WiFi_RTC.ino

/*
  MKR1000 WiFi RTC

  This sketch asks NTP for the Linux epoch and sets the internal Arduino MKR1000's RTC accordingly.

  created 08 Jan 2016
  by Arturo Guadalupi <a.guadalupi@arduino.cc>

  http://arduino.cc/en/Tutorial/WiFiRTC
  This code is in the public domain.
*/

#include <SPI.h>
#include <WiFi101.h>
#include <WiFiUdp.h>
#include <RTCZero.h>

RTCZero rtc;

char ssid[] = "SSID";     //  your network SSID (name)
char pass[] = "key";   // your network password
int keyIndex = 0;            // your network key Index number (needed only for WEP)

int status = WL_IDLE_STATUS;

// Used for NTP
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
WiFiUDP Udp; // A UDP instance to let us send and receive packets over UDP

const int GMT = 1; //change this to adapt it to your time zone

void setup() {
  Serial.begin(9600);

  // check if the WiFi module works
  if (WiFi.status() == WL_NO_SHIELD) {
    Serial.println("WiFi shield not present");
    // don't continue:
    while (true);
  }

  // attempt to connect to WiFi network:
  while ( status != WL_CONNECTED) {
    Serial.print("Attempting to connect to SSID: ");
    Serial.println(ssid);
    // Connect to WPA/WPA2 network. Change this line if using open or WEP network:
    status = WiFi.begin(ssid, pass);

    // wait 10 seconds for connection:
    delay(10000);
  }

  // you're connected now, so print out the status:
  printWifiStatus();

  rtc.begin();

  unsigned long epoch;
  int numberOfTries = 0, maxTries = 6;
  do {
    epoch = readLinuxEpochUsingNTP();
    numberOfTries++;
  }
  while ((epoch == 0) || (numberOfTries > maxTries));

  if (numberOfTries > maxTries) {
    Serial.print("NTP unreachable!!");
    while (1);
  }
  else {
    Serial.print("Epoch received: ");
    Serial.println(epoch);
    rtc.setEpoch(epoch);

    Serial.println();
  }
}

void loop() {
  printDate();
  printTime();
  Serial.println();
  delay(1000);
}

unsigned long readLinuxEpochUsingNTP()
{
  Udp.begin(localPort);
  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("NTP time 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;

    // now convert NTP time into everyday time:
    // Unix time starts on Jan 1 1970. In seconds, that's 2208988800:
    const unsigned long seventyYears = 2208988800UL;
    // subtract seventy years:

    Udp.stop();
    return (secsSince1900 - seventyYears);
  }

  else {
    Udp.stop();
    return 0;
  }
}

void printTime()
{
  print2digits(rtc.getHours());
  Serial.print(":");
  print2digits(rtc.getMinutes());
  Serial.print(":");
  print2digits(rtc.getSeconds());
  Serial.println();
}

void printDate()
{
  Serial.print(rtc.getDay());
  Serial.print("/");
  Serial.print(rtc.getMonth());
  Serial.print("/");
  Serial.print(rtc.getYear());

  Serial.print(" ");
}

// 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();
}

void printWifiStatus() {
  // print the SSID of the network you're attached to:
  Serial.print("SSID: ");
  Serial.println(WiFi.SSID());

  // print your WiFi shield's IP address:
  IPAddress ip = WiFi.localIP();
  Serial.print("IP Address: ");
  Serial.println(ip);

  // print the received signal strength:
  long rssi = WiFi.RSSI();
  Serial.print("signal strength (RSSI):");
  Serial.print(rssi);
  Serial.println(" dBm");
}

void print2digits(int number) {
  if (number < 10) {
    Serial.print("0");
  }
  Serial.print(number);
}