正点例程修改了pwm但不知道为什么灯的亮度一直不变

WXM · 发表于 2016-8-2 15:56:00

void TIM4_PWM_Init(u16 arr,u16 psc)
{
GPIO_InitTypeDef GPIO_InitStructure;
TIM_TimeBaseInitTypeDef TIM_TimeBaseStructure;
TIM_OCInitTypeDef TIM_OCInitStructure;

RCC_APB1PeriphClockCmd(RCC_APB1Periph_TIM4, ENABLE);//使能定时器4时钟
RCC_APB2PeriphClockCmd(RCC_APB2Periph_GPIOD | RCC_APB2Periph_AFIO, ENABLE); //使能GPIO外设和AFIO复用功能模块时钟
//设置该引脚为复用输出功能,输出TIM4 CH2的PWM脉冲波形GPIOD.13
GPIO_InitStructure.GPIO_Pin = GPIO_Pin_13; //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(GPIOD, &GPIO_InitStructure);//初始化GPIO

GPIO_PinRemapConfig(GPIO_Remap_TIM4, ENABLE); //Timer4部分重映射 TIM4_CH2->PD13
//初始化TIM4
TIM_TimeBaseStructure.TIM_Period = arr; //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
TIM_TimeBaseStructure.TIM_Prescaler =psc; //设置用来作为TIMx时钟频率除数的预分频值
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(TIM4, &TIM_TimeBaseStructure); //根据TIM_TimeBaseInitStruct中指定的参数初始化TIMx的时间基数单位

//初始化TIM3 Channel2 PWM模式
TIM_OCInitStructure.TIM_OCMode = TIM_OCMode_PWM2; //选择定时器模式:TIM脉冲宽度调制模式2 小于规定值时为无效电平，大于规定值时为有效电平
TIM_OCInitStructure.TIM_OutputState = TIM_OutputState_Enable; //比较输出使能
TIM_OCInitStructure.TIM_OCPolarity = TIM_OCPolarity_High; //输出极性:TIM输出比较极性高有效电平为高电平
TIM_OC2Init(TIM4, &TIM_OCInitStructure); //根据T指定的参数初始化外设TIM4 OC2
TIM_OC2PreloadConfig(TIM4, TIM_OCPreload_Enable); //使能TIM4在CCR2上的预装载寄存器
TIM_Cmd(TIM4, ENABLE); //使能TIM4
}

int main(void)
{
u16 led0pwmval=0;
u8 dir=1;
delay_init();            //延时函数初始化
NVIC_PriorityGroupConfig(NVIC_PriorityGroup_2);    //设置NVIC中断分组2:2位抢占优先级，2位响应优先级
uart_init(115200);    //串口初始化为115200
// LED_Init();       //LED端口初始化
TIM4_PWM_Init(899,0);    //不分频。PWM频率=72000000/900=80Khz
     GPIO_ResetBits(GPIOD,GPIO_Pin_13);

   while(1)
{
delay_ms(10);
if(dir)led0pwmval++;
else led0pwmval--;

if(led0pwmval>300)dir=0;
if(led0pwmval==0)dir=1;
TIM_SetCompare2(TIM4,300);    //TIM_SetCompare2(TIM4,led0pwmval);
printf("PWM is %d\n",led0pwmval);
}
}