GSM Udp NTP Client

/*

  Udp NTP Client

  Get the time from a Network Time Protocol (NTP) time server

  Demonstrates use of UDP sendPacket and ReceivePacket

  For more on NTP time servers and the messages needed to communicate with them,

  see http://en.wikipedia.org/wiki/Network_Time_Protocol

  created 4 Sep 2010

  by Michael Margolis

  modified 9 Apr 2012

  by Tom Igoe

  modified 6 Dec 2017 ported from WiFi101 to MKRGSM

  by Arturo Guadalupi



  This code is in the public domain.

*/

#include <MKRGSM.h>

#include "arduino_secrets.h"
// Please enter your sensitive data in the Secret tab or arduino_secrets.h
// PIN Number

const char PINNUMBER[]     = SECRET_PINNUMBER;
// APN data

const char GPRS_APN[]      = SECRET_GPRS_APN;

const char GPRS_LOGIN[]    = SECRET_GPRS_LOGIN;

const char GPRS_PASSWORD[] = SECRET_GPRS_PASSWORD;

unsigned int localPort = 2390;      // local port to listen for UDP packets

IPAddress timeServer(129, 6, 15, 28); // time.nist.gov NTP server

const int NTP_PACKET_SIZE = 48; // NTP time stamp is in the first 48 bytes of the message

byte packetBuffer[ NTP_PACKET_SIZE]; //buffer to hold incoming and outgoing packets

// initialize the library instance

GSMClient client;

GPRS gprs;

GSM gsmAccess;

// A UDP instance to let us send and receive packets over UDP

GSMUDP Udp;

void setup()
{

  // Open serial communications and wait for port to open:

  Serial.begin(9600);

  while (!Serial) {

    ; // wait for serial port to connect. Needed for native USB port only

  }

  Serial.println("Starting Arduino GPRS NTP client.");

  // connection state

  bool connected = false;

  // After starting the modem with GSM.begin()

  // attach the shield to the GPRS network with the APN, login and password

  while (!connected) {

    if ((gsmAccess.begin(PINNUMBER) == GSM_READY) &&

        (gprs.attachGPRS(GPRS_APN, GPRS_LOGIN, GPRS_PASSWORD) == GPRS_READY)) {

      connected = true;

    } else {

      Serial.println("Not connected");

      delay(1000);

    }

  }

  Serial.println("\nStarting connection to server...");

  Udp.begin(localPort);
}

void loop()
{

  sendNTPpacket(timeServer); // send an NTP packet to a time server

  // wait to see if a reply is available

  delay(1000);

  if ( Udp.parsePacket() ) {

    Serial.println("packet received");

    // We've received a packet, read the data from it

    Udp.read(packetBuffer, NTP_PACKET_SIZE); // read the packet into the buffer

    //the timestamp starts at byte 40 of the received packet and is four bytes,

    // or two words, long. First, esxtract the two words:

    unsigned long highWord = word(packetBuffer[40], packetBuffer[41]);

    unsigned long lowWord = word(packetBuffer[42], packetBuffer[43]);

    // combine the four bytes (two words) into a long integer

    // this is NTP time (seconds since Jan 1 1900):

    unsigned long secsSince1900 = highWord << 16 | lowWord;

    Serial.print("Seconds since Jan 1 1900 = " );

    Serial.println(secsSince1900);

    // now convert NTP time into everyday time:

    Serial.print("Unix time = ");

    // Unix time starts on Jan 1 1970. In seconds, that's 2208988800:

    const unsigned long seventyYears = 2208988800UL;

    // subtract seventy years:

    unsigned long epoch = secsSince1900 - seventyYears;

    // print Unix time:

    Serial.println(epoch);

    // print the hour, minute and second:

    Serial.print("The UTC time is ");       // UTC is the time at Greenwich Meridian (GMT)

    Serial.print((epoch  % 86400L) / 3600); // print the hour (86400 equals secs per day)

    Serial.print(':');

    if ( ((epoch % 3600) / 60) < 10 ) {

      // In the first 10 minutes of each hour, we'll want a leading '0'

      Serial.print('0');

    }

    Serial.print((epoch  % 3600) / 60); // print the minute (3600 equals secs per minute)

    Serial.print(':');

    if ( (epoch % 60) < 10 ) {

      // In the first 10 seconds of each minute, we'll want a leading '0'

      Serial.print('0');

    }

    Serial.println(epoch % 60); // print the second

  }

  // wait ten seconds before asking for the time again

  delay(10000);
}

// send an NTP request to the time server at the given address
unsigned long sendNTPpacket(IPAddress& address)
{

  //Serial.println("1");

  // set all bytes in the buffer to 0

  memset(packetBuffer, 0, NTP_PACKET_SIZE);

  // Initialize values needed to form NTP request

  // (see URL above for details on the packets)

  //Serial.println("2");

  packetBuffer[0] = 0b11100011;   // LI, Version, Mode

  packetBuffer[1] = 0;     // Stratum, or type of clock

  packetBuffer[2] = 6;     // Polling Interval

  packetBuffer[3] = 0xEC;  // Peer Clock Precision

  // 8 bytes of zero for Root Delay & Root Dispersion

  packetBuffer[12]  = 49;

  packetBuffer[13]  = 0x4E;

  packetBuffer[14]  = 49;

  packetBuffer[15]  = 52;

  //Serial.println("3");

  // all NTP fields have been given values, now

  // you can send a packet requesting a timestamp:

  Udp.beginPacket(address, 123); //NTP requests are to port 123

  //Serial.println("4");

  Udp.write(packetBuffer, NTP_PACKET_SIZE);

  //Serial.println("5");

  Udp.endPacket();

  //Serial.println("6");
}