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ctimerstm32hal
Andrea
Andrea

Reputation: 109

Issue with timer Input Capture mode in STM32

I would like to trigger a timer with an external signal which happens every 1ms. Then, the timer has to count up to 90us at every rising edge of the external signal. The question is, can I do that using a general purpose timer configured as Input Compare? I don’t understand which callBack to use for this purpose.

I’m using the HAL library and TIM2 peripheral in STM32F446 microcotnroller.

This is how I configured my timer peripheral

void TIMER2_Config(void)
{
TIM_IC_InitTypeDef timer2IC_Config;
htimer2.Instance = TIM2;
htimer2.Init.CounterMode = TIM_COUNTERMODE_UP;
htimer2.Init.Period = 89; //Fck=50MHz, Timer period = 90us

htimer2.Init.Prescaler = 49;
if ( HAL_TIM_IC_Init(&htimer2) != OK)
   Error_handler();
timer2IC_Config.ICPolarity = TIM_ICPOLARITY_RISING; 
timer2IC_Config.ICPrescaler = TIM_ICPSC_DIV1;
if (HAL_TIM_IC_ConfigChannel(&htimer2, &timer2IC_Config, TIM_CHANNEL_1) != OK)
  Error_handler();

}

Upvotes: 2

Views: 2080

Answers (1)

Tom V
Tom V

Reputation: 5510

What you are asking for is well within the features of this peripheral, but you must remember that the HAL library is not capable of using the full features of the chip. Sometimes you have to use access the registers directly (the LL library is another way to do this).

To have the external signal start the timer you need to use trigger mode, not input capture. Input capture means record the value of the timer which is already started. You need to set the field TIMx_CCMRx_CCxS to 0b11 (3) to make the input a trigger, then set the field TIMx_SMCR_TS to select the channel you are using, and TIMx_SMCR_SMS to 0b110 (6) to select start on trigger mode.

Next set up the prescaler and reload register to to count for the 90 microsecond delay that you want, and set TIMx_CR1_OPM to 1 to stop the counter wrapping when it reaches the limit.

Next set TIMx_CR2_MMS to 0b010 to output a trigger on the update event.

Finally you can set the ADCx_CR2_EXTSEL bits to 0b00110 to trigger on TIM2_TRGO trigger output.

This is all a bit complicated, but the reference manual is very thorough and you should read the whole chapter through and check every field in the register description section. I would recommend not mixing the HAL library with direct register access, it will probably interfere with what you are trying to do.

Upvotes: 4

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