SystemInit()函数的结构分析

系统函数调用顺序startup_stm32f10x_cl.s→ SystemInit() → SetSysClock()→ SetSysClockTo72()

总结:开始是在keil4里看代码，很混乱，后来把他粘到Notepad编辑器，一点击就可以看出这个子函数到哪结束

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1. #ifdefined(STM32F10X_LD_VL)||(definedSTM32F10X_MD_VL)||(definedSTM32F10X_HD_VL)
2. /*#defineSYSCLK_FREQ_HSEHSE_VALUE*/
3. #defineSYSCLK_FREQ_24MHz24000000
4. #else
5. /*#defineSYSCLK_FREQ_HSEHSE_VALUE*/
6. /*#defineSYSCLK_FREQ_24MHz24000000*/
7. /*#defineSYSCLK_FREQ_36MHz36000000*/
8. /*#defineSYSCLK_FREQ_48MHz48000000*/
9. /*#defineSYSCLK_FREQ_56MHz56000000*/
10. #defineSYSCLK_FREQ_72MHz72000000
11. #endif

下面定义的SystemCoreClock 变量是为了方便取出几种情况下系统时钟的实际值，例SYSCLK_FREQ_24MHz 也就是24000000。

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1. #ifdefSYSCLK_FREQ_HSE
2. uint32_tSystemCoreClock=SYSCLK_FREQ_HSE;/*!equency(CoreClock)*/
3. #elifdefinedSYSCLK_FREQ_24MHz
4. uint32_tSystemCoreClock=SYSCLK_FREQ_24MHz;/*!
5. #elifdefinedSYSCLK_FREQ_36MHz
6. uint32_tSystemCoreClock=SYSCLK_FREQ_36MHz;/*!
7. #elifdefinedSYSCLK_FREQ_48MHz
8. uint32_tSystemCoreClock=SYSCLK_FREQ_48MHz;/*!
9. #elifdefinedSYSCLK_FREQ_56MHz
10. uint32_tSystemCoreClock=SYSCLK_FREQ_56MHz;/*!
11. #elifdefinedSYSCLK_FREQ_72MHz
12. uint32_tSystemCoreClock=SYSCLK_FREQ_72MHz;/*!
13. #else/*!
14. uint32_tSystemCoreClock=HSI_VALUE;/*!
15. #endif

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1. staticvoidSetSysClock(void)
2. {
3. #ifdefSYSCLK_FREQ_HSE
4. SetSysClockToHSE();
5. #elifdefinedSYSCLK_FREQ_24MHz
6. SetSysClockTo24();
7. #elifdefinedSYSCLK_FREQ_36MHz
8. SetSysClockTo36();
9. #elifdefinedSYSCLK_FREQ_48MHz
10. SetSysClockTo48();
11. #elifdefinedSYSCLK_FREQ_56MHz
12. SetSysClockTo56();
13. #elifdefinedSYSCLK_FREQ_72MHz
14. SetSysClockTo72();
15. #endif
17. /*Ifnoneofthedefineaboveisenabled,theHSIisusedasSystemclock
18. source(defaultafterreset)*/
19. }

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1. #ifdefSYSCLK_FREQ_HSE
2. /**
3. *@briefSelectsHSEasSystemclocksourceandconfigureHCLK,PCLK2
4. *andPCLK1prescalers.
5. *@noteThisfunctionshouldbeusedonlyafterreset.
6. *@paramNone
7. *@retvalNone
8. */
9. staticvoidSetSysClockToHSE(void)
10. {
11. ......
12. }

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1. #elifdefinedSYSCLK_FREQ_24MHz
2. /**
3. *@briefSetsSystemclockfrequencyto24MHzandconfigureHCLK,PCLK2
4. *andPCLK1prescalers.
5. *@noteThisfunctionshouldbeusedonlyafterreset.
6. *@paramNone
7. *@retvalNone
8. */
9. staticvoidSetSysClockTo24(void)
10. {
11. ........
12. }

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1. #elifdefinedSYSCLK_FREQ_36MHz
2. /**
3. *@briefSetsSystemclockfrequencyto36MHzandconfigureHCLK,PCLK2
4. *andPCLK1prescalers.
5. *@noteThisfunctionshouldbeusedonlyafterreset.
6. *@paramNone
7. *@retvalNone
8. */
9. staticvoidSetSysClockTo36(void)
10. {
11. ......
12. }

省略几个......

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1. #elifdefinedSYSCLK_FREQ_72MHz
2. /**
3. *@briefSetsSystemclockfrequencyto72MHzandconfigureHCLK,PCLK2
4. *andPCLK1prescalers.
5. *@noteThisfunctionshouldbeusedonlyafterreset.
6. *@paramNone
7. *@retvalNone
8. */
9. staticvoidSetSysClockTo72(void)
10. {
11. .......
12. }

这样结构就很明晰了。