GD32官方提供的固件库中使用的晶振配置一般为8M或25M，如果读者使用其他频率的晶振如何修改配置呢？本文为大家讲解如何修改。
以GD32F303为例，官方固件库中的晶振及时钟配置代码如下，改配置代码为使用外部8M晶振倍频到120M时钟。
/* 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)#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 */static void system_clock_120m_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 */
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/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);
/* CK_PLL = (CK_HXTAL/2) * 30 = 120 MHz */
RCU_CFG0 &= ~(RCU_CFG0_PLLMF | RCU_CFG0_PLLMF_4 | RCU_CFG0_PLLMF_5);
RCU_CFG0 |= RCU_PLL_MUL30;
#elif defined(GD32F30X_CL)
/* CK_PLL = (CK_PREDIV0) * 30 = 120 MHz */
RCU_CFG0 &= ~(RCU_CFG0_PLLMF | RCU_CFG0_PLLMF_4 | RCU_CFG0_PLLMF_5);
RCU_CFG0 |= (RCU_PLLSRC_HXTAL_IRC48M | RCU_PLL_MUL30);
/* 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) == 0U){
}
#endif /* GD32F30X_HD and GD32F30X_XD */
/* 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 120 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_PLL;
/* wait until PLL is selected as system clock */
while(0U == (RCU_CFG0 & RCU_SCSS_PLL)){
}
}在此我们举例，若外部晶振使用16M该如何配置，主要修改以下两点：
修改HXTAL_VALUE为16M，如下红色底纹部分。
#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)16000000) /* !< from 4M to 32M *!< value of the external oscillator in Hz*/#endif /* HXTAL_VALUE */ #endif /* high speed crystal oscillator value */
修改时钟倍频到120M.如下图红色底纹部分，配置15倍频，计算公式为16M/2*15=120M.
/* select HXTAL/2 as clock source */ RCU_CFG0 &= ~(RCU_CFG0_PLLSEL | RCU_CFG0_PREDV0); RCU_CFG0 |= (RCU_PLLSRC_HXTAL_IRC48M | RCU_CFG0_PREDV0); /* CK_PLL = (CK_HXTAL/2) * 15 = 120 MHz */ RCU_CFG0 &= ~(RCU_CFG0_PLLMF | RCU_CFG0_PLLMF_4 | RCU_CFG0_PLLMF_5); RCU_CFG0 |= RCU_PLL_MUL15;
PS：GD固件库中修改使用内部时钟非常方便，只要打开内部时钟的宏定义就可以啦。
/* 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)
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