Entering Low Power Mode on STM32L0 to use USART1

Question

I want to use as little power as possible reading USART1 at 300 baud approx. 40 bytes. There are numerous other peripherals but they don't need to run- all that needs to be running is the RTC in parallel. Peripherals need to be frozen, ram needs to be the same.

The way I see it Low power run mode is the optimal mode (please correct me if I'm wrong here) for this:

void HAL_PWREx_EnableLowPowerRunMode(void)
{
  /* Enters the Low Power Run mode */
  SET_BIT(PWR->CR, PWR_CR_LPSDSR);
  SET_BIT(PWR->CR, PWR_CR_LPRUN);
}

Now the clock configuration at the moment is

System Clock source = PLL (HSI)
SYSCLK(Hz) = 32000000
HCLK(Hz) = 32000000
AHB Prescaler = 1
APB1 Prescaler = 1
APB2 Prescaler = 1
HSI Frequency(Hz) = 16000000
PLLMUL = 6
PLLDIV = 3
Flash Latency(WS) = 1
Power regulator voltage = SCALE 1

How do I go into this mode and recover from it?

// Init?
HAL_PWREx_EnableLowPowerRunMode();
HAL_PWREx_DisableLowPowerRunMode();
// Deinit?

My attempt at init, what am I missing here?

void init_clock(){


  RCC_OscInitTypeDef RCC_OscInitStruct;
  RCC_ClkInitTypeDef RCC_ClkInitStruct;
  RCC_PeriphCLKInitTypeDef PeriphClkInit;

  /**Initializes the CPU, AHB and APB busses clocks 
  */
  RCC_ClkInitStruct.ClockType = RCC_CLOCKTYPE_HCLK|RCC_CLOCKTYPE_SYSCLK
                              |RCC_CLOCKTYPE_PCLK1|RCC_CLOCKTYPE_PCLK2;
  RCC_ClkInitStruct.SYSCLKSource = RCC_SYSCLKSOURCE_MSI;
  RCC_ClkInitStruct.AHBCLKDivider = RCC_SYSCLK_DIV1;
  RCC_ClkInitStruct.APB1CLKDivider = RCC_HCLK_DIV1;
  RCC_ClkInitStruct.APB2CLKDivider = RCC_HCLK_DIV1;

  if (HAL_RCC_ClockConfig(&RCC_ClkInitStruct, FLASH_LATENCY_0) != HAL_OK)
  {
    Error_Handler();
  }
    /**Configure the main internal regulator output voltage 
    */
  __HAL_PWR_VOLTAGESCALING_CONFIG(PWR_REGULATOR_VOLTAGE_SCALE2);

    /**Initializes the CPU, AHB and APB busses clocks 
    */
  RCC_OscInitStruct.OscillatorType = RCC_OSCILLATORTYPE_HSI|RCC_OSCILLATORTYPE_MSI;
  RCC_OscInitStruct.HSIState = RCC_HSI_DIV4;
  RCC_OscInitStruct.HSICalibrationValue = 16;
  RCC_OscInitStruct.MSIState = RCC_MSI_ON;
  RCC_OscInitStruct.MSICalibrationValue = 0;
  RCC_OscInitStruct.MSIClockRange = RCC_MSIRANGE_0;
  RCC_OscInitStruct.PLL.PLLState = RCC_PLL_NONE;
  if (HAL_RCC_OscConfig(&RCC_OscInitStruct) != HAL_OK)
  {
    Error_Handler();
  }

  PeriphClkInit.PeriphClockSelection = RCC_PERIPHCLK_USART1;
  PeriphClkInit.Usart1ClockSelection = RCC_USART1CLKSOURCE_SYSCLK;

  if (HAL_RCCEx_PeriphCLKConfig(&PeriphClkInit) != HAL_OK)
  {
    Error_Handler();
  }

}

Deinit = Same as inital init of clock config

You might have better luck asking on electronics.stackexchange. Note that cross posting causes some people to become unreasonably angry and your question is likely to be deleted from both sites, so choose one. — BurnsBA
@BurnsBA I'm going to try my luck here. Last time it worked out. See my similar question stackoverflow.com/questions/34874020/… — Flying Swissman
UART1 is not low power. That would be is LPUART1. And just because someone did not notice site-rules does not make the question on-topic. We are not a consulting service. You better try elsewhere. — too honest for this site
In my experience you need to know the right "recommmeded sequence" and it is not necessarily correct or even only mentioned in the manual. You did read the manual thoroughly, didn't you? It might be "hidden". Do you have access to support/coaching by the chip supplier? This is of course only applicable if you have a corresponding contract or are otherwise an important customer. — Yunnosch

Flying Swissman Flying Swissman · Accepted Answer · 2017-05-11T08:13:18

The USART1 can receive a byte in stop mode and is also able to wake up.

The procedure to achieve low power is to use LSE for USART1 and wake up from stop mode on RXNE.

  UART_WakeUpTypeDef wakeup;
  wakeup.WakeUpEvent=UART_WAKEUP_ON_READDATA_NONEMPTY;
  HAL_UARTEx_StopModeWakeUpSourceConfig(&huart1,wakeup);   
  HAL_UARTEx_EnableStopMode(&huart1);

This is simpler and equal to if not better than BAM with DMA and Low Power Sleep.

Entering Low Power Mode on STM32L0 to use USART1

1 Answers