*=============================================================================
*=============================================================================
* Supported STM32F4xx device revision | Rev A
*-----------------------------------------------------------------------------
* System Clock source | PLL (HSE)
*-----------------------------------------------------------------------------
* SYSCLK(Hz) | 168000000
*-----------------------------------------------------------------------------
* HCLK(Hz) | 168000000
*-----------------------------------------------------------------------------
* AHB Prescaler | 1
*-----------------------------------------------------------------------------
* APB1 Prescaler | 4
*-----------------------------------------------------------------------------
* APB2 Prescaler | 2
*-----------------------------------------------------------------------------
* HSE Frequency(Hz) | 25000000
*-----------------------------------------------------------------------------
* PLL_M | 25
*-----------------------------------------------------------------------------
* PLL_N | 336
*-----------------------------------------------------------------------------
* PLL_P | 2
*-----------------------------------------------------------------------------
* PLL_Q | 7
*-----------------------------------------------------------------------------
* PLLI2S_N | NA
*-----------------------------------------------------------------------------
* PLLI2S_R | NA
*-----------------------------------------------------------------------------
* I2S input clock | NA
*-----------------------------------------------------------------------------
* VDD(V) | 3.3
*-----------------------------------------------------------------------------
* Main regulator output voltage | Scale1 mode
*-----------------------------------------------------------------------------
* Flash Latency(WS) | 5
*-----------------------------------------------------------------------------
* Prefetch Buffer | OFF
*-----------------------------------------------------------------------------
* Instruction cache | ON
*-----------------------------------------------------------------------------
* Data cache | ON
*-----------------------------------------------------------------------------
* Require 48MHz for USB OTG FS, | Enabled
* SDIO and RNG clock | 什么意思 |