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examples/ntp_demo.ino

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+// change next line to use with another board/shield
+#include <WiFi.h>
+//#include <ESP8266WiFi.h>
+//#include <WiFi.h>
+//#include <WiFi101.h>
+#include <WiFiUdp.h>
+#include "NTPClient.h"
+
+WiFiUDP ntpUDP;
+NTPClient my_time_client(ntpUDP);
+
+void connect_wifi(char * ssid,char * password){
+    Serial.print("wifi connecting...");
+    WiFi.begin(ssid,password);
+    while(WiFi.status()!= WL_CONNECTED){
+        delay(1000);
+        Serial.print(".");
+    }
+    
+    Serial.println("\nwifi connected!");
+    Serial.print("ip: ");
+    Serial.println(WiFi.localIP());
+    Serial.print("netmask: ");
+    Serial.println(WiFi.subnetMask());
+    Serial.print("gateway: ");
+    Serial.println(WiFi.gatewayIP());
+    Serial.print("channel: ");
+    Serial.println(WiFi.channel());
+    Serial.print("auto-reconnect: ");
+    Serial.println(WiFi.getAutoReconnect());
+}
+
+inline void sync_time(){
+    my_time_client.begin();
+    my_time_client.setTimeOffset(28800);
+    my_time_client.setUpdateInterval(20000);
+    //my_time_client.setPoolServerName("0.ubuntu.pool.ntp.org");
+    my_time_client.setPoolServerName("192.168.1.200");
+    //smaller timeout will give you more accuracy 
+    //but also larger possibility to fail 
+    my_time_client.setTimeout(800); 
+    Serial.println("syncing...");
+
+    while(my_time_client.update()!=1){
+        delay(2000);
+        my_time_client.forceUpdate();
+    }
+
+    Serial.print("success: ");
+    Serial.println(my_time_client.getFormattedTime());
+}
+
+void setup(){
+    Serial.begin(230400);
+    Serial.println("serial inited");
+
+    connect_wifi((char *)"ssid",(char *)"pwd");
+    sync_time();
+
+    Serial.println("ready!");
+}
+
+String s_last_time="s_last_time";
+
+void loop(){
+    String s_time=my_time_client.getFormattedTime();
+    if(s_time!=s_last_time){
+        Serial.print("a second passed ");
+        Serial.print(s_time);Serial.print(" ");
+        Serial.print(my_time_client.get_millis(),3);
+        Serial.println("ms");
+        s_last_time=s_time;
+
+        //please do not update too frequently
+        int8_t re=my_time_client.update();
+        if(re==0){
+            Serial.println("0: sync but failed");
+            delay(500);
+        }else if(re==1){
+            Serial.println("1: sync and suc");
+        }else if(re==2){
+            ;//Serial.println("2: not time to sync");
+        }else if(re==3){
+            Serial.println("3: last failed was just happen");
+        }else{
+            Serial.print("return value error: ");
+            Serial.println(re);
+        }
+    }
+
+    //float ms=my_time_client.get_millis();
+    
+    delay(1);
+}