A Beginner's Guide to the ESP8266 - NTP part

[DMike92]

Hi, Thank you very much for this so complete tutorial that deals with lot of useful concepts! I fully implement this and have a question about NTP. Somewhere in the code you write:

`if (time) { // If a new timestamp has been received timeUNIX = time; Serial.print("NTP response:\t"); Serial.println(timeUNIX); lastNTPResponse = currentMillis; // <============ } else if ((currentMillis - lastNTPResponse) > 3600000) { Serial.println("More than 1 hour since last NTP response. Rebooting."); Serial.flush(); ESP.reset(); }

uint32_t actualTime = timeUNIX + (currentMillis - lastNTPResponse)/1000; // <======== if (actualTime != prevActualTime && timeUNIX != 0) { // If a second has passed since last print prevActualTime = actualTime; Serial.printf("\rUTC time:\t%d:%d:%d ", getHours(actualTime), getMinutes(actualTime), getSeconds(actualTime)); `

But lastNTPResponse = currentMillis; clearly means that currentMillis - lastNTPResponse will always be 0 when computing actualTime. So, I'm a bit lost. What was your idea?

[tttapa]

unsigned long intervalNTP = 60000; // Request NTP time every minute
unsigned long prevNTP = 0;
unsigned long lastNTPResponse = millis();
uint32_t timeUNIX = 0;

unsigned long prevActualTime = 0;

void loop() {
  unsigned long currentMillis = millis();

  if (currentMillis - prevNTP > intervalNTP) { // If a minute has passed since last NTP request
    prevNTP = currentMillis;
    Serial.println("\r\nSending NTP request ...");
    sendNTPpacket(timeServerIP);               // Send an NTP request
  }

  uint32_t time = getTime();                   // Check if an NTP response has arrived and get the (UNIX) time
  if (time) {                                  // If a new timestamp has been received
    timeUNIX = time;
    Serial.print("NTP response:\t");
    Serial.println(timeUNIX);
    lastNTPResponse = currentMillis;
  } else if ((currentMillis - lastNTPResponse) > 3600000) {
    Serial.println("More than 1 hour since last NTP response. Rebooting.");
    Serial.flush();
    ESP.reset();
  }

  uint32_t actualTime = timeUNIX + (currentMillis - lastNTPResponse)/1000;
  if (actualTime != prevActualTime && timeUNIX != 0) { // If a second has passed since last print
    prevActualTime = actualTime;
    Serial.printf("\rUTC time:\t%d:%d:%d   ", getHours(actualTime), getMinutes(actualTime), getSeconds(actualTime));
  }  
}

lastNTPResponse is only set to currentMillis if there is a response from the NTP server (i.e. if time != 0). currentMillis is updated every time the loop updates.

So when there are no responses from the NTP server, lastNTPResponse is never updated, but currentMillis keeps on growing. The difference between the two is therefore only zero when a new NTP response has been received.

[DMike92]

I see, Thanks :-) (Sorry for mistyping and closing)

[DMike92]

Better later than never...