/**
??******************************************************************************
??*?@file????system_stm32f3xx.c
??*?@author??MCD?Application?Team
??*?@version?V2.3.1
??*?@date????16-December-2016
??*?@brief???CMSIS?Cortex-M4?Device?Peripheral?Access?layer?System?Source?File.
??*
??*?1.?This?file?provides?two?functions?and?one?global?variable?to?be?called?from
??*????user?application:
??*??????-?SystemInit（）:?This?function?is?called?at?startup?just?after?reset?and?
??*??????????????????????before?branch?to?main?program.?This?call?is?made?inside
??*??????????????????????the?“startup_stm32f3xx.s“?file.
??*
??*??????-?SystemCoreClock?variable:?Contains?the?core?clock?（HCLK）?it?can?be?used
??*??????????????????????????????????by?the?user?application?to?setup?the?SysTick
??*??????????????????????????????????timer?or?configure?other?parameters.
??*
??*??????-?SystemCoreClockUpdate（）:?Updates?the?variable?SystemCoreClock?and?must
??*?????????????????????????????????be?called?whenever?the?core?clock?is?changed
??*?????????????????????????????????during?program?execution.
??*
??*?2.?After?each?device?reset?the?HSI?（8?MHz）?is?used?as?system?clock?source.
??*????Then?SystemInit（）?function?is?called?in?“startup_stm32f3xx.s“?file?to
??*????configure?the?system?clock?before?to?branch?to?main?program.
??*
??*?3.?This?file?configures?the?system?clock?as?follows:
??*=============================================================================
??*?????????????????????????Supported?STM32F3xx?device
??*-----------------------------------------------------------------------------
??*????????System?Clock?source????????????????????|?HSI
??*-----------------------------------------------------------------------------
??*????????SYSCLK（Hz）?????????????????????????????|?8000000
??*-----------------------------------------------------------------------------
??*????????HCLK（Hz）???????????????????????????????|?8000000
??*-----------------------------------------------------------------------------
??*????????AHB?Prescaler??????????????????????????|?1
??*-----------------------------------------------------------------------------
??*????????APB2?Prescaler?????????????????????????|?1
??*-----------------------------------------------------------------------------
??*????????APB1?Prescaler?????????????????????????|?1
??*-----------------------------------------------------------------------------
??*????????USB?Clock??????????????????????????????|?DISABLE
??*-----------------------------------------------------------------------------
??*=============================================================================
??******************************************************************************
??*?@attention
??*
??*?
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??*
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