wifi NTP (Network Time Protocol) 校時

Ameba 開發板系列介紹


在 Arduino 官網, 有一個 NTP 校時 的 範例.

https://www.arduino.cc/en/Tutorial/UdpNTPClient

他走的是 UDP protocol.

所以在個人實驗版 1.0.10, 從 ARM mbed 把 UDP porting 進來, 並且設定成 non-blocking mode.

Ref: https://developer.mbed.org/handbook/Socket 





目前這隻校時程式, 是連接到 server 129.6.15.28; // time.nist.gov NTP server,

port 123 是 NTP protocol 定義的校時 port. 

範例程式. : WiFiUdpNtpClient

     ( 雖然我是在 Ameba 上跑, 其他 Arduino 開發板也可使用 )

     可以從 Wifi 範例拉進來. 記得要改 ssid , pass 

             連 沒有密碼的 AP : WiFi.begin(ssid)

             連  有密碼的 AP : WiFi.begin(ssid, pass)

/*
	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 <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 native USB port 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);
	}
	String fv = WiFi.firmwareVersion();
	if (fv != "1.1.0") {
	Serial.println("Please upgrade the firmware");
	}
	// 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("sendNTPPacket");
	// 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");
	}

程式說明. 

    wifi 連線部分請參考其他範例.

    Arduino 有個  WiFiUDP 物件 Udp
WiFiUDP Udp;

   begin localPort , 可以發現在 ARM mbed, 當 client 時, 並不需要  localPort, 可以隨便設一個.
      Udp.begin(localPort);

   sendNTPPacket() - 製作 NTP 格式封包, 並以 UDP 傳送出去

      beginPacket(address, 123) : address 是 NTP server ip, 123 是 port number
      write() : 寫入資料
      endPacket() : 送出  

	// 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");

     parsePacket() 其實她只是看有沒有讀到資料, 並不會真的處理資料
 
Udp.parsePacket()

   
     read() : 把資料讀到 packetBuffer

Udp.read(packetBuffer, NTP_PACKET_SIZE); // read the packet into the buffer

執行結果 : 

時區不大對呀, 下次來接個 GPS 同時換算時區.. 

---
另外有個 NTP pool project : http://www.pool.ntp.org/en/

可以用 pool.ntp.org 來對時.