F28335例程PLL配置问题

void InitPll(Uint16 val, Uint16 divsel)
{
   // Make sure the PLL is not running in limp mode
   if (SysCtrlRegs.PLLSTS.bit.MCLKSTS != 0)
   {
      // Missing external clock has been detected
      // Replace this line with a call to an appropriate
      // SystemShutdown(); function.
      asm("        ESTOP0");
   }

   if (SysCtrlRegs.PLLSTS.bit.DIVSEL != 0) 
   {
       EALLOW;
       SysCtrlRegs.PLLSTS.bit.DIVSEL = 0;
       EDIS;
   }

   // Change the PLLCR
   if (SysCtrlRegs.PLLCR.bit.DIV != val) //疑问，这里 val 是不是0?以前学习的C语言全部还给老师了，汗
   {

      EALLOW;
      // Before setting PLLCR turn off missing clock detect logic
      SysCtrlRegs.PLLSTS.bit.MCLKOFF = 1;
      SysCtrlRegs.PLLCR.bit.DIV = val;
      EDIS;
      DisableDog();

      while(SysCtrlRegs.PLLSTS.bit.PLLLOCKS != 1)
      {
	      // Uncomment to service the watchdog
          // ServiceDog();
      }

      EALLOW;
      SysCtrlRegs.PLLSTS.bit.MCLKOFF = 0;
      EDIS;
    }

	if((divsel == 1)||(divsel == 2))
	{
		EALLOW;
	    SysCtrlRegs.PLLSTS.bit.DIVSEL = divsel;
	    EDIS;
	}
	if(divsel == 3)
	{
		EALLOW;
	    SysCtrlRegs.PLLSTS.bit.DIVSEL = 2;
	    DELAY_US(50L);
	    SysCtrlRegs.PLLSTS.bit.DIVSEL = 3;
	    EDIS;
    }
}