stm32基于定时器对PWM频率进行修改，以此控制步进电机，做到步进电机速度可调，只做了加速减速没有做，原理相同，实测可用(STM32 based on the timer to modify the frequency of PWM, in order to control the stepper motor, so that stepper motor speed adjustable, only to do the acceler