1 STM32的时钟源主要有:
, v- o- K. o- R$ l) T内部时钟1 U& T& c5 |% |# d8 o5 `; u8 \$ N. T
外部时钟# L% c; U0 W/ |0 x3 b" f5 x# q! v
锁相环倍频输出时钟
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1.1 详细介绍8 A' n& N2 q$ a2 u
HSI(内部高速时钟)% m, I3 ^" m8 x) B, w3 X
它是RC振荡器,频率可以达到8MHZ,可作为系统时钟和PLL锁相环的输入
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8 ?( b6 ` ]) @1 x6 ^4 O8 IHSE(外部高速时钟)$ Z+ c; L5 ?9 `2 T0 O& u& A- D& n8 ~' A
接入晶振范围是4-16MHZ,可作为系统时钟和PLL锁相环的输入,还可以经过128分频之后输入给RTC。
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LSI(内部低速时钟)* Q' N, G2 V7 H% T) m
它是RC振荡器,频率大概为40KHZ,供给独立看门狗或者RTC,并且独立看门口只能依靠LSI作为时钟源 h9 T2 \( I/ T8 c1 g; X; u5 R
# U$ r1 f' `' ^; S! x, FLSE(外部低速时钟)( F1 ~* m* E6 Z1 `' x
通常外接32.768MHZ晶振提供给RTC% a8 f' U" i$ u: ?
8 n: u* G# z; b r" i, APLL(锁相环)
0 `% j( a% f! ]2 Q用来倍频输出。因为开发板外部晶振只有8MHZ,而STM32最大工作频率是72MHZ。他可以通过HSI输入,HSE输入或两分频输入,通过PLL倍频(2-16),倍频之后输入给系统时钟。
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MCO(时钟输出管脚)0 C3 y8 b4 n0 Q0 G2 `
通常对应STM32 PA8,它可以选择一个时钟信号输出,给外部的系统提供时钟源7 ~$ f2 O8 J' `* \, B# D
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2 标准库的时钟配置
8 Y0 E5 X# U* t$ d! N$ y& m2.1 STM32启动文件' A( w" e, @+ @/ Q
首先打开startup_stm32f10x_hd.s,该文件为stm32的启动文件,在该文件内会发现有这么一块用汇编写的代码。
9 a: c) t0 l6 d. P; G. {" w. N- Reset_Handler PROC8 v) {" g8 ]/ N9 t$ s( g; I
- EXPORT Reset_Handler [WEAK]* W% V" Z4 y7 j! j! F
- IMPORT __main
4 O! e7 v. D7 s Q, O+ t& m - IMPORT SystemInit
- c# g' a" v/ [( O6 O) f* w* {1 M0 n - LDR R0, =SystemInit
- L2 U0 I) t( Q$ @4 \ - BLX R0
% H! t( |8 a6 k A3 O7 Q! V - LDR R0, =__main
# c$ K! m! H9 `; \+ C - BX R07 J8 F4 n$ r2 V! b4 @
- ENDP
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通过这段汇编代码可以看出,程序在执行main函数之前,会先执行SystemInit函数。
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* G1 M! F, @8 E9 ~2 l3 z2.2 SystemInit函数详解- void SystemInit (void)2 o* Q+ a* }' |! z' i: D
- {
" w9 X, w. ]- g; O+ G4 J! ?' [ - /* Reset the RCC clock configuration to the default reset state(for debug purpose) */
' M( s& s' a2 D2 {! G' V - /* Set HSION bit */2 D2 e; w1 N. a( r7 @
- RCC->CR |= (uint32_t)0x00000001;1 |: M) |, u5 P. j
- % z* q4 b$ e. {; H L
- /* Reset SW, HPRE, PPRE1, PPRE2, ADCPRE and MCO bits */
4 F$ v T* h$ I6 @4 n2 K - #ifndef STM32F10X_CL* y ` N& P% p, @
- RCC->CFGR &= (uint32_t)0xF8FF0000;
7 y+ A6 {! Y2 p4 A; z9 j - #else
- p/ I6 z! l+ O1 G - RCC->CFGR &= (uint32_t)0xF0FF0000;
* k4 H: B4 J' T1 v - #endif /* STM32F10X_CL */
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- /* Reset HSEON, CSSON and PLLON bits */
+ j/ c1 p3 N) Y9 L3 E - RCC->CR &= (uint32_t)0xFEF6FFFF;
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- /* Reset HSEBYP bit */
% _3 X3 w2 x( q; _: V2 S5 m - RCC->CR &= (uint32_t)0xFFFBFFFF;& ~4 U& P8 c. a& ^
- 9 t8 L' r( k* S2 ]8 H% W7 S, [3 }
- /* Reset PLLSRC, PLLXTPRE, PLLMUL and USBPRE/OTGFSPRE bits */
# b. q- c9 b& _* Q2 f( C* {% Q: n+ k5 u8 W - RCC->CFGR &= (uint32_t)0xFF80FFFF;
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' j E; ~# h) ]$ ?! l1 u* j9 X- #ifdef STM32F10X_CL
2 S8 j" v* y1 x4 ? - /* Reset PLL2ON and PLL3ON bits */
; M2 j: S% n2 h0 H1 k, S% P - RCC->CR &= (uint32_t)0xEBFFFFFF;1 D$ U- M( a+ @! R" k: K/ m, V4 l
) F3 C, L- ^" z& N- /* Disable all interrupts and clear pending bits */! o. @6 k3 w5 J* T
- RCC->CIR = 0x00FF0000;
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- /* Reset CFGR2 register */$ h: x2 f% V3 b+ a2 V
- RCC->CFGR2 = 0x00000000;' |9 G; F3 U& n5 n: g4 e6 _
- #elif defined (STM32F10X_LD_VL) || defined (STM32F10X_MD_VL) || (defined STM32F10X_HD_VL)
- I4 e! I9 H, {& v - /* Disable all interrupts and clear pending bits */
" d2 v% V$ Y9 u$ n - RCC->CIR = 0x009F0000;
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- /* Reset CFGR2 register */5 T8 z& _8 b: i
- RCC->CFGR2 = 0x00000000; ( F2 a( l% `2 N$ Q! t n
- #else
: |0 f! h _' g! G! h - /* Disable all interrupts and clear pending bits */ {" V4 i9 l; ]* j% Y
- RCC->CIR = 0x009F0000;- u$ i% l$ O) x% K3 I+ f
- #endif /* STM32F10X_CL */
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- #if defined (STM32F10X_HD) || (defined STM32F10X_XL) || (defined STM32F10X_HD_VL)( B+ h0 y" i& J
- #ifdef DATA_IN_ExtSRAM
. T D- m6 n8 {/ S - SystemInit_ExtMemCtl();
1 E' G2 e/ _; ] S9 c) q - #endif /* DATA_IN_ExtSRAM */
# U0 K/ |- d3 o+ | - #endif
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* F& A9 V; q6 S- /* Configure the System clock frequency, HCLK, PCLK2 and PCLK1 prescalers */& M* _% e# m0 t: o- V- K
- /* Configure the Flash Latency cycles and enable prefetch buffer */
5 R, }! p N1 [9 q( [1 V' F4 I, h5 I - SetSysClock();
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- #ifdef VECT_TAB_SRAM
& x, f3 q: r' {2 u - SCB->VTOR = SRAM_BASE | VECT_TAB_OFFSET; /* Vector Table Relocation in Internal SRAM. */: }% `* _+ ~, F& s) U
- #else
* [% U6 o4 x2 |+ z7 D( A4 w# ] - SCB->VTOR = FLASH_BASE | VECT_TAB_OFFSET; /* Vector Table Relocation in Internal FLASH. */
* F: \" m' }2 W, a" I, I* m& A. y - #endif w8 u [, ^& u( y- P) g- L
- }
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/ f. l% I) o/ |9 I打开内部8M时钟:
8 h5 o4 A. W1 Z1 E9 @, P4 i- RCC->CR |= (uint32_t)0x00000001
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通过查看寄存器手册可知,这段代码为打开内部8M时钟。/ e( l* [0 O' y( s0 j9 y& A5 q+ @
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: F. K3 ~5 O$ e2 b设置时钟配置寄存器:
/ {' }; y2 Z8 D( G. l7 ]7 Q- #ifndef STM32F10X_CL3 j. H' A) i$ \3 V* ~' `9 w! |
- RCC->CFGR &= (uint32_t)0xF8FF0000;
6 O0 Q! I" v7 i - #else
4 w& R2 q0 g( D& E) P- b- X - RCC->CFGR &= (uint32_t)0xF0FF0000;! t9 F' @( [0 @/ g5 a3 R' H* Y* s1 a9 @
- #endif /* STM32F10X_CL */
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d* i8 X' V) A/ a, ^5 k对应寄存器说明可查看《STM32中文参考手册_V10》的6.3.2 时钟配置寄存器(RCC_CFGR)章节。
' T5 s2 e8 M+ c5 \8 y5 ^0 _+ p/ u后续代码,有兴趣可根据《STM32中文参考手册_V10》手册,查看代码具体作用。$ p$ X9 j6 i8 A8 a% d
1 U! R. ^/ E0 P+ M2.3 SetSysClock()函数详解1 e7 Y; H7 @, A
- static void SetSysClock(void)3 A+ ], n6 t' J, T, ?+ D. _
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- #ifdef SYSCLK_FREQ_HSE
# V. @' u7 V& z, r- O Q - SetSysClockToHSE();
7 F( T2 m% R$ X! M+ Y5 Q - #elif defined SYSCLK_FREQ_24MHz7 @( `% ?: w5 L/ S! Y' x$ p
- SetSysClockTo24();
( H& {3 X. h0 n# I0 ` R - #elif defined SYSCLK_FREQ_36MHz
" e# K- k$ M$ Q) N* S+ R - SetSysClockTo36();4 W: n& [6 n$ a! _
- #elif defined SYSCLK_FREQ_48MHz
5 p! t5 I7 G8 C% l9 A, r3 g3 n- V - SetSysClockTo48(); z8 z' _4 F. b% i
- #elif defined SYSCLK_FREQ_56MHz
2 G _. F7 ~( ]1 I0 a - SetSysClockTo56(); ) J/ _9 l: M2 E1 {" T6 w
- #elif defined SYSCLK_FREQ_72MHz
5 g0 ]2 M: _/ m# ]% Y1 z4 n - SetSysClockTo72();
- J* L4 m& [* } - #endif8 J L& s7 V5 Y; s- T
- }
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- J9 O7 v' k2 y s7 ^' d5 V7 usystem_stm32f10x.c文件中会根据芯片的型号定义对应的宏:
8 n* ?! M$ l; ?$ s( {! x5 N, u, H- #if defined (STM32F10X_LD_VL) || (defined STM32F10X_MD_VL) || (defined STM32F10X_HD_VL)" \. G$ \. e' G2 v# |
- /* #define SYSCLK_FREQ_HSE HSE_VALUE */) T, P$ h0 n$ z4 W5 x( y' A
- #define SYSCLK_FREQ_24MHz 24000000
4 c! b+ ^9 W5 u. n; M - #else" ^1 ]5 Z# s7 l" D: K5 P
- /* #define SYSCLK_FREQ_HSE HSE_VALUE */7 C; r- r6 M& S
- /* #define SYSCLK_FREQ_24MHz 24000000 */ 4 q( L& f* |9 C9 O- D3 g1 N
- /* #define SYSCLK_FREQ_36MHz 36000000 */$ @* h6 @" y) b( J+ C- b/ x. f
- /* #define SYSCLK_FREQ_48MHz 48000000 */1 n- x% v9 J1 m2 ~
- /* #define SYSCLK_FREQ_56MHz 56000000 */* y0 e$ n2 L3 h4 Z
- #define SYSCLK_FREQ_72MHz 72000000
5 x+ {: l( I9 A6 v9 u, K - #endif
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3 时钟配置函数8 u- X3 [2 ]9 n7 g% s( D
3.1 时钟初始化配置函数- void SystemInit(void);
6 `( Z, G. U( y4 {' {" x" I - SYSCLK(系统时钟)=72MHZ;2 y, O1 t' Y; M% _9 A: }2 S
- AHB总线时钟(HCLK=SYSCLK)=72MHZ;" i9 [: _ ?6 }2 [4 F
- APB1总线时钟(PCLK1=SYSCLK/2)=36MHZ;
0 [ m/ N/ y$ b: k - APB2总线时钟(PCLK1=SYSCLK/1)=72MHZ;
7 M; m9 I5 Z, _# t' E* s5 R1 e - PLL主时钟=72MHZ;
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0 W/ R v4 ]7 c* T! X9 s3.2 外设时钟使能配置函数 [: I- W" j! s9 ~+ w' _; ]
- void RCC_AHBPeriphClockCmd(uint32_t RCC_AHBPeriph, FunctionalState NewState);9 U! j5 E# I. N5 B+ \
- void RCC_APB2PeriphClockCmd(uint32_t RCC_APB2Periph, FunctionalState NewState);
" ~3 U6 D2 W, c - void RCC_APB1PeriphClockCmd(uint32_t RCC_APB1Periph, FunctionalState NewState);
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3.3 时钟源使能函数- void RCC_HSICmd(FunctionalState NewState);
; u# g( {/ w& O% d. r - void RCC_LSICmd(FunctionalState NewState);
: j) z; y) Y' \3 `0 ~ - void RCC_PLLCmd(FunctionalState NewState);
* q5 v: J* ^# x: M* e! ?, X% T - void RCC_RTCCLKCmd(FunctionalState NewState);
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* j3 u7 h3 M* D# j v9 }3.4 时钟源和倍频因子配置函数
7 u6 ?- v8 ]0 |! a- void RCC_HSEConfig(uint32_t RCC_HSE);
7 J( P4 L3 J6 G6 F& K" i - void RCC_SYSCLKConfig(uint32_t RCC_SYSCLKSource);
4 x3 T7 ^6 Q% J& i$ g9 G+ s - void RCC_HCLKConfig(uint32_t RCC_SYSCLK);7 ], N3 [2 ? n7 ~3 \5 m1 O( G
- void RCC_PCLK1Config(uint32_t RCC_HCLK);
- |7 r4 b5 h& [6 L - void RCC_PCLK2Config(uint32_t RCC_HCLK);
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P( t# C% u. w4 I2 n; f9 C8 F2 S3.5 外设时钟复位函数
3 A/ Q% F2 ], C- void RCC_APB2PeriphResetCmd(uint32_t RCC_APB2Periph, FunctionalState NewState);
! U( L O \6 I# S - void RCC_APB1PeriphResetCmd(uint32_t RCC_APB1Periph, FunctionalState NewState);
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! ~, h6 r5 x/ w/ k9 y3.6 自定义系统时钟
! S' o( T; G+ e/ Q! R9 [; t- void RCC_HSE_Config(u32 div,u32 pllm)* H: [" N- ?: t% J& f
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- RCC_DeInit();8 @$ x' I$ D9 q V# p
- RCC_HSEConfig(RCC_HSE_ON);. @% T( m6 _. r* k3 g
- if(RCC_WaitForHSEStartUp()==SUCCESS)4 P. x/ I! l S- N
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- RCC_HCLKConfig(RCC_SYSCLK_Div1);" X3 r: P4 i8 I0 D e7 `1 B
- RCC_PCLK1Config(RCC_HCLK_Div2);
$ a. Y# X. j8 b* h3 k7 j: v3 S5 { - RCC_PCLK2Config(RCC_HCLK_Div1);
3 p0 ]' T( u! g% P6 J8 P - RCC_PLLConfig(div,pllm);
; W, s* x g |9 X' L1 e - RCC_PLLCmd(ENABLE);
. L9 D& o: j* q& }. u+ }. D% \ - while(RCC_GetFlagStatus(RCC_FLAG_PLLRDY)==RESET)
' q C# _) X1 j: I& V5 Z) [0 m. R- ~ - RCC_SYSCLKConfig(RCC_SYSCLKSource_PLLCLK)
+ ^6 W! h) M0 q; ` - while(RCC_GetSCLKSource()!=0x08);& C& L/ N# h! H% G7 s# |3 ]
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复制代码 转载自:STM32嵌入式开发
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* X$ j: v, p- i( ]) I如有侵权请联系删除0 s/ }# Q8 C- ]0 P5 i6 A/ a
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