twimaster.c

/*************************************************************************

* Title:    I2C master library using hardware TWI interface

* Author:   Peter Fleury <pfleury@gmx.ch>  http://jump.to/fleury

* File:     $Id: twimaster.c,v 1.3 2005/07/02 11:14:21 Peter Exp $

* Software: AVR-GCC 3.4.3 / avr-libc 1.2.3

* Target:   any AVR device with hardware TWI 

* Usage:    API compatible with I2C Software Library i2cmaster.h

**************************************************************************/

#include <inttypes.h>

#include <compat/twi.h>

#include "i2cmaster.h"

/* define CPU frequency in Mhz here if not defined in Makefile */

#ifndef F_CPU

#define F_CPU 4000000UL

#endif

/* I2C clock in Hz */

#define SCL_CLOCK  10000L

/*************************************************************************

 Initialization of the I2C bus interface. Need to be called only once

*************************************************************************/

void i2c_init(void)

{

  /* initialize TWI clock: 100 kHz clock, TWPS = 0 => prescaler = 1 */

  TWSR = 0;                         /* no prescaler */

  TWBR = ((F_CPU/SCL_CLOCK)-16)/2;  /* must be > 10 for stable operation */

}/* i2c_init */

/*************************************************************************  

  Issues a start condition and sends address and transfer direction.

  return 0 = device accessible, 1= failed to access device

*************************************************************************/

unsigned char i2c_start(unsigned char address)

{

    uint8_t   twst;

  // send START condition

  TWCR = (1<<TWINT) | (1<<TWSTA) | (1<<TWEN);

  // wait until transmission completed

  while(!(TWCR & (1<<TWINT)));

  // check value of TWI Status Register. Mask prescaler bits.

  twst = TW_STATUS & 0xF8;

  if ( (twst != TW_START) && (twst != TW_REP_START)) return 1;

  // send device address

  TWDR = address;

  TWCR = (1<<TWINT) | (1<<TWEN);

  // wail until transmission completed and ACK/NACK has been received

  while(!(TWCR & (1<<TWINT)));

  // check value of TWI Status Register. Mask prescaler bits.

  twst = TW_STATUS & 0xF8;

  if ( (twst != TW_MT_SLA_ACK) && (twst != TW_MR_SLA_ACK) ) return 1;

  return 0;

}/* i2c_start */

/*************************************************************************

 Issues a start condition and sends address and transfer direction.

 If device is busy, use ack polling to wait until device is ready

 Input:   address and transfer direction of I2C device

*************************************************************************/

void i2c_start_wait(unsigned char address)

{

    uint8_t   twst;

    while ( 1 )

    {

      // send START condition

      TWCR = (1<<TWINT) | (1<<TWSTA) | (1<<TWEN);

      // wait until transmission completed

      while(!(TWCR & (1<<TWINT)));

      // check value of TWI Status Register. Mask prescaler bits.

      twst = TW_STATUS & 0xF8;

      if ( (twst != TW_START) && (twst != TW_REP_START)) continue;

      // send device address

      TWDR = address;

      TWCR = (1<<TWINT) | (1<<TWEN);

      // wail until transmission completed

      while(!(TWCR & (1<<TWINT)));

      // check value of TWI Status Register. Mask prescaler bits.

      twst = TW_STATUS & 0xF8;

      if ( (twst == TW_MT_SLA_NACK )||(twst ==TW_MR_DATA_NACK) ) 

      {          

          /* device busy, send stop condition to terminate write operation */

          TWCR = (1<<TWINT) | (1<<TWEN) | (1<<TWSTO);

          // wait until stop condition is executed and bus released

          while(TWCR & (1<<TWSTO));

          continue;

      }

      //if( twst != TW_MT_SLA_ACK) return 1;

      break;

     }

}/* i2c_start_wait */

/*************************************************************************

 Issues a repeated start condition and sends address and transfer direction 

 Input:   address and transfer direction of I2C device

 Return:  0 device accessible

          1 failed to access device

*************************************************************************/

unsigned char i2c_rep_start(unsigned char address)

{

    return i2c_start( address );

}/* i2c_rep_start */

/*************************************************************************

 Terminates the data transfer and releases the I2C bus

*************************************************************************/

void i2c_stop(void)

{

    /* send stop condition */

  TWCR = (1<<TWINT) | (1<<TWEN) | (1<<TWSTO);

  // wait until stop condition is executed and bus released

  while(TWCR & (1<<TWSTO));

}/* i2c_stop */

/*************************************************************************

  Send one byte to I2C device

  Input:    byte to be transfered

  Return:   0 write successful 

            1 write failed

*************************************************************************/

unsigned char i2c_write( unsigned char data )

{  

    uint8_t   twst;

  // send data to the previously addressed device

  TWDR = data;

  TWCR = (1<<TWINT) | (1<<TWEN);

  // wait until transmission completed

  while(!(TWCR & (1<<TWINT)));

  // check value of TWI Status Register. Mask prescaler bits

  twst = TW_STATUS & 0xF8;

  if( twst != TW_MT_DATA_ACK) return 1;

  return 0;

}/* i2c_write */

/*************************************************************************

 Read one byte from the I2C device, request more data from device 

 Return:  byte read from I2C device

*************************************************************************/

unsigned char i2c_readAck(void)

{

  TWCR = (1<<TWINT) | (1<<TWEN) | (1<<TWEA);

  while(!(TWCR & (1<<TWINT)));    

    return TWDR;

}/* i2c_readAck */

/*************************************************************************

 Read one byte from the I2C device, read is followed by a stop condition 

 Return:  byte read from I2C device

*************************************************************************/

unsigned char i2c_readNak(void)

{

  TWCR = (1<<TWINT) | (1<<TWEN);

  while(!(TWCR & (1<<TWINT)));

    return TWDR;

}/* i2c_readNak */