File content as of revision 0:516e11acba42:

//! @todo Review this document.
/*!
LT_SPI: Routines to communicate with ATmega328P's hardware SPI port.

@verbatim

LT_SPI implements the low level master SPI bus routines using
the hardware SPI port.

SPI Frequency = (CPU Clock frequency)/(16+2(TWBR)*Prescaler)
SPCR = SPI Control Register (SPIE SPE DORD MSTR CPOL CPHA SPR1 SPR0)
SPSR = SPI Status Register (SPIF WCOL - - - - - SPI2X)

Data Modes:
CPOL  CPHA  Leading Edge    Trailing Edge
0      0    sample rising   setup falling
0      1    setup rising    sample falling
1      0    sample falling  setup rising
1      1    sample rising   setup rising

CPU Frequency = 16MHz on Arduino Uno
SCK Frequency
SPI2X  SPR1  SPR0  Frequency  Uno_Frequency
  0      0     0     fosc/4     4 MHz
  0      0     1     fosc/16    1 MHz
  0      1     0     fosc/64    250 kHz
  0      1     1     fosc/128   125 kHz
  0      0     0     fosc/2     8 MHz
  0      0     1     fosc/8     2 MHz
  0      1     0     fosc/32    500 kHz

@endverbatim

REVISION HISTORY
$Revision: 6237 $
$Date: 2016-12-20 15:09:16 -0800 (Tue, 20 Dec 2016) $

Copyright (c) 2013, Linear Technology Corp.(LTC)
All rights reserved.

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modification, are permitted provided that the following conditions are met:

1. Redistributions of source code must retain the above copyright notice, this
   list of conditions and the following disclaimer.
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   this list of conditions and the following disclaimer in the documentation
   and/or other materials provided with the distribution.

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.

The views and conclusions contained in the software and documentation are those
of the authors and should not be interpreted as representing official policies,
either expressed or implied, of Linear Technology Corp.

The Linear Technology Linduino is not affiliated with the official Arduino team.
However, the Linduino is only possible because of the Arduino team's commitment
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*/

//! @ingroup Linduino
//! @{
//! @defgroup LT_SPI LT_SPI: Routines to communicate with ATmega328P's hardware SPI port.
//! @}

/*! @file
    @ingroup LT_SPI
    Library for LT_SPI: Routines to communicate with ATmega328P's hardware SPI port.
*/
#include <stdint.h>
#include "LT_SPI.h"

//DigitalOut QUIKEVAL_GPIO D9;          //!< Linduino QuikEval GPIO pin (QuikEval connector pin 14) connects to Arduino pin 9
//DigitalOut QUIKEVAL_CS A3;        //!< QuikEval CS pin (SPI chip select on QuikEval connector pin 6) connects to Arduino SS pin.
//DigitalInOut QUIKEVAL_MUX_MODE_PIN(8,output);  /*!< QUIKEVAL_MUX_MODE_PIN defines the control pin for the QuikEval MUX.
//The I2C port's SCL and the SPI port's SCK signals share the same pin on the Linduino's QuikEval connector.
//Additionally, the I2C port's SDA and the SPI port's MOSI signals share the same pin on the Linduino's QuikEval connector.
//The pair of pins connected to the QuikEval connector is switched using a MUX on the Linduino board.
//The control pin to switch the MUX is defined as QUIKEVAL_MUX_MODE_PIN (Arduino pin 8). */

void output_low(uint8_t pin)
{
    pin = 0;
}
void output_high(uint8_t pin)
{
    pin = 1;
}


// Reads and sends a byte
// Return 0 if successful, 1 if failed
void spi_transfer_byte(uint8_t cs_pin, uint8_t tx, uint8_t *rx)
{
  output_low(cs_pin);                 //! 1) Pull CS low

  *rx = spi.write(tx);             //! 2) Read byte and send byte

  output_high(cs_pin);                //! 3) Pull CS high
}

// Reads and sends a word
// Return 0 if successful, 1 if failed
void spi_transfer_word(uint8_t cs_pin, uint16_t tx, uint16_t *rx)
{
  union
  {
    uint8_t b[2];
    uint16_t w;
  } data_tx;

  union
  {
    uint8_t b[2];
    uint16_t w;
  } data_rx;

  data_tx.w = tx;

  output_low(cs_pin);                         //! 1) Pull CS low

  data_rx.b[1] = spi.write(data_tx.b[1]);  //! 2) Read MSB and send MSB
  data_rx.b[0] = spi.write(data_tx.b[0]);  //! 3) Read LSB and send LSB

  *rx = data_rx.w;

  output_high(cs_pin);                        //! 4) Pull CS high
}

// Reads and sends a byte array
void spi_transfer_block(uint8_t cs_pin, uint8_t *tx, uint8_t *rx, uint8_t length)
{
  int8_t i;

  output_low(cs_pin);                 //! 1) Pull CS low

  for (i=(length-1);  i >= 0; i--)
    rx[i] = spi.write(tx[i]);    //! 2) Read and send byte array

  output_high(cs_pin);                //! 3) Pull CS high
}

// Connect SPI pins to QuikEval connector through the Linduino MUX. This will disconnect I2C.
//void quikeval_SPI_connect()
//{
//  output_high(QUIKEVAL_CS); //! 1) Pull Chip Select High
//
//  //! 2) Enable Main SPI
//  pinMode(QUIKEVAL_MUX_MODE_PIN, OUTPUT);
//  QUIKEVAL_MUX_MODE_PIN = 0;
//}

// Configure the SPI port for 4MHz SCK.
// This function or spi_enable() must be called
// before using the other SPI routines.
//void quikeval_SPI_init(void)  // Initializes SPI
//{
//  spi_enable(SPI_CLOCK_DIV16);  //! 1) Configure the spi port for 4MHz SCK
//}

// Setup the processor for hardware SPI communication.
// Must be called before using the other SPI routines.
// Alternatively, call quikeval_SPI_connect(), which automatically
// calls this function.
void spi_enable(void) // Configures SCK frequency. Use constant defined in header file.
{
  //pinMode(SCK, OUTPUT);             //! 1) Setup SCK as output
  //pinMode(MOSI, OUTPUT);            //! 2) Setup MOSI as output
  //pinMode(QUIKEVAL_CS, OUTPUT);     //! 3) Setup CS as output
  spi.format(16,3);
  spi.frequency(1000000);
}

// Disable the SPI hardware port
//void spi_disable()
//{
//  spi.end();
//}

// Write a data byte using the SPI hardware
//void spi_write(int8_t  data)  // Byte to be written to SPI port
//{
//  SPDR = data;                  //! 1) Start the SPI transfer
//  while (!(SPSR & _BV(SPIF)));  //! 2) Wait until transfer complete
//}

// Read and write a data byte using the SPI hardware
// Returns the data byte read
//int8_t spi_read(int8_t  data) //!The data byte to be written
//{
//  SPDR = data;                  //! 1) Start the SPI transfer
//  while (!(SPSR & _BV(SPIF)));  //! 2) Wait until transfer complete
//  return SPDR;                  //! 3) Return the data read
//}

// Below are implementations of spi_read, etc. that do not use the
// Arduino SPI library.  To use these functions, uncomment them and comment out
// the correcsponding function above.
//
// // Reads and sends a byte
// // Return 0 if successful, 1 if failed
// uint8_t spi_transfer_byte(uint8_t cs_pin, uint8_t tx, uint8_t *rx)
// {
//     output_low(cs_pin);                 //! 1) Pull CS low
//
//     *rx = spi_read(tx);                 //! 2) Read byte and send byte
//
//     output_high(cs_pin);                //! 3) Pull CS high
//
//     return(0);
// }
//
// // Reads and sends a word
// // Return 0 if successful, 1 if failed
// uint8_t spi_transfer_word(uint8_t cs_pin, uint16_t tx, uint16_t *rx)
// {
//     union
//     {
//         uint8_t b[2];
//         uint16_t w;
//     } data_tx;
//
//     union
//     {
//         uint8_t b[2];
//         uint16_t w;
//     } data_rx;
//
//     data_tx.w = tx;
//
//     output_low(cs_pin);                     //! 1) Pull CS low
//
//     data_rx.b[1] = spi_read(data_tx.b[1]);  //! 2) Read MSB and send MSB
//     data_rx.b[0] = spi_read(data_tx.b[0]);  //! 3) Read LSB and send LSB
//     *rx = data_rx.w;
//
//     output_high(cs_pin);                    //! 4) Pull CS high
//
//     return(0);
// }
//
// // Reads and sends a byte array
// // Return 0 if successful, 1 if failed
// uint8_t spi_transfer_block(uint8_t cs_pin, uint8_t *tx, uint8_t *rx, uint8_t length)
// {
//     int8_t i;
//
//     output_low(cs_pin);                 //! 1) Pull CS low
//
//     for(i=0;  i < length; i++)
//         rx[i] = spi_read(tx[i]);        //! 2) Read and send byte array
//
//     output_high(cs_pin);                //! 3) Pull CS high
//
//     return(0);
// }
//
// // Connect SPI pins to QuikEval connector through the Linduino MUX. This will disconnect I2C.
// void quikeval_SPI_connect()
// {
//   output_high(QUIKEVAL_CS); //! 1) Pull Chip Select High
//
//   //! 2) Enable Main SPI
//   pinMode(QUIKEVAL_MUX_MODE_PIN, OUTPUT);
//   digitalWrite(QUIKEVAL_MUX_MODE_PIN, LOW);
// }
//
// // Configure the SPI port for 4MHz SCK.
// // This function or spi_enable() must be called
// // before using the other SPI routines.
// void quikeval_SPI_init(void)  // Initializes SPI
// {
//   spi_enable(SPI_CLOCK_DIV32);  //! 2) Configure the spi port for 4MHz SCK
// }
//
// // Setup the processor for hardware SPI communication.
// // Must be called before using the other SPI routines.
// // Alternatively, call quikeval_SPI_connect(), which automatically
// // calls this function.
// void spi_enable(uint8_t spi_clock_divider) // Configures SCK frequency. Use constant defined in header file.
// {
//   pinMode(SCK, OUTPUT);             //! 1) Setup SCK as output
//   pinMode(MOSI, OUTPUT);            //! 2) Setup MOSI as output
//   pinMode(QUIKEVAL_CS, OUTPUT);     //! 3) Setup CS as output
//   output_low(SCK);
//   output_low(MOSI);
//   output_high(QUIKEVAL_CS);
//   SPCR |= _BV(MSTR);                //! 4) Set the SPI port to master mode
//   //! 5) Set the SPI hardware rate
//   SPCR = (SPCR & ~SPI_CLOCK_MASK) | (spi_clock_divider & SPI_CLOCK_MASK);
//   SPSR = (SPSR & ~SPI_2XCLOCK_MASK) | ((spi_clock_divider >> 2) & SPI_2XCLOCK_MASK);
//   SPCR |= _BV(SPE);                 //! 5) Enable the SPI port
// }
//
// // Disable the SPI hardware port
// void spi_disable()
// {
//   SPCR &= ~_BV(SPE);
// }