如何用TIMER3输出一个频率为36KHz占空比自动变化的PWM波形？

平台:KEIL5+stm32f103
功能：用TIMER3在通道1上输出一个频率为36KHz,占空比自动变化的PWM波形。为了效果更明显，我把其他通道都打开了。

代码如下：这个代码是在官方例程的基础上加了一些修改：
1.增加设置PWM的频率和占空比的函数，方便调用；
2.增加了关闭通道的功能（在该例程中没有使用）；


#define DUTY_CYCLCE_BUF_LEN 6//6种占空比

//DMA自动读取buf里面的内容到CCR1
uint16_t DutyCyclebuf[DUTY_CYCLCE_BUF_LEN] = {500,333,249,166,83,41};


/**
  * disable CHX output
  *
  */

void DisableChxOutput(uint8_t CHX)
{
        switch(CHX)
        {
                case 1:
                {
                        /* Disable the Channel 1: Reset the CC1E Bit */
                          TIM3->CCER &= (uint16_t)(~(uint16_t)TIM_CCER_CC1E);
                       
                        TIM_ITConfig(TIM3, TIM_IT_CC1 , DISABLE);
                }
                break;
                case 2:
                {
                        /* Disable the Channel 2: Reset the CC2E Bit */
                          TIM3->CCER &= (uint16_t)(~(uint16_t)TIM_CCER_CC2E);
                        TIM_ITConfig(TIM3, TIM_IT_CC2 , DISABLE);
                }
                break;
                case 3:
                {
                        TIM3->CCER &= (uint16_t)(~(uint16_t)TIM_CCER_CC3E);
                        TIM_ITConfig(TIM3, TIM_IT_CC3 , DISABLE);
                }
                break;
                case 4:
                {
                        TIM3->CCER &= (uint16_t)(~(uint16_t)TIM_CCER_CC4E);
                        TIM_ITConfig(TIM3, TIM_IT_CC4 , DISABLE);
                }
                break;

                default:
                break;
                       
        }

}

void TIMER3_PWM_GPIO_Configuration(void)
{
        GPIO_InitTypeDef GPIO_InitStructure;

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

        /* 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);
}




uint16_t SetPWMFreq(uint16_t TargetFreaq_KHz)
{
        uint16_t TIM_Period = 0;

        TIM_Period = 24000/TargetFreaq_KHz;

        return TIM_Period;
}


//DutyCycle:0~100
//TIM_Period:计数周期
uint16_t SetPWMDutyCycle(uint16_t TIM_Period,uint8_t DutyCycle)
{
        uint32_t TIM_Pulse = 0;
        uint32_t Period = TIM_Period;

        TIM_Pulse = (DutyCycle*Period)/100;
       
        return (uint16_t)TIM_Pulse;
}




void DMA_Configuration(void)
{
  DMA_InitTypeDef D;

  DMA_DeInit(DMA1_Channel3);                   //DMA1_3通道初始化

  D.DMA_PeripheralBaseAddr =(u32)&TIM3->CCR1;  //DMA外设基址 TIM3_CCR1_Address
  D.DMA_MemoryBaseAddr = (u32)DutyCyclebuf;    //DMA内存基址
  D.DMA_DIR = DMA_DIR_PeripheralDST;           //DST外设作为数据传送目的地址,SRC则作为源地址
  D.DMA_BufferSize = DUTY_CYCLCE_BUF_LEN;      //DMA缓存大小
  D.DMA_PeripheralInc = DMA_PeripheralInc_Disable; //外设地址寄存器不增加
  D.DMA_MemoryInc = DMA_MemoryInc_Enable;          //内存地址寄存器不增加
  D.DMA_PeripheralDataSize = DMA_PeripheralDataSize_HalfWord; //外存字宽16bit
  D.DMA_MemoryDataSize = DMA_MemoryDataSize_HalfWord;         //内存字宽16bit

  //D.DMA_Mode = DMA_Mode_Normal;     //工作在循环模式
  D.DMA_Mode =DMA_Mode_Circular;

  D.DMA_Priority = DMA_Priority_High; //DMA置为高优先级
  D.DMA_M2M = DMA_M2M_Disable;        //不置为内存到内存传输

  DMA_Init(DMA1_Channel3, &D);        //初始化DMA1
  DMA_Cmd(DMA1_Channel3, ENABLE);     //DMA1_3使能
}



void TIMER3_PWMMode_Config(void)       
{
    TIM_TimeBaseInitTypeDef  TIM_TimeBaseStructure;
    TIM_OCInitTypeDef  TIM_OCInitStructure;

    //uint16_t Timer3_PWM_CCR1_Val = 333;
    uint16_t Timer3_PWM_CCR2_Val = 249;
    uint16_t Timer3_PWM_CCR3_Val = 166;
    uint16_t Timer3_PWM_CCR4_Val = 83;
    uint16_t Timer3_PWM__PrescalerValue = 0;
    uint16_t Set_Period = 665;


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

  TIMER3_PWM_GPIO_Configuration();

  /* -----------------------------------------------------------------------
    TIM3 Configuration: generate 4 PWM signals with 4 different duty cycles:
    The TIM3CLK frequency is set to SystemCoreClock (Hz), to get TIM3 counter
    clock at 24 MHz the Prescaler is computed as following:
     - Prescaler = (TIM3CLK / TIM3 counter clock) - 1
    SystemCoreClock is set to 72 MHz for Low-density, Medium-density, High-density
   
    The TIM3 is running at 36 KHz: TIM3 Frequency = TIM3 counter clock/(ARR + 1)
                                                  = 24 MHz / 666 = 36 KHz
    TIM3 Channel1 duty cycle = (TIM3_CCR1/ TIM3_ARR)* 100 = 50%
    TIM3 Channel2 duty cycle = (TIM3_CCR2/ TIM3_ARR)* 100 = 37.5%
    TIM3 Channel3 duty cycle = (TIM3_CCR3/ TIM3_ARR)* 100 = 25%
    TIM3 Channel4 duty cycle = (TIM3_CCR4/ TIM3_ARR)* 100 = 12.5%
  ----------------------------------------------------------------------- */
  /* Compute the prescaler value */
  Timer3_PWM__PrescalerValue = (uint16_t) (SystemCoreClock / 24000000) - 1;

  Set_Period = SetPWMFreq(36);//配置输出频率为36kHz
  //Timer3_PWM_CCR1_Val = SetPWMDutyCycle(Set_Period,20);
  Timer3_PWM_CCR2_Val = SetPWMDutyCycle(Set_Period,50);
  Timer3_PWM_CCR3_Val = SetPWMDutyCycle(Set_Period,70);
  Timer3_PWM_CCR4_Val = SetPWMDutyCycle(Set_Period,90);

  
  /* Time base configuration */
  TIM_TimeBaseStructure.TIM_Period = Set_Period;
  TIM_TimeBaseStructure.TIM_Prescaler = Timer3_PWM__PrescalerValue;
  TIM_TimeBaseStructure.TIM_ClockDivision = 0;
  TIM_TimeBaseStructure.TIM_CounterMode = TIM_CounterMode_Up;

  TIM_TimeBaseInit(TIM3, &TIM_TimeBaseStructure);

  /* PWM1 Mode configuration: Channel1 */
  TIM_OCInitStructure.TIM_OCMode = TIM_OCMode_PWM1;
  TIM_OCInitStructure.TIM_OutputState = TIM_OutputState_Enable;
  TIM_OCInitStructure.TIM_Pulse = DutyCyclebuf[0];//Timer3_PWM_CCR1_Val;
  TIM_OCInitStructure.TIM_OCPolarity = TIM_OCPolarity_High;

  TIM_OC1Init(TIM3, &TIM_OCInitStructure);

  TIM_OC1PreloadConfig(TIM3, TIM_OCPreload_Enable);//下次更新事件时，更新寄存器的值

  /* PWM1 Mode configuration: Channel2 */
  TIM_OCInitStructure.TIM_OutputState = TIM_OutputState_Enable;
  TIM_OCInitStructure.TIM_Pulse = Timer3_PWM_CCR2_Val;

  TIM_OC2Init(TIM3, &TIM_OCInitStructure);

  TIM_OC2PreloadConfig(TIM3, TIM_OCPreload_Enable);

  /* PWM1 Mode configuration: Channel3 */
  TIM_OCInitStructure.TIM_OutputState = TIM_OutputState_Enable;
  TIM_OCInitStructure.TIM_Pulse = Timer3_PWM_CCR3_Val;

  TIM_OC3Init(TIM3, &TIM_OCInitStructure);

  TIM_OC3PreloadConfig(TIM3, TIM_OCPreload_Enable);

  /* PWM1 Mode configuration: Channel4 */
  TIM_OCInitStructure.TIM_OutputState = TIM_OutputState_Enable;
  TIM_OCInitStructure.TIM_Pulse = Timer3_PWM_CCR4_Val;

  TIM_OC4Init(TIM3, &TIM_OCInitStructure);

  TIM_OC4PreloadConfig(TIM3, TIM_OCPreload_Enable);

  TIM_ARRPreloadConfig(TIM3, ENABLE);

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

  TIM_DMACmd(TIM3, TIM_DMA_Update, ENABLE); //TIM3 DMA请求使能
  
  DMA_Configuration();
}


输出波形如下：绿色的是PA6，即通道1，是我们想要的效果。红色的PA7为通道2.