time.c and sntp.c doubt

[David8266]

Hi,
I am compiling a code on my ESP-12E to handle the heating of my house.
A fundamental variable is time.
I used the time.c function to get the time from NTP servers, as shown in the code below, and everything works properly. Every second the correct time and date is printed.
But I have a doubt about the method with which the time is maintained, and looking at the code contained in the library I honestly could not make it clear.
In practice I would like to know if every time the time parameter is requested it is always read by the ntp servers, or if there is an internal timer/ counter that add 1 seconds each time, leaving the update with the servers only when the ConfigTime function is called.
Thanks in advance for your answers.

MCVE Sketch

#include <time.h>
#include <ESP8266WiFi.h>

unsigned int timezone = 1;
unsigned int dst = 1;

void setup() {

  Serial.begin(115200);

    while (WiFi.status() != WL_CONNECTED) {
    delay(500);
    Serial.print(".");
  }

  configTime(timezone * 3600, dst * 3600, "1.it.pool.ntp.org", "2.it.pool.ntp.org", "3.it.pool.ntp.org");

  while (!time(nullptr)) {
    Serial.print(".");
    delay(1000);
  }
  
}

void loop() {
  
  time_t now = time(nullptr);
  Serial.println(ctime(&now));
  delay(1000);
}

[electrical-pro]

In practice I would like to know if every time the time parameter is requested it is always read by the ntp servers, or if there is an internal timer/ counter that add 1 seconds each time, leaving the update with the servers only when the ConfigTime function is called.

Hi, Just turn your router off (or disconnect internet cable) and test it yourself.
(tell the result, I also want to know)

[David8266]

Yes I tried and it continues to work properly.
But looking in time library seems that there is an if condition that discriminate if ntp servers are available or not, and in this case continue to manually increase the time variable.
But I'm not so expert to read that code... for this reason I prefer to ask someone.

[5chufti]

depends on which lwip version you use.
in general the first sync is done with dhcp answer and following updates are done periodically.
you can read up on that topic in #1679 and issues referenced by/within this issue

but: you being curious about the inner workings is not an issue with esp arduino core ... please close this issue as it does not confirm to the strict rules that you intentionally ignored when opening and deleting the questionair.

[d-a-v]

Once sntp is started (which is automatic with lwip2/STA and a dhcp server providing an NTP server address), NTP server is requested at start then every hour from inside lwIP/sntp.
Offline or not, Time is always "manually" updated, and synced when NTP data are received.

[David8266]

I'm sorry for the improper thread.
However I thank you very much for the help.
I understood the function, but just one last question. Is it possible to change the ntp update interval?

[electrical-pro]

@David8266
As far as I understand by default it updates every hour.
You can change with this :
#define SNTP_UPDATE_DELAY 3600000
look here: https://github.com/esp8266/Arduino/blob/ae13809c8184300aab9e3f09ef23af23d936b7ee/tools/sdk/lwip/src/core/sntp.c
(I am also not an expert, but I think it is correct way)

[d-a-v]

This delay is defined by SNTP_UPDATE_DELAY.
It is currently not defined in our lwIP options, so it defaults to 3600000 (ms).
If you need to change it,

• add your #define in tools/sdk/lwip/include/lwipopts.h for lwIP-v1.4
  then use the lwIP variant "v1.4 compile from sources"
• add it in ./tools/sdk/lwip2/builder/glue-lwip/arduino/lwipopts.h for lwip-v2
  then recompile lwip2 with make install in tools/sdk/lwip2

[devyte]

This is not an issue. Closing.