LT_SPI.cpp

//! @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: 3018 $
$Date: 2014-12-01 15:53:20 -0800 (Mon, 01 Dec 2014) $

Copyright (c) 2013, Linear Technology Corp.(LTC)
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*/

//! @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 <Arduino.h>
#include <stdint.h>
#include <SPI.h>
#include "Linduino.h"
#include "LT_SPI.h"

// 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.transfer(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.transfer(data_tx.b[1]);  //! 2) Read MSB and send MSB
    data_rx.b[0] = SPI.transfer(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.transfer(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);
  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_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(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
  SPI.begin();
  SPI.setClockDivider(spi_clock_divider);
}

// 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);
// }