library

/*! \file i2csw.c \brief Software I2C interface using port pins. */
//*****************************************************************************
//
// File Name    : 'i2csw.c'
// Title                : Software I2C interface using port pins
// Author               : Pascal Stang
// Created              : 11/22/2000
// Revised              : 5/2/2002
// Version              : 1.1
// Target MCU   : Atmel AVR series
// Editor Tabs  : 4
//
// 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 "i2csw.h"

// Standard I2C bit rates are:
// 100KHz for slow speed
// 400KHz for high speed

//#define QDEL  delay(5)                // i2c quarter-bit delay
//#define HDEL  delay(10)               // i2c half-bit delay

// i2c quarter-bit delay
#define QDEL    asm volatile("nop"); asm volatile("nop"); asm volatile("nop"); asm volatile("nop"); asm volatile("nop");
// i2c half-bit delay
#define HDEL    asm volatile("nop"); asm volatile("nop"); asm volatile("nop"); asm volatile("nop"); asm volatile("nop"); asm volatile("nop"); asm volatile("nop"); asm volatile("nop"); asm volatile("nop"); asm volatile("nop");

#define I2C_SDL_LO      cbi( SDAPORT, SDA)
#define I2C_SDL_HI      sbi( SDAPORT, SDA)

#define I2C_SCL_LO      cbi( SCLPORT, SCL); 
#define I2C_SCL_HI      sbi( SCLPORT, SCL); 

#define I2C_SCL_TOGGLE  HDEL; I2C_SCL_HI; HDEL; I2C_SCL_LO;
#define I2C_START       I2C_SDL_LO; QDEL; I2C_SCL_LO; 
#define I2C_STOP        HDEL; I2C_SCL_HI; QDEL; I2C_SDL_HI; HDEL;

/*
void i2ct(void)
{
        HDEL; I2C_SCL_HI; HDEL; I2C_SCL_LO;
}

void i2cstart(void)
{
        I2C_SDL_LO; QDEL; I2C_SCL_LO; 
}

void i2cstop(void)
{
        HDEL; I2C_SCL_HI; QDEL; I2C_SDL_HI; HDEL;
}


#define I2C_SCL_TOGGLE  i2ct();
#define I2C_START       i2cstart();
#define I2C_STOP        i2cstop();      
*/

UINT i2cPutbyte(u08 b)
{
        int i;
        
        for (i=7;i>=0;i--)
        {
                if ( b & (1<<i) )
                        I2C_SDL_HI;
                else
                        I2C_SDL_LO;                     // address bit
                        I2C_SCL_TOGGLE;         // clock HI, delay, then LO
        }

        I2C_SDL_HI;                                     // leave SDL HI
        // added    
        cbi(SDADDR, SDA);                       // change direction to input on SDA line (may not be needed)
        HDEL;
        I2C_SCL_HI;                                     // clock back up
        b = inb(SDAPIN) & (1<<SDA);     // get the ACK bit

        HDEL;
        I2C_SCL_LO;                                     // not really ??
        sbi(SDADDR, SDA);                       // change direction back to output
        HDEL;
        return (b == 0);                        // return ACK value
}


u08 i2cGetbyte(UINT last)
{
        int i;
        u08 c,b = 0;
                
        I2C_SDL_HI;                                     // make sure pullups are ativated
        cbi(SDADDR, SDA);                       // change direction to input on SDA line (may not be needed)

        for(i=7;i>=0;i--)
        {
                HDEL;
                I2C_SCL_HI;                             // clock HI
                c = inb(SDAPIN) & (1<<SDA);  
                b <<= 1;
                if(c) b |= 1;
                HDEL;
        I2C_SCL_LO;                             // clock LO
        }

        sbi(SDADDR, SDA);                       // change direction to output on SDA line
  
        if (last)
                I2C_SDL_HI;                             // set NAK
        else
                I2C_SDL_LO;                             // set ACK

        I2C_SCL_TOGGLE;                         // clock pulse
        I2C_SDL_HI;                                     // leave with SDL HI
        return b;                                       // return received byte
}


//************************
//* I2C public functions *
//************************

//! Initialize I2C communication
void i2cInit(void)
{
        sbi( SDADDR, SDA);                      // set SDA as output
        sbi( SCLDDR, SCL);                      // set SCL as output
        I2C_SDL_HI;                                     // set I/O state and pull-ups
        I2C_SCL_HI;                                     // set I/O state and pull-ups
}

//! Send a byte sequence on the I2C bus
void i2cSend(u08 device, u08 subAddr, u08 length, u08 *data)
{
        I2C_START;                              // do start transition
        i2cPutbyte(device);             // send DEVICE address
        i2cPutbyte(subAddr);            // and the subaddress

        // send the data
        while (length--)
                i2cPutbyte(*data++);

        I2C_SDL_LO;                                     // clear data line and
        I2C_STOP;                                       // send STOP transition
}

//! Retrieve a byte sequence on the I2C bus
void i2cReceive(u08 device, u08 subAddr, u08 length, u08 *data)
{
        int j = length;
        u08 *p = data;

        I2C_START;                                      // do start transition
        i2cPutbyte(device);                     // send DEVICE address
        i2cPutbyte(subAddr);            // and the subaddress
        HDEL;
        I2C_SCL_HI;                             // do a repeated START
        I2C_START;                                      // transition

        i2cPutbyte(device | READ);      // resend DEVICE, with READ bit set

        // receive data bytes
        while (j--)
                *p++ = i2cGetbyte(j == 0);

        I2C_SDL_LO;                                     // clear data line and
        I2C_STOP;                                       // send STOP transition
}