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Ash1
Associate III
February 5, 2025
Solved

Calculate ARR value for Timer TIM2, TIM3 in STM32F407

  • February 5, 2025
  • 3 replies
  • 3944 views

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

Best answer by gbm

Read The Fine Document - the Reference Manual, GPIO section. The only register needed for simple output setup is MODER; you don't need to touch the others.

 

Regarding the timer setup: why should you calculate the values? Leave it to the compiler. For simple timebase setup:

#define TIMCLK_FREQ 84000000u

#define TIM_PERIOD_us 1000u

TIMx->PSC = TIMCLK_FREQ / 1000000u - 1;

TIMx->ARR = TIM_PERIOD_us - 1;

 

3 replies

mƎALLEm
mƎALLEm
ST Technical Moderator
February 5, 2025

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

 

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    Andrew Neil
    Andrew Neil
    Super User
    February 5, 2025

    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

     

    A complex system that works is invariably found to have evolved from a simple system that worked.A complex system designed from scratch never works and cannot be patched up to make it work.
    H
    Hl_st
    ST Employee
    February 5, 2025

    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.

    To give better visibility on the answered topics, please click on Accept as Solution on the reply which solved your issue or answered your question.
      A
      Ash1Author
      Associate III
      February 5, 2025

      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
      Andrew Neil
      Super User
      February 5, 2025
      @Ash1 wrote:

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

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

      See also the clock configuration in CubeMX.

       

      @Ash1 wrote:

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

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

      A complex system that works is invariably found to have evolved from a simple system that worked.A complex system designed from scratch never works and cannot be patched up to make it work.
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