GD32F4xx芯片开发记录—系统时钟设置

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#单片机 #嵌入式硬件 #arm开发

本文详细介绍了GD32F4xx微控制器中时钟控制单元的功能，特别是系统时钟的配置方法，包括使用不同时钟源（IRC16M、HXTAL和PLL）以及通过锁相环实现频率倍频。还提供了查看系统时钟频率的示例代码和调试方法。

总结一下近段学习，便于以后查看。

1.时钟简介

手册上写到：

时钟控制单元提供了一系列频率的时钟功能，包括一个内部16M RC振荡器时钟（IRC16M）、一个内部48M RC振荡器时钟（IRC48M）、一个外部高速晶体振荡器时钟（HXTAL）、一个内部32K RC振荡器时钟（IRC32K）、一个外部低速晶体振荡器时钟（LXTAL）、三个锁相环（PLL）、一个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。 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 IRC16M、HXTAL或PLL。系统时钟的最大运行时钟频率可以达到240MHz。具体的时钟配置可以参考数据手册上的时钟树。这里主要介绍一下系统时钟的配置。

重点是这句话

系统时钟的时钟源可以选择 IRC16M、HXTAL或PLL。

2.系统时钟配置

首先，在官方例程中的system_gd32f4xx.c文件里，有这样一段宏定义

/* system frequency define 具体数值修改在GD32F4xx.h里*/
#define __IRC16M          (IRC16M_VALUE)            /* internal 16 MHz RC oscillator frequency 内部部振荡器频率*/
#define __HXTAL           (HXTAL_VALUE)             /* high speed crystal oscillator frequency 高速外部振荡器频率*/
#define __SYS_OSC_CLK     (__HXTAL)                /* main oscillator frequency 主振荡器频率 选择外部晶振或内部晶振 */

这里主要是起提示作用，我是用外部晶振倍频，所以 __SYS_OSC_CLK (__HXTAL)。

确定好外部高速晶振的频率后，在gd32f4xx.h文件里修改HXTAL_VALUE的值。我用的8M晶振，所以修改如下

#define HXTAL_VALUE    ((uint32_t)8000000)

主振荡器频率确定好后，再回到这句话“系统时钟的时钟源可以选择 IRC16M、HXTAL或PLL。”这里面pll是指将IRC16M或者HXTAL倍频到一定的频率。

/* select a system clock by uncommenting the following line 选择系统时钟 ：直接使用内、外部晶振频率 or 将其倍频*/
//#define __SYSTEM_CLOCK_IRC16M                   (uint32_t)(__IRC16M)
//#define __SYSTEM_CLOCK_HXTAL                    (uint32_t)(__HXTAL)
//#define __SYSTEM_CLOCK_120M_PLL_IRC16M          (uint32_t)(120000000)
//#define __SYSTEM_CLOCK_120M_PLL_8M_HXTAL        (uint32_t)(120000000)
//#define __SYSTEM_CLOCK_120M_PLL_25M_HXTAL       (uint32_t)(120000000)
//#define __SYSTEM_CLOCK_168M_PLL_IRC16M          (uint32_t)(168000000)
//#define __SYSTEM_CLOCK_168M_PLL_8M_HXTAL        (uint32_t)(168000000)
//#define __SYSTEM_CLOCK_168M_PLL_25M_HXTAL       (uint32_t)(168000000)
//#define __SYSTEM_CLOCK_200M_PLL_IRC16M          (uint32_t)(200000000)
//#define __SYSTEM_CLOCK_200M_PLL_8M_HXTAL        (uint32_t)(200000000)
//#define __SYSTEM_CLOCK_200M_PLL_25M_HXTAL       (uint32_t)(200000000)
//#define __SYSTEM_CLOCK_240M_PLL_IRC16M          (uint32_t)(240000000)
#define __SYSTEM_CLOCK_240M_PLL_8M_HXTAL          (uint32_t)(240000000)//外部晶振8M 通过锁相环将系统时钟分、倍频到 240M
//#define __SYSTEM_CLOCK_240M_PLL_25M_HXTAL       (uint32_t)(240000000)

在system_gd32f4xx.c文件中主要通过上面的宏定义，去选择相应的函数来确定系统时钟。

我这里选择将外部晶振8M通过锁相环将系统时钟倍频到 240M。具体的倍频代码如下

static void system_clock_240m_8m_hxtal(void)
{
    uint32_t timeout = 0U;
    uint32_t stab_flag = 0U;
    
    /* enable HXTAL */
    RCU_CTL |= RCU_CTL_HXTALEN;

    /* wait until HXTAL is stable or the startup time is longer than HXTAL_STARTUP_TIMEOUT 等待高速振荡器稳定*/
    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_CTL |= PMU_CTL_LDOVS;

    /* HXTAL is stable */
    /* AHB = SYSCLK */
    RCU_CFG0 |= RCU_AHB_CKSYS_DIV1;
    /* APB2 = AHB/2 */
    RCU_CFG0 |= RCU_APB2_CKAHB_DIV2;
    /* APB1 = AHB/4 */
    RCU_CFG0 |= RCU_APB1_CKAHB_DIV4;

    /* Configure the main PLL, PSC = 8, PLL_N = 480, PLL_P = 2, PLL_Q = 10 */ 
    RCU_PLL = (8U | (480U << 6U) | (((2U >> 1U) - 1U) << 16U) |
                   (RCU_PLLSRC_HXTAL) | (10U << 24U));

    /* enable PLL */
    RCU_CTL |= RCU_CTL_PLLEN;

    /* wait until PLL is stable */
    while(0U == (RCU_CTL & RCU_CTL_PLLSTB)){
    }
    
    /* Enable the high-drive to extend the clock frequency to 240 Mhz */
    PMU_CTL |= PMU_CTL_HDEN;
    while(0U == (PMU_CS & PMU_CS_HDRF)){
    }
    
    /* select the high-drive mode */
    PMU_CTL |= PMU_CTL_HDS;
    while(0U == (PMU_CS & PMU_CS_HDSRF)){
    } 
    
    /* select PLL as system clock */
    RCU_CFG0 &= ~RCU_CFG0_SCS;
    RCU_CFG0 |= RCU_CKSYSSRC_PLLP;

    /* wait until PLL is selected as system clock */
    while(0U == (RCU_CFG0 & RCU_SCSS_PLLP)){
    }
}

你也可以通过查看数据手册修改相应的倍频系数。

3.查看系统时钟

在gd32f4xx_rcu.c文件中有

uint32_t rcu_clock_freq_get(rcu_clock_freq_enum clock)
{
    uint32_t sws, ck_freq = 0U;
    uint32_t cksys_freq, ahb_freq, apb1_freq, apb2_freq;
    uint32_t pllpsc, plln, pllsel, pllp, ck_src, idx, clk_exp;

    /* exponent of AHB, APB1 and APB2 clock divider */
    const uint8_t ahb_exp[16] = {0, 0, 0, 0, 0, 0, 0, 0, 1, 2, 3, 4, 6, 7, 8, 9};
    const uint8_t apb1_exp[8] = {0, 0, 0, 0, 1, 2, 3, 4};
    const uint8_t apb2_exp[8] = {0, 0, 0, 0, 1, 2, 3, 4};

    sws = GET_BITS(RCU_CFG0, 2, 3);
    switch(sws) {
    /* IRC16M is selected as CK_SYS */
    case SEL_IRC16M:
        cksys_freq = IRC16M_VALUE;
        break;
    /* HXTAL is selected as CK_SYS */
    case SEL_HXTAL:
        cksys_freq = HXTAL_VALUE;
        break;
    /* PLLP is selected as CK_SYS */
    case SEL_PLLP:
        /* get the value of PLLPSC[5:0] */
        pllpsc = GET_BITS(RCU_PLL, 0U, 5U);
        plln = GET_BITS(RCU_PLL, 6U, 14U);
        pllp = (GET_BITS(RCU_PLL, 16U, 17U) + 1U) * 2U;
        /* PLL clock source selection, HXTAL or IRC16M/2 */
        pllsel = (RCU_PLL & RCU_PLL_PLLSEL);
        if(RCU_PLLSRC_HXTAL == pllsel) {
            ck_src = HXTAL_VALUE;
        } else {
            ck_src = IRC16M_VALUE;
        }
        cksys_freq = ((ck_src / pllpsc) * plln) / pllp;
        break;
    /* IRC16M is selected as CK_SYS */
    default:
        cksys_freq = IRC16M_VALUE;
        break;
    }
    /* calculate AHB clock frequency */
    idx = GET_BITS(RCU_CFG0, 4, 7);
    clk_exp = ahb_exp[idx];
    ahb_freq = cksys_freq >> clk_exp;

    /* calculate APB1 clock frequency */
    idx = GET_BITS(RCU_CFG0, 10, 12);
    clk_exp = apb1_exp[idx];
    apb1_freq = ahb_freq >> clk_exp;

    /* calculate APB2 clock frequency */
    idx = GET_BITS(RCU_CFG0, 13, 15);
    clk_exp = apb2_exp[idx];
    apb2_freq = ahb_freq >> clk_exp;

    /* return the clocks frequency */
    switch(clock) {
    case CK_SYS:
        ck_freq = cksys_freq;
        break;
    case CK_AHB:
        ck_freq = ahb_freq;
        break;
    case CK_APB1:
        ck_freq = apb1_freq;
        break;
    case CK_APB2:
        ck_freq = apb2_freq;
        break;
    default:
        break;
    }
    return ck_freq;
}

可以通过调试信息来查看系统时钟频率