Track when sentence received

Improve the time information by tracking from when a sentence is received, rather than when it is parsed. Track last valid Date, Time, and Fix separately.

Adafruit_GPS.cpp

@@ -103,7 +103,7 @@ boolean Adafruit_GPS::parse(char *nmea) {
       fixquality = atoi(p);
       if(fixquality > 0){
         fix = true; 
-        lastFix = millis();
+        lastFix = recvdTime;
       } else
         fix = false;
     }
@@ -178,6 +178,7 @@ boolean Adafruit_GPS::parse(char *nmea) {
       day = fulldate / 10000;
       month = (fulldate % 10000) / 100;
       year = (fulldate % 100);
+      lastDate = recvdTime;
     }
     return true;
   }
@@ -226,6 +227,7 @@ void Adafruit_GPS::parseTime(char *p) {
     seconds = (time % 100);
 
     milliseconds = fmod(timef, 1.0) * 1000;
+    lastTime = recvdTime;
 }
 
 /**************************************************************************/
@@ -332,7 +334,7 @@ boolean Adafruit_GPS::parseLonDir(char *p) {
 boolean Adafruit_GPS::parseFix(char *p) {
     if (p[0] == 'A'){
       fix = true;
-      lastFix = millis();
+      lastFix = recvdTime;
       }
     else if (p[0] == 'V')
       fix = false;
@@ -343,15 +345,37 @@ boolean Adafruit_GPS::parseFix(char *p) {
 
 /**************************************************************************/
 /*!
-    @brief Time in seconds since the last fix was obtained. Will fail by 
+    @brief Time in seconds since the last position fix was obtained. Will 
-    rolling over to zero after one millis() cycle, about 6-1/2 weeks.
+    fail by rolling over to zero after one millis() cycle, about 6-1/2 weeks.
     @return float value in seconds since last fix.
 */
 /**************************************************************************/
-float Adafruit_GPS::timeSinceFix() {
+float Adafruit_GPS::secondsSinceFix() {
     return (millis()-lastFix) / 1000.;
 }
 
+/**************************************************************************/
+/*!
+    @brief Time in seconds since the last GPS time was obtained. Will fail 
+    by rolling over to zero after one millis() cycle, about 6-1/2 weeks.
+    @return float value in seconds since last GPS time.
+*/
+/**************************************************************************/
+float Adafruit_GPS::secondsSinceTime() {
+    return (millis()-lastTime) / 1000.;
+}
+
+/**************************************************************************/
+/*!
+    @brief Time in seconds since the last GPS date was obtained. Will fail 
+    by rolling over to zero after one millis() cycle, about 6-1/2 weeks.
+    @return float value in seconds since last GPS date.
+*/
+/**************************************************************************/
+float Adafruit_GPS::secondsSinceDate() {
+    return (millis()-lastDate) / 1000.;
+}
+
 /**************************************************************************/
 /*!
     @brief Read one character from the GPS device
@@ -400,6 +424,7 @@ char Adafruit_GPS::read(void) {
     //Serial.println("----");
     lineidx = 0;
     recvdflag = true;
+    recvdTime = millis();	// time we got the end of the string
   }
 
   return c;

Adafruit_GPS.h

@@ -119,7 +119,9 @@ class Adafruit_GPS {
 
   char read(void);
   boolean parse(char *);
-  float timeSinceFix();
+  float secondsSinceFix();
+  float secondsSinceTime();
+  float secondsSinceDate();
 
   boolean wakeup(void);
   boolean standby(void);
@@ -179,7 +181,12 @@ class Adafruit_GPS {
   void parseLon(char *);
   boolean parseLonDir(char *);
   boolean parseFix(char *);
-  time_t lastFix;
+  // Make all of these times far in the past by setting them near the middle of the 
+  // millis() range. Timing assumes that sentences are parsed promptly. 
+  time_t lastFix = 2000000000L;		// millis() when last fix received
+  time_t lastTime = 2000000000L;    // millis() when last time received
+  time_t lastDate = 2000000000L;    // millis() when last date received
+  time_t recvdTime = 2000000000L;   // millis() when last full sentence received
   boolean paused;
 
   uint8_t parseResponse(char *response);

examples/GPS_HardwareSerial_Timing/GPS_HardwareSerial_Timing.ino

@@ -0,0 +1,136 @@
+// Test code for Ultimate GPS Using Hardware Serial (e.g. GPS Flora or FeatherWing)
+//
+// This code is similar to GPS_HardwareSerial_Parsing, except for the additional 
+// elements to keep track of how long it has been since time and fix data have been 
+// received. This approach lets you keep an up to date clock based on GPS time at 
+// any time in between GPS fixes.
+//
+// This code shows how to listen to the GPS module via polling. Best used with
+// Feathers or Flora where you have hardware Serial and no interrupt
+//
+// Tested and works great with the Adafruit GPS FeatherWing
+// ------> https://www.adafruit.com/products/3133
+// or Flora GPS
+// ------> https://www.adafruit.com/products/1059
+// but also works with the shield, breakout
+// ------> https://www.adafruit.com/products/1272
+// ------> https://www.adafruit.com/products/746
+//
+// Pick one up today at the Adafruit electronics shop
+// and help support open source hardware & software! -ada
+
+#include <Adafruit_GPS.h>
+
+// what's the name of the hardware serial port?
+#define GPSSerial Serial1
+
+// Connect to the GPS on the hardware port
+Adafruit_GPS GPS(&GPSSerial);
+
+// Set GPSECHO to 'false' to turn off echoing the GPS data to the Serial console
+// Set to 'true' if you want to debug and listen to the raw GPS sentences
+#define GPSECHO true
+
+uint32_t timer = millis();
+
+
+void setup()
+{
+  //while (!Serial);  // uncomment to have the sketch wait until Serial is ready
+
+  // connect at 115200 so we can read the GPS fast enough and echo without dropping chars
+  // also spit it out
+  Serial.begin(115200);
+  Serial.println("Adafruit GPS library basic test!");
+
+  // 9600 NMEA is the default baud rate for Adafruit MTK GPS's- some use 4800
+  GPS.begin(9600);
+  // uncomment this line to turn on RMC (recommended minimum) and GGA (fix data) including altitude
+  GPS.sendCommand(PMTK_SET_NMEA_OUTPUT_RMCGGA);
+  // uncomment this line to turn on only the "minimum recommended" data
+  //GPS.sendCommand(PMTK_SET_NMEA_OUTPUT_RMCONLY);
+  // For parsing data, we don't suggest using anything but either RMC only or RMC+GGA since
+  // the parser doesn't care about other sentences at this time
+  // Set the update rate (uncomment the one you want.)
+  //GPS.sendCommand(PMTK_SET_NMEA_UPDATE_1HZ); // 1 Hz update rate
+  //GPS.sendCommand(PMTK_SET_NMEA_UPDATE_200_MILLIHERTZ); // 5 second update time
+  GPS.sendCommand(PMTK_SET_NMEA_UPDATE_100_MILLIHERTZ); // 10 second update time
+  // For the parsing code to work nicely and have time to sort thru the data, and
+  // print it out we don't suggest using anything higher than 1 Hz
+
+  // Request updates on antenna status, comment out to keep quiet
+  GPS.sendCommand(PGCMD_ANTENNA);
+
+  delay(1000);
+
+  // Ask for firmware version
+  GPSSerial.println(PMTK_Q_RELEASE);
+}
+
+void loop() // run over and over again
+{
+  // read data from the GPS in the 'main loop'
+  char c = GPS.read();
+  // if you want to debug, this is a good time to do it!
+  if (GPSECHO)
+    if (c) Serial.print(c);
+  // if a sentence is received, we can check the checksum, parse it...
+  if (GPS.newNMEAreceived()) {
+    // a tricky thing here is if we print the NMEA sentence, or data
+    // we end up not listening and catching other sentences!
+    // so be very wary if using OUTPUT_ALLDATA and trytng to print out data
+    //Serial.println(GPS.lastNMEA()); // this also sets the newNMEAreceived() flag to false
+    if (!GPS.parse(GPS.lastNMEA())) // this also sets the newNMEAreceived() flag to false
+      return; // we can fail to parse a sentence in which case we should just wait for another
+  }
+  // if millis() or timer wraps around, we'll just reset it
+  if (timer > millis()) timer = millis();
+
+  // approximately every 2 seconds or so, random intervals, print out the current stats
+  static unsigned nextInterval = 2000;
+  if (millis() - timer > nextInterval) {
+    timer = millis(); // reset the timer
+    nextInterval = 1500 + random(1000);
+    // Time in seconds keeps increasing after we get the NMEA sentence.
+    // This estimate will lag real time due to transmission and parsing delays,
+    // but the lag should be small and should also be consistent.
+    float s = GPS.seconds + GPS.milliseconds/1000. + GPS.secondsSinceTime(); 
+    int m = GPS.minute;
+    int h = GPS.hour;
+    int d = GPS.day;
+    // Adjust time and day forward to account for elapsed time.
+    // This will break at month boundaries!!! Humans will have to cope with April 31,32 etc.
+    while(s > 60){ s -= 60; m++; }    
+    while(m > 60){ m -= 60; h++; }
+    while(h > 24){ h -= 24; d++; }
+    // ISO Standard Date Format, with leading zeros https://xkcd.com/1179/ 
+    Serial.print("\nDate: ");  
+    Serial.print(GPS.year+2000, DEC); Serial.print("-");
+    if(GPS.month < 10) Serial.print("0");
+    Serial.print(GPS.month, DEC); Serial.print("-");
+    if(d < 10) Serial.print("0");
+    Serial.print(d, DEC);
+    Serial.print("   Time: ");
+    if(h < 10) Serial.print("0");
+    Serial.print(h, DEC); Serial.print(':');
+    if(m < 10) Serial.print("0");
+    Serial.print(m, DEC); Serial.print(':');
+    if(s < 10) Serial.print("0");
+    Serial.println(s, 3);
+    Serial.print("Fix: "); Serial.print((int)GPS.fix);
+    Serial.print(" quality: "); Serial.println((int)GPS.fixquality);
+    Serial.print("Times [s] since last fix: "); Serial.print(GPS.secondsSinceFix(),3); 
+    Serial.print(",  GPS time: "); Serial.print(GPS.secondsSinceTime(),3); 
+    Serial.print(",  GPS date: "); Serial.println(GPS.secondsSinceDate(),3); 
+    if (GPS.fix) {
+      Serial.print("Location: ");
+      Serial.print(GPS.latitude, 4); Serial.print(GPS.lat);
+      Serial.print(", ");
+      Serial.print(GPS.longitude, 4); Serial.println(GPS.lon);
+      Serial.print("Speed (knots): "); Serial.println(GPS.speed);
+      Serial.print("Angle: "); Serial.println(GPS.angle);
+      Serial.print("Altitude: "); Serial.println(GPS.altitude);
+      Serial.print("Satellites: "); Serial.println((int)GPS.satellites);
+    }
+  }
+}