Additional GNSS IO shutdown to save battery power during shipping mode

src/tracker.cpp

@@ -168,6 +168,15 @@ void Tracker::enableIoCanPower(bool enable)
     digitalWrite(MCP_CAN_PWR_EN_PIN, (_canPowerEnabled = enable) ? HIGH : LOW);
 }
 
+void Tracker::forceShutdownGnss()
+{
+    // Forceably shutdown the GNSS module
+    digitalWrite(UBLOX_RESETN_PIN, LOW);
+    delay(100);
+    digitalWrite(UBLOX_RESETN_PIN, HIGH);
+    digitalWrite(UBLOX_PWR_EN_PIN, LOW);
+}
+
 int Tracker::initEsp32()
 {
     // ESP32 related GPIO
@@ -640,7 +649,7 @@ int Tracker::init()
 
     shipping.init();
     shipping.regShutdownBeginCallback(std::bind(&Tracker::stop, this));
-    shipping.regShutdownIoCallback(std::bind(&Tracker::end, this));
+    shipping.regShutdownIoCallback(std::bind(&Tracker::shutdown, this));
     shipping.regShutdownFinalCallback(
         [this](){
             enableWatchdog(false);
@@ -752,6 +761,12 @@ int Tracker::end() {
     return SYSTEM_ERROR_NONE;
 }
 
+int Tracker::shutdown() {
+    end();
+    forceShutdownGnss();
+    return SYSTEM_ERROR_NONE;
+}
+
 int Tracker::reset() {
     stop();
     end();

src/tracker.h

@@ -314,12 +314,19 @@ class Tracker {
         int stop();
 
         /**
-         * @brief Prepare tracker IO and peripherals for shutdown
+         * @brief Prepare tracker IO and peripherals for low power
          *
          * @retval SYSTEM_ERROR_NONE
          */
         int end();
 
+        /**
+         * @brief Prepare tracker IO and peripherals for shutdown
+         *
+         * @retval SYSTEM_ERROR_NONE
+         */
+        int shutdown();
+
         /**
          * @brief Prepare tracker for reset and issue
          *
@@ -388,6 +395,12 @@ class Tracker {
          */
         void enableIoCanPower(bool enable);
 
+        /**
+         * @brief Force the GNSS module into low power state
+         *
+         */
+        void forceShutdownGnss();
+
         /**
          * @brief Indicates whether device can accept commands through USB interface
          *