Timer Set up conf: intriguing issue.

[bl_it]

Posted on May 20, 2013 at 16:04

Hi Folks 

I have this simple example program that I am modifying and by moving one statement into a while statement it breaks it. I'm working on the STM32F4 Discovery board

Here is the code:- 

/*

 ===============================================================================

 Name        : main.cpp

 Author      : 

 Version     :

 Copyright   : Copyright (C)

 Description : main definition

 ===============================================================================

 */

&sharpifdef __USE_CMSIS

&sharpinclude ''stm32f4xx.h''

&sharpendif

&sharpinclude <stdio.h>

/* Private typedef -----------------------------------------------------------*/

GPIO_InitTypeDef GPIO_InitStructure;

TIM_TimeBaseInitTypeDef TIM_TimeBaseStructure;

/* Private define ------------------------------------------------------------*/

/* Private macro -------------------------------------------------------------*/

/* Private variables ---------------------------------------------------------*/

/* Private function prototypes -----------------------------------------------*/

void

LED_Config(void);

void

INTTIM_Config(void);

/* Private functions ---------------------------------------------------------*/

/**

 * @brief  Main program

 * @param  None

 * @retval None

 */

int

main(void)

{

  /* LED Configuration */

  LED_Config();

  INTTIM_Config();

  while (1)

    {

      //INTTIM_Config();

      while (TIM_GetFlagStatus(TIM2, TIM_FLAG_Update ) == RESET)

        {

        };

      TIM_ClearFlag(TIM2, TIM_IT_Update );

      GPIO_ToggleBits(GPIOD, GPIO_Pin_13 );

    }

}

/**

 * @brief  Setup an interval timer

 * @param  None

 * @retval None

 */

void

INTTIM_Config(void)

{

  /* TIM2 clock enable */

  RCC_APB1PeriphClockCmd(RCC_APB1Periph_TIM2, ENABLE);

  /* Time base configuration */

  TIM_TimeBaseStructure.TIM_Period = 200 - 1; // 1 MHz down to 10 KHz (0.1 ms) between 0x0000 and 0xFFFF.

  TIM_TimeBaseStructure.TIM_Prescaler = 134 - 1; // 24 MHz Clock down to 1 MHz (adjust per your clock)  between 0x0000 and 0xFFFF

  TIM_TimeBaseStructure.TIM_ClockDivision = 0;

  TIM_TimeBaseStructure.TIM_CounterMode = TIM_CounterMode_Up;

  TIM_TimeBaseInit(TIM2, &TIM_TimeBaseStructure);

  /* 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);

}

As it stands the code works fine - however if I commit out the active INTTIM_Config() and make the INTTIM_Config() in the loop active the time base init does not work and the timer stays at default values. 

Any thoughts welcome.

CS

#timer-set-up-stm32f4

[andreasfinkelmeyer9]

Posted on May 20, 2013 at 23:57

I'm not sure why you are surprised by this behaviour. After the initialization, all the timer flags are likely cleared. Therefore it would never enter the inner while{} loop. Once you complete the outer/main while loop, you re-initialize the timer, resetting its counter value, clearing flags etc. Of course your LED should toggle - very quickly probably!

[bl_it]

Posted on May 21, 2013 at 10:44

Hi Finkelmeyer

I think I understand what you are saying, however why on the first loop does it not work if the INTTIM_Config(); is inside the while(1) statement. 

In the working case (first time) it executes INTTIM_Config(); then  while(1) and then even thing is fine, however in the second case it executes while(1) then INTTIM_Config(); and the values are not loaded. 

This morning I tried running a number of  INTTIM_Config(); outside the loop to see if that would break it - but it didn't. 

So next I'm going to simulate a number of the loops with in line code to see what happens. 

CS

[bl_it]

Posted on May 21, 2013 at 12:42

Hi Folks 

Interestingly this looks like a timing issue, if I change the loop code to 

  while (1)

    {

      INTTIM_Config();

      int i = 0;

      while (i < 1000)

        {

          i++;

        };

          while (TIM_GetFlagStatus(TIM2, TIM_FLAG_Update ) == RESET)

            {

            };

          TIM_ClearFlag(TIM2, TIM_IT_Update );

          GPIO_ToggleBits(GPIOD, GPIO_Pin_13 );

        }

This works, however if I change it to ''while (i < 100)'' it breaks, so it shows there needs to be a time between setting up the timer and using it. Probably some parrellalism going on in the compiler, which is flushed by the 'while' statement. 

..Mmm interesting!!

[yuvanelex]

Posted on May 21, 2013 at 13:48

Hi are you try for the Channel 3 and 4 of timer 2...?