endif
+
 class MainBoard {
+
+  bool     _tx_active           = false;
+  uint32_t _last_tx_complete_ms = 0;
+
 public:
+  // Called by the radio layer — not meant to be overridden.
+  void notifyTxStart()                   { _tx_active = true; }
+  void notifyTxComplete(uint32_t now_ms) { _tx_active = false; _last_tx_complete_ms = now_ms; }
+
+  // Returns true when it is safe to read the battery ADC (TX not in progress
+  // and enough time has elapsed since the last transmission for voltage to recover).
+  bool isBattReadSafe(uint32_t now_ms, uint32_t settle_ms = POST_TX_BATT_SETTLE_MS) const {
+    return !_tx_active && (now_ms - _last_tx_complete_ms >= settle_ms);
+  }
+
   virtual uint16_t getBattMilliVolts() = 0;
   virtual float getMCUTemperature() { return NAN; }
   virtual bool setAdcMultiplier(float multiplier) { return false; };

src/helpers/radiolib/RadioLibWrappers.cpp

@@ -151,6 +151,7 @@ uint32_t RadioLibWrapper::getEstAirtimeFor(int len_bytes) {
 }
 
 bool RadioLibWrapper::startSendRaw(const uint8_t* bytes, int len) {
+  _board->notifyTxStart();
   _board->onBeforeTransmit();
   int err = _radio->startTransmit((uint8_t *) bytes, len);
   if (err == RADIOLIB_ERR_NONE) {
@@ -160,6 +161,7 @@ bool RadioLibWrapper::startSendRaw(const uint8_t* bytes, int len) {
   MESH_DEBUG_PRINTLN("RadioLibWrapper: error: startTransmit(%d)", err);
   idle();   // trigger another startRecv()
   _board->onAfterTransmit();
+  _board->notifyTxComplete(millis());
   return false;
 }
 
@@ -175,6 +177,7 @@ bool RadioLibWrapper::isSendComplete() {
 void RadioLibWrapper::onSendFinished() {
   _radio->finishTransmit();
   _board->onAfterTransmit();
+  _board->notifyTxComplete(millis());
   state = STATE_IDLE;
 }