int main(void)
{
	float length;
	delay_init();  //延时函数初始化
	NVIC_Configuration();  //设置NVIC中断分组2:2位抢占优先级，2位响应优先级
	uart_init(9600); //串口初始化为9600
	Hcsr04Init();
	printf("串口测试\n");
	Hcsr04Init();
	printf("超声波初始化成功！\n");
	while(1)
	{
		length = Hcsr04GetLength();
		printf("Length = %.3f cm\n",length);
		delay_ms(50);
	}
}