1.使用CORTEX-M4核，实验中断实验和串口实验结合--->上传到CSDN
    按键触发时，LED灯状态取反，并且在串口工具打印一句话
    KEY1按键按下，LED1状态取反，串口工具打印key1 down!!!!

主要代码gpio.c

void HAL_GPIO_EXTI_Falling_Callback(uint16_t GPIO_Pin)
{switch(GPIO_Pin){case GPIO_PIN_7:HAL_GPIO_TogglePin(GPIOE,GPIO_PIN_10);printf("key2 down\n");break;case GPIO_PIN_8:HAL_GPIO_TogglePin(GPIOE,GPIO_PIN_8);printf("key3 down\n");break;case GPIO_PIN_9:HAL_GPIO_TogglePin(GPIOF,GPIO_PIN_10);printf("key1 down\n");break;default:break;}}

uart.c

int fputc(int ch,FILE *stream)
{while(!(huart4.Instance->ISR &(0x1<<7)));huart4.Instance->TDR =ch;if(ch=='\n'){while(!(huart4.Instance->ISR &(0x1<<7)));huart4.Instance->TDR ='\r';}return ch;}