ESP32_WkeupOnLow.ino

const ulp_insn_t ulp_program[] = {
  // Label to loop back to
  M_LABEL(1),

  // Read GPIO18 state (bit 28) via RTC_GPIO_IN_REG
  I_RD_REG(RTC_GPIO_IN_REG, RTC_GPIO_INDEX + RTC_GPIO_IN_NEXT_S, RTC_GPIO_INDEX + RTC_GPIO_IN_NEXT_S),

  // Check if GPIO18 is low (R0 < 1). If low, wake up the CPU.
  M_BL(2, 1),  // If R0 < 1 (i.e., if GPIO18 is low, branch to wakeup)

  // Loop back to the start (label 1) if GPIO18 is not low
  M_BX(1),  // Unconditional branch back to label 1

  // Label 2: Wake up the main CPU
  M_LABEL(2),

  // Wake up the main CPU
  I_WAKE(),  // Wake up the main CPU
  I_HALT(),  // Halt the ULP program after waking the CPU
};

// make sure to include esp_sleep_enable_ulp_wakeup(); to allow ULP to wakeup