Calculation of the timing time of the general timer of the STM32 microcontroller

    There are many types of timers in STM32, which are divided into 2 advanced controller timers, 4 ordinary timers, 2 basic timers, 2 watchdog timers, and 1 system tick timer SysTICk according to their functions.

    The key to the timer is the calculation of the timing time. For example, when using a timer to control the switch of a relay, it needs to be delayed for a period of time before closing or opening, and the timer timing is indispensable at this time.

    General timer timing calculation. Basic implementation of 1 second interrupt:

    The input clock of the general timer module is divided to obtain the clock of the counter, which is represented by CK_CNT. The coefficient of the pre-divider is: TIMx_PSC. When TIMx_PSC=0, it means no division, when =1, it means 2 division. And so on.

    The formula is: CK_CNT=fclk_PSC/(PSC[15:0]+1), where the maximum value of PSC is 65535.

    The second step is to set the count value of the TIM5 counter. The TIM5 counter uses CK_CNT as the clock to count. When the count reaches the set value, an interrupt is generated.

    (1/counting clock after frequency division)*counting value=set time. Take 1 second as an example

    (1/(72MHz/7200))*10000=1s

    Initialize an important structure of the general timer TIM_TimeBaseInitTypeDef

• typedef struct   

• {   

• u16 TIM_Period; //Count value automatically loaded, 

• u16 TIM_Prescaler; //Division value, when it is 0, it means no frequency division, so it needs to be subtracted by 1. 

• u8 TIM_CLOCkDivision; //Set clock division, 

• u16 TIM_CounterMode; //Up, down, etc. counting modes 

• } TIM_TimeBaseInitTypeDef; 

    Calling a function after initializing the structure

    void TIM_TimeBaseInit(TIM_TypeDef* TIMx, TIM_TimeBaseInitTypeDef * TIM_TimeBaseInitStruct) Initializes the time base unit of the TIMx timer.

    Secondly, the interrupt pending bit must be cleared, and the function void TIM_ClearITPendingBit(TIM_TypeDef* TIMx, u16 TIM_IT) does this work. TIM_IT: TIM interrupt pending bit to be checked.