通用定时器pwm输出

秋夜月汐

定时器初始化函数
void PWM_F_Init(u16 arr,u16 psc)
{
GPIO_InitTypeDef GPIO_InitStructure;
TIM_TimeBaseInitTypeDef  TIM_TimeBaseStructure;
TIM_OCInitTypeDef  TIM_OCInitStructure;

RCC_APB1PeriphClockCmd(RCC_APB1Periph_TIM3,ENABLE);
RCC_APB2PeriphClockCmd(RCC_APB2Periph_GPIOB,ENABLE);

GPIO_InitStructure.GPIO_Pin=GPIO_Pin_0;
GPIO_InitStructure.GPIO_Mode=GPIO_Mode_AF_PP;
GPIO_InitStructure.GPIO_Speed=GPIO_Speed_50MHz;
GPIO_Init(GPIOB,&GPIO_InitStructure);

TIM_TimeBaseStructure.TIM_Period=arr;
TIM_TimeBaseStructure.TIM_Period=psc;
TIM_TimeBaseStructure.TIM_ClockDivision=0;
TIM_TimeBaseStructure.TIM_CounterMode=TIM_CounterMode_Up;
TIM_TimeBaseInit(TIM3, &TIM_TimeBaseStructure);

TIM_OCInitStructure.TIM_OCMode = TIM_OCMode_PWM2; 
TIM_OCInitStructure.TIM_OutputState = TIM_OutputState_Enable;
TIM_OCInitStructure.TIM_Pulse = 0; 
TIM_OCInitStructure.TIM_OCPolarity = TIM_OCPolarity_High; 
TIM_OC3Init(TIM3, &TIM_OCInitStructure); 
TIM_CtrlPWMOutputs(TIM3,ENABLE);
TIM_OC3PreloadConfig(TIM3, TIM_OCPreload_Enable);

TIM_ARRPreloadConfig(TIM3, ENABLE); 
TIM_Cmd(TIM3, ENABLE); 

}

MAIN文件
#include <stm32f10x.h>
#include "PWM_F.h"
#include "sys.h"
#include <stm32f10x_tim.h>


int main(void)
{
PWM_F_Init(899,0);
while(1)
{
TIM_SetCompare3(TIM3,500);
}
}

就是出不来波，哪里错了？