mcg.c

freescale k40/k60 cortex m4 library

/*
 * File:    mcg.c
 * Purpose: Driver for enabling the PLL in 1 of 4 options
 *
 * Notes:
 * Assumes the MCG mode is in the default FEI mode out of reset
 * One of 4 clocking oprions can be selected.
 * One of 16 crystal values can be used
 */

#include "common.h"
#include "mcg.h"

extern int core_clk_khz;
extern int core_clk_mhz;
extern int periph_clk_khz;

unsigned char pll_init(unsigned char clk_option, unsigned char crystal_val)
{
  unsigned char pll_freq;

  if (clk_option > 3) {return 0;} //return 0 if one of the available options is not selected
  if (crystal_val > 15) {return 1;} // return 1 if one of the available crystal options is not available
//This assumes that the MCG is in default FEI mode out of reset.

// First move to FBE mode
#if (defined(K60_CLK) || defined(ASB817))
     MCG_C2 = 0;
#else
// Enable external oscillator, RANGE=2, HGO=1, EREFS=1, LP=0, IRCS=0
    MCG_C2 = MCG_C2_RANGE(2) | MCG_C2_HGO_MASK | MCG_C2_EREFS_MASK;
#endif

// after initialization of oscillator release latched state of oscillator and GPIO
    SIM_SCGC4 |= SIM_SCGC4_LLWU_MASK;
    LLWU_CS |= LLWU_CS_ACKISO_MASK;
  
// Select external oscilator and Reference Divider and clear IREFS to start ext osc
// CLKS=2, FRDIV=3, IREFS=0, IRCLKEN=0, IREFSTEN=0
  MCG_C1 = MCG_C1_CLKS(2) | MCG_C1_FRDIV(3);

  /* if we aren't using an osc input we don't need to wait for the osc to init */
#if (!defined(K60_CLK) && !defined(ASB817))
    while (!(MCG_S & MCG_S_OSCINIT_MASK)){};  // wait for oscillator to initialize
#endif

  while (MCG_S & MCG_S_IREFST_MASK){}; // wait for Reference clock Status bit to clear

  while (((MCG_S & MCG_S_CLKST_MASK) >> MCG_S_CLKST_SHIFT) != 0x2){}; // Wait for clock status bits to show clock source is ext ref clk

// Now in FBE

#if (defined(K60_CLK))
   MCG_C5 = MCG_C5_PRDIV(0x18);
#else
// Configure PLL Ref Divider, PLLCLKEN=0, PLLSTEN=0, PRDIV=5
// The crystal frequency is used to select the PRDIV value. Only even frequency crystals are supported
// that will produce a 2MHz reference clock to the PLL.
  MCG_C5 = MCG_C5_PRDIV(crystal_val); // Set PLL ref divider to match the crystal used
#endif

  // Ensure MCG_C6 is at the reset default of 0. LOLIE disabled, PLL disabled, clk monitor disabled, PLL VCO divider is clear
  MCG_C6 = 0x0;
// Select the PLL VCO divider and system clock dividers depending on clocking option
  switch (clk_option) {
    case 0:
      // Set system options dividers
      //MCG=PLL, core = MCG, bus = MCG, FlexBus = MCG, Flash clock= MCG/2
      set_sys_dividers(0,0,0,1);
      // Set the VCO divider and enable the PLL for 50MHz, LOLIE=0, PLLS=1, CME=0, VDIV=1
      MCG_C6 = MCG_C6_PLLS_MASK | MCG_C6_VDIV(1); //VDIV = 1 (x25)
      pll_freq = 50;
      break;
   case 1:
      // Set system options dividers
      //MCG=PLL, core = MCG, bus = MCG/2, FlexBus = MCG/2, Flash clock= MCG/4
     set_sys_dividers(0,1,1,3);
      // Set the VCO divider and enable the PLL for 100MHz, LOLIE=0, PLLS=1, CME=0, VDIV=26
      MCG_C6 = MCG_C6_PLLS_MASK | MCG_C6_VDIV(26); //VDIV = 26 (x50)
      pll_freq = 100;
      break;
    case 2:
      // Set system options dividers
      //MCG=PLL, core = MCG, bus = MCG/2, FlexBus = MCG/2, Flash clock= MCG/4
      set_sys_dividers(0,1,1,3);
      // Set the VCO divider and enable the PLL for 96MHz, LOLIE=0, PLLS=1, CME=0, VDIV=24
      MCG_C6 = MCG_C6_PLLS_MASK | MCG_C6_VDIV(24); //VDIV = 24 (x48)
      pll_freq = 96;
      break;
   case 3:
      // Set system options dividers
      //MCG=PLL, core = MCG, bus = MCG, FlexBus = MCG, Flash clock= MCG/2
      set_sys_dividers(0,0,0,1);
      // Set the VCO divider and enable the PLL for 48MHz, LOLIE=0, PLLS=1, CME=0, VDIV=0
      MCG_C6 = MCG_C6_PLLS_MASK; //VDIV = 0 (x24)
      pll_freq = 48;
      break;
  }
  while (!(MCG_S & MCG_S_PLLST_MASK)){}; // wait for PLL status bit to set

  while (!(MCG_S & MCG_S_LOCK_MASK)){}; // Wait for LOCK bit to set

// Now running PBE Mode

// Transition into PEE by setting CLKS to 0
// CLKS=0, FRDIV=3, IREFS=0, IRCLKEN=0, IREFSTEN=0
  MCG_C1 &= ~MCG_C1_CLKS_MASK;

// Wait for clock status bits to update
  while (((MCG_S & MCG_S_CLKST_MASK) >> MCG_S_CLKST_SHIFT) != 0x3){};

// Now running PEE Mode

return pll_freq;
} //pll_init

void set_sys_dividers(uint32 outdiv1, uint32 outdiv2, uint32 outdiv3, uint32 outdiv4)
{
 /*
  * This routine must be placed in RAM. It is a workaround for errata e2448.
  * Flash prefetch must be disabled when the flash clock divider is changed.
  * This cannot be performed while executing out of flash.
  * There must be a short delay after the clock dividers are changed before prefetch
  * can be re-enabled.
  */
  uint32 temp_reg;
  uint8 i;
  
  temp_reg = FMC_PFAPR; // store present value of FMC_PFAPR
  
  // set M0PFD through M7PFD to 1 to disable prefetch
  FMC_PFAPR |= FMC_PFAPR_M7PFD_MASK | FMC_PFAPR_M6PFD_MASK | FMC_PFAPR_M5PFD_MASK
             | FMC_PFAPR_M4PFD_MASK | FMC_PFAPR_M3PFD_MASK | FMC_PFAPR_M2PFD_MASK
             | FMC_PFAPR_M1PFD_MASK | FMC_PFAPR_M0PFD_MASK;
  
  // set clock dividers to desired value  
  SIM_CLKDIV1 = SIM_CLKDIV1_OUTDIV1(outdiv1) | SIM_CLKDIV1_OUTDIV2(outdiv2) 
              | SIM_CLKDIV1_OUTDIV3(outdiv3) | SIM_CLKDIV1_OUTDIV4(outdiv4);

  // wait for dividers to change
  for (i = 0 ; i < outdiv4 ; i++)
  {}
  
  FMC_PFAPR = temp_reg; // re-store original value of FMC_PFAPR
  
  return;
} // set_sys_dividers


/********************************************************************/
void mcg_pee_2_blpi(void)
{
    uint8 temp_reg;
    // Transition from PEE to BLPI: PEE -> PBE -> FBE -> FBI -> BLPI
  
    // Step 1: PEE -> PBE
    MCG_C1 |= MCG_C1_CLKS(2);  // System clock from external reference OSC, not PLL.
    while (((MCG_S & MCG_S_CLKST_MASK) >> MCG_S_CLKST_SHIFT) != 0x2){};  // Wait for clock status to update.
    
    // Step 2: PBE -> FBE
    MCG_C6 &= ~MCG_C6_PLLS_MASK;  // Clear PLLS to select FLL, still running system from ext OSC.
    while (MCG_S & MCG_S_PLLST_MASK){};  // Wait for PLL status flag to reflect FLL selected.
    
    // Step 3: FBE -> FBI
    MCG_C2 &= ~MCG_C2_LP_MASK;  // FLL remains active in bypassed modes.
    MCG_C2 |= MCG_C2_IRCS_MASK;  // Select fast (1MHz) internal reference
    temp_reg = MCG_C1;
    temp_reg &= ~(MCG_C1_CLKS_MASK | MCG_C1_IREFS_MASK);
    temp_reg |= (MCG_C1_CLKS(1) | MCG_C1_IREFS_MASK);  // Select internal reference (fast IREF clock @ 1MHz) as MCG clock source.
    MCG_C1 = temp_reg;
  
    while (MCG_S & MCG_S_IREFST_MASK){};  // Wait for Reference Status bit to update.
    while (((MCG_S & MCG_S_CLKST_MASK) >> MCG_S_CLKST_SHIFT) != 0x1){};  // Wait for clock status bits to update
    
    // Step 4: FBI -> BLPI
    MCG_C1 |= MCG_C1_IREFSTEN_MASK;  // Keep internal reference clock running in STOP modes.
    MCG_C2 |= MCG_C2_LP_MASK;  // FLL remains disabled in bypassed modes.
    while (!(MCG_S & MCG_S_IREFST_MASK)){};  // Wait for Reference Status bit to update.
    while (((MCG_S & MCG_S_CLKST_MASK) >> MCG_S_CLKST_SHIFT) != 0x1){};  // Wait for clock status bits to update.
  
} // end MCG PEE to BLPI
/********************************************************************/
void mcg_blpi_2_pee(void)
{
    uint8 temp_reg;
    // Transition from BLPI to PEE: BLPI -> FBI -> FEI -> FBE -> PBE -> PEE
  
    // Step 1: BLPI -> FBI
    MCG_C2 &= ~MCG_C2_LP_MASK;  // FLL remains active in bypassed modes.
    while (!(MCG_S & MCG_S_IREFST_MASK)){};  // Wait for Reference Status bit to update.
    while (((MCG_S & MCG_S_CLKST_MASK) >> MCG_S_CLKST_SHIFT) != 0x1){};  // Wait for clock status bits to update
    
    // Step 2: FBI -> FEI
    MCG_C2 &= ~MCG_C2_LP_MASK;  // FLL remains active in bypassed modes.
    temp_reg = MCG_C2;  // assign temporary variable of MCG_C2 contents
    temp_reg &= ~MCG_C2_RANGE_MASK;  // set RANGE field location to zero
    temp_reg |= (0x2 << 0x4);  // OR in new values
    MCG_C2 = temp_reg;  // store new value in MCG_C2
    MCG_C4 = 0x0E;  // Low-range DCO output (~10MHz bus).  FCTRIM=%0111.
    MCG_C1 = 0x04;  // Select internal clock as MCG source, FRDIV=%000, internal reference selected.
 
    while (!(MCG_S & MCG_S_IREFST_MASK)){};   // Wait for Reference Status bit to update 
    while (((MCG_S & MCG_S_CLKST_MASK) >> MCG_S_CLKST_SHIFT) != 0x0){}; // Wait for clock status bits to update
    
    // Handle FEI to PEE transitions using standard clock initialization routine.
    core_clk_mhz = pll_init(CORE_CLK_MHZ, REF_CLK); 

    /* Use the value obtained from the pll_init function to define variables
    * for the core clock in kHz and also the peripheral clock. These
    * variables can be used by other functions that need awareness of the
    * system frequency.
    */
    core_clk_khz = core_clk_mhz * 1000;
    periph_clk_khz = core_clk_khz / (((SIM_CLKDIV1 & SIM_CLKDIV1_OUTDIV2_MASK) >> 24)+ 1);        
} // end MCG BLPI to PEE
/********************************************************************/

void mcg_pbe_2_pee(void)
{  
  MCG_C1 &= ~MCG_C1_CLKS_MASK; // select PLL as MCG_OUT
  // Wait for clock status bits to update 
  while (((MCG_S & MCG_S_CLKST_MASK) >> MCG_S_CLKST_SHIFT) != 0x3){}; 

  switch (CORE_CLK_MHZ) {
    case PLL50:
      core_clk_khz = 50000;
      break;
    case PLL100:
      core_clk_khz = 100000;
      break;
    case PLL96:
      core_clk_khz = 96000;
      break;  
    case PLL48:
      core_clk_khz = 48000;
      break;  
  }
}