text: #ifndef SPI_H
  #define SPI_H
  
  /*
   * Author: Omar Rizwan <osnr@stanford.edu>
   *
   * Date: May 9, 2016
   */
  
  #define SPI_CE0 0
  #define SPI_CE1 1
  
  void spi_init(unsigned chip_select, unsigned clock_divider);
  void spi_transfer(unsigned char *tx, unsigned char *rx, unsigned len);
  
  #endif /* SPI_H */
  