STM32f103R8实验：SysTick实验中的有关问题

STM32f103R8实验：SysTick实验中的问题
 最近在看《STM32自学笔记》，仿照书上的例子写了个用SysTick查询方式定时，控制LED灯闪烁的实验程序，源代码如下：

#include "stm32f10x_lib.h"


void RCC_Configuration(void);

void GPIO_Configuration(void);

void SysTick_Configuration(void);

void Delay_Second(void);


int main(void)

{

        RCC_Configuration();

        GPIO_Configuration();

        SysTick_Configuration();


        while(1)

        {

                GPIO_SetBits(GPIOB, GPIO_Pin_12 | GPIO_Pin_13 | GPIO_Pin_14 | GPIO_Pin_15);

                Delay_Second();

                GPIO_ResetBits(GPIOB, GPIO_Pin_12 | GPIO_Pin_13 | GPIO_Pin_14 | GPIO_Pin_15);

                Delay_Second();                

        }


}


void RCC_Configuration(void)

{

        RCC_DeInit();

        RCC_HSEConfig(RCC_HSE_ON);

        if(RCC_WaitForHSEStartUp() == SUCCESS)

        {

                RCC_HCLKConfig(RCC_SYSCLK_Div1);

                RCC_PCLK2Config(RCC_HCLK_Div1);

                RCC_PCLK1Config(RCC_HCLK_Div2);

                FLASH_SetLatency(FLASH_Latency_2);

                FLASH_PrefetchBufferCmd(FLASH_PrefetchBuffer_Enable);

                

                RCC_PLLConfig(RCC_PLLSource_HSE_Div2, RCC_PLLMul_9);//16M晶振，16/2*9 = 72M

                RCC_PLLCmd(ENABLE);

                while(RCC_GetFlagStatus(RCC_FLAG_PLLRDY) == RESET);

                RCC_SYSCLKConfig(RCC_SYSCLKSource_PLLCLK);

                while(RCC_GetSYSCLKSource() != 0x08);        

        }

        

        RCC_APB2PeriphClockCmd(RCC_APB2Periph_GPIOB,ENABLE);        

}


void GPIO_Configuration(void)

{

        GPIO_InitTypeDef GPIO_InitStructure;

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