说明：  stm32定时器实现按键控制开启定时器通过led灯状态来检测。按键消抖有多种方法，初学者一般采用延时来达到消抖的目的。一般的延时消抖分两种：一种是先判断有键按下，延时几十毫秒再判断有无键按下，有则执行按键对应的程序。另一种是在延时几十毫秒之后，判断有无键按下；若有键按下，不立即响应按键程序，而是进入一个循环，循环的条件是有键按下。
(STM32 timer realizes key control and opening timer, which is detected by LED lamp status. There are many ways to eliminate button jitter. Beginners usually use delay to achieve the purpose of jitter elimination. Generally, there are two kinds of delay jitter elimination: one is to judge whether the key is pressed, the other is to judge whether the key is pressed or not after tens of milliseconds, and the other is to execute the corresponding program of the key. The other is to judge whether a key is pressed after a delay of tens of milliseconds; if a key is pressed, it does not immediately respond to the key program, but enters a cycle, the condition of which is that the key is pressed.)