NTP_server

NTP_server.cpp

IPAddress timeServerIP; // time.nist.gov NTP server address
const char *ntpServerName = "tick.stdtime.gov.tw";// this is one of the NTP server

const int NTP_PACKET_SIZE = 48; 
byte packetBuffer[NTP_PACKET_SIZE];

WiFiUDP udp;

unsigned long sendNTPpacket(IPAddress &address)
{
  Serial.println("sending NTP packet...");
  // 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();
}

void ntpServer(char *NTP)
{
  //get a random server from the pool
  WiFi.hostByName(NTP, timeServerIP); 

  sendNTPpacket(timeServerIP); // send an NTP packet to a time server
  delay(1000);
  
  int alreadyConnected = udp.parsePacket();//return true or false
  if (!alreadyConnected) {
    Serial.println("no packet yet");
  }
  else {
    Serial.print("packet received, length= ");
    Serial.println(alreadyConnected);
    // 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:
    epoch = secsSince1900 - seventyYears;
    // print Unix time:
    Serial.println(epoch);

    // print the hour, minute and second:
    Serial.print("The UTC time is ");
    Serial.print(((epoch % 86400L) / 3600) + 8); //hour (GMT+8)
    Serial.print(':');
    if ( ((epoch % 3600) / 60) < 10 ) {
      Serial.print('0');
    }
    Serial.print((epoch % 3600) / 60);//minute
    Serial.print(':');
    if ( (epoch % 60) < 10 ) {
      Serial.print('0');
    }
    Serial.println(epoch % 60); //second
  }
}