使用内部晶振程序是可以跑起来的，但是使用外部晶振，程序一直在等待，请问这是什么原因？（晶振使用的是12M无源晶振，不知道是不是有源无源的问题）
void SYS_Init(void)
{
/*---------------------------------------------------------------------------------------------------------*/
/* Init System Clock */
/*---------------------------------------------------------------------------------------------------------*/
/* Enable Internal RC 22.1184MHz clock */
CLK->PWRCON |= CLK_PWRCON_OSC22M_EN_Msk;
/* Waiting for Internal RC clock ready */
while(!(CLK->CLKSTATUS & CLK_CLKSTATUS_OSC22M_STB_Msk));
/* Switch HCLK clock source to Internal RC */
CLK->CLKSEL0 &= ~CLK_CLKSEL0_HCLK_S_Msk;
CLK->CLKSEL0 |= CLK_CLKSEL0_HCLK_S_HIRC;
/* Enable external XTAL 12MHz clock */
CLK->PWRCON |= CLK_PWRCON_XTL12M_EN_Msk;
/* Waiting for external XTAL clock ready */
//死在这里！！
while(!(CLK->CLKSTATUS & CLK_CLKSTATUS_XTL12M_STB_Msk));
/* Set core clock as PLL_CLOCK from PLL */
CLK->PLLCON = PLLCON_SETTING;
while(!(CLK->CLKSTATUS & CLK_CLKSTATUS_PLL_STB_Msk));
CLK->CLKSEL0 &= (~CLK_CLKSEL0_HCLK_S_Msk);
CLK->CLKSEL0 |= CLK_CLKSEL0_HCLK_S_PLL;
/* Update System Core Clock */
/* User can use SystemCoreClockUpdate() to calculate PllClock, SystemCoreClock and CycylesPerUs automatically. */
//SystemCoreClockUpdate();
PllClock = PLL_CLOCK; // PLL
SystemCoreClock = PLL_CLOCK / 1; // HCLK
CyclesPerUs = PLL_CLOCK / 1000000; // For SYS_SysTickDelay()
/* Enable UART module clock */
CLK->APBCLK |= CLK_APBCLK_UART0_EN_Msk | CLK_APBCLK_I2C0_EN_Msk;
/* Select UART module clock source */
CLK->CLKSEL1 &= ~CLK_CLKSEL1_UART_S_Msk;
CLK->CLKSEL1 |= CLK_CLKSEL1_UART_S_HXT;
/*---------------------------------------------------------------------------------------------------------*/
/* Init I/O Multi-function */
/*---------------------------------------------------------------------------------------------------------*/
/* Set P3 multi-function pins for UART0 RXD and TXD, and set P3.4 and P3.5 for I2C0 SDA and SCL */
SYS->P3_MFP &= ~(SYS_MFP_P30_Msk | SYS_MFP_P31_Msk | SYS_MFP_P34_Msk | SYS_MFP_P35_Msk);
SYS->P3_MFP |= (SYS_MFP_P30_RXD0 | SYS_MFP_P31_TXD0 | SYS_MFP_P34_SDA0 | SYS_MFP_P35_SCL0);
}
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