About the application configuration of stm32 timer

The timer is a powerful tool of stm32. It can be said that there is no project that does not use the timer, so only by mastering and understanding the use of timers can we make good products.
This chapter talks about the use of stm32 timer TIM_GetCounter (TIMx). This has been used in previous projects to obtain the duration of high and low levels, and has been used in ultrasonic ranging and infrared remote control decoding. Except for 1 and 8, the other timers of stm32 are general timers. How to use this function to capture the duration of the level? First, let's look at the initialization content, taking TIM4 as an example
void Timer4_CFG()
{

TIM_TimeBaseInitTypeDef TIM_TimeBaseStructure;
NVIC_InitTypeDef NVIC_InitStructure;
RCC_APB1PeriphClockCmd(RCC_APB1Periph_TIM4, ENABLE);
GPIO_InitTypeDef GPIO_InitStructure;


RCC_APB2PeriphClockCmd( RCC_APB2Periph_GPIOE | RCC_APB2Periph_AFIO , ENABLE);
 
GPIO_InitStructure.GPIO_Pin = IR_LED_PIN;
GPIO_InitStructure.GPIO_Speed ​​= GPIO_Speed_50MHz;
GPIO_InitStructure.GPIO_Mode = GPIO_Mode_IN_FLOATING;
GPIO_Init(IR_LED_PORT, &GPIO_InitStructure);


TIM_TimeBaseStructure.TIM_Prescaler = 3599; //TIM_CKD_DIV1
TIM_TimeBaseStructure.TIM_CounterMode = TIM_CounterMode_Up; //
TIM_TimeBaseStructure.TIM_Period = 200; // ARR
TIM_TimeBaseStructure.TIM_ClockDivision = TIM_CKD_DI V1;
//TIM_TimeBaseStructure.TIM_RepetitionCounter = 4;
TIM_TimeBaseInit(TIM4, &TIM_TimeBaseStructure);

//TIM_PrescalerConfig(TIM4,3599,TIM_PSCReloadMode_Immediate);//72MHz/(3599+1)=20 000 HZ 50uS
TIM_ARRPreloadConf ig(TIM4,DISABLE);

TIM_ITConfig(TIM4,TIM_IT_Update,ENABLE);
TIM_ITConfig(TIM4,TIM_IT_Trigger,ENABLE);
TIM_Cmd(TIM4, DISABLE);
     

}
APB1 is a 36M clock, which generates a 20KHZ 50us period waveform after frequency division. TIM->CNT is a counter. There is a certain rule when calculating the value of TIM_TimeBaseStructure.TIM_Period here. That is, you need to know the maximum high and low levels you collected. For example, the longest level in the waveform I collected is 4ms, and the base timer is 50us. Then I have to calculate 80 to reach 4ms, so the value of TIM_TimeBaseStructure.TIM_Period must be greater than 80, otherwise it will go wrong. Here I want to remind everyone that when the value of TIM-CNT reaches the value of TIM_TimeBaseStructure.TIM_Period, it will be cleared and counted again as shown in the figure below. This is the register configuration method for obtaining high and low levels using the TIMX-CNT counter of the timer. Of course, cnt=TIM_GetCounter(TIMx); cnt must be multiplied by 50us to get the real time. If you don't use a counter, and want to use a global variable in the interrupt to represent the number of interrupts to calculate the duration of high and low levels, please note that this method may be inaccurate due to the large number of program functions. You can try it when there are fewer functions. Then the configuration of the timer must be changed again. The benchmark is still 50us. TIM_TimeBaseStructure.TIM_Prescaler =3599; //TIM_CKD_DIV1 At this time, the maximum value cannot be considered, but a minimum common divisor should be considered. For example, how many high and low levels do I want to collect? There are 8ms, 4ms, 1ms, and 500us. Then the value of TIM_TimeBaseStructure.TIM_Period has requirements. As long as it is a multiple of 50us and is less than 500us or its divisor after multiplying with 50us, it will be fine. For example, TIM_TimeBaseStructure.TIM_Prescaler = 3599; // TIM_TimeBaseStructure.TIM_Period=1; // These two sentences mean that an interrupt occurs every 50us.