/**
??******************************************************************************
??*?@file????system_stm32f4xx.c
??*?@author??MCD?Application?Team
??*?@version?V1.8.0
??*?@date????09-November-2016
??*?@brief???CMSIS?Cortex-M4?Device?Peripheral?Access?layer?System?Source?File.
??*??????????This?file?contains?the?system?clock?configuration?for?STM32F4xx?devices.
??*?????????????
??*?1.??This?file?provides?two?functions?and?one?global?variable?to?be?called?from?
??*?????user?application:
??*??????-?SystemInit（）:?Setups?the?system?clock?（System?clock?source?PLL?Multiplier
??*??????????????????????and?Divider?factors?AHB/APBx?prescalers?and?Flash?settings）
??*??????????????????????depending?on?the?configuration?made?in?the?clock?xls?tool.?
??*??????????????????????This?function?is?called?at?startup?just?after?reset?and?
??*??????????????????????before?branch?to?main?program.?This?call?is?made?inside
??*??????????????????????the?“startup_stm32f4xx.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?（16?MHz）?is?used?as?system?clock?source.
??*????Then?SystemInit（）?function?is?called?in?“startup_stm32f4xx.s“?file?to
??*????configure?the?system?clock?before?to?branch?to?main?program.
??*
??*?3.?If?the?system?clock?source?selected?by?user?fails?to?startup?the?SystemInit（）
??*????function?will?do?nothing?and?HSI?still?used?as?system?clock?source.?User?can?
??*????add?some?code?to?deal?with?this?issue?inside?the?SetSysClock（）?function.
??*
??*?4.?The?default?value?of?HSE?crystal?is?set?to?25MHz?refer?to?“HSE_VALUE“?define
??*????in?“stm32f4xx.h“?file.?When?HSE?is?used?as?system?clock?source?directly?or
??*????through?PLL?and?you?are?using?different?crystal?you?have?to?adapt?the?HSE
??*????value?to?your?own?configuration.
??*
??*?5.?This?file?configures?the?system?clock?as?follows:
??*=============================================================================
??*=============================================================================
??*????????????????????Supported?STM32F40xxx/41xxx?devices
??*-----------------------------------------------------------------------------
??*????????System?Clock?source????????????????????|?PLL?（HSE）
??*-----------------------------------------------------------------------------
??*????????SYSCLK（Hz）?????????????????????????????|?168000000
??*-----------------------------------------------------------------------------
??*????????HCLK（Hz）?????????????????????

?屬性????????????大小?????日期????時(shí)間???名稱
-----------?---------??----------?-----??----
?????目錄???????????0??2018-08-14?11:55??V1.9\
?????目錄???????????0??2018-08-14?11:55??V1.9\Doc\
?????文件??????????74??2018-07-17?15:34??V1.9\Doc\ReadMe.txt
?????目錄???????????0??2018-08-14?11:55??V1.9\Lib\
?????目錄???????????0??2018-08-14?11:55??V1.9\Lib\CMSIS\
?????目錄???????????0??2018-08-14?11:55??V1.9\Lib\CMSIS\Include\
?????文件????????7253??2016-11-05?01:33??V1.9\Lib\CMSIS\Include\arm_common_tables.h
?????文件????????3942??2016-11-05?01:33??V1.9\Lib\CMSIS\Include\arm_const_structs.h
?????文件??????252177??2016-11-05?01:33??V1.9\Lib\CMSIS\Include\arm_math.h
?????文件???????36181??2016-11-05?01:33??V1.9\Lib\CMSIS\Include\core_cm0.h
?????文件???????43812??2016-11-05?01:33??V1.9\Lib\CMSIS\Include\core_cm0plus.h
?????文件??????103865??2016-11-05?01:33??V1.9\Lib\CMSIS\Include\core_cm3.h
?????文件??????114403??2016-11-05?01:33??V1.9\Lib\CMSIS\Include\core_cm4.h
?????文件??????138654??2016-11-05?01:33??V1.9\Lib\CMSIS\Include\core_cm7.h
?????文件???????18323??2016-11-05?01:33??V1.9\Lib\CMSIS\Include\core_cmFunc.h
?????文件???????27908??2016-11-05?01:33??V1.9\Lib\CMSIS\Include\core_cmInstr.h
?????文件???????22947??2016-11-05?01:33??V1.9\Lib\CMSIS\Include\core_cmSimd.h
?????文件???????44330??2016-11-05?01:33??V1.9\Lib\CMSIS\Include\core_sc000.h
?????文件??????102775??2016-11-05?01:33??V1.9\Lib\CMSIS\Include\core_sc300.h
?????目錄???????????0??2018-08-14?11:55??V1.9\Lib\CMSIS\arm\
?????文件???????25819??2016-11-07?23:02??V1.9\Lib\CMSIS\arm\startup_stm32f401xx.s
?????文件???????29607??2016-11-07?23:02??V1.9\Lib\CMSIS\arm\startup_stm32f40_41xxx.s
?????文件???????29696??2016-11-07?23:02??V1.9\Lib\CMSIS\arm\startup_stm32f40xx.s
?????文件???????19189??2016-11-07?23:02??V1.9\Lib\CMSIS\arm\startup_stm32f410xx.s
?????文件???????26519??2016-11-07?23:02??V1.9\Lib\CMSIS\arm\startup_stm32f411xe.s
?????文件???????21484??2016-11-07?23:02??V1.9\Lib\CMSIS\arm\startup_stm32f412xg.s
?????文件???????23401??2016-11-07?23:02??V1.9\Lib\CMSIS\arm\startup_stm32f413_423xx.s
?????文件???????30981??2016-11-07?23:02??V1.9\Lib\CMSIS\arm\startup_stm32f427_437xx.s
?????文件???????31056??2016-11-07?23:02??V1.9\Lib\CMSIS\arm\startup_stm32f427x.s
?????文件???????31136??2016-11-07?23:02??V1.9\Lib\CMSIS\arm\startup_stm32f429_439xx.s
?????文件???????22148??2016-11-07?23:02??V1.9\Lib\CMSIS\arm\startup_stm32f446xx.s
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