该例使用systick定时器作为系统滴答定时器, 每隔1ms执行依次systick定时中断服务程序。

　　此后所有的例程都会和这个滴答定时器相关。

　　

　　本例程可以用来检测按键和摇杆以及LED指示灯、串口1的硬件功能是否正常。

　　-This example uses systick timer as a system tick timer, 1ms sequentially　d every systick timer interrupt service routine. Since then all the routines are associated with this ticking timer. This routine can be used to detect and rocker buttons and LED indicators, 1 serial port hardware function is normal.