WWDG: Getting started

[Sam4]

Hello there,

I am new to STM32 MCUs and been experimenting with different examples. I have below questions regarding WWDG.

1. If you look commented section at line# 101 below. I understand the role of counter and window value but wondering where values 4096 and 64 are coming from?

/**
  ******************************************************************************
  * @file    WWDG/WWDG_Example/Src/main.c
  * @author  MCD Application Team
  * @brief   This sample code shows how to use the STM32F769xx WWDG HAL API
  *          to update at regular period the WWDG counter and how to simulate
  *          a software fault generating an MCU WWDG reset on expiry of a
  *          programmed time period.
  ******************************************************************************
  * @attention
  *
  * Copyright (c) 2016 STMicroelectronics.
  * All rights reserved.
  *
  * This software is licensed under terms that can be found in the LICENSE file
  * in the root directory of this software component.
  * If no LICENSE file comes with this software, it is provided AS-IS.
  *
  ******************************************************************************
  */

/* Includes ------------------------------------------------------------------*/
#include "main.h"

/** @addtogroup STM32F7xx_HAL_Examples
  * @{
  */

/** @addtogroup WWDG_Example
  * @{
  */

/* Private typedef -----------------------------------------------------------*/
/* Private define ------------------------------------------------------------*/
/* Private macro -------------------------------------------------------------*/
/* Private variables ---------------------------------------------------------*/
/* WWDG handler declaration */
static WWDG_HandleTypeDef   WwdgHandle;

/* Private function prototypes -----------------------------------------------*/
static void MPU_Config(void);
static void SystemClock_Config(void);
static void Error_Handler(void);
static void CPU_CACHE_Enable(void);
/* Private functions ---------------------------------------------------------*/

/**
  * @brief  Main program
  * @PAram  None
  * @retval None
  */
int main(void)
{
  /* Configure the MPU attributes */
  MPU_Config();

  /* Enable the CPU Cache */
  CPU_CACHE_Enable();

  /* STM32F7xx HAL library initialization:
       - Configure the Flash prefetch
       - Systick timer is configured by default as source of time base, but user
         can eventually implement his proper time base source (a general purpose
         timer for example or other time source), keeping in mind that Time base
         duration should be kept 1ms since PPP_TIMEOUT_VALUEs are defined and
         handled in milliseconds basis.
       - Set NVIC Group Priority to 4
       - Low Level Initialization
     */
  HAL_Init();

  /* Configure the system clock to 216 MHz */
  SystemClock_Config();

  /* Configure LED1, LED2, LED3 */
  BSP_LED_Init(LED1);
  BSP_LED_Init(LED2);
  BSP_LED_Init(LED3);

  /* Configure User push-button */
  BSP_PB_Init(BUTTON_USER, BUTTON_MODE_EXTI);
  //BSP_LED_On(LED1);
  /*##-1- Check if the system has resumed from WWDG reset ####################*/
  if (__HAL_RCC_GET_FLAG(RCC_FLAG_WWDGRST) != RESET)
  {
    /* WWDGRST flag set: Turn LED1 on */
    BSP_LED_On(LED1);
	  //BSP_LED_Off(LED1);

    /* Clear reset flags */
    __HAL_RCC_CLEAR_RESET_FLAGS();
  }
  else
  {
    /* WWDGRST flag is not set: Turn LED1 off */
    //BSP_LED_Off(LED1);
	  //BSP_LED_On(LED1);
  }


  /*##-2- Configure the WWDG peripheral ######################################*/
  /* WWDG clock counter = (PCLK1 (216MHz)/4096)/8) = 6592 Hz (~158 us)
     WWDG Window value = 120 means that the WWDG counter should be refreshed only
     when the counter is below 120 (and greater than 64/0x40) otherwise a reset will
     be generated.
     WWDG Counter value = 127, WWDG timeout = ~158 us * 64 = 11 ms */
  WwdgHandle.Instance = WWDG;

  WwdgHandle.Init.Prescaler = WWDG_PRESCALER_8;
  WwdgHandle.Init.Window    = 120;
  WwdgHandle.Init.Counter   = 127;

  if (HAL_WWDG_Init(&WwdgHandle) != HAL_OK)
  {
    /* Initialization Error */
    Error_Handler();
  }

  /* Infinite loop */
  while (1)
  {
    /* Toggle LED2 */
    //BSP_LED_Toggle(LED2);
    /* Insert 20 ms delay */
	BSP_LED_Off(LED1);
    HAL_Delay(20);

    /* Refresh WWDG: update counter value to 127, the refresh window is:
       between 1 ms (~158 * (127-120)) and 11 ms (~158 * 64) */

    if (HAL_WWDG_Refresh(&WwdgHandle) != HAL_OK)
    {
      Error_Handler();
    }
  }
}

2. There supposed to be a interrupt happening after pressing user push-button (PC.13), that should tie to EXT1 line but if you look below the interrupt handler is other than EXT1, does it mean I have create a interrupt handler for EXT1?

/******************************************************************************/
/*                 STM32F7xx Peripherals Interrupt Handlers                   */
/*  Add here the Interrupt Handler for the used peripheral(s) (PPP), for the  */
/*  available peripheral interrupt handler's name please refer to the startup */
/*  file (startup_stm32f7xx.s).                                               */
/******************************************************************************/

/**
  * @brief  This function handles External line 15_10 interrupt request.
  * @PAram  None
  * @retval None
  */
void EXTI15_10_IRQHandler(void)
{
  /* As the following address is invalid (not mapped), a Hardfault exception
  will be generated with an infinite loop and when the WWDG counter falls to 63
  the WWDG reset occurs */
  *(__IO uint32_t *) 0xA0003000 = 0xFF;
}

3. I am looking into stm32f7xx_hal_wwdg.c file for the interrupt handler callback. I can see there is a callback " HAL_WWDG_EarlyWakeupCallback(hwwdg);" wondering if this is the callback for EXT1, to me it doesn't seem like it is. Could you explain me the how to setup IRQ handler that takes care of interrupt EXT1 which is being generated by pressing user button.

/**
  * @brief  Handle WWDG interrupt request.
  * @note   The Early Wakeup Interrupt (EWI) can be used if specific safety operations
  *         or data logging must be performed before the actual reset is generated.
  *         The EWI interrupt is enabled by calling HAL_WWDG_Init function with
  *         EWIMode set to WWDG_EWI_ENABLE.
  *         When the downcounter reaches the value 0x40, and EWI interrupt is
  *         generated and the corresponding Interrupt Service Routine (ISR) can
  *         be used to trigger specific actions (such as communications or data
  *         logging), before resetting the device.
  * @PAram  hwwdg  pointer to a WWDG_HandleTypeDef structure that contains
  *                the configuration information for the specified WWDG module.
  * @retval None
  */
void HAL_WWDG_IRQHandler(WWDG_HandleTypeDef *hwwdg)
{
  /* Check if Early Wakeup Interrupt is enable */
  if (__HAL_WWDG_GET_IT_SOURCE(hwwdg, WWDG_IT_EWI) != RESET)
  {
    /* Check if WWDG Early Wakeup Interrupt occurred */
    if (__HAL_WWDG_GET_FLAG(hwwdg, WWDG_FLAG_EWIF) != RESET)
    {
      /* Clear the WWDG Early Wakeup flag */
      __HAL_WWDG_CLEAR_FLAG(hwwdg, WWDG_FLAG_EWIF);

#if (USE_HAL_WWDG_REGISTER_CALLBACKS == 1)
      /* Early Wakeup registered callback */
      hwwdg->EwiCallback(hwwdg);
#else
      /* Early Wakeup callback */
      HAL_WWDG_EarlyWakeupCallback(hwwdg);
#endif /* USE_HAL_WWDG_REGISTER_CALLBACKS */
    }
  }
}


/**
  * @brief  WWDG Early Wakeup callback.
  * @PAram  hwwdg  pointer to a WWDG_HandleTypeDef structure that contains
  *                the configuration information for the specified WWDG module.
  * @retval None
  */
__weak void HAL_WWDG_EarlyWakeupCallback(WWDG_HandleTypeDef *hwwdg)
{
  /* Prevent unused argument(s) compilation warning */
  UNUSED(hwwdg);

  /* NOTE: This function should not be modified, when the callback is needed,
           the HAL_WWDG_EarlyWakeupCallback could be implemented in the user file
   */
}

Thanks,

[Sarra.S]

Hello @Sam4, 

"4096" is used to calculate the WWDG clock counter, here is the formula:

"64" is used to calculate the timeout using this formula: 

WWDG timeout= 158ms x (127-64) =11ms 

Regarding the interrupt handler: The interrupt handler EXTI15_10_IRQHandler handles external interrupts for lines 15 to 10, the user push-button (PC13) is connected to EXTI line 13, which falls within this range.

[Sam4]

Hello @Sarra.S 

thanks for your quick response. regarding the 64 (window value) in the example window value is 127 (not 64) but the comment still says that the refresh time should be between 1 ms to 11 ms.

/* Refresh WWDG: update counter value to 127, the refresh window is:

between 1 ms (~158 * (127-120)) and 11 ms (~158 * 64) */

Also, so in the example below function is not being used? Button press is directly calling the

the "void EXTI15_10_IRQHander(void)" ?

void HAL_WWDG_IRQHandler(WWDG_HandleTypeDef *hwwdg)
{
  /* Check if Early Wakeup Interrupt is enable */
  if (__HAL_WWDG_GET_IT_SOURCE(hwwdg, WWDG_IT_EWI) != RESET)
  {
    /* Check if WWDG Early Wakeup Interrupt occurred */
    if (__HAL_WWDG_GET_FLAG(hwwdg, WWDG_FLAG_EWIF) != RESET)
    {
      /* Clear the WWDG Early Wakeup flag */
      __HAL_WWDG_CLEAR_FLAG(hwwdg, WWDG_FLAG_EWIF);

#if (USE_HAL_WWDG_REGISTER_CALLBACKS == 1)
      /* Early Wakeup registered callback */
      hwwdg->EwiCallback(hwwdg);
#else
      /* Early Wakeup callback */
      HAL_WWDG_EarlyWakeupCallback(hwwdg);
#endif /* USE_HAL_WWDG_REGISTER_CALLBACKS */
    }
  }
}