此代码为适用于STM32 F4系列单片机，实现了PWM频率以及占空比按键可控。在正点原子所提供的库函数中二次开发所得。-This code is applicable to the STM32 F4 series of microcontrollers, to achieve a PWM frequency and duty cycle control buttons. In the punctual atom provided by the library function secondary