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why led blink when any clock source not selected?

Question asked by hossein hosseini on Oct 19, 2017
Latest reply on Oct 19, 2017 by ra hummel


on this code:

#include "stm32f10x.h"
#include "delay.h"

int main()
  SystemInit ();

  RCC_APB2PeriphClockCmd(RCC_APB2Periph_GPIOA , ENABLE);  
  GPIO_InitTypeDef gpio;
  gpio.GPIO_Pin = GPIO_Pin_0;
  gpio.GPIO_Speed = GPIO_Speed_2MHz;
  gpio.GPIO_Mode = GPIO_Mode_Out_PP;
  GPIO_Init(GPIOA , &gpio);  
    GPIOA->BSRR = GPIO_Pin_0;

    GPIOA->BSRR = (GPIO_Pin_0<<16);

when there is SystemInit ();   , it work corrctly. 

and when  i delete the SystemInit ();  when the system clock not set , but the led blink and time is more then 300 ms , i dont know why the clock isnt set , but the led blink ??
i write RCC_LSICmd  ( DISABLE) ; to disable internal clock , but this CMD doesnt work , and the led still blink.



i want to understand how does the clock or RCC work in stm32 , for this , i try to test these ways.And i want to set the RCC myself.



so thanks.