MCU的时钟体系

stm32F4的时钟体系图
1MHZ = 10^6 HZ
系统时钟频率是168MHZ;
AHB1、AHB2、AHB3总线上的时钟频率是168MHz;
APB1总线上的时钟频率为42MHz；
APB2总线上的时钟频率为84MHz；
stm32F4的时钟体系图 在system_stm32f4xx.c文件中查看APB1和APB2的预分频值到底是多少；
cpp 复制代码
/**
  ******************************************************************************
  * @file    system_stm32f4xx.c
  * @author  MCD Application Team
  * @version V1.8.1
  * @date    27-January-2022
  * @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)                               | 168000000
  *-----------------------------------------------------------------------------
  *        AHB Prescaler                          | 1
  *-----------------------------------------------------------------------------
  *        APB1 Prescaler                         | 4
  *-----------------------------------------------------------------------------
  *        APB2 Prescaler                         | 2
  *-----------------------------------------------------------------------------
  *        HSE Frequency(Hz)                      | 25000000
  *-----------------------------------------------------------------------------
  *        PLL_M                                  | 25
  *-----------------------------------------------------------------------------
  *        PLL_N                                  | 336
  *-----------------------------------------------------------------------------
  *        PLL_P                                  | 2
  *-----------------------------------------------------------------------------
  *        PLL_Q                                  | 7
  *-----------------------------------------------------------------------------
  *        PLLI2S_N                               | NA
  *-----------------------------------------------------------------------------
  *        PLLI2S_R                               | NA
  *-----------------------------------------------------------------------------
  *        I2S input clock                        | NA
  *-----------------------------------------------------------------------------
  *        VDD(V)                                 | 3.3
  *-----------------------------------------------------------------------------
  *        Main regulator output voltage          | Scale1 mode
  *-----------------------------------------------------------------------------
  *        Flash Latency(WS)                      | 5
  *-----------------------------------------------------------------------------
  *        Prefetch Buffer                        | ON
  *-----------------------------------------------------------------------------
  *        Instruction cache                      | ON
  *-----------------------------------------------------------------------------
  *        Data cache                             | ON
  *-----------------------------------------------------------------------------
  *        Require 48MHz for USB OTG FS,          | Disabled
  *        SDIO and RNG clock                     |
  *-----------------------------------------------------------------------------
  *=============================================================================
  *=============================================================================
  *                    Supported STM32F42xxx/43xxx devices
  *-----------------------------------------------------------------------------
  *        System Clock source                    | PLL (HSE)
  *-----------------------------------------------------------------------------
  *        SYSCLK(Hz)                             | 180000000
  *-----------------------------------------------------------------------------
  *        HCLK(Hz)                               | 180000000
  *-----------------------------------------------------------------------------
  *        AHB Prescaler                          | 1
  *-----------------------------------------------------------------------------
  *        APB1 Prescaler                         | 4
  *-----------------------------------------------------------------------------
  *        APB2 Prescaler                         | 2
  *-----------------------------------------------------------------------------
  *        HSE Frequency(Hz)                      | 25000000
  *-----------------------------------------------------------------------------
  *        PLL_M                                  | 25
  *-----------------------------------------------------------------------------
  *        PLL_N                                  | 360
  *-----------------------------------------------------------------------------
  *        PLL_P                                  | 2
  *-----------------------------------------------------------------------------
  *        PLL_Q                                  | 7
  *-----------------------------------------------------------------------------
  *        PLLI2S_N                               | NA
  *-----------------------------------------------------------------------------
  *        PLLI2S_R                               | NA
  *-----------------------------------------------------------------------------
  *        I2S input clock                        | NA
  *-----------------------------------------------------------------------------
  *        VDD(V)                                 | 3.3
  *-----------------------------------------------------------------------------
  *        Main regulator output voltage          | Scale1 mode
  *-----------------------------------------------------------------------------
  *        Flash Latency(WS)                      | 5
  *-----------------------------------------------------------------------------
  *        Prefetch Buffer                        | ON
  *-----------------------------------------------------------------------------
  *        Instruction cache                      | ON
  *-----------------------------------------------------------------------------
  *        Data cache                             | ON
  *-----------------------------------------------------------------------------
  *        Require 48MHz for USB OTG FS,          | Disabled
  *        SDIO and RNG clock                     |
  *-----------------------------------------------------------------------------
  *=============================================================================
  *=============================================================================
  *                         Supported STM32F401xx devices
  *-----------------------------------------------------------------------------
  *        System Clock source                    | PLL (HSE)
  *-----------------------------------------------------------------------------
  *        SYSCLK(Hz)                             | 84000000
  *-----------------------------------------------------------------------------
  *        HCLK(Hz)                               | 84000000
  *-----------------------------------------------------------------------------
  *        AHB Prescaler                          | 1
  *-----------------------------------------------------------------------------
  *        APB1 Prescaler                         | 2
  *-----------------------------------------------------------------------------
  *        APB2 Prescaler                         | 1
  *-----------------------------------------------------------------------------
  *        HSE Frequency(Hz)                      | 25000000
  *-----------------------------------------------------------------------------
  *        PLL_M                                  | 25
  *-----------------------------------------------------------------------------
  *        PLL_N                                  | 336
  *-----------------------------------------------------------------------------
  *        PLL_P                                  | 4
  *-----------------------------------------------------------------------------
  *        PLL_Q                                  | 7
  *-----------------------------------------------------------------------------
  *        PLLI2S_N                               | NA
  *-----------------------------------------------------------------------------
  *        PLLI2S_R                               | NA
  *-----------------------------------------------------------------------------
  *        I2S input clock                        | NA
  *-----------------------------------------------------------------------------
  *        VDD(V)                                 | 3.3
  *-----------------------------------------------------------------------------
  *        Main regulator output voltage          | Scale1 mode
  *-----------------------------------------------------------------------------
  *        Flash Latency(WS)                      | 2
  *-----------------------------------------------------------------------------
  *        Prefetch Buffer                        | ON
  *-----------------------------------------------------------------------------
  *        Instruction cache                      | ON
  *-----------------------------------------------------------------------------
  *        Data cache                             | ON
  *-----------------------------------------------------------------------------
  *        Require 48MHz for USB OTG FS,          | Disabled
  *        SDIO and RNG clock                     |
  *-----------------------------------------------------------------------------
  *=============================================================================
  *=============================================================================
  *                Supported STM32F411xx/STM32F410xx devices
  *-----------------------------------------------------------------------------
  *        System Clock source                    | PLL (HSI)
  *-----------------------------------------------------------------------------
  *        SYSCLK(Hz)                             | 100000000
  *-----------------------------------------------------------------------------
  *        HCLK(Hz)                               | 100000000
  *-----------------------------------------------------------------------------
  *        AHB Prescaler                          | 1
  *-----------------------------------------------------------------------------
  *        APB1 Prescaler                         | 2
  *-----------------------------------------------------------------------------
  *        APB2 Prescaler                         | 1
  *-----------------------------------------------------------------------------
  *        HSI Frequency(Hz)                      | 16000000
  *-----------------------------------------------------------------------------
  *        PLL_M                                  | 16
  *-----------------------------------------------------------------------------
  *        PLL_N                                  | 400
  *-----------------------------------------------------------------------------
  *        PLL_P                                  | 4
  *-----------------------------------------------------------------------------
  *        PLL_Q                                  | 7
  *-----------------------------------------------------------------------------
  *        PLLI2S_N                               | NA
  *-----------------------------------------------------------------------------
  *        PLLI2S_R                               | NA
  *-----------------------------------------------------------------------------
  *        I2S input clock                        | NA
  *-----------------------------------------------------------------------------
  *        VDD(V)                                 | 3.3
  *-----------------------------------------------------------------------------
  *        Main regulator output voltage          | Scale1 mode
  *-----------------------------------------------------------------------------
  *        Flash Latency(WS)                      | 3
  *-----------------------------------------------------------------------------
  *        Prefetch Buffer                        | ON
  *-----------------------------------------------------------------------------
  *        Instruction cache                      | ON
  *-----------------------------------------------------------------------------
  *        Data cache                             | ON
  *-----------------------------------------------------------------------------
  *        Require 48MHz for USB OTG FS,          | Disabled
  *        SDIO and RNG clock                     |
  *-----------------------------------------------------------------------------
  *=============================================================================
  *=============================================================================
  *                         Supported STM32F446xx devices
  *-----------------------------------------------------------------------------
  *        System Clock source                    | PLL (HSE)
  *-----------------------------------------------------------------------------
  *        SYSCLK(Hz)                             | 180000000
  *-----------------------------------------------------------------------------
  *        HCLK(Hz)                               | 180000000
  *-----------------------------------------------------------------------------
  *        AHB Prescaler                          | 1
  *-----------------------------------------------------------------------------
  *        APB1 Prescaler                         | 4
  *-----------------------------------------------------------------------------
  *        APB2 Prescaler                         | 2
  *-----------------------------------------------------------------------------
  *        HSE Frequency(Hz)                      | 8000000
  *-----------------------------------------------------------------------------
  *        PLL_M                                  | 8
  *-----------------------------------------------------------------------------
  *        PLL_N                                  | 360
  *-----------------------------------------------------------------------------
  *        PLL_P                                  | 2
  *-----------------------------------------------------------------------------
  *        PLL_Q                                  | 7
  *-----------------------------------------------------------------------------
  *        PLL_R                                  | NA
  *-----------------------------------------------------------------------------
  *        PLLI2S_M                               | NA
  *-----------------------------------------------------------------------------
  *        PLLI2S_N                               | NA
  *-----------------------------------------------------------------------------
  *        PLLI2S_P                               | NA
  *-----------------------------------------------------------------------------
  *        PLLI2S_Q                               | NA
  *-----------------------------------------------------------------------------
  *        PLLI2S_R                               | NA
  *-----------------------------------------------------------------------------
  *        I2S input clock                        | NA
  *-----------------------------------------------------------------------------
  *        VDD(V)                                 | 3.3
  *-----------------------------------------------------------------------------
  *        Main regulator output voltage          | Scale1 mode
  *-----------------------------------------------------------------------------
  *        Flash Latency(WS)                      | 5
  *-----------------------------------------------------------------------------
  *        Prefetch Buffer                        | ON
  *-----------------------------------------------------------------------------
  *        Instruction cache                      | ON
  *-----------------------------------------------------------------------------
  *        Data cache                             | ON
  *-----------------------------------------------------------------------------
  *        Require 48MHz for USB OTG FS,          | Disabled
  *        SDIO and RNG clock                     |
  *-----------------------------------------------------------------------------
  *=============================================================================
  ******************************************************************************
  * @attention
  *
  * Copyright (c) 2016 STMicroelectronics.
  * All rights reserved.
  *
  * This software is licensed under terms that can be found in the LICENSE file
  * in the root directory of this software component.
  * If no LICENSE file comes with this software, it is provided AS-IS.
  *
  ******************************************************************************
  */