text: //*****************************************************************************
  //
  // system_clock_pll.c - Example demonstrating setting the clock using the PLL.
  //
  // Copyright (c) 2010-2016 Texas Instruments Incorporated.  All rights reserved.
  // Software License Agreement
  // 
  //   Redistribution and use in source and binary forms, with or without
  //   modification, are permitted provided that the following conditions
  //   are met:
  // 
  //   Redistributions of source code must retain the above copyright
  //   notice, this list of conditions and the following disclaimer.
  // 
  //   Redistributions in binary form must reproduce the above copyright
  //   notice, this list of conditions and the following disclaimer in the
  //   documentation and/or other materials provided with the  
  //   distribution.
  // 
  //   Neither the name of Texas Instruments Incorporated nor the names of
  //   its contributors may be used to endorse or promote products derived
  //   from this software without specific prior written permission.
  // 
  // THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
  // "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
  // LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
  // A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
  // OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
  // SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
  // LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
  // DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
  // THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
  // (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
  // OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
  // 
  // This is part of revision 2.1.3.156 of the Tiva Firmware Development Package.
  //
  //*****************************************************************************
  
  #include <stdbool.h>
  #include <stdint.h>
  #include "driverlib/sysctl.h"
  
  //*****************************************************************************
  //
  //! \addtogroup sysctl_examples_list
  //! <h1>System Clock Configuration with PLL (system_clock_pll)</h1>
  //!
  //! This example shows how to set up the system clock to use the PLL.
  //
  //*****************************************************************************
  
  //*****************************************************************************
  //
  // Set up the system clock using the PLL
  //
  //*****************************************************************************
  int
  main(void)
  {
  #if defined(TARGET_IS_TM4C129_RA0) ||                                         \
      defined(TARGET_IS_TM4C129_RA1) ||                                         \
      defined(TARGET_IS_TM4C129_RA2)
      uint32_t ui32SysClock;
  #endif
  
      //
      // Set the clocking to run directly from the PLL at 20 MHz.
      // The following code:
      // -sets the system clock divider to 10 (200 MHz PLL divide by 10 = 20 MHz)
      // -sets the system clock to use the PLL
      // -uses the main oscillator
      // -configures for use of 16 MHz crystal/oscillator input
      //
  #if defined(TARGET_IS_TM4C129_RA0) ||                                         \
      defined(TARGET_IS_TM4C129_RA1) ||                                         \
      defined(TARGET_IS_TM4C129_RA2)
      ui32SysClock = SysCtlClockFreqSet((SYSCTL_XTAL_25MHZ |
                                         SYSCTL_OSC_MAIN |
                                         SYSCTL_USE_PLL |
                                         SYSCTL_CFG_VCO_480), 20000000);
  #else
      SysCtlClockSet(SYSCTL_SYSDIV_10 | SYSCTL_USE_PLL | SYSCTL_OSC_MAIN |
                     SYSCTL_XTAL_16MHZ);
  #endif
  
      //
      // Return with no errors.
      //
      return(0);
  }
  