Independent watchdog timer is not accurate

[JJohn.3]

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.

[Uwe Bonnes]

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...

[waclawek.jan · Accepted solution]

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

[JJohn.3]

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

[JJohn.3]

Thank you very much for your comment.