text: /*******************************************************************************
   * Copyright (C) 2015 Maxim Integrated Products, Inc., All Rights Reserved.
   *
   * Permission is hereby granted, free of charge, to any person obtaining a
   * copy of this software and associated documentation files (the "Software"),
   * to deal in the Software without restriction, including without limitation
   * the rights to use, copy, modify, merge, publish, distribute, sublicense,
   * and/or sell copies of the Software, and to permit persons to whom the
   * Software is furnished to do so, subject to the following conditions:
   *
   * The above copyright notice and this permission notice shall be included
   * in all copies or substantial portions of the Software.
   *
   * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS
   * OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
   * MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.
   * IN NO EVENT SHALL MAXIM INTEGRATED BE LIABLE FOR ANY CLAIM, DAMAGES
   * OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE,
   * ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR
   * OTHER DEALINGS IN THE SOFTWARE.
   *
   * Except as contained in this notice, the name of Maxim Integrated
   * Products, Inc. shall not be used except as stated in the Maxim Integrated
   * Products, Inc. Branding Policy.
   *
   * The mere transfer of this software does not imply any licenses
   * of trade secrets, proprietary technology, copyrights, patents,
   * trademarks, maskwork rights, or any other form of intellectual
   * property whatsoever. Maxim Integrated Products, Inc. retains all
   * ownership rights.
   *******************************************************************************
   */
  
  #include "cmsis.h"
  #include "gpio_regs.h"
  #include "clkman_regs.h"
  
  /* Application developer should override where necessary with different external HFX source */
  #ifndef __SYSTEM_HFX
  #define __SYSTEM_HFX 24000000
  #endif
  
  //******************************************************************************
  // This function will get called early in system initialization
  void low_level_init(void)
  {
      /* wait for the RO to stabilize */
      while (!(MXC_CLKMAN->intfl & MXC_F_CLKMAN_INTFL_RING_STABLE));
  
      /* Configure and enable the oscillator */
      if (!(MXC_CLKMAN->clk_config & MXC_F_CLKMAN_CLK_CONFIG_HFX_ENABLE)) {
  
          MXC_CLKMAN->clk_config = (0x4 << MXC_F_CLKMAN_CLK_CONFIG_HFX_GM_ADJUST_POS);
  
          /* Enable the external crystal */
          MXC_CLKMAN->clk_config |= MXC_F_CLKMAN_CLK_CONFIG_HFX_ENABLE;
      }
  
      /* Wait for external crystal to stabilize */
      for (volatile int waitcnt = 0; waitcnt < 0x4000; waitcnt++);    // 0x4000 ~10ms 0x10000 ~35ms, 0x20000 ~75ms
  
      /* Configure the PLL */
      uint32_t clk_config = MXC_CLKMAN->clk_config;
      clk_config  = (clk_config & ~MXC_F_CLKMAN_CLK_CONFIG_PLL_INPUT_SELECT) | (MXC_E_CLKMAN_PLL_INPUT_SELECT_HFX << MXC_F_CLKMAN_CLK_CONFIG_PLL_INPUT_SELECT_POS);
  
  #if (__SYSTEM_HFX == 8000000)
      clk_config  = (clk_config & ~MXC_F_CLKMAN_CLK_CONFIG_PLL_DIVISOR_SELECT) | (MXC_E_CLKMAN_PLL_DIVISOR_SELECT_8MHZ << MXC_F_CLKMAN_CLK_CONFIG_PLL_DIVISOR_SELECT_POS);
  #elif (__SYSTEM_HFX == 12000000)
      clk_config  = (clk_config & ~MXC_F_CLKMAN_CLK_CONFIG_PLL_DIVISOR_SELECT) | (MXC_E_CLKMAN_PLL_DIVISOR_SELECT_12MHZ << MXC_F_CLKMAN_CLK_CONFIG_PLL_DIVISOR_SELECT_POS);
  #elif (__SYSTEM_HFX == 24000000)
      clk_config  = (clk_config & ~MXC_F_CLKMAN_CLK_CONFIG_PLL_DIVISOR_SELECT) | (MXC_E_CLKMAN_PLL_DIVISOR_SELECT_24MHZ << MXC_F_CLKMAN_CLK_CONFIG_PLL_DIVISOR_SELECT_POS);
  #else
  #error Invalid __SYSTEM_HFX setting
  #endif
  
      clk_config |=  MXC_F_CLKMAN_CLK_CONFIG_PLL_8MHZ_ENABLE;
      clk_config &= ~MXC_F_CLKMAN_CLK_CONFIG_PLL_BYPASS;
      clk_config  = (clk_config & ~MXC_F_CLKMAN_CLK_CONFIG_PLL_STABILITY_COUNT) | (MXC_E_CLKMAN_STABILITY_COUNT_2_13_CLKS << MXC_F_CLKMAN_CLK_CONFIG_PLL_STABILITY_COUNT_POS);
      MXC_CLKMAN->clk_config = clk_config;
  
      /* Enable the PLL and wait for stable */
      MXC_CLKMAN->clk_config |= (MXC_F_CLKMAN_CLK_CONFIG_PLL_ENABLE | MXC_F_CLKMAN_CLK_CONFIG_PLL_RESET_N);
      while (!(MXC_CLKMAN->intfl & MXC_F_CLKMAN_INTFL_PLL_STABLE));
  
      /* Switch to the PLL */
      MXC_CLKMAN->clk_ctrl = (MXC_CLKMAN->clk_ctrl & ~MXC_F_CLKMAN_CLK_CTRL_SYSTEM_SOURCE_SELECT) |
                             ((MXC_E_CLKMAN_SYSTEM_SOURCE_SELECT_PLL_48MHZ_DIV_2 << MXC_F_CLKMAN_CLK_CTRL_SYSTEM_SOURCE_SELECT_POS));
  }
  