STM32 ---- PWM

TIM_ARRPreloadConfig//开启/关闭ARR预转载

TIM_OCxPreloadConfig//开启/关闭CCRx预转载

//GPIOA.6
//TIM3 CHANNEL1
//freq:20Hz--100KHz  越小精度越高
void PWM_Init(u32 freq,double ratio)
{
    GPIO_InitTypeDef GPIO_InitStructure;
    TIM_TimeBaseInitTypeDef  TIM_TimeBaseStructure;
    TIM_OCInitTypeDef  TIM_OCInitStructure;
    
    RCC_APB1PeriphClockCmd(RCC_APB1Periph_TIM3, ENABLE);//###
     RCC_APB2PeriphClockCmd(RCC_APB2Periph_GPIOA, ENABLE);//###  //使能GPIO外设和AFIO复用功能模块时钟使能
    
    GPIO_InitStructure.GPIO_Pin = GPIO_Pin_7;//### //TIM_CH2
    GPIO_InitStructure.GPIO_Mode = GPIO_Mode_AF_PP;  //复用推挽输出
    GPIO_InitStructure.GPIO_Speed = GPIO_Speed_50MHz;
    GPIO_Init(GPIOA, &GPIO_InitStructure);//###
    //GPIO_WriteBit(GPIOA, GPIO_Pin_7,Bit_SET); // PA7上拉    
    TIM_TimeBaseStructure.TIM_Period =(u16)(1000000.0/freq); //设置在下一个更新事件装入活动的自动重装载寄存器周期的值     80K
    TIM_TimeBaseStructure.TIM_Prescaler =71; //设置用来作为TIMx时钟频率除数的预分频值  不分频
    TIM_TimeBaseStructure.TIM_ClockDivision = 0; //设置时钟分割:TDTS = Tck_tim
    TIM_TimeBaseStructure.TIM_CounterMode = TIM_CounterMode_Up;  //TIM向上计数模式
    TIM_TimeBaseInit(TIM3, &TIM_TimeBaseStructure); //###//根据TIM_TimeBaseInitStruct中指定的参数初始化TIMx的时间基数单位
    
     
    TIM_OCInitStructure.TIM_OCMode = TIM_OCMode_PWM1; //选择定时器模式:TIM脉冲宽度调制模式2
    TIM_OCInitStructure.TIM_OutputState = TIM_OutputState_Enable; //比较输出使能
    TIM_OCInitStructure.TIM_Pulse = 0; //设置待装入捕获比较寄存器的脉冲值
    TIM_OCInitStructure.TIM_OCPolarity = TIM_OCPolarity_High; //输出极性:TIM输出比较极性高
    TIM_OC2Init(TIM3, &TIM_OCInitStructure); //### //根据TIM_OCInitStruct中指定的参数初始化外设TIMx
    TIM_OC2PreloadConfig(TIM3, TIM_OCPreload_Enable); //### //使能TIMx在CCR2上的预装载寄存器
    
    //TIM_ARRPreloadConfig(TIM3, ENABLE); //使能TIMx在ARR上的预装载寄存器

    TIM_Cmd(TIM3, ENABLE); //### //使能TIMx外设
    
    TIM_SetCompare2(TIM3,(u16)(1000000.0/freq*ratio));//###

}