LM3S1138 Getting Started 7, PLL (Phase-Locked Loop) Setting System Clock

After using PLL, the CPU running speed is greatly increased, but the power consumption will also increase significantly. Therefore, the use of PLL should be limited in low-power applications.

Main function:

#include  "LED.H"
#include 
#include 
#include 
#include 
#include 
#include 

// Define longer identifiers as shorter forms
#define SysCtlPeriEnable SysCtlPeripheralEnable
#define SysCtlPeriDisable SysCtlPeripheralDisable
#define GPIOPinTypeIn GPIOPinTypeGPIOInput
#define GPIOPinTypeOut GPIOPinTypeGPIOOutput

//  定义KEY
#define  KEY_PERIPH             SYSCTL_PERIPH_GPIOG
#define  KEY_PORT               GPIO_PORTG_BASE
#define  KEY_PIN                GPIO_PIN_5

// Prevent JTAG from failing
void JTAG_Wait(void)
{
    SysCtlPeriEnable(KEY_PERIPH); // Enable the GPIO port where KEY is located
    GPIOPinTypeIn(KEY_PORT, KEY_PIN); // Set the pin where KEY is located to input

    if ( GPIOPinRead(KEY_PORT , KEY_PIN) == 0x00 ) // If KEY is pressed during reset, enter
    {
        for (;;); // Infinite loop to wait for JTAG connection
    }

    SysCtlPeriDisable(KEY_PERIPH); // Disable the GPIO port where KEY is located
}

// Define the global system clock variable
unsigned long TheSysClock = 12000000UL;

//  延时
void  Delay(unsigned long  ulVal)
{
    while ( --ulVal  !=  0 );
}

// System initialization
void SystemInit(void)
{
    SysCtlLDOSet(SYSCTL_LDO_2_75V); // Set the LDO voltage to 2.75V before configuring PLL

    SysCtlClockSet(SYSCTL_USE_PLL | // System clock setting, using PLL
                   SYSCTL_OSC_MAIN | // Main oscillator
                   SYSCTL_XTAL_6MHZ | // External 6MHz crystal oscillator
                   SYSCTL_SYSDIV_4); // The frequency division result is 50MHz

    TheSysClock = SysCtlClockGet(); // Get the system clock, unit: Hz

    LED_Init(LED2 | LED3); //LED initialization
}

int main(void)
{
    JTAG_Wait(); // Prevent JTAG failure, important!

    SystemInit(); // System initialization

    LED_On(LED2); // Turn on LED2
    LED_Off(LED3); // Turn off LED3

    for (;;)
    {
        LED_Toggle(LED2 | LED3);
        Delay(150 * (TheSysClock / 4000)); // Delay about 150ms
    }
}