说明：  STM32F407时钟，中断，精确延时配置，该文件包含HSE,HSI,LSE,LSI,I2S,MCO时钟的初始化；PLL时钟配置，PLL,SYSCLK,CLK,PCLK1，PCLK2时钟的配置；RCC,GPIO,EXIT,NVIC的配置.
(STM32F407 clock, interrupt, precision delay configuration, the file contains HSE, HSI, LSE, LSI, I2S, MCO clock initialization PLL clock configuration, PLL, SYSCLK, HCLK, PCLK1, PCLK2 clock configuration RCC, GPIO, EXIT , NVIC configuration )