How to make use of ESP32 internal RTC to setup Epoch time?

As mentioned in the datasheet of ESP32, I was trying to make use of the internal RTC. But not able to find any example or APIs related to it. Is there any way to access the RTC?

[lbernstone]

The default timer system uses both the RTC and the APB timers to track the internal time. It is possible to force the system to use only the RTC for time keeping (config). This requires recompiling the libraries, but I am not even sure arduino would function if you did so.
Why don't you explain what you would like to achieve by doing so? Perhaps just this?

[chegewara]

setTime(epoch)
epoch = now()

[everslick]

maybe a misunderstanding? RTC != real time clock like DS3231 !!!

[chegewara]

This is code i am using to get time from NTP and set local time (internal RTC) and DS1307:

const char* ntpServer = "pool.ntp.org";
  const long  gmtOffset_sec = 3600;
  const int   daylightOffset_sec = 3600;

  // get NTP time every time connect to wifi, not necessary but wont hurts
  configTime(gmtOffset_sec, daylightOffset_sec, ntpServer);
  struct tm timeinfo;

  if (getLocalTime(&timeinfo)) {
    timeAdjusted = true;
    setTime(timeinfo.tm_hour, timeinfo.tm_min, timeinfo.tm_sec,
            timeinfo.tm_mday, timeinfo.tm_mon+1,timeinfo.tm_year - 100); // <--- set internal RTC

    RTC.set(now()); // <--- read internal RTC (epoch) with now() and set DS1307
  }

[a-c-sreedhar-reddy]

Hi @chegewara. can you try this

if (getLocalTime(&timeinfo)) {
    timeAdjusted = true;
    time_t now;
    time(&now);
    RTC.set(now); // <--- read internal RTC (epoch) with now() and set DS1307
  }

Got it from #935 (comment)

I have seen in the library, the now() function actually runs millis() to increment count. Using the time.h library and now() function, I kept my ESP 32 over night after once getting EPOCH from NTP server. After getting the EPOCH once I turned the wifi off and in the morning after about 12 hrs, I found that the time has actually elapsed by 30 minutes. So what I can see now is there is no such internal RTC which works like an external RTC(like DS3231 !!!) generally which runs on battery, as said by "everslick".

[a-c-sreedhar-reddy]

What I do is update for every 10 loops. I am not sure whats the correct way to fix this.

[lbernstone]

As I mentioned, the time keeping is based on the APB clock. This, in turn, is based on an external oscillator. I think the ones used by espressif are probably +-1%, which is 864 seconds over a day. If you want accuracy, use a purpose built ASIC. The device was built around network connectivity, and it is simple to sync your time over the network.

[chegewara]

Hi @chegewara. can you try this

if (getLocalTime(&timeinfo)) {
    timeAdjusted = true;
    time_t now;
    time(&now);
    RTC.set(now); // <--- read internal RTC (epoch) with now() and set DS1307
  }

Got it from #935 (comment)

I dont have issues with my code, it works exactly as intended. It was exaampple to show how to use internal RTC with now() to get epoch and how to set internal RTC with NTP call.

[chegewara]

@Gopal123456789 You asked how to use internal RTC, you got the answer. Now about accuracy:
https://www.esp32.com/viewtopic.php?t=3715#p17038

[stickbreaker]

@Gopal123456789 The RTC need an external 32.768KHz crystal.
ESP32 Hardware doc

Chuck.

Thank you all of you for your help.
@chegewara, Can you please tell me which library do you use for the example code you have given, for the below lines? Or give a link to the library?

setTime(timeinfo.tm_hour, timeinfo.tm_min, timeinfo.tm_sec,
timeinfo.tm_mday, timeinfo.tm_mon+1,timeinfo.tm_year - 100); // <--- set internal RTC

RTC.set(now()); // <--- read internal RTC (epoch) with now() and set DS1307

[chegewara]

https://github.com/PaulStoffregen/Time
https://github.com/PaulStoffregen/DS1307RTC.git

PS in Time library is Time.h header file, which is causing conflict on esp32, i had to rename it

Thank you chegewara.

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