Timer interrupt and GPIO toggling

[Ala]

hey there

I have a STM32f030k6t6 which I wish to set a timer(TIM16 in this case) and each time timer interrupts, a GPIO pin toggles. I attach the clock configuration.

and here is my tim16 config

htim16.Instance = TIM16;
  htim16.Init.Prescaler = 10;
  htim16.Init.CounterMode = TIM_COUNTERMODE_UP;
  htim16.Init.Period = 44236;
  htim16.Init.ClockDivision = TIM_CLOCKDIVISION_DIV1;
  htim16.Init.RepetitionCounter = 0;
  htim16.Init.AutoReloadPreload = TIM_AUTORELOAD_PRELOAD_DISABLE;
  if (HAL_TIM_Base_Init(&htim16) != HAL_OK)
  {
    Error_Handler();
  }

and this is start of timer

if(HAL_TIM_Base_Start_IT(&htim16)!=HAL_OK)//
	{	
		 Error_Handler();		
	}

and finally timer interrupt and GPIO toggling

void HAL_TIM_PeriodElapsedCallback(TIM_HandleTypeDef *htim)
{
	 if (htim->Instance == TIM16) 
	 {
		 HAL_GPIO_TogglePin(GPIOA,GPIO_PIN_3);
	 }
 }

now funny thing is that as I have set timer to interrupt every 10ms, but when I use oscilloscope, each timer interrupt is shown to be 4ms.

so why is that?

[thundertronics.com]

Output frequency is

f=(44.2368*10^6)/(10+1)/(44236+1) ' frequency in Hz

f = 90.9086799

period is

t=1/f *10^3 ' period in ms

t = 11.000049732

(if prescaler=0, frequency divided by 1, if prescaler=1 then division /2, .)

For ~10ms period prescaler must be set to 9, period to 44235

it does not explain why you observe 4ms though.

[Ala]

yeap, and more curious is this one

void HAL_TIM_PeriodElapsedCallback(TIM_HandleTypeDef *htim)
{
	 if (htim->Instance == TIM16) 
	 {
		 cnt++;
		 if(cnt==1000) 
		 { 
			  cnt=0;
		          HAL_GPIO_TogglePin(GPIOA,GPIO_PIN_3);
		 }
		
	 }
	 
 }

i wish to get a 1sec toggle when I count cnt each time, but same result... why is that?

[waclawek.jan]

What is "same result"? 4ms between edges?

JW

[Ala · Accepted solution]

sorry all my fault...

first of all my oscilloscope was not calibrated, so false results is not unexpected...

and second is that

htim16.Init.Prescaler = 10;

so this is crucial, as I forgot that Prescaler is added up by 1 in calculations.

when I wanted for example 10ms or more, this was ok(10 and 10+1 is almost the same)

nut when I wanted 1ms, this made me huge mistakes in measurments, as I expected 1ms but I forgot that in formula we use 1+1=2! which gave me 2times greater results...

anyways guys, thanks for you hints and clues