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I'm trying to create a sensor sampling project using ESP32 ( battery, solar panel and temperature affects are not part of test right now to reduce external effects that may cause/ increase such behaviour ).

In current phase, I'm only testing the sleep & waking up process.

A short description: System wakes up after deep sleep cycle, connects to Wifi, MQTT, NTP - and checks if wake up time ( wake up value is stored in ׳RTC_DATA_ATTR long calc_waketime׳ variable from previous cycle ), posting IFTTT, goes to deep sleep for another 10 min. cycle.

The phenomena I wish to share is: The longer deep sleep is the NTP has few seconds drift which gets longer (again - NTP sync has a drift and not RTC clock).

I'm aware that wake time/ RTC drifts during deep sleep ( especially in ESP8266 chips that wake up can be not accurate in terms of minute - I'm using ESP32). Since ESP32 uses RTC, waking up is very accurate ( matter of seconds ). In order to wake up in exact time ( 18:00, 18:10, 18:20... every hour ) code connects to Wifi& NTP, and verify that wake time was as intended (comparing the epoch value that was stored during the end of previous cycle and current epoch time ) if it woke up earlier, it will got to sleep for that missing time.

But - What puzzles me is why updated NTP time ( which is not related what so ever to RTC drifts ), is drifted the longer to sleep is ( for comparison : when less than a minute - almost no drift, when sleeping for 10 minutes, 3 seconds drift, 20 minutes get up to 5 seconds drifts ).

Please see NOTE(1) to witness the drift in 10 min sleep.

Posting terminal output: some explantions: NOTE (1) displays the 3 seconds drift , NOTE(2) calculated time that was stored at previous wake cycle, NOTE (3) shows that that drift get synced during the code run - 594 sec for next wake 18:50:00.

18:39:58.032 -> 09B⸮⸮L⸮1U1V(⸮⸮⸮1m1m1F⸮Connecting to Xiaomi_D6C8 .... // WAKING UP 18:39:58.595 -> 192.168.3.186 18:39:59.013 -> now is: 1580575203 **// NOTE (1)** 18:39:59.013 -> sleep time was: 1580574611 18:39:59.048 -> expected wake time: 1580575200 // NOTE (2) 18:39:59.085 -> total time delta: 3 18:39:59.122 -> OK - WOKE UP after due time: 18:39:59.419 -> Attempting MQTT connection...connected 18:40:04.544 -> Connecting to maker.ifttt.com 18:40:04.855 -> Request resource: /trigger/send_reading/with/key/cFLymB4JT9tlODsKLFn9TA 18:40:05.376 -> HTTP/1.1 200 OK 18:40:05.376 -> Date: Sat, 01 Feb 2020 16:40:05 GMT 18:40:05.414 -> Content-Type: text/html; charset=utf-8 18:40:05.447 -> Content-Length: 52 18:40:05.480 -> Connection: close 18:40:05.515 -> X-Top-SecreTTT: VG9vIGVhc3k/IElmIHlvdSBjYW4gcmVhZCB0aGlzLCBFbWFpbCB1cyBhdCBqb2JzK3NlY3JldEBpZnR0dC5jb20uIFdlIHdhbnQgTWFrZXJzLg== 18:40:05.619 -> Server: web_server 18:40:05.619 -> 18:40:05.619 -> Congratulations! You've fired the send_reading event 18:40:05.689 -> closing connection 18:40:07.007 -> Last Sleep: 1580574611 18:40:07.007 -> Time left: 594 // NOTE (3) 18:40:07.041 -> Going to DeepSleep for [594] sec

Relevant code:

void sleepNOW(int sec2sleep = 2700) { char tmsg[30]; sprintf(tmsg, "Going to DeepSleep for [%d] sec", sec2sleep); Serial.println(tmsg); // mqtt_pubmsg(tmsg); Serial.flush(); esp_sleep_enable_timer_wakeup(sec2sleep * uS_TO_S_FACTOR); esp_deep_sleep_start(); } bool getTime() { delay(200); if (getLocalTime(&timeinfo)) { time(&now1); delay(200); return 1; } else { return 0; } } bool check_awake_ontime() { getTime(); if (timeinfo.tm_year >= 120) // year 2020 { if (lastsleeptime != 0) { // not first boot long current_boottime = now1; int t_delta = now1 - calc_waketime; // int t_delta1 = TIME_TO_SLEEP * 60 - (t_delta + TIME_AWAKE); Serial.print("now is: "); Serial.println(now1); Serial.print("sleep time was: "); Serial.println(lastsleeptime); Serial.print("expected wake time: "); Serial.println(calc_waketime); Serial.print("total time delta: "); Serial.println(t_delta); if (t_delta >= 0) { Serial.println("OK - WOKE UP after due time: "); return 1; } else { Serial.println("FAIL- woke up before time: "); sleepNOW(-1 * t_delta); return 0; } } else { return 1; } } else { return 0; } }

inside setup()

#if USE_WIFI if (startWifi()) { mqttConnect(); startNTP(); #if USE_SLEEP check_awake_ontime(); // PLEASE PAY ATTN ONLY THIS LINE #endif }

inside loop()

#if USE_SLEEP if (millis() >= TIME_AWAKE * 1000) { getTime(); Serial.print("Last Sleep: "); Serial.println(lastsleeptime); long clockCount = TIME_TO_SLEEP * 60 - (timeinfo.tm_min * 60 + timeinfo.tm_sec) % (TIME_TO_SLEEP * 60); // Serial.print(timeinfo.tm_hour); // Serial.print(":"); // Serial.print(timeinfo.tm_min); // Serial.print(":"); // Serial.print(timeinfo.tm_sec); // Serial.println(""); Serial.print("Time left: "); Serial.println(clockCount); lastsleeptime = now1; calc_waketime = now1 + clockCount; sleepNOW(clockCount); }

I'm not posting entire code, but only relevant parts. Appreciate any help,

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  • 1
    the NTP only sets the RTC. and NTP is not immediate Commented Feb 1, 2020 at 17:49
  • @Juraj would you recommend a delay ? since getTime() has 2 delays of 200 mili's Commented Feb 1, 2020 at 17:50
  • 1
    5 seconds is usually enough. you can do a trick. reset the RTC time to 0 and then you can check if it is set by NTP already Commented Feb 1, 2020 at 17:52
  • @Juraj can you please explain how? Commented Feb 1, 2020 at 18:03
  • 1
    sorry, I forgot that there is no API for setting the RTC time on esp32. arduino.stackexchange.com/questions/72010/… Commented Feb 1, 2020 at 18:15

1 Answer 1

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As Juraj commented, a 2.5 [sec] delay, solved it, and NTP update was correct.

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  • It's OK to accept your own answer as the solution to the problem. Commented Mar 16, 2020 at 17:03

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