GD32_时钟配置解析

本文以GD32F303型号为基础,依照标准库GD32F30x_Firmware_Library_V2.1.5为例,作为笔记简单记录个人对其时钟配置的理解,后续会持续更新本篇笔记内容。


文章目录

  • GD32_时钟配置解析
  • 前言
  • 一、时钟源简介
  • 二、时钟配置步骤
  • 1.SystemInit (void)
  • 2.system_clock_config();
  • 3. system_clock_108m_hxtal();
  • 三、修改参数详解
  • 四、测试方法及注意事项
  • 1.测试方法
  • 2.注意事项
  • 总结

  • 前言

    因为某些原因,国外半导体供应供应短缺,以STM32为例的系列芯片紧缺,价格跳水严重。技术群的部分码友们所在公司纷纷寻找替代产品,将头转向兆易创新的GD32,在将以前的STM32项目移植到国产GD32过程中,踩坑是在所难免,我也重新梳理了对GD32的理解。作为笔记加深理解。本篇主要是对时钟树的配置的一些理解和问题,欢迎各位码友指点!


    一、时钟源简介

    时钟控制单元提供有五个时钟源,见时钟树标记,包括:
    1:内部8M RC振荡器时钟(IRC8M):高速内部8MHz时钟,拥有8MHz的固定频率,设备上电后CPU默认选择的时钟源就是IRC8M时钟
    2:内部48M RC 振荡器时钟(IRC48): 有一个固定的频率48MHz,可用作USB时钟或者PLL时钟源
    3:外部高速晶体振荡器时钟(HXTAL:4到32MHz的外部振荡器,可为系统提供精确的主时钟。带有特定频率的晶体必须靠近两个HXTAL的引脚。和晶体连接的外部电阻和电容必须根据所选择的振荡器来调整
    4:内部40K RC振荡器时钟(IRC40K):它的时钟频率大约40 kHz,为独立看门狗定时器和实时时钟电路提供时钟。
    5:外部低速晶体振荡器时钟(LXTA):一个32.768kHz的低速外部晶体或陶瓷谐振器。它为实时时钟电路提供一个低功耗且精确的时钟源。
    内部锁相环(PLL):对输入参考频率为4到32MHz时钟进行分频操作,输出一个8-120 MHz的时钟输出
    剩下就是HXTAL时钟监视器、时钟预分频器、时钟多路复用器和时钟门控电路等。
    AHB、 APB和Cortex®-M4时钟都源自系统时钟(CK_SYS),系统时钟的时钟源可以选择IRC8M、HXTAL或PLL。系统时钟的最大运行时钟频率可以达到120MHz。
    严格来说锁相环不算时钟源,它是其他时钟源头配置而来

    二、时钟配置步骤

    1.SystemInit (void)

    此函数中主要操作为依内部8MHz时钟为时钟源,驱动时钟配置,线路为红色线路所示,步骤如下图:

    代码如下(示例):

    void SystemInit (void)
    {
      /* FPU settings */
    #if (__FPU_PRESENT == 1) && (__FPU_USED == 1)
        SCB->CPACR |= ((3UL << 10*2)|(3UL << 11*2));  /* set CP10 and CP11 Full Access */
    #endif
        /* reset the RCU clock configuration to the default reset state */
        /* Set IRC8MEN bit */
        RCU_CTL |= RCU_CTL_IRC8MEN;						//打开内部8MHz RC振荡器
        while(0U == (RCU_CTL & RCU_CTL_IRC8MSTB)){  	//等待内部8MHz RC振荡器稳定
        }
        RCU_MODIFY(0x50);								//AHB时钟分频设置 先二分频再四分频
        
        RCU_CFG0 &= ~RCU_CFG0_SCS;						//00:选择 CK_IRC8M 时钟作为 CK_SYS 时钟源
    
    #if (defined(GD32F30X_HD) || defined(GD32F30X_XD))
        /* reset HXTALEN, CKMEN and PLLEN bits */
    	/*外部高速时钟使能位、HXTAL 时钟监视器使能位、PLL使能位 复位,方便后续操作*/
        RCU_CTL &= ~(RCU_CTL_PLLEN | RCU_CTL_CKMEN | RCU_CTL_HXTALEN);
        /* disable all interrupts */
        /*关闭中断位*/
        RCU_INT = 0x009f0000U;
    #elif defined(GD32F30X_CL)
        /* Reset HXTALEN, CKMEN, PLLEN, PLL1EN and PLL2EN bits */
        RCU_CTL &= ~(RCU_CTL_PLLEN |RCU_CTL_PLL1EN | RCU_CTL_PLL2EN | RCU_CTL_CKMEN | RCU_CTL_HXTALEN);
        /* disable all interrupts */
        RCU_INT = 0x00ff0000U;
    #endif
    
        /* reset HXTALBPS bit */
        RCU_CTL &= ~(RCU_CTL_HXTALBPS); //旁路模式位复位
        
        /* Reset CFG0 and CFG1 registers */
        RCU_CFG0 = 0x00000000U;
        RCU_CFG1 = 0x00000000U;
        /* configure the system clock source, PLL Multiplier, AHB/APBx prescalers and Flash settings */
        system_clock_config();
    }
    

    2.system_clock_config();

    根据宏定义,选择相关的时钟频率配置函数,我的是高速外部时钟源配置108MHz系统时钟
    配置函数为;system_clock_108m_hxtal();
    代码如下(示例):

    static void system_clock_config(void)
    {
    #ifdef __SYSTEM_CLOCK_IRC8M
        system_clock_8m_irc8m();
    #elif defined (__SYSTEM_CLOCK_48M_PLL_IRC8M)
        system_clock_48m_irc8m();
    #elif defined (__SYSTEM_CLOCK_72M_PLL_IRC8M)
        system_clock_72m_irc8m();
    #elif defined (__SYSTEM_CLOCK_108M_PLL_IRC8M)
        system_clock_108m_irc8m();
    #elif defined (__SYSTEM_CLOCK_120M_PLL_IRC8M)
        system_clock_120m_irc8m();
    #elif defined (__SYSTEM_CLOCK_HXTAL)
        system_clock_hxtal();
    #elif defined (__SYSTEM_CLOCK_48M_PLL_HXTAL)
        system_clock_48m_hxtal();
    #elif defined (__SYSTEM_CLOCK_72M_PLL_HXTAL)
        system_clock_72m_hxtal();
    #elif defined (__SYSTEM_CLOCK_108M_PLL_HXTAL)
        system_clock_108m_hxtal();
    #elif defined (__SYSTEM_CLOCK_120M_PLL_HXTAL)
        system_clock_120m_hxtal();
    #endif /* __SYSTEM_CLOCK_IRC8M */
    }
    

    3. system_clock_108m_hxtal();

    该函数以外部时钟源配置108兆系统时钟步骤如图,时钟线路为绿色线路所示:

    代码如下(示例):

    static void system_clock_108m_hxtal(void)
    {
        uint32_t timeout = 0U;
        uint32_t stab_flag = 0U;
    
        /* enable HXTAL */
        RCU_CTL |= RCU_CTL_HXTALEN;  			//使能外部晶振
    
        /* wait until HXTAL is stable or the startup time is longer than HXTAL_STARTUP_TIMEOUT */
        do{
            timeout++;
            stab_flag = (RCU_CTL & RCU_CTL_HXTALSTB);
        }while((0U == stab_flag) && (HXTAL_STARTUP_TIMEOUT != timeout));
    
        /* if fail */
        if(0U == (RCU_CTL & RCU_CTL_HXTALSTB)){
            while(1){
            }
        }
    
        RCU_APB1EN |= RCU_APB1EN_PMUEN;   //PMU 时钟使能
        PMU_CTL |= PMU_CTL_LDOVS;		  //11: LDO 输出高电压模式
    
        /* HXTAL is stable */
        /* AHB = SYSCLK */
        RCU_CFG0 |= RCU_AHB_CKSYS_DIV1;
        /* APB2 = AHB/1 */
        RCU_CFG0 |= RCU_APB2_CKAHB_DIV1;
        /* APB1 = AHB/2 */
        RCU_CFG0 |= RCU_APB1_CKAHB_DIV2;
    
    #if (defined(GD32F30X_HD) || defined(GD32F30X_XD))
        /* select HXTAL/2 as clock source */
        RCU_CFG0 &= ~(RCU_CFG0_PLLSEL | RCU_CFG0_PREDV0);
        RCU_CFG0 |= (RCU_PLLSRC_HXTAL_IRC48M | RCU_CFG0_PREDV0);//HXTAL 时钟或者 IRC48M 时钟(寄存器 RCU_CFG1 位 PLLPRESEL 决定)被选择为 PLL 时钟的时钟源
    
        /*CK_PLL = (CK_HXTAL/2) * 27 = 108 MHz*/
        RCU_CFG0 &= ~(RCU_CFG0_PLLMF | RCU_CFG0_PLLMF_4 | RCU_CFG0_PLLMF_5);
        RCU_CFG0 |= RCU_PLL_MUL27;			//30 27 21 20 19 18:011010
    
    #elif defined(GD32F30X_CL)
        /* CK_PLL = (CK_PREDIV0) * 27 = 108 MHz */ 
        RCU_CFG0 &= ~(RCU_CFG0_PLLMF | RCU_CFG0_PLLMF_4 | RCU_CFG0_PLLMF_5);
        RCU_CFG0 |= (RCU_PLLSRC_HXTAL_IRC48M | RCU_PLL_MUL27);
    
        /* CK_PREDIV0 = (CK_HXTAL)/5 *8 /10 = 4 MHz */ 
        RCU_CFG1 &= ~(RCU_CFG1_PLLPRESEL | RCU_CFG1_PREDV0SEL | RCU_CFG1_PLL1MF | RCU_CFG1_PREDV1 | RCU_CFG1_PREDV0);
        RCU_CFG1 |= (RCU_PLLPRESRC_HXTAL | RCU_PREDV0SRC_CKPLL1 | RCU_PLL1_MUL8 | RCU_PREDV1_DIV5 | RCU_PREDV0_DIV10);
    
        /* enable PLL1 */
        RCU_CTL |= RCU_CTL_PLL1EN;
        /* wait till PLL1 is ready */
        while((RCU_CTL & RCU_CTL_PLL1STB) == 0){
        }
    #endif /* GD32F30X_HD and GD32F30X_XD */
    
        /* enable PLL */
        RCU_CTL |= RCU_CTL_PLLEN;  //PLL 被打开
    
        /* wait until PLL is stable */
        while(0U == (RCU_CTL & RCU_CTL_PLLSTB)){
        }
    
        /* enable the high-drive to extend the clock frequency to 120 MHz */
        PMU_CTL |= PMU_CTL_HDEN;  //使能高驱动模式
        while(0U == (PMU_CS & PMU_CS_HDRF)){
        }
    
        /* select the high-drive mode */
        PMU_CTL |= PMU_CTL_HDS;		//有高驱动模式切换器
        while(0U == (PMU_CS & PMU_CS_HDSRF)){
        }
    
        /* select PLL as system clock */
        RCU_CFG0 &= ~RCU_CFG0_SCS; 
        RCU_CFG0 |= RCU_CKSYSSRC_PLL; 	//10:选择 CK_PLL 时钟作为 CK_SYS 时钟源
    
        /* wait until PLL is selected as system clock */
        while(0U == (RCU_CFG0 & RCU_SCSS_PLL)){
        }
    }
    

    三、修改参数详解

    1.外部晶振时钟频率,在gd32f30x.h文件中,根据实际外部晶振频率修改参数,我的板子是8兆晶振,选择:
    #define HXTAL_VALUE ((uint32_t)8000000)

    /* define value of high speed crystal oscillator (HXTAL) in Hz */
    #if !defined  HXTAL_VALUE
    #ifdef GD32F30X_CL
    #define HXTAL_VALUE    ((uint32_t)25000000) /*!< value of the external oscillator in Hz */
    #else
    #define HXTAL_VALUE    ((uint32_t)8000000) /* !< from 4M to 32M *!< value of the external oscillator in Hz*/
    #endif /* HXTAL_VALUE */
    #endif /* high speed crystal oscillator value */
    

    2.外部晶振时钟频率,在system_gd32f30x.c文件中,_SYS_OSC_CLK为系统时钟主频率选择宏定义,使用内部晶振选择__IRC8M
    我需要的系统时钟配置函数为:__SYSTEM_CLOCK_108M_PLL_HXTAL()

    /* system frequency define */
    #define __IRC8M           (IRC8M_VALUE)            /* internal 8 MHz RC oscillator frequency */
    #define __HXTAL           (HXTAL_VALUE)            /* high speed crystal oscillator frequency */
    #define __SYS_OSC_CLK     (__IRC8M)                /* main oscillator frequency */
    
    /* select a system clock by uncommenting the following line */
    /* use IRC8M */
    //#define __SYSTEM_CLOCK_IRC8M                    (uint32_t)(__IRC8M) 
    //#define __SYSTEM_CLOCK_48M_PLL_IRC8M            (uint32_t)(48000000)
    //#define __SYSTEM_CLOCK_72M_PLL_IRC8M            (uint32_t)(72000000)
    //#define __SYSTEM_CLOCK_108M_PLL_IRC8M           (uint32_t)(108000000)
    //#define __SYSTEM_CLOCK_120M_PLL_IRC8M           (uint32_t)(120000000)
    
    /* use HXTAL(XD series CK_HXTAL = 8M, CL series CK_HXTAL = 25M) */
    //#define __SYSTEM_CLOCK_HXTAL                    (uint32_t)(__HXTAL)
    //#define __SYSTEM_CLOCK_48M_PLL_HXTAL            (uint32_t)(48000000)
    //#define __SYSTEM_CLOCK_72M_PLL_HXTAL            (uint32_t)(72000000)
    #define __SYSTEM_CLOCK_108M_PLL_HXTAL           (uint32_t)(108000000)
    //#define __SYSTEM_CLOCK_120M_PLL_HXTAL           (uint32_t)(120000000)
    
    1. 在system_gd32f30x.c文件中修改PLL分频倍频系数,带入公式:CK_PLL = (CK_HXTAL/分频系数) * PLL倍频系数 = xx MHz
      CFG0寄存器的30 27 21 20 19 18位:011010即倍频为27,最终系统时钟频率:108MHz
    #if (defined(GD32F30X_HD) || defined(GD32F30X_XD))
        /* select HXTAL/2 as clock source */
        RCU_CFG0 &= ~(RCU_CFG0_PLLSEL | RCU_CFG0_PREDV0);
        RCU_CFG0 |= (RCU_PLLSRC_HXTAL_IRC48M | RCU_CFG0_PREDV0);//HXTAL 时钟或者 IRC48M 时钟(寄存器 RCU_CFG1 位 PLLPRESEL 决定)被选择为 PLL 时钟的时钟源
    
        /*CK_PLL = (CK_HXTAL/2) * 27 = 108 MHz*/
        RCU_CFG0 &= ~(RCU_CFG0_PLLMF | RCU_CFG0_PLLMF_4 | RCU_CFG0_PLLMF_5);
        RCU_CFG0 |= RCU_PLL_MUL27;
    

    四、测试方法及注意事项

    系统时钟准确与否关系到整个工程的功能能否正常运行,拿到祖传代码或者移植新项目一定记得先测时钟,别问为什么,问就是教训!!!

    1.测试方法

    1.通过系统函数获取时钟配置,uint32_t rcu_clock_freq_get(rcu_clock_freq_enum clock)函数可用来获取时钟参数,
    获取APB1时钟:uclk = rcu_clock_freq_get(CK_APB1);
    获取APB2时钟:uclk = rcu_clock_freq_get(CK_APB2);
    获取CK_AHB时钟:uclk = rcu_clock_freq_get(CK_AHB);
    获取CK_SYS时钟:uclk = rcu_clock_freq_get(CK_SYS);
    STM32中函数测试方法位:
    RCC_ClocksTypeDef RCC_Clocks;
    RCC_GetClocksFreq(&RCC_Clocks);
    2.上述方法是配置参数,结果是跟着参数走的,有时候与实际情况不一样,一般情况是写一个简单的定时器或延时函数,周期性改变某个GPIO电平,通过示波器进行检测是最准的
    3.如图,通过配置CK_OUTO时钟输出引脚,配置引脚位复用输出模式,使用void rcu_ckout0_config(uint32_t ckout0_src)进行配置,然后也是通过示波器看波形

    2.注意事项

    1.#define HXTAL_VALUE ((uint32_t)8000000)外部晶振时钟频率,这个时钟频率与实际晶振频率不一样可能导致串口输出异常
    2.如果没有外部晶振,被迫使用内部时钟,记得一定要通过配置的到并测试,不要不管配置等待系统默认选择内部时钟。
    3.后续跟进

    总结

    系统时钟非常重要,各个板子的支持时钟可能不同,但是配置方法大同小异
    如有错误,欢迎指正,原创不易,转载留名!

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