USE_STDPERIPH_DRIVER的意思是:to use or not the peripheral’s drivers in application code(i.e. code will be based on direct access to peripheral’s registers rather than drivers API),this option is controlled by the #define USE_STDPERIPH_DRIVER,也就是这个定义控制了是否在应用中启用外设驱动,我们使用标准外设库本来就是为了方便控制外设,所以添加这个定义,以启用外设驱动。