How to implement low-power support with tickless mode in FreeRTOS

[kein]

Hello everyone,

I'm using Board NUCLEO-U031R8 for testing now.

I have an old FreeRTOS project designed for a power-saving application, and I am preparing to migrate it to a new IC STM32U031 series MCU.

In the old project, setting configUSE_TICKLESS_IDLE to 1 allowed the system to enter low-power mode when tasks were idle, and the low-power support feature provided by the manufacturer.

So I started with STM32CubeMX to create a simple project and install "X-CUBE-FREERTOS" middleware (CMSIS RTOS2), and set configUSE_TICKLESS_IDLE to 1. then using STM32CubeIDE to import the .ioc file, last adding a long-duration LED blink task to make sure the system would entry tickless idle mode.

The LED operates as expected, but I noticed that the current consumption averages around 5mA, which suggests that low-power features might not be functioning as intended. Do I missing something or wrong understanding?

Is there a recommended way to achieve low-power mode with tickless functionality in FreeRTOS?

Regards

Kein.

[SofLit]

Hello,

---

@kein wrote:

The LED operates as expected, but I noticed that the current consumption averages around 5mA, which suggests that low-power features might not be functioning as intended.

---

How are you measuring the power consumption as your are turning ON a LED?. It could be you are measuring the LED consumption. So don't turn it ON.- 

Refer also to these videos:

FreeRTOS on STM32 v2 - 21a Low power modes (tickless mode) 

FreeRTOS on STM32 v2 - 21b Low power modes (tickless SLEEP mode)

[kein]

Hi SofLit:

Thanks for the reply, The LED ON time is very short, and the OFF time is a long delay to make sure system idle, and measure the current in the same time, so i think it won't be a problem, here's my task simple code:

  while(1) {
    // LED ON with 100ms.
    LL_GPIO_SetOutputPin(LED4_GPIO, LED4_PIN);
    HAL_Delay(100);
    LL_GPIO_ResetOutputPin(LED4_GPIO, LED4_PIN);
    // LED OFF with 5000ms, ensure system entry tickless state.
    osDelay(5000);
  }

I follow the video and create LPTIM, and add the code in fucntion as below, the current is 400uA in LED OFF time, and the LED blink time as excepted.

---

void PreSleepProcessing(uint32_t ulExpectedIdleTime) {
  HAL_SuspendTick();
  HAL_LPTIM_TimeOut_Start_IT(&hlptim1, ulExpectedIdleTime);
}
void PostSleepProcessing(uint32_t ulExpectedIdleTime) {
  HAL_LPTIM_TimeOut_Stop_IT(&hlptim1);
  HAL_ResumeTick();
}​

The next step is modify vPortSuppressTicksAndSleep().

But when i commit out the restart systick part, It seems that osDelay(5000) been skipped, lead to LED working abnormally and it seems like always ON.

// port.c
__attribute__( ( weak ) ) void vPortSuppressTicksAndSleep( TickType_t xExpectedIdleTime ) {
  // ......
  /* Restart SysTick. */
  // TODO: commit out the restart systick, osDelay() would been skipped.
  // portNVIC_SYSTICK_CTRL_REG |= portNVIC_SYSTICK_ENABLE_BIT;    

  xModifiableIdleTime = xExpectedIdleTime;
  configPRE_SLEEP_PROCESSING( xModifiableIdleTime );

  if( xModifiableIdleTime > 0 ) {
    __asm volatile ( "dsb" ::: "memory" );
    // __asm volatile ( "wfi" );    // using HAL function to instead of this.
    HAL_PWREx_EnterSTOP1Mode(PWR_STOPENTRY_WFI);
    __asm volatile ( "isb" );
  }
  // ......
}

Regards.

[SofLit]

Did you watch the videos I shared? they contain how to implement low-power mode in tickless mode in FreeRTOS as well as how to measure. Did you reproduce the hands-on?

[kein]

Yes, I follow the vedio and create a new project, everything goes fine until modify the code to enter STOP1, after the changed the function osDelay() seem been skipped and not works as expected.

Kein wrote:

The next step is modify vPortSuppressTicksAndSleep().

But when i commit out the restart systick part, It seems that osDelay(5000) been skipped, lead to LED working abnormally and it seems like always ON.

---

here is the test project if you needed.

Regards.

[kein · Accepted solution]

I found the problem, here is the situation:

// FreeRTOSConfig.h
#define configPRE_SLEEP_PROCESSING(__x__)                           \
                                       do {                         \
                                         PreSleepProcessing(__x__); \
                                         __x__ = 0;                 \
                                      }while(0)
// ------------------------------------------------------------------------------------
// port.c
__attribute__( ( weak ) ) void vPortSuppressTicksAndSleep( TickType_t xExpectedIdleTime ) {
  // .......
  xModifiableIdleTime = xExpectedIdleTime;
  configPRE_SLEEP_PROCESSING( xModifiableIdleTime );
  if( xModifiableIdleTime > 0 )
  {
    // TODO: this region won't excute, because xModifiableIdleTime is set to 0 by macro configPRE_SLEEP_PROCESSING()
    __asm volatile ( "dsb" ::: "memory" );
    __asm volatile ( "wfi" );
    __asm volatile ( "isb" );
  }
  configPOST_SLEEP_PROCESSING( xExpectedIdleTime );
  // .......
}

The solution is simple just add sleep function maybe HAL_PWR_EnterSTOPMode() in configPRE_SLEEP_PROCESSING() and the code looks like this:

void PreSleepProcessing(uint32_t ulExpectedIdleTime) {
  RTC_StartWakeUpTimer(ulExpectedIdleTime);
  timeBeforeSleep = RTC_GetCount();
  LL_SYSTICK_DisableIT();

  {
    // ----------------------------- Sleep ------------------------------
    LL_LPUART_EnableInStopMode(LPUART1);                      // Set   LPUART1->CR1.UESM
    Power_EnterSleep();
    LL_LPUART_DisableInStopMode(LPUART1);                     // Clear LPUART1->CR1.UESM
    // ------------------------------------------------------------------
  }
}
//======================================================================================
void PostSleepProcessing(uint32_t ulExpectedIdleTime) {
  uint32_t sleepTime = (timeBeforeSleep - RTC_GetCount()) >> 5;   // 32k LSI, convert counter to ms with /32

  RTC_StopWakeUpTimer();
  LL_SYSTICK_EnableIT();                                    // HAL_ResumeTick();

//   NOTE: call vTaskStepTick() here, must commit out the vTaskStepTick() in file port.c
  vTaskStepTick( sleepTime );
}

hope this would help someone.