写一段STM32输出PWM波形的代码

好的，以下是一段简单的STM32输出PWM波形的代码：

#include "stm32f4xx.h"

int main(void)
{
    // 初始化GPIO和定时器
    RCC_AHB1PeriphClockCmd(RCC_AHB1Periph_GPIOA, ENABLE);
    RCC_APB1PeriphClockCmd(RCC_APB1Periph_TIM2, ENABLE);

    GPIO_InitTypeDef GPIO_InitStruct;
    GPIO_InitStruct.GPIO_Pin = GPIO_Pin_5;
    GPIO_InitStruct.GPIO_Mode = GPIO_Mode_AF;
    GPIO_InitStruct.GPIO_Speed = GPIO_Speed_100MHz;
    GPIO_InitStruct.GPIO_OType = GPIO_OType_PP;
    GPIO_InitStruct.GPIO_PuPd = GPIO_PuPd_UP;
    GPIO_Init(GPIOA, &GPIO_InitStruct);

    GPIO_PinAFConfig(GPIOA, GPIO_PinSource5, GPIO_AF_TIM2);

    TIM_TimeBaseInitTypeDef TIM_InitStruct;
    TIM_InitStruct.TIM_Period = 999;
    TIM_InitStruct.TIM_Prescaler = 8399;
    TIM_InitStruct.TIM_ClockDivision = 0;
    TIM_InitStruct.TIM_CounterMode = TIM_CounterMode_Up;
    TIM_TimeBaseInit(TIM2, &TIM_InitStruct);

    TIM_OCInitTypeDef TIM_OCInitStruct;
    TIM_OCInitStruct.TIM_OCMode = TIM_OCMode_PWM1;
    TIM_OCInitStruct.TIM_OutputState = TIM_OutputState_Enable;
    TIM_OCInitStruct.TIM_OCPolarity = TIM_OCPolarity_High;
    TIM_OCInitStruct.TIM_Pulse = 500;
    TIM_OC1Init(TIM2, &TIM_OCInitStruct);

    // 启动定时器
    TIM_Cmd(TIM2, ENABLE);

    while (1) {}
}

这段代码使用了TIM2定时器和GPIOA的第5个引脚，输出了一个500Hz，占空比为50%的PWM波形。如果需要更改输出频率和占空比，只需要修改TIM_InitStruct和TIM_OCInitStruct中的参数即可。