Added NTP Client example

Author: cmaglie

examples/udp_ntp_client/udp_ntp_client.ino

@@ -0,0 +1,106 @@
+/*
+  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 https://en.wikipedia.org/wiki/Network_Time_Protocol
+
+  Example freely inspired from the Arduino Ethernet library
+  https://github.com/arduino-libraries/Ethernet/blob/master/examples/UdpNtpClient/UdpNtpClient.ino
+  
+  This code is in the public domain.
+*/
+
+#include <Arduino_RouterBridge.h>
+
+unsigned int localPort = 8888;             // local port to listen for UDP packets
+const char timeServer[] = "time.nist.gov"; // time.nist.gov NTP server
+int NTP_PACKET_SIZE = 48;                  // NTP time stamp is in the first 48 bytes of the message
+
+// A UDP instance to let us send and receive packets over UDP
+BridgeUDP<4096> Udp(Bridge);
+
+void setup() {
+  Monitor.begin();
+  Udp.begin(localPort);
+}
+
+void loop() {
+  sendNTPpacket(timeServer); // send an NTP packet to a time server
+
+  // wait one second to see if a reply is available
+  Udp.setTimeout(1000);
+  if (Udp.parsePacket()) {
+    // We've received a packet, read the data from it
+    byte packetBuffer[NTP_PACKET_SIZE];
+    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, extract 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;
+    Monitor.print("Seconds since Jan 1 1900 = ");
+    Monitor.println(secsSince1900);
+
+    // 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:
+    unsigned long epoch = secsSince1900 - seventyYears;
+    Monitor.print("Unix time = ");
+    Monitor.println(epoch);
+
+    // print the hour, minute and second:
+    Monitor.print("The UTC time is ");       // UTC is the time at Greenwich Meridian (GMT)
+    Monitor.print((epoch  % 86400L) / 3600); // print the hour (86400 equals secs per day)
+    Monitor.print(':');
+    if (((epoch % 3600) / 60) < 10) {
+      // In the first 10 minutes of each hour, we'll want a leading '0'
+      Monitor.print('0');
+    }
+    Monitor.print((epoch % 3600) / 60); // print the minute (3600 equals secs per minute)
+    Monitor.print(':');
+    if ((epoch % 60) < 10) {
+      // In the first 10 seconds of each minute, we'll want a leading '0'
+      Monitor.print('0');
+    }
+    Monitor.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
+void sendNTPpacket(const char * address) {
+  byte packetBuffer[NTP_PACKET_SIZE]; // buffer to hold incoming and outgoing packets
+  
+  // 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();
+}
+