LPC1768 CPU 时钟配置

调试LPC1768， NXP的库好像不如Luminary的好用（大家都这么说，也就跟着人云亦云了）。对照LPC1768的手册看了看Keil例程的PLL0配置过程，记录如下：

#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;
}
}