LPC1114_Clock System Analysis

Generally, we need to initialize the clock at the beginning of main(). We can select the clock source, whether to turn on PLL multiplication, and PLL configuration to achieve the required output clock according to our needs, and then select the multiplied clock as the main clock source.

As shown in the following figure: We need to pay attention to the concepts of several clocks.

 

#define CLOCK_SETUP           1
#define MAIN_PLL_SETUP        1
#define MAIN_CLKSRCSEL_Val    0x00000001
#define MAIN_PLL_M_Val        0x00000003
#define MAIN_PLL_P_Val        0x00000001
#define SYS_AHB_DIV_Val       1   /* 1 through 255, typical is 1 or 2 or 4 */

#define XTAL        (12000000UL)        /* Oscillator frequency               */
#define OSC_CLK     (      XTAL)        /* Main oscillator frequency          */
#define IRC_OSC     (12000000UL)        /* Internal RC oscillator frequency   */
#define WDT_OSC     (  250000UL)        /* WDT oscillator frequency           */

uint32_t ClockSource = IRC_OSC;
uint32_t SystemFrequency = IRC_OSC; /*!< System Clock Frequency (Core Clock)  */
uint32_t SystemAHBFrequency = IRC_OSC;

void Main_PLL_Setup ( void )
{
  uint32_t regVal;
  ClockSource = OSC_CLK;
  LPC_SYSCON->SYSPLLCLKSEL = MAIN_CLKSRCSEL_Val; /* Select system OSC--system oscillator*/
  LPC_SYSCON->SYSPLLCLKUEN = 0x01;                 /* Update clock source */
  LPC_SYSCON->SYSPLLCLKUEN = 0x00;                 /* toggle Update register once */
  LPC_SYSCON->SYSPLLCLKUEN = 0x01;
  while ( !(LPC_SYSCON->SYSPLLCLKUEN & 0x01) );    /* Wait until updated */
  regVal = LPC_SYSCON->SYSPLLCTRL;
  regVal &= ~0x1FF;
  LPC_SYSCON->SYSPLLCTRL = (regVal | (MAIN_PLL_P_Val<<5) | MAIN_PLL_M_Val);/* P=1, M=4 FCLKOUT=12*4=48Mhz */
 
  /* Enable main system PLL, main system PLL bit 7 in PDRUNCFG. */
  LPC_SYSCON->PDRUNCFG &= ~(0x1<<7); /* Write 0 to the seventh bit of PDRUNCFG, i.e. the system PLL is powered on*/
  while ( !(LPC_SYSCON->SYSPLLSTAT & 0x01) ); /* Wait until it's locked. Execute the following code after confirming that PLL is locked.*/
  LPC_SYSCON->MAINCLKSEL = 0x03; /* Select PLL clock output--Select PLL output as the main clock*/
  LPC_SYSCON->MAINCLKUEN = 0x01; /* Update MCLK clock source -- allows updating the main clock */
  LPC_SYSCON->MAINCLKUEN = 0x00;                /* Toggle update register once */
  LPC_SYSCON->MAINCLKUEN = 0x01;
  while ( !(LPC_SYSCON->MAINCLKUEN & 0x01) ); /* Wait until updated. After confirming that the main clock is locked, execute the following steps*/
  LPC_SYSCON->SYSAHBCLKDIV = SYS_AHB_DIV_Val; /* SYS AHB clock, typical is 1 or 2 or 4 --The value of SYSAHBCLKDIV is 1, which means no frequency division, so the AHB clock is set to 48Mhz */
#if MAIN_PLL_SETUP
  SystemFrequency = ClockSource * (MAIN_PLL_M_Val+1);
#else
  SystemFrequency = ClockSource;
#endif
  SystemAHBFrequency = (uint32_t)(SystemFrequency/SYS_AHB_DIV_Val);
  return;
}
/**
 * Initialize the system
 *
 * @param  none
 * @return none
 *
 * @brief  Setup the microcontroller system.
 *         Initialize the System and update the SystemFrequency variable.
 */
void SystemInit (void)
{
  uint32_t i;
#ifdef __DEBUG_RAM   
  LPC_SYSCON->SYSMEMREMAP = 0x1;  /* remap to internal RAM */
#else
#ifdef __DEBUG_FLASH   
  LPC_SYSCON->SYSMEMREMAP = 0x2;  /* remap to internal flash */
#endif
#endif
#if (CLOCK_SETUP)                       /* Clock Setup */
  /* bit 0 default is crystal bypass,
  bit1 0=0~20Mhz crystal input, 1=15~50Mhz crystal input. */
  LPC_SYSCON->SYSOSCCTRL = 0x00;
  /* main system OSC run is cleared, bit 5 in PDRUNCFG register */
  LPC_SYSCON->PDRUNCFG &= ~(0x1<<5); /* Write 0 to the fifth bit of PDRUNCFG, which means the system oscillator is powered on*/
  /* Wait 200us for OSC to be stablized, no status
  indication, dummy wait. */
  for ( i = 0; i < 0x100; i++ );
#if (MAIN_PLL_SETUP)
  Main_PLL_Setup(); 
#endif
#endif /* endif CLOCK_SETUP */
  /* System clock to the IOCON needs to be enabled or
  most of the I/O related peripherals won't work. */
  LPC_SYSCON->SYSAHBCLKCTRL |= (1<<16); //Enable the clock of the IO module
  return;
}