我用TIM2做主模式 TIM1和TIM3做从模式，用TIM2门控方式成功触发同步TIM1和TIM3，但是如果用TIM3做主，TIM2和TIM1做从，则无法实现，按理说通用定时器区别是不大的，为什么会出现这种情况？请大家帮忙看看，下面是代码：
 
 #include "stm32f10x.h"
 
 /* Private function prototypes -----------------------------------------------*/
 void RCC_Configuration(void);
 void GPIO_Configuration(void);
 
 
 int main(void)
 {
   /* System Clocks Configuration */
   RCC_Configuration();
 
   /* GPIO Configuration */
  GPIO_Configuration();
 
  /* Timers synchronisation in parallel mode ----------------------------
     1/TIM3 is configured as Master Timer:
     - PWM Mode is used
     - The TIM2 Update event is used as Trigger Output  
     2/TIM1 and TIM2 are slaves for TIM3,
     - PWM Mode is used
     - The ITR1(TIM3) is used as input trigger for both slaves
     - Gated mode is used, so starts and stops of slaves counters
       are controlled by the Master trigger output signal(update event).
     
     
   -------------------------------------------------------------------- */
 
  /* Time base configuration */
   TIM_TimeBaseStructure.TIM_Period = 255;
 TIM_TimeBaseStructure.TIM_Prescaler = 0;
   TIM_TimeBaseStructure.TIM_ClockDivision = 0;
  TIM_TimeBaseStructure.TIM_CounterMode = TIM_CounterMode_Up;
 
  TIM_TimeBaseInit(TIM3, &TIM_TimeBaseStructure);
 
   TIM_TimeBaseStructure.TIM_Period = 9;
  TIM_TimeBaseInit(TIM2, &TIM_TimeBaseStructure);
 
  TIM_TimeBaseStructure.TIM_Period = 4;
  TIM_TimeBaseInit(TIM1, &TIM_TimeBaseStructure);
 
   /* Master Configuration in PWM1 Mode */
   TIM_OCInitStructure.TIM_OCMode = TIM_OCMode_PWM1;
   TIM_OCInitStructure.TIM_OutputState = TIM_OutputState_Enable;
  TIM_OCInitStructure.TIM_Pulse = 64;
   TIM_OCInitStructure.TIM_OCPolarity = TIM_OCPolarity_High;
 
   TIM_OC1Init(TIM3, &TIM_OCInitStructure);
 
   /* Select the Master Slave Mode */
   TIM_SelectMasterSlaveMode(TIM3, TIM_MasterSlaveMode_Enable);
 
   /* Master Mode selection */
  TIM_SelectOutputTrigger(TIM3, TIM_TRGOSource_Update);
 
   /* Slaves Configuration: PWM1 Mode */
  TIM_OCInitStructure.TIM_OCMode = TIM_OCMode_PWM1;
   TIM_OCInitStructure.TIM_OutputState = TIM_OutputState_Enable;
  TIM_OCInitStructure.TIM_Pulse = 3;
 
  TIM_OC1Init(TIM2, &TIM_OCInitStructure);
 
   TIM_OC1Init(TIM1, &TIM_OCInitStructure);
 
   /* Slave Mode selection: TIM3 */
   TIM_SelectSlaveMode(TIM2, TIM_SlaveMode_Gated);
   TIM_SelectInputTrigger(TIM2, TIM_TS_ITR1);
 
   /* Slave Mode selection: TIM4 */
   TIM_SelectSlaveMode(TIM1, TIM_SlaveMode_Gated);
   TIM_SelectInputTrigger(TIM1, TIM_TS_ITR1);
 
   /* TIM enable counter */
   TIM_Cmd(TIM3, ENABLE);
   TIM_Cmd(TIM2, ENABLE);
   TIM_Cmd(TIM1, ENABLE);
 
  TIM_CtrlPWMOutputs(TIM1, ENABLE);
 
   while (1)
   {}
 }
 
/**
   * @brief  Configures the different system clocks.
   * @param  None
   * @retval : None
   */
 void RCC_Configuration(void)
 {
  /* Setup the microcontroller system. Initialize the Embedded Flash Interface,  
     initialize the PLL and update the SystemFrequency variable. */
   SystemInit();
  
   /* TIM2, TIM3 and TIM4 clock enable */
   RCC_APB1PeriphClockCmd(RCC_APB1Periph_TIM2 | RCC_APB1Periph_TIM3 |
                          RCC_APB1Periph_TIM4, ENABLE);
 
   RCC_APB2PeriphClockCmd(RCC_APB2Periph_TIM1, ENABLE);
   /* GPIOA and GPIOB clock enable */
   RCC_APB2PeriphClockCmd(RCC_APB2Periph_GPIOA | RCC_APB2Periph_GPIOB, ENABLE);
 }
 
 /**
  * @brief  Configure the GPIOD Pins.
   * @param  None
   * @retval : None
   */
 void GPIO_Configuration(void)
 {
   GPIO_InitTypeDef GPIO_InitStructure;
 
   /* GPIOA Configuration: PA0(TIM2 CH1) and PA6(TIM3 CH1) as alternate function push-pull */
   GPIO_InitStructure.GPIO_Pin = GPIO_Pin_0 | GPIO_Pin_6 | GPIO_Pin_8;
   GPIO_InitStructure.GPIO_Mode = GPIO_Mode_AF_PP;
   GPIO_InitStructure.GPIO_Speed = GPIO_Speed_50MHz;
 
   GPIO_Init(GPIOA, &GPIO_InitStructure);
 
   /* GPIOB Configuration: PB6(TIM4 CH1) as alternate function push-pull */
   GPIO_InitStructure.GPIO_Pin = GPIO_Pin_6;
 
   GPIO_Init(GPIOB, &GPIO_InitStructure);
 }
 
 #ifdef  USE_FULL_ASSERT
 
 /**
  * @brief  Reports the name of the source file and the source line number
  *   where the assert_param error has occurred.
   * @param file: pointer to the source file name
  * @param line: assert_param error line source number
   * @retval : None
   */
 void assert_failed(uint8_t* file, uint32_t line)
 {
   /* User can add his own implementation to report the file name and line number,
      ex: printf("Wrong parameters value: file %s on line %d\r\n", file, line) */
 
  while (1)
   {}
 }
 #endif