stm32F4系列MCU，視窗看門狗 WWDG中的bug

stm32F4系列MCU，視窗看門狗 WWDG中的bug。


1. 如果使能預喂狗中斷，那麼必須滿足如下兩點
（1）在開啟wwdg中斷之前，需要先將 SR 寄存器中的EWI標誌位清零，否則會看門狗會不斷複位
（2）在wwdg_irq裡加上一小段延時，否則看門狗會不斷複位
2. 如果系統裡還有其他中斷，比如按鍵，在按鍵中斷中設定一個變數，這個變數在wwdg_isr中讀取，來決定是否停止喂狗
這樣按下按鍵以後，系統直接就飛了。
這裡給出一個測試代碼。 如下所示。

/**  ******************************************************************************  * @file    USART/USART_Printf/main.c   * @author  MCD Application Team  * @version V1.0.1  * @date    13-April-2012  * @brief   Main program body  ******************************************************************************  * @attention  *  * <h2><center>© COPYRIGHT 2012 STMicroelectronics</center></h2>  *  * Licensed under MCD-ST Liberty SW License Agreement V2, (the "License");  * You may not use this file except in compliance with the License.  * You may obtain a copy of the License at:  *  *        http://www.st.com/software_license_agreement_liberty_v2  *  * Unless required by applicable law or agreed to in writing, software   * distributed under the License is distributed on an "AS IS" BASIS,   * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.  * See the License for the specific language governing permissions and  * limitations under the License.  *  ******************************************************************************  *//* Includes ------------------------------------------------------------------*/#include "stm32f4xx.h"#include "stm324xg_eval.h"#include <stdio.h>/** @addtogroup STM32F4xx_StdPeriph_Examples  * @{  *//** @addtogroup USART_Printf  * @{  */ /* Private typedef -----------------------------------------------------------*//* Private define ------------------------------------------------------------*//* Private macro -------------------------------------------------------------*//* Private variables ---------------------------------------------------------*/USART_InitTypeDef USART_InitStructure;/* Private function prototypes -----------------------------------------------*/#ifdef __GNUC__  /* With GCC/RAISONANCE, small printf (option LD Linker->Libraries->Small printf     set to 'Yes') calls __io_putchar() */  #define PUTCHAR_PROTOTYPE int __io_putchar(int ch)#else  #define PUTCHAR_PROTOTYPE int fputc(int ch, FILE *f)#endif /* __GNUC__ */  /* Private functions ---------------------------------------------------------*/void delay(int t);void wwdg_nvic_config(void);void key_init(void);/**  * @brief  Main program  * @param  None  * @retval None  */int main(void){  int i = 0;  RCC_AHB1PeriphClockCmd(RCC_AHB1Periph_GPIOB, ENABLE);    /*!< At this stage the microcontroller clock setting is already configured,        this is done through SystemInit() function which is called from startup       file (startup_stm32f4xx.s) before to branch to application main.       To reconfigure the default setting of SystemInit() function, refer to       system_stm32f4xx.c file     */              /* USARTx configured as follow:        - BaudRate = 115200 baud          - Word Length = 8 Bits        - One Stop Bit        - No parity        - Hardware flow control disabled (RTS and CTS signals)        - Receive and transmit enabled  */  USART_InitStructure.USART_BaudRate = 115200;  USART_InitStructure.USART_WordLength = USART_WordLength_8b;  USART_InitStructure.USART_StopBits = USART_StopBits_1;  USART_InitStructure.USART_Parity = USART_Parity_No;  USART_InitStructure.USART_HardwareFlowControl = USART_HardwareFlowControl_None;  USART_InitStructure.USART_Mode = USART_Mode_Rx | USART_Mode_Tx;  STM_EVAL_COMInit(COM1, &USART_InitStructure);  /* Output a message on Hyperterminal using printf function */  printf("\n\rUSART Printf Example\n\r");    /* key configuration */  key_init();    /* WWDG configuration */  /* Enable WWDG clock */  RCC_APB1PeriphClockCmd(RCC_APB1Periph_WWDG, ENABLE);  /* WWDG clock counter = (PCLK1 (42MHz)/4096)/8 = 1281 Hz (~780 us)  */  WWDG_SetPrescaler(WWDG_Prescaler_8);  /* Set Window value to 80; WWDG counter should be refreshed only when the counter    is below 80 (and greater than 64) otherwise a reset will be generated */  WWDG_SetWindowValue(120);  /* Enable WWDG and set counter value to 127, WWDG timeout = ~780 us * 64 = 49.92 ms     In this case the refresh window is: ~780 * (127-80) = 36.6ms < refresh window < ~780 * 64 = 49.9ms  */  WWDG_Enable(127);  wwdg_nvic_config();    WWDG->SR = 0;  WWDG_EnableIT();    while (1)  {    printf("%d\r\n", i++);    delay(1000);  }}void delay(int t){    int i,j;    for(i=0; i<t; i++)        for(j=0; j<10000;j++)            ;}/**  * @brief  Retargets the C library printf function to the USART.  * @param  None  * @retval None  */PUTCHAR_PROTOTYPE{  /* Place your implementation of fputc here */  /* e.g. write a character to the USART */  USART_SendData(EVAL_COM1, (uint8_t) ch);  /* Loop until the end of transmission */  while (USART_GetFlagStatus(EVAL_COM1, USART_FLAG_TC) == RESET)  {}  return ch;}#ifdef  USE_FULL_ASSERT/**  * @brief  Reports the name of the source file and the source line number  *         where the assert_param error has occurred.  * @param  file: pointer to the source file name  * @param  line: assert_param error line source number  * @retval None  */void assert_failed(uint8_t* file, uint32_t line){   /* User can add his own implementation to report the file name and line number,     ex: printf("Wrong parameters value: file %s on line %d\r\n", file, line) */  /* Infinite loop */  while (1)  {  }}#endif/**  * @}  */ static int wwdg_clear_flag = 0;void WWDG_IRQHandler(void){       WWDG->SR = 0;        if (wwdg_clear_flag == 0) //wwdg_clear_flag 在按鍵中斷中被設定為1    {        /* Update WWDG counter */        WWDG->CR = 127 & 0x7F;        delay(1);    }}void wwdg_nvic_config(void) { NVIC_InitTypeDef NVIC_InitStructure;    NVIC_InitStructure.NVIC_IRQChannel = WWDG_IRQn;    NVIC_InitStructure.NVIC_IRQChannelPreemptionPriority = 0;    NVIC_InitStructure.NVIC_IRQChannelSubPriority = 1;    NVIC_InitStructure.NVIC_IRQChannelCmd = ENABLE;    NVIC_Init(&NVIC_InitStructure);}static void key_gpio_init(void){    GPIO_InitTypeDef GPIO_InitStructure;    /* 使能時鐘 */    RCC_AHB1PeriphClockCmd(RCC_AHB1Periph_GPIOA | \                          RCC_AHB1Periph_GPIOF | \                          RCC_AHB1Periph_GPIOD,                            ENABLE);    GPIO_InitStructure.GPIO_Mode  = GPIO_Mode_IN;    GPIO_InitStructure.GPIO_Speed = GPIO_Speed_2MHz;    GPIO_InitStructure.GPIO_OType = GPIO_OType_PP;    GPIO_InitStructure.GPIO_PuPd  = GPIO_PuPd_DOWN;      /* 初始化中斷按鍵 */    GPIO_InitStructure.GPIO_Pin   = GPIO_Pin_0;    GPIO_Init(GPIOA, &GPIO_InitStructure);      /* 初始化輪詢按鍵 */    GPIO_InitStructure.GPIO_Pin   = GPIO_Pin_6 | GPIO_Pin_7 | GPIO_Pin_8                                    | GPIO_Pin_9 | GPIO_Pin_10 | GPIO_Pin_11;    GPIO_Init(GPIOF, &GPIO_InitStructure);      /* 初始化LED引腳 */    GPIO_InitStructure.GPIO_Pin = GPIO_Pin_3;    GPIO_InitStructure.GPIO_Mode = GPIO_Mode_OUT;    GPIO_Init(GPIOD, &GPIO_InitStructure);}static void key_exti_config(void){    EXTI_InitTypeDef   EXTI_InitStructure;    /* 串連PA0到外部中斷線0 */    SYSCFG_EXTILineConfig(EXTI_PortSourceGPIOA, EXTI_PinSource0);    /* 配置外部中斷線0 */    EXTI_InitStructure.EXTI_Line = EXTI_Line0;    EXTI_InitStructure.EXTI_Mode = EXTI_Mode_Interrupt;    EXTI_InitStructure.EXTI_Trigger = EXTI_Trigger_Rising_Falling;    EXTI_InitStructure.EXTI_LineCmd = ENABLE;    EXTI_Init(&EXTI_InitStructure);}static void key_nvic_config(void){    NVIC_InitTypeDef NVIC_InitStructure;    /* 使能外部中斷0 */    NVIC_InitStructure.NVIC_IRQChannel = EXTI0_IRQn;    NVIC_InitStructure.NVIC_IRQChannelPreemptionPriority = 0x3;    NVIC_InitStructure.NVIC_IRQChannelSubPriority = 0x3;    NVIC_InitStructure.NVIC_IRQChannelCmd = ENABLE;    NVIC_Init(&NVIC_InitStructure);}void key_init(void){    key_gpio_init();    key_exti_config();    key_nvic_config();}void EXTI0_IRQHandler(void){     extern int stop_feed_dog;  /* 清除中斷標誌 */    printf("key isr\r\n");    wwdg_clear_flag = 1;    EXTI_ClearITPendingBit(EXTI_Line0);}/**  * @}  */ /************************ (C) COPYRIGHT STMicroelectronics *****END OF FILE****/