#include <SPI.h>

#include <Ethernet.h>

#include <EthernetUdp.h>

byte mac[] = { 0xDE, 0xAD, 0xBE, 0xEF, 0xFE, 0xED};

unsigned int localPort = 8888;      // local port to listen for UDP packets

IPAddress timeServer(128, 138, 141, 172); // 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

EthernetUDP Udp;

void setup()

{

  Serial.begin(9600);

  if (Ethernet.begin(mac) == 0) {

    Serial.println("Failed to configure Ethernet using DHCP");

    for (;;)

      ;

  }

  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() ) {

    // 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 = " );

    

    const unsigned long seventyYears = 2208988800UL;

    // subtract seventy years:

    unsigned long epoch = secsSince1900 - seventyYears; //количество секунд прошедших с начала эпохи по UTC

    // print Unix time:

    

    int TimeZone = 3600*6; //+6 GMT (for Ekat)

    epoch +=TimeZone; 

    // 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(2000);

}

// send an NTP request to the time server at the given address

unsigned long sendNTPpacket(IPAddress& address)

{

  // 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)

  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;

  // 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

  Udp.write(packetBuffer, NTP_PACKET_SIZE);

  Udp.endPacket();

}