STM32 change PWM Duty Cycle dynamically in RTOS

Question

I'm using this code below trying to achieve a intensity transition effect upon turning on a light:

void output2ControlTask(void *argument)
{
  /* USER CODE BEGIN output2ControlTask */
  uint32_t DutyCycle = 0;
  /* Infinite loop */
  for(;;)
  {
    if(flag_EN_OUTPUT2 == ON){
      SteadyBurn_PWM_RTOS(&htim2, TIM_CHANNEL_3, DutyCycle);
      if(DutyCycle < 100){
        DutyCycle++;
      }
    }
    if(flag_EN_OUTPUT2 == OFF){
      SteadyBurn_PWM_RTOS(&htim2, TIM_CHANNEL_3, DutyCycle);
      if(DutyCycle > 0){
        DutyCycle--;
      }
    }
    osDelay(100);
  }
  /* USER CODE END output2ControlTask */
}

void SteadyBurn_PWM_RTOS(TIM_HandleTypeDef *htim, uint32_t Channel, uint32_t intensity_percentage){
    __HAL_TIM_SET_COMPARE(htim, Channel, (uint32_t)(COUNTER_PERIOD * (float)(intensity_percentage/100)));
}

Somehow when observed with an oscilloscope the output delayed for like 10 seconds (make sense with osDelay(100)) and then outputted a 100% Duty Cycle PWM, with no transition effect.

I remember using this code without in RTOS environment works fine. I thought about priority issues but when I changed DutyCycle to any int and left out the DutyCycle it outputs the corresponding PWM instantly.

I also debugged the DutyCycle and it was in the correct increment in runtime as well. Is it a HAL problem?

What does "changed DutyCycle to any int and left out the DutyCycle" mean? — pmacfarlane
– pmacfarlane, Commented Nov 15, 2023 at 22:43
Wouldn't it make more sense to change the DutyCycle variable first, then call SteadyBurn_PWM_RTOS()? You do it backwards - you set the current duty cycle, modify the variable, then delay. — pmacfarlane
– pmacfarlane, Commented Nov 15, 2023 at 22:45
@pmacfarlane SteadyBurn_PWM_RTOS(&htim2, TIM_CHANNEL_3, 100); will work. without DutyCycle variable involved. I mean do it backwards make sense, but still the HAL function won't take it — Travis Su
– Travis Su, Commented Nov 16, 2023 at 8:07

Travis Su · Accepted Answer · 2023-11-16 09:19:33Z

0

Right, it was a casting problem afterall.

removed a pair of parentheses on the math function and it works.

__HAL_TIM_SET_COMPARE(htim, Channel, (uint32_t)(COUNTER_PERIOD * (float)intensity_percentage/100));

answered Nov 16, 2023 at 9:19

Travis Su

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