File content as of revision 0:f269e3021894:

/* mbed Microcontroller Library
 * Copyright (c) 2006-2015 ARM Limited
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
#ifndef CLK_FREQS_H
#define CLK_FREQS_H

#ifdef __cplusplus
extern "C" {
#endif

/*!
 * \brief Get the peripheral bus clock frequency
 * \return Bus frequency
 */
static inline uint32_t bus_frequency(void) {
    return SystemCoreClock / (((SIM->CLKDIV1 & SIM_CLKDIV1_OUTDIV2_MASK) >> SIM_CLKDIV1_OUTDIV2_SHIFT) + 1);
}

/*!
 * \brief Get external oscillator (crystal) frequency
 * \return External osc frequency
 */
static uint32_t extosc_frequency(void) {
    uint32_t MCGClock = SystemCoreClock * (1u + ((SIM->CLKDIV1 & SIM_CLKDIV1_OUTDIV1_MASK) >> SIM_CLKDIV1_OUTDIV1_SHIFT));

    if ((MCG->C1 & MCG_C1_CLKS_MASK) == MCG_C1_CLKS(2))     //MCG clock = external reference clock
        return MCGClock;

    if ((MCG->C1 & MCG_C1_CLKS_MASK) == MCG_C1_CLKS(0)) {   //PLL/FLL is selected
        uint32_t divider, multiplier;
        if ((MCG->C6 & MCG_C6_PLLS_MASK) == 0x0u) {         //FLL is selected
            if ((MCG->S & MCG_S_IREFST_MASK) == 0x0u) {     //FLL uses external reference
                divider = (uint8_t)(1u << ((MCG->C1 & MCG_C1_FRDIV_MASK) >> MCG_C1_FRDIV_SHIFT));
                if ((MCG->C2 & MCG_C2_RANGE0_MASK) != 0x0u)
                    divider <<= 5u;
                /* Select correct multiplier to calculate the MCG output clock  */
                switch (MCG->C4 & (MCG_C4_DMX32_MASK | MCG_C4_DRST_DRS_MASK)) {
                    case 0x0u:
                      multiplier = 640u;
                      break;
                    case 0x20u:
                      multiplier = 1280u;
                      break;
                    case 0x40u:
                      multiplier = 1920u;
                      break;
                    case 0x60u:
                      multiplier = 2560u;
                      break;
                    case 0x80u:
                      multiplier = 732u;
                      break;
                    case 0xA0u:
                      multiplier = 1464u;
                      break;
                    case 0xC0u:
                      multiplier = 2197u;
                      break;
                    case 0xE0u:
                    default:
                      multiplier = 2929u;
                      break;
                }

                return MCGClock * divider / multiplier;
            }
        } else {             //PLL is selected
            divider = (1u + (MCG->C5 & MCG_C5_PRDIV0_MASK));
            multiplier = ((MCG->C6 & MCG_C6_VDIV0_MASK) + 24u);
            return MCGClock * divider / multiplier;
        }
    }

    //In all other cases either there is no crystal or we cannot determine it
    //For example when the FLL is running on the internal reference, and there is also an
    //external crystal. However these are unlikely situations
    return 0;
}

//Get MCG PLL/2 or FLL frequency, depending on which one is active, sets PLLFLLSEL bit
static uint32_t mcgpllfll_frequency(void) { 
    if ((MCG->C1 & MCG_C1_CLKS_MASK) != MCG_C1_CLKS(0))   //PLL/FLL is not selected
        return 0;
    
    uint32_t MCGClock = SystemCoreClock * (1u + ((SIM->CLKDIV1 & SIM_CLKDIV1_OUTDIV1_MASK) >> SIM_CLKDIV1_OUTDIV1_SHIFT));
    if ((MCG->C6 & MCG_C6_PLLS_MASK) == 0x0u) {         //FLL is selected
        SIM->SOPT2 &= ~SIM_SOPT2_PLLFLLSEL_MASK;        //MCG peripheral clock is FLL output
        return MCGClock;
    } else {                                            //PLL is selected
        SIM->SOPT2 |= SIM_SOPT2_PLLFLLSEL_MASK;         //MCG peripheral clock is PLL output
        return MCGClock;
    }
    
    //It is possible the SystemCoreClock isn't running on the PLL, and the PLL is still active 
    //for the peripherals, this is however an unlikely setup
}


#ifdef __cplusplus
}
#endif

#endif