F4单片机高级定时器输出PWM问题

Sxxyly · 发表于 2020-5-9 21:42:28

请各位帮我看看这段代码到底哪里有问题。函数是控制舵机的PWM输出的初始化。调用 TIM8_PWM_Out_Init(50,75)函数原本期望能输出50hz，7.5%占空比的pwm波。最后输出的结果频率没问题，但是占空莫名其妙的保持40%,不能控制舵机，修改CCR寄存器的值也完全不能起作用。
使用的是高级定时器8的通道3和4。系统主频是168MHZ。

下面是函数代码：
#define ACCURACY 10000 //u16(2500/0.25)

//TIM8控制舵机 servo_hz=50hz ，init_duty= 75‰（千分制避免小数）
u8 TIM8_PWM_Out_Init(uint16_t servo_hz,u8 init_duty)
{
TIM_TimeBaseInitTypeDef  TIM_TimeBaseStructure;
TIM_OCInitTypeDef  TIM_OCInitStructure;
GPIO_InitTypeDef GPIO_InitStructure;

uint16_t PrescalerValue = 0;
u32 hz_set = ACCURACY*servo_hz;//50Hz*10000

RCC_APB2PeriphClockCmd(RCC_APB2Periph_TIM8, ENABLE);

RCC_AHB1PeriphClockCmd(RCC_AHB1Periph_GPIOC, ENABLE);

TIM_TimeBaseStructInit(&TIM_TimeBaseStructure);
      TIM_OCStructInit(&TIM_OCInitStructure);

hz_set = LIMIT (hz_set,1,84000000);

  GPIO_InitStructure.GPIO_Pin = GPIO_Pin_8 | GPIO_Pin_9; //PC8-TIM8CH3  PC9-TIM8CH4
  GPIO_InitStructure.GPIO_Mode = GPIO_Mode_AF;
  GPIO_InitStructure.GPIO_Speed = GPIO_Speed_100MHz;
  GPIO_InitStructure.GPIO_OType = GPIO_OType_PP;
  GPIO_InitStructure.GPIO_PuPd = GPIO_PuPd_UP ;
  GPIO_Init(GPIOC, &GPIO_InitStructure);

  GPIO_PinAFConfig(GPIOC, GPIO_PinSource8, GPIO_AF_TIM8);
  GPIO_PinAFConfig(GPIOC, GPIO_PinSource9, GPIO_AF_TIM8);

  PrescalerValue = (uint16_t) ( ( SystemCoreClock ) / hz_set ) - 1;//SystemCoreClock————168Mhz 168000000/（10000*50） =336

  /* Time base configuration */
  TIM_TimeBaseStructure.TIM_Period = ACCURACY-1;    //9999
  TIM_TimeBaseStructure.TIM_Prescaler = PrescalerValue; //168000000/（10000*50） =336
  TIM_TimeBaseStructure.TIM_ClockDivision = 0;
  TIM_TimeBaseStructure.TIM_CounterMode = TIM_CounterMode_Up;
  TIM_TimeBaseStructure.TIM_RepetitionCounter = 0;
  TIM_TimeBaseInit(TIM8, &TIM_TimeBaseStructure);

  TIM_OCInitStructure.TIM_OCMode = TIM_OCMode_PWM1;
  TIM_OCInitStructure.TIM_OutputNState = TIM_OutputNState_Enable;
  TIM_OCInitStructure.TIM_OCPolarity = TIM_OCPolarity_High;
//TIM_OCInitStructure.TIM_OCNPolarity = TIM_OCNPolarity_Low;
//TIM_OCInitStructure.TIM_OCIdleState = TIM_OCIdleState_Set;
//TIM_OCInitStructure.TIM_OCNIdleState = TIM_OCNIdleState_Reset;

  /* PWM1 Mode configuration: Channe3 */
  TIM_OCInitStructure.TIM_OutputState = TIM_OutputState_Enable;
  TIM_OCInitStructure.TIM_Pulse = init_duty*10;  //写入CCRx寄存器
  TIM_OC3Init(TIM8, &TIM_OCInitStructure);
  TIM_OC3PreloadConfig(TIM8, TIM_OCPreload_Enable);

  /* PWM1 Mode configuration: Channe4 */
  TIM_OCInitStructure.TIM_OutputState = TIM_OutputState_Enable;
  TIM_OCInitStructure.TIM_Pulse = init_duty*10;
  TIM_OC4Init(TIM8, &TIM_OCInitStructure);
  TIM_OC4PreloadConfig(TIM8, TIM_OCPreload_Enable);

  TIM_CtrlPWMOutputs(TIM8, ENABLE);

  TIM_ARRPreloadConfig(TIM8, ENABLE);
  TIM_Cmd(TIM8, ENABLE);

if( hz_set > 84000000 )
{
return 0;
}
else
{
return 1;
}
}