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Exercise: FreeRTOS Hook Functions

Problem Statement

• Write a program to send MCU to go to sleep mode when the idle task is scheduled to run on the CPU, and measure the current.

• Hint: Begin with the project 03_LED_Task_Delay, enable the configuration item configUSE_IDLE_HOOK defined in the FreeRTOSConfig.h and implement the vApplicationIdleHook() in the application.

• Low power mode:

WFI (Wait For Interrupt) makes the processor suspended execution (Clock is stopped) until one of the following events take place:

• An IRQ interrupt

• An FIQ interrupt

• A Debug Entry request made to the processor

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/* Project/Drivers/STM32F4xx_HAL_Driver/Src/stm32f4xx_hal_pwr.c */
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/**
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  * @brief Enters Sleep mode.
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  *   
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  * @note In Sleep mode, all I/O pins keep the same state as in Run mode.
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  * 
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  * @note In Sleep mode, the systick is stopped to avoid exit from this mode with
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  *       systick interrupt when used as time base for Timeout 
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  *                
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  * @param Regulator Specifies the regulator state in SLEEP mode.
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  *            This parameter can be one of the following values:
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  *            @arg PWR_MAINREGULATOR_ON: SLEEP mode with regulator ON
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  *            @arg PWR_LOWPOWERREGULATOR_ON: SLEEP mode with low power regulator ON
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  * @note This parameter is not used for the STM32F4 family and is kept as parameter
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  *       just to maintain compatibility with the lower power families.
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  * @param SLEEPEntry Specifies if SLEEP mode in entered with WFI or WFE instruction.
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  *          This parameter can be one of the following values:
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  *            @arg PWR_SLEEPENTRY_WFI: enter SLEEP mode with WFI instruction
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  *            @arg PWR_SLEEPENTRY_WFE: enter SLEEP mode with WFE instruction
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  * @retval None
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  */
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void HAL_PWR_EnterSLEEPMode(uint32_t Regulator, uint8_t SLEEPEntry)
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{
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  /* Check the parameters */
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  assert_param(IS_PWR_REGULATOR(Regulator));
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  assert_param(IS_PWR_SLEEP_ENTRY(SLEEPEntry));
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  /* Clear SLEEPDEEP bit of Cortex System Control Register */
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  CLEAR_BIT(SCB->SCR, ((uint32_t)SCB_SCR_SLEEPDEEP_Msk));
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  /* Select SLEEP mode entry -------------------------------------------------*/
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  if(SLEEPEntry == PWR_SLEEPENTRY_WFI)
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  {   
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    /* Request Wait For Interrupt */
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    __WFI();
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  }
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  else
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  {
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    /* Request Wait For Event */
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    __SEV();
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    __WFE();
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    __WFE();
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  }
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}

Analysis

• In the case of 03_LED_Task_Delay project where the processor was never sent to the low-power mode while running the idle task, the current was measured at around 60 mA.

  But in this project (08_Idle_Hook) where the processor was sent to the low-power mode by using the Idle Hook function, the current was measured at around 20 mA. (Less power consumption!)

• How to measure the current of STM32F407G-Discovery board? See the section 6.8 of "Discovery kit with STM32F407G MCU" manual.

   

  

References

Nayak, K. (2022). Mastering RTOS: Hands on FreeRTOS and STM32Fx with Debugging [Video file]. Retrieved from https://www.udemy.com/course/mastering-rtos-hands-on-with-freertos-arduino-and-stm32fx/