Added Wifi NTP client example

Author: cmaglie

libraries/WiFi/examples/WiFiUdpNtpClient/WiFiUdpNtpClient.ino

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+/*
+
+ 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
+ 
+ This code is in the public domain.
+ 
+ */
+
+#include <SPI.h>         
+#include <WiFi.h>
+#include <WiFiUdp.h>
+
+int status = WL_IDLE_STATUS;
+char ssid[] = "mynetwork";  //  your network SSID (name)
+char pass[] = "mypassword";       // your network password
+int keyIndex = 0;            // your network key Index number (needed only for WEP)
+
+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 
+
+// A UDP instance to let us send and receive packets over UDP
+WiFiUDP 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 Leonardo only
+  }
+
+  // check for the presence of the shield:
+  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);
+  }
+
+  Serial.println("Connected to wifi");
+  printWifiStatus();
+
+  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);  
+  Serial.println( Udp.parsePacket() );
+  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");
+}
+
+
+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");
+}
+
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