基本所有的程序开头都包含了如下：
/* Unlock protected registers */
SYS_UnlockReg();
/* Init System, peripheral clock and multi-function I/O */
SYS_Init();
/* Lock protected registers */
SYS_LockReg();
/* Init UART0 for printf */
UART0_Init();
而其中的sys_init又包含如下
/* Enable HIRC clock (Internal RC 22.1184MHz) */
CLK_EnableXtalRC(CLK_PWRCTL_HIRCEN_Msk);
/* Wait for HIRC clock ready */
CLK_WaitClockReady(CLK_STATUS_HIRCSTB_Msk);
/* Select HCLK clock source as HIRC and and HCLK clock divider as 1 */
CLK_SetHCLK(CLK_CLKSEL0_HCLKSEL_HIRC, CLK_CLKDIV0_HCLK(1));
/* Enable HXT clock (external XTAL 12MHz) */
CLK_EnableXtalRC(CLK_PWRCTL_HXTEN_Msk);
/* Wait for HXT clock ready */
CLK_WaitClockReady(CLK_STATUS_HXTSTB_Msk);
/* Set core clock as PLL_CLOCK from PLL */
CLK_SetCoreClock(PLL_CLOCK);
/* Enable UART module clock */
CLK_EnableModuleClock(UART0_MODULE);
/* Select UART module clock source as HXT and UART module clock divider as 1 */
CLK_SetModuleClock(UART0_MODULE, CLK_CLKSEL1_UARTSEL_HXT, CLK_CLKDIV0_UART(1));
/*---------------------------------------------------------------------------------------------------------*/
/* Init I/O Multi-function */
/*---------------------------------------------------------------------------------------------------------*/
/* Set PD multi-function pins for UART0 RXD(PD.6) and TXD(PD.1) */
SYS->GPD_MFPL &= ~(SYS_GPD_MFPL_PD6MFP_Msk | SYS_GPD_MFPL_PD1MFP_Msk);
SYS->GPD_MFPL |= (SYS_GPD_MFPL_PD6MFP_UART0_RXD | SYS_GPD_MFPL_PD1MFP_UART0_TXD);
我想请教，这么繁琐的过程有无必要性？
初始化过程中的各个步骤有何实际意义？如果不这么做可能会导致什么问题？
特别是先打开寄存器，系统初始化后紧接着又锁定寄存器，为什么？ |
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