原创 LPC1768 CPU 时钟配置【转】

#if (CLOCK_SETUP)                       /* Clock Setup                        */
  LPC_SC->SCS       = SCS_Val;          // 启用外部主时钟
  if (SCS_Val & (1 << 5)) {             /* If Main Oscillator is enabled      */
    while ((LPC_SC->SCS & (1<<6)) == 0);/* Wait for Oscillator to be ready    */
  }

//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;      /* Setup Clock Divider                */

  LPC_SC->PCLKSEL0  = PCLKSEL0_Val;     /* Peripheral Clock Selection         */
  LPC_SC->PCLKSEL1  = PCLKSEL1_Val;

  LPC_SC->CLKSRCSEL = CLKSRCSEL_Val;    /* Select Clock Source for PLL0       */

#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;             /* PLL0 Enable                        */

//确认序列
  LPC_SC->PLL0FEED  = 0xAA;
  LPC_SC->PLL0FEED  = 0x55;
  while (!(LPC_SC->PLL0STAT & (1<<26)));/* Wait for PLOCK0                    */

  LPC_SC->PLL0CON   = 0x03;             /* PLL0 Enable & Connect              */
  LPC_SC->PLL0FEED  = 0xAA;
  LPC_SC->PLL0FEED  = 0x55;
#endif

#if (PLL1_SETUP)
  LPC_SC->PLL1CFG   = PLL1CFG_Val;
  LPC_SC->PLL1CON   = 0x01;             /* PLL1 Enable                        */
  LPC_SC->PLL1FEED  = 0xAA;
  LPC_SC->PLL1FEED  = 0x55;
  while (!(LPC_SC->PLL1STAT & (1<<10)));/* Wait for PLOCK1                    */

  LPC_SC->PLL1CON   = 0x03;             /* PLL1 Enable & Connect              */
  LPC_SC->PLL1FEED  = 0xAA;
  LPC_SC->PLL1FEED  = 0x55;
#else
  LPC_SC->USBCLKCFG = USBCLKCFG_Val;    /* Setup USB Clock Divider            */
#endif

  LPC_SC->PCONP     = PCONP_Val;        /* Power Control for Peripherals      */

  LPC_SC->CLKOUTCFG = CLKOUTCFG_Val;    /* Clock Output Configuration         */
#endif

  /* Determine clock frequency according to clock register values             */
  if (((LPC_SC->PLL0STAT >> 24)&3)==3) {/* If PLL0 enabled and connected      */
    switch (LPC_SC->CLKSRCSEL & 0x03) {
      case 0:                           /* Internal RC oscillator => PLL0     */
      case 3:                           /* Reserved, default to Internal RC   */
        SystemFrequency = (IRC_OSC *
                          ((2 * ((LPC_SC->PLL0STAT & 0x7FFF) + 1)))  /
                          (((LPC_SC->PLL0STAT >> 16) & 0xFF) + 1)    /
                          ((LPC_SC->CCLKCFG & 0xFF)+ 1));
        break;
      case 1:                           /* Main oscillator => PLL0            */

     //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:                           /* RTC oscillator => PLL0             */
        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:                           /* Internal RC oscillator => PLL0     */
      case 3:                           /* Reserved, default to Internal RC   */
        SystemFrequency = IRC_OSC / ((LPC_SC->CCLKCFG & 0xFF)+ 1);
        break;
      case 1:                           /* Main oscillator => PLL0            */
        SystemFrequency = OSC_CLK / ((LPC_SC->CCLKCFG & 0xFF)+ 1);
        break;
      case 2:                           /* RTC oscillator => PLL0             */
        SystemFrequency = RTC_CLK / ((LPC_SC->CCLKCFG & 0xFF)+ 1);
        break;
    }
  }