使用stm32f407实现pwm的

步骤如下：

1. 配置GPIO为PWM输出模式。

2. 配置定时器为PWM模式，设置周期和占空比。

3. 启动定时器。

代码示例：

#include "stm32f4xx.h"

void PWM_GPIO_Config(void)
{
    GPIO_InitTypeDef GPIO_InitStructure;
    
    RCC_AHB1PeriphClockCmd(RCC_AHB1Periph_GPIOA, ENABLE); //使能GPIOA时钟
    
    GPIO_InitStructure.GPIO_Pin = GPIO_Pin_0; //设置GPIOA0为PWM输出
    GPIO_InitStructure.GPIO_Mode = GPIO_Mode_AF; //复用模式
    GPIO_InitStructure.GPIO_Speed = GPIO_Speed_100MHz; //速度100MHz
    GPIO_InitStructure.GPIO_OType = GPIO_OType_PP; //推挽输出
    GPIO_InitStructure.GPIO_PuPd = GPIO_PuPd_UP; //上拉
    GPIO_Init(GPIOA, &GPIO_InitStructure); //初始化GPIOA0
    
    GPIO_PinAFConfig(GPIOA, GPIO_PinSource0, GPIO_AF_TIM2); //将GPIOA0与TIM2通道1相连
}

void PWM_TIM_Config(void)
{
    TIM_TimeBaseInitTypeDef TIM_TimeBaseInitStructure;
    TIM_OCInitTypeDef TIM_OCInitStructure;
    
    RCC_APB1PeriphClockCmd(RCC_APB1Periph_TIM2, ENABLE); //使能TIM2时钟
    
    TIM_TimeBaseInitStructure.TIM_Period = 9999; //定时器周期
    TIM_TimeBaseInitStructure.TIM_Prescaler = 83; //定时器预分频
    TIM_TimeBaseInitStructure.TIM_ClockDivision = 0; //时钟分频
    TIM_TimeBaseInitStructure.TIM_CounterMode = TIM_CounterMode_Up; //向上计数模式
    TIM_TimeBaseInit(TIM2, &TIM_TimeBaseInitStructure); //初始化TIM2
    
    TIM_OCInitStructure.TIM_OCMode = TIM_OCMode_PWM1; //PWM模式1
    TIM_OCInitStructure.TIM_OutputState = TIM_OutputState_Enable; //输出使能
    TIM_OCInitStructure.TIM_Pulse = 5000; //占空比50%
    TIM_OCInitStructure.TIM_OCPolarity = TIM_OCPolarity_High; //输出极性为高
    TIM_OC1Init(TIM2, &TIM_OCInitStructure); //初始化TIM2通道1
    
    TIM_Cmd(TIM2, ENABLE); //使能TIM2
}

int main(void)
{
    PWM_GPIO_Config(); //配置GPIO为PWM输出模式
    PWM_TIM_Config(); //配置定时器为PWM模式
    while(1);
}