/**
??******************************************************************************
??*?@file????system_stm32f4xx.c
??*?@author??MCD?Application?Team
??*?@version?V1.5.0
??*?@date????06-March-2015
??*?@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(chēng)
-----------?---------??----------?-----??----
?????目錄???????????0??2018-01-02?14:11??Doc\
?????文件?????????456??2015-03-25?16:45??Doc\01.例程功能說(shuō)明.txt
?????文件?????????609??2015-03-25?16:42??Doc\02.例程修改記錄.txt
?????文件????????7044??2013-06-20?09:34??Doc\03.開(kāi)發(fā)環(huán)境說(shuō)明.txt
?????文件????????7564??2013-06-20?06:09??Doc\04.STM32F407IGT6引腳定義（原始定義）.txt
?????文件????????9924??2013-06-20?08:58??Doc\05.GPIO分配表（按GPIO次序排列）.txt
?????文件???????10725??2013-06-20?22:46??Doc\06.GPIO分配表（按功能排列）.txt
?????文件??????195963??2013-07-22?07:14??Doc\F4-001_接線圖.jpg
?????目錄???????????0??2018-01-02?14:11??Libraries\
?????目錄???????????0??2018-01-02?14:11??Libraries\CMSIS\
?????文件??????172641??2015-02-13?19:07??Libraries\CMSIS\CMSIS_END_USER_LICENCE_AGREEMENT.pdf
?????文件??????178493??2015-02-13?19:07??Libraries\CMSIS\CMSIS_END_USER_LICENCE_AGREEMENT.rtf
?????目錄???????????0??2015-03-25?14:18??Libraries\CMSIS\Device\
?????目錄???????????0??2015-03-25?14:18??Libraries\CMSIS\Device\ST\
?????目錄???????????0??2018-01-02?14:11??Libraries\CMSIS\Device\ST\STM32F4xx\
?????目錄???????????0??2018-01-03?23:47??Libraries\CMSIS\Device\ST\STM32F4xx\Include\
?????文件??????767941??2018-01-03?23:47??Libraries\CMSIS\Device\ST\STM32F4xx\Include\stm32f4xx.h
?????文件????????2232??2015-02-13?17:00??Libraries\CMSIS\Device\ST\STM32F4xx\Include\system_stm32f4xx.h
?????文件???????38760??2015-03-06?18:00??Libraries\CMSIS\Device\ST\STM32F4xx\Release_Notes.html
?????目錄???????????0??2015-03-25?14:18??Libraries\CMSIS\Device\ST\STM32F4xx\Source\
?????目錄???????????0??2018-01-02?14:11??Libraries\CMSIS\Device\ST\STM32F4xx\Source\Templates\
?????目錄???????????0??2018-01-02?14:11??Libraries\CMSIS\Device\ST\STM32F4xx\Source\Templates\TASKING\
?????文件????????3672??2015-02-10?21:40??Libraries\CMSIS\Device\ST\STM32F4xx\Source\Templates\TASKING\cstart_thumb2.asm
?????目錄???????????0??2018-01-02?14:11??Libraries\CMSIS\Device\ST\STM32F4xx\Source\Templates\TrueSTUDIO\
?????文件???????20689??2015-02-13?19:01??Libraries\CMSIS\Device\ST\STM32F4xx\Source\Templates\TrueSTUDIO\startup_stm32f401xx.s
?????文件???????24147??2015-02-13?19:01??Libraries\CMSIS\Device\ST\STM32F4xx\Source\Templates\TrueSTUDIO\startup_stm32f40_41xxx.s
?????文件???????24232??2015-02-13?19:01??Libraries\CMSIS\Device\ST\STM32F4xx\Source\Templates\TrueSTUDIO\startup_stm32f40xx.s
?????文件???????22199??2015-02-13?19:01??Libraries\CMSIS\Device\ST\STM32F4xx\Source\Templates\TrueSTUDIO\startup_stm32f411xe.s
?????文件???????25885??2015-02-13?19:01??Libraries\CMSIS\Device\ST\STM32F4xx\Source\Templates\TrueSTUDIO\startup_stm32f427_437xx.s
?????文件???????25979??2015-02-13?19:01??Libraries\CMSIS\Device\ST\STM32F4xx\Source\Templates\TrueSTUDIO\startup_stm32f427xx.s
?????文件???????25885??2015-02-13?19:01??Libraries\CMSIS\Device\ST\STM32F4xx\Source\Templates\TrueSTUDIO\startup_stm32f429_439xx.s
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