With the esp32, when using light sleep, deep sleep, or hibernation, you need to select the wake-up source to turn the device back on.
ESP32 practical power-saving preserve data on deep sleep timer and touch wake-up There are many solutions, and some are the standard RTC or external. Others are new entries like touch or ULP.
Suppose you have already read the previous chapter. In that case, you know that there are significant differences in power consumption if you select an external or timer to wake up the source, so pay attention to your choice.
But (and now you think I’m boring) you also need to pay attention to the type of sleep mode you use because light sleep has more varieties of wake-up sources than others and can come in handy.
Storing value across deep sleep and load code after wake
I use the Serial2 to debug; you can find more information in this article “ESP32: manage multiple Serial and logging for debugging “.
Here is the connection schema to use external FDTI on Serial2.
esp32 DOIT DEV KIT v1 Serial2 UART2 TTL to USB schema The wake stub code must be resident in RTC Fast Memory. Develop can do this in one of two ways.
Function Block diagram Espressif esp32 Wi-Fi Bluetooth Microcontroller The first way is to use the RTC_IRAM_ATTR attribute to place a function into RTC memory:
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void RTC_IRAM_ATTR esp_wake_deep_sleep(void) {
esp_default_wake_deep_sleep();
}
The second way is to place the function into any source file whose name starts with rtc_wake_stub. Files names rtc_wake_stub* have their contents automatically put into RTC memory by the linker.
Storing data during deep sleep can be done in two ways, but the simplest is to use RTC_DATA_ATTR and RTC_RODATA_ATTR to specify all data (writable or read-only, respectively) that should be loaded into RTC memory:
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RTC_DATA_ATTR int wake_count;
void RTC_IRAM_ATTR esp_wake_deep_sleep(void) {
esp_default_wake_deep_sleep();
wake_count++;
}
Here is a complete sketch to verify its behavior
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#include "Arduino.h"
RTC_DATA_ATTR int wake_count = 0;
RTC_DATA_ATTR int wake_count2 = 0;
int wake_count3 = 0;
void RTC_IRAM_ATTR esp_wake_deep_sleep(void) {
esp_default_wake_deep_sleep();
wake_count2++;
}
void setup()
{
++wake_count;
++wake_count3;
Serial2.begin(115200);
while(!Serial2){delay(500);}
Serial2.println("Wake count in setup: " + String(wake_count));
Serial2.println("Wake count2 in setup: " + String(wake_count2));
Serial2.println("Wake count3 in setup: " + String(wake_count3));
Serial2.println();
Serial2.println("DEEP SLEEP ENABLED FOR 5secs");
delay(100);
esp_sleep_enable_timer_wakeup(5 * 1000 * 1000);
esp_deep_sleep_start();
Serial2.println();
Serial2.println("DEEP SLEEP WAKE UP");
}
void loop()
{
}
Here is the Serial2 result:
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Wake count in setup: 1
Wake count2 in setup: 0
Wake count3 in setup: 1
DEEP SLEEP ENABLED FOR 5secs
Wake count in setup: 2
Wake count2 in setup: 1
Wake count3 in setup: 1
DEEP SLEEP ENABLED FOR 5secs
Wake count in setup: 3
Wake count2 in setup: 2
Wake count3 in setup: 1
DEEP SLEEP ENABLED FOR 5secs
Wake count in setup: 4
Wake count2 in setup: 3
Wake count3 in setup: 1
DEEP SLEEP ENABLED FOR 5secs
Wake types
You can have some information when the sketch restart from a deep sleep, the first in the wake-up source, and you can check that with these commands
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void print_wakeup_reason(){
esp_sleep_wakeup_cause_t wakeup_reason;
wakeup_reason = esp_sleep_get_wakeup_cause();
switch(wakeup_reason)
{
case ESP_SLEEP_WAKEUP_EXT0 : Serial2.println("Wakeup caused by external signal using RTC_IO"); break;
case ESP_SLEEP_WAKEUP_EXT1 : Serial2.println("Wakeup caused by external signal using RTC_CNTL"); break;
case ESP_SLEEP_WAKEUP_TIMER : Serial2.println("Wakeup caused by timer"); break;
case ESP_SLEEP_WAKEUP_TOUCHPAD : Serial2.println("Wakeup caused by touchpad"); break;
case ESP_SLEEP_WAKEUP_ULP : Serial2.println("Wakeup caused by ULP program"); break;
default : Serial2.printf("Wakeup was not caused by deep sleep: %d\n",wakeup_reason); break;
}
}
And when you select a particular wake-up source, you probably have a command to retrieve other information, but we will check that soon.
Timer
RTC controller has a built-in timer that It can use to wake up the chip after a predefined amount of time. Time is specified at microsecond precision, but the resolution depends on the clock source selected for RTC SLOW_CLK.
This wake-up mode doesn’t require RTC peripherals or RTC memories to be powered on during sleep (check the previous article to understand the benefit) .
esp_err_tesp_sleep_enable_timer_wakeup(uint64_t time_in_us )
Enable wake-up by timer.
Return
ESP_OK on successESP_ERR_INVALID_ARG if value is out of rangeParameters
time_in_us: time before wakeup, in microseconds (time_in_us * 1000 = milliseconds * 1000 = seconds) Here is the complete sketch:
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#define TIME_TO_SLEEP 5
RTC_DATA_ATTR int bootCount = 0;
void print_wakeup_reason(){
esp_sleep_wakeup_cause_t wakeup_reason;
wakeup_reason = esp_sleep_get_wakeup_cause();
switch(wakeup_reason)
{
case ESP_SLEEP_WAKEUP_EXT0 : Serial2.println("Wakeup caused by external signal using RTC_IO"); break;
case ESP_SLEEP_WAKEUP_EXT1 : Serial2.println("Wakeup caused by external signal using RTC_CNTL"); break;
case ESP_SLEEP_WAKEUP_TIMER : Serial2.println("Wakeup caused by timer"); break;
case ESP_SLEEP_WAKEUP_TOUCHPAD : Serial2.println("Wakeup caused by touchpad"); break;
case ESP_SLEEP_WAKEUP_ULP : Serial2.println("Wakeup caused by ULP program"); break;
default : Serial2.printf("Wakeup was not caused by deep sleep: %d\n",wakeup_reason); break;
}
}
void setup(){
Serial2.begin(115200);
delay(1000);
++bootCount;
Serial2.println("Boot number: " + String(bootCount));
print_wakeup_reason();
esp_sleep_enable_timer_wakeup(TIME_TO_SLEEP * 1000 * 1000);
Serial2.println("Setup ESP32 to sleep for every " + String(TIME_TO_SLEEP) +
" Seconds");
Serial2.println("Going to sleep now");
Serial2.flush();
esp_deep_sleep_start();
Serial2.println("This will never be printed");
}
void loop(){
}
The result is:
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Boot number: 1
Wakeup was not caused by deep sleep: 0
Setup ESP32 to sleep for every 5 Seconds
Going to sleep now
Boot number: 2
Wakeup caused by timer
Setup ESP32 to sleep for every 5 Seconds
Going to sleep now
Boot number: 3
Touch
RTC IO module contains logic to trigger wake-up when a touch sensor interrupt occurs. You need to configure the touchpad interrupt before the chip starts deep sleep.
esp32 DOIT DEV KIT v1 Serial2 FTDI and touch on a breadboard Revisions 0 and 1 of the ESP32 only support this wake-up mode when RTC peripherals are not forced to be powered on.
esp_err_t esp_deep_sleep_enable_touchpad_wakeup()
Enable the wake-up touch sensor.
Note : in revisions 0 and 1 of the ESP32, the touch wake-up source can not be used when the RTC_PERIPH power domain is forced to be powered on (ESP_PD_OPTION_ON) or when the ext0 wake-up source is used.
Return
ESP_OK on successESP_ERR_INVALID_STATE if wakeup triggers conflictAnd there is a function to set the correct wake-up touch pin
void touchAttachInterrupt(uint8_t pin, void (*userFunc)(void), uint16_t threshold);
Select the correct touch pin and define the callback and threshold.
For more information on the device, refer to “DOIT ESP32 DEV KIT v1 high resolution pinout and specs “.
Here is the code of touch pins.
T0: GPIO 4T1: GPIO 0T2: GPIO 2T3: GPIO 15T4: GPIO 13T5: GPIO 12T6: GPIO 14T7: GPIO 27T8: GPIO 33T9: GPIO 32There is a command to check which pins have been touched
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void print_wakeup_touchpad(){
touchPin = esp_sleep_get_touchpad_wakeup_status();
switch(touchPin)
{
case 0 : Serial2.println("Touch detected on GPIO 4"); break;
case 1 : Serial2.println("Touch detected on GPIO 0"); break;
case 2 : Serial2.println("Touch detected on GPIO 2"); break;
case 3 : Serial2.println("Touch detected on GPIO 15"); break;
case 4 : Serial2.println("Touch detected on GPIO 13"); break;
case 5 : Serial2.println("Touch detected on GPIO 12"); break;
case 6 : Serial2.println("Touch detected on GPIO 14"); break;
case 7 : Serial2.println("Touch detected on GPIO 27"); break;
case 8 : Serial2.println("Touch detected on GPIO 33"); break;
case 9 : Serial2.println("Touch detected on GPIO 32"); break;
default : Serial2.println("Wakeup not by touchpad"); break;
}
}
Very simple but very important, and now the complete sketch:
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#define Threshold 60
RTC_DATA_ATTR int bootCount = 0;
touch_pad_t touchPin;
void print_wakeup_reason(){
esp_sleep_wakeup_cause_t wakeup_reason;
wakeup_reason = esp_sleep_get_wakeup_cause();
switch(wakeup_reason)
{
case ESP_SLEEP_WAKEUP_EXT0 : Serial2.println("Wakeup caused by external signal using RTC_IO"); break;
case ESP_SLEEP_WAKEUP_EXT1 : Serial2.println("Wakeup caused by external signal using RTC_CNTL"); break;
case ESP_SLEEP_WAKEUP_TIMER : Serial2.println("Wakeup caused by timer"); break;
case ESP_SLEEP_WAKEUP_TOUCHPAD : Serial2.println("Wakeup caused by touchpad"); break;
case ESP_SLEEP_WAKEUP_ULP : Serial2.println("Wakeup caused by ULP program"); break;
default : Serial2.printf("Wakeup was not caused by deep sleep: %d\n",wakeup_reason); break;
}
}
void print_wakeup_touchpad(){
touchPin = esp_sleep_get_touchpad_wakeup_status();
switch(touchPin)
{
case 0 : Serial2.println("Touch detected on GPIO 4"); break;
case 1 : Serial2.println("Touch detected on GPIO 0"); break;
case 2 : Serial2.println("Touch detected on GPIO 2"); break;
case 3 : Serial2.println("Touch detected on GPIO 15"); break;
case 4 : Serial2.println("Touch detected on GPIO 13"); break;
case 5 : Serial2.println("Touch detected on GPIO 12"); break;
case 6 : Serial2.println("Touch detected on GPIO 14"); break;
case 7 : Serial2.println("Touch detected on GPIO 27"); break;
case 8 : Serial2.println("Touch detected on GPIO 33"); break;
case 9 : Serial2.println("Touch detected on GPIO 32"); break;
default : Serial2.println("Wakeup not by touchpad"); break;
}
}
void callback(){
}
void setup(){
Serial2.begin(115200);
delay(1000);
++bootCount;
Serial2.println("Boot number: " + String(bootCount));
print_wakeup_reason();
print_wakeup_touchpad();
touchAttachInterrupt(T6, callback, Threshold);
touchAttachInterrupt(T7, callback, Threshold);
esp_sleep_enable_touchpad_wakeup();
Serial2.println("Going to sleep now");
esp_deep_sleep_start();
Serial2.println("This will never be printed");
}
void loop(){
}
and here is a piece of Serial2 output:
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Boot number: 3
Wakeup caused by touchpad
Touch detected on GPIO 14
Going to sleep now
Boot number: 4
Wakeup caused by touchpad
Touch detected on GPIO 27
Going to sleep now
Boot number: 5
Thanks
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