STM32 - input capture experiment

One 、 General timer input capture overview

STM32 PWM working process

STM32 Input capture workflow （ passageway 1 For example ）

By testing TIMx_CHx Edge signal on , At the edge, the signal jumps （ For example, the rising edge / Falling edge ） When , Set the current timer value （TIMx_CNT） Store in the corresponding capture / Compare register （TIMx_CCRx） Inside , Complete a capture .

1、 Set the input capture filter （ passageway 1 For example ）

hypothesis IC1F[3:0]=0011, And set up IC1 Map to channel 1 On , And it is triggered by the rising edge , Then when the rising edge is captured, use fDTS The frequency is continuously sampled to 8 Secondary channel 1 The level of , If it's all high , It means it is an effective trigger , An input capture interrupt is triggered , This can filter out those high-level pulse width lower than 8 Pulse signal with sampling period , So as to achieve the effect of filtering . If you don't do filtering , Is set IC1F[3:0]=0000, As long as the rising edge is collected, the capture is triggered .

2、 Set input capture polarity （ passageway 1 For example ）

Suppose it is set to rising edge , When the edge detector detects a rising edge, it will capture .

CC1 The channel is configured to output ：

0：OC1 High active                                                               1：OC1 Low level active

CC1 The channel is configured as input ：（ choice IC1 still IC1 As a trigger or capture signal ）

0： Non antiphase ： Capture occurs at IC1 The rising edge of ： When used as an external trigger ,IC1 Reverse phase .

1： Reverse phase ： Capture occurs at IC1 The falling edge of ： When used as an external trigger ,IC1 Reverse phase .

3、 Set the input capture mapping channel （ passageway 1 For example ）

IC1 Can be mapped to TI1 Can also be mapped to TI2 On ;IC2 Can be mapped to TI2 Can also be mapped to TI1 On .

4、 Set the input acquisition divider （ passageway 1 For example ）

1 frequency division ： A rising edge triggers a capture

2 frequency division ： Every time 2 An event triggers a capture （ It will not be captured until two rising edges are detected ）

4 frequency division ： Every time 4 An event triggers a capture

8 frequency division ： Every time 8 An event triggers a capture

Trigger capture is to load the value of the counter into the capture register

5、 Capturing a valid signal can turn on the interrupt

For example, the rising edge is captured and the frequency is not divided , Then each rising edge captured will trigger a capture , At the same time, if capture interrupt is enabled , The interrupt will be triggered .

namely ： First filtering , Then judge whether the rising edge or the falling edge , Then map the last frequency division to select when the interrupt event occurs

Two 、 Library function configuration input capture

Input capture channel initialization function ：

void TIM_ICInit (TIM_TypeDef* TIMx , TIM_ICInitTypeDef* TIM_ICInitStruct);

typedef struct
{
  uint16_t TIM_Channel;// Capture channels 1-4
  uint16_t TIM_ICPolarity;// Capture polarity 
  uint16_t TIM_ICSelection;// The mapping relationship 
  uint16_t TIM_ICPrescaler;// Division coefficient 
  uint16_t TIM_ICFilter;// filter 
} TIM_ICInitTypeDef;

TIM5_ICInitABC.TIM_Channel=TIM_Channel_1;
TIM5_ICInitABC.TIM_ICPolarity=TIM_ICPolarity_Rising;
TIM5_ICInitABC.TIM_INSelection=TIM_ICSelection_DirectTI;
TIM5_ICInitABC.TIM_ICPrescaler=TIM_ICPSC_DIV1;
TIM5_ICInitABC.TIM_ICFilter=0x00;
TIM_ICInit(TIM5,&TIM5_ICInitABC);

Channel polarity setting independent function ：

void TIM_OCxPolarityConfig(TIM_TypeDef* TIMx , uint16_t TIM_OCPolarity);

Get channel capture value ：

uint32_t TIM_GetCapture1(TIM_TypeDef* TIMx);

3、 ... and 、 Enter the general configuration steps for capture ：

1、 The initialization timer corresponds to the channel IO The clock .

2、 initialization IO mouth , The mode is reuse ： GPIO_Init();

3、 Set the pin reuse mapping ：GPIO_PinAFConfig();

4、 Initialize the timer ARR、PSC：TIM_TimeBaseInit();

5、 Initialize the input capture channel ：TIM_ICInit();

6、 Enable capture interrupt ：TIM_ITConfig();  NVIC_init();

7、 Enable timer ：TIM_Cmd();

8、 Write interrupt service function ：TIMx_IRQHandler();

The experiment purpose ： Measure the pulse width of the signal

Measurement principle ：TIM5_Cap_Init It is set when the function is executed , Then wait for the rising edge interrupt to arrive , When the rising edge is captured, the interrupt , If at this time TIM5CH1_CAPTURE_STA Of the 6 Position as 0, Indicates that a new rising edge has not been captured , As the first TIM5CH1_CAPTURE_STA、TIM5CH1_CAPTURE_VAL and TIM5->CNT Equal clearing , And then set TIM5CH1_CAPTURE_STA Of the 6 Position as 1, Flag capture to high level , Finally set to falling edge capture , Wait for the falling edge to come . If waiting for the falling edge to arrive , The timer overflowed , It's just TIM5CH1_CAPTURE_STA It counts the overflow time , When the maximum overflow time comes , Force tag capture to complete （ At this time, the falling edge has not been captured ）. When the falling edge comes , First set up TIM5CH1_CAPTURE_STA Of the 7 Position as 1, The flag successfully captures a high level , Then read the value of the timer at this time to TIM5C1_CAPTURE_VAL Inside , Finally set to rising edge capture , Go back to the original state . as long as TIM5CH1_CAPTURE_STA Of the 7 I've always been for 1, Then there will be no second capture .

Input capture experiments