GD32E230F8修改时钟源-切换为内部震荡时钟源

GD32E230的Firmware Library默认时钟源为外部高速晶振，内部PLL为72M时钟，在一些非常小的方案板子上没设计外部HXTAL，所以需要使用内部RC时钟

修改方法：

• 打开 Firmware/CMSIS/GD/GD32E23x/source/system_gd32e23x.c
• 在第45-49行，修改宏定义，可以选择 __system_CLOCK_8M_IRC8M 也可以选择 __system_CLOCK_72M_PLL_IRC8M_DIV2

/* select a system clock by uncommenting the following line */
//#define __SYSTEM_CLOCK_8M_HXTAL              (__HXTAL)
//#define __SYSTEM_CLOCK_8M_IRC8M              (__IRC8M)
#define __SYSTEM_CLOCK_72M_PLL_HXTAL         (uint32_t)(72000000)
//#define __SYSTEM_CLOCK_72M_PLL_IRC8M_DIV2    (uint32_t)(72000000)

• 也可以单独使用函数修改。参考官方demo

static void switch_system_clock_to_72m_irc8m(void)
{
    uint32_t timeout = 0U;
    uint32_t stab_flag = 0U;

    /* select IRC8M as system clock source, deinitialize the RCU */
    rcu_system_clock_source_config(RCU_CKSYSSRC_IRC8M);
    rcu_deinit();
  
    /* enable IRC8M */
    RCU_CTL0 |= RCU_CTL0_IRC8MEN;

    /* wait until IRC8M is stable or the startup time is longer than IRC8M_STARTUP_TIMEOUT */
    do{
        timeout++;
        stab_flag = (RCU_CTL0 & RCU_CTL0_IRC8MSTB);
    }
    while((0U == stab_flag) && (IRC8M_STARTUP_TIMEOUT != timeout));

    /* if fail */
    if(0U == (RCU_CTL0 & RCU_CTL0_IRC8MSTB)){
        while(1){
        }
    }

    FMC_WS = (FMC_WS & (~FMC_WS_WSCNT)) | WS_WSCNT_2;
  
    /* AHB = SYSCLK */
    RCU_CFG0 |= RCU_AHB_CKSYS_DIV1;
    /* APB2 = AHB */
    RCU_CFG0 |= RCU_APB2_CKAHB_DIV1;
    /* APB1 = AHB */
    RCU_CFG0 |= RCU_APB1_CKAHB_DIV1;
    /* PLL = (IRC8M/2) * 18 = 72 MHz */
    RCU_CFG0 &= ~(RCU_CFG0_PLLSEL | RCU_CFG0_PLLMF);
    RCU_CFG0 |= (RCU_PLLSRC_IRC8M_DIV2 | RCU_PLL_MUL18);

    /* enable PLL */
    RCU_CTL0 |= RCU_CTL0_PLLEN;

    /* wait until PLL is stable */
    while(0U == (RCU_CTL0 & RCU_CTL0_PLLSTB)){
    }

    /* 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)){
    }
}