Code to set the Freedom Board MCG to 48MHz.
/*
* init_clocks()
* Set the PLL to 48MUz from the 8Mz xtal on the
* Freedom board.
* Returns:
* The freequency set from the divide/multiply register values.
*/
int init_clocks()
{
signed char prdiv; signed char vdiv;
// Set the core/system clock to divide by 2.
SIM_CLKDIV1 = SIM_CLKDIV1_OUTDIV1(1);
// 12.2.3 Selects the MCGPLLCLK or MCGFLLCLK clock for various peripheral
// clocking options.
SIM_SOPT2 |= SIM_SOPT2_PLLFLLSEL_MASK;
// 12.2.1 Set OSC32KSEL to 00 to select the System oscillator
SIM_SOPT1 &= ~(SIM_SOPT1_OSC32KSEL(3));
// Select MCGFLLCLK clock or MCGPLLCLK/2 fpr TPM
SIM_SOPT2 &= ~SIM_SOPT2_TPMSRC(3);
SIM_SOPT2 |= SIM_SOPT2_TPMSRC(1);
// Set up for external XTAL. 10.3.1 KL25 Signal Multiplexing and Pin Assignments
// Set pin function to EXTAL - Clear to 0 (pin 40)
PORTA_PCR18 &= ~(PORT_PCR_ISF_MASK | PORT_PCR_MUX(7));
// Set pin function to XTAL - Clear to 0
PORTA_PCR19 &= ~(PORT_PCR_ISF_MASK | PORT_PCR_MUX(7));
// FBE Mode
OSC0_CR = OSC_CR_ERCLKEN_MASK;
MCG_C2 = (MCG_C2_RANGE0(2) | MCG_C2_EREFS0_MASK);
MCG_C1 = (MCG_C1_CLKS(2) | MCG_C1_FRDIV(3) | MCG_C1_IRCLKEN_MASK);
MCG_C4 &= ~(MCG_C4_DMX32_MASK | MCG_C4_DRST_DRS(3));
MCG_C5 = MCG_C5_PRDIV0(3);
MCG_C6 = 0x00U;
// Wait for FLL extern ref.
while((MCG_S & MCG_S_IREFST_MASK) != 0)
;
// Wait for external ref. select.
while((MCG_S & MCG_S_CLKST_MASK) != 8)
;
// PBE
MCG_C2 = (MCG_C2_RANGE0(2) | MCG_C2_EREFS0_MASK);
MCG_C6 = MCG_C6_PLLS_MASK;
// Wait for lock.
while((MCG_S & MCG_S_LOCK0_MASK) == 0)
;
// PEE Mode
MCG_C1 = (MCG_C1_FRDIV(3) | MCG_C1_IRCLKEN_MASK);
// Wait for PLL select.
while((MCG_S &MCG_S_CLKST_MASK) !=MCG_S_CLKST_MASK)
;
// Use actual PLL settings to calculate PLL frequency
prdiv = ((MCG_C5 & MCG_C5_PRDIV0_MASK) + 1);
vdiv = ((MCG_C6 & MCG_C6_VDIV0_MASK) + 24);
return ((8000000 / prdiv) * vdiv);
}
