LPC1768 CPU 时钟配置

#if (CLOCK_SETUP)                      
  LPC_SC->SCS       = SCS_Val;          // 启用外部主时钟
  if (SCS_Val & (1 << 5)) {            
    while ((LPC_SC->SCS & (1<<6)) == 0);
  }

//PLL倍频出来的时钟送给CPU前的分频，CCLKCFG_Val=3，为4分频

  LPC_SC->CCLKCFG   = CCLKCFG_Val;     

  LPC_SC->PCLKSEL0  = PCLKSEL0_Val;    
  LPC_SC->PCLKSEL1  = PCLKSEL1_Val;

  LPC_SC->CLKSRCSEL = CLKSRCSEL_Val;   

#if (PLL0_SETUP)

//PLL0CFG_Val = 0x00050063， 5为pre-div的值既N，所以除数为N+1=6

// 0x63为乘数M，M+1=100，记得要把16进制换算为10进制

//Fcco = 2*100*12/6 = 400，然后再除以CPU clock的4，即该设置主频为100M
  LPC_SC->PLL0CFG   = PLL0CFG_Val;
  LPC_SC->PLL0CON   = 0x01;            

//确认序列
  LPC_SC->PLL0FEED  = 0xAA;
  LPC_SC->PLL0FEED  = 0x55;
  while (!(LPC_SC->PLL0STAT & (1<<26)));

  LPC_SC->PLL0CON   = 0x03;            
  LPC_SC->PLL0FEED  = 0xAA;
  LPC_SC->PLL0FEED  = 0x55;
#endif

#if (PLL1_SETUP)
  LPC_SC->PLL1CFG   = PLL1CFG_Val;
  LPC_SC->PLL1CON   = 0x01;            
  LPC_SC->PLL1FEED  = 0xAA;
  LPC_SC->PLL1FEED  = 0x55;
  while (!(LPC_SC->PLL1STAT & (1<<10)));

  LPC_SC->PLL1CON   = 0x03;            
  LPC_SC->PLL1FEED  = 0xAA;
  LPC_SC->PLL1FEED  = 0x55;
#else
  LPC_SC->USBCLKCFG = USBCLKCFG_Val;   
#endif

  LPC_SC->PCONP     = PCONP_Val;       

  LPC_SC->CLKOUTCFG = CLKOUTCFG_Val;   
#endif

 
  if (((LPC_SC->PLL0STAT >> 24)&3)==3) {
    switch (LPC_SC->CLKSRCSEL & 0x03) {
      case 0:                          
      case 3:                          
        SystemFrequency = (IRC_OSC * 
                          ((2 * ((LPC_SC->PLL0STAT & 0x7FFF) + 1)))  /
                          (((LPC_SC->PLL0STAT >> 16) & 0xFF) + 1)    /
                          ((LPC_SC->CCLKCFG & 0xFF)+ 1));
        break;
      case 1:                          

     //待Pll锁定和连接后PLL0STAT中有M和N，可以计算出实际频率
        SystemFrequency = (OSC_CLK * 
                          ((2 * ((LPC_SC->PLL0STAT & 0x7FFF) + 1)))  /
                          (((LPC_SC->PLL0STAT >> 16) & 0xFF) + 1)    /
                          ((LPC_SC->CCLKCFG & 0xFF)+ 1));
        break;
      case 2:                          
        SystemFrequency = (RTC_CLK * 
                          ((2 * ((LPC_SC->PLL0STAT & 0x7FFF) + 1)))  /
                          (((LPC_SC->PLL0STAT >> 16) & 0xFF) + 1)    /
                          ((LPC_SC->CCLKCFG & 0xFF)+ 1));
        break;
    }
  } else {
    switch (LPC_SC->CLKSRCSEL & 0x03) {
      case 0:                          
      case 3:                          
        SystemFrequency = IRC_OSC / ((LPC_SC->CCLKCFG & 0xFF)+ 1);
        break;
      case 1:                          
        SystemFrequency = OSC_CLK / ((LPC_SC->CCLKCFG & 0xFF)+ 1);
        break;
      case 2:                          
        SystemFrequency = RTC_CLK / ((LPC_SC->CCLKCFG & 0xFF)+ 1);
        break;
    }
  }