File content as of revision 306:d33324c3b5a2:

/* mbed Microcontroller Library

 * Copyright (c) 2013 Nordic Semiconductor.
 *
 * 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.
 */


#include <stdint.h>
#include <stdbool.h>
#include "nrf51822.h"
#include "system_nrf51822.h"


#define __SYSTEM_CLOCK      (16000000UL)     /*!< nRF51 devices use a fixed System Clock Frequency of 16MHz */

static bool is_manual_peripheral_setup_needed(void);
static bool is_disabled_in_debug_needed(void);


#if defined ( __CC_ARM )
    uint32_t SystemCoreClock __attribute__((used)) = __SYSTEM_CLOCK;
#elif defined ( __ICCARM__ )
    __root uint32_t SystemCoreClock = __SYSTEM_CLOCK;
#elif defined   ( __GNUC__ )
    uint32_t SystemCoreClock __attribute__((used)) = __SYSTEM_CLOCK;
#endif

void SystemCoreClockUpdate(void)
{
    SystemCoreClock = __SYSTEM_CLOCK;
}

void SystemInit(void)
{
    /* If desired, switch off the unused RAM to lower consumption by the use of RAMON register.
       It can also be done in the application main() function. */

    // Prepare the peripherals for use as indicated by the PAN 26 "System: Manual setup is required
    // to enable the use of peripherals" found at Product Anomaly document for your device found at
    // https://www.nordicsemi.com/. The side effect of executing these instructions in the devices
    // that do not need it is that the new peripherals in the second generation devices (LPCOMP for
    // example) will not be available.
    if (is_manual_peripheral_setup_needed())
    {
        *(uint32_t volatile *)0x40000504 = 0xC007FFDF;
        *(uint32_t volatile *)0x40006C18 = 0x00008000;
    }

    // Disable PROTENSET registers under debug, as indicated by PAN 59 "MPU: Reset value of DISABLEINDEBUG
    // register is incorrect" found at Product Anomaly document four your device found at
    // https://www.nordicsemi.com/. There is no side effect of using these instruction if not needed.
    if (is_disabled_in_debug_needed())
    {
        NRF_MPU->DISABLEINDEBUG = MPU_DISABLEINDEBUG_DISABLEINDEBUG_Disabled << MPU_DISABLEINDEBUG_DISABLEINDEBUG_Pos;
    }

    // Start the external 32khz crystal oscillator.
    NRF_CLOCK->LFCLKSRC             = (CLOCK_LFCLKSRC_SRC_Xtal << CLOCK_LFCLKSRC_SRC_Pos);
    NRF_CLOCK->EVENTS_LFCLKSTARTED  = 0;
    NRF_CLOCK->TASKS_LFCLKSTART     = 1;

    // Wait for the external oscillator to start up.
    while (NRF_CLOCK->EVENTS_LFCLKSTARTED == 0) {
        // Do nothing.
    }
}

static bool is_manual_peripheral_setup_needed(void)
{
    if ((((*(uint32_t *)0xF0000FE0) & 0x000000FF) == 0x1) && (((*(uint32_t *)0xF0000FE4) & 0x0000000F) == 0x0))
    {
        if ((((*(uint32_t *)0xF0000FE8) & 0x000000F0) == 0x00) && (((*(uint32_t *)0xF0000FEC) & 0x000000F0) == 0x0))
        {
            return true;
        }
        if ((((*(uint32_t *)0xF0000FE8) & 0x000000F0) == 0x10) && (((*(uint32_t *)0xF0000FEC) & 0x000000F0) == 0x0))
        {
            return true;
        }
        if ((((*(uint32_t *)0xF0000FE8) & 0x000000F0) == 0x30) && (((*(uint32_t *)0xF0000FEC) & 0x000000F0) == 0x0))
        {
            return true;
        }
    }

    return false;
}

static bool is_disabled_in_debug_needed(void)
{
    if ((((*(uint32_t *)0xF0000FE0) & 0x000000FF) == 0x1) && (((*(uint32_t *)0xF0000FE4) & 0x0000000F) == 0x0))
    {
        if ((((*(uint32_t *)0xF0000FE8) & 0x000000F0) == 0x40) && (((*(uint32_t *)0xF0000FEC) & 0x000000F0) == 0x0))
        {
            return true;
        }
    }

    return false;
}