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/spi.c

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/*! \file spi.c \brief SPI interface driver. */
//*****************************************************************************
//
// File Name    : 'spi.c'
// Title        : SPI interface driver
// Author       : Pascal Stang - Copyright (C) 2000-2002
// Created      : 11/22/2000
// Revised      : 06/06/2002
// Version      : 0.6
// Target MCU   : Atmel AVR series
// Editor Tabs  : 4
//
// NOTE: This code is currently below version 1.0, and therefore is considered
// to be lacking in some functionality or documentation, or may not be fully
// tested.  Nonetheless, you can expect most functions to work.
//
// This code is distributed under the GNU Public License
//      which can be found at http://www.gnu.org/licenses/gpl.txt
//
//*****************************************************************************

#include <avr/io.h>
#include <avr/signal.h>
#include <avr/interrupt.h>

#include "spi.h"

// Define the SPI_USEINT key if you want SPI bus operation to be
// interrupt-driven.  The primary reason for not using SPI in
// interrupt-driven mode is if the SPI send/transfer commands
// will be used from within some other interrupt service routine
// or if interrupts might be globally turned off due to of other
// aspects of your program
//
// Comment-out or uncomment this line as necessary
//#define SPI_USEINT

// global variables
volatile u08 spiTransferComplete;

// SPI interrupt service handler
#ifdef SPI_USEINT
SIGNAL(SIG_SPI)
{
    spiTransferComplete = TRUE;
}
#endif

// access routines
void spiInit()
{
#ifdef __AVR_ATmega128__
    // setup SPI I/O pins
    sbi(PORTB, 1);  // set SCK hi
    sbi(DDRB, 1);   // set SCK as output
    cbi(DDRB, 3);   // set MISO as input
    sbi(DDRB, 2);   // set MOSI as output
    sbi(DDRB, 0);   // SS must be output for Master mode to work
#else
    // setup SPI I/O pins
    sbi(PORTB, 7);  // set SCK hi
    sbi(DDRB, 7);   // set SCK as output
    cbi(DDRB, 6);   // set MISO as input
    sbi(DDRB, 5);   // set MOSI as output
    sbi(DDRB, 4);   // SS must be output for Master mode to work
#endif
    
    // setup SPI interface :
    // clock = f/16
    // select clock phase positive-going in middle of data
    // master mode
    // enable SPI
    outp((1<<MSTR)|(1<<SPE)|(1<<SPR0), SPCR );
    
    // some other possible configs
    //outp((1<<CPHA)|(1<<CPOL)|(1<<MSTR)|(1<<SPE)|(1<<SPR0)|(1<<SPR1), SPCR );
    //outp((1<<CPHA)|(1<<MSTR)|(1<<SPE)|(1<<SPR0), SPCR );
    
    // clear status
    inp(SPSR);
    spiTransferComplete = TRUE;

    // enable SPI interrupt
    #ifdef SPI_USEINT
    sbi(SPCR, SPIE);
    #endif
}

void spiSendByte(u08 data)
{
    // send a byte over SPI and ignore reply
    if(spiTransferComplete)
    {
        spiTransferComplete = FALSE;
        outp(data, SPDR);
    }
}

u08 spiTransferByte(u08 data)
{
    // send the given data
    if(spiTransferComplete)
    {
        spiTransferComplete = FALSE;
        outp(data, SPDR);
    }
    // wait for transfer to complete
    #ifdef SPI_USEINT
        while(!spiTransferComplete);
    #else
        while(!(inp(SPSR) & (1<<SPIF)));
        // *** reading of the SPSR and SPDR are crucial
        // *** to the clearing of the SPIF flag
        // *** in non-interrupt mode
        //inp(SPDR);
        // set flag
        spiTransferComplete = TRUE;
    #endif
    // return the received data
    return inp(SPDR);
}

u16 spiTransferWord(u16 data)
{
    u16 rxData = 0;

    // send MS byte of given data
    rxData = (spiTransferByte((data>>8) & 0x00FF))<<8;
    // send LS byte of given data
    rxData |= (spiTransferByte(data & 0x00FF));

    // return the received data
    return rxData;
}

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