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gps_src/main.cpp

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+#include <TinyGPS++.h>
+#include <time.h>
+
+// Objects for GNSS parsing and serial communication
+TinyGPSPlus gps;
+HardwareSerial GNSSSerial(2);
+
+// Pin definitions for GNSS module communication
+const int GNSS_RXPin = 34;
+const int GNSS_TXPin = 33;
+const int GNSS_RSTPin = 35; // There is a function built for this in the example below-
+                            // currently it isn't used
+const int GNSS_PPS_Pin = 36;
+
+// Flags for PPS handling and synchronization status
+volatile bool ppsFlag = false;
+volatile bool initialSyncDone = false;
+
+// Timestamp for the last valid GNSS data received
+unsigned long lastGNSSDataMillis = 0;
+
+void setup()
+{
+    // Initialize serial communication for debugging
+    USBSerial.begin(115200);
+    while (!USBSerial)
+        ;
+
+    // Start GNSS module communication
+    GNSSSerial.begin(115200, SERIAL_8N1, GNSS_TXPin, GNSS_RXPin);
+    while (!GNSSSerial)
+        ;
+
+    // Configure GNSS reset pin
+    pinMode(GNSS_RSTPin, OUTPUT);
+    digitalWrite(GNSS_RSTPin, HIGH);
+
+    // Set up PPS pin and attach an interrupt handler
+    pinMode(GNSS_PPS_Pin, INPUT);
+    attachInterrupt(digitalPinToInterrupt(GNSS_PPS_Pin), ppsInterrupt, RISING);
+
+    // Short delay for GNSS module initialization
+    delay(1000);
+}
+
+void loop()
+{
+    // Process incoming GNSS data
+    while (GNSSSerial.available())
+    {
+        if (gps.encode(GNSSSerial.read()))
+        {
+            // Update the timestamp when valid GNSS data is received
+            lastGNSSDataMillis = millis();
+            displayGNSSData(); // Display GNSS data for debugging
+        }
+    }
+
+    // Perform initial synchronization using NMEA time data
+    if (!initialSyncDone && gps.date.isValid() && gps.time.isValid())
+    {
+        setSystemTime();
+        initialSyncDone = true;
+        USBSerial.println("Initial time synchronization done using NMEA data.");
+    }
+
+    // Disable interrupts to safely check and reset the PPS flag
+    noInterrupts();
+    if (ppsFlag)
+    {
+        fineTuneSystemTime(); // Adjust system time based on the PPS pulse
+        ppsFlag = false;
+    }
+    // Re-enable interrupts
+    interrupts();
+
+    // Check if GNSS data has been absent for more than a minute
+    if (millis() - lastGNSSDataMillis > 60000)
+    {
+        USBSerial.println("Warning: Haven't received GNSS data for more than 1 minute!");
+        // Additional actions can be added here, like alerts or module resets.
+    }
+}
+
+// Interrupt handler for the PPS signal
+void ppsInterrupt() { ppsFlag = true; }
+
+// Function to set system time using GNSS data
+void setSystemTime()
+{
+    struct tm timeinfo;
+    timeinfo.tm_year = gps.date.year() - 1900;
+    timeinfo.tm_mon = gps.date.month() - 1;
+    timeinfo.tm_mday = gps.date.day();
+    timeinfo.tm_hour = gps.time.hour();
+    timeinfo.tm_min = gps.time.minute();
+    timeinfo.tm_sec = gps.time.second();
+    time_t t = mktime(&timeinfo);
+
+    timeval tv = {t, 0};
+    settimeofday(&tv, NULL); // Update system time
+}
+
+// Function to fine-tune system time using the PPS pulse
+void fineTuneSystemTime()
+{
+    timeval tv;
+    gettimeofday(&tv, NULL);
+    tv.tv_usec = 0;          // Reset microseconds to zero
+    settimeofday(&tv, NULL); // Update system time
+    USBSerial.println("System time fine-tuned using PPS signal.");
+}
+
+// Debugging function to display GNSS data
+void displayGNSSData()
+{
+    USBSerial.print("Latitude: ");
+    USBSerial.println(gps.location.lat(), 6);
+    USBSerial.print("Longitude: ");
+    USBSerial.println(gps.location.lng(), 6);
+    USBSerial.print("Altitude: ");
+    USBSerial.println(gps.altitude.meters());
+    USBSerial.print("Speed: ");
+    USBSerial.println(gps.speed.kmph());
+    USBSerial.println("-----------------------------");
+}