Configure LPC43xx ARM Cortex M4 microcontroller to 204 MHz using 12 MHz crystal.

System_Configuration_LPC43xx.cpp

//
// Configure LPC43xx ARM Cortex M4 microcontroller to 204 MHz using 12 MHz crystal
//

#define CMSIS_BITPOSITIONS
#include "lpc43xx.h"


void Configure_Clocks()
{
    // Enable crystal oscillator
    LPC_CGU->XTAL_OSC_CTRL = 0;
    for (volatile uint32_t i = 0; i < 1000000; ++i);

    // Set the PLL to 204 MHz  
    uint32_t control_register = LPC_CGU->PLL1_CTRL;

    control_register &= ~(CGU_PLL1_CTRL_MSEL_Msk | CGU_PLL1_CTRL_CLK_SEL_Msk | CGU_PLL1_CTRL_PD_Msk);
    control_register |= 16 << CGU_PLL1_CTRL_MSEL_Pos;           // Feedback-divider division ratio = 17 ---> 17 * 12 MHz = 204 MHz
    control_register |= 6  << CGU_PLL1_CTRL_CLK_SEL_Pos;        // Clock source = crystal oscillator

    LPC_CGU->PLL1_CTRL = control_register;
    while (!(LPC_CGU->PLL1_STAT & CGU_PLL1_STAT_LOCK_Msk));

    // Set M4 clock to PLL1
    LPC_CGU->BASE_M4_CLK = 9 << CGU_BASE_M4_CLK_CLK_SEL_Pos |   // Clock source = PLL1
                           1 << CGU_BASE_M4_CLK_AUTOBLOCK_Pos;  // Block clock automatically during frequency change
}