text: // SysTick.h
  // Runs on LM4F120/TM4C123
  // Provide functions that initialize the SysTick module, wait at least a
  // designated number of clock cycles, and wait approximately a multiple
  // of 10 milliseconds using busy wait.  After a power-on-reset, the
  // LM4F120 gets its clock from the 16 MHz precision internal oscillator,
  // which can vary by +/- 1% at room temperature and +/- 3% across all
  // temperature ranges.  If you are using this module, you may need more
  // precise timing, so it is assumed that you are using the PLL to set
  // the system clock to 50 MHz.  This matters for the function
  // SysTick_Wait10ms(), which will wait longer than 10 ms if the clock is
  // slower.
  // Daniel Valvano
  // September 11, 2013
  
  /* This example accompanies the books
     "Embedded Systems: Introduction to ARM Cortex M Microcontrollers",
     ISBN: 978-1469998749, Jonathan Valvano, copyright (c) 2014
     Volume 1, Program 4.7
  
     "Embedded Systems: Real Time Interfacing to ARM Cortex M Microcontrollers",
     ISBN: 978-1463590154, Jonathan Valvano, copyright (c) 2014
     Program 2.11, Section 2.6
  
   Copyright 2014 by Jonathan W. Valvano, valvano@mail.utexas.edu
      You may use, edit, run or distribute this file
      as long as the above copyright notice remains
   THIS SOFTWARE IS PROVIDED "AS IS".  NO WARRANTIES, WHETHER EXPRESS, IMPLIED
   OR STATUTORY, INCLUDING, BUT NOT LIMITED TO, IMPLIED WARRANTIES OF
   MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE APPLY TO THIS SOFTWARE.
   VALVANO SHALL NOT, IN ANY CIRCUMSTANCES, BE LIABLE FOR SPECIAL, INCIDENTAL,
   OR CONSEQUENTIAL DAMAGES, FOR ANY REASON WHATSOEVER.
   For more information about my classes, my research, and my books, see
   http://users.ece.utexas.edu/~valvano/
   */
  
  // Initialize SysTick with busy wait running at bus clock.
  void SysTick_Init(void);
  
  // Time delay using busy wait.
  // The delay parameter is in units of the core clock. (units of 20 nsec for 50 MHz clock)
  void SysTick_Wait(uint32_t delay);
  
  // Time delay using busy wait.
  // This assumes 50 MHz system clock.
  void SysTick_Wait10ms(uint32_t delay);
  