STM32F4 timer (Prescaler Value)

[kazafwing]

Posted on January 24, 2013 at 03:46

Hi, I have just saw a program about a interrupt time. The program can let the LED on and off in a specified period. But I have some question about the prescaler value, can anyone help me to understand the prescale value of this case, thanks a lot. My problem is that, I don't know why the period value is 10000-1 for 1 ms delay, is there any equation for this case and why the prescaler value is 336-1 for 1MHz. Also, why the period and prescaler value is alway -1?

Thanks.The program is as follow:/**  ******************************************************************************  * @file    USART/main.c   * @author  Andrew Markham  * @version V1.0.0  * @date    27-April-2012  * @brief   Main program body  ******************************************************************************  */ /* Includes ------------------------------------------------------------------*/&sharpinclude ''stm32f4xx.h''&sharpinclude <stdio.h>/* Private typedef -----------------------------------------------------------*/GPIO_InitTypeDef  GPIO_InitStructure;TIM_TimeBaseInitTypeDef  TIM_TimeBaseStructure;/* Private define ------------------------------------------------------------*//* Private macro -------------------------------------------------------------*//* Private variables ---------------------------------------------------------*//* Private function prototypes -----------------------------------------------*/void INTTIM_Config(void);void LED_Config(void);/* Private functions ---------------------------------------------------------*/void TIM2_IRQHandler(void){  if (TIM_GetITStatus(TIM2, TIM_IT_Update) != RESET)  {    TIM_ClearITPendingBit(TIM2, TIM_IT_Update); GPIO_ToggleBits(GPIOD, GPIO_Pin_14);    GPIO_ToggleBits(GPIOD, GPIO_Pin_13); GPIO_ToggleBits(GPIOD, GPIO_Pin_12);  }}/**  * @brief  Main program  * @param  None  * @retval None  */int main(void){  INTTIM_Config();  /* LED Configuration */  LED_Config();  while (1)  {    }}/**  * @brief  Setup an interval timer  * @param  None  * @retval None  */void INTTIM_Config(void){  NVIC_InitTypeDef NVIC_InitStructure;    NVIC_InitStructure.NVIC_IRQChannel = TIM2_IRQn;            /* Enable the TIM2 gloabal Interrupt */  NVIC_InitStructure.NVIC_IRQChannelPreemptionPriority = 0;  /* value = 0 - 15*/  NVIC_InitStructure.NVIC_IRQChannelSubPriority = 1;         /* value = 0 - 15*/  NVIC_InitStructure.NVIC_IRQChannelCmd = ENABLE;  NVIC_Init(&NVIC_InitStructure);  /* TIM2 clock enable */  RCC_APB1PeriphClockCmd(RCC_APB1Periph_TIM2, ENABLE);  /* Time base configuration */  TIM_TimeBaseStructure.TIM_Period = 10000 - 1;  // 1 MHz down to 1 KHz (1 ms)  TIM_TimeBaseStructure.TIM_Prescaler = 336 - 1; // 24 MHz Clock down to 1 MHz (adjust per your clock)  TIM_TimeBaseStructure.TIM_ClockDivision = 0;  TIM_TimeBaseStructure.TIM_CounterMode = TIM_CounterMode_Up;  TIM_TimeBaseInit(TIM2, &TIM_TimeBaseStructure);  /* TIM IT enable */  TIM_ITConfig(TIM2, TIM_IT_Update, ENABLE);  /* TIM2 enable counter */  TIM_Cmd(TIM2, ENABLE);}void LED_Config(void){  /* GPIOD Periph clock enable */  RCC_AHB1PeriphClockCmd(RCC_AHB1Periph_GPIOD, ENABLE);  /* Configure PD12, PD13, PD14 and PD15 in output pushpull mode */  GPIO_InitStructure.GPIO_Pin = GPIO_Pin_12 | GPIO_Pin_13| GPIO_Pin_14| GPIO_Pin_15;  GPIO_InitStructure.GPIO_Mode = GPIO_Mode_OUT;  GPIO_InitStructure.GPIO_OType = GPIO_OType_PP;  GPIO_InitStructure.GPIO_Speed = GPIO_Speed_100MHz;  GPIO_InitStructure.GPIO_PuPd = GPIO_PuPd_NOPULL;  GPIO_Init(GPIOD, &GPIO_InitStructure);}&sharpifdef  USE_FULL_ASSERT/**  * @brief  Reports the name of the source file and the source line number  *         where the assert_param error has occurred.  * @param  file: pointer to the source file name  * @param  line: assert_param error line source number  * @retval None  */void assert_failed(uint8_t* file, uint32_t line){  /* User can add his own implementation to report the file name and line number,     ex: printf(''Wrong parameters value: file %s on line %d\r\n'', file, line) */  while (1)  {}}&sharpendif/**  * @}  */ /**  * @}  */ /******************* (C) COPYRIGHT 2011 STMicroelectronics *****END OF FILE****/ #calculate-presc #stm32f2 #set-time-base #bxcan #filter

[abuchholz91]

Posted on October 01, 2014 at 08:07

I have some very basic code working (MOSTY)

@Clive - I wonder if you can please help me out?

I have a problem, above 1282Hz I get normal and expected readings.

Below 1282Hz I get random un-expected readings that can vary fro 2x Clock to 5x Clock...

My Code:

/// <summary>

/// Need more work here... /// </summary> /// <param name=''TIMx_BASE''>The timer BASE to configure.</param> /// <returns>bool true of false.</returns> private bool CalculateFrequency(UInt32 TIMx_BASE) { UInt32 SYSTEM_APB1_CLOCK_HZ = 42000000; // 42MHz UInt32 SYSTEM_APB2_CLOCK_HZ = 84000000; // 84MHz

if (TIMx_BASE == STM32F4xx.TIM1_BASE | TIMx_BASE == STM32F4xx.TIM8_BASE)

{ debug = true;

// Calculate the Number needed to get the Prime Factors...

UInt32 PxQ = (SYSTEM_APB1_CLOCK_HZ / this.Frequency);

// Get the list of Prime Factors...

List = GetFactors(PxQ);

for (int i = 0; i < (List.Count - 1); i++)

{ if (debug) Debug.Print(''i = '' + i); if ((Convert.ToInt32(List[i].ToString())) >= (65535 / 2)) { // Factor is too large... } else { if (0 != (i % 2)) { this.Prescalar = (UInt16)Convert.ToInt16(List[i - 1].ToString()); this.Period = (UInt32)Convert.ToInt32(List[i].ToString()); break; } else if (List.Count == 2) { this.Prescalar = (UInt16)Convert.ToInt16(List[0].ToString()); this.Period = (UInt16)Convert.ToInt16(List[1].ToString()); } } } if (debug) { Debug.Print(''PxQ = '' + PxQ); Debug.Print(''List Length = '' + List.Count); Debug.Print(''Period = '' + Period); Debug.Print(''Prescalar = '' + Prescalar); Debug.Print(''Frequency = '' + (SYSTEM_APB1_CLOCK_HZ / (Prescalar * Period))); } } else { } // Calculate the Duty Cycle... this.DutyCycle = (this.Period * this.DutyCycle); debug = false; return true; }

/// <summary>

/// Thanks to those involved in getting this excellent Function together!!! /// See:

http://stackoverflow.com/questions/239865/best-way-to-find-all-factors-of-a-given-number-in-c-sharp

/// This Function has been slightly modified by myself to suit the purposes of this application. /// </summary> /// <param name=''number''>Number to get the Factored Numbers for. E.G: (3 * 2) = 6. 6 Being the Number.</param> /// <returns>List<uint></returns> public static ArrayList GetFactors(UInt32 number) { ArrayList factors = new ArrayList(); // Round down the Number to check... UInt32 max = (UInt32)System.Math.Sqrt(number);

for (UInt32 factor = 1; factor <= max; ++factor)

{ // Test from 1 to the square root, or the int below it, inclusive... if (number % factor == 0) { factors.Add(factor); if (factor != number / factor) { // Don't add the square root twice! Thanks Jon factors.Add(number / factor); } } } return factors; }

I am not sure what it is that I am missing. The Clock frequency appears to be correct for all frequencies above 1282Hz.

EDIT:

PxQ = 32786

List Length = 12 Period = 16393 Prescalar = 2 Frequency = 1281 42000000 / 2 * 16393 = 1281

but instead at this calculated frequency (1.281KHz) I get: 1.708KHz

All the best

  Chris

[abuchholz91]

Posted on October 05, 2014 at 23:20

I have carried this code on here: [DEAD LINK /public/STe2ecommunities/mcu/Lists/cortex_mx_stm32/Flat.aspx?RootFolder=/public/STe2ecommunities/mcu/Lists/cortex_mx_stm32/STM32%20Series%20-%20Calculations%20of%20Timer%20Variables&FolderCTID=0x01200200770978C69A1141439FE559EB459D7580009C4E14902C3CDE46A77F0FFD06506F5B&TopicsView=https://my.st.com/public/STe2ecommunities/mcu/Lists/cortex_mx_stm32/AllItems.aspx&currentviews=0]https://my.st.com/public/STe2ecommunities/mcu/Lists/cortex_mx_stm32/Flat.aspx?RootFolder=%2fpublic%2fSTe2ecommunities%2fmcu%2fLists%2fcortex%5fmx%5fstm32%2fSTM32%20Series%20%2d%20Calculations%20of%20Timer%20Variables&FolderCTID=0x01200200770978C69A1141439FE559EB459D7580009C4E14902C3CDE46A77F0FFD06506F5B&TopicsView=https%3A%2F%2Fmy%2Est%2Ecom%2Fpublic%2FSTe2ecommunities%2Fmcu%2FLists%2Fcortex%5Fmx%5Fstm32%2FAllItems%2Easpx&currentviews=0

[rm239955]

Posted on November 27, 2014 at 13:51

Hallo

How to set the value of APB1 Clock of STM32F429 to 42Mhz.

[waclawek.jan]

Posted on November 27, 2014 at 14:09

> How to set the value of APB1 Clock of STM32F429 to 42Mhz.

Don't hijack threads - start your own. JW