1 STM32的时钟源主要有:! A0 p8 R3 h. Z! R) A
内部时钟) L G. W$ |% L5 o
外部时钟
# |* w2 E& X1 h' p6 @) u锁相环倍频输出时钟
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$ G A; n- |% p" I0 T1.1 详细介绍
& r+ l' E9 C0 B$ X& c3 [HSI(内部高速时钟)
6 d$ j* z' C. i% f$ i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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& a6 q% ^$ B8 ]8 wHSE(外部高速时钟)
4 u- F* a) H \: ^! X2 l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)
G, i* p2 ^1 I( f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
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LSE(外部低速时钟)
% I. g8 v- X* c m+ k- U+ n通常外接32.768MHZ晶振提供给RTC
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$ {: k$ L! I @$ o/ [' V0 ePLL(锁相环)* t" Y: |( |& S# m
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。/ ~, o. } {2 ]( Q
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MCO(时钟输出管脚)
$ u9 L* l, }% i9 [) ?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
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2 y' `) w! [- g( d* ^. _2 标准库的时钟配置9 D0 v8 u$ ^6 s k. m
2.1 STM32启动文件1 ^2 g1 }' d m6 r/ k3 b" u7 L
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。
& O( y! f$ \9 B- _5 p- Reset_Handler PROC
$ l1 |6 k6 N n0 c6 \ - EXPORT Reset_Handler [WEAK]! F8 e# ]0 C6 Q0 V
- IMPORT __main% ?& @, G7 E, l0 F% f
- IMPORT SystemInit3 e S! I+ j% q; @
- LDR R0, =SystemInit
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: I \/ z+ l- D0 J - LDR R0, =__main) B( t! h7 f0 E3 e+ v- f
- BX R0 T- `, @; a) B& W j1 j9 o# x
- ENDP
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5 j! G& [ Y$ l2 R9 h) j# r% ^" M' E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。: G7 T; p3 h" w. j0 A0 f
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2.2 SystemInit函数详解- void SystemInit (void)2 ]& Y) d1 i+ S8 r3 N2 r1 k5 e
- {
( p4 z* x' Z" `3 }/ m - /* Reset the RCC clock configuration to the default reset state(for debug purpose) */+ u% b: m* ^ ]# r
- /* Set HSION bit *// ~6 Q# J6 u% {% w* d$ v& n( f4 p# S
- RCC->CR |= (uint32_t)0x00000001;( z) g/ I, T, ?6 ]9 O6 _' d
- " ?# O1 x6 M! X3 y! J+ `
- /* Reset SW, HPRE, PPRE1, PPRE2, ADCPRE and MCO bits */
9 N; m3 `/ C; n! y/ ^6 ] - #ifndef STM32F10X_CL) U+ e( X0 Q3 b; Z9 R0 o2 C, r9 n D
- RCC->CFGR &= (uint32_t)0xF8FF0000;% _' n+ E, p) ]/ q2 O9 J( H
- #else, u: u' K( A4 {* B( C
- RCC->CFGR &= (uint32_t)0xF0FF0000;/ @$ O1 A, v- v
- #endif /* STM32F10X_CL */
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- /* Reset HSEON, CSSON and PLLON bits */
8 r4 x8 w: X" n r3 ^ - RCC->CR &= (uint32_t)0xFEF6FFFF;5 ]9 o* L! B' }+ J9 A( ~: L
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- /* Reset HSEBYP bit */
8 v0 p9 C5 _: p+ z6 Y" Q - RCC->CR &= (uint32_t)0xFFFBFFFF;
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- /* Reset PLLSRC, PLLXTPRE, PLLMUL and USBPRE/OTGFSPRE bits */
8 a5 F2 k& R% D - RCC->CFGR &= (uint32_t)0xFF80FFFF;0 k5 I' c0 C" o" F9 i @# ^, v: j
- ; V5 M' P+ F) ^9 W) B$ U$ q
- #ifdef STM32F10X_CL4 P! N) {0 m; a5 d6 x1 v9 ?
- /* Reset PLL2ON and PLL3ON bits */
% [- w0 w: I9 _+ d: c - RCC->CR &= (uint32_t)0xEBFFFFFF;
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' I: A/ Q. r+ U* U j/ Y- /* Disable all interrupts and clear pending bits */
: `) i9 b/ M/ V* |( b1 x v2 @ - RCC->CIR = 0x00FF0000;. x/ i; J2 Y. y+ v S4 R& X/ T9 j
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- /* Reset CFGR2 register */' H+ i# a: P6 @* i
- RCC->CFGR2 = 0x00000000;1 }9 o7 ?1 ~) \& c# A! C0 C$ m
- #elif defined (STM32F10X_LD_VL) || defined (STM32F10X_MD_VL) || (defined STM32F10X_HD_VL)8 t1 k; `0 d) U# k5 J
- /* Disable all interrupts and clear pending bits */: |* h5 s' x( X
- RCC->CIR = 0x009F0000;
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' \' ^2 t# p( A% ?( Z' C9 C- /* Reset CFGR2 register */
& j# b) a! R' h# R$ w8 a0 G9 b* I - RCC->CFGR2 = 0x00000000;
( ]9 {$ U& H7 U. S - #else
+ N! s, z. T1 }- V% E* ` - /* Disable all interrupts and clear pending bits */5 i* _9 j3 ~2 @3 [
- RCC->CIR = 0x009F0000;& V, J7 N6 l9 S: d- h& f4 @
- #endif /* STM32F10X_CL */+ F6 b0 P, u9 Y% i) r$ w- G7 f
; F |8 f; Z; e. z4 O- #if defined (STM32F10X_HD) || (defined STM32F10X_XL) || (defined STM32F10X_HD_VL)6 X& e# l- Y4 Y: W& m6 C
- #ifdef DATA_IN_ExtSRAM0 S: @! p- r6 t& C, F
- SystemInit_ExtMemCtl(); % j2 }2 n; F: q2 T3 @7 p
- #endif /* DATA_IN_ExtSRAM */6 Z$ k4 y/ B, f |/ |. |
- #endif 0 p& G( S. H) j; N: X q8 m
- / H1 V8 [" t7 A3 ], W
- /* Configure the System clock frequency, HCLK, PCLK2 and PCLK1 prescalers */9 ]6 k2 i, h6 B7 _$ i/ h
- /* Configure the Flash Latency cycles and enable prefetch buffer */
2 o) j m3 l! b - SetSysClock();
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y# I. I0 P; ]0 `1 n) S* n/ O6 V8 Y- #ifdef VECT_TAB_SRAM" a1 l* x3 W- T: [8 A
- SCB->VTOR = SRAM_BASE | VECT_TAB_OFFSET; /* Vector Table Relocation in Internal SRAM. */
! U( \9 h9 Y4 f% u: d2 d: b - #else3 E, p- f4 D( B M: W3 L; X
- SCB->VTOR = FLASH_BASE | VECT_TAB_OFFSET; /* Vector Table Relocation in Internal FLASH. */
+ r' U& z) } V' F% P0 |( M - #endif
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打开内部8M时钟:
9 {' c6 J) [- L' t" X- 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。
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) ?: ^: N! e# c( }, V5 Y* S设置时钟配置寄存器:" x" o* g# Z% L" [6 M8 O
- #ifndef STM32F10X_CL
! |" W2 i' f/ e: u# c- N& }* |0 K - RCC->CFGR &= (uint32_t)0xF8FF0000;
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- RCC->CFGR &= (uint32_t)0xF0FF0000;& g( }( Y( n+ X M
- #endif /* STM32F10X_CL */
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) o. s; G7 o J% O% n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。& m$ _5 S4 m) M# 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。( e* s0 W4 {1 ?/ s- N" l* P
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2.3 SetSysClock()函数详解, Z- M6 _6 ]+ D7 x- @# {6 f
- static void SetSysClock(void)4 W. b0 G7 Z" {! i" m
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- #ifdef SYSCLK_FREQ_HSE
- Q- G8 H. R! w( @! w - SetSysClockToHSE();1 W1 W# z: I+ J' u1 i- @( j
- #elif defined SYSCLK_FREQ_24MHz( G) ]0 N! [3 a/ b' k
- SetSysClockTo24();
: }: T! L! n2 F2 [% C1 S. p - #elif defined SYSCLK_FREQ_36MHz
9 o. ^. P ^6 n) f; Z+ \ - SetSysClockTo36();
' y5 u0 f" p5 V - #elif defined SYSCLK_FREQ_48MHz
' C) T1 U7 S- E% z - SetSysClockTo48();
5 O8 d6 D, E, v5 u$ ~7 p - #elif defined SYSCLK_FREQ_56MHz( `/ H) A9 S7 V( b9 Z& P5 E# \
- SetSysClockTo56();
5 s; Q+ O+ W8 A( q - #elif defined SYSCLK_FREQ_72MHz' D7 r$ a6 G# U% ]1 ~: }. q- E
- SetSysClockTo72();* F, g @+ v" v9 {/ u
- #endif
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" Z) V# Q, y5 ~' D! G! K, [system_stm32f10x.c文件中会根据芯片的型号定义对应的宏:
, k/ a, |! Y; y& w+ Y9 H9 H- #if defined (STM32F10X_LD_VL) || (defined STM32F10X_MD_VL) || (defined STM32F10X_HD_VL)
$ V8 ]4 S$ `% _+ O8 ` - /* #define SYSCLK_FREQ_HSE HSE_VALUE */( x3 I' P ^7 h; {+ L8 ~2 N
- #define SYSCLK_FREQ_24MHz 24000000
& \; c3 O( }+ a5 N& p2 w) }% Y& ] - #else9 K- x; ]: G4 f& k, _1 C. a" Z4 s
- /* #define SYSCLK_FREQ_HSE HSE_VALUE */- L$ Y2 q" h" O8 w" p5 m0 r5 {
- /* #define SYSCLK_FREQ_24MHz 24000000 */ / D; b, A- y9 W( Q# B3 D: L( r
- /* #define SYSCLK_FREQ_36MHz 36000000 */6 ~9 d* Q1 O# Y. N
- /* #define SYSCLK_FREQ_48MHz 48000000 */
, X5 [4 O+ ~9 q1 D - /* #define SYSCLK_FREQ_56MHz 56000000 */& ]! m% q6 h0 v4 W5 M1 m4 S
- #define SYSCLK_FREQ_72MHz 72000000
: |9 R W& v. @# N - #endif
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3 时钟配置函数
0 {8 z) n' _: B& ?! w# J7 k# a3 f3.1 时钟初始化配置函数- void SystemInit(void);
- }; v3 l% N4 A - SYSCLK(系统时钟)=72MHZ;8 J, \3 _0 b0 H5 ?' y
- AHB总线时钟(HCLK=SYSCLK)=72MHZ;# e. \* [, i" s: E( Y
- APB1总线时钟(PCLK1=SYSCLK/2)=36MHZ;
9 ]* W9 m) L* C1 R4 }0 o - APB2总线时钟(PCLK1=SYSCLK/1)=72MHZ;
1 n$ { I6 ^/ }4 w6 ^ - PLL主时钟=72MHZ;
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3.2 外设时钟使能配置函数3 H- h2 k' g( ]' A, d- K
- void RCC_AHBPeriphClockCmd(uint32_t RCC_AHBPeriph, FunctionalState NewState);
2 ~( J, n7 Y# y - void RCC_APB2PeriphClockCmd(uint32_t RCC_APB2Periph, FunctionalState NewState);9 C. i( ]) c3 ?9 m b
- void RCC_APB1PeriphClockCmd(uint32_t RCC_APB1Periph, FunctionalState NewState);
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% }* i- h' q: v+ R0 |8 I3 B8 v8 F3.3 时钟源使能函数- void RCC_HSICmd(FunctionalState NewState);: h7 l* p* s0 l
- void RCC_LSICmd(FunctionalState NewState);
. l& a3 ^$ T7 {& n - void RCC_PLLCmd(FunctionalState NewState);
2 V- N$ I* _9 |) q - void RCC_RTCCLKCmd(FunctionalState NewState);
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3.4 时钟源和倍频因子配置函数" u' l8 B; F0 b" {% `
- void RCC_HSEConfig(uint32_t RCC_HSE);( I+ s. s& L) M1 b2 Z
- void RCC_SYSCLKConfig(uint32_t RCC_SYSCLKSource);
2 Z: M9 D2 H. c; ^4 D/ H - void RCC_HCLKConfig(uint32_t RCC_SYSCLK);
% |* s7 n$ Z' X6 a$ E- b5 b - void RCC_PCLK1Config(uint32_t RCC_HCLK);3 e- E: [9 X6 [ o" \
- void RCC_PCLK2Config(uint32_t RCC_HCLK);
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2 d8 p+ c4 _. ^9 d( R- j; {3.5 外设时钟复位函数
, ?" z7 u, i4 q& M- void RCC_APB2PeriphResetCmd(uint32_t RCC_APB2Periph, FunctionalState NewState);
; L: y+ K* {# ~ - void RCC_APB1PeriphResetCmd(uint32_t RCC_APB1Periph, FunctionalState NewState);
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( e! A- @6 Q* b4 e5 B3.6 自定义系统时钟, q2 J. S% s5 g: F5 H1 i& I* H+ i
- void RCC_HSE_Config(u32 div,u32 pllm)( b5 b+ I+ z& D, ^
- {
: P6 \( m2 Y0 h1 i0 f6 s) K5 w# Y - RCC_DeInit();& W8 h& D' l: i5 M0 c8 B5 u" a
- RCC_HSEConfig(RCC_HSE_ON);. d2 C; x* O4 ~! F+ |0 } ~
- if(RCC_WaitForHSEStartUp()==SUCCESS)" q$ f' T) Q3 @5 Y! q
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- RCC_HCLKConfig(RCC_SYSCLK_Div1);
4 [/ ?7 ^+ [- n* M - RCC_PCLK1Config(RCC_HCLK_Div2);
9 F% F" J/ c7 Y# B v! ~4 @+ o! Z2 c1 T - RCC_PCLK2Config(RCC_HCLK_Div1);3 Y0 R r3 J( B% v" g: v
- RCC_PLLConfig(div,pllm);6 \5 r0 F6 v$ Q- u; B
- RCC_PLLCmd(ENABLE); ; X, K$ @4 n) ]7 e0 g1 d
- while(RCC_GetFlagStatus(RCC_FLAG_PLLRDY)==RESET)
* b- V" G' k0 M- ^% J; \ - RCC_SYSCLKConfig(RCC_SYSCLKSource_PLLCLK)) H u4 q5 A( K3 Q( _4 e
- while(RCC_GetSCLKSource()!=0x08);
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复制代码 转载自:STM32嵌入式开发
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3 g% C/ b; A+ F; g" h# h如有侵权请联系删除
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