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Ash1
Associate III
Feb 5, 2025 8:49 AM UTC
Solved

Calculate ARR value for Timer TIM2, TIM3 in STM32F407

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

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gbm
gbmBest answer
Super User
Feb 6, 2025 6:23 AM UTC

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;

 

My STM32 stuff on github - compact USB device stack and more: https://github.com/gbm-ii/gbmUSBdevice
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19 replies

mƎALLEm
mƎALLEm
ST Technical Moderator
Feb 5, 2025 8:55 AM UTC

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

 

To give better visibility on the answered topics, please click "Best answer" on the reply which solved your issue or answered your question.
    Andrew Neil
    Andrew Neil
    Super User
    Feb 5, 2025 9:02 AM UTC

    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.
    Hl_st
    ST Employee
    Feb 5, 2025 9:11 AM UTC

    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.
      Ash1Author
      Associate III
      Feb 5, 2025 9:37 AM UTC

      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
      Feb 5, 2025 9:52 AM UTC
      @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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