项目需要：计算PWM脉冲的个数解决办法：采用定时器级联：TIM3做master，TIM4做slave.
具体配置如下：

void TIM3_PWM_Init(u32 arr,u32 psc)
{                                                          

        GPIO_InitTypeDef GPIO_InitStructure;
        NVIC_InitTypeDef NVIC_InitStructure;
        TIM_TimeBaseInitTypeDef  TIM_TimeBaseStructure;
        TIM_OCInitTypeDef  TIM_OCInitStructure;
       
        RCC_APB1PeriphClockCmd(RCC_APB1Periph_TIM3,ENABLE);          //TIM14ê±Öóê1Äü   
        RCC_AHB1PeriphClockCmd(RCC_AHB1Periph_GPIOC, ENABLE);         //ê1ÄüPORTFê±Öó       
       
        GPIO_PinAFConfig(GPIOC,GPIO_PinSource8,GPIO_AF_TIM3); //GPIOF9¸′óÃÎa¶¨ê±Æ÷14
       
        GPIO_InitStructure.GPIO_Pin = GPIO_Pin_8;           //GPIOF9
        GPIO_InitStructure.GPIO_Mode = GPIO_Mode_AF;        //¸′óÃ1|Äü
        GPIO_InitStructure.GPIO_Speed = GPIO_Speed_100MHz;        //Ëù¶è100MHz
        GPIO_InitStructure.GPIO_OType = GPIO_OType_PP;      //íÆíì¸′óÃêä3ö
        GPIO_InitStructure.GPIO_PuPd = GPIO_PuPd_UP;        //éÏà-
        GPIO_Init(GPIOC,&GPIO_InitStructure);              //3õê¼»ˉPF9
          
        TIM_TimeBaseStructure.TIM_Prescaler=psc;  //¶¨ê±Æ÷·ÖÆμ
        TIM_TimeBaseStructure.TIM_CounterMode=TIM_CounterMode_Up; //ÏòéϼÆêyÄ￡ê½
        TIM_TimeBaseStructure.TIM_Period=arr;   //×Ô¶ˉÖØ×°ÔØÖμ
        TIM_TimeBaseStructure.TIM_ClockDivision=TIM_CKD_DIV1;        
        TIM_TimeBaseInit(TIM3,&TIM_TimeBaseStructure);//3õê¼»ˉ¶¨ê±Æ÷14
       
//TIM_UpdateRequestConfig(TIM3,TIM_UpdateSource_Regular);
        //3õê¼»ˉTIM14 Channel1 PWMÄ￡ê½         
        TIM_OCInitStructure.TIM_OCMode = TIM_OCMode_PWM2; //Ñ¡Ôñ¶¨ê±Æ÷Ä￡ê½:TIMÂö3å¿í¶èμ÷ÖÆÄ￡ê½2
        TIM_OCInitStructure.TIM_OutputState = TIM_OutputState_Enable; //±è½Ïêä3öê1Äü
        TIM_OCInitStructure.TIM_OCPolarity = TIM_OCPolarity_Low; //êä3ö¼«DÔ:TIMêä3ö±è½Ï¼«DÔμí
  TIM_OCInitStructure.TIM_Pulse                        = 0xFF;
        TIM_OC3Init(TIM3, &TIM_OCInitStructure);  //¸ù¾YTÖ¸¶¨μÄ2Îêy3õê¼»ˉíaéèTIM1 4OC1

// TIM_ITConfig(TIM3,TIM_IT_Update,ENABLE);

  TIM_SelectMasterSlaveMode(TIM3, TIM_MasterSlaveMode_Enable);
  TIM_SelectOutputTrigger(TIM3, TIM_TRGOSource_Update);
        TIM_OC3PreloadConfig(TIM3, TIM_OCPreload_Enable);  //ê1ÄüTIM14ÔúCCR1éÏμÄԤװÔؼÄ′æÆ÷

  TIM_ARRPreloadConfig(TIM3,ENABLE);//ARPEê1Äü
       
        NVIC_InitStructure.NVIC_IRQChannel=TIM3_IRQn; //¶¨ê±Æ÷4ÖD¶Ï
        NVIC_InitStructure.NVIC_IRQChannelPreemptionPriority=0x02; //ÇàÕ¼óÅÏ輶1
        NVIC_InitStructure.NVIC_IRQChannelSubPriority=0x04; //×óóÅÏ輶4
        NVIC_InitStructure.NVIC_IRQChannelCmd=ENABLE;
        NVIC_Init(&NVIC_InitStructure);
       

  TIM_Cmd(TIM3, ENABLE);  //ê1ÄüTIM14
                                                                          
}



void TIM4_Int_Init(u16 arr,u16 psc)
{
        TIM_TimeBaseInitTypeDef TIM_TimeBaseInitStructure;
        NVIC_InitTypeDef NVIC_InitStructure;
       
        RCC_APB1PeriphClockCmd(RCC_APB1Periph_TIM4,ENABLE);  ///ê1ÄüTIM3ê±Öó
                TIM_SelectSlaveMode(TIM4, TIM_SlaveMode_External1);
  TIM_SelectInputTrigger(TIM4, TIM_TS_ITR2);
       
  TIM_TimeBaseInitStructure.TIM_Period = arr;         //×Ô¶ˉÖØ×°ÔØÖμ
        TIM_TimeBaseInitStructure.TIM_Prescaler=psc;  //¶¨ê±Æ÷·ÖÆμ
        TIM_TimeBaseInitStructure.TIM_CounterMode=TIM_CounterMode_Up; //ÏòéϼÆêyÄ￡ê½
        TIM_TimeBaseInitStructure.TIM_ClockDivision=TIM_CKD_DIV1;
       
        TIM_TimeBaseInit(TIM4,&TIM_TimeBaseInitStructure);//3õê¼»ˉTIM4
       
        TIM_ITConfig(TIM4,TIM_IT_Update,ENABLE);

        NVIC_InitStructure.NVIC_IRQChannel=TIM4_IRQn; //¶¨ê±Æ÷4ÖD¶Ï
        NVIC_InitStructure.NVIC_IRQChannelPreemptionPriority=0x02; //ÇàÕ¼óÅÏ輶1
        NVIC_InitStructure.NVIC_IRQChannelSubPriority=0x03; //×óóÅÏ輶4
        NVIC_InitStructure.NVIC_IRQChannelCmd=ENABLE;
        NVIC_Init(&NVIC_InitStructure);
       
        TIM_Cmd(TIM4,ENABLE); //ê1Äü¶¨ê±Æ÷4       
}


void TIM4_IRQHandler(void)
{
       
        if(TIM_GetITStatus(TIM4,TIM_IT_Update)!=RESET) //òç3öÖD¶Ï
        {
                x=x+1;   
        }
        TIM_ClearITPendingBit(TIM4,TIM_IT_Update);  //Çå3yÖD¶Ï±ê־λ
}