ESP32 Wake Stub Not Executing

In this tutorial, you'll learn about ESP32 Wake Stub Not Executing. We cover key concepts, practical examples, and best practices.

The Problem

ESP32 wake stub (RTC fast memory code) runs on cold boot but not on wake from deep sleep.

Quick Fix

Wrong

// No wake stub defined. Full setup() runs on every wake.

Full boot takes 150ms. Extra power consumed on every wake.

Right

void RTC_IRAM_ATTR esp_wake_deep_sleep() {
  esp_default_wake_deep_sleep();
  // Quick actions: increment counter, read sensor, set GPIO
  RTC_DATA_ATTR int count = 0;
  count++;
  if (count % 10 == 0) {
    esp_deep_sleep_start();  // Continue sleep for 9/10 wakes
  }
}
void setup() {
  // Runs only when ESP decides to boot fully
  Serial.begin(115200);
  Serial.println("Full boot");
}

(Wakes 9 times without serial output, 10th wake: Full boot)

Prevention

Place wake stub in RTC_IRAM_ATTR section. Stub runs before DRAM is restored. Keep stub minimal (<512 bytes). Use stub to decide whether full boot is needed. Stub can access RTC_DATA_ATTR variables.

DodaTech engineers apply these same patterns across Doda Browser, DodaZIP, and Durga Antivirus Pro for production IoT reliability.

FAQ