ESP32 Light sleep and time accuracy

[eugeniusz.gienek]

I am trying to make power saving for my ESP32 smart watch based on ESP32 - Lillygo TTGo 1.54 e-ink. The idea is that it shows the time, then goes to light sleep for almost a minute, gets back from sleep and draws new time. The problem is the time accuracy - for some reason when I am using this approach (without light sleep no issues with time btw) the time shifts forwards - about a minute every couple of hours. Btw I have limited the cpu frequency to 10 MHz - don't know if that can somehow affect the end result. Any ideas how to fix the time inaccuracy? I've seen the similar post about that but with deep sleep (without resolution) - this one is related to light sleep and I leave the XTAL oscillator on - that doesn't help for some reason...

The sleep function looks like that:

Code: [Select all] [Expand/Collapse]

1. void lightSleep(int tm) {
2.   bool is_in_light_sleep=false;
3.   if(tm <= 0) tm = DEFAULT_LIGHT_SLEEP_TIME_S * uS_TO_S_FACTOR;
4.   else tm *= uS_TO_S_FACTOR;
5.   esp_sleep_pd_config(ESP_PD_DOMAIN_RTC_PERIPH,   ESP_PD_OPTION_ON);//!< RTC IO, sensors and ULP co-processor
6.   esp_sleep_pd_config(ESP_PD_DOMAIN_XTAL,         ESP_PD_OPTION_ON);//!< XTAL oscillator
7.   esp_sleep_disable_wakeup_source(ESP_SLEEP_WAKEUP_ALL);
8.   for(gpio_num_t button_pin : buttons){
9.     if(gpio_wakeup_enable(button_pin, GPIO_INTR_LOW_LEVEL) != ESP_OK) {
10.       Serial.print("Error setting up the wakeup pin '");
11.       Serial.print(button_pin);
12.       Serial.println("'!");
13.     }
14.   }
15.   //https://github.com/espressif/arduino-esp32/issues/5107
16.   PIN_FUNC_SELECT(PERIPHS_IO_MUX_U0RXD_U, FUNC_U0RXD_GPIO3);
17.   if(gpio_wakeup_enable(GPIO_NUM_3, GPIO_INTR_LOW_LEVEL) != ESP_OK) {
18.     Serial.println("Error setting UART via GPIO pin '3' wakeup!");
19.     is_in_light_sleep = false;
20.     return;
21.   }
22.   is_in_light_sleep = true;
23.   if(esp_sleep_enable_gpio_wakeup() != ESP_OK) {
24.     Serial.println("Error setting gpio wakeup!");
25.     is_in_light_sleep = false;
26.     return;
27.   }
28.   if(tm > 0)
29.     if(esp_sleep_enable_timer_wakeup(tm) != ESP_OK) {
30.       Serial.println("Error setting timer wakeup!");
31.       is_in_light_sleep = false;
32.       return;
33.     }
34.   Serial.println("Starting light sleep.");
35.   Serial.print("Sleep time set to ");
36.   Serial.print(round(tm/uS_TO_S_FACTOR));
37.   Serial.println(" seconds.");
38.   Serial.flush();
39.   delay(100); // https://rntlab.com/question/how-to-use-esp32-light-sleep/
40.   esp_err_t t = esp_light_sleep_start();
41.   if(t != ESP_OK) {
42.     Serial.println("Sleep mode NOT enabled due to an error!");
43.   }
44.   Serial.println("Back from light sleep!");
45.   PIN_FUNC_SELECT(PERIPHS_IO_MUX_U0RXD_U, FUNC_U0RXD_U0RXD); // https://github.com/espressif/arduino-esp32/issues/5107
46.   if(is_in_light_sleep) {
47.     esp_sleep_wakeup_cause_t wakeup_reason;
48.     wakeup_reason = esp_sleep_get_wakeup_cause();
49.     switch(wakeup_reason)
50.     {
51.       case ESP_SLEEP_WAKEUP_EXT0 : Serial.println("Wakeup caused by external signal using RTC_IO"); break;
52.       case ESP_SLEEP_WAKEUP_EXT1 : Serial.println("Wakeup caused by external signal using RTC_CNTL"); break;
53.       case ESP_SLEEP_WAKEUP_TIMER : Serial.println("Wakeup caused by timer"); break;
54.       case ESP_SLEEP_WAKEUP_TOUCHPAD : Serial.println("Wakeup caused by touchpad"); break;
55.       case ESP_SLEEP_WAKEUP_ULP : Serial.println("Wakeup caused by ULP program"); break;
56.       case ESP_SLEEP_WAKEUP_GPIO : Serial.println("Wakeup caused by GPIO interruption"); break;
57.       case ESP_SLEEP_WAKEUP_UART : Serial.println("Wakeup caused by UART"); break;
58.       //case ESP_SLEEP_WAKEUP_BT : Serial.println("Wakeup caused by Bluetooth"); break;
59.       //case ESP_SLEEP_WAKEUP_WIFI : Serial.println("Wakeup caused by WiFi"); break;
60.       default : Serial.printf("Wakeup was not caused by deep sleep: %d\n",wakeup_reason); break;
61.     }
62.     is_in_light_sleep = false;
63.   }
64. }

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