STM32 休眠模式下如何喂狗？

 在STM32开发中经常会用到独立看门狗（IWDG）和低功耗模式，看门狗是为了检测和解决由软件错误引起的故障，低功耗模式是为了在CPU不需要继续运行时进入到休眠模式用以节省电能。其中独立看门狗的时钟由独立的RC振荡器（STM32F10x一般为40kHz）提供，即使在主时钟出现故障时，也仍然有效，因此可以在停止和待机模式下工作。而且独立看门狗一旦启动，除了系统复位，它不能再被停止。但这样引发的一个问题是当MCU进入到低功耗模式后由于CPU停止运行无法喂狗，会导致系统频繁复位。那如何解决这个问题呢，难道独立看门狗和低功耗模式没法同时使用？

        一个很好的方式是在休眠模式下通过RTC定时唤醒来喂狗，喂完够在进入继续进入到休眠模式。比如看门狗复位的时间间隔为10s。那么在进入休眠模式前设置RTC闹钟中断时间为5s。这样每隔5s唤醒一次喂一次狗。便可以很好的解决这个问题。

 while(1)
   {
     // 执行任务
     Task1();
     Task2();
     // ..

     // 喂狗
     dev_iwdg_feed();

     // 进入待机模式开关
     if(m_bEnterStandByMode)
     {
         // 使能外部中断，GPIOB3，用以MCU从待机模式唤醒
         dev_exti_enable(TRUE);
 ENTERSTOPMODE:
         // 设置RTC闹钟，5秒钟产生一次RTC闹钟中断*/
         dev_rtc_setAlarm(5);

         // 进入停止模式（低功耗），直至外部中断触发时被唤醒
         PWR_EnterSTOPMode(PWR_Regulator_LowPower, PWR_STOPEntry_WFI);

         // 是否是RTC闹钟中断唤醒
         if(dev_rtc_isAlarm())
         {
             // 喂狗
             dev_iwdg_feed();
             // 喂完狗继续进入停止模式
             goto ENTERSTOPMODE;
         }
         // 禁止外部中断
         dev_exti_enable(FALSE);
         // 从停止模式唤醒后恢复系统时钟
         dev_clk_restore();
     }
   }

以下是完整的参考代码：

 //**********************************************************************************************
 //  STM32F10x StopMode RTC Feed Dog
 //  compiler: Keil UV3
 //  2013-01-04 , By friehood
 //**********************************************************************************************
 #include "stm32f10x_lib.h"
 #include "platform_config.h"
 static Boolean g_bRTCAlarm = FALSE;

 /*******************************************************************************
 * Function Name  : RCC_Configuration
 * Description    : Configures the different system clocks.
 * Input          : None
 * Output         : None
 * Return         : None
 *******************************************************************************/
 void RCC_Configuration(void)
 {
     /* RCC system reset(for debug purpose) */
     RCC_DeInit();

     /* Enable HSE */
     RCC_HSEConfig(RCC_HSE_ON);

     /* Wait till HSE is ready */
     if(RCC_WaitForHSEStartUp() == SUCCESS)
     {
         /* Enable Prefetch Buffer */
         FLASH_PrefetchBufferCmd(FLASH_PrefetchBuffer_Enable);

         //FLASH时序控制
         //推荐值：SYSCLK = 0~24MHz   Latency=0
         //        SYSCLK = 24~48MHz  Latency=1
         //        SYSCLK = 48~72MHz  Latency=2
         //FLASH_SetLatency(FLASH_Latency_1);        //警告:修改为1会对DMA值有影响（如ADC采集值会错位）
         FLASH_SetLatency(FLASH_Latency_2);

         /* HCLK = SYSCLK */
         RCC_HCLKConfig(RCC_SYSCLK_Div1);

         /* PCLK2 = HCLK */
         RCC_PCLK2Config(RCC_HCLK_Div1);

         /* PCLK1 = HCLK/2 */
         RCC_PCLK1Config(RCC_HCLK_Div2);

         /* PLLCLK = 12MHz * 3 = 36 MHz */
         RCC_PLLConfig(RCC_PLLSource_HSE_Div1, RCC_PLLMul_3);

         /* Enable PLL */
         RCC_PLLCmd(ENABLE);

         /* Wait till PLL is ready */
         while(RCC_GetFlagStatus(RCC_FLAG_PLLRDY) == RESET)
         {
         }

         /* Select PLL as system clock source */
         RCC_SYSCLKConfig(RCC_SYSCLKSource_PLLCLK);

         /* Wait till PLL is used as system clock source */
         while(RCC_GetSYSCLKSource() != 0x08)
         {
         }
     }
     /* Enable PWR and BKP clock */
     RCC_APB1PeriphClockCmd(RCC_APB1Periph_PWR | RCC_APB1Periph_BKP, ENABLE);

     /* Enable AFIO clock */
     RCC_APB2PeriphClockCmd(RCC_APB2Periph_AFIO, ENABLE);
 }

 /*******************************************************************************
 * Function Name  : NVIC_Configuration
 * Description    : Configures the nested vectored interrupt controller.
 * Input          : None
 * Output         : None
 * Return         : None
 *******************************************************************************/
 void NVIC_Configuration(void)
 {
   NVIC_InitTypeDef NVIC_InitStructure;

 #ifdef  VECT_TAB_RAM
   /* Set the Vector Table base location at 0x20000000 */
   NVIC_SetVectorTable(NVIC_VectTab_RAM, 0x0);
 #else  /* VECT_TAB_FLASH  */
   /* Set the Vector Table base location at 0x08000000 */
   NVIC_SetVectorTable(NVIC_VectTab_FLASH, 0x0);
 #endif

   /* Configure one bit for preemption priority */
   NVIC_PriorityGroupConfig(NVIC_PriorityGroup_1);
 }

 /*******************************************************************************
 * Function Name  : SysTick_Configuration
 * Description    : Configures the SysTick to generate an interrupt each 1 millisecond.
 * Input          : None
 * Output         : None
 * Return         : None
 *******************************************************************************/
 void SysTick_Configuration(void)
 {
   /* Select AHB clock(HCLK) as SysTick clock source */
   SysTick_CLKSourceConfig(SysTick_CLKSource_HCLK);

   /* Set SysTick Priority to 3 */
   NVIC_SystemHandlerPriorityConfig(SystemHandler_SysTick, 3, 0);

   /* SysTick interrupt each 1ms with HCLK equal to 72MHz */
   SysTick_SetReload(72000);

   /* Enable the SysTick Interrupt */
   SysTick_ITConfig(ENABLE);
 }

 /*******************************************************************************
 * Function Name  : Delay
 * Description    : Inserts a delay time.
 * Input          : nTime: specifies the delay time length, in milliseconds.
 * Output         : None
 * Return         : None
 *******************************************************************************/
 void Delay(u32 nTime)
 {
   /* Enable the SysTick Counter */
   SysTick_CounterCmd(SysTick_Counter_Enable);

   TimingDelay = nTime;

   while(TimingDelay != 0);

   /* Disable the SysTick Counter */
   SysTick_CounterCmd(SysTick_Counter_Disable);
   /* Clear the SysTick Counter */
   SysTick_CounterCmd(SysTick_Counter_Clear);
 }


 /*******************************************************************************
 * Function Name  : RTC_Configuration
 * Description    : Configures RTC clock source and prescaler.
 * Input          : None
 * Output         : None
 * Return         : None
 *******************************************************************************/
 void RTC_Configuration(void)
 {
     EXTI_InitTypeDef EXTI_InitStructure;
     NVIC_InitTypeDef NVIC_InitStructure;

     /* RTC clock source configuration ------------------------------------------*/
     /* Allow access to BKP Domain */
     PWR_BackupAccessCmd(ENABLE);

     /* Reset Backup Domain */
     BKP_DeInit();

     /* Enable the LSI OSC */
     RCC_LSICmd(ENABLE);

     /* Wait till LSI is ready */
     while (RCC_GetFlagStatus(RCC_FLAG_LSIRDY) == RESET){}

     /* Select the RTC Clock Source */
     RCC_RTCCLKConfig(RCC_RTCCLKSource_LSI);

     /* Enable the RTC Clock */
     RCC_RTCCLKCmd(ENABLE);

     /* RTC configuration -------------------------------------------------------*/
     /* Wait for RTC APB registers synchronisation */
     RTC_WaitForSynchro();

     /* Set RTC prescaler: set RTC period to 1sec */
     RTC_SetPrescaler(40000);

     /* Wait until last write operation on RTC registers has finished */
     RTC_WaitForLastTask();

     /* Enable the RTC Alarm interrupt */
     RTC_ITConfig(RTC_IT_ALR, ENABLE);

     /* Wait until last write operation on RTC registers has finished */
     RTC_WaitForLastTask();

     /* Configure EXTI Line17(RTC Alarm) to generate an interrupt on rising edge */
     EXTI_ClearITPendingBit(EXTI_Line17);
     EXTI_InitStructure.EXTI_Line = EXTI_Line17;
     EXTI_InitStructure.EXTI_Mode = EXTI_Mode_Interrupt;
     EXTI_InitStructure.EXTI_Trigger = EXTI_Trigger_Rising;
     EXTI_InitStructure.EXTI_LineCmd = ENABLE;
     EXTI_Init(&EXTI_InitStructure);

     /* Enable the RTC Interrupt */
     NVIC_InitStructure.NVIC_IRQChannel = RTCAlarm_IRQChannel;
     NVIC_InitStructure.NVIC_IRQChannelPreemptionPriority = 0;
     NVIC_InitStructure.NVIC_IRQChannelSubPriority = 0;
     NVIC_InitStructure.NVIC_IRQChannelCmd = ENABLE;
     NVIC_Init(&NVIC_InitStructure);
 }

 /*******************************************************************************
 * Function Name  : RTCAlarm_IRQHandler
 * Description    : This function handles RTC Alarm interrupt request.
 * Input          : None
 * Output         : None
 * Return         : None
 *******************************************************************************/
 void RTCAlarm_IRQHandler(void)
 {
     if(RTC_GetITStatus(RTC_IT_ALR) != RESET)
     {
         /* Set the RTC alarm flag */
         g_bRTCAlarm = TRUE;

         /* Clear EXTI line17 pending bit */
         EXTI_ClearITPendingBit(EXTI_Line17);

         /* Check if the Wake-Up flag is set */
         if(PWR_GetFlagStatus(PWR_FLAG_WU) != RESET)
         {
             /* Clear Wake Up flag */
             PWR_ClearFlag(PWR_FLAG_WU);
         }

         /* Wait until last write operation on RTC registers has finished */
         RTC_WaitForLastTask();
         /* Clear RTC Alarm interrupt pending bit */
         RTC_ClearITPendingBit(RTC_IT_ALR);
         /* Wait until last write operation on RTC registers has finished */
         RTC_WaitForLastTask();
     }
 }

 /*******************************************************************************
 * Function Name  : dev_rtc_setAlarm
 * Description    : 设置RTC闹钟.
 * Input          : 闹钟时间
 * Output         : None
 * Return         : None
 *******************************************************************************/
 void dev_rtc_setAlarm(u32 AlarmValue)
 {
     /* Clear the RTC SEC flag */
     RTC_ClearFlag(RTC_FLAG_SEC);
     /* Wait clear RTC flag sccess */
     while(RTC_GetFlagStatus(RTC_FLAG_SEC) == RESET);
     /* Wait until last write operation on RTC registers has finished */
     RTC_WaitForLastTask();

     /* Sets the RTC alarm value */
     RTC_SetAlarm(RTC_GetCounter() + AlarmValue);
     /* Wait until last write operation on RTC registers has finished */
     RTC_WaitForLastTask();
 }

 /*******************************************************************************
 * Function Name  : dev_rtc_isAlarm
 * Description    : RTC闹钟是否触发
 * Input          : None
 * Output         : None
 * Return         : TRUE:已触发，FALSE，未触发
 *******************************************************************************/
 Boolean dev_rtc_isAlarm(void)
 {
     if(g_bRTCAlarm)
     {
         /* Clear the RTC alarm flag */
         g_bRTCAlarm = FALSE;
         return TRUE;
     }
     return FALSE;
 }

 void dev_iwdg_init(void)
 {
     /* Enable write access to IWDG_PR and IWDG_RLR registers */
     IWDG_WriteAccessCmd(IWDG_WriteAccess_Enable);
     /* IWDG counter clock: 40KHz(LSI) / 256 = 0.15625 KHz */
     IWDG_SetPrescaler(IWDG_Prescaler_256);
     /* Set counter reload value to 1562 */
     IWDG_SetReload(1562);   // 10s
     /* Reload IWDG counter */
     IWDG_ReloadCounter();
     /* Enable IWDG (the LSI oscillator will be enabled by hardware) */
     IWDG_Enable();
 }

 void dev_iwdg_feed(void)
 {
     IWDG_ReloadCounter();
 }

 /*******************************************************************************
 * Function Name  : dev_clk_restore
 * Description    : Restore system clock after wake-up from STOP: enable HSE, PLL
 *                  and select PLL as system clock source.
 * Input          : None
 * Output         : None
 * Return         : None
 *******************************************************************************/
 void dev_clk_restore(void)
 {
   /* Enable HSE */
   RCC_HSEConfig(RCC_HSE_ON);

   /* Wait till HSE is ready */
   HSEStartUpStatus = RCC_WaitForHSEStartUp();

   if(HSEStartUpStatus == SUCCESS)
   {
     /* Enable PLL */
     RCC_PLLCmd(ENABLE);

     /* Wait till PLL is ready */
     while(RCC_GetFlagStatus(RCC_FLAG_PLLRDY) == RESET)
     {
     }

     /* Select PLL as system clock source */
     RCC_SYSCLKConfig(RCC_SYSCLKSource_PLLCLK);

     /* Wait till PLL is used as system clock source */
     while(RCC_GetSYSCLKSource() != 0x08)
     {
     }
   }
 }

 /*******************************************************************************
 * Function Name  : EXTI_Configuration
 * Description    : Configures EXTI Line3.
 * Input          : None
 * Output         : None
 * Return         : None
 *******************************************************************************/
 void EXIT_Configuration(void)
 {
     EXTI_InitTypeDef EXTI_InitStructure;

     GPIO_EXTILineConfig(GPIO_PortSourceGPIOB,GPIO_PinSource3);
     EXTI_ClearITPendingBit(EXTI_Line3);
     EXTI_InitStructure.EXTI_Line = EXTI_Line3;
     EXTI_InitStructure.EXTI_Mode = EXTI_Mode_Interrupt;
     EXTI_InitStructure.EXTI_Trigger = EXTI_Trigger_Falling;
     EXTI_InitStructure.EXTI_LineCmd = ENABLE;
     EXTI_Init(&EXTI_InitStructure);
 }

 void dev_exti_enable(Boolean bEnable)
 {
     NVIC_InitTypeDef NVIC_InitStructure;

     /* Clear the Key Button EXTI line pending bit */
     EXTI_ClearITPendingBit(EXTI_Line3);

     NVIC_ClearIRQChannelPendingBit(EXTI3_IRQChannel);
     NVIC_InitStructure.NVIC_IRQChannel = EXTI3_IRQChannel;
     NVIC_InitStructure.NVIC_IRQChannelPreemptionPriority = 0;
     NVIC_InitStructure.NVIC_IRQChannelSubPriority = 0;
     NVIC_InitStructure.NVIC_IRQChannelCmd = bEnable ? ENABLE : DISABLE;
     NVIC_Init(&NVIC_InitStructure);
 }

 /*******************************************************************************
 * Function Name  : main
 * Description    : Main program.
 * Input          : None
 * Output         : None
 * Return         : None
 *******************************************************************************/
 int main(void)
 {
   /* System Clocks Configuration */
   RCC_Configuration();

   /* NVIC configuration */
   NVIC_Configuration();

   /* Configure RTC clock source and prescaler */
   RTC_Configuration();

   /* Configure the SysTick to generate an interrupt each 1 millisecond */
   SysTick_Configuration();

   /* Configures EXTI Line3 */
   EXIT_Configuration();

   /* IWDG initialize*/
   dev_iwdg_init();

   while(1)
   {
     // 执行任务
     Task1();
     Task2();
     // ..

     // 喂狗
     dev_iwdg_feed();

     // 进入待机模式开关
     if(m_bEnterStandByMode)
     {
         // 使能外部中断，GPIOB3，用以MCU从待机模式唤醒
         dev_exti_enable(TRUE);
 ENTERSTOPMODE:
         // 设置RTC闹钟，5秒钟产生一次RTC闹钟中断*/
         dev_rtc_setAlarm(5);

         // 进入停止模式（低功耗），直至外部中断触发时被唤醒
         PWR_EnterSTOPMode(PWR_Regulator_LowPower, PWR_STOPEntry_WFI);

         // 是否是RTC闹钟中断唤醒
         if(dev_rtc_isAlarm())
         {
             // 喂狗
             dev_iwdg_feed();
             // 喂完狗继续进入停止模式
             goto ENTERSTOPMODE;
         }
         // 禁止外部中断
         dev_exti_enable(FALSE);
         // 从停止模式唤醒后恢复系统时钟
         dev_clk_restore();
     }
   }
 }