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stm32f4 discovery - strange frequency

petr2
Associate II
Posted on June 27, 2016 at 21:31

Hi, I am new at programming ARM microcontrollers and I use stm32f4 discovery board. I have tried to program blinking of the 4 user LEDs on the board so that it should change its state every 10 seconds assuming 16MHz internal oscilator. I have set prescaller to 16000, thus I have got 1000Hz and autoreload register to 10000, but when I run the program, the LEDs change their state every approximately 6 seconds. It behaves like the oscilator is approximately 26.6MHz, but it is impossible. Has anyone experience with similar problem? My code is here:

#include ''stm32f4xx.h''

#include ''stm32f4xx_conf.h''

#include ''misc.h''

#include ''core_cmInstr.h''

char state = 0;

void TIM7_IRQHandler(void)

{

    if (state == 0)

        {

            GPIO_SetBits(GPIOD, GPIO_Pin_12 | GPIO_Pin_13 | GPIO_Pin_14 | GPIO_Pin_15); //LEDs on

            state = 1;

        }

    else

        {

            GPIO_ResetBits(GPIOD, GPIO_Pin_12 | GPIO_Pin_13 | GPIO_Pin_14 | GPIO_Pin_15);   //LEDs off

            state = 0;

        }

    TIM_ClearITPendingBit(TIM7, TIM_IT_Update);

    return;

}

int main(void)

{

    //timer7 interrupt settings

    NVIC_InitTypeDef NVIC_InitStructure;

    NVIC_InitStructure.NVIC_IRQChannel = TIM7_IRQn;

    NVIC_InitStructure.NVIC_IRQChannelPreemptionPriority = (uint8_t)1;

    NVIC_InitStructure.NVIC_IRQChannelSubPriority =(uint8_t)1;

    NVIC_InitStructure.NVIC_IRQChannelCmd = ENABLE;

    NVIC_Init(&NVIC_InitStructure);

    //timer7 settings

    RCC_APB1PeriphClockCmd(RCC_APB1Periph_TIM7, ENABLE);

    TIM_PrescalerConfig(TIM7, (uint16_t)16000, TIM_PSCReloadMode_Immediate);

    TIM_SelectOnePulseMode(TIM7, TIM_OPMode_Repetitive);

    TIM_SetAutoreload(TIM7, (uint32_t)10000);

    TIM_UpdateRequestConfig(TIM7, TIM_UpdateSource_Global);

    TIM_UpdateDisableConfig(TIM7, DISABLE);

    TIM_ITConfig(TIM7, TIM_IT_Update, ENABLE);

    TIM_Cmd(TIM7, ENABLE);

    //GPIO settings

    GPIO_InitTypeDef GPIO_InitStructure;

    RCC_AHB1PeriphClockCmd(RCC_AHB1Periph_GPIOD, ENABLE);

    GPIO_InitStructure.GPIO_Mode = GPIO_Mode_OUT;

    GPIO_InitStructure.GPIO_OType = GPIO_OType_PP;

    GPIO_InitStructure.GPIO_Pin = GPIO_Pin_12 | GPIO_Pin_13 | GPIO_Pin_14 | GPIO_Pin_15;

    GPIO_InitStructure.GPIO_PuPd = GPIO_PuPd_NOPULL;

    GPIO_InitStructure.GPIO_Speed = GPIO_Speed_100MHz;

    GPIO_Init(GPIOD, &GPIO_InitStructure);

    GPIO_SetBits(GPIOD, GPIO_Pin_12 | GPIO_Pin_13 | GPIO_Pin_14 | GPIO_Pin_15); //LEDs on

  while(1)

  {

      __NOP();

  }

}
1 REPLY 1
Posted on June 28, 2016 at 01:53

The clocks are usually configured in SystemInit() system_stm32f4xx.c, which is called prior to main() for most CMSIS implementations.

You should check the RCC registers, or do a GetClocks type call to pull data about what frequency the CPU and buses are clocking at.

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