Calculate ARR value for Timer TIM2, TIM3 in STM32F407

[Ash1]

Hi

Can you tell me how I can calculate a value for ARR for timer 2(32bit timer) and timer3(16bit timer)

I am using STM32F407 APB1 timer clock is 12MHz prescaler is 6

[SofLit]

Hello,

For which purpose? time base?

Inspire from:

https://github.com/STMicroelectronics/stm32f4xx-hal-driver/blob/4ae1c83b8aa574042fee644688d406b2429a95d6/Src/stm32f4xx_hal_timebase_tim_template.c

 /* Get clock configuration */
  HAL_RCC_GetClockConfig(&clkconfig, &pFLatency);

  /* Get APB1 prescaler */
  uwAPB1Prescaler = clkconfig.APB1CLKDivider;

  /* Compute TIM6 clock */
  if (uwAPB1Prescaler == RCC_HCLK_DIV1)
  {
    uwTimclock = HAL_RCC_GetPCLK1Freq();
  }
  else
  {
    uwTimclock = 2 * HAL_RCC_GetPCLK1Freq();
  }

  /* Compute the prescaler value to have TIM6 counter clock equal to 1MHz */
  uwPrescalerValue = (uint32_t) ((uwTimclock / 1000000U) - 1U);

  /* Initialize TIM6 */
  TimHandle.Instance = TIM6;

  /* Initialize TIMx peripheral as follow:
  + Period = [(TIM6CLK/1000) - 1]. to have a (1/1000) s time base.
  + Prescaler = (uwTimclock/1000000 - 1) to have a 1MHz counter clock.
  + ClockDivision = 0
  + Counter direction = Up
  */
  TimHandle.Init.Period = (1000000U / 1000U) - 1U;
  TimHandle.Init.Prescaler = uwPrescalerValue;
  TimHandle.Init.ClockDivision = 0U;
  TimHandle.Init.CounterMode = TIM_COUNTERMODE_UP;
  TimHandle.Init.AutoReloadPreload = TIM_AUTORELOAD_PRELOAD_DISABLE;
  status = HAL_TIM_Base_Init(&TimHandle);

See also the application note AN4013 "Introduction to timers for STM32 MCUs " / section 2.2 Time base generator

[Andrew Neil]

See also the Timer section in the Reference Manual for your chip.

And: https://wiki.st.com/stm32mcu/wiki/Getting_started_with_TIM

And Application note AN4776, General-purpose timer cookbook for STM32 microcontrollers

ST Videos on timers: https://www.youtube.com/@stmicroelectronics/search?query=timer

Many 3rd-parties also have resources; eg, https://www.digikey.co.uk/en/maker/projects/getting-started-with-stm32-timers-and-timer-interrupts/d08e6493cefa486fb1e79c43c0b08cc6

[Hl_st]

Hello,

can you show what should be the purpose of each timers?

If you have timer clock on 12 MHz and prescaler is 6 the timer counter will be counted with frequency

12 MHz / (6+1) = 1.71 MHz. ARR register defines when timer counter will be reloaded. Frequency of reloading the timer counter is calculated as: 1.71 MHz / (ARR+1) in this case.

[Ash1]

Hi

I will again refreshed my query my APB1 timer clock is 72Mhz so does it mean my timer are running on 72Mhz?

prescaler value which I said earlies it was CAN prescaler so plz ignore previous query.

second I want to create a delay like 10millisec 100millisec e.g every 10ms interrupt will generate.

for explanation you can take any 10ms ,100ms

note: at the time of Timer_Initialization I loaded ARR value with 0xFFFFFFFF and Counter value with 0x00000000

auto preload is disabled.

and at runtime time I am want to change ARR value with desired value I am using upcounter. so i want to know what will prescaler value and method to create a delay.

[Andrew Neil]

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@Ash1 wrote:

my APB1 timer clock is 72Mhz so does it mean my timer are running on 72Mhz?

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See the Reference Manual - that will show how the timer's counter is clocked.

See also the clock configuration in CubeMX.

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@Ash1 wrote:

second I want to create a delay like 10millisec 100millisec e.g every 10ms interrupt will generate.

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So that's a Timebase - as illustrated by @SofLit 

[Hl_st]

Yes, your timer clock should be 72 MHz. If you can create an interrupt every 10 ms timer can be configured like this:  PSC = 72 - 1    (counter frequency will be 1 MHz), ARR = 10000 - 1      (counter will be reloaded every 10 ms),

and for interrupt every 100 ms timer can be configured like this: PSC = 72 - 1    (counter frequency will be 1 MHz), ARR = 100000 - 1      (counter will be reloaded every 100 ms).

[Ash1]

Hi

can you explain me this part ARR = 10000 - 1 and does this mean (PSC = 72 - 1) 71 value I have to load in prescaler register

[Hl_st]

If value of ARR register (Counter period in CubeMX) is 9999 the counter will counts from 0 to 9999 (it is 10000 clock cycles in total with reload). So if the input frequency to the timer will be 1 MHz and you need reload the timer with frequency 100 Hz (period 10 ms) there should be ARR set to 9999 or 10000-1.  And yes (PSC = 72 - 1) means that you should load 71 to prescaler register.

[Ash1]

I am trying to run timer5 create  interrupt for one minute .

I have loaded 59,999,999 in ARR register and 71 in pSC prescaler register is it correct?

I am sharing you screenshot of tim5 register at runtime but my timer is expiring at 50(approx.) second I have loaded prescaler and ARR as you said.

note: instead of one minute it is expiring before that...also I have configured CKD in (TIMx_CR1) as 00 is it correct too

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Here is the screenshot - pasted into the post for easier viewing: