帮我写一个stm32f4直流电机pwm调速程序

好的，以下是基本的PWM调速程序，你可以根据具体的硬件电路和电机参数进行适当的修改。

#include "stm32f4xx.h"

void PWM_Init(void)
{
    RCC_APB1PeriphClockCmd(RCC_APB1Periph_TIM2, ENABLE); //使能TIM2时钟
    RCC_AHB1PeriphClockCmd(RCC_AHB1Periph_GPIOA, ENABLE); //使能GPIOA时钟

    GPIO_InitTypeDef GPIO_InitStructure;
    GPIO_InitStructure.GPIO_Pin = GPIO_Pin_5; //GPIOA5
    GPIO_InitStructure.GPIO_Mode = GPIO_Mode_AF; //复用功能
    GPIO_InitStructure.GPIO_Speed = GPIO_Speed_100MHz; //速度100MHz
    GPIO_InitStructure.GPIO_OType = GPIO_OType_PP; //推挽复用输出
    GPIO_InitStructure.GPIO_PuPd = GPIO_PuPd_UP; //上拉
    GPIO_Init(GPIOA, &GPIO_InitStructure); //初始化GPIOA5

    GPIO_PinAFConfig(GPIOA, GPIO_PinSource5, GPIO_AF_TIM2); //将GPIOA5复用为TIM2

    TIM_TimeBaseInitTypeDef TIM_TimeBaseInitStructure;
    TIM_TimeBaseInitStructure.TIM_Period = 9999; //重载值，PWM频率 = 84M / (9999 + 1) = 8.4KHz
    TIM_TimeBaseInitStructure.TIM_Prescaler = 83; //预分频器，时钟频率 = 84M / (83 + 1) = 1MHz
    TIM_TimeBaseInitStructure.TIM_ClockDivision = TIM_CKD_DIV1; //时钟分频
    TIM_TimeBaseInitStructure.TIM_CounterMode = TIM_CounterMode_Up; //向上计数模式
    TIM_TimeBaseInit(TIM2, &TIM_TimeBaseInitStructure);

    TIM_OCInitTypeDef TIM_OCInitStructure;
    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_OCPolarity = TIM_OCPolarity_High; //输出极性为高
    TIM_OCInitStructure.TIM_Pulse = 5000; //占空比50%
    TIM_OC1Init(TIM2, &TIM_OCInitStructure); //初始化TIM2的通道1

    TIM_Cmd(TIM2, ENABLE); //启动TIM2
}

int main(void)
{
    PWM_Init();

    while (1) {
        //可以通过修改TIM2的CCR1寄存器值改变占空比，从而改变电机转速
    }
}

注意，这只是基本的PWM调速程序，如果需要更精准的控制电机转速，需要进行PID控制等更高级的算法实现。同时，也需要根据具体的硬件电路和电机参数进行适当的修改。