帮我写一个基于函数库的stm32f103使用PA4引脚输出PWM波形代码

#include "stm32f10x.h"

void PWM_Init(void)
{
/*启用GPIOA时钟*/
RCC_APB2PeriphClockCmd(RCC_APB2Periph_GPIOA, ENABLE);

/*设置PA4为复用推挽输出*/
GPIO_InitTypeDef GPIO_InitStructure;
GPIO_InitStructure.GPIO_Pin = GPIO_Pin_4;
GPIO_InitStructure.GPIO_Mode = GPIO_Mode_AF_PP;
GPIO_InitStructure.GPIO_Speed = GPIO_Speed_50MHz;
GPIO_Init(GPIOA, &GPIO_InitStructure);

/*启用TIM2时钟*/
RCC_APB1PeriphClockCmd(RCC_APB1Periph_TIM2, ENABLE);

/*设置TIM2的时基参数*/
TIM_TimeBaseInitTypeDef TIM_TimeBaseInitStructure;
TIM_TimeBaseInitStructure.TIM_Prescaler = 72 - 1;
TIM_TimeBaseInitStructure.TIM_CounterMode = TIM_CounterMode_Up;
TIM_TimeBaseInitStructure.TIM_Period = 1000 - 1;
TIM_TimeBaseInitStructure.TIM_ClockDivision = TIM_CKD_DIV1;
TIM_TimeBaseInit(TIM2, &TIM_TimeBaseInitStructure);

/*设置TIM2通道1为PWM模式*/
TIM_OCInitTypeDef TIM_OCInitStructure;
TIM_OCInitStructure.TIM_OCMode = TIM_OCMode_PWM1;
TIM_OCInitStructure.TIM_OutputState = TIM_OutputState_Enable;
TIM_OCInitStructure.TIM_Pulse = 500 - 1;
TIM_OCInitStructure.TIM_OCPolarity = TIM_OCPolarity_High;
TIM_OC1Init(TIM2, &TIM_OCInitStructure);

/*启用TIM2*/
TIM_Cmd(TIM2, ENABLE);
}

int main(void)
{
PWM_Init();

while(1)
{
}
}