no RTC wake up

[MichalPorazko]

I’m working on a project with the Nucleo-L476RG. I want to perform a measurement, then put the microcontroller into Sleep Mode for 2 seconds, after which it should be woken up by the RTC clock.

I followed the tutorial:

How to configure the RTC to wake up the STM32 from Low Power modes

Unfortunately, Sleep Mode is entered but not exited properly.

Down below are my project settings:

In my measurement function, I call a custom sleep() function.

void start_measurement(hx711_t *hx711){

	hx711->processed_reading = get_weight(active_hx711, 10);
	menu_refresh();
	pack_data(hx711);
	if (HAL_UART_Transmit_DMA(&huart2, (uint8_t *)( active_hx711->tx_buffer), HX711_TX_BUFFER_SIZE) == HAL_OK){
						active_hx711->measurement_count = 0U;
						active_hx711->tx_in_progress = 1U;
	}

	sleep();


}

there's the call of the sleep function:

void HAL_RTCEx_WakeUpTimerEventCallback(RTC_HandleTypeDef *hrtc)
{
	//HAL_ResumeTick();
	printf("Inside the HAL_RTCEx_WakeUpTimerEventCallback function");
	rtc_wakeup_flag = 1;
	start_measurement(active_hx711);
	HAL_GPIO_WritePin(LD2_GPIO_Port, LD2_Pin, GPIO_PIN_SET);
}


void sleep(void){

	HAL_GPIO_WritePin(LD2_GPIO_Port, LD2_Pin, GPIO_PIN_RESET);


	if (HAL_RTCEx_SetWakeUpTimer_IT(&hrtc, 4096, RTC_WAKEUPCLOCK_RTCCLK_DIV16) != HAL_OK) {
		Error_Handler();
	}
	printf("the HAL_RTCEx_SetWakeUpTimer_IT has been called \n");

	uint32_t pending = HAL_NVIC_GetPendingIRQ(RTC_WKUP_IRQn);

	printf("the pending bit for the RTC clock interrupt %lu\n", pending);

	//HAL_SuspendTick();
	counter++;

	DBGMCU->CR = 0;
	
	printf("Entering the sleep mode...");
	HAL_PWR_EnterSLEEPMode(PWR_MAINREGULATOR_ON, PWR_SLEEPENTRY_WFI);



}

void disable_wakeup(void) {
    HAL_RTCEx_DeactivateWakeUpTimer(&hrtc);
    //HAL_ResumeTick();
    rtc_wakeup_flag = 0;
}

Initially, when I used the default debugging configuration, the HAL_RTCEx_WakeUpTimerEventCallback() function was successfully entered — but only during debugging. Without the debugger attached, it was never called.

Later, I enabled SWV ITM Data printing, and observed the following:

• HAL_RTCEx_SetWakeUpTimer_IT() was called successfully.

• The pending bit for the RTC wake-up interrupt appeared to be set.

However, after enabling SWV/ITM, the debugger began printing the following repeatedly:

Target is not responding, retrying...
Target is not responding, retrying...
Target is not responding, retrying...

Even after I disabled SWV ITM again, the message “Target is not responding...” continued to appear. At this point, things became a bit confusing and I’m unsure what’s causing this behavior.

[TDK]

Debugging is difficult when entering low-power modes. Typically the processor needs to remain response for about 500 ms after reset to allow the debugger to do what it needs to do. If you drop to a low-power mode before that, things can break.

If your printf statements are hooked up to ITM, they will not work unless the debugger is present. This means your code will only work with the debugger present. I recommend using UART here instead.