Solve the problem of entering an interrupt program immediately when the STM32 timer is turned on

When configuring the STM32 timer, the timer interrupt enable, timer enable, and clear update interrupt flag have different effects when the three programs are executed in different orders, as follows:

TIM_ClearITPendingBit(TIM1, TIM_IT_Update); //Clear update interrupt request bit

    TIM_ITConfig(TIM1, TIM_IT_Update, ENABLE); //Enable timer 1 update interrupt

TIM_Cmd(TIM1, ENABLE); //Start the timer

         (1) The update interrupt routine will not be entered immediately.

    TIM_ClearITPendingBit(TIM1, TIM_IT_Update); //Clear update interrupt request bit

TIM_Cmd(TIM1, ENABLE); 

    TIM_ITConfig(TIM1, TIM_IT_Update, ENABLE); //Enable timer 1 update interrupt

     (2) The update interrupt routine will not be entered immediately.

TIM_Cmd(TIM1, ENABLE);

   TIM_ClearITPendingBit(TIM1, TIM_IT_Update); //Clear update interrupt request bit

  TIM_ITConfig(TIM1, TIM_IT_Update, ENABLE); //Enable timer 1 update interrupt

   (3) The update interrupt procedure will not be entered immediately.

    TIM_Cmd(TIM1, ENABLE);

    TIM_ITConfig(TIM1, TIM_IT_Update, ENABLE); //Enable timer 1 update interrupt

    TIM_ClearITPendingBit(TIM1, TIM_IT_Update); //Clear update interrupt request bit

       (4) Immediately enter the update interrupt program.

     TIM_ITConfig(TIM1, TIM_IT_Update, ENABLE); //Enable timer 1 update interrupt

   TIM_ClearITPendingBit(TIM1, TIM_IT_Update); //Clear update interrupt request bit

TIM_Cmd(TIM1, ENABLE);  

  (5) . . . . . . Enter the update interrupt procedure immediately.

     TIM_ITConfig(TIM1, TIM_IT_Update, ENABLE); //Enable timer 1 update interrupt

     TIM_Cmd(TIM1, ENABLE); 

     TIM_ClearITPendingBit(TIM1, TIM_IT_Update); //Clear update interrupt request bit

  (6) . . . . . . Enter the update interrupt procedure immediately.

Reference: http://www.51hei.com/bbs/dpj-40940-1.html

         http://www.openedv.com/posts/list/41019.htm