/* Check if the system has resumed from IWDG reset，检查当前复位是否有独立看门狗导致 */if (RCC_GetFlagStatus(RCC_FLAG_IWDGRST) != RESET){/* IWDGRST flag set */printf("iwdt reset cpu\r\n");/* Clear reset flags */RCC_ClearFlag();}else{/* IWDGRST flag is not set */printf("normal reset cpu\r\n");}

/* Enable write access to IWDG_PR and IWDG_RLR registers，独立看门狗是受到保护的，现在进行解锁动作 */IWDG_WriteAccessCmd(IWDG_WriteAccess_Enable);/* IWDG counter clock: LSI/256 ，设置看门狗的时钟 = 32KHz / 256 =125Hz */IWDG_SetPrescaler(IWDG_Prescaler_256);/* 设置看门狗的超时时间，也就是设置它的计数值当前看门狗的时钟为125Hz，然后设置超时时间为1秒，那么重载值为125当前看门狗的时钟为125Hz，然后设置超时时间为2秒，那么重载值为250*/   IWDG_SetReload(125);/* Reload IWDG counter，重载独立看门狗的计数值，说白了就是喂狗 */IWDG_ReloadCounter();/* Enable IWDG (the LSI oscillator will be enabled by hardware)，使能独立看门狗 */IWDG_Enable();

#include "stm32f4xx.h"
#include "stm32f4xx_gpio.h"
#include "stm32f4xx_rcc.h"
#include "stm32f4xx_usart.h"
#include "stdio.h"static GPIO_InitTypeDef      GPIO_InitStructure;
static USART_InitTypeDef     USART_InitStructure;
static NVIC_InitTypeDef     NVIC_InitStructure;           void delay_us(uint32_t nus)
{        uint32_t temp;             SysTick->LOAD =SystemCoreClock/8/1000000*nus;     //时间加载               SysTick->VAL  =0x00;                            //清空计数器SysTick->CTRL|=SysTick_CTRL_ENABLE_Msk ;         //使能滴答定时器开始倒数      do{temp=SysTick->CTRL;}while((temp&0x01)&&!(temp&(1<<16)));            //等待时间到达   SysTick->CTRL&=~SysTick_CTRL_ENABLE_Msk;         //关闭计数器SysTick->VAL =0X00;                               //清空计数器
}void delay_ms(uint16_t nms)
{                     uint32_t temp;           SysTick->LOAD=SystemCoreClock/8/1000*nms;        //时间加载(SysTick->LOAD为24bit)SysTick->VAL =0x00;                               //清空计数器SysTick->CTRL|=SysTick_CTRL_ENABLE_Msk ;        //能滴答定时器开始倒数 do{temp=SysTick->CTRL;}while((temp&0x01)&&!(temp&(1<<16)));            //等待时间到达   SysTick->CTRL&=~SysTick_CTRL_ENABLE_Msk;        //关闭计数器SysTick->VAL =0X00;                               //清空计数器
} void LED_Init(void)
{         //使能GPIOE，GPIOF时钟RCC_AHB1PeriphClockCmd(RCC_AHB1Periph_GPIOE | RCC_AHB1Periph_GPIOF, ENABLE);            //GPIOF9,F10初始化设置 GPIO_InitStructure.GPIO_Pin   = GPIO_Pin_9 | GPIO_Pin_10;        //LED0和LED1对应IO口GPIO_InitStructure.GPIO_Mode  = GPIO_Mode_OUT;                    //普通输出模式，GPIO_InitStructure.GPIO_OType = GPIO_OType_PP;                    //推挽输出，驱动LED需要电流驱动GPIO_InitStructure.GPIO_Speed = GPIO_Speed_100MHz;                //100MHzGPIO_InitStructure.GPIO_PuPd  = GPIO_PuPd_UP;                    //上拉GPIO_Init(GPIOF, &GPIO_InitStructure);                            //初始化GPIOF，把配置的数据写入寄存器                        //GPIOE13,PE14初始化设置 GPIO_InitStructure.GPIO_Pin   = GPIO_Pin_13 | GPIO_Pin_14;        //LED2和LED3对应IO口GPIO_InitStructure.GPIO_Mode  = GPIO_Mode_OUT;                    //普通输出模式GPIO_InitStructure.GPIO_OType = GPIO_OType_PP;                    //推挽输出GPIO_InitStructure.GPIO_Speed = GPIO_Speed_100MHz;                //100MHzGPIO_InitStructure.GPIO_PuPd  = GPIO_PuPd_UP;                    //上拉GPIO_Init(GPIOE, &GPIO_InitStructure);                            //初始化GPIOE，把配置的数据写入寄存器
GPIO_SetBits(GPIOF,GPIO_Pin_9  | GPIO_Pin_10);                    //GPIOF9,PF10设置高，灯灭GPIO_SetBits(GPIOE,GPIO_Pin_13 | GPIO_Pin_14);
}void USART1_Init(uint32_t baud)
{RCC_AHB1PeriphClockCmd(RCC_AHB1Periph_GPIOA,ENABLE);                             //使能GPIOA时钟RCC_APB2PeriphClockCmd(RCC_APB2Periph_USART1,ENABLE);                            //使能USART1时钟//串口1对应引脚复用映射GPIO_PinAFConfig(GPIOA,GPIO_PinSource9,GPIO_AF_USART1);                         //GPIOA9复用为USART1GPIO_PinAFConfig(GPIOA,GPIO_PinSource10,GPIO_AF_USART1);                         //GPIOA10复用为USART1//USART1端口配置GPIO_InitStructure.GPIO_Pin = GPIO_Pin_9 | GPIO_Pin_10;                         //GPIOA9与GPIOA10GPIO_InitStructure.GPIO_Mode = GPIO_Mode_AF;                                    //复用功能GPIO_InitStructure.GPIO_Speed = GPIO_Speed_50MHz;                                //速度50MHzGPIO_InitStructure.GPIO_OType = GPIO_OType_PP;                                     //推挽复用输出GPIO_InitStructure.GPIO_PuPd = GPIO_PuPd_UP;                                     //上拉GPIO_Init(GPIOA,&GPIO_InitStructure);                                             //初始化PA9，PA10//USART1 初始化设置USART_InitStructure.USART_BaudRate = baud;                                        //波特率设置USART_InitStructure.USART_WordLength = USART_WordLength_8b;                        //字长为8位数据格式USART_InitStructure.USART_StopBits = USART_StopBits_1;                            //一个停止位USART_InitStructure.USART_Parity = USART_Parity_No;                                //无奇偶校验位USART_InitStructure.USART_HardwareFlowControl = USART_HardwareFlowControl_None;    //无硬件数据流控制USART_InitStructure.USART_Mode = USART_Mode_Rx | USART_Mode_Tx;                    //收发模式USART_Init(USART1, &USART_InitStructure);                                         //初始化串口1
    USART_Cmd(USART1, ENABLE);                                                      //使能串口1
    USART_ITConfig(USART1, USART_IT_RXNE, ENABLE);                                    //开启相关中断//Usart1 NVIC 配置NVIC_InitStructure.NVIC_IRQChannel = USART1_IRQn;                                //串口1中断通道NVIC_InitStructure.NVIC_IRQChannelPreemptionPriority=3;                            //抢占优先级3NVIC_InitStructure.NVIC_IRQChannelSubPriority =3;                                //子优先级3NVIC_InitStructure.NVIC_IRQChannelCmd = ENABLE;                                    //IRQ通道使能NVIC_Init(&NVIC_InitStructure);                                                    //根据指定的参数初始化VIC寄存器
}//重定义fputc
int fputc(int ch,FILE *f)
{USART_SendData(USART1,ch);while(USART_GetFlagStatus(USART1,USART_FLAG_TXE)==RESET);return ch;
}void usart1_send_bytes(uint8_t *pbuf,uint32_t len)
{while(len--){USART_SendData(USART1,*pbuf++);while(USART_GetFlagStatus(USART1,USART_FLAG_TXE)==RESET);}
}void usart1_send_str(char *pbuf)
{while(pbuf && *pbuf){USART_SendData(USART1,*pbuf++);while(USART_GetFlagStatus(USART1,USART_FLAG_TXE)==RESET);}
}int main(void)
{ LED_Init();        //系统定时器初始化，时钟源来自HCLK，且进行8分频，//系统定时器时钟频率=168MHz/8=21MHz
    SysTick_CLKSourceConfig(SysTick_CLKSource_HCLK_Div8); //设置中断优先级分组2
    NVIC_PriorityGroupConfig(NVIC_PriorityGroup_2);//串口1,波特率115200bps,开启接收中断USART1_Init(115200);/* Check if the system has resumed from IWDG reset，检查当前复位是否有独立看门狗导致 */if (RCC_GetFlagStatus(RCC_FLAG_IWDGRST) != RESET){/* IWDGRST flag set */printf("iwdt reset cpu\r\n");/* Clear reset flags */RCC_ClearFlag();}else{/* IWDGRST flag is not set */printf("normal reset cpu\r\n");}/* Enable write access to IWDG_PR and IWDG_RLR registers，独立看门狗是受到保护的，现在进行解锁动作 */IWDG_WriteAccessCmd(IWDG_WriteAccess_Enable);/* IWDG counter clock: LSI/256 ，设置看门狗的时钟 = 32KHz / 256 =125Hz */IWDG_SetPrescaler(IWDG_Prescaler_256);/* 设置看门狗的超时时间，也就是设置它的计数值当前看门狗的时钟为125Hz，然后设置超时时间为1秒，那么重载值为125当前看门狗的时钟为125Hz，然后设置超时时间为2秒，那么重载值为250*/   IWDG_SetReload(125);/* Reload IWDG counter，重载独立看门狗的计数值，说白了就是喂狗 */IWDG_ReloadCounter();/* Enable IWDG (the LSI oscillator will be enabled by hardware)，使能独立看门狗 */IWDG_Enable();while(1){//重载计数值，就是喂狗，就是不让计数值变为0
        IWDG_ReloadCounter();  }
}void USART1_IRQHandler(void)                                //串口1中断服务程序
{uint8_t d;if(USART_GetITStatus(USART1, USART_IT_RXNE) != RESET)      //接收中断
    {//接收数据d = USART_ReceiveData(USART1);                        //发送数据usart1_send_bytes(&d,1);} }