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PWM Input Mode to capture [0% 100%] - Peripheral Alternate Functions

Question asked by carlosH on Aug 28, 2012
Hi,

I have several questions concerning STM32 timer configured in PWM input.

First, I need to capture 3 PWM signals. Each signal to measure needs two timer channels in order to capture Period and Duty cycle. On a single timer it is not possible to have channel 3 and 4 capturing external input signal. It implies I must have 3 timers to do my capture? Is it right? 

Then, during capture. How can I capture 0% and 100% duty cycle value? I thought about this solution : I only enable TIM_IT_Update interrupt.
And my interrupt handler : 
void TIM5_IRQHandler(void){
  TIM_ClearITPendingBit(TIM5, TIM_IT_Update);
 
  /* ]0%, 100%[ duty cycle */
  if(TIM_GetFlagStatus(TIM5, TIM_IT_CC1) == SET && TIM_GetFlagStatus(TIM5, TIM_IT_CC2) == SET)
  {
    /* I can compute and save duty cycle and frequency */
  }
  else /* 0% or 100% duty cycle */
  {
    /* Counter overflow with no duty cycle and period capture
     * ie signal has a 0% or 100% duty cycle value (prescaler
     * configured according to signal frequency range) get
     * signal state calling GPIO_ReadInputDataBit
     */
  }
  TIM_ClearFlag(TIM5, TIM_IT_CC1);
  TIM_ClearFlag(TIM5, TIM_IT_CC2);
}

What about this solution (in comparison to a solution based on a timeout using another timer channel)? 

And another question about alternate peripheral function. On PA0 I have following alternate functions (no remap) : WKUP/USART2_CTS(7)/ADC_IN0/TIM5_CH1/TIM2_CH1_ETR(7)
I have TIM2 clock already enabled, and channel 3 and 4 enabled as output. 
If I want to use TIM5 on PA0 is it possible? what are limitations on mode?
According to ST doc :
"If several peripherals share the same I/O pin, to avoid conflict between these alternate functions only one peripheral should be enabled at a time through the peripheral clock enable bit (in the corresponding RCC peripheral clock enable register)."
If I refer to this rule I cannot use TIM5 on PA0 as TIM2 clock already enabled. But,
 * if TIM2 channel 1 is disabled and TIM5 channel 1 configured as output 
 * if TIM2 channel 1 and  TIM5 channel 1 configured as input
will I have some conflicts? And more generaly In other terms, if I have several peripheral Inputs sharing same input PIN will it cause conflicts? (In output case, with a PIN configured as output shared by several peripheral output, for sure this will leads to conflicts...)

Thanks for your help

Carlos.

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