STM32F103R8时钟分频问题？

大家帮忙看看下面的问题，谢谢了！

void RCC_Config(void)
{
/* SYSCLK, HCLK, PCLK2 and PCLK1 configuration -----------------------------*/
/* RCC system reset(for debug purpose) */
RCC_DeInit();

/* Enable HSE */
RCC_HSEConfig(RCC_HSE_ON);

/* Wait till HSE is ready */
//  HSEStartUpStatus = RCC_WaitForHSEStartUp();

if (RCC_WaitForHSEStartUp() == SUCCESS)
{
/* Enable Prefetch Buffer */
FLASH_PrefetchBufferCmd(FLASH_PrefetchBuffer_Enable);

/* Flash 2 wait state */
FLASH_SetLatency(FLASH_Latency_2);

/* HCLK = SYSCLK */
RCC_HCLKConfig(RCC_SYSCLK_Div1);

/* PCLK2 = HCLK */
RCC_PCLK2Config(RCC_HCLK_Div1);

/* PCLK1 = HCLK/2 */
RCC_PCLK1Config(RCC_HCLK_Div2);  // 已经设置2分频，应该是72/2=36MHz

/* PLLCLK = 8MHz * 9 = 72 MHz */
RCC_PLLConfig(RCC_PLLSource_HSE_Div1, RCC_PLLMul_9);

/* Enable PLL */
RCC_PLLCmd(ENABLE);

/* Wait till PLL is ready */
while (RCC_GetFlagStatus(RCC_FLAG_PLLRDY) == RESET)
{
}

/* Select PLL as system clock source */
RCC_SYSCLKConfig(RCC_SYSCLKSource_PLLCLK);

/* Wait till PLL is used as system clock source */
while(RCC_GetSYSCLKSource() != 0x08)
{
}
}

}

已经设置好APB1总线频率是36MHz，下面使用APB1总线挂外的TIM3产生以秒为单位的中断，程序如下：

/*******************************************************************************
* Function Name  : TIM3_LIGHTSOURCE_DELAY_Config
* Description    : 通过TIM3中断以秒为单位，产生光源TIMEOUT。
* Input          : lightsource_timeout
* Output         : None
* Return         : None
*******************************************************************************/
void TIM3_LIGHTSOURCE_DELAY_Config(void)
{



NVIC_InitTypeDef NVIC_InitStructure;
TIM_TimeBaseInitTypeDef  TIM_TimeBaseStructure;

RCC_APB1PeriphClockCmd(RCC_APB1Periph_TIM3, ENABLE); //使能TIM3总线

TIM_Cmd(TIM3, DISABLE);     //关闭TIM3
TIM_DeInit(TIM3); //复位TIM3



TIM_TimeBaseStructure.TIM_ClockDivision = 0;   // 定时器基准频率36M
TIM_TimeBaseStructure.TIM_Prescaler = 36000-1; //分频系数,1khz
TIM_TimeBaseStructure.TIM_CounterMode = TIM_CounterMode_Up; // 向上计数
TIM_TimeBaseStructure.TIM_Period = 1000-1; //自动重载值 ARR   1HZ
TIM_TimeBaseInit(TIM3, &TIM_TimeBaseStructure); //初始化定时器



NVIC_PriorityGroupConfig(NVIC_PriorityGroup_1);   //使用中断优先组1

/* Enable the TIM3 gloabal Interrupt */
NVIC_InitStructure.NVIC_IRQChannel = TIM3_IRQn;
NVIC_InitStructure.NVIC_IRQChannelPreemptionPriority = 1;
NVIC_InitStructure.NVIC_IRQChannelSubPriority = 4;
NVIC_InitStructure.NVIC_IRQChannelCmd = ENABLE;
NVIC_Init(&NVIC_InitStructure);

}