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Independent watchdog timer is not accurate

JJohn.3
Associate II

Here is my source code:

  void CLOCK(void){
    
    RCC_DeInit();   
    
    RCC_LSICmd(ENABLE);
    
    RCC_HSEConfig(RCC_HSE_ON);
    while(RCC_WaitForHSEStartUp()==ERROR);
    
    FLASH_PrefetchBufferCmd(FLASH_PrefetchBuffer_Enable);   
    FLASH_SetLatency(FLASH_Latency_2);  
    
    RCC_PLL2Cmd(DISABLE);
 
    RCC_PLLCmd(DISABLE);
    RCC_PREDIV1Config(RCC_PREDIV1_Source_HSE,RCC_PREDIV1_Div1); 
    RCC_PLLConfig(RCC_PLLSource_PREDIV1,RCC_PLLMul_8);
    RCC_PLLCmd(ENABLE);
    
    while(RCC_GetFlagStatus(RCC_FLAG_PLLRDY)!=SET);
    
    RCC_SYSCLKConfig(RCC_SYSCLKSource_PLLCLK);
 
    RCC_HCLKConfig(RCC_SYSCLK_Div1);
    RCC_PCLK1Config(RCC_HCLK_Div2);
    RCC_PCLK2Config(RCC_HCLK_Div1);
    
    while (RCC_GetSYSCLKSource() != 0x08){} 
        
 
}
 
int main(){ 
    unsigned long int counter;  
    CLOCK();
    GPIOS();
 
        IWDG_WriteAccessCmd(IWDG_WriteAccess_Enable);
        IWDG_SetPrescaler(IWDG_Prescaler_32);
        IWDG_SetReload(500);
        IWDG_Enable();
 
    while(1)
        {   
            counter=counter+1;      
            Print(counter);
            if(counter>6553500){counter=0;}
            IWDG_ReloadCounter();           
        }
    
}

I have set my watchdog counter to 500( .

second)(Stm32f107, LSI=40Khz,Prescale=32 ). By ignoring the "IWDG_ReloadCounter(); " (I commented //IWDG_ReloadCounter();) , this watchdog resets my MCU after about 3 seconds instead of .4 seconds. I need what my problem is.

1 ACCEPTED SOLUTION

Accepted Solutions

Is this SPL? What do those function do? Do they wait until the status register indicates the writes are finished?

Try one call of IWDG_ReloadCounter() just after IWDG_Enable(), before while(1). Does it make any difference?

JW

View solution in original post

4 REPLIES 4
Uwe Bonnes
Principal II

Look in the datasheet for the tolerance of LSI. For F072 it is 30 min, 40 typ, 50 max kHz. But your error 0.4 vs 3 points to errors in your code. For me it does not make sense...

Is this SPL? What do those function do? Do they wait until the status register indicates the writes are finished?

Try one call of IWDG_ReloadCounter() just after IWDG_Enable(), before while(1). Does it make any difference?

JW

Thank you very much, it works fine. I really appreciate your help.

Thank you very much for your comment.