RTT定时器输出比较模式下输出方波不连续问题

wqtslove

TIM3-CH4  想输出70Khz的方波，发现我的程序最多能上24Khz，再高就会看到比较明显的方波不连续现象。
TIM3初始化和中断函数  单独拿出来不跑系统，到70Khz没问题。
新手，不了解RTT的工作原理，向大家请教原因是什么，谢谢。
工程文件时从RTT1.2.0版改的，直接把led闪灯程序删掉，添加了TIM3初始化和中断函数。
大概修改如下：

#include "led.h"

TIM_TimeBaseInitTypeDef  TIM_TimeBaseStructure;
TIM_OCInitTypeDef  TIM_OCInitStructure;
__IO uint16_t CCR1_Val = 32768;
__IO uint16_t CCR2_Val = 108;
__IO uint16_t CCR3_Val = 8192;
__IO uint16_t CCR4_Val = 300;
uint16_t PrescalerValue = 0;

/* Private function prototypes -----------------------------------------------*/
void RCC_Configuration(void);
void GPIO_Configuration(void);
static void NVIC_Configuration(void);

ALIGN(RT_ALIGN_SIZE)
static rt_uint8_t led_stack[ 512 ];
static struct rt_thread led_thread;
static void led_thread_entry(void* parameter)
{
  /* System Clocks Configuration */
  RCC_Configuration();

  /* NVIC Configuration */
  NVIC_Configuration();

  /* GPIO Configuration */
  GPIO_Configuration();

  /* ---------------------------------------------------------------------------
    TIM3 Configuration: Output Compare Toggle Mode:
    TIM3CLK = SystemCoreClock / 2,
    The objective is to get TIM3 counter clock at 12 MHz:
     - Prescaler = (TIM3CLK / TIM3 counter clock) - 1
    CC1 update rate = TIM3 counter clock / CCR1_Val = 366.2 Hz
    CC2 update rate = TIM3 counter clock / CCR2_Val = 732.4 Hz
    CC3 update rate = TIM3 counter clock / CCR3_Val = 1464.8 Hz
    CC4 update rate = TIM3 counter clock / CCR4_Val = 2929.6 Hz
  ----------------------------------------------------------------------------*/
  /* Compute the prescaler value */
  PrescalerValue = (uint16_t) (SystemCoreClock / 12000000) - 1;

  /* Time base configuration */
  TIM_TimeBaseStructure.TIM_Period = 65535;
  TIM_TimeBaseStructure.TIM_Prescaler = PrescalerValue;
  TIM_TimeBaseStructure.TIM_ClockDivision = 0;
  TIM_TimeBaseStructure.TIM_CounterMode = TIM_CounterMode_Up;

  TIM_TimeBaseInit(TIM3, &TIM_TimeBaseStructure);

  /* Output Compare Toggle Mode configuration: Channel1 */
  TIM_OCInitStructure.TIM_OCMode = TIM_OCMode_Toggle;
  TIM_OCInitStructure.TIM_OCPolarity = TIM_OCPolarity_Low;


  /* Output Compare Toggle Mode configuration: Channel4 */
  TIM_OCInitStructure.TIM_OutputState = TIM_OutputState_Enable;
  TIM_OCInitStructure.TIM_Pulse = CCR4_Val;

  TIM_OC4Init(TIM3, &TIM_OCInitStructure);

  TIM_OC4PreloadConfig(TIM3, TIM_OCPreload_Disable);

  /* TIM enable counter */
  TIM_Cmd(TIM3, ENABLE);

  /* TIM IT enable */
  TIM_ITConfig(TIM3, TIM_IT_CC4, ENABLE);

    while (1)
    {

        rt_thread_delay( 5 );
    }
}

uint16_t capture = 0;
/**
  * @brief  This function handles TIM3 global interrupt request.
  * @param  None
  * @retval None
  */
void TIM3_IRQHandler(void)
{


  /* TIM3_CH4 toggling with frequency = 1464.8 Hz */
  if (TIM_GetITStatus(TIM3, TIM_IT_CC4) != RESET)
  {
    TIM_ClearITPendingBit(TIM3, TIM_IT_CC4);
    capture = TIM_GetCapture4(TIM3);
    TIM_SetCompare4(TIM3, capture + CCR4_Val);
  }
}



/**
  * @brief  Configures the different system clocks.
  * @param  None
  * @retval None
  */
void RCC_Configuration(void)
{
  /* PCLK1 = HCLK/4 */
//  RCC_PCLK1Config(RCC_HCLK_Div4);

  /* TIM3 clock enable */
  RCC_APB1PeriphClockCmd(RCC_APB1Periph_TIM3, ENABLE);

  /* GPIOA clock enable */
  RCC_APB2PeriphClockCmd(RCC_APB2Periph_GPIOA | RCC_APB2Periph_GPIOB|
                         RCC_APB2Periph_GPIOC | RCC_APB2Periph_AFIO, ENABLE);
}

/**
  * @brief  Configure the TIM3 Pins.
  * @param  None
  * @retval None
  */
void GPIO_Configuration(void)
{
  GPIO_InitTypeDef GPIO_InitStructure;

#ifdef STM32F10X_CL
  /*GPIOB Configuration: TIM3 channel1, 2, 3 and 4 */
  GPIO_InitStructure.GPIO_Pin =  GPIO_Pin_6 | GPIO_Pin_7 | GPIO_Pin_8 | GPIO_Pin_9;
  GPIO_InitStructure.GPIO_Mode = GPIO_Mode_AF_PP;
  GPIO_InitStructure.GPIO_Speed = GPIO_Speed_50MHz;

  GPIO_Init(GPIOC, &GPIO_InitStructure);

  GPIO_PinRemapConfig(GPIO_FullRemap_TIM3, ENABLE);

#else
  /* GPIOA Configuration:TIM3 Channel1, 2, 3 and 4 as alternate function push-pull */
  GPIO_InitStructure.GPIO_Pin = GPIO_Pin_6 | GPIO_Pin_7;
  GPIO_InitStructure.GPIO_Mode = GPIO_Mode_AF_PP;
  GPIO_InitStructure.GPIO_Speed = GPIO_Speed_50MHz;

  GPIO_Init(GPIOA, &GPIO_InitStructure);

  GPIO_InitStructure.GPIO_Pin = GPIO_Pin_0 | GPIO_Pin_1;
  GPIO_Init(GPIOB, &GPIO_InitStructure);
#endif
}

/**
  * @brief  Configure the nested vectored interrupt controller.
  * @param  None
  * @retval None
  */
static void NVIC_Configuration(void)
{
  NVIC_InitTypeDef NVIC_InitStructure;

  /* Enable the TIM3 global Interrupt */
  NVIC_InitStructure.NVIC_IRQChannel = TIM3_IRQn;
  NVIC_InitStructure.NVIC_IRQChannelPreemptionPriority = 0;
  NVIC_InitStructure.NVIC_IRQChannelSubPriority = 0;
  NVIC_InitStructure.NVIC_IRQChannelCmd = ENABLE;
  NVIC_Init(&NVIC_InitStructure);
}