arduino-esp32/libraries/WiFi/examples/NTPClient/NTPClient.ino

/*

 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
 updated for the ESP8266 12 Apr 2015
 by Ivan Grokhotkov

 This code is in the public domain.

 */

#include <WiFi.h>
#include <WiFiUdp.h>

char ssid[] = "*************";  //  your network SSID (name)
char pass[] = "********";       // your network password


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

/* Don't hardwire the IP address or we won't get the benefits of the pool.
 *  Lookup the IP address for the host name instead */
//IPAddress timeServer(129, 6, 15, 28); // time.nist.gov NTP server
IPAddress timeServerIP; // time.nist.gov NTP server address
const char* ntpServerName = "time.nist.gov";

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

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

void setup()
{
    Serial.begin(115200);
    Serial.println();
    Serial.println();

    // We start by connecting to a WiFi network
    Serial.print("Connecting to ");
    Serial.println(ssid);
    WiFi.begin(ssid, pass);

    while (WiFi.status() != WL_CONNECTED) {
        delay(500);
        Serial.print(".");
    }
    Serial.println("");

    Serial.println("WiFi connected");
    Serial.println("IP address: ");
    Serial.println(WiFi.localIP());

    Serial.println("Starting UDP");
    udp.begin(localPort);
    Serial.print("Local port: ");
    Serial.println(udp.localPort());
}

void loop()
{
    //get a random server from the pool
    WiFi.hostByName(ntpServerName, timeServerIP);

    sendNTPpacket(timeServerIP); // send an NTP packet to a time server
    // wait to see if a reply is available
    delay(1000);

    int cb = udp.parsePacket();
    if (!cb) {
        Serial.println("no packet yet");
    } else {
        Serial.print("packet received, length=");
        Serial.println(cb);
        // 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("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();
}