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/*

  twi.c - TWI/I2C library for Wiring & Arduino

  Copyright (c) 2006 Nicholas Zambetti.  All right reserved.

  This library is free software; you can redistribute it and/or

  modify it under the terms of the GNU Lesser General Public

  License as published by the Free Software Foundation; either

  version 2.1 of the License, or (at your option) any later version.

  This library is distributed in the hope that it will be useful,

  but WITHOUT ANY WARRANTY; without even the implied warranty of

  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU

  Lesser General Public License for more details.

  You should have received a copy of the GNU Lesser General Public

  License along with this library; if not, write to the Free Software

  Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA  02110-1301  USA

  Modified 2012 by Todd Krein (todd@krein.org) to implement repeated starts

*/

#include <math.h>

#include <stdlib.h>

#include <inttypes.h>

#include <avr/io.h>

#include <avr/interrupt.h>

#ifndef cbi

#define cbi(sfr, bit) (_SFR_BYTE(sfr) &= ~_BV(bit))

#endif

#ifndef sbi

#define sbi(sfr, bit) (_SFR_BYTE(sfr) |= _BV(bit))

#endif

#include "twi.h"

static volatile uint8_t twi_state;

static volatile uint8_t twi_slarw;

static volatile uint8_t twi_sendStop;	// should the transaction end with a stop

static volatile uint8_t twi_inRepStart;	// in the middle of a repeated start

static void (*twi_onSlaveTransmit)(void);

static void (*twi_onSlaveReceive)(uint8_t*, int);

static uint8_t twi_masterBuffer[TWI_BUFFER_LENGTH];

static volatile uint8_t twi_masterBufferIndex;

static volatile uint8_t twi_masterBufferLength;

static uint8_t twi_txBuffer[TWI_BUFFER_LENGTH];

static volatile uint8_t twi_txBufferIndex;

static volatile uint8_t twi_txBufferLength;

static uint8_t twi_rxBuffer[TWI_BUFFER_LENGTH];

static volatile uint8_t twi_rxBufferIndex;

static volatile uint8_t twi_error;

/* 

 * Function twi_init

 * Desc     readys twi pins and sets twi bitrate

 * Input    none

 * Output   none

 */

void twi_init(void)

{

  // initialize state

  twi_state = TWI_READY;

  twi_sendStop = true;		// default value

  twi_inRepStart = false;

  // activate internal pullups for twi.

  // @TODO: activate pullups

  //digitalWrite(SDA, 1);

  //digitalWrite(SCL, 1);

  // initialize twi prescaler and bit rate

  cbi(TWSR, TWPS0);

  cbi(TWSR, TWPS1);

  TWBR = ((F_CPU / TWI_FREQ) - 16) / 2;

  /* twi bit rate formula from atmega128 manual pg 204

  SCL Frequency = CPU Clock Frequency / (16 + (2 * TWBR))

  note: TWBR should be 10 or higher for master mode

  It is 72 for a 16mhz Wiring board with 100kHz TWI */

  // enable twi module, acks, and twi interrupt

  TWCR = _BV(TWEN) | _BV(TWIE) | _BV(TWEA);

}

/* 

 * Function twi_slaveInit

 * Desc     sets slave address and enables interrupt

 * Input    none

 * Output   none

 */

void twi_setAddress(uint8_t address)

{

  // set twi slave address (skip over TWGCE bit)

  TWAR = address << 1;

}

/* 

 * Function twi_readFrom

 * Desc     attempts to become twi bus master and read a

 *          series of bytes from a device on the bus

 * Input    address: 7bit i2c device address

 *          data: pointer to byte array

 *          length: number of bytes to read into array

 *          sendStop: Boolean indicating whether to send a stop at the end

 * Output   number of bytes read

 */

uint8_t twi_readFrom(uint8_t address, uint8_t* data, uint8_t length, uint8_t sendStop)

{

  uint8_t i;

  // ensure data will fit into buffer

  if(TWI_BUFFER_LENGTH < length){

    return 0;

  }

  // wait until twi is ready, become master receiver

  while(TWI_READY != twi_state){

    continue;

  }

  twi_state = TWI_MRX;

  twi_sendStop = sendStop;

  // reset error state (0xFF.. no error occured)

  twi_error = 0xFF;

  // initialize buffer iteration vars

  twi_masterBufferIndex = 0;

  twi_masterBufferLength = length-1;  // This is not intuitive, read on...

  // On receive, the previously configured ACK/NACK setting is transmitted in

  // response to the received byte before the interrupt is signalled. 

  // Therefor we must actually set NACK when the _next_ to last byte is

  // received, causing that NACK to be sent in response to receiving the last

  // expected byte of data.

  // build sla+w, slave device address + w bit

  twi_slarw = TW_READ;

  twi_slarw |= address << 1;

  if (true == twi_inRepStart) {

    // if we're in the repeated start state, then we've already sent the start,

    // (@@@ we hope), and the TWI statemachine is just waiting for the address byte.

    // We need to remove ourselves from the repeated start state before we enable interrupts,

    // since the ISR is ASYNC, and we could get confused if we hit the ISR before cleaning

    // up. Also, don't enable the START interrupt. There may be one pending from the 

    // repeated start that we sent outselves, and that would really confuse things.

    twi_inRepStart = false;			// remember, we're dealing with an ASYNC ISR

    TWDR = twi_slarw;

    TWCR = _BV(TWINT) | _BV(TWEA) | _BV(TWEN) | _BV(TWIE);	// enable INTs, but not START

  }

  else

    // send start condition

    TWCR = _BV(TWEN) | _BV(TWIE) | _BV(TWEA) | _BV(TWINT) | _BV(TWSTA);

  // wait for read operation to complete

  while(TWI_MRX == twi_state){

    continue;

  }

  if (twi_masterBufferIndex < length)

    length = twi_masterBufferIndex;

  // copy twi buffer to data

  for(i = 0; i < length; ++i){

    data[i] = twi_masterBuffer[i];

  }

  return length;

}

/* 

 * Function twi_writeTo

 * Desc     attempts to become twi bus master and write a

 *          series of bytes to a device on the bus

 * Input    address: 7bit i2c device address

 *          data: pointer to byte array

 *          length: number of bytes in array

 *          wait: boolean indicating to wait for write or not

 *          sendStop: boolean indicating whether or not to send a stop at the end

 * Output   0 .. success

 *          1 .. length to long for buffer

 *          2 .. address send, NACK received

 *          3 .. data send, NACK received

 *          4 .. other twi error (lost bus arbitration, bus error, ..)

 */

uint8_t twi_writeTo(uint8_t address, uint8_t* data, uint8_t length, uint8_t wait, uint8_t sendStop)

{

  uint8_t i;

  // ensure data will fit into buffer

  if(TWI_BUFFER_LENGTH < length){

    return 1;

  }

  // wait until twi is ready, become master transmitter

  while(TWI_READY != twi_state){

    continue;

  }

  twi_state = TWI_MTX;

  twi_sendStop = sendStop;

  // reset error state (0xFF.. no error occured)

  twi_error = 0xFF;

  // initialize buffer iteration vars

  twi_masterBufferIndex = 0;

  twi_masterBufferLength = length;

  // copy data to twi buffer

  for(i = 0; i < length; ++i){

    twi_masterBuffer[i] = data[i];

  }

  // build sla+w, slave device address + w bit

  twi_slarw = TW_WRITE;

  twi_slarw |= address << 1;

  // if we're in a repeated start, then we've already sent the START

  // in the ISR. Don't do it again.

  //

  if (true == twi_inRepStart) {

    // if we're in the repeated start state, then we've already sent the start,

    // (@@@ we hope), and the TWI statemachine is just waiting for the address byte.

    // We need to remove ourselves from the repeated start state before we enable interrupts,

    // since the ISR is ASYNC, and we could get confused if we hit the ISR before cleaning

    // up. Also, don't enable the START interrupt. There may be one pending from the 

    // repeated start that we sent outselves, and that would really confuse things.

    twi_inRepStart = false;			// remember, we're dealing with an ASYNC ISR

    TWDR = twi_slarw;				

    TWCR = _BV(TWINT) | _BV(TWEA) | _BV(TWEN) | _BV(TWIE);	// enable INTs, but not START

  }

  else

    // send start condition

    TWCR = _BV(TWINT) | _BV(TWEA) | _BV(TWEN) | _BV(TWIE) | _BV(TWSTA);	// enable INTs

  // wait for write operation to complete

  while(wait && (TWI_MTX == twi_state)){

    continue;

  }

  if (twi_error == 0xFF)

    return 0;	// success

  else if (twi_error == TW_MT_SLA_NACK)

    return 2;	// error: address send, nack received

  else if (twi_error == TW_MT_DATA_NACK)

    return 3;	// error: data send, nack received

  else

    return 4;	// other twi error

}

/* 

 * Function twi_transmit

 * Desc     fills slave tx buffer with data

 *          must be called in slave tx event callback

 * Input    data: pointer to byte array

 *          length: number of bytes in array

 * Output   1 length too long for buffer

 *          2 not slave transmitter

 *          0 ok

 */

uint8_t twi_transmit(const uint8_t* data, uint8_t length)

{

  uint8_t i;

  // ensure data will fit into buffer

  if(TWI_BUFFER_LENGTH < length){

    return 1;

  }

  // ensure we are currently a slave transmitter

  if(TWI_STX != twi_state){

    return 2;

  }

  // set length and copy data into tx buffer

  twi_txBufferLength = length;

  for(i = 0; i < length; ++i){

    twi_txBuffer[i] = data[i];

  }

  return 0;

}

/* 

 * Function twi_attachSlaveRxEvent

 * Desc     sets function called before a slave read operation

 * Input    function: callback function to use

 * Output   none

 */

void twi_attachSlaveRxEvent( void (*function)(uint8_t*, int) )

{

  twi_onSlaveReceive = function;

}

/* 

 * Function twi_attachSlaveTxEvent

 * Desc     sets function called before a slave write operation

 * Input    function: callback function to use

 * Output   none

 */

void twi_attachSlaveTxEvent( void (*function)(void) )

{

  twi_onSlaveTransmit = function;

}

/* 

 * Function twi_reply

 * Desc     sends byte or readys receive line

 * Input    ack: byte indicating to ack or to nack

 * Output   none

 */

void twi_reply(uint8_t ack)

{

  // transmit master read ready signal, with or without ack

  if(ack){

    TWCR = _BV(TWEN) | _BV(TWIE) | _BV(TWINT) | _BV(TWEA);

  }else{

	  TWCR = _BV(TWEN) | _BV(TWIE) | _BV(TWINT);

  }

}

/* 

 * Function twi_stop

 * Desc     relinquishes bus master status

 * Input    none

 * Output   none

 */

void twi_stop(void)

{

  // send stop condition

  TWCR = _BV(TWEN) | _BV(TWIE) | _BV(TWEA) | _BV(TWINT) | _BV(TWSTO);

  // wait for stop condition to be exectued on bus

  // TWINT is not set after a stop condition!

  while(TWCR & _BV(TWSTO)){

    continue;

  }

  // update twi state

  twi_state = TWI_READY;

}

/* 

 * Function twi_releaseBus

 * Desc     releases bus control

 * Input    none

 * Output   none

 */

void twi_releaseBus(void)

{

  // release bus

  TWCR = _BV(TWEN) | _BV(TWIE) | _BV(TWEA) | _BV(TWINT);

  // update twi state

  twi_state = TWI_READY;

}

SIGNAL(TWI_vect)

{

  switch(TW_STATUS){

    // All Master

    case TW_START:     // sent start condition

    case TW_REP_START: // sent repeated start condition

      // copy device address and r/w bit to output register and ack

      TWDR = twi_slarw;

      twi_reply(1);

      break;

    // Master Transmitter

    case TW_MT_SLA_ACK:  // slave receiver acked address

    case TW_MT_DATA_ACK: // slave receiver acked data

      // if there is data to send, send it, otherwise stop 

      if(twi_masterBufferIndex < twi_masterBufferLength){

        // copy data to output register and ack

        TWDR = twi_masterBuffer[twi_masterBufferIndex++];

        twi_reply(1);

      }else{

	if (twi_sendStop)

          twi_stop();

	else {

	  twi_inRepStart = true;	// we're gonna send the START

	  // don't enable the interrupt. We'll generate the start, but we 

	  // avoid handling the interrupt until we're in the next transaction,

	  // at the point where we would normally issue the start.

	  TWCR = _BV(TWINT) | _BV(TWSTA)| _BV(TWEN) ;

	  twi_state = TWI_READY;

	}

      }

      break;

    case TW_MT_SLA_NACK:  // address sent, nack received

      twi_error = TW_MT_SLA_NACK;

      twi_stop();

      break;

    case TW_MT_DATA_NACK: // data sent, nack received

      twi_error = TW_MT_DATA_NACK;

      twi_stop();

      break;

    case TW_MT_ARB_LOST: // lost bus arbitration

      twi_error = TW_MT_ARB_LOST;

      twi_releaseBus();

      break;

    // Master Receiver

    case TW_MR_DATA_ACK: // data received, ack sent

      // put byte into buffer

      twi_masterBuffer[twi_masterBufferIndex++] = TWDR;

    case TW_MR_SLA_ACK:  // address sent, ack received

      // ack if more bytes are expected, otherwise nack

      if(twi_masterBufferIndex < twi_masterBufferLength){

        twi_reply(1);

      }else{

        twi_reply(0);

      }

      break;

    case TW_MR_DATA_NACK: // data received, nack sent

      // put final byte into buffer

      twi_masterBuffer[twi_masterBufferIndex++] = TWDR;

	if (twi_sendStop)

          twi_stop();

	else {

	  twi_inRepStart = true;	// we're gonna send the START

	  // don't enable the interrupt. We'll generate the start, but we 

	  // avoid handling the interrupt until we're in the next transaction,

	  // at the point where we would normally issue the start.

	  TWCR = _BV(TWINT) | _BV(TWSTA)| _BV(TWEN) ;

	  twi_state = TWI_READY;

	}    

	break;

    case TW_MR_SLA_NACK: // address sent, nack received

      twi_stop();

      break;

    // TW_MR_ARB_LOST handled by TW_MT_ARB_LOST case

    // Slave Receiver

    case TW_SR_SLA_ACK:   // addressed, returned ack

    case TW_SR_GCALL_ACK: // addressed generally, returned ack

    case TW_SR_ARB_LOST_SLA_ACK:   // lost arbitration, returned ack

    case TW_SR_ARB_LOST_GCALL_ACK: // lost arbitration, returned ack

      // enter slave receiver mode

      twi_state = TWI_SRX;

      // indicate that rx buffer can be overwritten and ack

      twi_rxBufferIndex = 0;

      twi_reply(1);

      break;

    case TW_SR_DATA_ACK:       // data received, returned ack

    case TW_SR_GCALL_DATA_ACK: // data received generally, returned ack

      // if there is still room in the rx buffer

      if(twi_rxBufferIndex < TWI_BUFFER_LENGTH){

        // put byte in buffer and ack

        twi_rxBuffer[twi_rxBufferIndex++] = TWDR;

        twi_reply(1);

      }else{

        // otherwise nack

        twi_reply(0);

      }

      break;

    case TW_SR_STOP: // stop or repeated start condition received

      // put a null char after data if there's room

      if(twi_rxBufferIndex < TWI_BUFFER_LENGTH){

        twi_rxBuffer[twi_rxBufferIndex] = '\0';

      }

      // sends ack and stops interface for clock stretching

      twi_stop();

      // callback to user defined callback

      twi_onSlaveReceive(twi_rxBuffer, twi_rxBufferIndex);

      // since we submit rx buffer to "wire" library, we can reset it

      twi_rxBufferIndex = 0;

      // ack future responses and leave slave receiver state

      twi_releaseBus();

      break;

    case TW_SR_DATA_NACK:       // data received, returned nack

    case TW_SR_GCALL_DATA_NACK: // data received generally, returned nack

      // nack back at master

      twi_reply(0);

      break;

    // Slave Transmitter

    case TW_ST_SLA_ACK:          // addressed, returned ack

    case TW_ST_ARB_LOST_SLA_ACK: // arbitration lost, returned ack

      // enter slave transmitter mode

      twi_state = TWI_STX;

      // ready the tx buffer index for iteration

      twi_txBufferIndex = 0;

      // set tx buffer length to be zero, to verify if user changes it

      twi_txBufferLength = 0;

      // request for txBuffer to be filled and length to be set

      // note: user must call twi_transmit(bytes, length) to do this

      twi_onSlaveTransmit();

      // if they didn't change buffer & length, initialize it

      if(0 == twi_txBufferLength){

        twi_txBufferLength = 1;

        twi_txBuffer[0] = 0x00;

      }

      // transmit first byte from buffer, fall

    case TW_ST_DATA_ACK: // byte sent, ack returned

      // copy data to output register

      TWDR = twi_txBuffer[twi_txBufferIndex++];

      // if there is more to send, ack, otherwise nack

      if(twi_txBufferIndex < twi_txBufferLength){

        twi_reply(1);

      }else{

        twi_reply(0);

      }

      break;

    case TW_ST_DATA_NACK: // received nack, we are done 

    case TW_ST_LAST_DATA: // received ack, but we are done already!

      // ack future responses

      twi_reply(1);

      // leave slave receiver state

      twi_state = TWI_READY;

      break;

    // All

    case TW_NO_INFO:   // no state information

      break;

    case TW_BUS_ERROR: // bus error, illegal stop/start

      twi_error = TW_BUS_ERROR;

      twi_stop();

      break;

  }

}